• Advances in concrete construction
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• v.13 no.4
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• pp.339-347
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• 2022

Retrofitting in reinforced concrete structures has been one of the most important research topics in recent years. There are several methods for retrofitting RC moment-resisting frames. the most important of which is the use of steel bracing systems with yielding dampers. With a proper design of yielding dampers, the stiffness of RC frame systems can be increased to the required extent so that the ductility of the structure is not significantly reduced. In the present study, two experimental samples of a one-third scale RC moment-resisting frame were loaded in the laboratory. In these experiments, the retrofitting effect of RC frames was investigated using Non-uniform Slit Dampers (NSDs). Based on the experimental results of the samples, seismic parameters, i.e., stiffness, ductility, ultimate strength, strength reduction coefficient, and energy dissipation capacity, were compared. The results demonstrated that the retrofitted frame had very significant growth in terms of stiffness, ultimate strength, and energy dissipation capacity. Although the strength reduction factor and ductility decreased in the retrofitted sample. In general, the behavior of the frame with NSDs was evaluated better than the bare frame.

• Journal of Welding and Joining
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• v.8 no.3
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• pp.79-88
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• 1990

Welded joint often contains soft or softened regions such as the HAZ of TMCP steel welded with high heat input. In this study, the equivalent yield strength of plate structure containing softened region was predicted by FEM analysis, and its incremental behavior was explained with the results of the analysis. The calculated results of yield strength indicated the following for the plate structures. 1) As the softened region starts to yield, shear stress begins to build up along the boundary between base metal and softened region. This results in multi-axial stress condition which gives restraint on the softened region. 2) Restraint effect has a significant influence on the distribution of the shear stress, the nominal stress, and the strain. 3) The yielding behavior of softened region becomes the same as that of base metal when both ratios of length to width and thickness to width of softened region are larger than 30 and 13 respectively.

• Journal of the Korea Concrete Institute
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• v.13 no.5
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• pp.466-475
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• 2001

The potential shear strength of reinforced concrete beams decreases after flexural yielding due to the decrease of the effective compressive strength of concrete in plastic hinge zone. A truss model considering shear deterioration in the plastic hinge zone was proposed in order to evaluate the ductile capacity of reinforced concrete beams failing in shear after flexural yielding This model can determine the potential shear strength of the beam by using a truss model. The potential shear strength gradually decreases as the increase of the axial strain of member. When the calculated potential shear strength decreases up to the flexural yielding strength, the corresponding rotation angle is defined as the ductile capacity of the beam. The predicted ductile capacity of reinforced concrete beams is shown to be in a good agreement with experimental results.

• Structural Engineering and Mechanics
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• v.28 no.3
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• pp.295-316
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• 2008

In the present paper a mechanical model to predict the compressive response of high strength short concrete columns with square cross-section confined by transverse steel is presented. The model allows one to estimate the equivalent confinement pressures exercised by transverse steel during the loading process taking into account of the interaction of the stirrups with the inner core both in the plane of the stirrups and in the space between two successive stirrups. The lateral pressure distributions at hoop levels are obtained by using a simple model of elastic beam on elastic medium simulating the interaction between stirrups and concrete core, including yielding of steel stirrups and damage of concrete core by means of the variation in the elastic modulus and in the Poisson's coefficient. Complete stress-strain curves in compression of confined concrete core are obtained considering the variation of the axial forces in the leg of the stirrup during the loading process. The model was compared with some others presented in the literature and it was validated on the basis of the existing experimental data. Finally, it was shown that the model allows one to include the main parameters governing the confinement problems of high strength concrete members such as: - the strength of plain concrete and its brittleness; - the diameter, the pitch and the yielding stress of the stirrups; - the diameter and the yielding stress of longitudinal bars; - the side of the member, etc.

• Journal of the Korean Society of Hazard Mitigation
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• v.2 no.1 s.4
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• pp.119-126
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• 2002

This paper presents the appropriateness for using high strength reinforcement according to the use of high strength concrete. Nine flexural tests were conducted on full-scale beam specimens according to the concrete strength, reinforcement strength and reinforcement ratio as main variable. The structural behavior was analyzed due to the flexural strength, stress-strain curve, deflections at yielding and fracture point, crack appearance and ductility factor. The member with high-strength reinforcements showed large deflection at yielding point and this was analyzed as a main cause to decrease the ductility factor. Structural behavior after yielding point, however, showed similarity to behavior of members with normal strength reinforcements of same stiffness. It was found that in the case of using reinforcements of $5500kgf/cm^2$ strength, the combination with concrete of $800kgf/cm^2$ strength demonstrated the great appropriateness which can increase the flexural capacity without any reduction of maximum reinforcement ratio.

• Proceedings of the Korea Concrete Institute Conference
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• 2000.10a
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• pp.583-588
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• 2000

While a great progress has been achieved in predicting the ultimate shear strength in the RC members, it is a fact that a method in order to estimate the ductility of RC members still has to be looked for. This study theoretically predict the ductility of RC beams which fail in shear after flexural yielding by considering the deterioration of concrete strength in plastic hinge region.

• Structural Engineering and Mechanics
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• v.38 no.4
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• pp.385-403
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• 2011

Continuous deep girders which transmit the gravity load from the upper wall to the lower columns have frequently long end shear spans between the boundary of the upper wall and the face of the lower column. This paper presents the results of tests and analyses performed on three 1:2.5 scale specimens with long end shear spans, (the ratios of shear-span/total depth: 1.8 < a/h < 2.5): one designed by the conventional approach using the beam theory and two by the strut-and-tie approach. The conclusions are as follows: (1) the yielding strength of the continuous RC deep girders is controlled by the tensile yielding of the bottom longitudinal reinforcements, being much larger than the nominal strength predicted by using the section analysis of the girder section only or using the strut-and-tie model based on elastic-analysis stress distribution. (2) The ultimate strengths are 22% to 26% larger than the yielding strength. This additional strength derives from the strain hardening of yielded reinforcements and the shear resistance due to continuity with the adjacent span. (3) The pattern of shear force flow and failure mode in shear zone varies depending on the amount of vertical shear reinforcement. And (4) it is necessary to take into account the existence of the upper wall in the analysis and design of the deep continuous transfer girders that support the upper wall with a long end shear span.

• Journal of the Korean Society of Propulsion Engineers
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• v.8 no.4
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• pp.36-42
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• 2004

The Properties of material, C18200 which is used for development of high performance liquid rocket engine combustor chamber were obtained by tension tests. The specimen for regenerative combustor was designed by structural analysis using that Properties. After the designed specimen was manufactured by the same manufacturing process of regenerative combustor. the yielding stress and yielding strain were obtained by strength tests. The properties of C18200 was degraded very much after brazing. The estimation of yielding pressure by structural analysis was almost same as that of strength test. The collector Part was yielded and failed previously than that of cooling channel part during strength test.

• Structural Engineering and Mechanics
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• v.58 no.4
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• pp.661-676
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• 2016

This paper presents an elastic/plastic model that neglects strain hardening during loading, but accounts for the Bauschinger effect. These mathematical features of the model represent reasonably well the actual behavior of several materials such as high strength steels. Previous attempts to describe the behavior of this kind of materials have been restricted to a class of boundary value problems in which the state of stress in the plastic region is completely controlled by the yield stress in tension or torsion. In particular, the yield stress is supposed to be constant during loading and the forward plastic strain reduces the yield stress to be used to describe reversed yielding. The new model generalizes this approach on plane stress problems assuming that the material obeys the von Mises yield criterion during loading. Then, the model is adopted to describe reversed yielding in thin hollow discs subject to external pressure.

• Structural Engineering and Mechanics
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• v.33 no.6
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• pp.725-745
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• 2009

In this paper, probabilistic seismic performance assessment of a typical non-seismic RC frame building representative of a large inventory of existing buildings in developing countries is conducted. Nonlinear time-history analyses of the sample building are performed with 20 large-magnitude medium distance ground motions scaled to different levels of intensity represented by peak ground acceleration and 5% damped elastic spectral acceleration at the first mode period of the building. The hysteretic model used in the analyses accommodates stiffness degradation, ductility-based strength decay, hysteretic energy-based strength decay and pinching due to gap opening and closing. The maximum inter story drift ratios obtained from the time-history analyses are plotted against the ground motion intensities. A method is defined for obtaining the yielding and collapse capacity of the analyzed structure using these curves. The fragility curves for yielding and collapse damage levels are developed by statistically interpreting the results of the time-history analyses. Hazard-survival curves are generated by changing the horizontal axis of the fragility curves from ground motion intensities to their annual probability of exceedance using the log-log linear ground motion hazard model. The results express at a glance the probabilities of yielding and collapse against various levels of ground motion intensities.