Structural Performance Evaluation of R/C Exterior/Partition Flat Walls Monolithically Constructed in Moment Resisting Frames

Abstract eng:
Exterior/partition flat walls monolithically constructed in concrete buildings were severely damaged by the 2011 earthquake off the Pacific coast of Tohoku, Japan. Damage to exterior/partition flat walls significantly prevented concrete buildings from immediate occupancy. Although this type of wall is commonly regarded as non-structural wall, it seems to potentially affect the seismic performance and behavior of overall buildings because of its monolithic connection to structural components. Therefore, this paper investigates fundamental behavior and performance of a typical flat wall through experimental and analytical approaches. This paper focuses on a steel reinforced concrete (SRC) residential building that was damaged by the 2011 earthquake off the Pacific coast of Tohoku. Exterior flat walls with the width of approximately 1 m were monolithically connected to structural beams and significantly damaged during the earthquake. A 1/2.5 scale one-bay frame model partially representing the 10th story of the building was designed, fabricated, and tested under static cyclic loads. Contributions of the flat wall to the overall performance/behavior were obtained by measuring shear and axial forces of each column. A beam yielding mechanism was formed in the overall specimen with a shear failure of the flat wall. The specimen deteriorated with buckling of beam longitudinal rebars. The maximum shear force of 87 kN, which corresponded to approximately one-third of the overall strength, was sustained by the flat wall until the shear failure, which means that this type of wall is not necessarily negligible for the seismic performance/behavior of buildings at design drift levels. Such high contribution of the flat wall attributed a passive compression caused by its nonlinear axial elongation. On the other hand, the resistance was completely lost after the shear failure. Experimental results were simulated by numerical analyses using several macro models. In particular, the flat wall was replaced by three types of macro models: Case 1a, Case 1b, and Case 2. Multi Spring (MS) model was used for Case 1a and Case 1b. Shear strength deterioration was considered only for Case 1b. On the other hand, Isoparametric Element (IPE) model was used for Case 2 which considered the axial-flexural-shear behavior interactions. Consequently, Case 1b and Case 2 successfully simulated the experimental lateral force-story drift angle relationship for the overall specimen as well as flat wall. Shear strength drop of the flat wall was represented except for Case 1a. However, only Case 2 could evaluate the loss of axial resistance with shear failure of the flat wall, because the axial-flexural-shear behavior interactions were considered only for the model.

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