Web Openings Analysis

Height limitations are often imposed on multistory buildings based on zoning regulations, economic requirements, and aesthetic considerations, including the need to match the floor heights of existing buildings. Web openings can be used to pass utilities through beams and, thus, help minimize story height. A decrease in building height reduces both the exterior surface and the interior volume of a building, which lowers the operational and maintenance costs. On the negative side, web openings can significantly reduce the shear and bending capacity of steel or composite beams.

The program calculates the combined bending and shear capacity of steel and composite beams with web openings. Composite members may have solid or ribbed slabs. Ribs may be parallel or perpendicular to the steel beam.

Openings may be reinforced or unreinforced. The procedures are compatible with LRFD of the AISC: the applied loads must be factored (generally 1.2 for DL and 1.6 for LL) and the program applies internally the resistance factors to both moment and shear capacities at the opening (0.90 for steel members and 0.85 for composite members).

Input Data

The input data required by this program includes the steel beam and concrete slab information, the opening dimensions, and eccentricity measured from the beam mid-depth, positive downward, and the factored applied loads at opening location.

Example

An A36 W18x60 steel beam supports a 51/2" concrete slab in composite construction. The slab is cast on metal decking with 3" deep ribs parallel to the 40-ft long beams, which are spaced 40 ft apart. The design calls for pairs of 3/4 x 5" shear studs spaced every foot and normal weight concrete with f'c = 4 ksi. How much reinforcement is required for a concentric 10 x 24" opening if the factored loads at that location are Vu = 46 k and Mu = 300 k-ft?

Output

Once the input data is entered, the program calculates the bending and shear capacities, and generates the interaction diagram. If any reinforcement is specified, the bar length and type of weld are calculated. The figure to the right shows the template of this module with the example data.

Procedure

This program also determines the capacity ratio based on the position of the applied loads in the moment-shear interaction diagram. For the design to be adequate, this ratio must not be greater than 1.0.

In addition, the program performs the design check based on limitations and guidelines that must be followed in order to ensure that the design equations used by the program are fully applicable.

When reinforcement for the opening is required, it consists of horizontal bars above and below the opening, at both sides of the web. The program calculates the length of the bars beyond the opening edge, and designs the continuous weld on both sides of the bar to be used.