Special Report

Overview of Canadian Practices inArchitectural Precast Concrete

for Building Facades

John R. Fowler, P.Eng.Executive DirectorCanadian Prestressed Concrete InstituteOttawa, Canada

T he buildings we construct reflectstrongly the values, needs and as-

pirations of the culture that we live in.All our notable new works are builtupon a firm base of past experienceusing current science and technology.In the Canadian construction market,cladding materials (masonry, glass,metal, stone, stucco, tile and precastconcrete) compete vigorously for a shareof the $35 billion (Canadian) beingspent annually on building construction.

Architectural precast concrete en-compasses all precast concrete unitsemployed as elements of architecturaldesign. Such units can be structural,loadbearing by themselves, act as per-manent formwork for cast-in-place con-crete or be mainly decorative,

The ability of concrete to flow and as-sume the contours of its mold, combined

with the enormous number of finishesand textures which can be produced onthe face of architectural precast concretepanels, gives a designer tremendousfreedom to select the color, texture andshape he/she wishes to impart to his/herbuilding.

High quality precast concrete pro-duced in a plant under controlled con-ditions is extremely durable and resis-tant to weathering and abrasion. Theeffects of weathering, dirt accumulationand air pollution can he minimized bycareful consideration of how rainwaterwill flow down the face of a building.The provision of drips, channels andscuppers can be used to direct this flow.Penetrating sealers are often used torepel water from absorbent surfaces,particularly where soft aggregates and alight colored matrix is used.

24

The adding of large amounts of in-sulation to new buildings following theenergy crisis in the 1970s can be largelyineffective if pressures generated bywind, mechanical systems and stack ef-fect cause air to exliltrate and infiltratethe exterior wall. The 1985 NationalBuilding Code made air barriers man-datory on virtually all new buildings.

Systems assembled at the site areoften ineffective due to poor workman-ship and a lack of coordination amongthe trades. Starting in 1972, the de-velopment of panelized wall systems in-corporating a vented exterior skin ofprecast concrete, brick or stone, air gap,insulation and structural precast con-crete backing have been successfullyused in Canada to reduce cladding costsand build a better wall (Fig. 1). Otherbenefits include fast enclosure of abuilding to shield other trades from badweather, reduced construction time andthinner wall construction to providemore rentable space.

The precise sizing of openings andthe incorporation of window fasteningsand gaskets into architectural precastconcrete panels will speed the installa-tion of windows and cut glazing costs.On some projects the complete frameand window assembly is cast into panelsat the factory.

BASIC PANEL TYPES

While there is a bewildering variety ofarchitectural precast concrete usedeverywhere, most building applicationscan be broken down into the followingcategories:

(a) Spandrel and Fascia Panels. Thesepanels are placed to provide horizontalbands around a structure. They may becast flat, have returns at the top and/orbottom and be heavily sculptured.

(b) Column Covers and Mullions.These panels are usually narrow and runvertically up a structure. They are oftenused to hide the structural columns and

SynopsisThis paper examines trends and

techniques used in Canada for themanufacture of architectural precastconcrete spandrel. column cover.mullion and window panels. The ad-vantages and recommended appli-cations of different form materials arediscussed and suggestions are of-fered on how to achieve efficient pro-duction of units in a precast factory.The methods of achieving and the endresults of various finishing methodsare illustrated. Practical suggestionsfor transporting and erecting differenttypes of panels are given. Many of theconcepts are illustrated with examplesof outstanding products and buildingswhere the architect's concept wassuccessfully and economicallyrealized by the use of different archi-tectural precast concrete panel sys-tems.

may completely surround them at theground level.

(c) Window Panels. These panels mayhe flat or be heavily sculptured. Theymay contain a single opening or a seriesof windows. They are either one storyin height and made as wide as possibleor cast narrower to span vertically fortwo to four floors.

(d) Solid Panels. These panels areused to dress tip and enclose any blankwall. Properly designed, these panelscan be used to support vertical loads andmay be used as diaphragms to resist lat-eral forces on a structure.

PANEL SIZES

Typical panels used for a projectshould he drawn as large as is practica-ble. Since many of the manufacturing,handling and erection costs are inde-

PCI JOURNAUJanuary-February 1988 25

pendent of the size of a piece, makingpanels larger can substantially reducethe cost. To determine the optimum sizeof architectural panels, a close collab-oration between the designers and pre-cast supplier is required. The trend overthe past 20 years has been to increase

both the size and weight of architecturalprecast concrete panels.

The size of the cranes in a precastplant and yard is the first constraint.Making the panel thinner wiII reducethe weight, but care should be takento avoid cracking and warpage during

(OiCONVENTIONAL WALL

GOOD SYSTEM

INTERIOR MEMBRANEDIFFICULT TO MAINTAINOVER THE ENTIRE WALLSURFACE

- DEW POINT FALLS WITHINTHE INSULATION ON THEINTERIOR OF THE BUILDING

-AIR BARRIER DEPENDSON THE CAULKINGBETWEEN PRECAST PANELSWHICH HAS AN AVERAGELIFE OF 5 YEARS

PRECAST PANEL

STUDS & INSULATION

MEMBRANE

GYPSUM BOARD

- WALL MUST 8E MAINTAINEDTO BE EFFECTIVE

Ib)SANDWICH WALL

BETTER SYSTEM

- WARM CONCRETE INNER WYTHEFORMS THE VAPOUR BARRIER

- INTERIOR AND EXTERIORCAULKED JOINTS ARE SUBJECTTO PRESSURE DIFFERENCES ANDPENETRATION BY WIND DRIVENRAIN

IIi.II-

EXTERIOR CONCRETE WYTHE

EXTRUDED POLYSTYRENEINSULATION

STRUCTURAL INTERIORCONCRETE WY THE

METAL FURRING STRIP(OPTIONAL)

GYPSUM BOARDIOPTIONAL)

IC }RAIN SCREEN WALL

BEST SYSTEM

CAVITY IS VENTED TO THE OUTSIDEBY OPENINGS IN THE OUTERLAYER

EQUALIZED PRESSURE ACROSSTHE OUTER LAYER PREVENTS WINDDRIVEN RAIN FROM ENTERINGTHE CAVITY

- ENTIRE WIND LOAD IS TRANSFERREDTO THE INNER WYTHE WHICH ISTHE AIR BARRIER

VENTED EXTERIOR FACING(STONE, BRICK, PRECAST)

12 MM AIR GAP CAVITY

EXTRUDED POLYSTYRENE.INSULATION

STRUCTURAL INTERIORCONCRETE WYTHE

METAL FURRING STRIP(OPTIONAL)

GYPSUM BOARD(OPTIONAL)

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

26

only to resist wind loads. It is beingrecognized that the rigidity of the panelstogether with the interconnection to thebuilding frame adds significant stiffnessto the building structure. Methods ofanalysis to quantify this resistance anduse this benefit in the overall buildingdesign are being developed.

stripping, stockpiling, yard handlingand transportation to the site. Panels aremost vulnerable to cracking at the timeof stripping when the concrete strengthis lowest and the panel is in its weakestconfiguration. Stripping panels usingmultiple pickup points, spreader beamsand rolling blocks will reduce bendingand impact forces on thin panels. Someplants cast unbonded post-tensioningtendons into large or irregularly shapedpanels and stress these tendons prior toremoving the panels from the molds.Most precast plants can handle panels of15 t (17 tons), with many able to strippieces of40 t (44 tons) or more.

The second constraint is the ability totransport the element to the site. Allarchitectural precast concrete manu-facturers own or have access tospecialized hauling equipment whichwill transport large heavy pieces andconform to highway regulations. Tosupply large window panels for officebuildings, hill-story 3.2 to 3.7 m (10.5 to12.1 ft) high panels must be shipped.Lengths vary from 9 to 12 m (29.5 to 39.3ft). In some special cases when ajobsiteis near a plant and no overhead obstruc-tions are present, enormous pieces canhe shipped.

The third constraint is the cost andcapacity of the cranes at the jobsite.Where mobile cranes are used, crane lo-cations, radius and height of lift, andpossible obstructions for various sizedcranes should be carefully checked.Where the contractor's crane is likely tobe used to erect the architectural panels,the capacity of standard and heavy dutytower cranes should be investigated todetermine the economics of buildinglarger panels.

Another advantage of increasing panelsizes is structural. Sometimes multistorypanels can rest directly on foundationwalls rather than being hung from thestructure. Often it is advantageous tohave panels span between columns toavoid placing vertical loads on the floorslab or edge beams. Many buildings arefaced with curtain wall panels designed

MOLDS

GeneralTogether with the freedom available

through use of architectural precast con-crete, considerable discipline must beemployed by the architect to produce aneconomical design.

Forms to produce complex architec-tural shapes are extremely costly tomake. However, if a large number ofpieces can be produced in each mold,then the cost per square metercan be rea-sonable and affordable. One way to as-sist in this endeavor is to use the mastermold technique (Fig. 2). Here, all or alarge number of panels can be producedfrom a single mold built to accommo-date the largest piece and variouslysubdivided to produce the other sizesrequired. Whenever possible, the largestpieces are produced first to avoid cast-ing on areas worn and damaged throughplacing and fastening the side formbulkheads.

Details of individual panels shouldalways be left to the precaster. Eleva-tions, wall sections and details of eachdifferent type of wall panel should bedrawn by the architect. When usinglarge pieces, if the appearance ofsmaller panels is desired for aestheticreasons, false joints (rustications) can beused to achieve this effect (see Figs, 3and 4).

The number of forms required for ajob will be determined by the time al-lowed to complete the job and by thefacilities available. Casting can usuallyproceed during most of the erection pro-cess if the panels are manufactured in

PCI JOURNAL . January-February 1988 27

wt - •t:Z

WJ Ui 2 "1

a aza a

•I •oo } - [

0 JLL 0 <

J U0 IL d^ a.>.0

TYPICAL PANEL

CORNER PANEL

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

the correct sequence. Keeping this inmind, a creative designer can producean intricate design using variations of afew basic shapes (Fig. 5). As buildingconfigurations are tending to get morecomplex, producers are having to copewith a greater variety of shapes andsizes. Computerized drafting tech-niques are increasing the speed and ac-curacy of producing Iayout drawings andthe individual detai Is of each piece.

Mold Materials(1) Wood — Wood is the cheapest and

most commonly used material for themanufacturing of molds. Sheets of 1200x2400mmx20inm(4x8ftx%in.)thickplywood are used for the construction ofmost molds and side rails, with two ormore layers laminated together where

added stiffness is required. The ply-wood can be purchased with a smoothplastic finish or a resin finish can beapplied after fabrication of the form. Forheavy use or complex shapes, a layer offiberglass cloth impregnated with resinis applied to the surface of the mold.Care in sanding the form is required toavoid gouges which will show up on thesurface of the panel. For large flat sur-faces, a large diameter disc sander workswell. Many plants have a large flat cast-ing area set up to make assorted flatpieces using adjustable side rails. Astandard wood mold will produce about30 panels before it wears out. A strongerversion, with careful stripping, can beused for60 or 70 castings.

(2) Steel — Steel molds are stronger,are much more expensive than woodenforms and can produce hundreds of

28

RIBS REVEAL SIDEFALSE JOINTS FORMS 2

rPANELPROJECTIONS Iz

Fig. 3. Total envelope mold showing minimum positive draft.Advantages:

— Accurate panel dimensions as side forms are fixed throughoutproduction.

— Reduced labor costs as side forms are not removed and replacedeach 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 thinplate sections without warpage is an art.They should be manufactured by firmswho specialize in this work. Seamsshould be disguised and any grinding ofthe surface, unless extremely well exe-cuted, will show on the face of a precastpanel. Steel forms can he made very ac-curately and are ideal for producingstandardized components which will beproduced on demand over a period ofyears, complex shapes with much repe-tition and deep sections which must re-sist a large hydraulic head of concrete.Steel forms can be made self stressing toallow prestressed reinforcement to beused through the panels,

(3) Concrete — Concrete molds aredurable and relatively inexpensive tomake, particularly when a number ofnearly identical forms can be cast from a

single master mold. This will permitproduction to start sooner. Avoid con-crete forms for shapes which have sharpcomers. These corners get chipped andbroken and can be very difficult to re-pair.

(4) polyurethane — This new moldmaterial is being used to cast some veryintricate shapes. Two-part polyurethaneis cast against a wooden master mold.The resulting material has a 50 to 60durometer hardness. The forms are ex-tremely durable and are capable of pro-ducing extremely fine detail for largenumbers of casts with virtually no wear.

(5) Form Liners — Standard manu-factured form liners can be purchased ina variety of textures to insert in forms toadd a profile to all or part of the surfaceof a panel. There are two types, a rigidPVC plastic material and a soft pliable

PCI JOURNALIJanuary- February 1988 29

SIDE FORM COMPRESSIBLESEAL OR CORNERCAULK

6

a

LIFT LOOPCOMPRESSIBLE CAN PENETRATESEALOR CORNER SIDE FORMCAULK

WOOD WEDGE

BASE ALLOWS QUICK ACCURATE RELOCATIONOF 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-chased loose or prebonded to a plywoodbacking.

CONCRETEAggregates — The selection of aggre-

gates ranges from economical local rivergravel and crushed limestone to veryexpensive dolomite, marble, quartz andgranite materials. Practically any coloror size anyone could ask for is availablefrom aggregate brokers.

Manufactured sand crushed from amatching coarse aggregate is very ex-pensive and not always available. lf pos-sible use white or gray sand at a fractionof the cost.

The aggregate supplier should deter-mine that the aggregates and sand se-

lected are sound, stable and free of or-ganic impurities. In particular, avoidany aggregates containing iron pyritewhich can bleed and stain the surface ofPanels for years.

Face Mixes

For materials alone, architectural con-crete mixes can range from about a55/ms($1.56/ft3) using local aggregates andgray cement to $300/m 3 ($8.49/ft3) ormore when white cement, white silicasand, quartz or granite coarse aggregateand pigments are used. To reduce costswhen expensive mixes are specified forflatwork, precast manufacturers place athin layer of this face mix on the form(Fig. 6).

The face mix should not be thinnerthan twice the diameter of the coarse

30

(Q)SPANDREL PANEL

(b)COLUMN COVER

Fig. 5. Examples of face and back forming for deeplysculptured panels.

aggregate. The face mix can he com-pacted with internal form vibrators orexternal air driven grid vibrators. Theface mix is heaped up at the side formwhere the edge of the panel is exposedon a building, After placing the rein-forcing cage, a backup mix using normalweight concrete is poured with a mini-mum of vibration and not later than 1½hours after the face mix to ensure anadequate bond to the face mix.

The actual mix design used should bedetermined by the precaster. At least

1060 kg of coarse aggregate per cubicmeter (66 Ihlft 3) is required to have gooddistribution both on the face of a paneland on any returns that are 90 degrees tothe face.

Cost Comparison (ConcreteIngredients Only)Assumed prices (Canadian dollars):Graycement ...................$110)tWhitecement ..................$240/tGraylocal sand ...................$6/t

PCI JOURNAL/January-February 1988 31

WELDEDWIREMESH

•,1K`ROTATEPANEL-PLACE {.IN SECOND BACK UP MIXFORM

4qa. c

FACE MIX QUIRK MITRE FACE MIXCORNER 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/tLocal limestone coarse

aggregate......................$9/tLocal pea gravel coarse

aggregate............I........310ItDolomite or marble coarse

aggregate................$35/t-$60/tCrushed quartz or granite

coarse aggregate . , .. , ...$65/t-$I00/tPigment.....................$2.50/kg

Typical mix per cubic meter:Cement .......................360 kgSand..........................800 kgCoarse aggregate ..............1100 kgPigment if required

..... 2 to 5 percent of mass of cementNote: I ton = 9.907 t; 1 lb = 0.454 kg.

For a 40 mm (1.6 in.) thick layer of facemix (materials only):Basicgray mix ...............$2.20/m2Change gray cement to white

cement............... •add $1.90 /m2

Change gray sand to whitesilicasand .............add $2.30/m2

Change limestone coarse aggregateto medium priced quartz orgranite coarse aggregate add 53.00/m2

Use 5 percent pigmentinmix .................add $1.80/m2

Note: 1 sq ft = 0.0929 m1.

These figures are included to give thedesigner a feel for the costs involved byusing different ingredients in the mix.The numbers do not include plant labor,wastage factor, handling charges, mixingcharges, overhead or profit.

SURFACE FINISHES(a) Smooth Formed — Not all produc-

ers will attempt this finish. The qualityand maintenance of the formwork mustbe outstanding. The use of white ce-ment will give better color uniformity

32

than gray cement. This finish is subjectto visible crazing, a network of tiny non-structtrral surface cracks that penetrateonly as deep as the thin layer of cementpaste at the surface of a panel. To reducethe possibility of crazing, use a mini-mum amount of cement and water in themix and consolidate well.

(b) Acid Etched — This finish isachieved by using a muriatic acid solu-tion to dissolve away the surface cementpaste to reveal the sand and, with fur-ther etching, the coarse aggregate. Theharder materials (granite, quartz, silica,etc.) will not react with the acid and willlook bright and sparkle when exposed.The finish is best suited to the produc-tion of small pieces because of the diffi-culty in maintaining uniformity on largeflat areas. Concentrations of cementpaste and under and over etching ofdifferent parts of a panel can causestreaking. Panels are normally finishedby placing them face up in the yard,wetting the surface, applying the acidwith" stiff bristle brushes, rinsing andremoving to storage racks. Other methodsof dipping the panels in large acid bathsand of spraying the acid on the panelsusing specially designed stainless steelpumps, tanks and nozzles have beensuccessfully used.

(c) Sandblasted — Sandblasting is themost popular and normally the least ex-pensive way to add a texture to precastconcrete panels. The depth of a lightsandblast made with a single pass of thejet stream is extremely difficult to con-trol, particularly when the panels aresculptured. A medium sandblast whichremoves about 3 nim ( 1/a in.) of thesurface will mainly reveal the sand andcement paste. When the coarse aggre-gate is exposed by deeper sandblasting,the surface of the stone will he perma-nently frosted by the action of the abra-sive. This dulling action will lighten thecolor of dark aggregates and will vary indegree depending on the hardness ofthe stone. Portions of a panel can be leftunblasted by making a shield of wood or

sheet metal to fit over the panel andcover those areas.

(d) Surface Retarded — This is a non-abrasive process which is very effectivein bringing out the full color and textureof the coarse aggregate. After the formshave been coated with a mold release,one or two coats of a chemical retarderare painted or sprayed on to the formsurfaces where the aggregate is to beexposed. The strength of the retarder isselected to vary the depth of exposure,normally one-third to one-half the diam-eter of the coarse aggregate. After strip-ping the retarded cement paste cover-ing, the stone is removed using a highpressure water spray. It is advisable tomatch the color or tone of the matrix tothat of the stone so minor segregation ofthe aggregate will not be noticeable.This finish, when used with closelypacked, hard, stable aggregates, ishighly resistant to staining from dirt andair pollution. It is also the easiest finishto repair when damaged.

(e) Water Washed — Water washingnormally refers to exposing the aggre-gate by brushing away the surface ce-ment paste on unformed surfaces or tosurfaces where the mold has been re-moved prior to the hardening of the con-crete. When an exposed aggregate finishmust return on the cast up face of apanel, the top surface may he seededwith coarse aggregate which is workedinto the concrete with a trowel. Retardersprayed on to the fresh concrete is oftenused to assist in removing the cementpaste.

(f) Other Finishes — While the abovedescribed finishes are the most popular,many other finishes can he applied tothe surfaces of architectural precastpanels. Panels may be bushhammeredusing electric or pneumatic hammers tofracture the surface of the concrete. Ribsformed on the surface of panels can berandomly broken to give a very appeal-ing effect. Some companies have theequipment and capability to hone andpolish the surfaces of flat concrete panels

PCI JOURNAL/January-February 1988 33

to various degrees. The entire panel canbe done or the finish applied only tocertain raised flat areas of a piece.

(g) Veneer Facings --- Precast con-crete units faced with brick, tile andnatural stone such as marble, graniteand limestone have recently becomeextremely popular with architects. Thepanel can be completely covered orbands or strips of brick or stone can beembedded in a panel to form featurestrips. Design values and procedures formanufacturing veneer faced precastconcrete panels are. given in Chapter 6,CPCI Metric Design Manual, SecondEdition.

(h) Combined Finishes — Combina-tions of finishes using the same concretemix are often produced. Some of thecombinations are smooth and sand-blasted, smooth and retarded, retardedand sandblasted, and retarded and acidetched. When a retarded texture is com-bined with another finish, the area to beretarded should be outlined with araised demarcation strip placed in theform to prevent the retarder fromspreading to the other part of the form. Itis virtually impossible to selectivelyacid wash only a portion of a panel, Thistreatment should be superimposed overother finished areas.

Using two different facing mixes inthe same panel is an expensive pro-cedure. The first mix is poured withinan area bounded by a raised wood stripthe thickness of the face mix. Within I Vshours the form surface around the firstpour is carefully mopped clean and thesecond mix is poured and vibrated.

PANEL REINFORCEMENTTo facilitate casting panels on a daily

cycle, most precasters prefabricate cagesin a steel assembly area from one to sev-eral days before casting. Welded wirefabric is usually chosen as the mainreinforcement with reinforcing barsadded by the designer to suit Ioadingconditions or to strengthen the panel

around openings, Mesh can be customordered and made to the exact sizeneeded for large jobs with much repeti-tion. Otherwise, flat sheets of two stan-dard sizes are kept on hand and cut andbent to suit.

A single layer of mesh is placed at thecenter of panels below 150 mm (5.9 in.)thick and two layers, one in each face,are placed at the center of panels 150mm (5.9 in.) and thicker. For mesh andbars No. 30 and smaller, clear concretecover to reinforcement should not beless than 20 mm (0.79 in.) (30 mm (1.18in.) where panels are exposed to deicingsalts].

In thin panels where this cover cannotbe maintained, the reinforcementshould be galvanized. Galvanized meshis available as a stock item from manu-facturers (currently at a 36 percent pre-mium over regular mesh). Galvanizedrebar is double the price of ordinaryreinforcing bars.

The detailed design of' architecturalpanels is covered in Chapters 3 and 6 ofthe CPCI Metric Design Manual, Sec-ond Edition.

CONNECTIONS

It is the practice of Canadian manu-facturers of architectural precast con-crete to install their own products andsystems at the jobsite. They, therefore,realize that connection design is criticalto the economical and safe use of theirproducts. Poorly designed connectionscan reduce the normal rate of installa-tion to half. The gap between the back ofa panel and the supporting structureshould be 25 to 40 mm (I to 1.6 in.) toallow for construction tolerances.

To simplify analysis, employ only twoload support connections for each panel.In addition, supply enough lateral sup-port connections in each piece to pre-vent panel rotation and to resist windpressure, wind suction and panel bow-ing. For non-loadbearing panels theconnections should allow for thermal

34

movements without affecting adjacentpanels.

Connections should he of simple con-struction, be placed in an accessible lo-cation and allow for an adjustment of 25mm (1 in,) in three dimensions from thedesign location. Standardize designsand, when panel weights are within atonne of each other, size the connectionsfor the heaviest panel and use the sameone for all similar conditions,

Many producers favor the use oflevelling bolts for loadbearing connec-tions and threaded rods for lateral con-nections to permit fast temporary fixingto the building (Fig. 7). The final ad-justment can be made without the use ofthe erection crane.

Detailed procedures for the design ofconnections are presented in Chapter 4of the CPCI Metric Design Manual,Second Edition.

LEVELLING BOLT

. ,FIELD WELD

LOADBEARINGCON NECTION

0 r c

. •o

A

•.a

AA

• 11,4A

Q p ,

d p.

POCKET TO RECESSCONNECTION BELOWFLOOR LEVELWHERE REQUIRED)

- BAR TO PREVENT PANEL FROMSLIDING OFF EDGE OF BUILDING

FIELD WELDED CLIP ANGLELATERAL WITH HORIZONTAL SLOTCONNECTION • a

THREADED ROD WITH DOUBLE• NUTS AND WASHERS

• 4• VERTICALLY SLOTTED INSERTCONTAINING SPRING LOADED NUT

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

PCI JOtJRNALJJanuary-February 1988 35

TRANSPORTATION

Most precast units are transported onstandard 2.4 m wide x 12.2 m (8 x 40 ft)flat deck trailers with drop deck trailersused for some taller units. Standard A-frames and finger racks are used to sup-port panels vertically during shipping.Special custom frames are fabricated totransport sculptured panels. Panels arechained tight to the trailers. Special caremust be taken to prevent the cracking ofpanels by selecting the correct blockingpoints and to prevent marring of theconcrete surfaces through the use ofnonstaining softening material andcomer protectors.

ERECTION

Safe and efficient erection proceduresare the key to the economical use of pre-cast concrete architectural panels. It isstrongly recommended that the precast

manufacturer take contractual responsi-bility for the installation of the precastconcrete work either by use of his ownforces or by an independent erectorhired and controlled by him. This willhelp to insure a quality job, better ad-herence to schedules and a minimum ofdisputes over split responsibilities.

The expense of an idle crane and crewcan run from $4000 to $5000 per work-ing day. It is imperative, therefore, thatthe erector perform a field check prior tostarting the installation of the precastunits. This will determine whether theIocation, line and grade of the supportsfor the panels is within the given toler-ances and that adequate clearance be-tween the building structure and panelshas been maintained. Also, a field sur-vey to establish an offset line of thebuilding face, elevation marks and paneljoint locations should be marked at eachfloor using the contractor's controlpoints, bench marks and centerlines.Erection should not proceed until the

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

36

Fig. 9. Industrial Life Tower, Montreal. Architect: Tolchinskyand Goodz. Polished pink granite faced architectural precastpanels provide a beautiful, durable, insulated, weathertightenclosure for this office building. The stepped corners doublethe number of corner offices and add visual interest.

contractor has corrected any deficien-cies in the work.

Mobile cranes are usually selected toinstall architectural precast panels onlow or medium-sized buildings whichhave adequate access around the site atthe ground level. Cranes with dual hoistdrums allow panels shipped on theirside to be rotated in the air and placed

directly on the building. Telescopingboom hydraulic cranes are useful for in-stalling panels under overhangingstructural elements. Often the employ-ment of a large crane will justify itsadditional expense by reducing cranemovement about the site and allowingthe panels to be erected at each floorbefore moving to the next level. This

PCI JOUFNALJJanuary-February 1988 37

Fig. 10. Rowes Wharf, Boston. Architect: Skidmore Owings and Merrill, A wood form isused to cast these complex curved window units. Eight stripping points connected torolling blocks on the spreader beams are used to gently remove each panel from themold. Note the cast in inserts for attaching the window frames.

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

38

Fig. 12. John H. Winters Headquarters Building, Austin. Architect:J. P. J. Architects. Custom-made steel stands were used to safelytransport spandrel panels back to back on flat deck trailers. Aspreader beam with C-hooks bolted to diaphragms cast on the backof the panels is used to lift the panels into position. After an initiallearning period, panels were erected at a rate of 24 per day usingan eight man crew and a 160 megagramme crane.

avoids moving men, materials andequipment up and down the building.

Figs. 8-20 show various applications ofarchitectural precast concrete in Canada.

CONCLUSION

The fabrication and installation ofcustom architectural precast concrete

panels is a thriving industry in Canada.Forty plants spread across the countryproduce these products. These com-panies routinely combine high levels ofcraftsmanship with amazing ingenuityto transmit a designer's wishes into con-crete. At the same time, the marketplaceinsists that they give due regard toeconomy and close adherence to projectschedules.

PCI JOURNALIJanuary-February 1988 39

PL

Fig. 13. Hyatt Hotel, Greenwich. Architect: Kohn Pederson Fox Associates. These ornatecolumns 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 thejoining blocks were cast in a separate pour. Prior to stripping, the columns werepost-tensioned over their full length using deformed prestressing bars.

Fig. 14. Hyatt Hotel, Greenwich. Architect:Kohn Pederson Fox Associates. Forty-two14.6 m (48 ft) tall columns support a glassroof which encloses the atrium. This areaserves as the interior focal point for thedesign.

Fig. 15. Hyatt Hotel, Greenwich. Architect:Kohn Pederson Fox Associates. Thisphotograph shows the panel reinforcingand back forming for the production of sixTuscan arches for the project. The piecesare so complex it took five weeks and 600man hours for the carpenters to build thiswooden mold.

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

Fig. 17. Hyatt Hotel, Greenwich. Architect: Kohn Pederson Fox Associates. The exteriorof the hotel was designed to have the appearance of an English manor house. Thebuff-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 totransport two 18 t (20 tons) 3.8 m (12.5 ft) high, 4 m (13.1 ft) long spandrel panels. Thecenter of the panel is faced with red brick. The sculptured top and bottom sections have alightly 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 astriking exterior facade for this hospital building. A mechanical space with walkwaysbehind the panels and above the ceiling is used to deliver heating, air conditioning,electrical power and gases to all parts of the hospital.

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Fig. 20. Regina City Hall. Architect: Joseph Pettick. Thisbeautiful 17 story office structure uses sculptured panels facedwith a white quartz exposed aggregate. The exterior panels areloadbearing window units which support prestressed beams anddouble tee floor and roof slabs. The vertical look is achieved byfacing the panels with opaque glass between the windows.

REFERENCES1. CPCI Metric Design Manual, Second

Edition, 1987, Canadian PrestressedConcrete Institute, Ottawa, Canada, 417PP.

2. Architectural Precast Concrete, 1973,Prestressed Concrete Institute, Chicago,Illinois, 174 pp.

3. Precast Concrete - Materials and Con-struction - CAN3-A23,4-M78, CanadianStandards Association, Ottawa, Canada.

4. Qualification Code for Manufacturers ofArchitectural and Structural PrecastConcrete –A25I-M1982, Canadian Stan-dards Association, Ottawa, Canada.

5. Quirouette, Richard L., "The Air Barrier:A Misunderstood Element," Construc-tion Canada, November 1986.

6. Ganguli, Udeepta, "The Air Barrier:Pressure Loads," Construction Canada,January 1987.

7. Cooper, D. R., "Precast Concrete WallsReplace Traditional Wall Systems,' En-gineering]ournal, Spring 1982.

8. Lockmon, Daniel M., "Design &Troubleshooting Guide for ArchitecturalPrecast Concrete," Precast Consultant,1983.

9. Perez, Al, "'Patching Architectural Con-crete," Concrete Construction, July1986.

10. PCI Erectors Committee, "Recom-mended Practice for Erection of PrecastConcrete," 1985, Prestressed ConcreteInstitute, Chicago, Illinois, 88 pp.

PCI JOURNALJJanuary-February 1988 43