7.10Temporary Support of Structural Steel Frames

The intent of Section 7.10.1 of the Code is to alert the ODRC and the erector of the means for lateral force resistance in the completed structure so that appropriate planning can occur for construction of the building. Examples of a description of the lateral force-resisting system as required in Section 7.10.1(a) are shown in the following.

Example 1 is an all-steel building with a composite metal deck and concrete floor system. All lateral force resistance is provided by welded moment frames in each orthogonal building direction. One suitable description of this lateral force-resisting system is as follows:

All lateral force resistance and stability of the building in the completed structure is provided by moment frames with welded beam-to-column connections framed in each orthogonal direction (see plan sheets for locations). The composite metal deck and concrete floors serve as horizontal diaphragms that distribute the lateral wind and seismic forces horizontally to the vertical moment frames. The vertical moment frames carry the applied lateral loads to the building foundation.

Example 2 is a steel-framed building with a composite metal deck and concrete floor system. All beam-to-column connections are simple connections and all lateral force resistance is provided by reinforced concrete shear walls in the building core and in the stairwells. One suitable description of this lateral force-resisting system is as follows:

All lateral force resistance and stability of the building in the completed structure is provided exclusively by cast-in-place reinforced concrete shear walls in the building core and stairwells (see plan sheets for locations). These walls provide all lateral force resistance in each orthogonal building direction. The composite metal deck and concrete floors serve as horizontal diaphragms that distribute the lateral wind and seismic forces horizontally to the concrete shear walls. The concrete shear walls carry the applied lateral loads to the building foundation.

See also Commentary Section 7.10.3.

Section 7.10.1(b) is intended to apply to special requirements inherent in the design concept that could not otherwise be known by the erector. Such conditions might include designs that require the use of shores or jacks to impart a load or to obtain a specific elevation or position in a subsequent step of the erection process in a sequentially erected structure or member. These requirements would not be apparent to an erector and must be identified so the erector can properly bid, plan, and perform the erection.

The erector is responsible for installation of all members (including canti-levered members) to the specified plumbness, elevation, and alignment within the erection tolerances specified in this Code. The erector must provide all temporary supports and devices to maintain elevation or position within these tolerances. This work is part of the means and methods of the erector and the ODRD need not specify these methods or related equipment.

See also the preset elevation requirements for cantilevered members in Section A4 of ANSI/AISC 360.

See Commentary Section 7.10.3.

Many structural steel frames have lateral force-resisting systems that are activated during the erection process. Such lateral force-resisting systems may consist of welded moment frames, braced frames, or, in some instances, columns that cantilever from fixed-base foundations. Such frames are normally braced with temporary guys that, together with the steel deck floor and roof diaphragms or other diaphragm bracing that may be included as part of the design, provide stability during the erection process. The guy cables are also commonly used to plumb the structural steel frame. The erector normally furnishes and installs the required temporary supports and bracing to secure the bare structural steel frame, or portion thereof, during the erection process. When erection bracing drawings are required in the contract documents, those drawings show this information. The need for and selection or design of temporary supports should be based on industry standards such as AISC Design Guide 10, Erection Bracing of Low-Rise Structural Steel Frames.

If the ODRC determines that steel decking is not installed by the erector, temporary diaphragm bracing may be required if a horizontal diaphragm is not available to distribute loads to the vertical and lateral force-resisting system. If the steel deck will not be available as a diaphragm during structural steel erection, the ODRC must communicate this condition to the erector prior to bidding. If such diaphragm bracing is required, it must be furnished and installed by the erector.

Sometimes structural systems that are employed by the ODRD rely upon other elements besides the structural steel frame for lateral force resistance. For instance, concrete or masonry shear walls or precast spandrels may be used to provide resistance to vertical and lateral forces in the completed structure. Because these situations may not be obvious to the contractor or the erector, it is required in this Code that the ODRD must identify such situations in the contract documents. Similarly, if a structure is designed so that special erection techniques are required, such as jacking to impose certain loads or position during erection, it is required in this Code that such requirements be specifically identified in the contract documents.

In some instances, the ODRD may elect to show erection bracing in the structural design documents. When this is the case, the ODRD should then confirm that the bracing requirements were understood by review and approval of the erection documents during the submittal process.

Sometimes during construction of a building, collateral building elements, such as exterior cladding, may be required to be installed on the bare structural steel frame prior to completion of the lateral force-resisting system. These elements may increase the potential for lateral loads on the temporary supports. Such temporary supports may also be required to be left in place after the structural steel frame has been erected. Special provisions should be made by the ODRC for these conditions.