ABSTRACTSteel bar fracture of reinforced concrete (RC) column under strong cyclic load has been tested. On the basis of the test results, the steel bar fracture of specimen is consid-ered as the very low cycle fatigue behavior and the calculation method of steel bar frac-ture is derived by the use of Coffin-Manson equation and the Palmgren-Miner rule. The obtained damage ratio equation of steel bar fracture can be easily applied to the seismic response damage analysis of multi-story RC frame under extremely strong ground motion. By the use of the derived damage analysis method, the effects of design conditions on the seismic response damage of RC frame are investigated. 42078
1. INTRODUCTIONIn the earthquake resistant design of reinforced concrete (RC) frame it is important to prevent the brittle shear fracture of RC column. But even if the brittle shear fracture is prevented by the enough transverse reinforcement, RC column may fail in brittle by the steel bar fracture of longitudinal reinforcement under strong cyclic load. Concern-ing with the steel bar fracture J. Brown and S.K. Kunnah [Brown, J., 2004] investigated the low cycle fatigue of independent steel bar but the confining effect of concrete on the steel bar fracture was not studied. In this study the fracture test of RC column under strong cyclic load has been car-ried out and the steel bar fracture of RC column is analyzed. By the use of the analysis method of steel bar fracture, the seismic response damages of RC frame are investi-gated in relation with the structural design conditions.2. STEEL BAR FRACTURE TEST OF RC COLUMN UNDER CYCLIC LOAD2.1 RC column specimenThe specimens are the cantilever RC columns as shown in Figure1. The test condi-tions and the test results are explained in Table 1. All specimens are fully reinforced by transverse reinforcement to prevent the shear fracture of column. The concrete strength, the reinforcement ratio, the axial load and the amplitude of cyclic deforma-tion are different among the specimens and the effects of them on the steel bar fracture of RC column have been examined. The material properties and the tension test results of steel bars are explained in Table 2 and Figure 2.
1Department of Architecture, Kumamoto University; Kumamoto 860-8555, Japan;   PH (+81) 96-342-3557; FAX (+81) 96-342-3569; email 2.2 Loading conditions Figure 3 shows the test conditions and Figure 4 is the test setup in which the loading conditions of lateral cyclic load (F) and varying axial load (N) are explained. To simulate the seismic response behavior of RC column, the lateral cyclic load and the varying axial load were applied dynamically. The lateral load and the axial load varied independently with time and there was no relation between them. The time histories of the deforma-tion (δ) and the axial load are explained in Figure 5. In the dynamic loading test the maximum velocity of lateral deformation at the loading point was nearly 100 mm/sec. and the maximum strain rate of the longitudinal steel bar was about 0.15 -0.20 /sec. as shown in Figure 6.2.3 Steel bar fracture of specimen The steel bar fracture of every specimen was obtained from the steel bar strains which were measured by the wire strain gages (WSG-0, WSG-1, WSG-2) attached to the longitudinal reinforcements shown in Figure 1.
The time histories of the steel bar strains measured by WSG-2 and the time histories of restoring force and deformation are shown in Figure 7 in which the fracture point is indicated by the dashed line. The strain of steel bar which did not fracture is also shown in Figure 7(C) to compare with the strain of the fractured steel bar in Figure 7(B). When the steel bar fractured, the steel bar strain decreased suddenly and extremely (Figure 7(B)) even if the direction of incremental deformation did not change (Figure 7(A)). Furthermore, the restoring force deteriorated suddenly when the steel bar fractured (Figure 7(D)). From these behaviors observed in Figure 7, the following conditions to decide the steel bar fracture of every specimen are assumed to be satisfied simultaneously. i) Steel bar strain decreases suddenly and extremely. After that the steel bar strain does not increase again.ii) The steel bar is subjected to tensile stress.iii) The direction of incremental deformation of specimen does not change when the steel bar strain decrease suddenly and extremely.The loading of every specimen stopped just after the first fracture of steel bar was observed. From this reason among the 31 longitudinal steel bars under the same loading condition the 16 steel bars fractured and the other steel bars did not fracture. 钢筋混凝土框架英文文献和中文翻译:http://www.751com.cn/fanyi/lunwen_42388.html