Masaki Maeda

Experimental observations on the in-plane behaviour of masonry wall infilled RC frames; focusing on deformation limits and backbone curve

The ratio of frame strength and stiffness to masonry infill are major parameters that influence the seismic capacity of masonry infill. The influence of such parameters to seismic capacity in terms of strength, stiffness and deformation has significant variations between different design codes and past literature on the topic. This study focused on the in-plane behaviour of unreinforced masonry infill walls installed in reinforced concrete (RC) frames with different strengths. In the first part of this study, two ½ scale specimens with different RC frames and identical masonry infill walls were tested using a static cyclic loading protocol. The main objective was investigating the influence of changing frame strength to seismic capacity in terms of: strength, stiffness and deformation. Results of the presented experiment showed that as the ratio of frame shear strength to masonry shear strength increased, there was great improvement of the masonry infill walls in terms of strength and avoidance of sudden brittle behaviour of the masonry infill. However, varying frame strength did not significantly influence the initial stiffness and story drift at maximum strength. In the second part of this study, an investigation was conducted on the deformation limits of masonry infilled RC frames and the influence of various parameters, based on data collected from many recent experimental tests. Based on these experimental results, the deformation limits of masonry infill were found to be directly proportional to both the compressive prism strength of the masonry infill and the ratio of shear strength of frame to that of the masonry infill. The influence of aspect ratio showed large variation and it is difficult to conclude its level of influence on deformation. A simplified procedure based on experimental data was proposed that can estimate the backbone curve and gave good estimation of the post-peak lateral strength degradation slope based on the ratio of frame strength with simple hand calculation. Such a method is useful in the preliminary design process to help practicing engineers understand the general behaviour expected by infilled RC frames.

On the Seismic Response of the Faculty of Architecture and Engineering Building at Tohoku University

The Faculty of Architecture and Engineering Building at Tohoku University survived two strong ground motions. This is not surprising because the structure was stiff and strong. What is surprising is that the first ground motion did not cause severe structural damage but the second one caused so much structural damage that the building had to be evacuated and demolished. The damage occurred despite two key facts: (1) the intensities of the mentioned ground motions are understood to have been similar and (2) the building was strengthened after the first motion (and before the second) following stringent standards.

Damage of RC Building Structures due to 2011 East Japan Earthquake

This paper presented the investigation of reinforced concrete building structures by 2011 East Japan Earthquake. Generally, reinforced concrete structures in Miyagi region performed very well during the earthquake and effect of seismic retrofit was found in mitigation of damage, although severe damage to some seismically retrofitted buildings was noticed. A good correlation was observed between calculated seismic capacity Is-index and observed damage. Moreover, buildings designed according to the current seismic design code had minor damage in its structural members. However, major damage to non structural elements was commonly observed. Some typical damage observed by author’s field survey in Miyagi pref. which is conducted mainly as an activity of the AIJ committee is described. Damage to structural members was not found in most of RC buildings which suffered tsunami, although damage to non structural elements was generally severe. However, severe structural damage induced by devastating tsunami was observed in some buildings.

Study of Seismic Capacity of Masonry Infilled Reinforced Concrete Frames Considering the Influence of Frame Strength

Unreinforced masonry infilled-RC frames are widely used in many developing countries. Even though the influence of the masonry walls on the behavior of structure was recognized from the experience of past earthquake disasters, but many practicing engineers still assume that the infill walls are non-structural walls due to incomplete knowledge of the behavior of such structures. In this paper, an experimental study of two ½ scale specimens with different RC frames and masonry infill walls were tested using a static cyclic loading protocol. The main parameter was the influence of changing the RC frame strength on masonry infill seismic capacity. The results showed that shear strength and deformation capacity of masonry infill greatly improved by increasing the strength of boundary frame. The investigation of strength, ductility and initial stiffness based on experimental results and comparative study with existing methods showed large variations between several methods commonly used to assess the seismic capacity of masonry infill.

A Proposal on the Simplified Structural Evaluation Method for Existing Reinforced Concrete Buildings with Infilled Brick Masonry Walls

The developing countries in the earthquake prone regions in the world are still suffering a lot of casualties as well as building damage. These damages might be caused by inadequate structural design by engineers and/or poor quality control of construction works. In order to contribute to disaster mitigation for existing reinforced concrete (RC) buildings in developing countries, the simplified structural evaluation method based on the philosophy of Japanese evaluation standard; JBDPA (The Japan building disaster prevention association. Standard for seismic evaluation of existing reinforced concrete buildings, 2001) vis-a-vis the international seismic code; IBC (International Code Council, Inc. International Building Code, 2000) was developed by Seki (J Earthq Sci Eng, 2015). However, this evaluation method doesn’t consider the infilled brick masonry wall inside the beam and column. The usual RC building has many infilled brick masonry walls but these are not considered in the structural seismic design. They have the benefit in the strength capacity and the disadvantage in the brittle failure mode. For the structural evaluation of existing RC buildings, the consideration of the infilled brick masonry wall is quite important to get the actual behavior during the strong earthquake. The main objective of this study is to take the infilled brick masonry wall into the structural evaluation for the existing RC building in developing countries.

Damage Due to Earthquakes and Improvement of Seismic Performance of Reinforced Concrete Buildings in Japan

Japan, which is one of the most earthquake prone countries in the world, has suffered from damaging earthquakes repeatedly and learned lessons from damages. First, history of damages to existing reinforced concrete (RC) buildings due to previous earthquakes and seismic code revision are summarized. Secondly, basic concept and procedure of Japanese seismic evaluation method were outlined and seismic capacity index, I s , of buildings suffered Kobe Earthquake. Strong correlation between damage level and seismic capacity index, I s , was found. After the 1995 Kobe Earthquake, the law for promotion of seismic evaluation and retrofit was enforced based on the lessons learnt from the damage and investigation. Seismic evaluation and retrofit were widely applied to existing RC buildings in all over Japan and contributed to improvement of seismic capacities of existing RC buildings designed by old seismic code. The improvement was proved by recent major earthquakes such as 2011 Tohoku Earthquake and 2016 Kumamoto Earthquake. Typical damage pattern, failure modes and tendency in each earthquake were introduced and effectiveness of seismic evaluation and retrofit was discussed.

Damages to Reinforced Concrete Buildings

Typical damages to reinforced concrete buildings, both by the ground motions and the tsunami waves, are outlined in this section. The report herein is based primarily on the field survey of the AIJ members and collected through the members of the Reinforced Concrete Steering Committee of AIJ. The typical damages to reinforced concrete buildings are described below through the reports on the buildings selected and available for detailed survey. The damage reports below are translated selectively from the Chap. 6, Sect. 6.2 of AIJ report in Japanese version, which contains more photos and figures, especially on the structural plans as well as the damage rate evaluation of members. The reports on the buildings below are arranged as from the Japanese version: (1) school buildings located from north to south (Iwate, Miyagi, Fukushima and Kanto areas), (2) government offices, (3) residential buildings.