Bending Stress Response of Strap Beams

Abstract

A strap beam is designed to redistribute the weight of a column between two or more footings. The combination of the footings and the strap beams is known as strap footing. Strap footings are in practice are constructed either with the strap beams at the same level with the footing or at above the footing levels. All these are based on assumptions that the structural behavior of the two strap footings arrangements is the same in either arrangement. This study determined the structural response of strap beams based on physical footing models with two types of connections and compare the results with those from the conventional analysis approach, two assemblies of strap footing arrangements consisting of two RC columns 0.15m x0.15m x 0.6m on 0.5mx0.5mx 0.3m RC bases and connected by RC strap beams of 0.15m width by 0.3m depth by 1.5m length at different levels of connection were constructed and tested in a structural laboratory. The various strains were recorded on application jacking forces through steel I beam horizontally placed on the top of the two columns thus equally distributing the applied axial loads through a centrally placed loading cell. Conventional analysis was undertaken and the values compared with the experimental results. The study revealed that in above the footing level the deviations are between ±36-41% for same level as footing connection case, the deviations are more diverse with no clear pattern. The results for above footing level connection indicates a better agreement with the results of conventional methods with a correlation of 92.5% while for same level as footing has 88.7% correlation.