Concrete filled double skin circular tubular beams with large diameter-to-thickness ratio under shear

• Deep concrete filled double skin circular tubular beams under shear are provided.
• Effects of inner-to-outer diameter ratios on shear capacities are investigated.
• Methods to predict shear capacities of deep CFDST beam are proposed.
• Stress histories of both tubes are discussed based upon elasto-plastic stress.

Concrete filled double skin circular tubular (CFDST) members consist of double concentric circular steel tubes with concrete sandwiched between them. Having hollow cross-section, CFDST members are lighter than ordinary concrete filled steel tubular (CFT) members, which have solid cross-sections. Therefore, by alleviating seismic force against the foundation during earthquake, CFDST members can be effectively applied to seismic resistant structures such as a high raise bridge pier.The present study aims to investigate shear characteristics of deep CFDST beams experimentally through an asymmetric static four-point loading test. Two main parameters were selected, namely, the diameter-to-thickness and the inner-to-outer diameter ratios. The results showed that the shear resistance of CFDST gradually decreased as inner-to-outer diameter ratio increased. Methods to predict the shear resistance of deep CFDST beams are also provided. Additionally, stress histories of both tubes are discussed based upon their elasto-plastic stress behavior under plane stress condition.