Toshimi Kabeyasawa

Axial-Shear-Flexure Interaction Approach for Reinforced Concrete Columns

This paper modifies the conventional section analysis approach for shear behavior to be applicable for displacement-based evaluation of reinforced concrete columns and beams subjected to shear, flexural, and axial loads. The proposed approach is based on principles of axial-shear-flexure interaction. Shear behavior is modeled by applying the modified compression field theory, and flexure behavior is modeled by employing the conventional section analysis. The mechanisms of shear and flexure are coupled as springs in series, considering axial deformation interaction and concrete strength degradation, and satisfying compatibility and equilibrium relationships. The proposed approach is simplified to enable modeling a reinforced concrete column using a single section analysis with a single shear model for the entire element. The simplified approach is employed for displacement-based analysis of shear- and flexure-dominated reinforced concrete columns previously tested. Analyses are also performed for reinforced concrete columns tested by other authors. In order to verify the new displacement-based approach, analytical results, such as ultimate lateral loads and drifts as well as post-peak responses, were compared and found consistent with experimental data for a series of reinforced concrete columns.

Deformation Capacity of Reinforced Concrete Columns

An effective approach is presented for estimation of the ultimate deformation and load capacity of reinforced concrete columns based on principles of axial-shear-flexure interaction. Conventional section analysis techniques are employed for modeling the flexure mechanism, and the simplified modified compression field theory is implemented for modeling the shear behavior of elements. Average centroidal strains and average concrete compression strains derived from the flexural model are implemented in the shear model and used to calculate shear deformation and concrete strength degradation. This approximate procedure can be easily implemented in a hand-calculation method in a few steps. The approach is employed for the estimation of the ultimate deformation of shear- and flexure-dominated reinforced concrete columns previously tested. The analytical results are compared with the experimental data and consistent, strong agreement is achieved.

Influence of Axial Deformation on Ductility of High-Strength Reinforced Concrete Columns under Varying Triaxial Forces

A moment-curvature analysis based on hysteresis models of materials was conducted to reproduce the response of high-strength reinforced concrete column specimens subjected to varying triaxial forces. The relationships between the ductility and axial deformation of such columns were examined by a parametric analysis using the same models. The effects of varying axial load on the ductility and axial deformation characteristics of reinforced concrete columns are described, based on both the experimental and analytical results in this paper. The required items in a confinement design for reinforced concrete columns under varying triaxial forces are also examined.

DESIGN IMPLICATIONS OF A LARGE-SCALE SHAKING TABLE TEST ON A FOUR-STORY REINFORCED CONCRETE BUILDING

A full-scale, four-story, reinforced concrete building designed in accordance with the current Japanese seismic design code was tested under multi-directional shaking on the E-Defense shake table. A two-bay moment frame system was adopted in the longer plan direction and a pair of multi-story walls was incorporated in the exterior frames in the shorter plan direction. Minor adjustments to the designs were made to bring the final structure closer to U.S. practice and thereby benefit a broader audience. The resulting details of the test building reflected most current U.S. seismic design provisions. The structure remained stable throughout the series of severe shaking tests, even though lateral story drift ratios exceeded 0.04. The structure did, however, sustain severe damage in the walls and beam-column joints. Beams and columns showed limited damage and maintained core integrity throughout the series of tests. Implications of test results for the seismic design provisions of ACI 318-11 are discussed.

Earthquake-Resistance Design of Shearwalls With One Opening

Shearwalls with one opening have been designed according to the Architectural Institute of Japan (AIJ) standard for structural calculation of reinforced concrete structures using allowable stresses. However, effective reinforcement details have been developed by current research in the search for a new and rational design method. This paper reports the outline of earthquake-resistant design of shearwalls with openings according to a method based on ultimate capacity.

Damages to RC school buildings and lessons from the 2011 East Japan earthquake

Typical damages to reinforced concrete school buildings during the 2011 East Japan earthquake were reviewed. Procedures and causes of the damages are estimated as the specific responses to the ground motions at site with the spectral intensity of the ground motions recorded nearby. The lessons derived from the damages are discussed on peculiar design or general design requirements.

New Concept on Fail-Safe Design of Foundation Structure Systems Insensitive to Extreme Motions

Owing to systematic and dense seismic observation networks, extreme ground motions have been recorded in recent major earthquakes with high velocity or high acceleration far exceeding the conventional design code level. At the same time, most of reinforced concrete (RC) building structures in Japan survived these severe motions, probably because of higher capacity than design requirements or of input loss at the base. The authors have conducted shake table tests on full-scale RC buildings with flexible foundation at E-Defense to verify the input loss at the base. The test results are outlined in this paper, where the obvious reduction of damage to the building structure was observed owing to the slip behavior at the base. The results show that it is feasible to and apply in practice a fail-safe system against possible and yet unseen future extreme motions, by incorporating the slip behaviour positively to control damage or ensure safety.

3-D Dynamic Collapse Test of a Six-Story Full-Scale RC Wall- Frame Building

Response of reinforced concrete wall-frame structures subjected to earthquake motions was investigated by testing a full-scale six-story specimen on the world’s largest tri-axial shake table “E-Defense”. The specimen was designed based on the code of design and practice in 1970’, and columns and walls were defined as flexural yielding type based on current code calculation. The specimen was subjected to series of earthquake motions and finally collapsed due to shear failure in short columns and the structural wall at 1 st story during a strong earthquake motion.

Simulation of the Six-Story Full-Scale Wall-Frame Test

Pre-analytical research for the six-story reinforced concrete building tested at E-Defense has been done before the test was finished at January, 2006. Our pre-analytical results predicted either the base shear force or the final collapse type of test results with good accuracy by original JMA Kobe wave excitation. In this study, analyses are done by six motion components measured from test including rotations in three-dimensions. Usually we use only one panel model for one story shear wall. But from test results, we find the damage of shear wall is severely different from bottom to top at first story. In order to present the different damage at bottom and top of the first story shear wall, two analysis cases are done by the first story shear wall is modeled by one panel model and divided into two panel models. The main difference between two analytical methods shows on the evaluation of shear deformation.

Effective Slab Width for Evaluating Ultimate Seismic Capacities of Reinforced Concrete Buildings

A series of static and seismic loading tests of reinforced concrete frame assemblies were conducted in 2010, 2012, 2013 and 2014 to identify the effects of slab for evaluation of seismic capacities of reinforced concrete buildings as part of national research projects for review of the technical standards on seismic design practices in Japan. Two-fifth or half scale seven specimens were tested representing three-dimensional reinforced concrete beam-yielding frames with floor slab. A special loading set-up was invented and used to simulate the boundary conditions of the medium-story frame so that the axial elongation of the beams would not be constrained by the reaction supports consisting of pin-fixed and pin-roller. It was generally found from the series of tests and analyses that the slab reinforcing bars were increasing almost uniformly through the whole slab width and was fully effective to the flexural strength of the beams at around one percent story drift. The observed and calculated beam strengths with the full width of slab was much higher than those with the effective slab reinforcing bars assumed in the current design practice.