The Effect of infill walls on the seismic performance of boundary columns in reinforced concrete frames

Fenerci, Aksel
Reinforced concrete frames with unreinforced masonry infill walls constitute a significant portion of the building stock throughout the world. Infill walls in these buildings are generally considered as non-structural elements and neglected during design and assessment. On the other hand, observations after several earthquakes revealed that infill walls may have detrimental effects on the adjacent frame members. This observation brings out the requirement for further research on the effects of infill walls on the seismic performance of boundary columns. Additionally, current procedures for the design and assessment of such structures should be experimentally tested and validated along with the development of accurate numerical simulation tools is still in need for these purposes. In this study, seismic behavior of two test specimens which were designed, constructed and tested using the pseudo dynamic testing method in the Structural Mechanics Laboratory of Middle East Technical University are investigated. The two test frames were code conforming and seismically deficient frames. Numerical modeling of the test frames was conducted using DIANA (2008) finite element platform with the available constitutive models. The modeling approach was validated with the experimental results through comparisons. The analysis results are presented for a better understanding of the shear forces transferred from infill walls to the boundary columns. Seismic assessment of the two frames was conducted using ASCE/SEI 41-06 guidelines and the obtained results were compared to the damage observed during experiments. It was found that the presence of infill walls greatly altered the strength, stiffness, deformation capacity, ductility and failure mode of the reinforced concrete test frames. Significant amount of shear force transfer caused shear damage on boundary columns and decreased the ductility. ASCE/SEI 41-06 procedures for seismic assessment of reinforced concrete frames with infill walls are found as unsatisfactory in estimating the observed damage. Use of plastic hinge strains instead of average strain along the member length provided better estimations for boundary column damage levels.