STRUT AND TIE MODEL ANALYSIS OF SHEAR CAPACITY FOR STIRRUP IN COMPOSITELY REINFORCED COUPLING BEAMS WITH SPAN-TO-DEPTH RATIO L/h≤1.5

Experiment shows that the small span-to-depth ratio compositely reinforced coupling beams (CRCB) with symmetrical diagonal reinforcements have good seismic performance. Based on establishment of the statically indeterminate strut and tie united working model, which is comprised of main concrete diagonal struts, secondary-diagonal struts, diagonal reinforcement struts and ties and rhombic ribs under action of horizontal earthquake, and through mechanic analysis of stirrups in the coupling beam, a new stirrup macro truss model composed by stirrups and subsidiary struts is proposed. A total of 26 formula and a calculation program containing the geometric deformation,compatibility equations, constitutive equations and equilibrium equations are established. Comparative analysis on examples of two specimens illustrates that the model can reflect the stress state of stirrups on each loading stage after member yielding and the simulated results agree with the experiment.