コンクリートと耐震構造-研究生活40年を顧みて-

Abstract

This paper is an overview of 40 years research on concrete and concrete structures in seismic area conducted by the author in Kyoto University. Research had started in 1953. In the first 10 years, main theme was to provide rational seismic design procedures on prestressed concrete building structures. In accordance with the basic concept that occurrence of severe damege in the structure allows for strong ground motion but collapse should be avoided, ultimate strength design method had been proposed with design factored loads in 1956. This proposal was adopted into the first AIJ (Architectural Institute of Japan) design recommendation on prestressed concrete building structures in 1961 with the design formulae for service load condition developed by the author. In 1970, systematic research on unbonded prestressed concrete had been started for finding a way of applying it in seismic building structures. After vigorous research, the auther proposed the calculation method of ultimate flexural moment. Particularly, it should be noted that world-widely spreaded doubt for the fatigue fracturing of unbonded tendons at end anchorage portion against the earthquake cyclic high-over loads was wiped up by showing detailed low-cycle fatigue test results on unbonded tendon-anchorage assembly and unbonded beams. In 1980's, research on partially prestressed concrete had been carried out and skillful method of determining the required prestressing force and its eccentricity was proposed based on the lood-balancing method. This method was adopted in the first design recommendation on the AIJ partially prestressed concrete buildings. In addition to these researches, the author conducted research works on high-strength concrete, shear problem on reinforced concrete members and ductility improvement of concrete and structural concrete members, etc.Especially, on the shear problem, based on the fundamental concept that a part of applied shear force is carried by the truss mechanism and remaining by the strut mechanism, a set of calculation formulae on the shear failure strength was proposed. Also, test method for predicting the efficiency of shear reinforcement had been newly developed and the fact that the use of high strength shear reinforcement having 600 to 1300 Mpa in yield strength is essential for fully avoiding of shear failure, particularly in case of the member with high-strength concrete. As the ductility enhancement ofstructural concrete concerns, experiments covering wide-range of concrete strengths from 24 to 130 Mpa and yield strength of confining reinfcrcement from 160 to 1300 Mpa had been conducted on concrete prisms and structural concrete members including reinforced concrete columns and prestressed concrete members. From the test results it showed that the compressive ductility of concrete as well as that of structiral concrete members can be enhanced remarkably by the use of high strength lateral confining reinforcement. Also, the stress-strain curve models for confined concrete to be applicable to the wide-range concrete strength from 24 to 160 Mpa was presented. And further, the flexural ductility design procedure had been proposed based on those research results. Recent development of reinforced concrete high-rise buildings in Japan is owing to such author's research results on ductility enhancement of concrete and structural concrete members by high-yield strength lateral confining reinforcement.