SECTION CONCRETE FORMWORK PART 1 GENERAL 1.01 RELATED DOCUMENTS

Transcription

1 SECTION CONCRETE FORMWORK PART 1 GENERAL 1.01 RELATED DOCUMENTS 1.02 SCOPE A. Drawings and general provisions of the Contract, including General and Special Conditions and Division 01 Specification Sections, apply to this section. A. This Section supplements the Drawings and specifies project technical requirements, and defines workmanship, quality control procedures, and identifies governing codes and standards for formwork, and the design, installation and removal of shoring and reshoring for cast-in-place concrete structural components of this Project RELATED WORK SPECIFIED ELSEWHERE A. Division 01: General Requirements B. Section : Concrete Reinforcement C. Section : Anchors and Inserts D. Section : Cast-In-Place Concrete E. Section : Steel Deck 1.04 QUALITY ASSURANCE A. Comply with the requirements of the latest edition of the following codes, specifications and standards, except where more stringent requirements are shown or specified: 1. American Concrete Institute ACI 347R-03 - "Guide to Formwork for Concrete." 2. U.S. Department of Commerce: U.S. Voluntary Product Standard PS 1-83 "Construction and Industrial Plywood." B. Design, construct, erect, maintain and remove forms and related structures for cast-in-place concrete work in compliance with ACI ALLOWABLE TOLERANCES A. Construct formwork to provide completed cast-in-place concrete surfaces complying with the tolerances specified in ACI 347 and as follows: 1. Variation from plumb in lines and surfaces of columns, piers, walls, and arrises: 1/4 inch [5 mm] per 10 feet [3 m], but not more than 1 inch [25 mm]. For exposed corner columns, control joint grooves and other conspicuous lines: 1/4 inch [5 mm] 1510 CONCRETE FORMWORK

2 1.06 INSPECTION in any bay or 20 feet [6 m] maximum; 1/2 inch [10 mm] maximum in 40 feet [12 m] or more. 2. Variation from level or grade in beam soffits and in arrises: 1/4 inch [5 mm] in 10 feet [3 m], 3/8 inch [10 mm] in any bay or 20 feet [6 m] maximum, and 3/4 inch [20 mm] in 40 feet [12 m] or more. For exposed sills, horizontal grooves and other conspicuous lines: 1/4 inch [5 mm] in any bay or 20 feet [6 m] maximum and 1/2 inch [10 mm] in 40 feet [12 m] or more. 3. Variation from position of the linear building lines and related columns: 1/2 inch [10 mm] in any bay or 20 feet [6 m] maximum, and 1 inch [25 mm] in 40 feet [12 m] or more. 4. Variation in sizes and locations of sleeves, floor openings and wall openings: 1/4 inch [5 mm]. 5. Variation in cross-sectional dimensions of columns, piers and beams, thickness of slabs and walls: minus 1/4 inch [5 mm] and plus 1/2 inch [10 mm]. 6. Variation in footing plan dimensions: minus 1/2 inch [10 mm] and plus 2 inches [50 mm]; misplacement or eccentricity: 2% of the footings width in direction of misplacement but not more than 2 inches [50 mm]; thickness reduction: minus 5%. 7. Variation in steps in a flight of stairs and tread-and-riser type seating slabs: 1/8 inch [3 mm] for rise and 1/4 inch [5 mm] for treads; in consecutive steps: 1/16 inch [2 mm] for rise and 1/8 inch [3 mm] for treads. A. Before concrete placement: check the lines and levels of erected formwork. Make corrections and adjustments to ensure proper size and location of concrete members and stability of forming systems. B. During concrete placement: check formwork and related supports to ensure that forms are not displaced and that completed work will be within specified tolerances. PART 2 - PRODUCTS 2.01 FORM MATERIALS A. Forms for Exposed Finish Concrete: Unless otherwise indicated, construct formwork for exposed concrete surfaces with plywood, metal, metal-framed, plywood-faced or other type panel materials to provide continuous, straight, as-cast surfaces. Furnish in largest practicable sizes to minimize number of joints and to conform to joint system on the Drawings. Provide form material with sufficient thickness to withstand pressure of placed concrete without bow or deflection beyond allowable tolerances. B. Use overlaid plywood complying with U.S. Product Standard PS-1, "B-B High Density Overlaid Concrete Form", Class 1, or "B-B Plyform", Class 1, at architecturally exposed surfaces. C. Forms for Unexposed Finish Concrete: Form concrete surfaces which will be unexposed in 1510 CONCRETE FORMWORK

3 the finish structure with plywood, lumber, metal, or other acceptable material. Provide lumber that is dressed on at least 2 edges and 1 side for tight fit. D. Cylindrical Columns and Supports: Form round-section members with paper or fiber tubes, constructed of laminated plies using water resistant type adhesive with wax-impregnated exterior for weather and moisture protection. Round-section members may also be formed using steel forms, provided the seams on adjacent members are oriented in the same direction. 1. Provide units with sufficient wall thickness to resist loads imposed by wet concrete without deformation. 2. Paper or fiber units are to have a "seamless" interior surface to eliminate spiral gaps and seams. E. Metal Forms: 1. Corrugated from tough-temper low carbon reduced steel with a minimum yield strength of 80,000 psi [5600 kg/cm 2, 550 MPa] by 0.1% offset method to a gage and nominal corrugation depth as shown on the Drawings. 2. Manufacture metal forms from uncoated sheets. 3. Place metal forms with corrugation edges up and with corrugations perpendicular to supports. Lap sides one corrugation. Lap ends 4 inches [10 cm] and place end laps over supports. Where support is steel plate or steel beam, attach metal forms by plug welding through curved washers, or side clips. F. Earth Forms: 1. Earth forms for footings are acceptable provided the excavation is 2 inches larger on each earth-formed face than planned and the earth sides will form near vertical surfaces FORM TIES A. Provide factory-fabricated, adjustable-length, removable or snap-off form ties, designed to prevent deflection, and to prevent spalling concrete surfaces upon removal. B. Unless otherwise indicated, provide form ties which will leave a hole not larger than 1 inches diameter in the concrete surfaces. Provide ties so that portion remaining within concrete after removal of exterior parts is distant from the outer concrete surface by 2 inches [5 cm] FORM COATINGS A. Provide V.O.C. compliant commercial formulation form-coating compounds that will not bond with, stain nor adversely affect concrete surfaces, and will not impair subsequent treatment of concrete surfaces requiring bond or adhesion nor impede the wetting of surfaces to be cured with water or curing compounds. 1. V.O.C. content shall be a maximum 2.8 lbs/gal. [340 gm/liter], unless more stringent codes or laws apply CONCRETE FORMWORK

4 2.04 INSERTS A. Provide metal inserts and other embedded items as required for anchorage of materials or equipment to concrete construction, not supplied by other trades and as required for the work DESIGN OF FORMWORK A. Design, erect, support, brace and maintain formwork so that it will safely support vertical and lateral loads that might be applied, until such loads can be supported by the concrete structure. Carry vertical and lateral loads to the ground by formwork system and in-place construction that has attained adequate strength for that purpose. B. Design forms and falsework to include assumed values of live load, dead load, weight of moving equipment operated on formwork, ambient temperature, foundation pressures, stresses, lateral stability and other factors pertinent to the safety of the structure during construction. C. Design formwork to be readily removable without impact, shock or damage to cast-in-place concrete surfaces and adjacent materials. D. Provide formwork sufficiently tight to prevent leakage of cement paste during concrete placement. Solidly butt joints and provide backup material at joints as required to prevent leakage and fins. PART 3 - EXECUTION 3.01 INSPECTION A. The Installer must examine the substrate and the conditions under which concrete formwork is to be performed and notify the Construction Manager in writing of unsatisfactory conditions. Do not proceed with the work until unsatisfactory conditions have been corrected in a manner acceptable to the Installer FORM CONSTRUCTION A. Construct forms complying with ACI 347, to the sizes, shapes, lines, and dimensions shown and as required to obtain accurate alignment, location, grades, level, and plumb work in finished structure. Provide for openings, offsets, sinkages, keyways, recesses, chamfers, blocking, screeds, bulkheads, anchorages, and inserts and other features required. Use selected materials to obtain required finishes. B. Provide temporary openings in wall forms, column forms and at other locations necessary to permit inspection and clean-out CONCRETE FORMWORK

5 C. Provide temporary openings where interior area of formwork is inaccessible for cleanout, for inspection before concrete placement and for placement of concrete. Brace temporary closures and set tightly to forms to prevent loss of concrete mortar. Locate temporary openings on forms in as inconspicuous location as possible, consistent with project requirements. D. Fabricate forms for easy removal without hammering or prying against concrete surfaces. Provide crush plates or wrecking plates where stripping may damage cast concrete surfaces. Provide top forms for inclined surfaces where the slope is too steep to place concrete with bottom forms only. Kerf wood inserts for forming keyways, reglets, recesses and the like, to prevent swelling and assure ease of removal. E. Form intersecting planes to provide true, clean-cut corners, with edge of plywood not exposed as form for concrete. F. Erect falsework and support, brace and maintain it to safely support vertical, lateral and asymmetrical loads applied. G. Provide shores and struts with positive means of adjustment capable of taking up formwork settlement and deflection during concrete placing operations, using wedges or jacks or a combination thereof. Provide trussed supports when adequate foundations for shores and struts cannot be secured. H. Support form facing materials by structural members spaced sufficiently close to prevent deflection. Fit forms placed in successive units for continuous surfaces to accurate alignment, free from irregularities and within allowable tolerances. I. Provide camber in formwork as required for anticipated deflections due to weight and pressures of fresh concrete and construction loads for long span members without intermediate supports. J. Carefully inspect falsework and formwork during and after concrete placement operations to identify abnormal deflections or signs of failure; make necessary adjustments to produce work of required dimensions. K. Correct conditions which could cause an unsatisfactory finished product. If conditions are severe enough to endanger the safety of personnel in the area, stop the concrete placement until the unsafe condition has been corrected FORMS FOR EXPOSED CONCRETE A. Drill forms to suit ties used and to prevent leakage of concrete mortar around tie holes. Do not splinter forms by driving ties through improperly prepared holes. B. Do not use metal cover plates for patching holes on defects in forms CONCRETE FORMWORK

6 C. Provide sharp, clean corners at intersecting planes, without visible edges or offsets. Back joints with extra studs or girts to maintain true square intersections. D. Use extra studs, whalers and bracing to prevent bowing of forms between studs and to avoid bowed appearance in concrete. Do not use narrow strips to form materials which will produce bow. E. Assemble forms so they may be readily removed without damage to exposed concrete surfaces. F. Form molding shapes, recesses and projections with smooth-finish materials and install in forms with sealed joints to prevent displacement. G. Form exposed corners of beams, columns, piers and walls to produce square, smooth, solid unbroken lines, except as otherwise indicated. H. Form chamfers with 3/4 inch x 3/4 inch [2 cm x 2 cm] strips, accurately formed and surfaced to produce uniformly straight lines and tight edge joints. Extend terminal edges to required limit and miter chamfer at changes in direction. I. See specification section for treatment of control and construction joints, including wood screeds, metal keyways and sawcuts. Locate as indicated or specified PROVISIONS FOR OTHER TRADES A. Provide openings in concrete formwork to accommodate work of other trades, including those under separate prime contracts (if any). Size and location of openings, recesses and chases are the responsibility of the trade requiring such items. Accurately place and securely support items to be built into forms CLEANING AND TIGHTENING A. Thoroughly clean forms and adjacent surfaces to receive concrete. Remove chips, wood, sawdust, dirt or other debris just before concrete is to be placed. Re-tighten forms immediately after concrete placement as required to eliminate mortar leaks FORM COATINGS A. Coat form contact surfaces with form-coating compound before reinforcement is placed. Do not allow excess form coating material to accumulate in the forms or to come into contact with reinforcement or surfaces which will be bonded to fresh concrete. Apply in compliance with manufacturer's instructions. B. Coat steel forms with a non-staining, rust-preventative form oil or otherwise protect against rusting. Rust-stained steel formwork is not acceptable CONCRETE FORMWORK

7 3.07 EMBEDDED ITEMS A. Set and build into the work anchorage devices and other embedded items required for other work that is attached to, or supported by, cast-in-place concrete. Use setting drawings, diagrams, instructions and directions provided by suppliers of the items to be attached thereto EDGE FORMS AND SCREED STRIPS FOR SLABS A. Set edge forms or bulkheads and intermediate screed strips for slabs to obtain required elevations and contours in the finished slab surface. Provide and secure units to support types of screeds required DESIGN, INSTALLATION AND REMOVAL OF SHORES AND RESHORES A. Design, installation and performance of shoring and reshoring is the responsibility of the Contractor. B. Design shoring and reshoring to safely support the intended weight of supported concrete and all superimposed construction loads without imparting shoring or reshoring-settlementinduced deflections in the supported and supporting structures. C. Use actual calculated superimposed construction loads in the design of shoring and reshoring, but not less than 20 psf [100 kg/m 2, 1 kpa]. D. Submit shoring drawings to the Architect for review. Indicate loads calculated by the designer of the shores and reshores. Indicate individual members, connections and the extent of reshoring to floor below. Indicate the sequence and timing of shore and reshore removal, and designate the individual having responsibility for its production under the authority of the Contractor. The shoring drawings are to be sealed by a Registered Professional Engineer. E. Architect's and Engineer's review of shoring drawings is only for compliance with the requirement of its production, and does not represent approval in any way. F. Comply with ACI 347 for shoring and reshoring and as herein specified. G. Install shores and reshores which are easily adjustable. H. Provide adequate bracing to shores and reshores and install same in a way which precludes their displacement. I. Design sand plates to a size sufficient to safely support the shoring and reshoring load without settlement which would impart permanent deflections in the structural elements of the Project CONCRETE FORMWORK

8 J. Place sand plates on firm soil free from the possibility of washout or soil slope failure. K. Remove shores and reshores in a planned sequence to avoid damage to partially cured concrete. Locate and provide adequate reshoring to safely support the work without excessive stress or deflection REMOVAL OF FORMS A. Formwork not supporting concrete, such as sides of beams, columns, piers and walls, may be removed after cumulatively curing at not less than 50 degrees F. for 24 hours after placing concrete; provided concrete is sufficiently hard to not be damaged by form removal operations and provided that curing and protection operations are maintained. B. Formwork supporting weight of concrete, such as beam soffits, slabs and other structural elements may be removed after cumulatively curing for 72 hours, but only if shores are arranged to permit removal of form material without loosening, displacing or otherwise disturbing shores and reshores. C. Determine potential compressive strength of in-place concrete by testing field-cured specimens representative of the concrete location or members. D. Shores may be removed as determined by the shoring and reshoring design and established sequence, produced under the authority of the Contractor RE-USE OF FORMS A. Clean and repair surfaces of forms to be re-used in the work. Split, frayed, delaminated or otherwise damaged form facing material will not be acceptable. Apply new form coating compound material to concrete contact surfaces as specified for new formwork. B. When forms are extended for successive concrete placements, thoroughly clean surfaces, remove fins and laitance, and tighten forms to close all joints. Align and secure joints to avoid offsets. Do not use "patched" forms for exposed concrete surfaces, except as acceptable to the Architect. END OF SECTION CONCRETE FORMWORK