Yasushi Sanada

Investigation and Analysis of Buildings Damaged during the September 2007 Sumatra, Indonesia Earthquakes

Abstract Earthquakes occurring on September 12 (8.4 ML) and 13 (7.9 ML), 2007, in South and West Sumatra, Indonesia, respectively, damaged many buildings. This paper reports investigation results on damaged buildings in and around Padang, West Sumatra, and discusses the seismic performance of two reinforced concrete (RC) frame structures with unreinforced masonry (URM) brick walls. Observations revealed that several RC structures with URM walls suffered severe damage such as shear failure of columns, buckling of column longitudinal reinforcements, and collapse of brick walls. In confined and simple URM structures, damage mainly to brick walls was observed. On the contrary, timber structures performed relatively well during the earthquakes. Two calculations were performed—one with and one without infill walls, focusing on two three-story collapsed and surviving RC buildings in Padang. A distinct difference was identified between the seismic performance of the two buildings when considering infill walls. Therefore, these samples of earthquake-damaged buildings verify that nonstructural infill walls can significantly contribute to the seismic performance of this type of structure.

Seismic Performance of Nonstructural Brick Walls Used in Indonesian R/C Buildings

Abstract This paper describes the effects of nonstructural brick walls on the seismic performance of reinforced concrete (R/C) buildings. Experimental and analytical studies were conducted on two buildings: one of which collapsed and the other suffered moderate damage due to the 2007 Sumatra, Indonesia earthquakes. A brick wall was extracted from the moderately damaged building and transported to Japan from Indonesia to experimentally evaluate its seismic performance. Two R/C one-bay frame specimens were constructed, and the imported wall was installed in one of the specimens. Comparing the seismic performance of specimens with and without the brick wall through quasi-static cyclic loading tests, wall contributions were quantitatively evaluated. Moreover, the seismic performance of the earthquake-damaged Indonesian buildings was evaluated numerically considering the findings of the tests. The analyses revealed a possible reason for the collapse of one of the buildings due to the earthquakes.

Experimental evaluation of the in-plane behaviour of masonry wall infilled RC frames

This study focuses on the in-plane behaviour of unreinforced masonry (URM) infill walls installed in reinforced concrete (RC) frames. Five 1/4-scale model frames were designed based on a prototype RC building with URM infill walls in Turkey. The experimental parameters were the layout of the URM infill (its presence or absence), number of spans (single or double), number of stories (single or double), and stacking pattern of the URM infill (horizontal or vertical). Static cyclic loading tests were conducted to investigate the lateral force resisting mechanisms in the in-plane direction, which were evaluated based on the strain data measured on blocks forming the infill walls. The results indicated the following: (1) The vertically stacked infill did not form a typical diagonal compressive strut and showed lower seismic performance than the horizontally stacked infill. (2) For the specimens with horizontally stacked infill, the one-story, two-bay specimen formed a diagonal compressive strut in each infill wall similar to that formed in the one-story, one-bay specimen, whereas a steeper compressive strut through both stories appeared in the two-story, one-bay specimen. To verify the above strut mechanisms in the horizontally stacked infill, the compressive struts in the specimens were quantitatively identified based on strain data recorded on the infill. The identified compressive struts indicated that single strut models were applicable to multi-bay infilled frames; however, the stress transfer across floors should be considered in multi-story frames.

Flexure Mechanism and Deformation at Bending-Compression Failure of RC Structural Walls

AbstractThe objective of the present study is to contribute to the understanding of the seismic behavior and performance of reinforced concrete flexure-dominated walls when their boundaries are sub...

Seismic Performance Evaluation and Strengthening of RC Frames with Substandard Beam-Column Joint: Lessons Learned from the 2013 Bohol Earthquake

On October 15, 2013, a magnitude 7.1 earthquake severely damaged buildings on Bohol Island, the Philippines. This paper briefly reports on the typical damage to reinforced concrete (RC) buildings observed in the authors’ post-earthquake investigation. The current study focuses on the seismic performance of an earthquake-damaged building with exterior beam-column joint failure. Cyclic loading tests were conducted to propose a practical seismic strengthening method by installing RC wing walls for substandard moment-resisting frames with brittle beam-column joints. A scaled model representing the earthquake-damaged frame reproduced the damage to the exterior beam-column joint, which could not be evaluated using Japanese seismic evaluation methods because of an overestimation of the joint performance. Another specimen strengthened by the proposed method was successfully upgraded, forming a ductile beam yielding mechanism. The ultimate strength of the upgraded specimen estimated by the Japanese methods agreed well with the experimental results. The strengthening mechanism by wing walls was elucidated, knowledge of which will be useful for future applications to substandard buildings in developing countries.

Experimental Study on Performance Evaluation of an Indonesian R/C Building Damaged by the 2009 Sumatra Earthquake

The 2009 Sumatra, Indonesia earthquake attacked Padang, which is the capital of West Sumatra province, and damaged a large number of reinforced concrete (R/C) buildings. The first author of this paper had conducted a post-earthquake field investigation in Padang. As a result, it was found that one of typical damage to buildings was beam-column joint failure. This damage was caused by poor structural details at joints, nevertheless appropriate details were provided in the Indonesian design regulation. In this study, the structural performance of a typical beam-column joint was experimentally evaluated to investigate the seismic performance of earthquake-damaged buildings. The test results revealed that joint failure occurred prior to beam/column yielding. This means that the actual seismic performance of damaged buildings was less than the design calculations in which joint failure had not been assumed.