International Concrete Abstracts Portal

The main objective of this paper is to discuss the validity of seismic rehabilitation of concrete buildings in Japan based on the review of the behavior of seismically rehabilitated buildings during recent earthquakes. First, the state of seismic rehabilitation of concrete buildings is introduced. It is described that the seismic rehabilitation has been strongly promoted since 1) the enactment of the Law for Promotion of Seismic Rehabilitation of Existing Buildings in 1995 and 2) the declaration of the ten-year promotion plan of seismic rehabilitation as the government policy in 2005. Second, the behavior of rehabilitated buildings during recent earthquakes is introduced. It is described that 1) there were some insufficiencies in the early practice of seismic rehabilitation due to the lack of available guidelines, 2) the case of a rehabilitated building in Kobe that survived the 1995 Kobe Earthquake without any damage verified the validity of seismic rehabilitation, and 3) extensive nonstructural damage may result in the loss of building function, therefore, the target performance of “functional” may not be satisfied even if the performance of “life safety” is satisfied. Third, the behavior of un-rehabilitated local government buildings during the 2011 Great East Japan Earthquake is introduced. It is described that 1) extensive nonstructural damage may lead to shut down of the building even if structural damage is minor, 2) vulnerable essential buildings should be rehabilitated to satisfy the performance of “functional” as well as the performance of “life safety” and 3) essential building should be rehabilitated with highest priority.

The 2011 off the Pacific coast, Tohoku Earthquake (Mw=9.0) was the largest in the history of seismic observation in Japan. Seismology research community did not anticipate the possible occurrence of such a mega earthquake in the area. Main casualties were caused by tsunamis rather than by the collapse of buildings due to ground shaking. Structural engineering could not protect lives of building occupants if the building was buried under tsunami flood; good community planning is essential to mitigate the tsunami disaster in coast areas. Some low-rise reinforced concrete and steel buildings were moved or overturned by tsunami flood. Reinforced concrete structural walls failed by out-of-plane tsunami water pressure; floor slabs were lifted from floor girders by upward water pressure. Peak ground accelerations exceeding 1.0 g (g: acceleration of gravity, 9.81 m/s2 or 386 in./s2) were recorded at more than a dozen strong motion recording stations, but the destructive power of far-field earthquake motions was less for buildings than that of near-field earthquake motions. The seismic vulnerability of existing old buildings should be critically assessed, and vulnerable buildings should be retrofitted.

An experimental study was conducted in which 37 reinforced concrete deep beam specimens were tested. The specimens are some of the largest deep beams ever tested in the history of shear research. The data from the experimental program and from a database of 179 deep beam tests in the literature were used to assess the accuracy and conservatism of the strut and tie modeling provisions of ACI 318. In addition, the effects of the following variables were evaluated: distribution of stirrup legs across the web, triaxial confinement via concrete surrounding CCC and CCT nodal faces, quantity of web reinforcement, member depth, and a/d ratio. Based on the experimental findings of the study, suggested improvements to the ACI 318 STM provisions are discussed in this paper.

This paper describes a Collaborative Research project extending from 1982 to the mid 1990s between The University of Texas at Austin and Degenkolb Engineers on methods to strengthen existing concrete buildings for improved seismic performance. James Jirsa and the author were Principal Investigators for this series of national Science Foundation projects. The paper describes the collaborative process and summarizes some of the results of these research projects.

This paper reports the structural rehabilitation of a 28 story reinforced concrete building. Structural assessment of this building was initiated upon observing damage in one column after five years of service. As a result of this investigation it was concluded that the main cause of damage in the column was temperature induced deformations. A total of 36 circular (spiral) and 46 square (tied) columns were strengthened by steel jacketing. After the completion of rehabilitation, 122 sensors were placed in the building at different locations to monitor the temperature changes and deformations in structural members. In the paper results of seven years of monitoring are also given.