INVACO2: International Seminar, INNOVATION & VALORIZATION IN CIVIL ENGINEERING & CONSTRUCTION MATERIALS

N° 5P-232 EL KECHEBOUR B. University of Science and Technologie Houari Boumedien, ,

The Systemic approach of the endamagement of buildings in concrete reinforcement: Case study of Boumerdes (Algeria) earthquake on May 2003.

EL KECHEBOUR Boualem * *University of Science and Technologie Houari Boumedien, (USTHB), Faculty of civil engineering, Bab Ezzouar, Algiers, Algeria. Laboratoire Eau, Environnement, Geotechnique et Ouvrages (LEEGO). [email protected]

NECHNECH Ammar University of Science and Technologie Houari Boumedien, (USTHB), Faculty of civil engineering, Bab Ezzouar, Algiers, Algeria. Laboratoire Eau, Environnement, Geotechnique et Ouvrages (LEEGO). [email protected]

Abstract

The Goal of this study is an analysis of the endamagement structures of the buildings during the earthquake of Boumredes, on May 21th 2003, in the region of Algiers. The magnitude (6.8 Richter scale) is considered as very strong for the Algerian seismic historicity and strong for the Japan earthquake activity, but the duration (40 seconds) is considered as long. Until this event, the site is not declared as high seismic zone. So, this situation has been the cause of great destructions and damages. The level of the damages induced by this earthquake on the structures can be explained by the interaction between the soil and the building. These collapses are provoked by the real behavior between the soil and the foundations and in others cases, they are provoked by the weakness of the ductility of the reinforced concrete frame elements of the structure. The work begins by the analysis of the damages and the correlation of these damages with the site and the conception of the structures elements. The study finishes by the recommendations about the mitigation of the seismic disaster risk and a conclusion on the necessity to consider the endamagement of structures as impact of interaction of many elements composing a system.

KEYWORDS: building, behavior, systemic approach, earthquake of Boumerdes, site.

1. INTRODUCTION

Nowadays, earthquakes are capable of claiming more lives and doing more damage to the built environment than ever before [1]. The earthquake May 21st, 2003 in North A1geria (Mw~6.8) was a very destructive event which killed 2,273 people, injured more than 8,000 and left over 200,000 homeless, while total estimated economic impact is estimated to US$65 billion [2]. The causative fault is presumed to be an offshore structure, trending approximately NE-SW. Seismological data suggest that the length of the fault is around 40 km [3], while focal mechanism solutions showed reverse faulting, coherent with the compression regime which is present along this collision zone [4].

1.1. The historic of the earthquake in Algeria

In the frame of national expertise helping following the May 21st, 2003 Boumerdes Earthquake, the national institutions and persons specialized on the urban engineering were requested for an analysis on several axis such as micro zoning, assessment of vulnerability of the buildings and establishment of new code of construction. The Government has initiated many international actions for the studies and the reconstruction of the damaged site. The region of North Africa is classified as seismic zone [4]. In the old time, Algeria country has known much seismic disaster [5]. The figure 1 shows Algeria country in the North Africa region, and the figure 2 gives the seismic zone in Algeria. The figure 3 illustrates the parameters acceleration and duration of the Earthquake of Boumerdes.

1 INVACO2: International Seminar, INNOVATION & VALORIZATION IN CIVIL ENGINEERING & CONSTRUCTION MATERIALS

N° 5P-232 EL KECHEBOUR B. University of Science and Technologie Houari Boumedien, Algiers, Algeria

Figure 2. Map of great earthquakes in Algeria Figure 1. Map of the north Algeria country. during the last century (Benouar, 1994). Caracteristics of the Boumerdes Earthquake (Observatory of Monaco, France): Date : 21.05.2003 ; heure GMT : 18h 44' 18" ; Latitude : 36.880° ; longitude : 3.730° ; Profondeur : moyenne (15 km) ; magnitude : 6.7.

1.2. Geology and Tectonics

The area hit by the earthquake corresponds to the easternmost part of the Mitidja basin, an ENE-WSW elongated structure, bounded from the south by the Mts Dahra and Blida, members of the Tellian Atlas mountain range. The basin was formed in the Miocene, as a result of the N-S extensional stress field that was present then [6]; however, in the last 5 million years (since the Pliocene), the Africa - Eurasia convergence bas led to the establishment of a compression al stress regime, oriented approximately N-S to NNW-SSE [7]. The deposits in the alluvial plain consist mostly of sand and silt, which cover the Pliocene – Miocene sediments of the basin (mostly sandstones and silt of considerable thickness). The geological basement of the basin comprises rocks deformed in the Tertiary and Precambrian metamorphic. The fault that was activated in the May 21 earthquake was found to be an offshore structure, trending approximately N45E ("Zemmouri Fault"). The analysis of the earthquake parameters showed that it is a dip-slip, reverse fault that was previously unknown [8]. It is oblique to the well- known Thenia Fault, an active dextral strike-slip structure, which also displays some amount of reverse displacement (Boudiaf and al, 1998). The line of the Thenia fault is WNW-ESE and is linked to the arcuate thrust front of the Tellian Atlas (Kabylie), which, in turn, is also considered to be an active trust fault [9], running from Bouira at the SW of Kabylie, to Bejaia in the east, on the Mediterranean coast.

1.3. Geotechnical conditions and Site effects

The geotechnical conditions in Boumerdes are more or less uniform, which means that they did not play any important part in the spatial distribution of damage. The foundation soil consisted of dry, compact sandy material, a fact that prevented the occurrence of liquefaction in Boumerdes. However, it is noteworthy that the morphological conditions seemed to control the distribution and severity of damage, at least to some extent. Specifically, the collapses of buildings located along, or close to natural or artificial escarpments (such as river banks) were indicative of localized increase in peak ground acceleration. The situation in Boumerdes, in Zemmouri, and , liquefaction phenomena were quite widespread. The effect was quite serious close to the Zemmouri and Djinet, but occurred mainly in rural, uninhabited areas. Sand was liquefied and ejected through linear ground fissures of considerable length. There were also manifestations of lateral spreading on the banks of Isser River. Rockfalls and other slope failure occurrences were limited in number and magnitude. Most of them took place on the coastal national road and a few along the Mediterranean coast. The former affected well consolidated but densely fractured sandstones exposed on steep road cuts; the latter were noticed on loose sand dunes. Coastline retreat and uplift of the sea was also observed: the magnitude of uplift ranged between 0.4-0.8m, between Boumerdes and Zemmouri [10].

2 INVACO2: International Seminar, INNOVATION & VALORIZATION IN CIVIL ENGINEERING & CONSTRUCTION MATERIALS

N° 5P-232 EL KECHEBOUR B. University of Science and Technologie Houari Boumedien, Algiers, Algeria

2. ANALYSIS OF THE DAMAGES OF EARTHQUAKE AND CORRELATIONS

The Algerian earthquake was aggravated by various factors, such as the shallow focal depth (15 km) and the presence of phreatic water layer which is superficial (between 3 and 6 m). The superficial foundation soil consisted of dry, compact sandy material. In Boumerdes, the affected buildings were four- to six- story residential blocks. Most collapses or heavy damage were engendered by the fact that the constructions behaved as first and or second story. This is attributable to the following factors: the first stories (ground floors) were had commonly very large openings, as they were used for commercial purposes and the gravity load-carrying elements of the second floor were insufficient; the exterior cavity walls consisted of an outer leaf that enveloped the frame and the inner shell had usually very low cohesion with the frame.

2.1. The risk factor and interpretation of damages

There are a variety of problems which concern the buildings behavior under dynamic loading. But the areas complexity and loading conditions make the classification of the risk factor difficult. In fact, every building represents a small system which has interaction with the implantation site and the environment. Thus, there is the big system called site and the under systems composed by the buildings.

2.2. Characteristics of the Site

In seismic regions, geotechnical site investigations should obviously include the gathering of information about the physical nature of the site and its environs that will allow an adequate evaluation of seismic hazard to be made. The scope of the investigation will be a matter of professional judgment, depending on the seismicity of the area and the nature of the site, as well as of the proposed or existing construction. In addition to the effects of local soil conditions upon the severity of ground motion, the investigation should cover possible earthquake danger from geological or other consequential hazards such as: fault displacement; Subsidence (flooding and/or differential settlement); Liquefaction of not cohesion soils; Failure of sensitive or quick clays; Landslides; Mudflows; Dam failures; Water waves; Groundwater discharge changes.

2.3. Behavior of the soil

Some synthesized considerations may be afforded funded on the investigations about the collapse and damages of the buildings. In the area of classical soil mechanics dealing with static problems, a major concern has been to evaluate the degree of safety of foundations or soil structures against failure. In the case of vibration and waves, events with shorter period or higher frequency are deemed as phenomena with a shorter time of loading, and conversely a longer period, problem is regarded as the one with a longer time of loading. In what follows, the time of loading will be defined approximately as one quarter of the period at which the load is reciprocated. The problems where the load application lasts for more than tens of second are generally cited as static and those with a shorter time of load application are the target of dynamic problems. It has been generally accepted that the major part of the ground shaking during an earthquake is due to the upward propagation of body waves from an underlying rock formation. Although surface waves are also involved, their effects are generally considered of secondary importance. The body waves consist of shear waves and compressional (or longitudinal) waves. In the case of level ground, each of the waves produces, respectively, shear stress and compressional stress. During the propagation of compressional waves, normal stress is induced in the vertical as well as horizontal direction, thereby producing the triaxial mode of deformation in an element of soil under level ground. Static and dynamic phenomena according to the time of loading are modeled in practice [11].

2.4. The Liquefaction factor

During earthquake shaking, some saturated granular soils may compact, increasing the pore water

3 INVACO2: International Seminar, INNOVATION & VALORIZATION IN CIVIL ENGINEERING & CONSTRUCTION MATERIALS

N° 5P-232 EL KECHEBOUR B. University of Science and Technologie Houari Boumedien, Algiers, Algeria

pressure, thereby decreasing the effective stress which results in a loss of shear strength. This phenomenon is generally referred to as liquefaction . It is usually confined to sands and cohesionless coarse-grained silts, and is more severe in looser, uniformly graded soils, and those with more rounded particles. Also, in truly undrained conditions, gravelly soils can be susceptible to liquefaction. Engineering interest in liquefaction has been high since 1964, when the Great Alaska earthquake and the Niigata earthquake both caused extensive and spectacular liquefaction damage to the ground and structures alike. Flow liquefaction produces dramatic flow failures which are driven by static shear stresses, such as are seen in the failure of earth dams. Cyclic mobility produces deformations which develop incrementally during an earthquake, as a result of cyclic shear stresses with or without a static shear stress regime. Although in cyclic mobility situations, the static shear stresses remain less than the shear strength of the liquefied soil; their presence contributes to lateral spreading on gently sloping ground or essentially flat land adjacent to bodies of water. For example, many deep earthquakes (focal depths >50 km) have produced liquefaction at greater distances [12].

2.5. Effect of earthquake duration on structural reliability

Early studies determined some basic characteristics of strong earthquake duration; found that earthquake duration was critical when quantitatively measuring the damaging effect of strong ground motion on structures. The quantification of the effect of earthquake duration on structural reliability it is a procedure that combines order static and non-linear dynamics was used. Ultimate strength and low-cycle structural damage limit states were applied within a framework in order to estimate the probability of failure for a suite of idealized structures. The structural dynamics problem is formulated for structures that can be idealized as a system with a lumped mass and a massless supporting structure. Linearly elastic structures as well as inelastic Structures subjected to applied dynamic force or earthquake- induced ground motion are considered [13]. The phenomenon fatigue of structures depends of seismic duration. In this vision, the seismic replica can destroy the structures. The original resistance of buildings is very reduced by the number of tremor. This case has been reported about the Boumerdes earthquake. One day after the disaster, a replica provokes the collapse of many buildings. Many studies are engaged in the United States in this field. This problematic concerns the probability to exceed the duration of a normative seismic peak [14].

2.6. Ductility of the frame elements and behavior factor of buildings

Ductility demand in fixed-base structures is not necessarily a decreasing function of structural period, as suggested by traditional design procedures. Analyses of motions recorded on soft soils have shown increasing trends in ductility demand at periods higher than the predominant period of the motions [15]. The ductility of a member or structure may be defined in general terms by the ratio ductility = deformation at failure/deformation at yield. In the design of buildings, the taking in account of the material is imposed by the costs and the damping is not mastered. The disproportion of geometric sections between the columns and the beams induces plastic deformations on the columns. These phenomena can produce collapse of the columns. In forced-based seismic design procedures, behavior factor, R (or Rw) [16] also referred to by other terms including, response modification factor [17] and provisions for the seismic rehabilitation of buildings [18], is a force reduction factor used to reduce the linear elastic response spectra to the inelastic response spectra. In other words, behavior factor is the ratio of the strength required to maintain the structure elastic to the inelastic design strength of the structure.

2.7. The Algerian parasismic code

The Algerian code has been release during the last year of 1999 [19] and revised in 2003. After this disaster, the code [20] have been reviewed and updated at sever rules in August 2003 [21]. The important innovation is the factor of building behavior (R>1) and the factor of reduction of force (V) according this relation: R= V elastic /V calcul . The V elastic corresponds to the structure’s elastic response strength and V calcul corresponds to allowable stress design strength. For example, the interval of variation

4 INVACO2: International Seminar, INNOVATION & VALORIZATION IN CIVIL ENGINEERING & CONSTRUCTION MATERIALS

N° 5P-232 EL KECHEBOUR B. University of Science and Technologie Houari Boumedien, Algiers, Algeria

is 1 to 2 for the rock ground. This variation depends on the discontinuity of many characteristics as the elevation of building, the regularity of the bays and the non linearity of the behavior of the global structure and the material of the elements during the elasto- plastic behavior under seismic load. The practice have proved that this hypothesis (factor R = 1.6 to 2.2) are appropriate for the buildings with great elevation. For the little elevation (Factor R=1 to 1.3), this considerations give results smaller than the real basis shear forces on the structures. The figures 3 and 4 [22] illustrate the factor of building behavior according the index of stability ( θ) of the structure induced by the P- effect, the soil (site) and the period of the seismic response (T).

Figure 18. Factor of building behavior (R) Figure 19. Factor of building behavior (R) according the index of stability ( θ) and the period according the index of stability ( θ) and the of the seismic load for soft soil. period of the seismic load for rock and hard

3. Discussion and Recommendations

• Discussion Many phenomenons cannot be explained with rational method as the random collapses of neighbor structures and the site effect. But, the seismic engineering can reduce the damages of the structures and mitigate the loss of human live. As the United States, Japan, and Europe move towards the implementation of Performance Based on engineering philosophies in seismic design of civil structures. The new seismic design requires performing a nonlinear analysis of the structures. These analyses can take the form of a full, nonlinear dynamic analysis, or a static nonlinear Pushover Analysis. The Pushover Analysis is a very attractive method for use in a design office, because the computational time required to perform a full, nonlinear dynamic analysis is acceptable. The P- effect is important for the middle and little. Globally, the collapse of columns and the plastification of nodes are the man cause of the ruin of buildings.

• Recommendations In order to reduce the effect of earthquake duration on structures, and to enhance the behavior of the structures, it is necessary: - To use a procedure that combines order static and non-linear dynamics loads during the design. - To implement into the new Algerian concrete standards, some rules to provide sufficient ductility at reinforced concrete members. - To increase ductility for concrete structures subjected to bending in order to limit the depth of the compression zone (x/d). - To put a sufficient transversal reinforced pins at the node beam-column. - To avoid an great difference between the dimensions in elevation of the columns, - To have the inertia of column more great than the inertia of beam. - To drain the foundations of the site.

5 INVACO2: International Seminar, INNOVATION & VALORIZATION IN CIVIL ENGINEERING & CONSTRUCTION MATERIALS

N° 5P-232 EL KECHEBOUR B. University of Science and Technologie Houari Boumedien, Algiers, Algeria

- To analysis the vulnerability of the buildings by the acoustic method [23]. - To use seismic joint between the neighbor walls.

CONCLUSION

Several conclusions follow from this seismic disaster and can be cited. The earthquake duration has a significant effect on structural reliability and should be considered as one cause in the decrease of the resistance factor. The connection between the columns and beams is vital for a satisfactory performance of the structure under high seismic load. The strength and stiffness of the pins should be large enough to sustain the seismic forces in the transverse direction. The feebleness of the inertia of the columns led to excessive deformation under seismic excitation on the vertical structures elements. Several floating foundations repose on rock substratum but with shallow water layer` causing possible liquefaction phenomenon. It is very likely that urban density has an impact on the behavior of buildings. Indeed, the buildings represented by their mass, reposing on an elastic soil, can interact with each other and with the seismic wave. This interaction induces a resonance phenomenon. The information obtained from this post-earthquake analysis is very important for the understanding of the structures damages and the improvement of earthquake design procedure. In conclusion, the endamagement of structures must be considered as impact of interaction of system elements.

ACKNOWLEDGMENT

The authors thank the Director of urbanism of Boumerdes District and the colleagues of seismic engineering Center of Algiers (CTC) for providing data and information about this disaster.

REFERENCES

[1] Gioncu V., Mazzolani F., 2002. Ductility of seismical resistant steel structures, London, Spon Press EC4P 4EE. [2] EERI , 2003. The Boumerdes, Algeria Earthquake, May 21, 2003, Oakland, California, Earthquake Engineering Res. Institute. [3] Delouis B., Vallée M., 2003. The 2003 Bournerdes (Algeria) earthquake: source process from teleseismic data, .Newsletter of the EMSC, 20: 8-10, September 2003, EMSC . [4] Meghraoui M., 1988. Géologie sismique du Nord de l'Algérie: paléosismologie, tectoniques active et synthèse sismotectonique, Thèse de doctorat des sciences, Université de Paris 11, France. [5] Benouar D., 1994. « Materials of Investigations of the Seismicity of Algeria and Adjacent Regions », Annali Di Geofisica, vol. 37, n° 4, 1994, p. 860. [6] Philip H., 1983. La tectonique actuelle et récente dans le domaine Méditerranéen et ses bordures, ses relations avec la sismicité, Thèse de Doctorat, Université des Sciences et Techniques du Languedoc, France. [7] Philip H., 1987. Plio-Quaternary evolution of the stress field in Mediterranean zones of subduction and collision, Annal Geophysicae 1987; n° 5(B): p. 301-320. [8] Boudiaf A., Ritz J.F., Philip H., 1998. Drainage diversion as evidence of propagating active faults: exarnp1e of the El Asnam and Thenia faults, Algeria, Terra Nova, n°10, 1998, p. 236-244. [9] Boudiaf A., Philip H., Coutelle A., Ritz J.F., 1999. Découverte d'un chevauchement d'âge quaternaire au sud de la Grande Kabylie (Algérie), France, Editions Lavoisier, 1999. [10] Yelles C., Djelit H., Harndache M., The Boumerdes-Algiers (Algeria) earthquake of May 2lst, 2003 (Mw=6.3). Newsletter of the EMSC, vol.3, n°5, September 2003, p. 20. [11] ISHIHARA K., 2003. Soil Behaviour in Earthquake. Geotechnics, London, Oxford University, reprinted edition, 2003.

6 INVACO2: International Seminar, INNOVATION & VALORIZATION IN CIVIL ENGINEERING & CONSTRUCTION MATERIALS

N° 5P-232 EL KECHEBOUR B. University of Science and Technologie Houari Boumedien, Algiers, Algeria

[12] Ambraseys N., and Free MW, 1997. Surface-wave magnitude calibration for European region earthquakes, Journal Earthquake Eng vol. 1 n°1, p.1–22. [13] CHOPRA, A. K., 1995. Dynamics of Structures, New Jersey, Prentice Hall, 1995. [14] J.W. van de Lindt a, Gin-Huat Goh., 2004. Effect of earthquake duration on structural reliability, Journal of structural engineering, vol. 130, part 5, 2004, p. 821-826. [15] DOWRIK D., 2003, Earthquake Risk Reduction, London, John Wiley & Sons, 2003. [16] Eurocode 8, 1998. Design provisions for earthquake resistance of structures, Comité européen de normalisation, Bruxelles, European Pre-standard ENV 1998. [17] Uniform Building Code, 1997. International Conference of Building Officials, California, Whittier, 1997. [18] Federal Emergency Management Agency (FEMA), 1997. NEHRP: provisions for the seismic rehabilitation of buildings, Washington DC, Rep FEMA 273 and 274, 1997. [19] RPA99, 1999. Règles Parasismiques Algériennes, Alger, DTR (CGS), 1999. [20] RPA2003, 2003. Règles Parasismiques Algériennes, Alger, DTR (CGS), Jan.2003. [21] Addenda aux RPA99, 2003. Règles Parasismiques Algériennes, DTR (CGS), Alger, Août 2003. [22] Dunand F. and al, 2004. Utilisation du bruit de fond pour l’analyse des dommages des Bâtiments de Boumerdes suite au séisme du 21 mai 2003, mémoires du service géologique de l’Algérie, n°12, 2004, p. 177-191. [23] Djebbar N., Djebbar A., Nabil A., Athmani A., Chair A., 2009. Evaluation du facteur de comportement preconisé par le code RPA99, Acte du 1st International Conference on Sustainable Built Environment Infrastructures in Developing Countries (SBEIDCO), ENSET Oran (Algeria), October 12-14, 2009, p. 189-196.

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