Flexural Behavior of Double Skin Steel Tubular Beams Subjected to Monotonic and Cyclic Loading

Abstract

Double skin tubular members consist of two tubes placed concentrically or eccentrically having space between them which is filled with concrete. This thesis is concerned with the flexural properties of Concrete Filled Double Skin Tubular (CFDST) beams in which both inner and outer tubes are made up of Square Hollow Section (SHS) of steel. A steel strip is used to connect the two tubes. An experimental program consisting of performing four points loading tests on twelve specimens, six for monotonic and six for cyclic loading is carried out. In the study we will focus on effect of design parameter on flexural properties of CFDST beams. Parameters to be studied are the effect of presence of concrete in the inner tube, eccentricity of inner steel tube, provision of minimum steel reinforcement in addition to steel tubes and slip control with steel strip attachment at the end of tube. The CFDST beams fully filled with concrete have slightly higher strength and energy absorption capacity and have shown least deflection but are considered as uneconomical because of the presence of the concrete infill in the inner tube. Also, these members are very heavy due to additional concrete in the inner tube. Hollow CFDST beams with eccentric inner steel tube has higher strength and energy absorption capacity at a lower deflection as compared to the beams with concentric steel tubes. The CFDST beams having longitudinal reinforcement in addition to the steel tubes have shown increased ductility. For beams subjected to cyclic loading, the beams with longitudinal reinforcement have shown greater resistance to cyclic loading as compared to the beams having no longitudinal reinforcement. The failure loads at each point in cyclic loading beams is less or equal to the monotonic loading beams. Stiffness degradation ratio for cyclic loading beams is less than monotonic loading beams because the stiffness is degraded by the preceding cycles. The ultimate deflection value for cyclic loading is greater than the ultimate deflection value for monotonic loading.