Research on failure mode of fundamental frame structure in multi-ribbed composite wall

Fundamental frame structure is the basic mechanical element of multi-ribbed composite wall(MCW).Three specimens are tested under monotonic diagonal load in order to study the failure process,failure mode and interaction mechanism between concrete frame and infill.Experiments show that: one or two principle tensile cracks are produced near the diagonal of the infill at first;then vertical cracks appear in the ribbed beam-column and the joint;fundamental frame structures reach to ultimate bearing capacity after circular arc compression cracks appear in the angle region of the filling block.The final failure pattern is related to relative stiffness between infill and ribbed beam-column.Force behaviors of concrete grid and infill in loading process are analyzed based on elastic foundation beam theory.Three distinct failure modes are categorized diagonal compression mode,corner crushing mode and ribbed beam-column local compression mode.Among them,the second failure mode is in accordance with different failure stage of MCW,meanwhile the plastic hinges rotate fully,and it's a reasonable failure mode.The experiments and theoretical analysis show that effect of the infill can be equaled as hinged-diagonal strut.Formulas of width,strength and stiffness of the strut are presented,and simplified calculation model is established to simulate mechanical properties of the fundamental frame structure in elastic stage,which offers a theoretical basis for analysis the MCW.