Stiffness Degradation Of Specimens Research Articles

Seismic Behaviors of Novel Steel-Reinforced Concrete Composite Frames Prestressed with Bonding Tendons

To investigate the seismic behaviors of novel steel-reinforced concrete composite frames prestressed with bonding tendons (PSRCFs), 15 groups of PSRCF specimens were designed with the following main parameters: the cubic compressive strength of high-strength concrete (fcu), the axial compression ratio of frame columns (n), the slenderness ratio of frame columns (β), the steel ratio of angle steel (α), the span–height ratio of frame beams (L/hb), and the prestressing degree (λ). Based on the modified concrete constitutive model proposed by Mander and the prestressing effect applied by the cooling method, the finite element models of PSRCFs were established by using ABAQUS software, the static analysis on the frame structures under the combined actions of axial forces and horizontal loads was carried out, and the monotonic load–displacement curves were explored. By comparing with the skeleton curves obtained by the experimental hysteretic curves, the rationality of the modeling method was verified. The PSRCFs had good mechanisms of strong columns and weak beams. Based on this, the influences of different parameters on the seismic behaviors such as hysteretic curves, skeleton curves, stiffness degradations, energy dissipation capacities, and ductility of the specimens were investigated. The results show that the hysteretic curves of the PSRCFs are full and have no pinch phenomenon. The ultimate load and the stiffness degradation of specimens can be improved significantly by increasing α, and on the contrary, the ultimate load and stiffness degradation decreased by increasing β. The ductility of the specimens decreased gradually with the increasing β and n. The energy dissipation capacity of the specimens decreased with the increasing β. The trilinear model of the skeleton curves and the restoring force model of PSRCFS were established by statistical regression, which agree well with the numerically simulated results. These can provide theoretical support for the elastoplastic analysis on this kind of PSRCF structure.

Mechanical Behavior of CCA Wall Infilled Steel Frames with Preset Vertical Slits

In view of the unfavorable interaction between the steel frame and cellulose fiber cement sheets autoclaved (CCA) wall, preset vertical slits are adopted on the wallboard. Four 1:2-scale, single-bay, and single-storey steel frames, one bare steel frame, one CCA wall infilled steel frame without any measures, and two CCA wall infilled steel frames with different patterns of a slit, were tested under low cyclic load. The failure mode and additional stiffness of the CCA wall were obtained from the test. Besides, the effects of the vertical slits on hysteretic performance, bearing capacity, and the stiffness degradation of specimens were also studied. It was found that the preset vertical slits were effective in delaying the cracking of the CCA wall, and in reducing the additional stiffness of the CCA wall for the steel frame structures. To further study the failure characteristics of CCA wall, the finite element models of the CCA wall infilled steel frames were established and verified against the test results. The findings in this paper will have a certain reference value for the future research and engineering applications of similar steel frames with infill walls.

Seismic experiment and performance index studies on recycled aggregate concrete filled steel tube frames infilled with recycled hollow block filler walls

AbstractTo study the seismic behavior of recycled aggregate concrete filled steel tube (RACFST) frames infilled with recycled hollow block filler walls (RHBFW), four frame specimens were designed subjected to low cycle loading experiments. Through the test, the failure process and pattern of specimens were observed and the seismic performance indexes were obtained. The results show that the hysteretic curves of RACFST frames infilled with RHBFW are full; the equivalent viscous damping coefficients he of specimens when destroyed both exceed 0.2, and the interlayer displacement angle is between 1/34 and 1/33 when destroyed, meaning the frame structures having good energy dissipation and good collapse resistance abilities. The RAC beam section height has little effect on the ductility and stiffness degradation of specimens; however, the bearing capacities of specimens increase gradually with the increase of beam section height. The existence of RHBFW can be the first seismic defense line of RACFST frames, and they can improve the ductility of specimens, as well as the bearing capacities and initial elastic stiffness. Before RHBFW failed, the specimens with filler wall have better energy dissipation abilities than those without filler wall. After RHBFW failed, the specimens without filler wall have better energy dissipation abilities than those with filler wall.

Seismic performance of RCS beam-column joints using fiber reinforced concrete

This paper deals with the experimental investigation on the behavior of RCS beam-column exterior joints. Two full-scale specimens of joints between reinforced concrete columns and steel beams are tested under cyclic loading. The objective of the test is to study the effect of steel fiber reinforced concrete (SFRC) on the seismic behavior of RCS joints. The load bearing capacity, story drift capacity, ductility, energy dissipation, and stiffness degradation of specimens are evaluated. The experimental results point out that the FRC joint is increased 20% of load carrying capacity and 30% of energy dissipation capacity in comparison with the RC joint. Besides, the FRC joint shown lower damage and better ductility than RC joint.

Rapid evaluation of S-N curve for composite laminates on thermographic approach

A new fatigue life prediction model is developed for composite laminates based on both infrared thermographic data and stiffness degradation process. The fatigue limit is firstly determined by the improved thermographic method and then a two-parameter function is proposed to describe the normalized stiffness degradation of specimens subjected to various maximum loading stresses. These two parameters can be calibrated by the stiffness degradation data and stabilized temperature data. Thereafter, the calibrated model can be used to predict S-N curve. The proposed model is applied the experimental data from literature and the results show that the predicted S-N curve has a well agreement with the experimental one.

Experimental Research on Seismic Performance of Four-Element Variable Cross-Sectional Concrete Filled Steel Tubular Laced Columns

A total of 7 experimental tests were conducted to investigate seismic performance of four element variable cross-sectional Concrete Filled Steel Tubular (CFST) laced columns. The experimental parameters are longitudinal slope and arrangement type of lacing tubes. The rules on hysteresis loop, ductility, energy expenditure, and stiffness degradation of specimens are researched. Test results indicate that all specimens have good seismic performance; their hysteresis loops are full without obvious shrinkage. With the increase of longitudinal slope, the horizontal carrying capacity increases, energy dissipation capacity improve, and there is slightly increase in stiffness degradation. The influence of arrangement type of lacing tubes on displacement ductility of specimens is big.

Seismic performance of prefabricated high-strength concrete tube column–steel beam joints

This study proposes a new type of fabricated hybrid frame structure, which is a prefabricated high-strength concrete tube column–steel beam joint hybrid frame structure. A series of six full-scale cruciform prefabricated high-strength concrete tube column–H-shaped beam joint specimens was tested under cyclic loading to investigate the seismic performance of the new fabricated hybrid frame structure. We designed the connection in the manner that the capacity of beam was higher than that of the column. The cracking pattern, failure modes, energy dissipation capacity, and strain profiles of the specimens were obtained and discussed. The test results showed that some specimens collapsed due to ring plate tearing failure and weld fracture, while other specimens collapsed due to column flexural failure. Shear connectors (i.e. shear studs and shear reinforcement) could ensure the reliable transmission of shear force, and the compound stirrups can effectively improve bearing capacity and joint ductility. The stiffness degradation of specimens was smooth with a linearly decreasing trend because of the prestressed reinforcement. The new joints could be applied in a seismic region.