• Structural Engineering and Mechanics
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• 제81권1호
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• pp.11-28
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• 2022

This paper considers the combination of cyclic and axial loads to investigate the hysteretic performance of H-section 6061-T6 aluminum alloy members. The hysteretic performance of aluminum alloy members is the basis for the seismic performance of aluminum alloy structures. Despite the prevalence of aluminum alloy reticulated shells structures worldwide, research into the seismic performance of aluminum alloy structures remains inadequate. To address this deficiency, we design and conduct cyclic axial load testing of three H-section members based on a reliable testing system. The influence of slenderness ratios and bending direction on the failure form, bearing capacity, and stiffness degradation of each member are analyzed. The experiment results show that overall buckling dominates the failure mechanism of all test members before local buckling occurs. As the load increases after overall buckling, the plasticity of the member develops, finally leading to local buckling and fracture failure. The results illustrate that the plasticity development of the local buckling position is the main reason for the stiffness degradation and failure of the member. Additionally, with the increase of the slenderness ratio, the energy-dissipation capacity and stiffness of the member decrease significantly. Simultaneously, a finite element model based on the Chaboche hybrid strengthening model is established according to the experiment, and the rationality of the constitutive model and validity of the finite element simulation method are verified. The parameter analysis of twenty-four members with different sections, slenderness ratios, bending directions, and boundary conditions are also carried out. Results show that the section size and boundary condition of the member have a significant influence on stiffness degradation and energy dissipation capacity. Based on the above, the appropriate material constitutive relationship and analysis method of H-section aluminum alloy members under cyclic loading are determined, providing a reference for the seismic design of aluminum alloy structures.

• Computers and Concrete
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• 제30권3호
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• pp.175-183
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• 2022

To study the working mechanism and size effect of an innovative dovetail UHPC joint originated from the 5th Nanjing Yangtze River Bridge, a large-scale testing subject to negative bending moment was conducted and compared with the previous scaled specimens. The static responses, i.e., the crack pattern, failure mode, ductility and stiffness degradation were analyzed. It was found that the scaled specimens presented similar working stages and working mechanism with the large-scale ones. However, the post-cracking ductility and relative stiffness degradation all decrease with the enlarged length/scale, apart from the relative stiffness after flexural cracking. The slab stiffness at the flexural cracking stage is 90% of the initial stiffness while only 24% of the initial stiffness reserved in the ultimate stage. Finite element model (FEM) was established and compared with the experiments to verify its effectiveness in exploring the working mechanism of the innovative joint. Based on this effective method, a series of FEMs were established to further study the influence of material strength, pre-stressing level and ratio of reinforcement on its deflection-load relationship. It is found that the ratio of reinforcement can significantly improve its load-carrying capacity among the three major-influenced factors.

• 대한가정학회지
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• 제31권2호
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• pp.189-203
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• 1993

The objective of this study was to investigate the changes of the fabric absorbency, stiffness and antistatic property by using a fabric softner at laundering. The samples selected in this study were cotton and polyester fabrics. The cotton fabric was treated with 1/2 times(0.035%), 1 time(0.07%), 3 times(0.21%) and 10 times(0.7%) of the commercially suggested concentration (0.07%) of the fabric softner. And polyester fabric was done at 1 time(0.07%) of that. In order to examine the effect of the fabric by using a fabric softner, the abstraction of a surface active agent and quantitative analysis was performed by using a UV/VIS Spectroscopy and the correlations among the absorbency, stiffness and antistatic property was analyzed. The results obtained from this study were as follows; 1. In the cotton fabric, fabric softner gave the degradation of absorbency, and stiffness improvement was not shown by repeated fabric softner on the cotton fabric. 2. In the polyester fabric, the absorbency increased and the stiffness in creased very slightly. Specially, it is desirable to use fabric softner on the polyester due to improvement of antistatic property.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2008년도 추계학술대회 논문집
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• pp.1622-1627
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• 2008

A suspension is a core part, determining running stability and riding quality of vehicles and its stiffness is essential parameters in the process of vehicle designing. Suspension stiffness shall be adjusted to meet requirements of running stability and curve running performance, as adding stiffness to primary suspension for running stability in high-speed running results running performance degradation in curved track. The purpose of the report lies in utilization of usable data for optimization of suspension via analyzing running performance through changing stiffness of railway vehicle suspension.

• Geomechanics and Engineering
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• 제20권4호
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• pp.323-331
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• 2020

Pile foundation is widely used for railway bridges in loess throughout northwestern China. Modeling of the loess-pile interaction is an essential part for seismic analysis of bridge with pile foundation at seismically active regions. A quasi-static test is carried out to investigate the hysteretic behaviors of pile foundation in collapsible loess. The failure characteristics of the bridge pile-loess system under the cyclic lateral loading are summarized. From the test results, the energy dissipation, stiffness degradation and ductility of the pile foundation in loess are analyzed. Therefore, a bilinear model with stiffness degradation is recommended for the nonlinearity of the bridge pier-pile-loess system. It can be found that the stiffness of the bridge pier-pile-loess system decreases quickly in the initial stage, and then becomes more slowly with the increase of the displacement ductility. The equivalent viscous damping ratio is defined as the ratio of the dissipated energy in one cycle of hysteresis curves and increases with the lateral displacement.

• Earthquakes and Structures
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• 제7권5호
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• pp.735-751
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• 2014

In the previous paper, authors proposed the unified equivalent frame method (UEFM) for the lateral behavior analysis of the flat plate structure subjected to the combined gravity and lateral loads, in which the rotations of torsional members were distributed to the equivalent column and the equivalent slab according to the relative ratio of gravity and lateral loads. In this paper, the lateral behavior of the multi-span flat plate structures under various levels of combined gravity and lateral loads were analyzed by the proposed UEFM, which were compared with test results as well as those estimated by existing models. In addition, to consider the stiffness degradation of the flat plate system after cracking, the stiffness reduction factors for torsional members were derived from the test results of the interior and exterior slab-column connection specimens, based on which the simplified nonlinear push-over analysis method for flat plate structures was proposed. The simplified nonlinear analysis method provided good agreements with test results and is considered to be very useful for the practical design of the flat plate structures under the combined gravity and lateral loads.

• Structural Engineering and Mechanics
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• 제67권2호
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• pp.165-173
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• 2018

A simple predicted model using a modified Shear-lag method was used to represent the moisture absorption effect on the stiffness degradation for $[0/90]_{2s}$ composite laminates with transverse cracks and under flexural loading. Good agreement is obtained by comparing the prediction model and experimental data published by Smith and Ogin (2000). The material properties of the composite are affected by the variation of temperature and moisture absorption. The transient and non-uniform moisture concentration distribution give rise to the transient elastic moduli of cracked composite laminates. The hygrothermal effect is taken into account to assess the changes in the normalised axial and flexural modulus due to transverse crack. The obtained results represent well the dependence of the stiffness properties degradation on the cracks density, moisture absorption and operational temperature. The composite laminate with transverse crack loaded in axial tension is more affected by the hygrothermal condition than the one under flexural loading. Through this theoretical study, we hope to contribute to the understanding of the moisture absorption on the composite materials with matrix cracking.

• Earthquakes and Structures
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• 제16권1호
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• pp.97-107
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• 2019

The frame structures investigated in this paper is composed of Concrete encased columns with L-shaped steel section and steel beams. The seismic behavior of this structural system is studied through experimental and numerical studies. A 2-bay, 3-story and 1/3 scaled frame specimen is tested under constant axial loading and cyclic lateral loading applied on the column top. The load-displacement hysteretic loops, ductility, energy dissipation, stiffness and strength degradation are investigated. A typical failure mode is observed in the test, and the experimental results show that this type of framed structure exhibit a high strength with good ductility and energy dissipation capacity. Furthermore, finite element analysis software Perform-3D was conducted to simulate the behavior of the frame. The calculating results agreed with the test ones well. Further analysis is conducted to investigate the effects of parameters including concrete strength, column axial compressive force and steel ratio on the seismic performance indexes, such as the elastic stiffness, the maximum strength, the ductility coefficient, the strength and stiffness degradation, and the equivalent viscous damping ratio. It can be concluded that with the axial compression ratio increasing, the load carrying capacity and ductility decreased. The load carrying capacity and ductility increased when increasing the steel ratio. Increasing the concrete grade can improve the ultimate bearing capacity of the structure, but the ductility of structure decreases slightly.

• Structural Engineering and Mechanics
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• 제82권3호
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• pp.369-383
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• 2022

In this study, an equivalent boundary conditions (BCs) determination method is developed numerically for a panel reinforced concrete (RC) slab to realistically analyze the deformation and fatigue behaviors of a bridge RC slab. For this purpose, a finite element analysis of a bridge RC slab is carried out beforehand to calculate the stiffness of the bridge RC slab, and then the equivalent BCs for the panel RC slab are determined to achieve the same stiffness at the BCs to the obtained stiffness of the bridge RC slab at the corresponding locations of the bridge RC slab. Moreover, for the simulation of fatigue behaviors, fatigue analysis of the panel RC slab is carried out employing a finite element method based on a numerical model that considers the bridging stress degradation. Both the determined equivalent BCs and the BCs that have been typically applied in past studies are employed. The analysis results confirm that, in contrast to the panel RC slab with typically used BCs, the panel RC slab with equivalent BCs simulate the same bending moment distribution and deformation behaviors of the bridge RC slab. Furthermore, the equivalent BCs reproduce the extensive grid crack pattern in the panel RC slab, which is alike the pattern normally witnessed in a bridge RC slab. Conclusively, the panel RC slab with equivalent BCs behaves identical to the bridge RC slab, and, as a result, it shows more realistic fatigue behaviors observed in the bridge RC slab.

• 소성∙가공
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• 제4권2호
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• pp.131-140
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• 1995

In this paper damage propagation of a material during forming is investigated with the concept of continuum damage mechanics. An isotropic damage model based on the theory of materials of type N is adopted to describe the damage process of a ductile material with large elasto-viscoplastic deformation. The stiffness degradation of the loaded material is chosen as a damage measure. The highly nonlinear equilibrium equations are reduced to the incremental weak form and approximated by the total Lagrangian finite element method. To simulate contact condition, extended interior penalty method with modified coulomb friction law is adopted. The displacement control method along with the modified Riks' continuation technique is used to solve the incremental iterative equations. As numerical examples, upsetting problem and backward extrusion problem are simulated and the results of damage propagation and $J_2$ stress contours with and without friction are presented.