Design of composite beams with web openings
Summary Design techniques for composite beams with web openings have been under development for well over 30 years. During the past decade, these efforts have reached a level of maturity that allows for an accurate assessment of strength and the development of economical designs. This paper describes the behavior of steel}concrete composite beams with web openings and summarizes the key aspects of strength design and deflection calculation.
Tests of Composite Beams with Web Openings
An experimental investigation to study composite beams with rectangular web openings is presented. Six composite beams and one steel beam were tested. W14 × 34, W18 × 45 and W18 × 46 sections were used. Opening sizes were fixed, with depths equal to 60 percent of the steel beam depth and lengths equal to twice the opening depth. Concrete slab dimensions were held constant. Opening locations were varied to investigate moment-shear ratios ranging from 3 to 33 feet (0.9 to 10 m). Web openings reduce the strength of composite beams. Beams with high moment-shear ratios fail by general yielding in the steel below the neutral axis and crushing in the concrete. Beams with medium to low moment-shear ratios fail by the formation of plastic hinges in the steel below the opening, accompanied by a diagonal tension failure in the concrete slab. The concrete in composite beams contributes significantly not only to the flexural strength, but also to the shear strength of the beams at web openings.
STEEL BEAMS WITH WEB OPENINGS REINFORCED ON ONE SIDE
Tests are described on six beams containing mid-depth rectangular holes which were reinforced by welding horizontal bars to one side of the web. The objective was to evaluate the effect of one-sided reinforcement on the ultimate strength. Particular reference was made to beams with slender webs and to the effect of moment-to-shear ratio. The efficiency of the one-sided reinforcement was judged on the basis of the predicted capacity of a symmetrically reinforced beam with the same reinforcement area. It was found that, due to strain hardening, the ultimate strength achieved was in some cases equal to this predicted strength and, on the basis of such results, suggestions relating to design are made.