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.
DEFLECTIONS OF COMPOSITE BEAMS WITH WEB OPENINGS
Procedures for calculating the deflections of composite beams with web openings are described. Initially, a matrix formulation is used. Modeling assumptions are verified by comparison with experimental data, and recommendations for practical application of the matrix analysis procedures are made. The results of the comparison are used to develop a design aid for estimating the maximum deflection of beams with web openings and an expression for calculating the deflection across a web opening. The work demonstrates that, in most cases, a single web opening often has little effect on the total deflection of a composite beam. There are, however, important cases where the effect can be significant. The effects of an opening and of shear deflections are of the same order. Ignoring both the web opening and shear deformation can lead to significant error. The matrix stiffness method, the design aid, and closed form equations provide reasonable estimates of both total deflection and deflection across an opening.
Strength of Composite Beams with Web Openings
An ultimate strength analysis of composite beams with unreinforced, rectangular web openings is presented. The analysis is developed for general beam geometry and material properties, and for a single web opening of any practical depth, width and location. The beneficial effects of strain hardening and the shear contribution of the slab are neglected, and a four hinge failure mechanism at the opening is assumed. Analytical results indicate that a composite section with a web opening has a significantly higher bending strength than the corresponding noncomposite section, and that variations in opening length, height and eccentricity can have a significant effect on the ultimate strength. Comparison of the analytical results with the limited experimental data available indicates that the theory provides a very conservative estimate of the ultimate strength. The discrepancy between theory and test results is attributed primarily to strain hardening and the shear contribution of the slab.