Lateral Loading Experiments for Confined Masonry PanelsWith Different Opening Types

• Main Authors: Yuan-HsinHsu, 許元馨
• Other Authors: Yi-Hsuan Tu
• Format: Others
• Language: zh-TW
• Published: 2015
• Online Access: http://ndltd.ncl.edu.tw/handle/17548657262223659830

碩士 === 國立成功大學 === 建築學系 === 103 === SUMMARY Two full-scale specimens of confined masonry panels with openings were tested under in-plane lateral cyclic load and vertical forces. The purpose of this thesis is to study the behavior of confined masonry panels with different opening types. Therefore, two types of openings are schemed：door opening and window opening. The test results show that both specimens failed in diagonal compression. The panel and the frame resist lateral load as composite tie-and-strut system. The opening type affects the maximum strength of panels and the performance of the frame. Compared with existing analytical models, FEMA 356 shows that maximum strength are overestimated in panel with door opening but the evaluation of window specimen are conservative. Chuang’s model can accurately estimate the failure mode and conservatively evaluate initial stiffness, but the cracking and maximum strength are overestimated. INTRODUCTION Most of the existing low-rise buildings are constructed by confined masonry (CM) panels in Taiwan. In need of lighting and ventilation, panels are perforated by door or window opening. Since a panel with opening is obviously weaker than a complete panel, this kind of panels usually govern the capacity of seismic resistance of a building. Therefore, the seismic behavior of confined masonry panels with opening is an important issue. MATERIALS AND METHODS Two full-scale specimens of confined masonry panels with opening were tested under lateral cyclic in-plane loading and simultaneously subjected to vertical compression. The test factor is opening type. Specimens CD and CW have centrally positioned door opening and window opening, respectively. Specimen CW has 900mm-height windowsill. The masonry panels were laid in English bond by using solid clay bricks. The panel thickness is 198mm (double wythe). The column section is 300mm × 400mm (depth × width). Lateral cyclic in-plane loading was applied to the top beam. The loading is displacement-controlled with increasing drift, each drift is loaded for two cycles. Two vertical actuators provide vertical compression and restrain the top beam from rotation during the test to simulate the shear-building behavior. Total axial force of 470.88kN (48tf) was applied on each specimen. RESULTS AND DISCUSSION Test results The structural behavior of two directions are approximately the same. The test results showed that both specimens were in diagonal compression failure mode and showed similar damage progress. According to the cracking patterns observed, the tie column and masonry panels acted like tie-and-strut system. The diagonal crack lies approximately along the diagonal compression struts. Because of the exists of the windowsill, the slope of diagonal cracks in two directions of specimen CW were different. The major inclined cracks took place at early stage. Vertical split cracks and toe crushing showed at both the top and bottom opening edges when the specimens reached maximum strength. At the final stage, brick spalling happened along the major inclined cracks; the cracks divided the panels into segments that slided towards the opening. Initial stiffness and drift at cracking point were close in both specimens. The differences between two specimens include that specimen CW showed higher strength at cracking point and ultimate point. The columns in specimen CW failed in shear while the columns in specimen CD were only cracked. Comparison between experimental and analysis values The comparison between the experimental strength and the analytical models shows that FEMA 356 model for infill masonry overestimates the ultimate strength of specimen CD but is conservative of specimen CW. The analytical model can not evaluate the strength contribution of the windowsill. The failure mode of the specimens are also not consistent with the assumption of FEMA 356, so it is not recommended to use for confined masonry. Chuang’s model can accurately evaluate the failure mode. The prediction of initial stiffness are conservative, but the calculated strength at cracking point and Ultimate point are overestimated. After modifying the Chuang’s models, the analytical model can estimate the strength and drift at ultimate point reasonably. The analytical curve are approximately close to the experimental envelope curve. However, since the cracking strength are overestimated, the maximum strength of the whole specimen are controlled by cracking strength. This result is not consistent with the real situation of test. CONCLUSION 1. Both specimens failed in diagonal compression. The inclined cracks appeared at early stage. Vertical split cracks and toe crushing on the top and bottom opening sides were observed at ultimate point. 2. The presence of windowsill increases the strength of the panel and no obvious effect on initial stiffness is observed. However, stronger panels also cause shear failure in the columns and lead to a brittle behavior. 3. Chuang’s model can accurately evaluate the failure mode, but overestimate the cracking and ultimate strength. After modifying, it can reasonably estimate the strength and drift at ultimate point, and the analytical curve are approximately close to the experimental envelope curves. However, the maximum strength of the whole specimen are governed by cracking strength, this result is not consistent with the real damage progress. Therefore, further studies of analytical model are needed.