An ACI Manual Formwork For Concrete

An ACI ManualFormwork for Concrete8th EditionSP-4 (14)

CHAPTERS1: INTRODUCTION2: GENERAL OBJECTIVES IN FORMWORK BUILDING3: OVERALL PLANNING4: MATERIALS, ACCESSORIES, AND PROPRIETARY PRODUCTS5: LOADS AND PRESSURES6: SHORING AND FLOOR LOADS IN MULTI-STORY STRUCTURES7: DESIGN OF SLAB, WALL, BEAM, AND COLUMN FORMS8: DESIGN OF FORM SHORES AND BRACING9: DESIGN TABLES10: FORMWORK DRAWINGS11: BUILDING AND ERECTING THE FORMWORK12: USING THE FORMS13: FORMED CONCRETE SURFACE QUALITY14: FORMWORK FOR ARCHITECTURAL CONCRETE15: BRIDGE FORMWORK16: MASS CONCRETE FORMWORK17: TUNNEL AND SHAFT FORMWORK18: SPECIAL TECHNIQUES IN CONCRETE CONSTRUCTIONAPPENDIX A—REFERENCED STANDARDS AND REPORTSAPPENDIX B—NOTATIONAPPENDIX C—GLOSSARYAPPENDIX D—CONVERSIONSAPPENDIX E—ACI 347R-14 GUIDE TO FORMWORK FOR CONCRETEAPPENDIX F—ACI 318-11 CODE AND COMMENTARY PROVISIONSRELATED TO FORMWORKAPPENDIX G—OSHA REGULATIONS FOR FORMWORK AND SHORINGAPPENDIX H—PROBLEMSINDEXviii

(Photo courtesy Morley Builders)1: INTRODUCTIONFormwork development has paralleled the growth of concrete construction from itsearliest uses through its many applications today. As concrete has been used for increasingly complex and significant structural and architectural tasks, formwork engineersand contractors have had to keep pace. Projects involving rapid construction schedulescreate challenges for the form designer and for the control of field forming operations.The increasing use of concrete as an architectural medium presents the form builder withseveral challenges, ranging from the selection of appropriate sheathing materials to themaintenance of rigid tolerances.Sawn lumber, manufactured wood products, plywood, steel, aluminum, reinforcedpolymers, and other materials are widely used as formwork components. In addition, newand specialized accessories are frequently introduced by manufacturers. Form designers,builders, and manufacturers must keep abreast of advancing technology in other materialfields to develop and implement the creative and innovative solutions required to maintain both quality and economy.In the early days of the concrete industry, formwork was frequently built in place, usedonce, wrecked (or stripped), and discarded. Because of high labor costs in the UnitedStates and many other countries, the trend over the last several decades has been towardincreased prefabrication, assembly in large units, erection by mechanical means (suchas “flying” forms into place by crane), and reuse of the forms. These developments are inharmony with the increased mechanization often found in other fields and the desireduse of sustainable systems. Consequently, the forming system selection is often a primaryfactor in locating cranes and in allocating site space for storage and fabrication.Not all of the important ideas are new, however. As early as 1908, members of theAmerican Concrete Institute (then called the National Association of Cement Users) weredebating the relative merits of wood and steel formwork at their annual convention.The discussion followed a presentation proclaiming the advantages of a modular metalpanel forming system.1.1 It could be adapted for most any project, had its own connectinghardware, and was good for extensive reuse. By 1910, steel forms for paving were being1-1

Pier cap and strut forms may be made aspart of the shaft form or may be supportedby shoring up from the ground withshoring frames or timber posts. They canalso be supported on adjustable singlepost shores for low elevations, or on steelbeams attached to inserts or to largethrough-bolts placed in sleeves cast into aprevious lift of pier concrete. For light beamcaps on circular pier shafts, friction collars(Fig. 15.17) can be used to carry all or partof the cap formwork.15.3 SuperstructuresBridge superstructures include girders,a deck or roadway, curbs, sidewalks, andrailings or parapets. Concrete bridge decksmay be simple slabs for short spans orslab and girder construction for longerspans. They may be entirely cast-in-place,entirely precast, or a combination of castin-place slab with steel or precast concretesupporting girders. Many of the formingproblems and techniques are similar tothose for other slab work, the major difference being the problem of support forformwork when spans are at great height,over water, or above unsatisfactory earthsupport. For special considerations andrecommendations, refer to ACI 345R-11,“Guide for Concrete Highway Bridge DeckConstruction,” and ACI 345.2R-13, “Guidefor Widening Highway Bridges.” The use ofmortar-tight deck and superstructure formsprovides a smooth unblemished appearance that will enhance public confidence inthe soundness of the structure.Fig. 15.15: External ties and full-span wales used to avoid internal ties (Photo courtesy MEVAFormwork Systems)Fig. 15.16: Formwork for a hammerhead pier cap supported on brackets attached with throughbolts (Photo courtesy EFCO Corp.)15-815.3.1 Monolithic—Simple Slab,Beam, and GirderBridges with short spans between supports(less than 25 ft) may be built as simple slabdecks. Because these simple slab bridgesare sometimes designed with the expectation that the curbs will supply part of thebending resistance, the curbs may be castintegrally with the deck slab. Formwork fora slab deck is like that for any other slab;sheathing of metal, wood, plywood, orother material is supported on joists andstringers. Edge forms are equal in height tothe curbing and are braced externally fromjoists extending beyond the deck width.The form is supported from below by anyone of the various types of shoring, or onheavy horizontal members supported onthe piers. On projects where there are manyidentical short spans, large one-piece formshave been used for an entire span, thenlowered to barges and floated to the nextposition for reuse.CHAPTER 15

Fig. 15.17: Round column friction collarexample (Image courtesy EFCO Corp.)15.3.2 Cast-in-Place Deck Supported on Steel or Precast GirdersFig. 15.18: Stay-in-place steel forms attachedby self-tapping screws to angle ledgers thathave been welded to structural steel bridgegirders (Photo courtesy of New York StateDepartment of Transportation )Fig. 15.19: Stay-in-place precast concrete deckforms supported directly on concrete girdersFormwork details may differ, but thegeneral method of forming slabs isthe same whether supported on steelor precast concrete girders. Formworkmembers either rest on the lower flange orhaunch of the beam, or they are hung withvarious manufactured devices from theupper flange. Several hanging devices arediscussed in Chapter 11.To eliminate the problem of strippingforms high in the air, stay-in-place deck formsare sometimes laid directly on steel or precastconcrete bridge girders. The form materialmay be precast concrete, or corrugated metalFig. 15.20: Construction arrangement for removable bridge deck formwork (Image courtesyso that no stiffening joists are needed. SuchDayton Superior)stay-in-place forms (Fig 15.18) are usuallyused on short spans where intermediatesupports for the form are not required.Corrugated metal may rest on top of orbetween the already-placed bridge framing.Precast concrete deck forms (Fig. 15.19)usually become an integral part of the loadbearing deck after the cast-in-place deckconcrete hardens and bonds to the forms.The roughened top surface of the panelimproves bond with cast-in-place concrete.Projecting loops of reinforcing steel provideshear reinforcement and also serve as liftingattachment points. The panels are placedon a grout bed that provides both a sealerand elevation adjustment to compensate fordifferent stringer elevations and camber.When there are excessive variations inthe camber of steel or precast concretegirders, adjustment of the slab thicknessto give a smooth upper roadway maygo beyond tolerances permitted in slabFig. 15.21: Example hangers for bridge deck formwork (Image courtesy Dayton Superior)construction and result in greater deadload on the girders than anticipated. Atypical design approach uses small haunches over the top flange. Changing the depth ofhaunch compensates for camber variations without changing slab thickness. Forming forsuch a haunch is shown in Fig. 15.20.Figures 15.20 and 15.21 show example arrangements for forming a bridge deck usingadjustable hangers supported on the top flange of the steel beam. Main supporting formmembers are first hung between the steel girders and adjusted for elevation. Spacerblocks are set on these wood members and joists laid across the spacer blocks. DeckingBRIDGE FORMWORK15-9

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6: shoring and floor loads in multi-story structures 7: design of slab, wall, beam, and column forms 8: design of form shores and bracing 9: design tables 10: formwork drawings 11: building and erecting the formwork 12: using the forms 13: formed concrete surface quality 14: formwork for architectural concrete 15: bridge formwork 16: mass .