Load-displacement Hysteresis Curves Research Articles

Experimental seismic study of precast hybrid SFC/RC beam–column connections with different connection details

A new type of precast hybrid steel fiber concrete (SFC)/reinforced concrete (RC) beam–column connection with different connection details was developed for precast concrete frames. In this study, seven concrete beam–column connections, six precast specimens, and one monolithic joint were subjected to a constant axial load and a reversed cyclic loading. The main test variables were the end-plate connection forms and SFC usage in the core region and the connection section. The construction process of the proposed hybrid connections was convenient and fast. The load–displacement hysteresis curves and failure modes of the precast connections were obtained, and the seismic behaviors in terms of connection stiffness, strength, energy dissipation, and shear deformation in the joint core were evaluated. The results revealed that the proposed precast concrete connections had higher strength, slower stiffness degradation, and greater energy dissipation capacity, thereby illustrating that the specimens had a satisfactory ability to resist seismic loads. The shear deformation of the proposed joints was reduced because of the tensile deformability of the SFC and the yielding steel connectors, while the shear strength was considerably enhanced. The cracking pattern in the core region of the hybrid connections with the SFC was well controlled. The integrity of the connection section was maintained. Furthermore, the SFC and steel-plate connectors were vital to the performance of the system.

Investigation of the date palm fiber for green composites reinforcement: Quasi-static and fatigue characterization of the fiber

This work describes the quasi-static tensile behavior and cyclic fatigue of technical fibers from date palm tested for the first time according to the authors' knowledge, which can be used in the reinforcement of green composites.The values of the stress and strain at failure and Young's modulus for18 samples tested under quasi-static tensile loading are compared with results reported in the literature for other fibers. Cyclic fatigue tests were performed at a frequency of 2 Hz under sinusoidal solicitation for different loading levels ranging from 0.6 to 0.95 corresponding to maximum recorded forces of 15.36 and 39.82 N, respectively. The evolution of the force as a function of the number of cycles was recorded. This allows us to follow the stiffness degradation. The load-displacement hysteresis curves show the influence of the number of cycles and the loading level on the size and shape of the hysteresis loops, allowing the calculation of the dissipated energy per cycle for the technical fibers.

Study on the Bending Performance of Composite H-Shaped Piles

Abstract There has been a great increase in the number of structural members composed of two or more materials with different stress–strain distributions. This study investigated the bending performance of composite H-shaped piles subjected to bending moments. Load–displacement hysteresis curves were analyzed using limit state analysis, and eight specimens—six composite H-shaped piles made of reinforced concrete and H-shaped steel beams (i.e., composite H-shaped piles) and two conventional H-shaped steel piles—were tested using a loading apparatus. The test results show that the ductility capacity of the composite H-shaped pile is 138 % more than that of the conventional H-shaped steel pile.

Effect of different size of joint enlargement on seismic behavior of gravity load designed RC beam‐column connections

SummaryEffect of different size of planer joint enlargement as a noninvasive and practical strategy for seismic retrofit of gravity load designed external reinforced concrete beam‐column connections was experimentally investigated. The joint region was enlarged using steel angles that are mounted using prestressed cross‐ties. Reverse cyclic load tests on five half‐scale control and retrofitted external RC beam‐column connections were conducted. Three different size of planer joint enlargement being 180, 140, and 90 mm were considered for retrofitted specimens. The performance of the retrofitted specimens is compared with that of the control gravity load designed beam‐column connections, in terms of load–displacement hysteresis curve, energy dissipation and ductility capacities, and global strength and stiffness degradation behavior. The experimental results showed that increasing the size of planer joint enlargement significantly enhances the seismic capacity of the retrofitted connections, in terms of strength, stiffness, energy dissipation, and ductility capacity and also planer joint enlargement can relocate beam plastic hinges to outside the joint panel.

Experimental Study on Seismic Behavior of New Steel Box Bridge Piers with Embedded Energy Dissipation Shells

An investigation was conducted to evaluate the seismic behavior of a new type of steel box-section bridge piers with embedded energy dissipation shell plates. In this study, two sets of the new steel box-section bridge piers were designed and pseudo-static tests were carried out on ten steel box bridge piers under constant axial force, with a horizontal cyclic load on top of the piers. The change regularities of the failure mode, the patterns of local buckling, the load–displacement hysteresis curve and its curve skeletons, and the load-strain hysteresis curves of the specimens were analyzed. The rules of horizontal stiffener spacing on embedded shell plates, the axial compression ratio, the embedded shell strength, and the layout of longitudinal ribs in the box-section wallboards were obtained to evaluate their influence on the seismic behavior of the new-type steel piers. The test results indicated that, after installing the embedded shells, the deformation ability of steel box-section bridge piers was enhanced and their ductility was improved. The effects of axial compression ratio and the space of transverse stiffeners in embedded shells on the seismic behavior of the new steel piers were significant. When the space of the horizontal stiffeners on the embedded shells and the axial compression ratio become smaller, the bearing capacity and ultimate displacement capability of the specimens would be greater, the descent segment of the curve skeleton would be more gradual, and the deformability and ductility of the new-type steel piers would be better. The effects of setting longitudinal stiffening ribs and enhanced embedded shell strength on the bearing capacity and ductility of the steel box bridge piers were relatively small. Based on the experimental results, calculation equations were established for stable bearing capacity and maximum deformation of the new-type steel piers, under the constant axial force and horizontal cyclic loading, in order to promote their seismic design.

Seismic damage assessment of steel reinforced recycled concrete column-steel beam composite frame joints

Low cyclic loading tests are conducted on the steel reinforced recycled concrete (SRRC) column-steel (S) beam composite frame joints. This research aims to evaluate the earthquake damage performance of composite frame joints by performing cyclic loading tests on eight specimens. The experimental failure process and failure modes, load-displacement hysteresis curves, characteristic loads and displacements, and ductility of the composite frame joints are presented and analyzed, which shows that the composite frame joints demonstrate good seismic performance. On the basis of this finding, seismic damage performance is examined by using the maximum displacement, energy absorbed in the hysteresis loops and Park-Ang model. However, the result of this analysis is inconsistent with the test failure process. Therefore, this paper proposes a modified Park-Ang seismic damage model that is based on maximum deformation and cumulative energy dissipation, and corrected by combination coefficient a. Meanwhile, the effects of recycled coarse aggregate (RCA) replacement percentage and axial compression ratio on the seismic damage performance are analyzed comprehensively. Moreover, lateral displacement angle is used as the quantification index of the seismic performance level of joints. Considering the experimental study, the seismic performance level of composite frame joints is divided into five classes of normal use, temporary use, repair after use, life safety and collapse prevention. On this basis, the corresponding relationships among seismic damage degrees, seismic performance level and quantitative index are also established in this paper. The conclusions can provide a reference for the seismic performance design of composite frame joints.

Experimental Assessment on the Hysteretic Behavior of a Full‐Scale Traditional Chinese Timber Structure Using a Synchronous Loading Technique

In traditional Chinese timber structures, few tie beams were used between columns, and the column base was placed directly on a stone base. In order to study the hysteretic behavior of such structures, a full‐scale model was established. The model size was determined according to the requirements of an eighth grade material system specified in the architectural treatise Ying-zao-fa-shi written during the Song Dynasty. In light of the vertical lift and drop of the test model during horizontal reciprocating motions, the horizontal low‐cycle reciprocating loading experiments were conducted using a synchronous loading technique. By analyzing the load‐displacement hysteresis curves, envelope curves, deformation capacity, energy dissipation, and change in stiffness under different vertical loads, it is found that the timber frame exhibits obvious signs of self‐restoring and favorable plastic deformation capacity. As the horizontal displacement increases, the equivalent viscous damping coefficient generally declines first and then increases. At the same time, the stiffness degrades rapidly first and then decreases slowly. Increasing vertical loading will improve the deformation, energy‐dissipation capacity, and stiffness of the timber frame.

Seismic behavior of precast concrete coupled shear walls with engineered cementitious composite (ECC) in the critical cast-in-place regions

The seismic performance of precast reinforced concrete (RC) coupled shear walls is significantly influenced by coupling beams and the beam-to-wall joints during large deformations into plastic ranges. This study investigated the use of engineered cementitious composite (ECC) in the cast-in-place beam-to-wall joints and the upper regions of the composite coupling beams as an innovative method to improve the seismic performance of precast RC coupled shear walls. Two 1/2-scale precast coupled shear walls were tested under reversed cyclic loading and seismic behavior in terms of failure characteristic, mechanical characteristic value, load-displacement hysteresis curves, load-displacement envelope relationship, stiffness degradation, ductility and energy dissipation capacity were evaluated. Research results show that the substitution of concrete with ECC in the critical cast-in-place regions proved to be an effective method to improve the seismic performance of the two-story spatial of precast RC coupled shear walls.

Design of an Improved Nonlinear Disc Spring Vibration Isolator

An improved nonlinear vibration isolator is proposed in this paper. It uses the exact solution derived load-displacement hysteresis curve formula based on energy method to calculate disc spring, combined with the finite element analysis. The static load capacity and dynamic mechanical property of this new type disc spring vibration isolator is validated through the static load tests or fatigue analysis. Compared with the rubber vibration isolator, the conclusion can be found: the new type vibration isolator has wider scope of vibration isolation, and is better in low frequency vibration isolation. These research achievements are of significant importance in the vibration isolation of heavy load and great shock mechanical equipment.

Analytical performance evaluation of modified inclined studs for steel plate concrete wall subjected to cyclic loads

An analytical study was conducted to investigate the effect of the shape and spacing of modified inclined studs used as shear connector between concrete and steel plate on the cyclic behavior of steel plate concrete (SC) shear wall. 9 different analysis cases were adopted to determine the optimized shape and spacing of stud. As the results, the skeleton curves were obtained from the load-displacement hysteresis curves, and the ultimate and yielding strengths were increased as the spacing of studs decrease. In addition, the strength of inclined studs is shown to be bigger compared to that of conventional studs. The damping ratios increased as the decrease of stiffness ratio. Finally, with decreasing the spacing distance of studs, the cumulative dissipated energy was increased and the seismic performance was improved.

Experimental Research on Seismic Performance of Pre-Damaged RC Frame T-Beam Strengthened with Sprayed BFRP

This experimental program was designed for investigating the seismic performance and reinforcement effect of pre-damaged RC frame T-beams reinforced with sprayed basalt fiber reinforced polymer (BFRP). Four RC frame T-shape beams specimens, among which one was unstrengthened , one was undamaged and strengthened , and the other two were pre-damaged and strengthened, were tested under an incremental loading procedure of the pseudo-static, cyclic shear loads. The test results including the failure mode, ultimate bearing capacity, load-displacement hysteresis curves and ductility of specimens were obtained and analyzed. It indicates that spraying BFRP reinforcement can effectively increase the peak load and energy dissipation performance of damaged RC frame T-beams, ultimate lateral deformation and ductility of damaged RC frame T-beams can be improved obviously. Increasing the reinforcement thickness of sprayed BFRP can effectively improve the seismic reinforcement effect of T-shaped beams damaged by the earthquake.

Experimental Research on Seismic Behavior of Seismically Damaged RC Frame Column Strengthened with Sprayed Hybrid BF/CFRP

This experimental program was designed for investigating the seismic behaviors and strengthening effect of pre-damaged RC frame columns retrofitted with sprayed BFRP and hybrid BF/CFRP. Four RC frame column specimens, among which one was unstrengthened and three was pre-damaged and strengthened with sprayed FRP, were tested under an incremental loading procedure of the pseudo-static, cyclic shear loads combined with constant gravity loads. The test results including the failure mode, ultimate bearing load capacity, load-displacement hysteresis curves and ductility of specimens were obtained and analyzed. It indicates that spraying hybrid BF/CFRP strengthening scheme can effectively improve the ductility and energy dissipation ability of pre-damaged concrete frame columns. Although the improvement of the peak loads and ultimate lateral deformation of damaged frame columns were not obvious compared with those of the reference column, but it should be pointed out that the strengthened columns were pre-damaged seriously with yielded steel bars and the recover of load bearing ability resulted from spraying FRP retrofit can not be neglected. It also shows that increasing the thickness of spraying overcoat can effectively improve the energy dissipation ability of damaged frame columns.

Effect of Axial Compression Ratio and Concrete Strength on Seismic Performance of Concrete Filled Steel Tube Beam-Column Joints

Based on finite element analysis o f concrete filled steel tube beam-column joints under the single axial compression ratio and concrete strength, further research was done to analyze the seismic performance of concrete filled steel tube beam-column joints under different axial compression ratio and concrete strength. Beam-column joint which is connected by bolts with welding extended steel sheets at the beam root was analyzed. The results show that with the increase of axial compression ratio, strength and stiffness degradation of the joint accelerated gradually. Axial compression ratio at 0.3, 0.4 are appropriate values for joints specimen, load-displacement hysteresis curve of joint specimens is relatively plump and shows good seismic performance. Chance of concrete strength also had effect on seismic performance of joint specimen, but in contrast it is not so obviously.

Finite Element Analysis on Seismic Performance of Beam-Column Joint of Concrete Filled Steel Tube Structure

Rational finite element models established by ABAQUS to analysis the mechanical properties of square steel tubular beam-column joints under low cyclic loading. The two beam-column joints are connected with bolts, one is with welding extended steel sheets at the beam root and the other has no welding extended steel sheets. The calculation and analysis results show that the new joint style using concrete filled steel tube structure both in beams and columns has advantage on the seismic performance. The load-displacement hysteresis curve of the beam end is plump without significant pinching and the joint specimens showed good ductility. The comparative analysis reveals that the joint with welding extended steel sheets at the beam root is more superior in the seismic performance respected to the joint without welding extended steel sheets.

Experimental Study of Seismic Performance on Three-Story Prestressed Fabricated Concrete Frame

Based on the low reversed cyclic loading experiment of a specimen of three-story prestressed fabricated concrete frame, this paper investigates the carrying capacity, the failure mode, the load-displacement hysteresis curve of frame. The research includes the seismic performances such as failure mechanism, rigidity degradation, hysteretic behavior and etc. The results indicate that the plastic hinge first appears at the ends of beam at lower story. The connections of frame are in a state of bi-direction compression and have more joint stiffness, which therefore enhances the frame lateral stiffness and improves the deformation recovery capability. The carrying capacity of the frame hasn’t serious degradation at story drifts between 1/39 and 1/64. The post-tensioned prestressed fabricated concrete frame is a “strong column weak beam” structure.

축하중과 반복 횡하중을 받는 콘크리트 충진 원형 탄소섬유 튜브 기둥의 휨거동특성

The purpose of this study is to investigate the flexural behavior of circular concrete filled carbon tube(CFCT) columns subjected to constant axial load with the cyclic lateral load. Six numbers of composite columns were tested. Two parameters, winding angle and thickness of tube, were chosen to evaluate the flexural capacity and behavior of CFCT columns. Selected two parameters were considered simultaneously in order to evaluate the flexural behavior of CFCT columns more precisely. Flexural strength, deformation capacity, ductility and energy dissipation capacity of CFCT columns were evaluated by calculating the area of load-displacement envelop curves and load-displacement hysteresis curves obtained from experiment. Also, the ductile capacity obtained from experiment were compared to that of reinforced masonry wall for the comparison of existing structural element.