The design, fabrication and erection of forms shall comply with the requirements of section 1906.1.1 through 1906.1.6.
Formwork, including all related braces, shoring, framing, and auxiliary construction shall be proportioned, erected, supported, braced, and maintained so that it will safely support all vertical and lateral loads that might be applied until such loads can be supported by the permanent construction.
Vertical and lateral loads shall be carried to the ground by the formwork system, by the new construction after it has attained adequate strength for that purpose, or by existing structures. Forms and their supports shall be designed so as not to damage previously placed structures.
Forms shall be properly braced or tied together so as to maintain position and shape, and shall conform to the sizes and shapes of members as shown on the design drawings.
Design of formwork shall comply with ACI 318, Section 6.1.5.
Formwork, including shores, reshores, braces, and other supports, shall be inspected prior to placement of reinforcing steel to verify that the sizes of the concrete members that are being formed conform to the construction documents and form design drawings. Such inspections shall be performed by a qualified person designated by the contractor. Subsequently, inspections shall be performed by such person periodically during the placement of concrete. During and after concreting, the elevations, camber, and vertical alignment of formwork systems shall be inspected using tell-tale devices. A record of all such inspections shall be kept at the site available to the commissioner. The names of the persons responsible for such inspections and the foreman in charge of the formwork shall be posted in the field office.
Wherever the shore height exceeds 14 feet (4267 mm) or the total load on the forms exceeds 150 pounds per square foot (732 kg/m2 ), or wherever power buggies or two-stage shores are used, the forms, including shoring foundation, shall be designed by a registered design professional and shall be constructed in conformance with such design. A copy of the design drawings and any construction drawings and specifications shall be kept on the job site available to the commissioner.
Vertical loads shall include the total dead and live loads. Dead load shall include the weight of the formwork plus the weight of the reinforcement and fresh concrete. Live load shall allow for the weight of the workers and equipment, with allowance for impact, but in no case shall be less than 20 pounds per square foot (98 kg/m 2 ).
Design of forms, ties, and bracing shall satisfy the minimum lateral pressures of fresh concrete specified in Table 1906.3.2.
| TYPE OF WORK | MINIMUM LATER PRESSURE ASSUMED (psf) |
LIMITATIONS |
|---|---|---|
| Columns: Ordinary work with normal internal vibration |
p = 150 + 9000 R/T | 3,000 psf or 150h, whichever is less |
| Walls: Rate of placement at 7 ft. per hr. or less | p = 150 + 9000 R/T | Maximum 2,000 psf or 150h, whichever is less |
| Walls: Rate of placement at greater than 7 ft. per hr | p = 150 + 43,400 / T + 2800 R/T | Maximum 2,000 psf or 150h, whichever is less |
| Slabs | p = 150 h | None |
- Allowances for change in lateral pressure shall be made for concrete weighing other than 150 pcf; for concrete containing pozzolanic add itions or cements other than Type I, for concrete having slumps greater than 6 inches, or for concrete consolidated by revibration or external vibration of forms.
- Where retarding admixtures are employed under hot weather conditions an effective value of temperature less than that of the concrete in the forms shall be used in the above formula.
- If retarding admixtures are used in cold weather, the lateral pressure may be assumed as that exerted by a fluid weighing 150 pcf.
Braces and shores shall be designed to resist all external lateral loads including but not limited to wind, cable tensions, inclined supports, dumping of concrete, and starting and stopping of equipment. In no case shall the assumed value of lateral load due to wind, dumping of concrete, and equipment acting in any direction at each floorline be less than 100 plf edge or 2 percent of total dead load of the floor, whichever is greater. Except for foundation walls that are poured against a rigid backing, wall forms shall be designed for a minimum lateral load of 10 pounds per square foot (49 kg/m2 ), and bracing for wall forms shall be designed for a lateral load of at least 100 plf of wall, applied at the top. The lateral load acting on walls greater than 14 feet (4267 mm) high shall be determined by analysis of conditions applicable to the site and building.
The formwork shall be designed for any special conditions of construction likely to occur, such as unsymmetrical placement of concrete, impact of machine-delivered concrete, uplift, and concentrated loads.
Shoring and bracing shall comply with sections 1906.3.5.1 through 1906.3.5.4.
When patented or commercial devices that are not susceptible to design are used for shoring, bracing, or splicing, they shall be approved by the commissioner.
Splices shall develop the full strength of the spliced members.
Where shore height exceeds 10 feet (3048 mm), or when necessary to provide structural stability, diagonal bracing shall be provided. Struts, anchored into masonry or to panel joints of adjacent braced bays, may be used to prevent buckling of individual members not supported by the diagonal bracing; but, bracing an entire tier of shores with struts without diagonal bracing shall be prohibited unless the system can be demonstrated to be braced by other rigid construction.
The unbraced length of shores shall not exceed the maximum length determined in accordance with the requirements of this code for the structural material used.
Foundations for shores more than 10 feet (3048 mm) high and supported on the ground shall be designed by a registered design professional.
Formwork shall be so constructed that vertical adjustments can be made to compensate for take-up and settlements. Wedges, jacks, or other positive means shall be provided for this purpose.
Structural runways, ramps, and platforms shall comply with Section 3315 in addition to the requirements of Section 1906.3.
Construction of concrete formwork shall comply with the requirements of Section 1906.4.1 through 1906.4.4.
Field constructed lap splices, other than approved devices, shall not be used more often than for every other shore under slabs or for every third shore under beams, and shall develop the full strength of the members. Such spliced shores shall be uniformly distributed throughout the work. Splices shall not be located near the midheight of the shores unless lateral support is provided, nor midway between points of lateral support.
Vertical shores for multifloor forms shall be set plumb and in alignment with lower tiers so that loads from upper tiers are transferred directly to the lower tiers, or adequate transfer members shall be provided. Provision shall be made to transfer the lateral loads to the ground or to completed construction of adequate strength. Vertical shores shall be so erected that they cannot tilt, and shall have firm bearing. Inclined shores and the bearing ends of all shores shall be braced against slipping or sliding. The bearing surfaces shall be cut square and have a tight fit at splices.
Runways for moving equipment shall be provided with struts or legs as required, and shall be supported directly on the formwork or structural member and not on the reinforcement.
Any unsafe condition or necessary adjustment revealed by inspection shall be remedied immediately. If, during construction, any weakness develops and the formwork shows any undue settlement or distortion, the work shall be stopped, the affected construction removed if permanently damaged, and the formwork strengthened.
The removal of forms and shoring shall comply with the requirements of Section 1906.5.1 through 1906.5.6.
Before starting construction, the contractor shall develop a procedure and schedule for removal of shores and installation of reshores and for calculating the loads transferred to the structure during the process.
The structural analysis and concrete strength data used in planning and implementing form removal and reshoring shall be furnished by the registered design professional responsible for the removal schedule to the commissioner when so requested.
No construction loads shall be supported on, nor any shoring removed from, any part of the structure under construction except when that portion of the structure in combination with the remaining forming and shoring system has sufficient strength to support safely its weight and the loads placed thereon.
Sufficient strength shall be demonstrated by structural analysis of the proposed loads, the strength of the forming and shoring system, and concrete strength data. Concrete strength data shall be based on tests of field-cured cylinders or, when approved by the commissioner, on other procedures for evaluating concrete strength.
No construction loads exceeding the combination of superimposed dead load plus specified live load shall be supported on any unshored portion of the structure under construction, unless analysis indicates adequate strength to support such additional loads.
Form supports for prestressed concrete members shall not be removed until sufficient prestressing has been applied to prestressed members to carry their dead load and anticipated construction loads.
Forms shall be removed in such a manner as to assure the complete safety of the structure and workers.
Where the structure as a whole is supported on shores, beam and girder sides, columns, and similar vertical forms may be removed after the concrete is sufficiently hard to withstand damage from the removal. In no case shall the supporting forms or shoring be removed until the members have acquired sufficient strength to support safely their weight and the load thereon.
The results of control tests, including concrete cylinder specimens prepared in accordance with ANSI/ASTM C31, 2003a, cast-in-place cores, or other device that will produce test specimens representative of the condition of the concrete in place, of suitable size and proportions, and approved by the registered design professional of record shall be evidence that the concrete has attained sufficient strength or the strength as may be specified on the drawings. The contractor may submit alternate methods of stripping, reshoring, and strength control for approval by the registered design professional of record, subject to review by the commissioner.
Reshoring shall be provided to support the construction where forms and shores are stripped before the concrete has attained sufficient strength to support the superimposed loads due to construction above. Reshoring shall comply with Section 1906.6.1 through 1906.6.7.
Reshores within 10 feet (3048 mm) of the facade of a building shall be secured to prevent them from falling off the building.
Wedges shall not be used within 10 feet (3048 mm) of the facade or at such other locations as determined by the commissioner.
In no case shall shores be so located as to alter the pattern of stresses determined in the original structural analysis or to induce tensile stresses where reinforcing bars are not provided.
Reshores shall be perpendicular to the surface that they are supporting.
Adjusting devices shall not be used if heavily rusted, bent, dented, rewelded or having broken weldments or other defects.
Metal shoring and accessory parts shall be fully operative when in use.
Reshoring shall comply with all of the requirements of Chapter 33 regarding safeguards during construction and the requirements of Sections 1906.6.2.1 through 1906.6.2.3.
Extra shores or material and equipment that might be needed in an emergency shall be furnished.
Care shall be taken while stripping is underway to insure that material does not fall off the building.
Building materials shall be properly piled and tied or contained.
Lateral bracing shall be provided during reshoring operations, and reshores shall be located as close as practical to the same position on each floor to provide continuous support from floor to floor.
Where reshoring of beam and girder construction is required, the forms shall not be removed from more than one girder at a time, and the girder shall be reshored before any other supports are removed. After the supporting girders are reshored, the form shall be removed from one beam with its adjacent slabs and the beam shall be reshored before any other supports are removed. Slabs spanning 10 feet (3048 mm) or more shall be reshored along the center line of the span.
Where reshoring of flat slab construction is required, the formwork cannot be stripped until the concrete has acquired sufficient strength to safely support its weight and the load thereon, or temporary preshores are provided supporting the slab at intervals of no more than 8 feet (2438 mm) on center to be replaced by reshores prior to placing concrete on the floor above. Reshores must be installed and remain in place until the concrete reaches full or sufficient strength to sustain the superimposed loads to which the concrete will be subjected.
Waste debris as a result of stripping operations shall be immediately contained and removed at reasonable intervals. Stripping operations on concrete structures shall not be performed more than three stories below the story being formed.
Solid safety shields shall be provided at end anchorages of prestressing beds, or where necessary, for protection against breakage of prestressing strands, cables, or other assemblies during prestressing or casting operations.
Conduits, pipes and sleeves of any material not harmful to concrete and within the limitations of ACI 318, Section 6.3, are permitted to be embedded in concrete with approval of the registered design professional of record.
Immediately before new concrete is placed, construction joints shall be wetted and standing water removed.
Construction joints shall be so made and located as not to impair the strength of the structure. Provision shall be made for the transfer of shear and other forces through construction joints in accordance with ACI 318, Section 11.7.9.
Construction joints in floors shall be located within the middle third of spans of slabs, beams and girders. Joints in girders shall be offset a minimum distance of two times the width of intersecting beams.
Beams, girders, haunches, drop panels and capitals shall be placed monolithically as part of a slab system, unless otherwise shown in the design drawings or specifications.