Kazuto Matsukawa

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.

Study of the residual axial capacities of shear-damaged reinforced concrete columns: Part 1—development of an evaluation model:

This is the first of two companion papers addressing the residual axial capacities of shear-damaged reinforced concrete columns. To evaluate the residual axial capacity, this article presents an arch resistance model that is based on the theory of mechanics and can reasonably explain the collapse mechanism of shear-damaged reinforced concrete columns. In the proposed model, the residual axial capacity of the column is evaluated by considering the interaction between the contributions of the longitudinal bars and the concrete core rather than by simply adding the two contributions together. The proposed model is also verified using an experimental database of shear-damaged reinforced concrete column specimens compiled from previous studies. The result shows that the proposed arch resistance model has an improved level of accuracy for evaluating the residual axial capacities of most column specimens. However, because the available information about column specimens in the compiled experimental database is limited, it is difficult to further verify the proposed model, and a new experimental program will be presented in Part 2.

Study of the residual axial capacities of shear-damaged reinforced concrete columns: Part 2—experimental verification of an evaluation model

This article presents an experimental program to further verify the arch resistance model, which was proposed for evaluating the residual axial capacities of shear-damaged reinforced concrete columns in part 1 of the companion papers. Three reinforced concrete columns with different transverse reinforcement ratios are designed and tested up to axial collapse under different axial force levels. Based on the experimental results, the transverse reinforcement within the shear-damaged region of the designed specimens is confirmed to be able to fully develop their strength at axial collapse. With regard to the evaluation of residual axial capacities, when the damage pattern of the concrete core is consistent with that described in the proposed model, the residual axial capacity of the column along with the included two contributions of the concrete core and longitudinal bars are estimated with a high level of accuracy. When the damage pattern of the concrete core is not completely consistent with that described in the proposed model, although the contribution of the concrete core is not accurately estimated, the contribution of the longitudinal bars is still accurately evaluated. Furthermore, because of the low percentage of the contribution of the concrete core, the damage pattern of the concrete core has little effect on the evaluation accuracy of the residual axial capacity of the column. Thus, using the proposed model, the residual axial capacities of the columns with slightly different damage patterns of the concrete core are still estimated with a high accuracy in this experimental program.

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.