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Old buildings: earthquake performance and material testing Scrivener, J. C.

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by John Scrivener

Internal Report No. 624

Date of issue: March 1992

This is an internal report of the Institute for Research in Construction. Although not intended for general distribution, it may be cited as a reference in other publications.

OLD MASONRY BUILDINGS - EARTHQUAKE PERFORMANCE AND MATERIAL TESTING

by

JOHN C SCRIVENER

ABSTRACT

Some of the recent earthquakes (e.g. Newcastle, Australia in 1989) have been in areas not considered to have high seismicity. Accordingly old masonry buildings in areas of supposedly low earthquake risk may be vulnerable to damage and even collapse. When they are heritage buildings the cost of damage, whether financial, historical or architectural, may be very great. Thus it is sensible to assess the risk to old masonry heritage buildings even in zones of low seismicity. The old masonry buildings covered in the review may be of stonework, clay or adobe construction. They are most often thick-walled and not reinforced. Two major areas are discussed in the review: the determination of the material and structural properties of old masonry by direct and indirect testing and the performance of old masonry in earthquakes. PREFACE

The Structures Laboratory at the Institute for Research in Construction (IRC) has an ongoing research program to develop guidelines for evaluating the structural adequacy of existing buildings. Included is the seismic evaluation of older unreinforced masonry buildings. This report was prepared for the above program by Dr John Scrivener while he was on sabbatical leave at IRC from June to December 1991. He is Professor of Building in the Department of Architecture and Building, University of Melbourne, Australia. iii

TABLE OF CONTENTS

Section Page Abstract i Preface ii Table of Contents iii 1. INTRODUCTION. 2. MATERIAL PROPERTIES BY DIRECT MECHANIC?LG TESTS 2.1 Tests for Masonry Compressive Strength and Axial Deformation 2.1.1 Compression tests on large specimens cut out of structures 2.1.2 Compression tests on cores cut out of structures 2.1.3 Flat jack tests 2.1.4 Borehole dilatometer tests 2.1.5 Compression tests on reconstituted masonry 2.1.6 Alternative methods for determining masonry compressive strength 2.2 Tests for Properties 2.3 Tension Tests 2.4 Compression and Tension Test Results 2.5 Shear Tests 2.6 Flexural Tests 2.7 Mortar Bond Tests 3. MATERIAL AND STRUCTURAL PROPERTIES BY INDIRECT TESTS 3.1 Preliminary Investigations 3.2 Sonic and Ultrasonic Pulse Velocity Tests 3.3 Radar Method 3.4 Thermographic Analysis 3.5 Mortar Strength from Hardness Measurement 3.6 Monitoring 4. DYNAMIC TESTS 5. MODELLING OF OLD MASONRY 5.1 Static Modelling 5.2 Dynamic Modelling 6. FIELD PERFORMANCE OF OLD STONE AND BUILDINGS IN EARTHQUAKES 6.1 Larger Buildings 6.2 Smaller Buildings 7. SUMMARY AND DISCUSSION 35 7.1 Mechanical Tests for Compressive Strength and Axial Deformation 3 5 7.1.1 Direct compression tests on large specimens and cores 35 7.1.2 Flat jack testing of masonry 36 7.1.3 Borehole dilatometer test for masonry 37 7.1.4 Reconstituted masonry tests 37 7.1.5 Alternative methods for masonry compressive strength 37 7.1.6 Masonry compression test results 38 7.1.7 Mortar compression tests 39 7.2 Tension and Shear Tests 3 9 7.2.1 Tension tests 39 7.2.2 Shear tests 39 7.3 General Comments on Direct Mechanical Tests 4 0 7.4. Indirect Tests for Material and Structural Properties 40 7.4.1 Preliminary investigations and monitoring 40 7.4.2 Sonic and ultrasonic pulse tests 41 7.4.3 Radar method 41 7.4.4 Thermographic analysis 42 7.4.5 Mortar strength from hardness 42 7.5 Dynamic Tests and Modelling 42 7.6 Performance of Masonry in Earthquakes 43 7.6.1 Quality of materials and construction 43 7.6.2 Connections between structural elements 44 7.6.3 Structural layout 45 7.6.4 Soil-structure interaction 47 7.6.5 General comments on earthquake damage reports 47 8. ACKNOWLEDGEMENTS 48 9. REFERENCES CITED 48 10. REFERENCES CONSULTED BUT NOT CITED 56 11. APPENDIX 64 Table 1: Stonework compression and tension test results 64 Table 2: Brickwork compression and tension test results 65 Figure 1: Sheppard shear test arrangement 67 Figure 2:'Benussi and Mele shear test arrangement 68 1. INTRODUCTION Recently concern has been expressed on the vulnerability of older masonry building stock, particularly heritage buildings, to seismic shocks. In areas of high seismic activity, the likelihood of damage in earthquakes may be obvious. It has required the removal or strengthening of hazards such as parapets or ornaments; the strengthening ofthe building by prestressing; the incorporation of a ductile frame to which the masonry is tied; even the removal of the entire building. However in areas of low to medium seismic activity, such as eastern Canada and USA and most of Australia, while the potential for damage is less these areas may experience earthquakes sufficiently severe to cause not only loss of life but also severe damage to the fabric of buildings of historic, architectural or public importance including libraries, churches, schools and government buildings. Often the repair of such damage is expensive or it may be aesthetically impossible. There is a need to discriminate between buildings that need, and do not need, upgrading. The walls of old masonry buildings are usually thicker than those in modern buildings. Most often in stonework buildings, the exterior and interior wythes of the walls are of dressed stone with rubble in between which may or may not contain binding mortar or be bondedto the wythes. Not always is structural connection provided by through-the-wall units. Clay brick masonry walls usually have several wythes mortared together with collar joints and through- the-wall units may be used although there are some examples of construction similar to that of stonework walls. The seismic behaviour of more recent buildings of 'thin' masonry is fairly well known and understood and modern codes deal with their design and evaluation. Reinforcement is required in higher risk areas. For the older buildings in this group, evaluation has been treated by ABK (1986). Bruneau and Boussabah (1991) gave a survey of 'seismic performance of thick unreinforced masonry'. Their emphasis was on the 'seismic performance' rather than on the characteristics of 'thick masonry'. Accordingly this report is primarily concerned with testing for material properties of old stone and brick masonry and on appraisal of old masonry in earthquakes. The review is in two parts. In the first part is the determination of material properties including compressive, tensile, shear, flexural and dynamic properties of masonry, units and mortar using large specimens, cores, flat jack and borehole dilatometer tests, reconstituted masonry and alternative methods. Indirect tests, often termed non-destructive tests, such as sonic and ultrasonic pulse, radar, thermographic and mortar hardness tests are investigated. The results of many such tests are recorded. The field performance of old masonry is in the second part and the various factors causing damage, or survival, are discussed. Over 170 papers were studied in the preparation of this report. Of these, 95 papers turned out to be of direct relevance and are cited in the report and listed in Section 9, References Cited. While the other papers were not found to be of direct relevance to this report, they are sufficiently relevant to the study of seismic appraisal of old masonry buildings to warrant listing in Section 10, References Consulted But Not Cited.

2. MATERIAL PROPERTIES BY DIRECT MECHANICAL TESTS 2.1 Tests for Masonry Compressive Strength and Axial Deformation There have been several ways in which the vertical compressive strength and modulus of elasticity (E) of older masonry have been evaluated by direct tests: on large samples or on cores cut from the structure; on the structure in-situ by flat jack testing or by borehole dilatometertesting; on samples of re-constitutedmasonry; or by alternative methods. The methods are considered in turn. 2.1.1 Compression tests on large specimens cut out of structures The testing of specimens several courses high and the full thickness of the wall is probably the method most likely to provide the investigator with an accurate estimate of the behaviour of the masonry in the wall. However permission for such sampling may be impossible to obtain on aesthetic or structural grounds. Further it may be difficult to cut out a prismatic specimen, needed for an accurate assessment of stresses, particularly in masonry with weak mortar which can be damaged by the cutting out process. However these difficulties appear to have been overcome by Pistone and Roccati (1988 and 1991), Modena (1989) and Tomazevic and Anicic (1989) who reported results from wallettes and prisms of clay brickwork cut out from buildings. The latter authors also cut out some stonework specimens. Pistone and Rocatti compared their test results with those from specimens reconstituted in the laboratory and this is discussed in Section 2.1.5. Other researchers, having taken large samples out of walls, cut out from them smaller specimens for testing. Stonework samples were taken from a viaduct by Binda et a1 (1982) and 56mm diameter x 122mm high cylinders cut from them in the laboratory both normal and parallel to the bedding plane. Epperson and Abrams (1989) used parts of a four-wythe brick masonry building, built in 1917 and about to be demolished, to cut out walls and prisms for test. Baronio and Binda (1991) tested specimens from the 11th century Pavia Tower, which collapsed in 1989. "The medieval rubble walls, 2.8m thick at the ground floor, were internally made with a sort of conglomerate obtained with alternate layers of mortars and pieces of stones and and externally cladd with solid bricks. The average thickness of this cladding was 0.15 m." The average compressive strength of the masonry measured on prisms cut from large blocks was 2.8 MPa. The paper does not indicate whether the prisms were of the full width of the wall. Apparently in all of these cases the masonry was bonded with mortars which were strong enough to withstand the further cutting process. Schafer (1991), in a study of medieval masonry and mortar, dipped the samples cut out of walls in liquid paraffin wax which when dry held the masonry together while prismatic specimens were cut. The dried wax was melted off in hot water before testing of the specimens. With measurements taken of vertical deformation, the static stress/ strain behaviour under vertical uni-axial loading can be plotted. As the stress/strain curve for masonry is seldom a straight line even at low stresses, some researchers in order to indicate the shape of the stress/strain curve from zero to maximum stress quote more than one secant value of modulus of elasticity (E). For instance Pistone and Roccati (1991) quoted modulus of elasticity values obtained at 10, 40 and 80% of the maximum stress. Other researchers quote only one secant value and while it is often obtained at one third of the maximum compressive stress this is not universal. Johnson et a1 (1982) instrumented areas of brickwork cladding with Demec gauges and measured the distances between the gauge points before cutting the areas out of the building. In the laboratory the initial elastic recovery and stress/strain relationships were determined. The purpose of the investigation was to establish the loads on the supporting nibs when distressed brickwork was removed for replacement by new brickwork. The authors' wrote: "The interpretation of the on-site strain readings and their relationship to the laboratory tests is complicated by a number of factors - for example: (a) Brickwork is not perfectly elastic and on repeated loading it exhibits both permanent strain and hysteresis. (b) The repeated load tests on the specimens recovered from the gable walls produced stress/strain hysteresis effects which were not consistent. However, tests on laboratory- built samples do show a more consistent trend indicating increased permanent set with repeated loadings. (c) The amount of strain recovery measured on identical specimens varies depending on the length of time the load has been sustained. Generally, the longer the load has been applied the smaller the strain recovery. Thus the observed elastic modulus on recovery will vary depending on the length of time that the load has been maintained." The above is a good example of the need for proper test procedures and interpretation of results from samples cut out of buildings. The results of these tests and those to follow are recorded in Table 1 for stonework and Table 2 for brickwork in the Appendix. 2.1.2 Compression tests on cores cut out of structures Two corings of 80 mm diameter for sampling were taken from a pier of a viaduct by Binda et a1 (1982). Penelis et a1 (1983) reported that 19 cores of 100 mm diameter were taken from a monument from which mortar and brick specimens were prepared for mechanical tests, including bond strengths between bricks and mortar, and chemical analyses. The mechanical test data were also used for the indirect determination of compressive strength and modulus of elasticity of the masonry, using semi- empirical relationships established by current codes, and the results compared with test results from the full cores. Unfortunately the numerical results were not reported. 2.1.3 Flat jack tests Flat jack testing is well known for the determination of mechanical properties of rock masses. For brick masonry two plane cuttings perpendicular to the wall face are made in mortar bed joints a few units apart and special thin jacks, 400 x 200 x 10mm thickness (or less), are inserted in the cuts. The two jacks therefore compress a masonry sample of reasonable size (Rossi (1985) used 400 x 400 x 200mm). With the recording of deformations in the load direction, the stress - strain history can be obtained. The load to cause first cracks in the bricks enables the masonry compressive capacity to be estimated. The results have to be adjusted (see later) as the masonry on which the test is conducted is confined on three sides and free on the fourth. Cutting into a masonry bed releases stress and causes a partial closure of the cut. Use may be made of this with the first cut to determine the level of compressive stress in the masonry. Measuring points are installed on the face of the masonry above and below the cut and the initial distance between them recorded. On cutting this distance is reduced. The jacking force required to return the distance to its original amount may then be used to calculate the original stress level. A correction factor is required to take account of the effect of the flat jack. The tests of Rossi (1985) show that, for clay brick masonry laboratory specimens, the deformation behaviour on jack loading and unloading are nearly identical. 5 Rossi (1985) conducted a series of tests on large-size brick masonry specimens built in the laboratory to calibrate his jacks and to evaluate the reliability of flat jack tests in different loading conditions. He found that 400 x 200mm flat jacks gave reliable results - within 4% for stresses between 1.5 and 2.25 MPa and 12% low for stress of 0.75 MPa and within 9% for modulus of elasticity. A smaller jack, 240 x 120 mm, while satisfactory for the determination of masonry stress level was up to 116% in excess for modulus of elasticity. Rossi believed this to be due to the small number of mortar beds in the masonry sample tested by flat jack loading which was therefore unrepresentative of the overall behaviour of the masonry. Tests on existing structures are reported by Binda et a1 (1982), Tomazevic and Anicic (1989) and Modena et a1 (1991) on stone masonry, and by Binda et a1 (1982 and 1983), Rossi (1982, 1985, 1987, 1988 and 1990), Modena (19891, Tomazevic and Anicic (1989), and Epperson and Abrams (1989) on brick masonry. Kingsley and Noland (1987) wrote that most brick units made in USA prior to the early 1930's were not extruded and therefore may have a depression, termed a frog, caused by the manufacturing process. The frog is not always filled with mortar during bricklaying particularly when the brick is laid frog downward. When a frog is adjacent to the flat jack complete contact with the masonry surface cannot be achieved. They used one or more thin flat jacks inserted adjacent to the 'working' flat jack to act as fluid cushion 'shims' to overcome this problem. The shim jacks deformed into any voids or irregularities but they could be taken out easily after the removal of the undeformed working jack. Thus a uniform pressure was applied on an uneven surface of masonry. Wallettes and prisms cut out of a four-wythe brick masonry building constructed in 1917 were subjected to various compressive loads in a rig by Epperson and Abrams (1989). The results from flat jack testing were compared against the actual loads and stress/strain results. The authors concluded: (a) the estimation of vertical stress using a single flat jack exceededthe actual stress by less than 5 per cent. (b) as the deflection of the masonry surrounding the flat jack was sensitive to localvariations, the determination of the pressure required to restore the brickwork to its original position was slightly subjective. (c) the apparent modulus of elasticity as determined by the flat jacks increased as the applied vertical compressive stress on a test wall was increased. This may be due to an increase in the peripheral restraint to the brickwork immediately adjacent to the test location. (d) the ratio of moduli of elasticity obtained from flat jack results and prism tests varied from 1.0 at zero vertical stress to 1.6 at vertical stress of 0.79 MPa. (e) the ratio of moduli of elasticity obtained from flat jack results and wall tests varied from 1.7 at zero vertical stress to 0.9 at vertical stress of 0.79 MPa. The results from several flat jack tests are given in Tables 1 and 2 in the Appendix. Numerical modelling of flat jack testing of masonry has been carried out by Jurina and Peano (1982), Sacchi and Taliercio (1986) and Maydl (1991). In the second and third papers finite element computer programs were used and the experimental and computer results compared. Two draft standards for flat jack testing have been produced by ASTM (1991A and 1991B), one on co~mpressivestress estimation and other on deformability properties. 2.1.4 Borehole dilatometer tests Rossi (1990) reported: "Using the tests with parallel flat jacks can only determine the deformability characteristics of the superficial layer of masonry. In order to acquire information on the deformability characteristics of the internal masonry it becomes necessary to conduct dilatometric tests using boreholes made by coring. A special probe about 25 cm long applies uniform hydrostatic pressure on the borehole surface, and the measurement of the consequent deformation determines the modulus o f deformability." The borehole dilatometer was used in investigations on the Tower of Pisa foundation. According to de Vekey (1991A), the technique for the 'internal fracture test' was described by Chabowski et a1 (1980). de Vekey reported that recent calibration tests for U.K. masonry using various units showed that the method was not suitable for materials with a compressive strength below 7 MPa. The development of a more consistent version is underway. 2.1.5 Compression tests on reconstituted masonry Some researchers have reconstituted old masonry, or mortar, in the laboratory. Tomazevic and Sheppard (1982) constructed stone masonry walls in the laboratory, "using the materials and workmanship typical of the region of origin. In this way the original quality of the walls was successfully reproduced." Further details were not given. The walls were built of two layers of uncoursed or partially-coursed limestone blocks, the inner part of the wall being infilled with smaller stones. Lime-sand or clayey-sand mortar of poor quality was used. In most cases the wall thickness exceeded 500mrn. While the authors' prime objective was to compare the properties of 'original' walls against those of walls strengthened with cement , only the 'originalf properties are of interest in this study and they are recorded in Table 1 in the Appendix. Sheppard (1985), in attempting to compare the strength of an existing wall with the strength of the same wall incorporating cement grouting, built and tested two wall elements out of masonry taken from an adjacent and similar building. He used laboratory- prepared mortar of the estimated strength of that in the existing wall. Angotti et a1 (1991) also reported the tests and results. Pistone and Roccati (1988) compared the compression test results of 'undisturbed samples' (i.e. a wallette and two prisms cut out of a building) with the result obtained from a reconstituted prism of the same bricks and mortar imitating the actual bonding material. The reconstituted prism failed at a significantly lower stress than the 'undisturbed samples' and its deformability was much greater. The authors concluded that: "in all likelihood the phenomenon of mortar anelastic compaction, whose effects in undisturbed samples are to a considerable extent gradually exhausted under service conditions, had in this case its full effect during the (reconstituted prism) test." In a further paper, Pistone and Roccati (1991) aimed:

. ~ "to simulate the behaviour of this masonry by means of specimens produced with old bricks and freshly manufactured mortar, either identical to the ancient ones or possessing higher strength, but always within predetermined limits. As has been recognized in recent years, it is of essential importance to be able to reproduce ancient masonry with sufficient accuracy in order not to alter the fabric of existing buildings with the addition of modern materials whose long-term behaviour is unknown (such as, for instance, epoxy resins); or else with exceedingly stiff materials, such as high strength cement mortars, that may affect stiffness distribution in ancient walls. To attain this objective, the earlier stage of the research focused on the definition of suitable methods for the reproduction of ancient mortar with contemporary materials." They again compared results from an 'undisturbed sample' and reconstituted specimens constructed with two different lime mortars. The 'undisturbed sample' compressive strength lay between the mean strengths of the reconstituted specimens. In regard to deformation, the results ofthe stress-strain curves forthe weaker of the two reconstituted specimen series and the 'undisturbed sample' agreed reasonably closely (see Table 2). Accordingly the point made in their earlier paper could not be confirmed. Results of tests on brickwork built up from old bricks and new mortars are reported by Modena (1989). The mortars "were composed according to the ancient formulas" but no further explanation or reference was given. While some compressive strengths were comparable with results from actual old brickwork others were not and the moduli of elasticity were not comparable. The experimental evaluation of the compressive properties of tuff masonry wallettes, using tuff blocks obtained from the demolition of old buildings and mortar made up in the laboratory to have a compression strength (2.0 to 3.0 MPa) typical of the old pozzolan mortars, was conducted by Faella et a1 (1991). The data was needed for projects in which old masonry structures were to be strengthened. Further research, on the reconstitution of old mortars, is given in Section 2.2. 2.1.6 Alternative methods for determining masonry compressive strength Pume (1991) estimated the unconfined compressive strength of old brickwork in the following way. He obtained the brick strength, preferably from vertical cores taken from a brick removed from the wall, and adjusted for height/width ratio from calibration curves to get the unconfined brick strength. Then he determined the hardness of the mortar, by a technique described in Section 3.5, and used an empirical formula to estimate the mortar compressive strength. Finally, with both the brick and mortar strengths and using further calibration curves, he estimated the masonry unconfined compressive strength which he considered he obtained within 10% accuracy.

An interesting different approach was given by Berger (1989) who, from new masonry constructed in the laboratory, took 20 to 30mm diameter cores parallel to mortar beds, some in the bricks alone and some containing a mortar bed. He stated that he could show theoretically and experimentally that the ratio between the tensile strengths of the cores with and without mortar beds as obtained by the Brazilian test was the same as the ratio between the compressive strengths of the masonry and the unit. Accordingly masonry compressive strengths could be found fromtesting cores in diagonal compression provided that the compressive strength of the brick unit was known. He found that samples could be taken without damage if the operating speed of the diamond-tipped coring bit and the pressure of the cooling water was strictly controlled provided that the mortar compressive strength was above 0.55 MPa. The method was not suitable for brick masonry with thick bed joints, or for stone masonry and it has yet to be tried on old brickwork. In an attempt to remove this drawback Berger experimented with the determination of strengths using ultrasonic pulse velocities of brick and mortar with some success and he reported that tests on a larger number of specimens of different kinds of masonry were underway. 2.2 Tests for Mortar Properties With masonry comprised of relatively low strength units (say less than 10 ma), which is often the situation in historical buildings of brick, the compressive strength of the mortar has a more marked influence on the compressive strength of the masonry than for higher strength units. After chemical analyses of the existing mortar obtained from cores, Penelis et a1 (1983) prepared compatible for strengthening, and mechanical tests were conducted on these 'reconstituted' grouts. Results were not reported. Baronio and Binda (1991) investigated the mortar from the 11th century Pavia Tower which collapsed in 1989. The objective of the research was to determine a procedure for the investigation of historic mortars. In the process petrographic/mineralogical, chemical, physical and mechanical analyses were developed on the sampled mortars. "These tests are carried out in order to obtain information for various purposes in the conservation of historic buildings. Some of these purposes are listed below: (a) type of binder and aggregates used in the original mortar: sampling has to be done only in protected areas in order to avoid the recovering of leaked [leached] materials; (b) type of binder and aggregates plus grain size distribution: sampling has to be performed as in a), but a great quantity of material needs to be extracted; (c) kind and degree of deterioration: all the decayed areas of the walls have to be previously inspected in order to find the most representative sites for sampling; (d) strength and other mechanical parameters. Only specimens of significant size can be tested, then sampling is useful only in the case when these dimensions are guaranteed; (e) presence of soluble salts in the decayed materials: sampling must be done without use of water." The authors commented on the difficulty of directly measuring the mechanical strength of mortars as the mortar joints were thin and of variable thickness. However they were able to cut mortar cubes of mean side length 30 mm from the recovered blocks of masonry. The mean compressive strength obtained was high, some 2.3 times the mean wall strength, and the strengths ranged from 2.9 to 13.4 MPa. Their paper did not state whether the strengths quoted were adjusted to unconfined strengths which may have been difficult with such small specimens. Moduli of elasticity were found to lie between 270 and 1580 MPa. Three further papers from the 9th International Brick/Block Masonry Conference, held in October 1991, discussed the analysis of historic mortars, particularly chemical and mineralogical investigations, with the objective of finding satisfactory repair mortars. These papers, each written in German, were by Huesmann and Knofel (1991), Knofel and Schubert (1991) and Middendorf and Knofel (1991).

2.3 Tension Tests In the diagonal compression or Brazilian test, for brittle low tensile strength materials, a cylinder is loaded diametrically in compression causing a splitting tension failure along the loaded diameter. Assuming that the material is homogeneous and isotropic, the tension strength obtained is also the 'shear' strength. Splittingtension tests on laboratory-made limestone specimens were reported by Tomazevic and Sheppard (1982) and the results were used in direct comparison with other 'referential tensile strengths' calculated from the shear resistance of walls subjected to a constant vertical load and increasing horizontal load. Tomazevic and ~nicic(1989) reported results of tests on specimens cut out of old stonework and old brick masonry. Surprisingly they found that results from shearing tests were at least three times greater than the tensile test results and they suggest that "the differences in the results are due to the different testing procedures used for the determination of the tensile and shearing strength of the masonry, which have caused different stress states in the tested specimens, and consequently different failure mechanisms." While this is no doubt true, the author believes that the large difference is more likely due to the addition of vertical stresses from superimposed loads in the shear test specimens. 2.4 Compression and Tension Test Results Results of the tests described above are given, for stonework in Table 1 and for brickwork in Table 2, in the Appendix. 2.5 Shear Tests There are two types of shear tests, one to find the in-plane horizontal sliding resistance along a mortar bed (sometimes termed the 'shove' or 'push' test) and the other to determine the in-plane shear resistance of a wall or wallette which results in a diagonally-cracked specimen. For the latter case the specimen may be a wall supported at its base and 'racked' by a horizontal load applied, say, at the top of the wall or the specimen may be a wallette which is diagonally compressed. For the shear resistance of a portion of in-situ masonry, Sheppard (1985) used the following method. About 300 mm from a door opening two vertical slits, 1600 mm high and 1000 mm apart, were cut creating an intact wall element 1600 mm high and 800 mm effective width. At wall mid- height a bearing block was fixed to one edge of the wall element so that a horizontal load could be applied with a jack which acted on the wall via two horizontal steel ties fixed to two transverse I-beams as shown in Fig. 1. The jack's horizontal reaction was transferred to a vertically-erected I-beam whose points of support 1600mm apart coincided vertically with the two points of support of the tested wall element. This set-up creates two symmetrically-arranged wall elements, 800mm x 800mm, with practically full fixity on one surface (top and bottom respectively). As the horizontal load was increased monotonically and incrementally with intermediate loading steps, horizontal deformations were recorded enabling load-deformation diagrams to be plotted. Sheppard loaded to the maximum horizontal load when diagonal cracks occurred. The cracked masonry was repaired using cement grout and the wall was retested. The tests and results were also reported by Angotti et a1 (1991). Benussi and Mele (1988) conducted, "diagonal compression tests of a particularly arranged panel. A portion of (stone) masonry is partially isolated with cuts, whose width is the minimum to insert flat circular jacks, loading the panel in cyclic alternate stages. In all stages of the tests the diagonal compression was thrust as far as the beginning of the cracks, not to damage excessively the structure. The deformations of the panel were read with instruments, whose location is shown" (see Fig. 2). Unfortunately no further information was given. Tomazevic and Anicic (1989), for the sliding shear test, removed units on both sides of the unit under test and placed an hydraulic jack in one gap formed. While reacting against the main body of the wall, the jack pushed the test unit into the other gap. The load to cause this represented the sliding shear resistance of the masonry under its particular vertical load. Their paper also included two results of (racking) shear tests. They commented upon the insufficiency of experimental data to enable correlation between shove and racking test results. Using shove test results on four-wythe brickwork cut out of a 1917 brick building, Epperson and Abrams (1989) attempted to evaluate racking shear wall strength. In the shove test, the tested unit was pushed into the gap created by removing the head joint (or perpend) on the end of the unit opposite to the jack. Some difficulty was experienced in estimatingthe shearing area as there were some voids in the collar and bed joints. Further, as the bricks were frogged and there was no uniformity in orientation of the bricks so that the frog could be up or down, large differences in the mortar bedded areas were possible. This led to considerable scatter in the shear stress plots. To obtain racking shear strengths of five walls each subjected to a different level of vertical stress, calculations involving elementary principles of mechanics were used to convert shove test results to racking shear estimates. When the shove test data led to an overestimation of the racking strengths by an average factor of 2.9, reduction factors were incorporated so that shear strength estimates contained a margin of safety. There was still an overestimation by an average factor of 1.5. Epperson and Abrams commented that the overestimation "may be attributable to the (differences) in the observed modes of failure." The author agrees with this statement, although he would have expressed it more strongly, as the shove test mechanism involves only sliding along a brick-mortar interface whereas the racking test mechanism involves effects of shear in the bricks, flexural cracking, a complex shear stress distribution (a parabolic distribution was assumed by Epperson and Abrams), high compressive stress levels at the wall toe as well as brick-mortar interface sliding. The Epperson and Abrams conclusion is apt: "Shear strength estimations may be improved by consideration of the mechanics of shear stress transfer indicated in the failure patterns observed for the test walls and a method measuring the diagonal tensile strength of the masonry." Laboratory tests examining horizontal bed joint shear failures and shear load-displacement behaviour of unreinforced brick masonry were conducted by Atkinson et a1 (1989). The tests were on old and new clay units, with different and appropriate mortars, and on field specimens collected from older brick walls damaged during the Whittier earthquake (see Deppe, 1988). The authors commented that: "previous studies on bed joint shear behaviour, while providing insight into parameters influencing shear strength, do not, in general, provide the detailed information related to constitutive behaviour which would be requiredto construct analytical models to simulate response under realistic seismic loading conditions. Such a model will require definitions of [and their apparatus enabled the measurement]: (a) shear stiffness for both initial and repeated loading states; (b) peak and residual strength values; (c) normal load and stiffness effects on shear stiffness and dilatancy; (d) repeated shear reversals; and

(e) dynamic effects. " Atkinson et a1 found that: "In general under cyclic shear loading, masonry bed joints show a peak strength for the first cycle followed by a residual shear strength. Both peak and residual shear strengths are well represented by the Mohr Coulomb criterion, with friction coefficients ranging between 0.64 and 0.75 for the laboratory specimens. The field specimens show lower shear strength values." Shear test results are not reproduced in this report as they are so dependent upon the level of compressive stress on the specimen, whether sliding or racking shear is being determined. The compressive stress level is not always recorded in the literature. Two exceptions are the reports of Atkinson et a1 (1989), who also give a table of bed joint shear strengths obtained by themselves and other researchers, and of Epperson and Abrams (1989). In both papers shear strengths, obtained at a number of compressive stress levels, are given.

2.6 Flexural Tests

A 10-year old building, of two-wythed brickwork, which was due for demolition, had its walls tested in flexure (lateral loading test) by Hodgkinson et a1 (1982). Walls of the 10 year old brickwork had a mean strength in the 'parallel' direction (ie causing cracks in the horizontal mortar beds) higher than the mean strength of 'new' brickwork constructed with similar bricks. The strength in this direction is a function of bond between brick and mortar so the authors commented "it is tempting to find here evidence for increased bond with age." In the 'normal direction1 (ie causing cracks in the vertical mortar joints or across units), the flexural strengths of 'old' and 'new' masonry walls were similar. 2.7 Mortar Bond Tests Although the literature does not record any tests or results on old masonry for bond of mortar to the units, the equipment and procedure exists to enable such tests to be conducted in-situ. Hughes and Zsembury (1980) developed the 'bond wrench' which basically consists of a long lever one end of which is clamped to a masonry unit and an increasing load is applied to the other end. The moment of the load causing bond failure is a measure of the bond strength. There are now standardised bond wrench tests in the USA (ASTM 1986) and in Australia (SAA 1988). de Vekey (1991) and BRE (1991) reported a development of the bond wrench, the 'Brench', which allows easier handling (of particular advantage when climbing a ladder or scaffolding) and is safer as the operator holds the equipment throughout the test and at failure of bond the Brench moves in towards, rather than away from, the wall.

3. MATERIAL AND STRUCTURAL PROPERTIES BY INDIRECT TESTS Overviews of indirect testing of masonry (often termed non- destructive testing) have been written by Noland et a1 (1983 and 1988), de Vekey (1988), Epperson and Abrams (1989), Rossi (1990) and Maurenbrecher (1991) . It is useful to subdivide indirect tests into several categories: preliminary investigations, sonic and ultrasonic pulse velocity tests, radar method, thermographic analysis, strength of mortar by hardness measurement and monitoring. 3.1 Preliminary Investigations Before determination ofthe mechanical properties of an old masonry structure, some background knowledge of the structure is needed. Firstly the history of the construction is required. If at all possible the original design and plans should be located. Photographs, sketches, reports and newspaper cuttings made at any time may be most useful as often it is found from these that the original structure was altered or strengthened in some way. Secondly an accurate visual and geometric study of the structure must be made. The location and extent of cracks and other damage, the verticality and alignment of walls and towers, the change to a new material (eg a change of bricks or the use of a different stone) must all be known accurately in order that the current integrity of the structure can be determined. A description and location of architectural and historic points of interest must also be known. These investigations may involve conventional surveying, photogrammetry and photography. Thirdly it is usually necessary to core drill small diameter holes to collect samples of wall cross sections to determine internal materials, bonding and number of wythes and chemical, physical and mechanical characteristics of the materials. Foundation material and size may be also determined by cores. A small video camera can be inserted into the core hole for further information on the masonry composition and on internal cracks - see Modena et a1 (1991). Potter and Guant (1988) explained the use of precision electronic monitoring systems for the analysis and control of structures. In particular, foundation levels, wall and tower lateral displacements and cracks in historic structures were measured over an extended time period and the data analysed to determine trends and cyclic phenomena. 3.2 Sonic and Ultrasonic Pulse Velocity Tests The testing technique is based on the generation, by mechanical impact or by electrodynamic or pneumatic transducers, of impulses at a point on the surface of a structure or in a bore hole. Receivers placed in various positions, on the same or opposite surface at different heights, collect the transmitted pulses. Measuring the time the impulse takes to travel in the material between the transmitter and the receiver and analysing the signal wave gives information on the material and/or the structure. For sonic tests low frequency pulses in the range 0.5 to 10 kHz are used whereas ultrasonic pulse frequencies generally lie in the range 25 kHz to 1 MHz. Epperson and Abrams (1989) studied sonic and ultrasonic wave velocity tests for their effectiveness in assessing condition and in detecting uniformity of wall properties. They found that: "sonic wave velocity tests showed less scatter of measured data than ultrasonic tests because of the longer wave length. Attenuation of the sonic waves was less than ultrasonic waves and the sonic wave velocities could be measured over distances as long as 10 feet [3 ml ." Although various flaws and flawed regions were indicated by some of the results from both modes of transmission, the specific identification of the type of flaw was not possible. By use of the sonic test method, Rossi (1990) stated that the following information could be obtained: - estimate of the deformability modulus - homogeneity of the masonry material - homogeneity of a structural element - effect of grout or other strengthening - presence of cracks in continuous materials. With 'sonic tomography', which is the taking of some impulses along several directions to cover all of the section under investigation, a detailed map of the sonic velocity distribution on a plane section can be found. The technique has been used in concrete dams and on masonry pillars of a viaduct to determine areas where the material requires strengthening. Binda et a1 (1982) refer to 'geophysical' techniques which depend, "on the correlation between the propagation velocity of acoustic waves within a material and its mechanical properties ( Young's modulus, Poisson's ratio). Geophysical methods can be classified as active and passive. The former involve an acoustic excitation of the structure. The latter are based on the principle that cracks developing in the structure are always associated with the emission of elastic waves, which can be picked up at the surface: having at disposal a sufficient number of picking devices the emission point can be identified." Because of the non-homogeneity and anisotropy of stone and brick masonry, "geophysical methods are better used in this case with the aim of characterizing materials in terms of signal propagation and modes, rather than in terms of dynamic modulus of elasticity". Direct velocity measurement tests of the active type on stone piers of a 16/17th century viaduct gave the following: - components of maximum amplitude of signals received had a frequency of 5000 Hz. - outside parts of pier of blocks (2500 - 3000 m/s). - inside parts of pier of cohesionless materials (<2000 - m/s). - sonic velocity diagrams revealed a discontinuity in one pier, due to an additional structural part built up subsequently against one side. The authors commented that sonic logging surveys can use core holes made in sampling and that it is possible to obtain sonic velocity diagrams by a plotter and "to directly correlate velocity, damping and frequency of sonic signals with the characteristics of the material crossed by the borehole". Penelis et a1 (1983) conducted 600 'wide range tests' on a brick monument and the results had a high correlation rate of 0.87 with results from compression tests of cores. While 300 'ultrasonic measurements' gave a very low correlation with compression test results, "very good correlation results, concerning the dynamic modulus of elasticity, which is a quantity indispensable to the analysis as well as to the choice of the type of grout for the repair" were obtained. Low frequency, 1 to 2 kHz, sonic investigations were used by Forde et a1 (1987A) to monitor the quality of brickwork and the thicknesses of old masonry bridge abutments, Forde et a1 (1987B) to study the quality of brickwork bridge piers and Birjandi et a1 (1984) to successfully locate the position of cracks in brick walls previously failed in shear. Berra et a1 (1987) investigated ultrasonic pulse transmission to evaluate grout strengthening of brick masonry prisms. 3.3 Radar Method Rossi (1990) described the method as follows: "The radar testing technique uses high-frequency electro- magnetic waves (100 MHz - 1 GHz) emitted through an antenna with very short impulses (0.5 - 5 s and permits us to determine location of separate surfaces between materials with different dielectric constants. The investigation is based on reflection (the reflected waves from the contact surfaces between materials of different dielectric constants are received through an antenna and are transformed into electric signals) so internal defects in the masonry (damp areas, cavities, presence of metal structures, piping, flues) can be located. . . . Recently the radar technique has been used on the arches which support the roof of the Cathedral in Parma to determine the position of the joints between blocks of stone that are covered by a fresco." McCavitt and Forde (1991) successfully used 'ground probing radar' in the investigation of the internal structure of old masonry arch bridges. 3.4 Thennographic Analysis Based on the thermal conductivity of the material, thermographic analysis may be passive, such as natural cycles of thermal stress due to insulation and subsequent cooling, or active, where forced heating is applied, according to Rossi (1990). "Thermal radiation is collected by apparatus sensitive to infrared radiation, and is then transformed into electric signals, which in turn are converted into images in different shades of colour." It can distinguish between areas of different material or moisture content. While the penetration depth of this technique is only a few centimetres, it may be used advantageously on walls covered with plaster which may hide construction details such as blocked openings, flues, ducts and pipes. 3.5 Mortar Strength from Hardness Measurement The importance of finding the mortar compressive strength in old masonry was discussed in Section 2.2. As it is difficult to get a direct measurement of the compressive strength of existing mortar, non-destructive methods for mortar may be crucial. Pume (1989) gave a method for mortar compressive strength estimation in which a hand drill was modified with percussion and an impact counter. The depth of penetration into a mortar bed of an 8 mm diameter drill after 10 impacts at 150 N force was measured and the mortar strength calculated from an empirical formula. Pume (1991) used the results in an empirical formula to estimate the compressive strength of the mortar and, with the compressive strength of the bricks, he then estimated the compressive strength of the masonry - see Section 2.1.6. Another method for mortar compressive strength estimation is given by Pume (1989). The number of impacts of a 4 mm diameter cylindrical indentor, each with an energy of 1 Joule, to drive the indentor 5 mm into the mortar is related to the compressive strength of the mortar. A modification of the Schmidt pendulum hammer for plaster and aerated concrete has been developed by van der Klugt (1991) to measure the hardness of pointing in masonry. This apparatus gives an accurate measure of hardness as opposed to the crude assessment given by the traditional scratching of mortar with a knife, screwdriver or car keys! 3.6 Monitoring Measuring instruments installed in a building to monitor its behaviour over time can produce results of importance. Rossi (1990) reported that the principal features which were monitored in Italy and the methods of measurement used were: - openings of the main cracks in masonry structures, using removable mechanical extensometers or fixedextensometers with electric transducers connected to an automatic data collection system; - absolute horizontal movements of vertical structures, using a fixed pendulum with a measuring system based on a 'tele-coordinometer' - presumably a theodolite; - relative horizontal movements of vertical structures, using a long base extensometer equipped with an invar wire kept in tension with a weight and the movement of the weight measured by electric transducers; - rotation of horizontal and vertical structures, using fixed or removable clinometers; - internal and external temperature - behaviour of soil and rock foundations. Rossi cited six buildings and monuments of importance in Italy, including the Milan Cathedral, which were being monitored.

4. DYNAMIC TESTS A model of a single-storey stone masonry building, at a 1:5 scale, was built and tested on a laboratory shaking table by Turnsek et a1 (1978).

" The results of laboratory tests of the strengthening of stone masonry walls and buildings, together with methods developed for calculating the shear resistance of masonry buildings, have been verified on actual buildings which stood in an area where the two successive earthquakes of May and September 1976 were of a similar strong intensity (the village of Lusevera in Friuli) ." Tomazevic and Anicic (1989) commented on these tests as follows: "Although plain masonry is considered as a brittle material, even old masonry buildings possess a relatively high energy absorption capacity. As indicated by the analysis of earthquake - damaged buildings, the shaking table tests have shown that, when damaged during a strong earthquake, the dynamic characteristics of these buildings change, which results in a much lower level of effective seismic loads than expected theoretically." As the model became more damaged with larger ground acceleration so the dynamic amplification factor reduced from 3.7 to 1.2. Tomazevic and Sheppard (1982) conducted shaking tests on laboratory-made specimens, of limestone blocks with mortars equivalent to the lime mortars of old rural houses and public buildings which had been in an earthquake. Those specimens reflecting rural houses, with uncoursed stone and low quality mortars of clayey sand and earth, had ductility ratios of 8.2; those with clean sand lime mortars of compressive strength between 0.5 and 1.0 MPa had ductility ratios between 9.0 and 10.7; those reflecting public buildings with partly coursed stone and clean sand lime mortars of compressive strength 1.0 MPa had ductility ratios between 4.7 and 7.3. In Yugoslavia, UNESCO (1982 and 1983) reported that more than 70 buildings were subjected to forced vibrations using low excitation forces in the elastic range to determine dynamic characteristics ie natural frequencies, modes and damping coefficients. While some of these buildings were of brick masonry, it is not known whether they were of old masonry. On some buildings, the forced vibration testing focused on some special effects: - influence of non-structural components (eg cladding walls) on building stiffness, by testing the building before and after the construction of such walls; - effect of floor diaphragm stiffness, in its own plane, on the distribution of forces to individual vertical structural components; - effect of horizontal asymmetry on the occurrence of torsional oscillations; - effect of soil-structure interaction; - effect of inadequately spaced earthquake expansion joints. The natural period of vibration of a brick monument was found by Penelis et a1 (1983) by test to be 0.42 sec and estimated by analysis to be between 0.33 and 0.53 sec. The authors indicated that forced vibration measurements were underway. Tomazevic and Anicic (1989) reported: "Ambient vibration tests of two typical old stone masonry buildings in the historic centre of the city of Ljubljana, Yugoslavia have indicated almost the same values of fundamental frequencies (4.2 and 4.6 Hz respectively), although the two buildings were different in plan and elevation. Similar conclusions can be drawn from ambient vibration tests of several monumental buildings in the city of Dubrovnik and also from ambient vibration tests of post-war multi-storey masonry buildings in Ljubljana." Dynamic parameters such as natural frequencies, modal shapes and damping ratios can be evaluated, according to Rossi (1990), through spectral analysis of data gathered as a response to dynamic loads 'naturally' applied to structures such as road and rail traffic vibrating the structure through the foundation and the ringing of bells. Forced vibration tests, of low intensity so that the vibrations do not affect structural integrity, with the recording and analysis of the displacement, velocity and acceleration response of the system can also supply the dynamic modal parameters. With these parameters the structural response to any type of dynamic load and the seismic vulnerability of old masonry buildings, can be computed. Rossi reported that the forced vibration technique, together with flat jack tests, enabled the discovery of some structural weaknesses in some towers in Pavia, Italy. Modena et a1 (1991) measured the ambient vibrations at the top of an old stone masonry tower and used the results in a numerical model analysis. Two seismic diagnostic techniques were reported by Stockbridge and Crist (1988). In the first, the condition of an historic structure is evaluated by performing a random decrement analysis to develop a baseline response signature. This signature can then be used for comparison with a signature taken after an earthquake to assist in identifying internal damage. The initial displacement, in the signal processing technique of random decrement analysis, is normally induced by wind or other random forces, such as vehicular traffic, and the response of the building is measured with a seismometer held in contact with the building and appropriately oriented. The second technique involves the installation of recording accelerographs in the historic building. The record after an earthquake enables the evaluation of the potential for damage in future earthquakes.

5. MODELLING OF OLD MASONRY 5.1 Static Modelling Binda et a1 (1991) derived simple mathematical models to determine the load distribution between the wythes of multi-wythe masonry walls in two different limit situations. In the first the wythes were so connected by stiff elements that the load was transferred to the wythes as their axial stiffnesses. In the second the wythes were only connected by collar joints or by the mortar of the rubble filling so that the load distribution was mainly dependent on the bond strengths between the wythes. 5.2 Dynamic Modelling A full investigation into the literature pertaining to dynamic modelling of old masonry is beyond the scope of this report. Further the area has been covered by Bruneau and Boussabah (1991). However there are papers in the area which have been published since the Bruneau and Boussabah report and they are reported below. Calvi and Magenes (1991) conducted the first phase of an experimental evaluation of seismic strength of old masonry structures: "The experimental testing of masonry elements is the only viable method to investigate the conditions under which different events may take place, and to quantify the variation of the basic mechanical properties. Only on this basis rational and effective numerical models could be developed." The authors considered four possible limit states: - flexural cracking, which does not involve collapse but determines a variation of the stiffness and the formation of hysteresis loops, - flexural strength (rocking and toe crushing) - shear diagonal cracking, which is not an ultimate limit state if only one direction of loading is considered and if sufficient friction is developed in the cracks, but it might cause an out-of-plane failure. - shear sliding, which has to be considered as an ultimate limit state even if, in principle, it does not always involve a significant reduction in the load carrying capacity of the panel. Compression, tension and shear tests were conducted on specimens of mortar, brick units and triplets which were built with materials which could simulate historical materials closely. Full scale panel tests were still in progress at the time of the publication of the paper. The English abstract to the paper of Baggio and Masiani (1991), written in Italian, stated: "In a previous work a simplified dynamic model was developed, based on the idea that the collapse of masonry structures does not occur because of the exceeding of a limit strength, but because of the loss of equilibrium due to the formation of a mechanism of rigid bodies, as often observed in actual buildings under seismic action. To check the effectiveness of such an approach experimental work is strongly needed. In this paper some results of preliminary experimental tests on simple models under harmonic excitation are shown and discussed. Results fairly agreed with the theoretical model."

6. FIELD PERFORMANCE OF OLD STONE AND BRICK BUILDINGS IN EARTHQUAKES In a general paper on earthquake damage to historic masonry buildings, Balderrama (1990) stated: "Masonry is brittle. It has a high mass and, therefore, a high inertial response to earthquakes. It is rigid and has low tensile and shear strengths, little ductility and a low capacity for bearing reversal loads and the redistribution of stresses. In general, masonry structures are designed for static conditions and do not conform to the elastic theory. From a limited viewpoint, the characteristics of historic buildings are disadvantageous to earthquake resistance. The poor performance of some forms of masonry has resulted in cautious attitudes that presume the inferiority of masonry materials and forms of construction. There are, however, several observations that contradict such a presumption. Firstly, very little research has been done into the seismic response of masonry structures, whether reinforced or unreinforced, with or without a built-in frame. Most of the available knowledge is based largely on inferences from static loading tests. Secondly, field observations seldom mention the relationship between construction quality and the seismic structural performance of masonry buildings. Evidence has shown that there is a direct link between good quality construction and minimum damage. If properly used, masonry construction can have a reasonable resistance to earthquake movements. A common fallacy in field observations after earthquakes is the assumption that the performance of materials and structures is due to their inherent qualities. It is often assumed that certain materials are, in themselves, either good or bad, durable or non-durable, resistant or non-resistant, strong or weak. In reality, these properties are relative and vary according to the conditions of exposure of the structure, the level of its loading and its capacity to re-distribute stresses, amongst other factors. Historic buildings are not necessarily weak because they are old, or have been built with masonry. Some historic buildings, like some modern buildings, are weak because they are poorly constructed, or are subjected to abnormal stresses." The author agrees with the Balderrama thesis that it is incorrect to assume that, simply because a structure is built of unreinforced masonry and therefore of low ductility, its performance in an earthquake will always be disastrous. This fallacious attitude is apparent in many of the reports on earthquake damage which follow. And it is apparent that many old masonry buildings have survived severe earthquakes. As Baldarrama points out those buildings that have failed have usually been poorly constructed or subjected to abnormal or unusual 'loadings' rather than because of an inherently weak material. Poor structural layout can also contribute to premature failure. The author has attempted to keep these points in mind in his reporting of the literature on earthquake damage. The objective has been to find the factors which enable old masonry buildings to survive earthquakes. This section on field performance in earthquakes is subdivided into two sub-sections on larger buildings and on smaller buildings. Within each section the earthquakes, or reports, are considered chronologically. 6.1 Larger Buildings Jennings (1971) reports the damage in the 1971 San Fernando earthquake of magnitude 6.6. In the metropolitan Los Angeles area there were thousands of masonry bearing wall buildings that were designed prior to the earthquake-resistant design provisions put into the Los Angeles Building Code in 1933 following the Long Beach earthquake. While much damage and some collapses occurred in these buildings, mainly of unreinforced slay brick, there were some masonry buildings of pre 1933 vintage which sustained only moderate damage. In the case of the two-storey Morningside School building, though the brick walls were severely cracked, the building survived safely. It had brick corridor walls and crosswalls, concrete corridor slabs, and wood roof and flo~rs. The gable walls had been anchored to the roof framing in recent years. Under a magnitude 7.0 earthquake at Veracruz, Mexico, damage to churches, some 300 years old, at Orizaba was extensive, according to Irvine (1973). They were usually of stone or brick with clay or cement mortar. Many walls, spires and arch roofs collapsed. Damage from the 1976 Tangshan earthquake of magnitude 7.8, with several large after-shocks one at 7.1 magnitude, was reported by Yaoxian and Xihui (1980). "In Tangshan, hundreds of multi-story brick buildings collapsed mainly as a result of spread of shear cracks on load bearing walls. However a fsw brick buildings did not collapse, because reinforced coccrete columns, connected with closed ring-beams at each floor, were provided at the junctions of longitudinal and transversal walls. (This was confirmed by model testing.) ... Industrial buildings with unreinforced brick columns often failed due to ruptures at lower portions or partial failure of columns, showing little capability of earthquake resistance." The 1977 Romanian earthquake, of Richter magnitude 7.2, was reported by Tezcan et a1 (1978). Tiey classified buildings into ten groups including: (a) Monumental 18th and 19th century buildings. These buildings were generally heavy stone and brick masonry structures, two or three szories high, and massively ornamented. No apparent damage was observed in these buildings. (b) Century-old two or three storey mansions. These were constructed from heavy masonry. Timber systems carry the roofs and floors. The interiors had often been altered with the addition of light partition walls. It is likely that the earthquake widened cracks in the load bearing walls which had opened in earlier earthquakes. In general, these buildings withstood the earthquake well. (c) Classical buildings of pre-World War 1 era. The museums, libraries, ministries and universities were usually massive stone or brick structures, two to four stories high. Little damage to these buildings was observed. (d) Rural houses of brick or adobe. These suffered extensive damage. (e) Buildings of the Village Museum. Unlike the rural houses, buildings of various types and ages in a Village Museum, "resisted the earthquake splendidly. Although the short natural period of vibration and the light roof systems (often wood and straw) were undoubtedly two major factors in their excellent performance, it may be concludedthat careful building practice, like matching different shapes of stones together, is quite an important factor in providing resistance to such owner-built village structures against earthquakes." The 1981 earthquakes in central Greece were reported by Carydis et a1 (1982). The main shock was of Richter magnitude 6.7 and aftershocks of magnitude 5.0 to 6.3 continued for several days causing considerable damage in some of the masonry buildings. The report considered the following types of masonry buildings which are common in Greece: (a) Stone masonry buildings. Various kinds of behaviour were exhibited. The buildings built after the 1928 earthquake and those that had been repairedto the requirements of recent seismic codes fared well. But some old hotels and houses were damaged beyond repair. Some damage may be attributed to the various additions, renovations and alterations carried out over the years. In order to obtain open space, masonry walls were removed and replaced by slender steel columns. In some cases, stiff buildings suffered almost no damage in the epicentral region when founded on very soft soil, while stone masonry buildings on good soils were damaged. In one region many of the masonry walls were constructed as two separate faces without any connection and the cavity was filled with rubble and earth. Earth mortar without any cementing material was used. These buildings were extensively damaged. (b) Fired brick masonry buildings. As found in the 1981 and other earthquakes, the behaviour of buildings with solid brick walls was superior to that of the buildings with hollow brick walls probably due to the better quality of the traditional solid bricks. In some cases brick infills did not develop diagonal cracks but failed by crushing adjacent to elements such as concrete beams. (c) Concrete block buildings. As the concrete blocks were generally of poor quality material, they were used for secondary buildings. The performance of these buildings during the earthquake was uniformly poor. In Athens the Parthenon suffered some significant cracks but none of the large stones was dislodged. The 140 year old Athens Cathedral suffered numerous cracks over arches but parapets or ornamentation was not damaged. The cathedral had not been seriously damaged in previous earthquakes, even in the 1894 earthquake when all the surrounding buildings collapsed. Structural damage caused by earthquakes in Mexico City is always greatly influenced by the local geology. In 1985 an earthquake, of Richter magnitude 8.1, occurred off the Western coast of Mexico severely affecting Mexico City approximately 400km from the epicentre. According to Klingner et a1 (1987): "The resonant response of the deep, soft clay deposits underlying the centre of the city caused the lake zone to experience near-sinusoidal ground motions of more than 60 seconds in duration, with maximum accelerations near 20% g, and characteristic periods between 2.0 and 3.5 seconds, severely affected buildings with fundamental periods in that same range. Most collapsed or severely damagedbuildings were in the 7- to 20- story range." But stiff structures such as the older low-rise masonry buildings, which were not subjected to significant inertial forces, generally performed well even though their standard of construction was often not high. The report of the International Masonry Institute (undated) confirmed this : "Many stone masonry churches have been standing for several hundred years, and many residences and commercial buildings are close to a hundred years old. Such buildings generally suffered very little damage. This may have been less a function of their general structural integrity than of the fact that their fundamental periods of vibration were shorter than the characteristic periods of the lake zone ground motion. " Building damage in the 1985 Chilean earthquake, of Richter magnitude 7.4, was reported by Maitland (1988). While there was considerable structural damage overall, some adobe buildings survived undamaged. However the report of the Earthquake Engineering Research Institute (1986) stated that "adobe buildings throughout the areas of strong ground shaking were universally damaged and in various stages of partial collapse". The author accepts Maitland's account as being more accurate since she, as an architectural historian, has knowledge of buildings and she actually experienced the earthquake. Her report gives a clue to the reason for the incorrectness of the other report: "In the emotionally charged climate of the first few days succeeding the earthquake, the structure of older buildings was castigated as inadequate. Within days, bulldozers were leveling rows of structures. ... No one wanted to listen to the voices of caution. There seemed to be a general unwillingness to acknowledge that many adobe and brick houses had survived well. People ignored the fact that [some] noteworthy adobe buildings, ... , all 18th century adobe buildings, survived undamaged." Maitland has an explanation for the good seismic resistance of some of the older masonry buildings. She wrote that: "Chilean builders were able to find solutions for seismic structural problems in the eighteenth century. In the 1720rs, the Jesuit Order sent out some forty Bavarian brothers who were skilled in, among other things, the building trades. The Jesuits conducted several experiments into the best ways of using the local building materials. Their recommendations led to several changes. It was concluded that stone buildings (and churches were usually built of stone) unless made of ridiculously thick walls as was San Francisco (a pre-1647 church which survived the 1647, 1985 and other earthquakes), were inflexible and the first to be destroyed in an earthquake. ... When churches were rebuilt in the eighteenth century they were given wooden roofs, and the walls, columns, and buttresses were built of adobe or brick rather than stone. For brick and adobe buildings, the Jesuits recommended that wooden posts be inserted in the walls around door and window frames and at certain intervals down the length of the walls. ... The Jesuits made other recommendations concerning thicknesses and heights of walls, spacings of openings, types of soil, and straw and clay to be used for adobe and brick." In Salt Lake City an 1890 five story unreinforced masonry stone and brick bearing wall structure with a 76 m high clock tower showed signs of distress, due to settlement probably caused by earthquakes. Its condition occasioned a retrofit and base isolation described by Bailey and Allen (1987 and 1988) and Elsesser et a1 (1987) . The performance of masonry in the Whittier Narrows, California earthquake is extensively documented. It was a moderate earthquake, of magnitude 5.9 and short duration. Deppe (1988) catalogued the types and causes of damage of many relatively recent clay brick unreinforced masonry buildings. The considerably better performance of buildings strengthened with the incorporation of cross walls, often in wood frame, was noted. Deppe stated that: "there is ample evidence as a result of instrumented low-rise concrete and brick buildings, that the brick wall is an extension of the ground and that the shaking intensities of the ground are transferred up the building via the in-plane walls. The acceleration experienced at the diaphragm edge immediately adjacent to the wall is, therefore, approximately the same as the ground acceleration." Characteristic earthquake damage in old stone and brick buildings in Yugoslavia, according to Tomazevic and Anicic (1989) has been: - horizontal cracks at the joints between the walls and floors - vertical cracks at the joints between the walls at corners and at the intersections of walls. This is particularly common in stone buildings because of insufficient interlocking between intersecting walls and the lack of anchorage between walls and wooden floors. In some cases, separation of walls and even out-of-plane collapse of walls has occurred - separation of peripheral walls - out-of-plane collapse of peripheral walls - diagonal cracks in the walls, window piers and spandrels - partial disintegration or failure of walls - partial or complete collapse of the building.

The analysis of structural damage to old masonry buildings has shown that there were two major parameters influencing the seismic resistance of the buildings - the structural layout and the quality of materials and construction. "However quantitative data about the seismic resistance of a building cannot be determined unless additional investigations to establish the structural characteristics and the material properties are carried out." Wyllie and Filson (1989) report on the 1988 Armenia earthquake. While the main shock had a magnitude in the 6.5 - 7.0 range, suggesting a moderate earthquake, there was a major aftershock of 6.3 magnitude and hundreds of additional aftershocks over a four week period, some of which were near magnitude 5. Load bearing masonry wall buildings of three to five storey buildings were very common in large towns and cities in Armenia. The stone masonry units were of volcanic tuff and produced in various sizes with a single finished side. Typically, both interior and exterior walls were of double-wythe construction, which gave finished surfaces on both sides of the wall. In general, exterior walls were about 600mm thick and interior walls were about 460mm thick. In some cases, exterior walls had two wythes of finished masonry units separated with a gap that was filled with rough-cut stones. The floors consisted of hollow-core precast-concrete planks, spanning about 6 metres between exterior and interior walls without positive connections to the end or side walls and without interconnections between individual planks. As a result, in many instances, buildings lost either the end walls or the end portion of the building. There were many post 1960 one- and two-story stone masonry dwellings in the towns and countryside. Except for those dwellings in the epicentral region, which partially or totally collapsed, most one- and two-story dwellings and two- and three- story commercial buildings received little damage. In contrast, some of the old one- and two-storey buildings and historical buildings, such as churches, either collapsed totally or sustained severe damage. Their mortar was found to be relatively weak. In some older buildings, the mortar was actually worn away from between the masonry units. Large buildings in Armenia, and most industrial structures built prior to about 1970, are of masonry bearing wall construction with two wythes of carved stone blocks joined by mortar and some minimal steel reinforcement. Damage ranging from "substantial" to "total destruction'' was found. Damage to masonry construction in a Canadian earthquake, the 1988 Saguenay earthquake, is reported by Allen et a1 (1989). Cracking of window soffits in a thick stone masonry church occurred under maximum accelerations of approximately 20% g and "this damage is caused by forces in the plane of the wall amplified by stress concentration, and is often associated with changes in building stiffness." There was no indication of loss of wall stability. On the other hand, no sign of damage was observed on a large number of thick masonry cantilever walls, lm thick and 5m high with no roof support, at an old pulp mill which was subjected to the same maximum acceleration. In this case there were no sudden changes in the wall sections or wall stiffnesses and "...the wall displacement during the earthquake,. .. ., is a very small fraction of the thickness of the wall." In the few cases of partial collapse of masonry veneer and of block partitions, the main factor was the lack of adequate ties to the structure. The report by Pernica and Maurenbrecher (1984) of the 1982 New Brunswick earthquake, magnitude 5.7, also showed that masonry veneer behaved satisfactorily. Allen et a1 further concluded that: "Ground conditions are an important factor affecting the degree of building damage for earthquakes in this region. This is born out by the fact that, up to a distance of approximately 200 km, the degree of damage observed depended more on ground conditions than on distance from the epicentre. In addition to amplifying earthquake motions in the critical range of building frequencies, there is also the potential for settlement during an earthquake, which can affect the stability of masonry walls." The damage in the 1989 Loma Prieta (near San Francisco) earthquake, magnitude 7.0, is reported by Jablonski et a1 (1990) . Older unreinforced masonry structures, especially those near the epicentre or those in the area where the ground settlement was high, suffered heavily. Damage included: - out-of-plane collapse and local failure of masonry bearing walls - collapse of parapets - collapse of infill masonry walls - collapse of a brick veneer wall. In an unreinforced masonry storage building "the heavy shaking at the roof level and the different response of the roof structure from the bearing walls resulted in damage to the walls. Part of the roof collapsed into the top floor."

6.2 Smaller Buildings In the disastrous 1960 Agadir, Morocco earthquake, of magnitude 5.5 - 6.0, in which some 12000 deaths occurred when the buildings collapsed, the most prevalent material was older masonry which varied from stone, with mortar of mud and sand, to more modern construction of stone or clay tile with mortar ranging from weak mud and sand to good quality sand-cement. The National Oceanic and Atmospheric Administration (1972) reported this earthquake and the damage in the Dasht-e-Bayaz, Iran earthquake of 1968. At least 3,100 people died in the general building collapse in villages of adobe or mud wall construction, with domed adobe brick roofs or vault roofs.

In the 1970 Peru earthquake of Richter magnitude 7.7, there were in excess of 70,000 deaths and 100,000 collapses of adobe dwellings in what is cited by the Earthquake Engineering Research Institute (1970) as the most destructive earthquake in the Southern Hemisphere in terms of loss of life and property damage. The mud 31 mortar used in adobe construction "seemed to be almost a cohesionless material in its final form" Some of the adobe buildings were two or three storeys. Roofs were generally mud plastered over cane on timber joists or tiles on corrugated transite on wood pole rafters. Brick bearing walls were frequently used for shops, apartments and residences with or without bond beams. In many instances most of the adobe dwellings in towns or villages collapsed while reinforced frames with brick infill survived albeit with extensive cracking in the columns and infill. But there were instances of buildings of masonry surviving when all buildings in the vicinity collapsed. The hospital Obrero in Chimbote, 30 miles from the epicentre, a complex of brick bearing walls continued in operation despite severely cracked walls. An adobe 'sign' 20 ft. high, 13 ft. 6 in. wide and 16 in. thick in Trujillo suffered no damage whereas most adobe buildings nearby collapsed. One of the conclusions of the report was that "most collapses occurred in areas where structures had been constructed on alluvial deposits." Turnsek et a1 (1978) reported on the 1974 earthquake damage in Kozjansko, Slovenia and on the damage from two 1976 earthquakes in Friuli, Italy and the Soca valley region, Slovenia. The majority of the stone masonry buildings had wooden floors which were not stiff diaphragms. Accordingly unsynchronized oscillations of individual walls occurred causing cracks at wall junctions, pulling away of walls from the building and the collapse of head walls. Quantification of these phenomena was obtained on a 1:5 scale model of a single storey stone masonry building. Mud brick buildings in the 1976 Denizli, Turkey, earthquake were very badly damaged according to Bektas (1977). Afshar et a1 (1977) reported on the Bandar Abbass, Iran earthquake of 1977 and commented that the mud-brick walled buildings, with mud mortar, failed owing to the "lack of bonding through the width of the walls". Where timber had been embedded into the walls, for framing or reinforcing, it had been attacked by termites and weakened. Stone wythes, sometimes with mud mortar and sometimes with no bonding, with rubble between the wythes performed very badly. In the few examples of stones being laid in such a way as to bond one side of the wall to the other and with good mortar, the building damage was far less. At Tianjin, about 100 km from the epicentre, in areas of intensity Ix nearly all the brick buildings were damaged according to Guoliang (1979). Old brick buildings with timber floors were severely damaged because the connections between the floors and walls were weak and the mortar strength low. Many such buildings collapsed as a result of foundation settlement. Those buildings with mud mortar and wooden floors failed completely. In the report of the El-Asnam, Algeria earthquake, the Earthquake Engineering Research Institute (1983) stated that a large number of stone houses and adobe huts that were either on the fault or within 50 metres of the fault collapsed. "However, a few houses and a mosque, constructed of unreinforced masonry or adobe with loose tiled roofs, sustained surprisingly little or no damage although they were within 50 metres of the fault trace." The Richter magnitude of the earthquake was 7.2, with an aftershock on the same day of 6.0, and the peak ground acceleration was more than 0.409. Reitherman (1985) reported on the performance of unreinforced masonry in the 1983 Borah Peak, Idaho earthquake (Richter magnitude 7.3) at Mackay 30km from the epicentre. "Except for chimneys, which typically collapsed or were severely damaged, the level of damage was only slight to moderate, even though the earthquake resistance of the construction was very low, even for unreinforced masonry. The buildings were of one or two storeys, of small plan size typically 25 - 50 ft. width, usually rectangular with a 'soft front wall' typical of a storefront. There were four basic types of construction: - solid walls of two or three wythes of brick, with header courses completely absent or at long intervals (say, 10 courses) - walls of large concrete hollow blocks (24in. long, 10 in. high and 10 in. wide) - hollow tile bearing walls with brick veneer - unreinforced stonework walls."

In most buildings there was no sign of joist anchors and the diaphragm edge was exposed by the damage. The average level of quality of construction was considered to be "lower than in most older California central business districts" and "much lower than in the massive or monumental brick or stone buildings found in some older California cities and especially in eastern US cities." Few of the buildings were well maintained at the time of the earthquake. In some cases the mortar was soft enough to be able to be scraped with a key. Reitherman included a table in which unreinforced masonry damage in this earthquake was compared against that which occurred in other Californian earthquakes. He concluded: "The striking point of this comparison is quite clear: the proportionate amount of damage in Mackay was quite low compared with other earthquakes. The combination of little inherent earthquake resistance in the building construction and little damage leads to the inference that the buildings were subjected to only minor shaking." Erdik (1990) reported on the performance of rural stone masonry buildings in Turkey. In a table on earthquake damage statistics he listedthe performance under various intensities of earthquake for three levels of construction - poor, medium and good quality. For intensities equal to or greater than IX on the Medvedev-Sponhauer- Karnik (MSK) scale, 75% of poor quality rural stone masonry buildings collapsed whereas only 25% of good quality buildings collapsed. In addition to quality of construction he gave other factors affecting the earthquake performance: - poor quality mortar - inadequate connection of roof beams to the bearing walls - independent behaviour of the inner and outer skins of load bearing walls - inadequate construction or absence of tie-beams - inadequate construction or absence of corner connections between joining walls - an excessive number of wall openings leaving insufficient wall area to resist lateral shear. Erdik classified stone masonry structures as box-type where the primary lateral resistance against earthquakes was provided by the membrane action of the walls and the roof. Therefore: - the out-of-plane walls should be able to resist their own inertia forces through flexural action as beams - the in-plane walls should be able to resist the lateral inertia forces developed over the whole roof and in the top half of the out-of-plane walls through shear cantilever action - the roof structure must have sufficient strength and integrity to transmit the lateral inertia forces in an appropriate manner.

He singled out the collapse of the roof as being the primary hazard. The 1989 Newcastle, Australia earthquake was of the comparatively low magnitude of 5.6 but a disproportionate degree of damage was caused. Page (1991) wrote that this was due to the magnifying effects of the alluvial deposits underlying a large part of the city and due to lack of provision of earthquake loadings in design as Newcastle was perceived to have been in a region of low earthquake risk. "Damage was particularly bad in structures incorporating masonry due to poor standards of design, detailing, and workmanship. In older buildings general deterioration also played a significant role. ... When the ground motion was normal to the plane of a wall, the subsequent face loading caused failure in free standing elements such as parapets and chimneys, failure of inadequately tied gable ends, or collapse of complete wall panels which had inadequate lateral supports (due to lack of ties, corroded ties or tie pull-out from lime mortar joints). In other cases, although complete collapse of the masonry element did not occur, face loading produced excessive lateral movements or rotations in walls, requiring their subsequent replacement. This was often the result of the excessive lateral deflection of timber floors or roofs which in traditional Australian building practice are not usually designed to act as diaphragms. Many non-loadbearing walls were also damaged in this manner because of the lack of lateral support provided at the top and/or edges of the member. In some cases, the only lateral support present at the top of a wall was a window frame or a flexible ceiling system neither of which was capable of providing effective support. " On the question of building deterioration Page wrote: "Most of these buildings were constructed from brick masonry often with weak lime mortar joints (sometimes in a state of deterioration), and were loadbearing in most cases. The strength of the masonry was low, as was its capacity to anchor wall ties. . . . Wall tie corrosion was a major cause of failure of walls under face loading in older structures." Page made the important observation that there are "many lessons to be learned from this disaster, most of which have relevance not only for Australia but also for many overseas centres where unreinforced masonry is used in areas perceived to have a low earthquake risk. " In another report on the Newcastle earthquake, the Institution of Engineers Australia (1990) described the damage at ground floor level in a three storey unreinforced load bearing brick masonry apartment building. At the ground level the layout was highly asymmetrical, because of allowance for car parking, creating an eccentricity of stiffness in the bottom storey which had a section very weak in torsion. The stiff rear masonry walls were extensively cracked. In the Manjil, Iran earthquake of 1990 the traditional buildings of stone or sun dried mud brick walls with wooden pole roofs suffered heavy damage (Moinfar and Naderzadeh, 1990). The more recent buildings, "with brick, cement block, or stone walls and various roofing systems . . . also suffered heavy damages in the epicentral area where the maximum intensity was IX and X. .. . Generally, as it has been experienced through similar earthquakes in the past in Iran, if the RC tie beams under roofs were constructed well, they remained erected and in spite of collapse of masonry walls, roofs did not collapse." 35 7. SUMMMLY AND DISCUSSION 7.1 Mechanical Tests for Compressive Strength and Axial Deformation This section discusses the tests in seven parts; direct compression tests on large specimens and cores, flat jack testing of masonry, internal fracture test on masonry, reconstituted masonry tests, alternative methods for masonry compressive strength, masonry compression test results and mortar compression tests. 7.1.1 Direct compression tests on large specimens and cores Tests on large specimens, several courses high and the full thickness of the masonry, will usually provide the investigator with the most accurate estimate of the wall behaviour. European codes recognise this in their requirements for samples to be large (two or three units wide and four courses high). However it will not be often that an investigator has the luxury of being allowed to remove large specimens from a building for testing, particularly if the building is heritage-listed. Even then the removal of large samples from an existing structure without damage to the remaining structure or damage to the sample during removal or transportation to the laboratory, especially when the mortar beds are of low strength and bond which is likely with older buildings and lime mortar, is not easy. Nevertheless successful tests have been reported by several researchers - see Section 2.1. For accurate determinations of stresses, prismatic specimens are desirable which may require trimming the specimens in the laboratory. Further it may be advantageous, considering the variability in masonry test results, to get several smaller specimens out of the larger one cut out of the structure. Again with low strength mortars this may create difficulties. Schafer (1991) overcame the problem by dipping the large specimen in liquid paraffin wax which when dry held the masonry together while smaller prismatic specimens were cut. Where the stress/strain behaviour is required, vertical deformations are recorded during the compression loading. As old masonry is seldom linearly elastic even at low stresses, the modulus of elasticity recorded is usually a secant value often at one third of -the maximum stress. If the researcher wishes to express the stress/strain shape, more than one modulus is reported. For instance Pistone and Roccati (1991) gave secant values at 10, 40 and 80% of the maximum stress. Careful test procedures and interpretations of results are needed where wall strain behaviour is to be obtained in the laboratory from specimens cut out of a building. The effects of permanent strain, non-linear behaviour, hysteresis and strain recovery have been found to be substantial by Johnson et a1 (1982). For masonry strength and stress/strain behaviour, vertical cores including at least two mortar beds are necessary for results to fairly represent the vertical behaviour. Horizontal cores of piers have been taken but, owing to the anisotropy of masonry, the results may not have been of much value where vertical behaviour was required. If the masonry unit performance only is required an horizontal core within a unit may produce a satisfactory result as units are normally reasonably isotropic. However Pume (1991) preferred vertical cores which he obtained from removing a unit from the wall. Permission to take cores will usually be given by the building authorities as core holes are unlikely to have a detrimental effect on the wall appearance if carefully repaired. Further the core hole may be used to insert a video camera, for viewing the masonry internally perhaps for inside cracking, or to conduct dilatometer tests - see Section 2.1.4. 7.1.2 Flat jack testing of masonry Perhaps the most valuable method for determining in-situ properties of masonry is flat jack testing. Assessment of the in-situ state of compressive stress, compressive strength and stress/strain behaviour, and of shear behaviour, is possible using flat jacks. The fabric suffers little damage. Some mortar joints need to be raked out but they can be carefully replaced in such a manner that the repair is not noticeable. Accordingly it is a most satisfactory technique particularly for heritage buildings. The technique is now well established and Section 2.1.3 gives several examples from the literature of successful flat jack testing. Epperson and Abrams (1989) showed that flat jack results require some interpretation in order to convert to 'conventionally' obtained results. However as there is not an absolute standard for conventionally obtained results, the investigator should not be overly concerned by this. Nevertheless the flat jacks need to be calibrated, preferably on a material and structure similar to that being tested, in order that the results can be correctly and confidently interpreted. Kingsley and Noland (1987) drew attention to the situation when brickwork with frogged bricks is being tested as the presence of a frog may not enable full contact of jack and masonry. Their solution was to use very thin flat jacks as fluid cushion shims adjacent to the frog. 7.1.3 Borehole dilatometer test for masonry The borehole dilatometer test, or internal fracture test, in which a probe exerts hydrostatic pressure on the surface of a borehole (or core hole) enables additional information on deformability of masonry to that obtained by flat jack tests. There has been some doubt cast on the suitability of the method for low compressive strength (<7 MPa) materials by de Vekey (1991A). 7.1.4 Reconstituted masonry tests Most reconstituted masonry has been made using original stone or brick units bonded with mortar prepared in the laboratory to simulate the old mortar. Very often the objective of the researchers was to compare the properties of reconstituted walls with those strengthened with cement grout in order to find the likely effect of strengthening on the actual walls. The strength and stress/strain behaviour of ' old' and 'reconstitutedJ masonry were compared by Pistone and Roccati (1988, 1991). While the results were of the same order, which was to be expected as masonry strength depends more on unit strength than on mortar strength, the comparisons were not good. Perhaps this is not surprising as the interaction between unit and mortar is not well understood and simulated mortar is likely to have different interactions than old mortar. Conservation of older building stock, throughout the world, is now practised much more than it was even a few years ago. As the older societies, such as those in Europe, have a large number of old masonry buildings, it is understandable that masonry conservation techniques are to a large extent being led by European investigators. Certainly information on masonry conservation has proliferated in the last few years. While chemical, petrographic and mineralogical properties of historic mortars are interesting and informative, the author has yet to be convinced of the importance of tests for these properties when masonry is to be repaired or conserved. The emphasis should not be on imitating these properties but in ensuring that the short and long term movements of the new mortar (and masonry) imitates those of the old mortar (and masonry) and that the stiffnesses are comparable. 7.1.5 Alternative methods for masonry compressive strength Instead of cutting out a large sample from old masonry, Pume (1991) removed one brick from which he took several vertical cores. Using calibration curves he adjusted forthe height/width ratio to obtain an unconfined brick strength. With a hardness test on the mortar, described in Section 3.5, Pume was able to estimate the mortar strength. Again using calibration curves the unconfined compressive strength of the brickwork could be estimated from the brick and mortar strengths, to within 10% accuracy according to Pume. This procedure relies on having a large number of experimental results of three relationships between: (a) unconfined brick strength and compression test results on (short) cores incorporating the effect of the height/width ratio, (b) mortar hardness, obtained with a particular tool, and mortar strength, (c) masonry strength and the strength of its mortar and brick constituents. With such information on old masonry of the area, the method is a good one. Unfortunately most investigators do not have such background data. Where a large amount of restoration of old masonry is occurring, or will occur in the future, the collection of such data should be commenced so that this technique can be utilised in the future.

A different approach using horizontal cores was investigated by Berger (1989). He contended that the ratio between the Brazilian tensile strength of cores with and without mortar beds is the same as the ratio between masonry and brick strength. Given the brick unit strength, therefore only horizontal core tests are needed to estimate the masonry strength. While Berger showed that his contention was correct, it needs further verification experimentally before the method can be applied universally. Regrettably the technique is not suitable for stone masonry or for brickwork with low mortar strength. 7.1.6 Masonry compression test results The compression test results on old stonework and brickwork, given in the Appendix in Tables 1 and 2 respectively, must be viewed with caution as the results were obtained from several different test procedures with a variety of different boundary conditions, specimen sizes and loading methods. Notwithstanding this the results show a wide range of compressive strengths and moduli of elasticity. The comments of the above paragraph indicate a need in masonry research for either standardization across the world on methods of measurement of mechanical properties or for means of correlating results from one method with those of another. Currently researchers are getting results which, although invaluable for their particular investigation, are often of little use to others because of the particular test conditions used. 3 9 7.1.7 Mortar compression tests Direct compression tests on mortar samples are rare owing to the thinness of mortar beds and the difficulty in extracting a sample which can be satisfactorily tested. However Baronio and Binda (1991) were able to cut mortar cubes of mean side length 30 mm from the masonry of a collapsed tower and to obtain mortar strengths and moduli of elasticity. 7.2 Tension and Shear Tests 7.2.1 Tension tests In the Brazilian tension test a cylinder is diagonally compressed and the masonry or unit fails in splitting along the loaded diagonal. Assuming a homogeneous and isotropic material, the splitting strength is also the 'shear' strength. Some researchers have used this test on old masonry - see Section 2.3. 7.2.2 Shear tests There are two types of shear test: (a) the 'shove' test for in-plane sliding resistance along a mortar bed, and (b) tests resulting in cracks angled to the mortar beds which occurs in 'racking' of a wall or in a diagonally compressed wallette. The 'shove' test is less destructive of the masonry as it only requires the removal of one masonry unit, adjacent to the 'test' unit, and a perpend at the other end of the 'test' unit. While it may be useful to determine the sliding shear resistance, the 'diagonal shearJ resistance of masonry is more important as failure, particularly in seismic situations, is more likely in diagonal shear. Unfortunately the relationship between the two types of shear failure is not known though Epperson and Abrams (1989) attempted unsuccessfully to find one both theoretically and experimentally. There have been several sliding shear tests on old masonry - see Section 2.5 - with the findings of Atkinson et a1 (1989) being of particular significance. They found that under cyclic loading of masonry bed joints the shear strengths, whether peak strength during the first cycle or residual strength during later cycles, were well represented by the Mohr Coulomb criterion with friction coefficients between 0.64 and 0.75 for laboratory specimens. Field specimens had lower shear strengths. In both types of shear test the results are very dependent on the vertical stress level. Probably because of this the relationship between Brazilian tension results and shear test results is not apparent. Further it is unfortunate that not all researchers record this vertical stress level when giving their experimental shear strengths. 7.3 General Comments on Direct Mechanical Tests Tomazevic and Anicic (1989) made three forceful statements in regard to the determination of mechanical properties of old masonry: (a) as masonry, particularly old stone masonry, is non- elastic, non-homogeneous and anisotropic it is not possibleto determine mechanical properties with accuracy by testingtheir constituent materials in the laboratory. (b) it is difficult to reproduce old masonry in the laboratory even though chemical and mechanical tests of mortar and units have been conducted. (c) the only satisfactory methods of determining load- carrying capacity of old masonry walls involve either in- situ tests or the cutting out of specimens from the walls and testing them in the laboratory. The author is in general agreement with Tomazevic and Anicic with some minor modifications. In regard to (i), it is possible, albeit difficult, to determine unit and mortar strengths separately and to use the results to estimate masonry strength. The work of Pume (1991) is one such example. All of the evidence to date indicates that (ii) and (iii) are accurate statements provided that in statement (iii) flat jack and borehole dilatometric tests are considered as in-situ tests. 7.4 Indirect Tests for Material and Structural Properties Five subsections are considered in this discussion on indirect tests: preliminary investigations and monitoring, sonic and ultrasonic pulse tests, radar method, thermographic analysis and mortar strength from hardness. 7.4.1 Preliminary investigations and monitoring Prior to determining properties of materials and structures, the wise investigator will research the history of the structure, make a visual and geometric survey of the structure and take cores to determine the composition of the masonry. Each of these aspects are considered in detail in Section 3.1. The use of instruments in a building to measure crack widths and lengths, horizontal and vertical movements, rotations, temperature and soil behaviour over time may be essential. Sometimes the investigator while aware of structural defects, such as cracks or tilting, may wish to monitor the defects over a period of time to determine whether the situation is stable or the defect is increasing. The result of the monitoring adds to the investigators information on the structure and assists in determining the cause of the defect and in the most appropriate treatment to be undertaken. After the repair or conservation measure has been completed, it may be important for the investigator to further monitor the behaviour of the structure in order to glean the effectiveness of the repair. The measuring instruments used may include extensometers, clinometers, plumb bobs and tape measures all in association with recording equipment, cameras and photogrammetric equipment. Sections 3.1 and 3.6 give further details.

7.4.2 Sonic and ultrasonic pulse tests The measurement of the time taken for a pulse to travel in a material between a transmitter and a receiver and the analysis of the signal wave gives information on the material through which the pulse has travelled. Sonic and ultrasonic pulse velocitytests have proved invaluable in determining the condition of material and in detecting the uniformity of the material. For instance the location and extent of cracks can be found. It appears that the longer wavelength of the sonic pulses is more suitable for masonry as there is likely to be less scatter in the received signal according to Epperson and Abrams (1989). Section 3.2 gives a number of examples of the use of these methods in old masonry. Unfortunately researchers have not yet found a way to determine absolute strength properties using these tests although relative strengths in like material or construction is possible. In the author's opinion it is unlikely that sonic or ultrasonic testing will be able to be developed further in this regard. 7.4.3 Radar method The reflection of high frequency electromagnetic waves from materials of different dielectric constants are received and transformed into electrical signals in the radar method. This enables internal discontinuities in the masonry, e.g. damp areas, cavities and cracks, metal and other inserts, to be accurately located. The method is in its infancy for masonry but its potential is great according to de Vekey (1991B) and Forde (1991) both of whom have used the technique. They both have commented that the current drawback of the method is caused by the high sensitivity of the method as all changes of material are picked up. As masonry construction, even without defects, is so inhomogeneous the interpretation of the received signals requires considerable skill and experience. Further the apparatus required is expensive. Whether the method can eventually be used to determine absolute strengths remains to be seen. Some examples in which the radar method has been used are given in section 3.3. 7.4.4 Thermographic analysis By the measurement of radiant energy emitted from the surface, areas of different material or moisture content can be detected by thermographic analysis. The penetration depth possible, however, is a few centimetres which restricts the application to such a task as detecting 'surface' construction details behind a plaster layer for instance. 7.4.5 Mortar strength from hardness Three methods of measuring the hardness of mortar have been developed and are described in Section 3.5. Eachtechnique enables the traditional and crude method used by many engineers of scratching the mortar with a hard object and roughly guessing the mortar strength by the perceived hardness to be replaced by a scientific method. In the case of Pume (1989), the depth of penetration caused by a percussion drill is measured and the mortar strength estimated from an empirical formula which is the result of many tests. The mortar strength so obtained is used with effect by Pume to assist in the estimation of the masonry strength as indicated in Sections 2.1.6 and 3.5. 7.5 Dynamic Tests and Modelling

Surprisingly there are not many dynamic tests of old masonry buildings reported in the literature. While UNESCO (1982 and 1983) reported that more than 70 buildings have been subjected to forced vibrations the author found only three reports of dynamic tests; those of Penelis et a1 (1983), Tomazevic and Anicic (1989) and Modena (1991). In each of these cases fundamental frequencies were obtained by test but the reports gave little or no information on methods or further results. As Rossi (1990) pointed out, many dynamic parameters can be obtained using 'natural' loading such as the effect of traffic vibrating the building through the foundation or bell ringing.

Some dynamic tests on models were conducted - see Section 4. Obviously dynamic testing of the actual structure, particularly when the objective is the determination of likely seismic response, is an area of importance and it needs further investigation. The topic of dynamic modelling is beyond the scope of this report and it has been covered by Bruneau and Boussabah (1991). However some further papers of interest have been written since the Bruneau and Boussabah report and these are briefly discussed in Section 5.2. 7.6 Performance of Masonry in Earthquakes The damage to masonry buildings in earthquakes may be grouped into effects under four general categories: quality of materials and construction, connections between structural elements, structural layout and soil-structure interaction. 7.6.1 Quality of materials and construction The effect of poor quality mortar assisting in damage or failure was indicated in several reports: In the Tianjin earthquake, reported by Guoliang (1979), low mortar strength was instrumental in creating weak structural connections between timber floors and masonry walls; In the Agadir earthquake (National Oceanic and Atmospheric Administration 1972) and Peru earthquake (Earthquake Engineering Research Institute 1970) weak mud or earth mortar was used in the aciobe construction; Erdik (1990) reported that poor quality mortar badly affected performance in the Turkish earthquakes; In the Armenia earthquake (Wyllie and Filson 1989) and Newcastle earthquake (Page 1991) not only was the mortar weak but also the mortar was worn away and subsequent maintenance was not apparent. In the case of the Newcastle earthquake this meant that the wall ties were not satisfactorily anchored.

Better quality solid brick units fared considerably better than lower quality hollow bricks and concrete blocks in the Central Greece earthquake (Carydis et a1 1982). There are several examples showing that well constructed buildings give noticeably better performance in earthquakes:

Maitland (1988) reported that well constructed 18th century adobe and brick churches in the Peru earthquake survived whereas poorly constructed adobe houses in the same area collapsed. The churches often incorporated wooden posts within the masonry around doors and windows; In the Turkish earthquakes Erdik (1990) reported that 75% of good quality stone houses survived whereas only 25% of poor quality dwellings survived; The buildings of the Village Museum in Rumania (Tezcan et a1 1978) were owner-built, using good building practices and light roof systems, survived whereas mud houses of lower construction standards were extensively damaged; Damaged and collapsed buildings in Newcastle (Page 1991) generally exhibited low standards of design, detailing, workmanship and lack of maintenance. 7.6.2 Connection between structural elements Perhaps damage or collapse of masonry buildings in earthquakes has most frequently been attributed to the weakness in the connections between the various structural elements: In Tianjin (Guoliang, 1979) connections between walls and floors were weak and led to collapse; Tomazevic and Anicic (1989) reported that in Yugoslavian earthquakes separations at wall intersections and between walls and floors were common and frequently led to collapse; With no interconnection between precast concrete planks and between the plank floors and end and side masonry walls in the Armenia earthquake (Wyllie and Filson, 1989) floors and thick stone walls collapsed; In the Turkish earthquakes Erdik (1990) reported that inadequate connection of roof beams to external walls, inadequate construction or the absence of the beams and inadequate corner connections led to roof collapses. On the other hand instances are reported where survival of buildings was considered to be due to the provision of satisfactory anchoring of structural elements one to another: In the San Fernando earthquake, (Jennings, 1971) a two storey building survived as the masonry gable wall was anchored to the roof framing; Yaoxian and Xihui (1980) reported that brick buildings with closed ring beams did not collapse in the Tangshan earthquake; In the Manjil earthquake (Moinfar and Naderzadeh 1990) reinforced concrete tie beams under the roofs remained in position despite the collapse of parts of the masonry walls. Sometimes the connections of structural elements were supposed to be provided by metal ties. At Saguenay (Allen et al, 1989) some partial collapses of masonry veneer and block partitions occurred due to lack of ties and in Newcastle (Page 1991) inadequately tied gable ends and inadequate lateral supporting, due to lack of or corrosion of ties, exacerbated wall collapses. Several instances of inadequate bonding of wythes of walls, leading to wall failure, have been reported:

At Bandar Abbass, Iran (Afshar et al, 1977) cavities between wythes of mud brick walls were filled only with rubble and mud mortar and failure of the walls occurred. Where stone units connected one side of the wall with the other the damage was much less; In the Central Greece earthquake, Carydis et a1 (1982) mentioned the poor performance of stone masonry walls with two unconnected faces and the cavity filled with rubble and earth.

Wyllie and Filson (1989) reported that pre-1970 industrial structures, with stone wythes connected only with mortar collar joints, behaved badly in the Armenia earthquake; Separation of peripheral walls was reported by Tomazevic and Anicic (1989) in Yugoslavian earthquakes; Independent behaviour of inner and outer skins of walls was reported in Turkish earthquakes (Erdik 1990). 7.6.3 Structural layout Tezcan et a1 (1978), reporting on the Romanian earthquake and Deppe (1988), reporting on the Whittier Narrows earthquake, wrote on the improved performance of buildings 'strengthened' by light partitions or cross walls. In the author's view this 'strengthening' is due to the effect that the additions had in tying the building together. In contrast the additions, renovations and alterations to stone masonry buildings in central Greece, where masonry walls were removed to create more open space and replaced by slender steel columns, resulted in worsened performance according to Carydis et a1 (1982). The effect of door and window openings in masonry walls is indicated in some reports: In the Yugoslavian earthquakes (Tomazevic and Anicic, 1989) and at Saguenay (Allen et al, 1989) cracking at window soffits and diagonal cracks at window piers and spandrels sometimes leading to failure were recorded. It is interesting to note that Allen et a1 reported no damage in thick masonry walls, without roof support, which they suggested was due to the fact that, as there were no openings, there was no change in wall section and hence no sudden change in wall stiffness; Erdik (1990) reported that excessive number of openings in walls considerably weakened masonry walls in Turkish earthquakes and many such walls collapsed. Because some wooden floors were not stiff enough to provide adequate diaphragm action, such that unsynchronised oscillations occurred at the wall-floor connection, wall failures occurred in the Slovenia and Friuli earthquakes (Turnsek et al, 1978) and in the Newcastle earthquake (Page, 1991). A similar circumstance was reported by Jablonski et a1 (1990) in that the 'different responsef of a roof structure and the top of a masonry wall in the Loma Prieta earthquake resulted in the partial collapse of the roof. It has been suggested that the very massiveness of some old masonry walls attributed to their survival in earthquakes. Examples are: The Romanian earthquake (Tezcan et al, 1978); Carydis et a1 (1982) reported that the 140 year old Athens Cathedral, of massive construction, survived the 1894 earthquake whereas less massive masonry buildings in the same vicinity collapsed. Further the massive stonework of the Parthenon has also survived through many earthquakes; Allen et a1 (1989) on the Saguenay earthquake suggested that the wall displacement being only a small fraction of the wall thickness was a contributory factor in the survival of a massive wall. The author believes that the large thicknesses of massive walls provides the stability to withstand earthquake movements. But heaviness of roof structure, resulting in high inertial forces above the ground, has contributed to many failures particularly of adobe buildings, as indicated in the National Oceanic and Atmospheric Administration (1972) report on the Agadir earthquake. Light roof systems were reported by Tezcan et a1 (1978) as being instrumental in the survival of some Romanian buildings. The danger of torsional failures in buildings of asymmetrical plan shape is well known and documented in the literature of earthquake damage of every building material. A recent example occurred in a masonry building in the Newcastle earthquake (Institution of Engineers Australia 1990). The bottom floor of an apartment building was very asymmetric, to allow for vehicle access and parking, and the resulting eccentricity of stiffness caused extensive cracking to stiff masonry walls on one side of the building. 7.6.4 Soil-structure interaction As masonry structures particularly those of low height have high fundamental frequencies, for most earthquakes they have to carry considerably greater inertia forces than other buildings of lower fundamental frequencies. However the characteristics of the local soil can alter this situation dramatically as these two examples testify: In the 1985 earthquake off the western coast of Mexico (Klingner et a1 1987), the performance of buildings in Mexico City some 400 km from the epicentre was dominated by the underlying deep soft clay deposits. Stiff structures such as older low rise masonry buildings survived whereas higher more flexible buildings with longer periods of vibration failed; Carydis et a1 (1982) observed that in the Central Greece earthquake stiff structures in the epicentral region survived when founded on very soft soil but were badly damaged if founded on stiff soil. The performance of masonry buildings when on alluvial soils is generally not good as reported by the Earthquake Engineering Research Institute (1970) on the Peru earthquake and Page (1991) on the Newcastle earthquake. Foundation settlement is not well handled by masonry buildings as in the Tianjin earthquake (Guoliang 1979) and in the Loma Prieta earthquake (Jablonski et a1 1990) . Allen et a1 (1989) observed in the Saguenay earthquake that, up to 200 km from the epicentre, building damage was more dependent on the ground conditions than on the distance from the epicentre.

7.6.5 General comments on earthquake damage reports The above sections 7.6.1 to 7.6.4 indicate the effects of many factors on the likely survival of masonry buildings in earthquakes. However there are still some situations in which it is not clear why some masonry buildings failed and others were relatively undamaged when they appeared to be subjected to the same conditions. An example of this is in the El-Asnam earthquake (Earthquake Engineering Research Institute 1983) where a large number of stone houses and adobe huts on the fault or within 50m of the fault survived while other buildings collapsed. As there are different expressions for earthquake severity and damage levels given in the various reports on earthquakes, it is difficult to make comparisons between building performances. There are no world standards for quality of material or of construction, so statements on quality from one report may not be comparable with statements from another. However some reports do comment on the relative construction standards within a country e.g. Reitherman (1985). In some instances, damage reports suggest that the current earthquake probably widened and extended existing cracks caused by earlier earthquakes. This raises the important point that structures may be weakened by earlier earthquakes so that their performance in future earthquakes may be inferior.

8. ACKNOWLEDGEMENTS The author is grateful to the University of Melbourne for the study leave, and to the University, the Institute for Research in Construction, and Public Works Canada for financial assistance on expenses. The encouragement and assistance of Dr Paul Maurenbrecher and the help of the IRC library were appreciated.

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(editors) (1990), Conservation of Buildinq and Decorative Stone, Vol. 2, Butterworth-Heinemann, London, p 254. Augusti G. and D'Agastino S. (1988), "On the seismic protection of ancient monuments", Proc . 9th World Conference on Earthquake Enqineerinq, Tokyo-Kyoto, VII-12-4-14, VII, pp 481-486. Bahr H.P. (1988), "The use of photogrammetry in the analysis of deformation", Stable - Unstable? Structural Consolidation of Ancient Buildinqs, Centre for the Conservation of Historic Towns and Buildings, Leuven University Press, pp 195-213. Beckmann P. and Happold E. (1983), "Appraisal - a cyclical process of inspection and calculation", IABSE Symposium, Venice, pp 31-38. Benedetti D. and Castellani A. (1980), "Experimental determination of the seismic resistance of repaired masonry structures", Proc. 7th World Conference on Earthquake Enqineerinq, Istanbul, Structural Aspects Part 111, Vol. 6, pp 159-166. Beranek W. J. (1988), "Understanding of structures", Stable - Unstable? Structural Consolidation of Ancient Buildinqs, Centre for the Conservation of Historic Towns and Buildings, Leuven University Press, pp 29-43. Bernardini A., Modena C., Turnsek V. and Vescovi U. (1980), "A comparison of three laboratory test methods used to determine the shear resistance of masonry walls", Proc. 7th World Conference on Earthquake Enqineerinq, Istanbul, Structural Aspects Part IV, Vol. 7, pp 181-184. Braga F. and Dolce M. (1982), "A method for the analyses of anti- seismic masonry multi story buildings", Proc. 6th International Brick Masonry Conference, Rome, pp 1088-1099. Braga F., Dolce M., Fabrizi C. and Liberatore D. (1986), "Evaluation of a conventionally defined vulnerability of buildings based on surveyed damage data", Proc. 8th European Conference on Earthquake Enuineerinq, Lisbon, Vol. 1, Topic 2.3, pp 33-40. Chen Y.Q. and Soonq T.T. (19881, "Seismic performance of Chinese ancient pagodasw,- Proc. 9th World conference on Earthquake Enqineerinq, Tokyo-Kyoto, VII-12-4-15, VII, pp 487-492. CIB W23 Wall Structures (1990), Reporter Pume D., Assessment and redesiqn of masonrv wall structures, 5th (final) draft of report. Cifani G. et a1 (1988), "Retrofitting of old buildings -case study of Barrea (middle Italy) ", Proc. 9th World Conference on Earthquake Enqineerinq, Tokyo-Kyoto, VII-12-4-13, VII, pp 413-480. Como M., Grimaldi I. and Lanni G. (1988), "New results on the horizontal strength evaluation of masonry buildings and monuments", Proc. 9th World Conference on Earthquake Enqineerinq, Tokyo-Kyoto, VI-9-2-17, pp 187-192. Croci G. (1983), "Safety of the Tabularium and Palazzo Senatorio Monuments", IABSE Svmposium, Venice, pp 39-46. Delrue J. (1988), "Earthquakes as a major natural seiection of structural forms", Stable - Unstable? Structural Consolidation of Ancient Buildinqs, Centre for the Conservation of Historic Towns and Buildings, Leuven University Press, pp 287-298. Di Stefano R. (1988), "The limits of the intervention in the stability of monuments with regard to the problems of protection", Stable - Unstable? Structural Consolidation of Ancient Buildinqs, Centre for the Conservation of Historic Towns and Buildings, Leuven University Press, pp 277-285. Earthquake Engineering Research Institute (1980), "The 1976 Tangshan, China Earthquake", Proc. 2nd US National Conference on Earthquake Enqineerinq, Stanford. Fattal S.G. and Cattaneo L.E. (1977), "Evaluation of structural properties of masonry in existing buildings", NBS Building Science, Series 62, p 127. Forde M.C. and Batchelor A. J. (1984), "Low frequency NDT testing of historic structures", Proc. 3rd European Conference on NDT Testinq, Florence. Forell N.F. and Nordenson G.J.P. (1980), "A seismic reinforcement of existing buildings", Journal of the Structural Division. ASCE, Vol. 106, pp 1907-1919. Fournier D'Albe E.M. (1988), "The assessment of seismic risk" Seismic Risk Assessment and Desiqn of Building Structures, INEEC Series on Engineering Aspects of Earthquake Phenomena, A.Koridze (ed. ) , Omega Scientific, pp 31-46. Gavarini C. (1987A), "Evaluation and retrofit of ordinary and monumental masonry buildings in seismic zones of Italy", Proc. Second Joint USA-Italy Workshop on Evaluation and Retrofit of Masonry Structures, Los Angeles et al, pp 157-168. Gavarini C. (1987B), "Towards systematic seismic retrofitting of existing masonry buildings in Italy", Proc. 4th North American Masonrv Conference, Los Angeles, Vol. 1, pp 24-1 to 24-13. Gavarini C. (1988), "An attempt for a new definition of seismic vulnerability of masonry buildings", Proc. 9th World Conference on Earthquake Enqineerinq, Tokyo-Kyoto, SL-8, VIII, pp 1147-1152. Gavarini C. (1991), "Monumental buildings in seismic zones - conservation, restoration, retrofitting", Proc 9th International Brick/Block Masonrv Conference, Berlin, Vol. 3, pp 1539-1546. Gifford E.W.H. and Taylor P. (1964), "The restoration of ancient buildings", The Structural Engineer, No. 10, Vol. 42, pp 327-340. Grim C.T. (1979), "Masonry maintenance and restoration - a guide to the literature - Structural renovation and rehabilitation of buildings", Boston CSE/ASCE Structural Group Lecture Series. Grim C.T. (1980), "Masonry failure investigations", Masonrv: Materials, Properties and Performance. ASTM Symposium, Florida. Heyman J. (1966), "The Stone Skeleton", International Journal of Solids and Structures, Vol. 2, pp 249-279. Heyman J. (1982), The Masonrv Arch, Ellis Horwood Ltd. ICOMOS (1989), "La Sauvegarde du Patrimoine Architectonique de L'Armenie", ICOMOS Information, Comite National dfURSS de 1' Icomos, No. 2, pp 11-22. Institution of Structural Engineers (1980), Appraisal of Existinq Structures, I.Struct.E., London. Kariotis J.C., Ewing R.D. and Johnson A.W. (1985A), "Predictions of stability for unreinforced brick masonry walls shaken by earthquakes", Proc. 7th International Brick Masonrv Conference, Melbourne, Vol. 2, pp 1175-1183. Kariotis J.C., Ewing R.D. and Johnson A.W. (1985B), "Strength determination and shear failure moves of unreinforced brick masonry with low strength mortar", Proc. 7th International Brick Masonry Conference, Melbourne, Vol. 2, pp 1327-1337. Kariotis J.C., Ewing R.D., Johnson A.W. and Adham S.A. (1985), "Methodology for mitigation of earthquake hazards in unreinforced brick masonry buildings", Proc. 7th International Brick Masonrv Conference, Melbourne, Vol. 2, pp 1339-1350. Kingsley G.R. and Noland J.L. (1987), "An overview of non destructive techniques for evaluatins structural properties of brick masonry", pro&. Second Joint ~~~-7taly~orksho~~on'~va1uation and Retrofit of Masonrv Structures, Los Angeles et al, pp 226-237. Kingsley G.R., Noland J.L. and Atkinson, R.H. (1987), "Non destructive evaluation of masonry structures using sonic and ultrasonic pulse velocity techniques", Proc. 4th North American Masonry Conference, Los Angeles, pp 67-1 to 67-16. Koridze A. (ed.) (19871, Ensineerins Aspects of Earthquake Phenomena, INEEC Series on Engineering Aspects of Earthquake Phenomena, Omega Scientific. Koridze A. (ed.) (19881, Seismic Risk Assessment and Desiqn of Buildins Structures, INEEC Series on Engineering Aspects of Earthquake Phenomena, Omega Scientific.

Koridze A. (ed.) (19901, Earthquake Damase Evaluation and Vulnerabilitv Analysis of Buildins Structures,, INEEC Series on Engineering Aspects of Earthquake Phenomena, Omega Scientific. Langenbach R. (1989), "Bricks, mortar and earthquakes", Journal of Preservation Technoloqy, Vol. XXI, Nos. 3 and 4, pp 30-43. Lemaire R.M. and Van Balen K. (eds.) (1988), Stable - Unstable? Structural Consolidation of Ancient Buildinqs, Centre for the Conservation of Historic Towns and Buildings, Leuven University Press, p 342. Modena C. (1987), "Vulnerability analysis of large groups of buildings and of single buildings", Proc. Second Joint USA-Italv Workshop on Evaluation and Retrofit of Masonrv Structures, Los Angeles et al, pp 239-255. Palmer A.C. (19661, "A limit theorem for materials with non- associated flow laws", Journal de Mecanique, Vol. 5, No. 2, pp 217-222. Parducci A. and Vaselli R. (1988), "Structural rehabilitation of Palazzo Valadier in Rome", Proc. 8th International Brick Masonrv Conference, Dublin, pp 1812-1823. Petrovski J. (1988), "Earthquake vulnerability and loss assessment for physical and urban planning", Seismic Risk Assessment and ~esiqnof Buildinq Structures, INEEC Series on Engineering Aspects of Earthquake Phenomena, Omega Scientific, pp 1-17. Priestley M.J.N. (1985), "Seismic behaviour of unreinforcedmasonry walls", Bulletin of the New National Society for Earthquake Enqineerinq, Vol. 18, No. 2, pp 191-205. Pume D. (1987A), "Assessment of existing masonry buildings in Czechoslovakia", Masonry International, Vol. 1, pp 11-12. Pume D. (reporter) (1987B), "Assessment and redesign of masonry wall structures" 24th meetinq of CIB W23 - Wall Structures Committee, Stockholm. Qian Pei-Fenq and Qian D.A. (1985), "Analysis of earthquake damage to brick structures", Proc. 7th International Brick Masonry Conference, Vol. 2, Melbourne, pp 1207-1212. Qinglin W. and Xiuyi W. (1988), "The evaluation of compressive strength of brick masonry in situ", Proc. 8th International Brick and Block Masonry Conference, Dublin, pp 1725-1731. Reitherman R. (1984), "Seismic damage to unreinforced masonry buildings", Scientific Service. Rocchi P. and Bussi L. (1991), "Critical-historical analysis and in-situ tests of masonry in order to determine the characteristic strengths and group behaviour: first communication", (in Italian), Proc. 9th International Brick/Block Masonry Conference, Berlin, Vol. 3, pp 1481-1487. Sabnis G.M. and Millstein L. (1982), "Use of non-destructive methods to evaluate and investigate condition of buildings and bridges", Proc. International Conference on Rehabilitation of Buildinqs and Bridqes Includinq Investiqations, Part I, No. 5, pp 36-40. Shepherd R. (1978), "High earthquake risk buildings in New Zealand", Earthcruake Enqineerinq and Structural Dynamics, Vol. 6, pp 383-395. Sheppard P. (1988), "Dynamic characteristics of tall, pre-1965 masonry buildings, as a basis for their seismic analysis and strengthening", Preprints, Conference on Civil Enqineerinq Dvnamics, Bristol. Sheppard P. and Lutman M. (1988), "Estimation of expected seismic vulnerability: a simple methodology for medium sized groups of older buildi~gs", Seismic Risk ~ssessment and Desisn of-~uildinq Structures, INEEC Series on Engineering Aspects of Earthquake Phenomena, Omega Scientific, pp 47-62. Sheppard P. and Tercel J.S. (1980), "The effect of repair and strengthening methods for masonry walls", Proc. 7th World Conference on Earthquake Enqineerinq, Structural Aspects, Part 111, Vol. 6, pp 255-262. Snell L.M. (1978), "Non destructive testing techniques to evaluate existing masonry construction", Proc. North American Masonry Conference, Boulder, pp 73-1 to 73.6. Stockbridge J. (1988), "Field and laboratory testing for evaluating the condition of masonry buildings", Proc. 8th International Brick and Block Masonry Conference, Dublin, pp 1713-1724. Tomazevic M. and Turnsek V. (19821, "Verification of the seismic resistance of masonry buildings", Proc. British Ceramic Society, No.30, Sept., Load-bearing Brickwork (7), pp 360-369. Turnsek V. and Cacovic F. (1970), "Some experimental results on the strength of brick masonry walls", Proc. 2nd International Brick Masonry Conference, Stoke-on-Trent, pp 149-156. Turnsek V., Sheppard P. and Tercel J.S. (19821, "Parameters of the seismic resistance of stone-masonry walls and buildings", Proc. British Ceramic Societv, No.30, Sept., Load-bearing Brickwork (7), pp 370-380. Van Gemert D. (1988), "The use of grouting for the consolidation of historic masonry constructions. Advantages and limitations of the method", Stable - Unstable? Structural Consolidation of Ancient Buildinqs, Centre for the Conservation of Historic Towns and Buildings, Leuven University Press, pp 265-276. Wenzel F. (1988), "How to ensure that the next step in the conservation of a building will be an appropriate one?", Stable - Unstable? Structural Consolidation of Ancient Buildinqs, Centre for the Conservation of Historic Towns and Buildings, Leuven University Press, pp 327-338. Wesley D.A., Kennedy R.P. and Richter P. J. (1980), "Analysis of the seismic collapse capacity of unreinforced masonry wall structures", Proc. 7th World Conference on Earthquake Enqineerinq, Structural Aspects, Part 111, Vol. 6, pp 255-262. Whitman R.V., Heger R.J., Luft R.W. and Krimgold F. (1980), "Seismic resistance of existing buildings", Journal of the Structural Division, ASCE, Vol. 106, pp 1573-1592. Zaupa F., Modena C. and Odorizzi S. (1983), "A method to assess the reliability of actual buildings", IABSE Svm~osium,Venice, pp 259-266. 11. APPENDIX I, I I[ TABLE 1 STONEWORK COMPRESSION and TENSION TEST RESULTS I Reference Type of Stonework

Turnsek Model. 2 outer wythes uncoursed, rubble between Tomazevic Laboratory made specimens. and Limestone uncoursed, with 0.02 Sheppard earth mortar of lime/clay - (1982) sand. Limestone uncoursed, with 0.04 mortar of lime/clean sand, - compve.str. 0.5-1.0 MPa. - Limestone partly coursed, 0.08 with mortar of lime/clean t 0 sand, comDve.str. 1.0 MPa 0.12 Binda Weak sandstone. et a1 Hard sandstone. (1982) Limestone- normal to bed plane; parallel to bed plane. Mortar. Sheppard Stone and brick- (1985) reproduced (1), reproduced (2). Rossi Orvietto Cathedra1,1290-1330: (1987) wall- basalt and travertine; foundation-tuff; ground-pozzolan. Gubbio "Madonna del Prato". Tomazevic Uncoursed stone- and clayey sand mortar, 0.02 Anicic lime mortar, sand (1) , 0.08 (1989) lime mortar, sand (2), 0.08 lime mortar, sand (3) . 0.12 Modena Italian (1989) Basilica

- Baronio Pavia Tower, and Binda rubble of conglomerate and (1989) mortar, external brick face

lote: Expla lations of superscripts are in N and 2. 65

TABLE 2 BRICKWORK COMPRESSION and TENSION TEST RESULTS Reference Type of Brickwork Compl E2 ens^ (MPa) (MPa) (MPa) Kingsley and School-exterior wythe; 2640 Noland (1987) interior wythe. 7 93 200 year old house. 2620 Rossi Rome "Romolo's - 2860 (1987) Temple" 30 9AD. t o - 4800 Milan 1380-1600 -St Eustorgio. 3.1 1990 Milan 1496 -The Last Supper. 3.0 4000 Pistone 19th century column 8.1 and 8.2 Roccati 18th century building: (1988) wallette, 6.0 prisms; 5.6 4.5 rebuilt prism. 3.6 17th century building: rebuilt wallette, 4.4 rebuilt prisms. 3.8 to 5.2 Tomazevic and Masonry- Anicic (1989) lime mortar 2.0 800 0.09 Epperson and 1917 building Abrams (1989) 4-wythe 12.0 3500 Modena Reconstituted- 2.4 1010 (1989) old bricks and 2.6 1200 new mortars 3.1 1150 9.2 1400 Pistone 18th century building: and wallette; 7.3 905 Roccati reconstructed wallettes; (1991) with mortar 1, 5.0 975 t 0 t 0 6.1 1170 with mortar 2. 8.0 1740 t0 to 9.3 2140 Early 20th century 5.6 1740 building - wallettes. 6.7 1740 Tote: Explanations of superscripts are in Notes to Tables L and 2. Notes to Tables 1 and 2: Compression test results are from tests on large or small specimens cut out of walls, re-constituted masonry or from in- situ testing using flat jacks. Modulus of elasticity (E) results are from the same sources as above. Results from diagonal compression tests giving splitting tension failures. While the results presented in Tables 1 and 2 give the range of values of mechanical properties which have been obtained in old stone and brick structures, care must be exercised in comparing magnitudes as a variety of techniques, boundary conditions and specimen sizes were used in the various tests. ELEVATION

v.ltiC* mi* d WQ &mnt

3.n I* .DIO p4 LOI 6% 2.x m - 1- 1 ' I . 4 .I!. -*.-0.a _- ../- OY-. I -

. eonerala Uoeb d heiphl UZSm

Set-up for carrying out in-situ test of stone-and-brick masonry wall element.

Figure 1: Shear test arrangement due to Sheppard (1985) Panel diagram with positions of deformmetric bases and of cente- simal comparators.

Figure 2: Shear test arrangement due to Benussi and Mele (1988)