The effects of cyclic plastic strains on the fracture toughness of structural steels and also the effects of strain aging on the fracture toughness of structural steels subjected to cyclic plastic strains are investigated by Charpy V-notch impact tests. The Charpy V-notch absorbed energy decreases with the increase of cycles of plastic strains. Especially, it drops greatly at the early cycles. The decrease of the absorbed energy is larger with the increase of the magnitude of plastic strains. The influence of the strain aging is small on the absorbed energy for the specimens under no loads and monotonic loading, but it is large under cyclic loading. The Charpy V-notch impact toughness is examined on the top and bottom flanges of a girder of a highway bridge hit by the 1995 Hyogoken-Nanbu Earthquake, Japan. The girder is shown to have not been subjected to cyclic plastic strains during the earthquake.
The Hyogoken-Nanbu earthquake struck two power plants in east part of Hyogo-Prefecture. These are large steel structures with ribeted joints designed in conformity with the past criteria. The structures suffered not so severe damage and the damage were watched at some of the braces. We tried to simulate the state of damage based on seismic response analyses and a full scale test of brace joints. Consequently the simulation could express the real damage and the joints would be damaged around the stress calculated by these analyses. In this study it was proved that the analyses were effective.
A nine-story moment resisting steel frame consisting of cold formed hollow section columns and hot Rolled H-beams, which is located at the central part of Kobe city and was constructed in 1989, suffered severe damage to many welded beam-to-column connections during the 1995 Hyogoken-Nanbu earthquake. In this paper, damage to beamto-column was detailed and plausible causes of the damage were discussed from the perspectives of materials, connection details, and seismic capacity demands. And also, the repair works for the damage executed to recover the original strength, is introduced.
In this paper, a stress-strain relationship in concrete which takes account of the confining effect on the filled concrete is proposed to evaluate ultimate strength and deformation capacity of concrete filled circular steel tubular columns rationally. The confining effect is quantitatively derived from the characterization between Poisson's ratio and axial strain in steel and concrete filled tube under concentric loading. The applicability of the proposed stress-strain relationship in concrete as well as the influence of strain hardening in steel is discussed. Ultimate strength, curvature and deflection of the concrete filled circular columns are calculated on the basis of the proposed model in steel and concrete, comparing with the past test results. It is concluded that the predicted relations agree quite well with the test results.
Computational impact analysis has been applied to civil engineering structures. Most of previous studies, though, were focused on the behavior of RC structures subjected to impactors such as missiles or aircrafts. The effect of strain rate on composite structures has not been clear so far. In this study, several impact analyses considering strain rate effects of steel and concrete are performed and compared to the experimental results. Anochor system of metal liners and steel pipes filled or unfilled with concrete under impact force are successfully simulated.
In a previous paper, authors calculated buckling strength of concrete filled steel tubular columns in two different ways. One is performed using the tangent modulus theory (Nsc), considering steel portion and concrete portion behave as a one body. The second one is the method of superposed strength in which a simple sum of separately computed buckling load of steel and concrete columns is regarded as a buckling strength (Ns+c). Ramberg-Osgood equation was used as the stress-strain relations of a steel tube in the paper. In this paper, elastic-perfectly-plastic stress-strain relations are used. Effect of the analytical parameters on the correspondence between the two strength is examined.
This paper deals with steel frames combined with hysteretic dampers and examine the strength required for the main frames consisting of beams and columns not to go beyond yielding under earthquake loading. Dynamic response analysis is carried out for equivalent single degree of freedom system, and interaction between the obtained responses and various structural parameters including the base shear coefficient CB is quantified. An analytical expression of CB is also formulated based upon the energy balance consideration. Primary parameters that control CB are found to be (1) the damper's shear strength ratio to the maximum resistance (β) and (2) the relative stiffness between the damper and main frame. It is also pointed out that an optimum j3 does exist by which CB can be minimized.