ANSI/SDI-C1.0 Standard for Composite Floor Steel Deck 2

Design:

A. Deck as a form

1. The section properties for the steel floor deck unit (as a form in bending) shall be computed in accordance with the North American Specification for the Design of Cold-Formed Steel Structural Members.

2. Allowable Stress Design (ASD): Bending stress shall not exceed 0.60 times the yield strength, nor exceed 36 ksi (250MPa) under the combined loads of wet concrete, deck weight, and the following construction live loads: 20 pounds per square foot (1 kPa) uniform load or 150 pound concentrated load on a 1'-0" (300 mm) wide section of deck (2.2 kN per m). The nteraction of shear and bending shall be considered in the calculations.

3. Load and Resistance Factor Design (LRFD): The load combinations for construction are as shown in Attachment C1. Load factors shall be in accordance with ASCE 7 (See Section 1.2.A.5). The resistance factors and nominal resistances shall be in accordance with North American specification for the Design of Cold-Formed Steel Structural Members.

Commentary:  

The loading shown in Figure 1 of Attachment C1 is representative of the sequential loading of wet concrete on the deck. The 150 pound load (per foot of width) is the result of distributing a 300 pound (1.33 kN) man over a 2 foot (600 mm) width. Experience has shown this to be a conservative

distribution. The metric equivalent of the 150 pound load is 2.2 kN per meter of width. For single span deck conditions, the ability to control the concrete placement may be restricted and an amplification factor of 1.5 is applied to the concrete load to address this condition; however, in order to keep this 50% load increase within a reasonable limit, the increase is not to exceed 30 psf (1.44 kPa). In LRFD, a load factor for construction of 1.4 is applied to this load. Whenever possible, the deck shall be multi-span and not require shoring during concrete placement.

4. Deck Deflection: Calculated deflections of the deck, as a form, shall be based on the load of the wet concrete as determined by the design slab thickness and the weight of the steel deck, uniformly loaded on all spans, and shall be limited to 1/180 of the clear span or 3/4 inch (20 mm), whichever is smaller. Calculated deflections shall be relative to supporting members. Commentary: The deflection calculations do not take into account construction loads because these are considered temporary loads. The deck is designed to always be in the elastic range so removal of temporary loads should allow the deck to recover. The structural steel also deflects under the loading of the wet concrete.

The designer is urged to check the deflection of the total system, especially if composite beams and girders are being used. If the designer wants to include additional concrete loading on the deck because of frame deflection, the additional load should be shown on the design drawings or stated in the deck section of the job specifications.

5. Minimum Bearing: Minimum interior bearing lengths shall be determined in accordance with the web crippling provisions of the North American Specification for the Design of Cold-Formed Steel Structural Members; a uniform loading case of wet concrete, plus the weight of the steel deck, plus 20 psf (1 kPa) construction load shall be used.

Commentary:

Experience has shown that 1-1/2 inches (38 mm) of bearing is sufficient for composite floor decks. If less than 1-1/2 inches (38 mm) of end bearing is available, or if high support reactions are expected, the design professional should check the deck web crippling capacity. The deck must be adequately attached to the structure to prevent slip off.

6. Diaphragm Shear Capacity: Diaphragms without concrete shall be designed in accordance with the SDI Diaphragm Design Manual, or from tests conducted by an independent professional engineer.

Commentary:

Calculations of diaphragm strength and stiffness should be made using the SDI Diaphragm Design Manual. If testing is used as the means for determining the diaphragm strength and stiffness, then it should follow the AISI TS 7-02 test protocol.