Behavior of Deep Beams under Three-Point Loading – A Nonlinear Finite Element Investigation

Even when applied at midspan, unequal loading is a major driver of deep-beam response and capacity. By contrast, with a central, equal load, the compression-strut paths that carry force from the supports to the loading node(s) are typically symmetric. However, in the present study, the load inequality causes these struts to be asymmetrical. As a result, the strut carrying the larger load failed before the one carrying the smaller load. Therefore, the deep beam fails early. Twenty-one deep beam specimens were analyzed using SAP 2000 software, which is based on the well-known finite element method.  Three patterns of load distribution between three concentrated load points were adopted: 33%-33%-33%, 50%-25%-25%, 25%-50%-25%, 67%-16.5%-16.5%, 16.5%-67%-16.5%, 75%-12.5%-12.5% and 12.5%-75%-12.5%. These load cases were studied using different concrete's compressive strength values of 20, 30, and 40 MPa. Based on these results, load capacity remained essentially unchanged, while midspan deflection and shear stresses decreased by 4.0–4.6% and 3.8–17%, respectively; in contrast, the maximum positive moments increased by 0.55–7%.