Special Report

Overview of Canadian Practices in Architectural Precast Concrete for Building Facades

John R. Fowler, P.Eng. Executive Director Canadian Prestressed Concrete Institute Ottawa, Canada

he buildings we construct reflect with the enormous number of finishes T strongly the values, needs and as- and textures which can be produced on pirations of the culture that we live in. the face of architectural precast concrete All our notable new works are built panels, gives a designer tremendous upon a firm base of past experience freedom to select the color, texture and using current science and technology. shape he/she wishes to impart to his/her In the Canadian construction market, building. cladding materials (masonry, glass, High quality precast concrete pro- metal, stone, stucco, tile and precast duced in a plant under controlled con- concrete) compete vigorously for a share ditions is extremely durable and resis- of the $35 billion (Canadian) being tant to weathering and abrasion. The spent annually on building construction. effects of weathering, dirt accumulation Architectural precast concrete en- and air pollution can he minimized by compasses all precast concrete units careful consideration of how rainwater employed as elements of architectural will flow down the face of a building. design. Such units can be structural, The provision of drips, channels and loadbearing by themselves, act as per- scuppers can be used to direct this flow. manent formwork for cast-in-place con- Penetrating sealers are often used to crete or be mainly decorative, repel water from absorbent surfaces, The ability of concrete to flow and as- particularly where soft aggregates and a sume the contours of its mold, combined light colored matrix is used.

24 The adding of large amounts of in- sulation to new buildings following the Synopsis energy crisis in the 1970s can be largely This paper examines trends and ineffective if pressures generated by in Canada for the wind, mechanical systems and stack ef- techniques used manufacture of architectural precast fect cause air to exliltrate and infiltrate concrete spandrel. column cover. the exterior wall. The 1985 National mullion and window panels. The ad- Building Code made air barriers man- vantages and recommended appli- datory on virtually all new buildings. cations of different form materials are Systems assembled at the site are discussed and suggestions are of- often ineffective due to poor workman- fered on how to achieve efficient pro- ship and a lack of coordination among duction of units in a precast factory. the trades. Starting in 1972, the de- The methods of achieving and the end velopment of panelized wall systems in- results of various finishing methods corporating a vented exterior skin of are illustrated. Practical suggestions precast concrete, brick or stone, air gap, for transporting and erecting different insulation and structural precast con- types of panels are given. Many of the crete backing have been successfully concepts are illustrated with examples used in Canada to reduce cladding costs of outstanding products and buildings and build a better wall (Fig. 1). Other where the architects concept was benefits include fast enclosure of a successfully and economically building to shield other trades from bad realized by the use of different archi- weather, reduced construction time and tectural precast concrete panel sys- thinner wall construction to provide tems. more rentable space. The precise sizing of openings and the incorporation of window fastenings and gaskets into architectural precast concrete panels will speed the installa- may completely surround them at the tion of windows and cut glazing costs. ground level. These panels may On some projects the complete frame (c) Window Panels. and window assembly is cast into panels he flat or be heavily sculptured. They may contain a single opening or a series at the factory. of windows. They are either one story in height and made as wide as possible or cast narrower to span vertically for BASIC PANEL TYPES two to four floors. Solid Panels. These panels are While there is a bewildering variety of (d) used to dress tip and enclose any blank architectural precast concrete used wall. Properly designed, these panels everywhere, most building applications can be used to support vertical loads and can be broken down into the following may be used as diaphragms to resist lat- categories: eral forces on a structure. (a) Spandrel and Fascia Panels. These panels are placed to provide horizontal bands around a structure. They may be cast flat, have returns at the top and/or PANEL SIZES bottom and be heavily sculptured. (b) Column Covers and Mullions. Typical panels used for a project These panels are usually narrow and run should he drawn as large as is practica- vertically up a structure. They are often ble. Since many of the manufacturing, used to hide the structural columns and handling and erection costs are inde-

PCI JOURNAUJanuary-February 1988 25 pendent of the size of a piece, making both the size and weight of architectural panels larger can substantially reduce precast concrete panels. the cost. To determine the optimum size The size of the cranes in a precast of architectural panels, a close collab- plant and yard is the first constraint. oration between the designers and pre- Making the panel thinner wiII reduce cast supplier is required. The trend over the weight, but care should be taken the past 20 years has been to increase to avoid cracking and warpage during

(OiCONVENTIONAL WALL GOOD SYSTEM INTERIOR MEMBRANE DIFFICULT TO MAINTAIN OVER THE ENTIRE WALL SURFACE PRECAST PANEL

- DEW POINT FALLS WITHIN STUDS INSULATION THE INSULATION ON THE INTERIOR OF THE BUILDING MEMBRANE -AIR BARRIER DEPENDS ON THE CAULKING GYPSUM BOARD BETWEEN PRECAST PANELS WHICH HAS AN AVERAGE LIFE OF 5 YEARS

- WALL MUST 8E MAINTAINED TO BE EFFECTIVE

Ib)SANDWICH WALL

BETTER SYSTEM EXTERIOR CONCRETE WYTHE

- WARM CONCRETE INNER WYTHE EXTRUDED POLYSTYRENE FORMS THE VAPOUR BARRIER INSULATION

- INTERIOR AND EXTERIOR STRUCTURAL INTERIOR CAULKED JOINTS ARE SUBJECT CONCRETE WY THE TO PRESSURE DIFFERENCES AND PENETRATION BY WIND DRIVEN METAL FURRING STRIP RAIN IIi. (OPTIONAL)

GYPSUM BOARDIOPTIONAL) II-

IC }RAIN SCREEN WALL

BEST SYSTEM VENTED EXTERIOR FACING (STONE, BRICK, PRECAST) CAVITY IS VENTED TO THE OUTSIDE BY OPENINGS IN THE OUTER 12 MM AIR GAP CAVITY LAYER EXTRUDED POLYSTYRENE. INSULATION EQUALIZED PRESSURE ACROSS THE OUTER LAYER PREVENTS WIND STRUCTURAL INTERIOR DRIVEN RAIN FROM ENTERING CONCRETE WYTHE THE CAVITY METAL FURRING STRIP - ENTIRE WIND LOAD IS TRANSFERRED (OPTIONAL) TO THE INNER WYTHE WHICH IS THE AIR BARRIER GYPSUM BOARD(OPTIONAL)

Fig. 1. Typical wall systems incorporating architectural precast concrete wall panels.

26 stripping, stockpiling, yard handling only to resist wind loads. It is being and transportation to the site. Panels are recognized that the rigidity of the panels most vulnerable to cracking at the time together with the interconnection to the of stripping when the concrete strength building frame adds significant stiffness is lowest and the panel is in its weakest to the building structure. Methods of configuration. Stripping panels using analysis to quantify this resistance and multiple pickup points, spreader beams use this benefit in the overall building and rolling blocks will reduce bending design are being developed. and impact forces on thin panels. Some plants cast unbonded post-tensioning tendons into large or irregularly shaped MOLDS panels and stress these tendons prior to removing the panels from the molds. General Most precast plants can handle panels of 15 t (17 tons), with many able to strip Together with the freedom available pieces of40 t (44 tons) or more. through use of architectural precast con- The second constraint is the ability to crete, considerable discipline must be transport the element to the site. All employed by the architect to produce an architectural precast concrete manu- economical design. facturers own or have access to Forms to produce complex architec- specialized hauling equipment which tural shapes are extremely costly to will transport large heavy pieces and make. However, if a large number of conform to highway regulations. To pieces can be produced in each mold, supply large window panels for office then the cost per square metercan be rea- buildings, hill-story 3.2 to 3.7 m (10.5 to sonable and affordable. One way to as- 12.1 ft) high panels must be shipped. sist in this endeavor is to use the master Lengths vary from 9 to 12 m (29.5 to 39.3 mold technique (Fig. 2). Here, all or a ft). In some special cases when ajobsite large number of panels can be produced is near a plant and no overhead obstruc- from a single mold built to accommo- tions are present, enormous pieces can date the largest piece and variously he shipped. subdivided to produce the other sizes The third constraint is the cost and required. Whenever possible, the largest capacity of the cranes at the jobsite. pieces are produced first to avoid cast- Where mobile cranes are used, crane lo- ing on areas worn and damaged through cations, radius and height of lift, and placing and fastening the side form possible obstructions for various sized bulkheads. cranes should be carefully checked. Details of individual panels should Where the contractor's crane is likely to always be left to the precaster. Eleva- be used to erect the architectural panels, tions, wall sections and details of each the capacity of standard and heavy duty different type of wall panel should be tower cranes should be investigated to drawn by the architect. When using determine the economics of building large pieces, if the appearance of larger panels. smaller panels is desired for aesthetic Another advantage of increasing panel reasons, false joints (rustications) can be sizes is structural. Sometimes multistory used to achieve this effect (see Figs, 3 panels can rest directly on foundation and 4). walls rather than being hung from the The number of forms required for a structure. Often it is advantageous to job will be determined by the time al- have panels span between columns to lowed to complete the job and by the avoid placing vertical loads on the floor facilities available. Casting can usually slab or edge beams. Many buildings are proceed during most of the erection pro- faced with curtain wall panels designed cess if the panels are manufactured in

PCI JOURNAL. January-February 1988 27

- •t: Zwt

W "1 J Uia 2a az a •I • o } - [ o 0 J LL 0 < J U 0 IL d ^ a.>.0

TYPICAL PANEL

CORNER PANEL

Fig. 2. Master mold concept — A variety of different panels are all cast from a single form.

the correct sequence. Keeping this in added stiffness is required. The ply- mind, a creative designer can produce wood can be purchased with a smooth an intricate design using variations of a plastic finish or a resin finish can be few basic shapes (Fig. 5). As building applied after fabrication of the form. For configurations are tending to get more heavy use or complex shapes, a layer of complex, producers are having to cope fiberglass cloth impregnated with resin with a greater variety of shapes and is applied to the surface of the mold. sizes. Computerized drafting tech- Care in sanding the form is required to niques are increasing the speed and ac- avoid gouges which will show up on the curacy of producing Iayout drawings and surface of the panel. For large flat sur- the individual detai Is of each piece. faces, a large diameter disc sander works well. Many plants have a large flat cast- Mold Materials ing area set up to make assorted flat pieces using adjustable side rails. A (1) Wood — Wood is the cheapest and standard wood mold will produce about most commonly used material for the 30 panels before it wears out. A stronger manufacturing of molds. Sheets of 1200 version, with careful stripping, can be x2400mmx20inm(4x8ftx%in.)thick used for60 or 70 castings. plywood are used for the construction of (2) Steel — Steel molds are stronger, most molds and side rails, with two or are much more expensive than wooden more layers laminated together where forms and can produce hundreds of

28 RIBS REVEAL SIDE FALSE JOINTS FORMS 2 r PANEL PROJECTIONS Iz

Fig. 3. Total envelope mold showing minimum positive draft. Advantages: — Accurate panel dimensions as side forms are fixed throughout production. — Reduced labor costs as side forms are not removed and replaced each pour. Disadvantages: — Slightly wider joint required between panels due to draft on side forms. — Cannot penetrate side form with lift loops. — Must strip panel flat from mold and rotate to vertical position later.

castings. Assembling and welding thin single master mold. This will permit plate sections without warpage is an art. production to start sooner. Avoid con- They should be manufactured by firms crete forms for shapes which have sharp who specialize in this work. Seams comers. These corners get chipped and should be disguised and any grinding of broken and can be very difficult to re- the surface, unless extremely well exe- pair. cuted, will show on the face of a precast (4) polyurethane — This new mold panel. Steel forms can he made very ac- material is being used to cast some very curately and are ideal for producing intricate shapes. Two-part polyurethane standardized components which will be is cast against a wooden master mold. produced on demand over a period of The resulting material has a 50 to 60 years, complex shapes with much repe- durometer hardness. The forms are ex- tition and deep sections which must re- tremely durable and are capable of pro- sist a large hydraulic head of concrete. ducing extremely fine detail for large Steel forms can be made self stressing to numbers of casts with virtually no wear. allow prestressed reinforcement to be (5) Form Liners — Standard manu- used through the panels, factured form liners can be purchased in (3) Concrete Concrete molds are a variety of textures to insert in forms to durable and relatively inexpensive to add a profile to all or part of the surface make, particularly when a number of of a panel. There are two types, a rigid nearly identical forms can be cast from a PVC plastic material and a soft pliable

PCI JOURNALIJanuary- February 1988 29 SIDE FORM COMPRESSIBLE SEAL OR CORNER CAULK

6

a

LIFT LOOP COMPRESSIBLE CAN PENETRATE SEALOR CORNER SIDE FORM CAULK

WOOD WEDGE

BASE ALLOWS QUICK ACCURATE RELOCATION OF SIDE FORMS

rry. w. Conventional mold. Advantages: — Panel can be rotated to vertical position directly from the mold. — Less expensive mold to construct. — Allows smaller joint between panels. Disadvantages: — Side forms must be removed and replaced each pour. — Somewhat less accurate form than total envelope mold.

urethane material which can be pur- lected are sound, stable and free of or- chased loose or prebonded to a plywood ganic impurities. In particular, avoid backing. any aggregates containing iron pyrite which can bleed and stain the surface of Panels for years. CONCRETE Aggregates — The selection of aggre- Face Mixes gates ranges from economical local river For materials alone, architectural con- gravel and crushed limestone to very crete mixes can range from about a55/ms expensive dolomite, marble, quartz and ($1.56/ft3) using local aggregates and granite materials. Practically any color gray cement to $300/m 3 ($8.49/ft3) or or size anyone could ask for is available more when white cement, white silica from aggregate brokers. sand, quartz or granite coarse aggregate Manufactured sand crushed from a and pigments are used. To reduce costs matching coarse aggregate is very ex- when expensive mixes are specified for pensive and not always available. lf pos- flatwork, precast manufacturers place a sible use white or gray sand at a fraction thin layer of this face mix on the form of the cost. (Fig. 6). The aggregate supplier should deter- The face mix should not be thinner mine that the aggregates and sand se- than twice the diameter of the coarse

30 (Q)SPANDREL PANEL

(b)COLUMN COVER

Fig. 5. Examples of face and back forming for deeply sculptured panels. aggregate. The face mix can he com- 1060 kg of coarse aggregate per cubic pacted with internal form vibrators or meter (66 Ihlft3) is required to have good external air driven grid vibrators. The distribution both on the face of a panel face mix is heaped up at the side form and on any returns that are 90 degrees to where the edge of the panel is exposed the face. on a building, After placing the rein- forcing cage, a backup mix using normal Cost Comparison (Concrete weight concrete is poured with a mini- mum of vibration and not later than 1½ Ingredients Only) hours after the face mix to ensure an Assumed prices (Canadian dollars): adequate bond to the face mix. Graycement ...... $110)t The actual mix design used should be Whitecement ...... $240/t determined by the precaster. At least Graylocal sand ...... $6/t

PCI JOURNAL/January-February 1988 31 WELDED WIRE MESH

ROTATE •,1K` PANEL-PLACE {. IN SECOND BACK UP MIX FORM

a. c 4q

FACE MIX QUIRK MITRE FACE MIX CORNER JOINT

Fig. 6. Method for casting deep returns on panels. Advantages: — Saves face mix. — Quality finish achievable as both faces of panel are cast flat in same manner. — Back forming not required. Disadvantage: Two pours are required to produce each panel.

White silica sand ...... $77/t Change gray sand to white Local limestone coarse silicasand ...... add $2.30/m2 aggregate...... $9/t Change limestone coarse aggregate Local pea gravel coarse to medium priced quartz or aggregate...... I...... 310It granite coarse aggregate add 53.00/m2 Dolomite or marble coarse Use 5 percent pigment aggregate...... $35/t-$60/t inmix ...... add $1.80/m2 Crushed quartz or granite Note: 1 sq ft = 0.0929 m1. coarse aggregate . , .. , ...$65/t-$I00/t Pigment...... $2.50/kg These figures are included to give the designer a feel for the costs involved by Typical mix per cubic meter: using different ingredients in the mix. Cement ...... 360 kg The numbers do not include plant labor, Sand...... 800 kg wastage factor, handling charges, mixing Coarse aggregate ...... 1100 kg charges, overhead or profit. Pigment if required ..... 2 to 5 percent of mass of cement Note: I ton = 9.907 t; 1 lb = 0.454 kg. SURFACE FINISHES For a 40 mm (1.6 in.) thick layer of face (a) Smooth Formed — Not all produc- mix (materials only): ers will attempt this finish. The quality Basicgray mix ...... $2.20/m2 and maintenance of the formwork must Change gray cement to white be outstanding. The use of white ce- cement...... •add $1.90/m2 ment will give better color uniformity

32 than gray cement. This finish is subject sheet metal to fit over the panel and to visible crazing, a network of tiny non- cover those areas. structtrral surface cracks that penetrate (d) Surface Retarded — This is a non- only as deep as the thin layer of cement abrasive process which is very effective paste at the surface of a panel. To reduce in bringing out the full color and texture the possibility of crazing, use a mini- of the coarse aggregate. After the forms mum amount of cement and water in the have been coated with a mold release, mix and consolidate well. one or two coats of a chemical retarder (b) Acid Etched — This finish is are painted or sprayed on to the form achieved by using a muriatic acid solu- surfaces where the aggregate is to be tion to dissolve away the surface cement exposed. The strength of the retarder is paste to reveal the sand and, with fur- selected to vary the depth of exposure, ther etching, the coarse aggregate. The normally one-third to one-half the diam- harder materials (granite, quartz, silica, eter of the coarse aggregate. After strip- etc.) will not react with the acid and will ping the retarded cement paste cover- look bright and sparkle when exposed. ing, the stone is removed using a high The finish is best suited to the produc- pressure water spray. It is advisable to tion of small pieces because of the diffi- match the color or tone of the matrix to culty in maintaining uniformity on large that of the stone so minor segregation of flat areas. Concentrations of cement the aggregate will not be noticeable. paste and under and over etching of This finish, when used with closely different parts of a panel can cause packed, hard, stable aggregates, is streaking. Panels are normally finished highly resistant to staining from dirt and by placing them face up in the yard, air pollution. It is also the easiest finish wetting the surface, applying the acid to repair when damaged. with" stiff bristle brushes, rinsing and (e) Water Washed — Water washing removing to storage racks. Other methods normally refers to exposing the aggre- of dipping the panels in large acid baths gate by brushing away the surface ce- and of spraying the acid on the panels ment paste on unformed surfaces or to using specially designed stainless steel surfaces where the mold has been re- pumps, tanks and nozzles have been moved prior to the hardening of the con- successfully used. crete. When an exposed aggregate finish (c) Sandblasted — Sandblasting is the must return on the cast up face of a most popular and normally the least ex- panel, the top surface may he seeded pensive way to add a texture to precast with coarse aggregate which is worked concrete panels. The depth of a light into the concrete with a trowel. Retarder sandblast made with a single pass of the sprayed on to the fresh concrete is often jet stream is extremely difficult to con- used to assist in removing the cement trol, particularly when the panels are paste. sculptured. A medium sandblast which (f) Other Finishes — While the above removes about 3 nim ( 1/a in.) of the described finishes are the most popular, surface will mainly reveal the sand and many other finishes can he applied to cement paste. When the coarse aggre- the surfaces of architectural precast gate is exposed by deeper sandblasting, panels. Panels may be bushhammered the surface of the stone will he perma- using electric or pneumatic hammers to nently frosted by the action of the abra- fracture the surface of the concrete. Ribs sive. This dulling action will lighten the formed on the surface of panels can be color of dark aggregates and will vary in randomly broken to give a very appeal- degree depending on the hardness of ing effect. Some companies have the the stone. Portions of a panel can be left equipment and capability to hone and unblasted by making a shield of wood or polish the surfaces of flat concrete panels

PCI JOURNAL/January-February 1988 33 to various degrees. The entire panel can around openings, Mesh can be custom be done or the finish applied only to ordered and made to the exact size certain raised flat areas of a piece. needed for large jobs with much repeti- (g) Veneer Facings --- Precast con- tion. Otherwise, flat sheets of two stan- crete units faced with brick, tile and dard sizes are kept on hand and cut and natural stone such as marble, granite bent to suit. and limestone have recently become A single layer of mesh is placed at the extremely popular with architects. The center of panels below 150 mm (5.9 in.) panel can be completely covered or thick and two layers, one in each face, bands or strips of brick or stone can be are placed at the center of panels 150 embedded in a panel to form feature mm (5.9 in.) and thicker. For mesh and strips. Design values and procedures for bars No. 30 and smaller, clear concrete manufacturing veneer faced precast cover to reinforcement should not be concrete panels are. given in Chapter 6, less than 20 mm (0.79 in.) (30 mm (1.18 CPCI Metric Design Manual, Second in.) where panels are exposed to deicing Edition. salts]. (h) Combined Finishes — Combina- In thin panels where this cover cannot tions of finishes using the same concrete be maintained, the reinforcement mix are often produced. Some of the should be galvanized. Galvanized mesh combinations are smooth and sand- is available as a stock item from manu- blasted, smooth and retarded, retarded facturers (currently at a 36 percent pre- and sandblasted, and retarded and acid mium over regular mesh). Galvanized etched. When a retarded texture is com- rebar is double the price of ordinary bined with another finish, the area to be reinforcing bars. retarded should be outlined with a The detailed design of' architectural raised demarcation strip placed in the panels is covered in Chapters 3 and 6 of form to prevent the retarder from the CPCI Metric Design Manual, Sec- spreading to the other part of the form. It ond Edition. is virtually impossible to selectively acid wash only a portion of a panel, This CONNECTIONS treatment should be superimposed over other finished areas. It is the practice of Canadian manu- Using two different facing mixes in facturers of architectural precast con- the same panel is an expensive pro- crete to install their own products and cedure. The first mix is poured within systems at the jobsite. They, therefore, an area bounded by a raised wood strip realize that connection design is critical the thickness of the face mix. Within I Vs to the economical and safe use of their hours the form surface around the first products. Poorly designed connections pour is carefully mopped clean and the can reduce the normal rate of installa- second mix is poured and vibrated. tion to half. The gap between the back of a panel and the supporting structure PANEL REINFORCEMENT should be 25 to 40 mm (I to 1.6 in.) to allow for construction tolerances. To facilitate casting panels on a daily To simplify analysis, employ only two cycle, most precasters prefabricate cages load support connections for each panel. in a steel assembly area from one to sev- In addition, supply enough lateral sup- eral days before casting. Welded wire port connections in each piece to pre- fabric is usually chosen as the main vent panel rotation and to resist wind reinforcement with reinforcing bars pressure, wind suction and panel bow- added by the designer to suit Ioading ing. For non-loadbearing panels the conditions or to strengthen the panel connections should allow for thermal

34 movements without affecting adjacent Many producers favor the use of panels. levelling bolts for loadbearing connec- Connections should he of simple con- tions and threaded rods for lateral con- struction, be placed in an accessible lo- nections to permit fast temporary fixing cation and allow for an adjustment of 25 to the building (Fig. 7). The final ad- mm (1 in,) in three dimensions from the justment can be made without the use of design location. Standardize designs the erection crane. and, when panel weights are within a Detailed procedures for the design of tonne of each other, size the connections connections are presented in Chapter 4 for the heaviest panel and use the same of the CPCI Metric Design Manual, one for all similar conditions, Second Edition.

LEVELLING BOLT

. ,FIELD WELD r c 0 . •o POCKET TO RECESS CONNECTION BELOW

A FLOOR LEVEL LOAD WHERE REQUIRED) BEARING CON NECTION - BAR TO PREVENT PANEL FROM •.a SLIDING OFF EDGE OF BUILDING

A A

• 11,4 A Q p ,

d p.

FIELD WELDED CLIP ANGLE LATERAL WITH HORIZONTAL SLOT CONNECTION • a THREADED ROD WITH DOUBLE • NUTS AND WASHERS

VERTICALLY SLOTTED INSERT • 4• CONTAINING SPRING LOADED NUT

Fig. 7. Examples of connections--Connections such as these allow three-way adjustment and fast release of the erection crane.

PCI JOtJRNALJJanuary-February 1988 35 TRANSPORTATION manufacturer take contractual responsi- bility for the installation of the precast Most precast units are transported on concrete work either by use of his own standard 2.4 m wide x 12.2 m (8 x 40 ft) forces or by an independent erector flat deck trailers with drop deck trailers hired and controlled by him. This will used for some taller units. Standard A- help to insure a quality job, better ad- frames and finger racks are used to sup- herence to schedules and a minimum of port panels vertically during shipping. disputes over split responsibilities. Special custom frames are fabricated to The expense of an idle crane and crew transport sculptured panels. Panels are can run from $4000 to $5000 per work- chained tight to the trailers. Special care ing day. It is imperative, therefore, that must be taken to prevent the cracking of the erector perform a field check prior to panels by selecting the correct blocking starting the installation of the precast points and to prevent marring of the units. This will determine whether the concrete surfaces through the use of Iocation, line and grade of the supports nonstaining softening material and for the panels is within the given toler- comer protectors. ances and that adequate clearance be- tween the building structure and panels has been maintained. Also, a field sur- ERECTION vey to establish an offset line of the building face, elevation marks and panel Safe and efficient erection procedures joint locations should be marked at each are the key to the economical use of pre- floor using the contractor's control cast concrete architectural panels. It is points, bench marks and centerlines. strongly recommended that the precast Erection should not proceed until the

Fig. 8. Industrial Life Tower, Montreal. Architect: Tolchinsky and Goodz. This insulated rain screen double window panel contains 39 pieces of granite veneer fastened to the concrete backing by stainless steel anchor clips.

36 Fig. 9. Industrial Life Tower, Montreal. Architect: Tolchinsky and Goodz. Polished pink granite faced architectural precast panels provide a beautiful, durable, insulated, weathertight enclosure for this office building. The stepped corners double the number of corner offices and add visual interest. contractor has corrected any deficien- directly on the building. Telescoping cies in the work. boom hydraulic cranes are useful for in- Mobile cranes are usually selected to stalling panels under overhanging install architectural precast panels on structural elements. Often the employ- low or medium-sized buildings which ment of a large crane will justify its have adequate access around the site at additional expense by reducing crane the ground level. Cranes with dual hoist movement about the site and allowing drums allow panels shipped on their the panels to be erected at each floor side to be rotated in the air and placed before moving to the next level. This

PCI JOUFNALJJanuary-February 1988 37 Fig. 10. Rowes Wharf, Boston. Architect: Skidmore Owings and Merrill, A wood form is used to cast these complex curved window units. Eight stripping points connected to rolling blocks on the spreader beams are used to gently remove each panel from the mold. Note the cast in inserts for attaching the window frames.

Fig. 11. Rowes Wharf, Boston. Architect: Skidmore Owings and Merrill. The finished panels are chained to the truck, ready for shipment. The raised ribs are lightly sandblasted, Urethane molds were used to achieve the fine detail on the inserts on the lower panel face.

38 Fig. 12. John H. Winters Headquarters Building, Austin. Architect: J. P. J. Architects. Custom-made steel stands were used to safely transport spandrel panels back to back on flat deck trailers. A spreader beam with C-hooks bolted to diaphragms cast on the back of the panels is used to lift the panels into position. After an initial learning period, panels were erected at a rate of 24 per day using an eight man crew and a 160 megagramme crane. avoids moving men, materials and panels is a thriving industry in Canada. equipment up and down the building. Forty plants spread across the country Figs. 8-20 show various applications of produce these products. These com- architectural precast concrete in Canada. panies routinely combine high levels of craftsmanship with amazing ingenuity to transmit a designer's wishes into con- CONCLUSION crete. At the same time, the marketplace insists that they give due regard to The fabrication and installation of economy and close adherence to project custom architectural precast concrete schedules.

PCI JOURNALIJanuary-February 1988 39 PL

Fig. 13. Hyatt Hotel, Greenwich. Architect: Kohn Pederson Fox Associates. These ornate columns were produced by casting the various cylinders vertically in plastic lined molds. After stripping and acid washing, the cylinders were placed in a horizontal form and the joining blocks were cast in a separate pour. Prior to stripping, the columns were post-tensioned over their full length using deformed prestressing bars.

Fig. 15. Hyatt Hotel, Greenwich. Architect: Kohn Pederson Fox Associates. This Fig. 14. Hyatt Hotel, Greenwich. Architect: photograph shows the panel reinforcing Kohn Pederson Fox Associates. Forty-two and back forming for the production of six 14.6 m (48 ft) tall columns support a glass Tuscan arches for the project. The pieces roof which encloses the atrium. This area are so complex it took five weeks and 600 serves as the interior focal point for the man hours for the carpenters to build this design. wooden mold.

40 Fig. 16. Hyatt Hotel, Greenwich. Architect: Kohn Pederson Fox Associates. A finished Tuscan arch is ready for shipping. Notice the extremely fine detail reproduced from the formwork.

Fig. 17. Hyatt Hotel, Greenwich. Architect: Kohn Pederson Fox Associates. The exterior of the hotel was designed to have the appearance of an English manor house. The buff-colored precast units were acid etched to closely resemble Indiana limestone.

PCI JOURNALIJanuary-February 1988 41 Fig. 18. Walter McKenzie Hospital, University of Alberta Health Sciences Centre, Edmonton. Architects: V.H.S.C. Architects Group. This trailer is specially equipped to transport two 18 t (20 tons) 3.8 m (12.5 ft) high, 4 m (13.1 ft) long spandrel panels. The center of the panel is faced with red brick. The sculptured top and bottom sections have a lightly retarded surface finish. Panels are a full rain screen design with a 12 mm (0.5 in.) air gap, 64 mm (2.5 in.) rigid insulation and a 100 mm (4 in.) concrete backing.

Fig. 19. Walter McKenzie Hospital, University of Alberta Health Sciences Centre, Edmonton. Architects: V.H.S.C. Architects Group. Brick faced spandrel panels provide a striking exterior facade for this hospital building. A mechanical space with walkways behind the panels and above the ceiling is used to deliver heating, air conditioning, electrical power and gases to all parts of the hospital.

42 Fig. 20. Regina City Hall. Architect: Joseph Pettick. This beautiful 17 story office structure uses sculptured panels faced with a white quartz exposed aggregate. The exterior panels are loadbearing window units which support prestressed beams and double tee floor and roof slabs. The vertical look is achieved by facing the panels with opaque glass between the windows.

REFERENCES 1. CPCI Metric Design Manual, Second 6. Ganguli, Udeepta, "The Air Barrier: Edition, 1987, Canadian Prestressed Pressure Loads," Construction Canada, Concrete Institute, Ottawa, Canada, 417 January 1987. PP. 7. Cooper, D. R., "Precast Concrete Walls 2. Architectural Precast Concrete, 1973, Replace Traditional Wall Systems,' En- Prestressed Concrete Institute, Chicago, gineering]ournal, Spring 1982. Illinois, 174 pp. 8. Lockmon, Daniel M., "Design & 3. Precast Concrete - Materials and Con- Troubleshooting Guide for Architectural struction - CAN3-A23,4-M78, Canadian Precast Concrete," Precast Consultant, Standards Association, Ottawa, Canada. 1983. 4. Qualification Code for Manufacturers of 9. Perez, Al, "'Patching Architectural Con- Architectural and Structural Precast crete," Concrete Construction, July Concrete –A25I-M1982, Canadian Stan- 1986. dards Association, Ottawa, Canada. 10. PCI Erectors Committee, "Recom- 5. Quirouette, Richard L., "The Air Barrier: mended Practice for Erection of Precast A Misunderstood Element," Construc- Concrete," 1985, Prestressed Concrete tion Canada, November 1986. Institute, Chicago, Illinois, 88 pp.

PCI JOURNALJJanuary-February 1988 43