1 hr


Hr J

shall be used for reducing the allowable horizontal shear capacity of stud connectors. ASCE Requirements for Formed Steel Deck Construction.

Certain specific ASCE requirements applicable to formed steel deck construction are shown schematically in Fig. 7.53. More general comments follow:

Figure 7.52. Composite beam with deck parallel to beam: (a) schematic view; (b) section B showing equivalent thickness of slab.

1. The deck rib height shall not exceed 3 in. (76.5 mm).

2. Rib average width shall not be less than 2 in. (51 mm). If the deck profile is such that the width at the top of the steel deck is less than 2 in. (51 mm), this minimum clear width shall be used in the calculation.

3. The section properties do not change a great deal from deck running perpendicular or parallel to the beam, but the change in the number of studs can be significant.

4. The reduction formula for stud length is based on rib geometry, number of studs per rib, and embedment length of the studs.

5. The equation for calculating the partial section modulus makes the choice of heavier, stiffer beams with fewer studs economically more attractive.

6. Higher shear values can be used in longer shear studs. Concrete cover over the top of the stud is not limited by the AISC specifications, but for practical reasons the author recommends a minimum of Jrin. (12.7 mm).

7. Studs can be placed as close to the deck web as needed for installation and to maintain the necessary spacing.

8. Deck anchorages can be provided by the stud welds.

9. Maximum diameter of shear connectors is limited to 4 in. (19 mm).

10. After installation, the studs should extend a minimum of 1 in. (38 mm) above the steel deck.

11. Total slab thickness including the ribs is used in determining the effective width without regard to the orientation of the deck with respect to the beam axis.

12. The slab thickness above the steel deck shall not be less than 2 in. (51 mm).

Figure 7.53. Composite beam, AISC requirements: (a) deck perpendicular to beam; (b) deck parallel to beam.

For design purposes, a composite floor system is assumed to consist of a series of T-beams, each made up of one steel beam and a portion of the concrete slab. The AISC limits on the width of slab that can be considered effective in the composite action are shown in Fig. 7.54. When the slab extends on one side of the beam only, as in spandrel beams and beams adjacent to floor openings, the effective width naturally is less than when the slab extends on both sides of the beam. For slabs extending on both sides of the beam, the maximum effective flange width b may not exceed: 1) one-fourth of the beam span L; or 2) one-half the clear distances to adjacent beams on both sides plus bf, the width of steel beam flange. When the slab extends on only one side of the beam, the maximum effective width b may not exceed: 1) one-twelfth of the beam span L; or 2) one-half the clear distance to the adjacent beam plus bf. Furthermore, the outboard effective width may not exceed the actual width of overhang, and the inboard effective width must not extend beyond the centerline between the edge beam and the adjacent interior span.

The design of composite beams is usually achieved by the transformed area method, in which the concrete effective area of the composite beam is transformed into an equivalent steel area. It is equally admissible to transform the steel area into an equivalent concrete area, but the calculations are somewhat simplified by the former method. The method

Overhang + U12

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