Search

Currently, there is no research and few valid experiments of pile caps. And shear failure mechanism of a pile, exterior column and foundation beam and pile caps in RC structure is not resolved yet under bi-lateral loading. Therefore, a performance evaluation method based on mechanical behaviour for pile caps has not been established. First, the fracture type was specified from the experimental results. Secondary, the ultimate strength formula of the pile cap was proposed based on the previous experimental results. It is a theoretical formula based on the truss-arch theory. It was confirmed that this formula can accurately evaluate the ultimate strength of the pile cap.

Neutron diffraction is a noncontact method that can measure the rebar strain inside concrete. In this method, rebar strain and stress are calculated using the diffraction profile of neutrons irradiated during a specific time period. In general, measurement accuracy improves with the length of the measurement time. However, in previous studies, the measurement time was determined empirically, which makes the accuracy and reliability of the measurement results unclear. In this study, the relationship between the measurement time and the measurement standard deviation was examined for reinforced concrete specimens under different conditions. The aim was to clarify the accuracy of the measurement of rebar stress using the neutron diffraction method. It was found that if the optical setup of the neutron diffractometer and the conditions of the specimen are the same, there is a unique relationship between the diffraction intensity and the rebar stress standard deviation. Furthermore, using this unique relationship, this paper proposes a method for determining the measurement time from the allowable accuracy of the rebar stress, which ensures the accuracy of the neutron diffraction method.

Abstract The authors performed static analyses using a foundation structure model to simulate the process leading to distinctive damage to pile foundations during the 2011 off the Pacific coast of Tohoku earthquake. Notable aspects of the analytical method used for this simulation include consideration of the nonlinear load‐deformation characteristics of pile elements, the dependence of the rotational stiffness at the pile head on the axial load, and the nonlinear behavior of soil spring including the pile group effect. The results of the simulations of pile failure for each loading direction provide a useful explanation of the observed damage to pile foundations. The proposed analysis method can be considered a practical approach to the seismic design of foundations subject to severe earthquakes.

The required base shear and drift limit for post-disaster management buildings have increased in the Japanese Building Code following major seismic events. One method to satisfy these requirements for reinforced concrete frame buildings is to cast exterior non-structural concrete wall elements to be monolithic with frame elements, but without anchoring the longitudinal wall reinforcing. This provides additional stiffness and strength while limiting significant damage in the non-structural wall. In this study, the structural performances of such elements were evaluated using static and dynamic experimental tests. The result indicates that non-structural walls that were neither isolated by seismic slits nor anchored to the adjacent walls with longitudinal reinforcements experienced less damage and higher deformability compared with walls having seismic slits. The confinement reinforcing impact was not observed on the strength and drift capacity of the beam member, owing to the large number of transverse reinforcements. However, the confinements limited the damage and nearly prevented concrete crushing. The maximum horizontal load of the specimen could be predicted using cross-sectional analysis, and the authors propose a simple equation to predict it with sufficient accuracy.

Following the observation of severe damage to structurally isolated non-structural reinforced concrete walls after major earthquakes, researchers began to reassess the effectiveness and connection detail of non-structural walls to moment-resisting frames. A method to control damages to the non-structural wall, is to cast exterior non-structural concrete wall elements to be monolithic with frame elements, without anchoring the wall longitudinal bar. The non-anchorage of the wall longitudinal bar significantly increases the drift capacity of the wall and decreases damage. Using an experimental approach, this study assesses the influence of reinforcement detailing and quantity of the transverse reinforcements on the strength and drift capacity of the non-structural hanging wall. This study further evaluates the workability mechanism of the transverse reinforcements and reinforcement detailing with concrete. The non-anchorage of hanging walls, having boundary confinements, was found to exhibit a higher drift and strength capacity than similar walls with the anchored detailing without boundary confinements. The strength capacity of the anchored detailing hanging walls with minimum amounts of reinforcements was higher than that of the non-anchored specimen. The boundary confinements were found to be more influential on the capability of the hanging wall when placed along with non-anchored detailing reinforcement.

In this study, ultra-high-strength fiber-reinforced concrete (UFC) panels were used as a quick and effective measure for seismic strengthening of damaged reinforced concrete (RC) columns. Four 1/3-scale specimens, which replicated RC columns of the soft-first-story of a 10-story condominium building that was heavily damaged in the 2016 Kumamoto Earthquake, were constructed and tested. The specimens were strengthened using UFC panels after being preloaded to the drift ratio, at which the maximum load capacity of the target column was measured, and then subjected to the main loading until the ultimate state was reached. The UFC panels were installed on the two faces of the column in a direction parallel to the assumed loading direction. Two of the specimens had a UFC or RC wing wall attached to one side of the column, which was also aligned with the assumed loading direction. During the preloading and main loading, the specimens were subjected to a cyclic lateral load and varying axial load that simulated an earthquake load. The proposed method improved the maximum strength and ultimate drift ratio, and helped restore the initial stiffness of specimens with UFC panels and a wing wall to that of a column specimen during preloading. The test results of a previous study, wherein the target column, loading method, and strengthening method were the same but the specimens were not damaged before strengthening, were compared to study the impact of the damage on the RC column before strengthening. [ABSTRACT FROM AUTHOR]