Low-cyclic Reversed Loading Tests Research Articles

Low-Cyclic Reversed Loading Tests on Full-Scale Precast Concrete Composite Wall Connected by Tooth Groove and Grouted Sleeve.

In this paper, a novel precast concrete composite wall connected by tooth groove and grouted sleeve was introduced, which is produced in factories by means of structure-insulation integrated prefabrication, and the prefabrication and assembly process were presented minutely. To verify the feasibility and reliability of this novel tooth groove and grouted sleeve connection method and explore the joint connection performance and the seismic performance of the precast concrete composite wall connected by tooth groove and grouted sleeve, low-cyclic reversed loading tests with an axial compressive ratio of 0.1 were performed on two full-scale precast concrete composite walls. Moreover, the failure mode, hysteretic curve, skeleton curve, stiffness degradation, displacement ductility, energy dissipation capacity, and reinforcement strain were comprehensively discussed. The research results showed that under the vertical axial load and low-cyclic reversed load, the distributed reinforcements in the wall panel only played a structural role, while the connecting reinforcements at horizontal joints can always effectively transfer stress without bond failure, and the tooth groove and grouted sleeve connection performance was reliable. In addition, the hysteretic curves of the precast concrete composite wall connected by tooth groove and grouted sleeve were full, showing good ductile deformation capacity and energy dissipation capacity. In general, the precast concrete composite wall connected by tooth groove and grouted sleeve not only possessed favorable seismic performance but also showed obvious advantages such as green energy saving, high assembly rate, and less on-site wet operation, which can be applied to practical engineering under reasonable design.

Quasi-static cyclic test on seismic performance of steel reinforced concrete frame with replaceable energy-dissipating member

In view of damage controlling and earthquake-resilient performance, the steel reinforced concrete (SRC) frame with replaceable energy-dissipating member (REDM) is proposed. The REDM is consisted of high damping concrete (HDC) wall panel and several fuses made by low yielding-point (LYP) steel. At first, low-cyclic reversed loading test on fuse is carried out to explore its shear capacity and hysteretic behavior. The suitable dimension and shape of fuse is determined for further study. Then the quasi-static cyclic test considering two loading patterns is applied on two SRC-REDMs. One specimen is loaded until overall failure while another is repaired by installing a new set of REDM during the loading history. The analyses and comparisons are conducted in terms of failure mode, yielding pattern, hysteretic characteristics, stress distribution, stiffness degradation, dynamic characteristics, ductility and energy dissipation. The failure mode is summarized as bending-shear failure of the wall panel, local buckling of fuses and beam hinge failure mechanism of SRC frame. The hysteretic loops are plump while large energy dissipation capacity is represented. The seismic performance is verified by high bearing capacity and ductility. The bearing capacity and stiffness of repaired specimen is significantly rehabilitated. The new REDM has dissipated much more hysteresis energy than that of non-repairing case. The earthquake-resilient behavior is confirmed by the significant recovery in mechanical properties.

Quasi-static experimental study on precast concrete columns reinforced with bundled rebars

Bundled reinforcement is an alternative approach to improve the installation efficiency and structural integrity of precast concrete structures. With higher strength and lighter weight compared with steel bars, basalt fiber reinforced polymer (BFRP) bar is an attractive candidate material for concrete structures. Low-cyclic reversed loading tests on four precast concrete columns reinforced with different arrangements of longitudinal bars were conducted in this paper. The test specimens included singly arranged steel bars (S12-1P, S20-1P), three-bar bundled steel bars (S12-3P), and three-bar bundled hybrid BFRP bars/steel bars (S10/B13-3P). The test results showed that using bundled reinforcement in precast concrete columns could delay the yielding of longitudinal steel bars. Specimens S12-3P and S20-1P not only maintained the inherent bearing capacity and stiffness, but also demonstrated improved deformability of 18.1% and 6.9%, respectively, compared to the conventional precast column S12-1P. S10/B13-3P showed a 5.5% increase in peak load and a 9.1% increase in displacement ductility, which is expected to result in better seismic performance compared to that of the conventional columns. The corresponding repairable limits (based on the drift ratios) for S12-1P, S20-1P, and S10/B13-3P were 2.6%, 2.9% and 4.5%, respectively. In addition, the use of bundled bars could result in a wider curvature concentrated distribution zone, thereby increasing the plastic hinge length and providing a larger deformation capacity with the same peak curvature.

Seismic performance of reinforced concrete beam‐column joint made of post‐filling coarse aggregate concrete

AbstractPost‐filling coarse aggregate concrete is a new type of green concrete that not only saves the cost of cementitious material, improves the strength, cracking resistance and durability of concrete, but also reduces the carbon footprint. In view of the lack of research on the seismic performance of post‐filling coarse aggregate concrete, this study designs eight interior beam‐column joint specimens made of post‐filling coarse aggregate concrete and three beam‐column joint specimens made of conventional concrete. It studies the influence of post‐filling coarse aggregate ratio, axial compression ratio and stirrup volume ratio of node area on the seismic performance of joint specimens. Through low cyclic reversed loading test, the failure process and the failure pattern, hysteresis curves, skeleton curves, ductility, stiffness degeneration, residual strength and residual displacement, and plastic hinge rotation of interior joints with post‐filling coarse aggregate concrete are analyzed. Test results show that the failure mode of post‐filling coarse aggregate concrete joints is similar to that of the conventional concrete joints. As the axial compression ratio increases, the seismic performance of the joints shows a trend of increasing first and then decreasing, and it reaches the peak when the axial compression ratio is 0.2. It also demonstrates that the seismic performance of the joints is increased by increasing the stirrup volume ratio of node area. Ultimately, under the same axial compression ratio, the seismic performance of the post‐filling coarse aggregate concrete is not significantly different from that of the conventional concrete. It proves that the reinforced beam‐column joint made of post‐filling coarse aggregate concrete could fulfill the comparable seismic performance as that of conventional concrete.

Experimental Study on Seismic Behavior of Precast Bolt-Connected Steel-Members End-Embedded Concrete (PBSEC) Beam-Column Connections

With the rapid development and research of precast concrete frame structures, it is not difficult to find that the structural form and seismic performance of dry-connected precast joints have always been the focus of research. Since this type of structural system is complex, the construction is inconvenient in practical application, and many additional parts need to be installed, this paper develops a kind of precast bolt-connected steel-members end-embedded concrete (PBSEC) beam-column connection to solve the shortcomings of the current dry-connected precast joints. There is no wet work in the assembly process, and all-dry construction and assembly methods are used. There is no need to pour concrete and support formwork, which significantly improves construction efficiency compared to wet and cast-in-situ connections. Low cyclic reversed loading tests were conducted to obtain test data, such as failure mode, hysteresis curve, skeleton curve, stiffness, ductility, and deformation capacity of the precast concrete joint. The failure mode of the PBSEC joints is the buckling failure of the connecting steel plate, leading to a perfect seismic capacity and collapse resistance of the structure. The hysteresis curves of the PBSEC joints are bow-shaped and full in shape, showing high energy dissipation capacity. The bearing capacity of the joints begins to rise rapidly at the initial loading stage and then decreases slowly after reaching the peak, which is an ideal shape. By summarizing the average peak load, strength degradation coefficient, loop energy per cycle, loop energy per level, and cumulative energy damping coefficient, it is found that the joint using 10 mm thick Q235 steel can obtain the most suitable failure mode and obtain the best energy dissipation performance. When the strength of the steel plate material increases, the energy dissipation performance of the joint drops.

Seismic performance of precast concrete column with different longitudinal reinforcement diameters under different lateral loading directions

To improve the installation efficiency of precast concrete (PC) columns with grouted sleeve connections, increasing the diameter of longitudinal rebar but keeping similar reinforcement ratio is a solution. To quantify the effects of longitudinal reinforcement diameter on the seismic performance of PC columns, eight full-scale reinforced concrete columns (six PC columns and two cast-in-situ) with identical concrete strength, reinforcement ratio, and stirrup ratio were designed and fabricated. The longitudinal reinforcement diameters varied from 18 mm to 32 mm. Moreover, considering majority of existing tests on PC column were subjected to relatively low axial compression ratio due to limitation of test facilities. Low-cyclic reversed loading tests were conducted with a high axial compression ratio of 0.6. Furthermore, to evaluate the bilateral loading effects, the loading direction was either horizontal or diagonal. Test results showed that the PC column achieved even higher lateral load capacity than corresponding cast-in-situ column regardless of the loading directions. Moreover, the lateral load capacity of the column under diagonal loading is generally lower than that under horizontal loading. However, the ductility and energy dissipation capacity of the columns under diagonal loading were higher than those under horizontal loading. Increasing the diameter of the longitudinal reinforcement will increase the lateral load capacity of the PC columns. This is because increasing the diameter of the longitudinal reinforcement required larger size of grouted sleeve, which further shortened the effective length of the column due to plastic hinge shifting. However, increasing the diameter of the longitudinal reinforcement may require greater bond strength between rebar and concrete and aggravate the bond failure pre-mature, which resulted in the less of deformation capacity and ductility, as well as energy dissipation capacity.

Experimental Study of Emulative Precast Concrete Beam-to-Column Connections Locally Reinforced by U-Shaped UHPC Shells.

Precast beam–column connections act as vital elements of precast concrete frames. To enhance the resistance to the earthquake-induced damage and environment-induced deterioration of precast beam–column connections, an innovative precast concrete beam-to-column connection locally enhanced by prefabricated ultra-high-performance concrete (UHPC) shells was proposed. For studying the seismic behaviors of these novel connections and the influence caused by the prefabricated UHPC shell length, full-scale precast specimens were experimentally investigated using low-cyclic reversed loading tests. The obtained results were analyzed and discussed, including hysteresis curves, skeleton curves, strength and deformability, performance degradation, energy dissipation capacities, and plastic hinge length. The results reveal that the novel precast concrete beam–column connections with UHPC shells behaved satisfactorily under seismic loadings. The damage in the concrete near the lower part of the beam end is reduced by the prefabricated UHPC shells. The longer prefabricated UHPC shells were more useful for decreasing the damage to the precast concrete components and improved the structural performance. The precast specimen with 600-mm long UHPC shells can achieve a ductility of 4.87 and 4.0% higher strength than the monolithic reference specimen.

Study on the low cyclic loading test of a new reinforced tenon precast shear wall under different axial compression ratios

Precast shear wall is an important structural form of building industrialization and housing industrialization. In order to improve the seismic performance of precast shear wall, the reinforced tenon is presented to improve the shear performance of precast shear wall joints. In order to grasp the further difference of mechanical properties of reinforced tenon precast shear wall under different axial compression ratios, the low cyclic reversed loading tests were carried out on a cast-in-situ shear wall specimen and two reinforced tenon precast shear wall specimens with different axial compression ratios respectively. According to the test results, the hysteresis characteristics, bearing capacity, steel strain, energy dissipation capacity, rigidity degeneration and other seismic performance parameters of the three specimens were analyzed. The test results show that the failure modes of the three specimens were same, which was compression-bending failure. Connection form of reinforced tenon has good shear resistance. The reinforced tenon precast shear wall with the larger axial compression ratio has the worse ductility, the higher bearing capacity and stronger the rigidity.

Seismic Performance of Steel Reinforced Concrete Column-Steel Beam Joints after Exposure to Fire

Low cyclic reversed loading tests of six steel reinforced concrete column–steel beam joints were conducted to study the failure mode, hysteretic character, and shear mechanism of joints that had been exposed to fire. Two test parameters, i.e. the duration of fire exposure and axial compressive ratio were taken into consideration. Test results showed that the failure mode of the joints after exposure to fire was basically the same as that of joints maintained at room temperature. Due to the shear resistance of the steel reinforcement, the maximum loading strength of the joints after fire exposure declined indistinctively, however displacement corresponding to the maximum loading strength increased notably. The rigidity, ductility and energy dissipation of the joints after exposure to fire decreased compared to the joints maintained at room temperature, and the extent of reduction was related to heating time and axial compressive ratio.

Experiment on Seismic Behavior of Neotype Column-slab High Piers

The low-cyclic reversed loading test was carried out for a scale model of a neotype column-slab high pier. The test was designed to investigate its failure modes, hysteretic characteristics, ductility, energy dissipation, residual deformation stiffness degradation. Test results indicate that the neotype column-slab high pier has strong and stable bearing capacity, good ductility and energy dissipation capacity, small residual deformation. The destruction process of the structure components is that bending cracking of the wing slab buttom firstly, shear cracking at the juction of the web plates with the corner columns, then bending cracking at the roots of the corner columns. Cracking and energy dissipation of the slabs decrease the stiffness of the structure, which effectively protects the corner columns. The study contributes to the literature for developing future design guidelines, for the purpose of providing experimental and theoretical background of the neotype column-slab high pier.

Development and test of a self-centering fluidic viscous damper

This research presents a novel self-centering fluidic viscous damper that incorporates preloaded ring springs to offer self-centering capability and a fluidic viscous damper for energy dissipation. A full-scale self-centering fluidic viscous damper was developed and subjected to low-cyclic reversed loading tests. The test results show the self-centering fluidic viscous damper has both displacement-dependent and velocity-dependent hysteric responses with self-centering capability. Fatigue tests further show that the self-centering fluidic viscous damper maintains a stable hysteretic response under reversed loading. An analytical model and a numerical model are developed for the proposed self-centering fluidic viscous damper and analyzed. Comparisons of test results and the numerical and analytical models show similar hysteric responses, thereby validating the accuracy of the numerical and analytical models to simulate the behavior of the proposed damper.

Seismic Performance of Full-Scale Joints Composed by Concrete-Filled Steel Tube Column and Reinforced Concrete Beam with Steel Plate-Stud Connections

A concrete-filled steel tube (CFST) column has the advantages of high bearing capacity, high stiffness, and good ductility, while reinforced concrete (RC) structure systems are familiar to engineers. The combinational usage of CFST and RC components is playing an important role in contemporary projects. However, existing CFST column-RC beam joints are either too complex or have insufficient stiffness at the interface, so their practical engineering application has been limited. In this study, the results of a practical engineering project were used to develop two kinds of CFST column-RC beam joints that are connected by vertical or U-shaped steel plates and studs. The seismic performance of full-scale column-beam joints with a shear span ratio of 4 was examined when they were subjected to a low-cyclic reversed loading test. The results showed a plump load-displacement curve for the CFST column-RC beam joint connected by steel plates and studs, and the connection performance satisfied the building code. The beam showed a bending failure mode similar to that of traditional RC joints. The failure area was mainly concentrated outside the steel plate, and the plastic hinge moved outward from the ends of the beam. When the calculated cross section was set at the ends of the beam, the bending capacity of joints with the vertical or U-shaped steel plates and studs increased compared to the RC joint. However, when the calculated cross section was set to the failure area, the capacity was similar to that of the RC joint. The proposed joints showed increases in the energy dissipation, average energy dissipation coefficient, and ductility coefficient compared to the RC joint.

Lateral performance of traditional Chinese timber frames: Experiments and analytical model

This article presents test results of the lateral behavior of traditional Chinese timber frames (TCTF). Three 1/3.52-scaled single-span TCTF specimens, with different column heights and vertical loads application, were subjected to low-cyclic reversed loading tests. The force-rotation hysteretic and envelop curves of these specimens evidently indicate that both vertical loads and column heights have significant effects on the lateral performance of the TCTF. With the increase of vertical loads, specimens’ stiffness increase at the initial lateral shift stage and then decrease when larger displacement occurs. An analytical model was established based on the theory of beam-columns. Good consistency between analytical predictions and test results are obtained. The analytical model is well qualified for analysis of the two types of timber frames, one is the SHF (frame with semi-rigid mortise-tenon joints and hinged column-foot joints), another is the SSF (frame with semi-rigid mortise-tenon joints and semi-rigid column-foot joints). Parametric studies were carried out on the SHF and SSF using the established analytical model to further reveal the effects of vertical loads and column heights on the lateral resistance of the TCTF.

Seismic Behavior of Precast Concrete Shear Walls with Different Confined Boundary Elements

To ensure the mechanical property of lapped spliced reinforcement and concrete confinement of boundary elements for precast concrete shears, two kinds of constraints, local constraint by additional spiral stirrups placed around each reinforcement splicing and overall constraint by lapped welding closed stirrups replacing traditional stirrups and ties, were proposed in this paper. Low-cyclic reversed loading tests were conducted on three full scale specimens, including one reference cast-in-situ specimen, one precast concrete specimen with local constraint and one precast concrete specimen with overall constraint. By comparing the aspects of strength, stiffness, ductility and energy-dissipation capacity with that of cast-in-situ specimen, it is found that local constraint and overall constraint can be considered equivalent. However, due to the over restraint by local constraint detail, the specimen with local constraint exhibited earlier yielding, poorer energy-dissipation capacity and better ductility than that with overall constraint. Coupled with the consideration of steel usage and construction simplicity, overall constraint detail should be preferred in practical engineering.

Experimental Study on Seismic Performance of Through-Tenon Joints with Looseness in Ancient Timber Structures

ABSTRACTIn order to study the influence of looseness on seismic performance of through-tenon joints, six through-tenon joints specimens in 1:3.2 scale, including one tight-fitted joint and five loose joints, were fabricated according to the Engineering Fabrication Methods of Qing dynasty. The failure modes, mechanical behaviors such as the hysteresis and envelope curves, strength and stiffness degradations, energy dissipation, and deformation of the specimens under low cyclic reversed loading tests were analyzed. Results show that the failure modes of theses joints under positive and negative loadings are bending damage on the big tenon head and tearing damage on the variable cross-section, respectively. The hysteresis curves of joints appear to be anti-Z shape and present typical pinching effect. The greater the degree of looseness is, the more obvious the slippage is. The bending moment, stiffness and energy dissipation of loose joints are lower than those of the tight-fitted joint under the same rotation angle, and the increase in the loose degree cause them to gradually decrease. Meanwhile, the behavior of the through-tenon joints is further simulated by the nonlinear finite element analysis program, and the test results agree well with the numerical analysis results.

Mechanical properties of a new type of block made from shale and coal gangue

A fired heat-insulation hollow block, which has approximate dimensions of 240 mm (L) × 200 mm (W) × 190 mm (H) and a density of 850 kg/m3, is a new type of wall material made from shale and coal gangue. This material would protect cultivated lands and has less negative environmental effects. However, its mechanical properties must be examined to promote its popularisation and application. Hence, in this study, we determined the compression strength of block, mortar and masonry prisms under uniaxial compression, the shear strength of the specimens under biaxial stress state, and the shear resistance of the masonry wall via low-cyclic reversed loading test. The formulas for the compressive strength and the stress-strain curve were also provided. Result of this test process showed that the spalling of the external surface of the block occurred when the specimens lost their bearing capacity.

Cyclical behavior of timber mortise-tenon joints strengthened with shape memory alloy: experiments and moment-rotation model

ABSTRACTThis article presents the results of a study on the cyclical behavior of mortise-tenon joints strengthened with shape memory alloy (SMA) wires. Four 1/3.52 scaled joint specimens reinforced with different number of SMA wires were subjected to low-cyclic reversed loading tests and the moment-rotation hysteretic curves were obtained. The cyclic behavior of joints strengthened with SMA were compared with that of joints strengthened with conventional reinforcement methods, such as cramp, carbon fiber, steel pins, U-shaped hoop, angle steel, curved plate, etc. Results indicated that the strength, stiffness, and energy dissipation capacity of the mortise-tenon joints strengthened with SMA were improved markedly. The residual deformation of the mortise-tenon joints strengthened with SMA is approx. 20% less than that strengthened with the conventional strengthening methods. A nonlinear model composed of one three-parameter power function and one straight line was presented for the moment-rotation of the mortise-tenon joints and good agreement between predictions and tests were observed.

Structural performance of steel-truss-reinforced composite joints under cyclic loading

The steel-truss-reinforced composite beam is a type of steel-reinforced concrete structure, in which the concrete beam is reinforced by steel trusses. Unlike traditional reinforced concrete structures, the steel truss works as the main skeleton and takes the main responsibility for the whole structural strength. In order to fulfil energy dissipation requirements, diagonal angle steel crosses are placed at the end of the steel truss. Specimens are designed based on different key parameters, including axial compression ratio and dimensions of chord, web and angle steels. Low-cyclic reversed loading tests are carried out on eight interior joint specimens to simulate realistic reversed loading conditions under earthquake. Load–deflection hysteresis loops and skeleton curves of joint specimens are obtained. Ductility, hysteresis behaviour and seismic-resistant performance are evaluated. Equivalent viscous-damping coefficients and energy dissipation indicators are calculated. The influences of axial compression ratio and steel ratio on the seismic performances are analysed. It is found that a large steel ratio will generally increase the bearing capacity. However, a relatively high axial compression ratio will benefit the bearing capacity of joints, but has adverse effects on hysteresis behaviours. Further, some conclusions are drawn on the overall seismic performances of this type of joint.

Experimental studies on steel frame structures of traditional-style buildings

This paper experimentally investigated the behavior of steel frame structures of traditional-style buildings subjected to combined constant axial load and reversed lateral cyclic loading conditions. The low cyclic reversed loading test was carried out on a 1/2 model of a traditional-style steel frame. The failure process and failure mode of the structure were observed. The mechanical behaviors of the steel frame, including hysteretic behaviors, order of plastic hinges, load-displacement curve, characteristic loads and corresponding displacements, ductility, energy dissipation capacity, and stiffness degradation were analyzed. Test results showed that the Dou-Gong component (a special construct in traditional-style buildings) in steel frame structures acted as the first seismic line under the action of horizontal loads, the plastic hinges at the beam end developed sufficiently and satisfied the Chinese Seismic Design Principle of columns-weak beams, strong joints-weak members. The pinching phenomenon of hysteretic loops occurred and it changed into Z-shape, indicating shear-slip property. The stiffness degradation of the structure was significant at the early stage of the loading. When failure, the ultimate elastic-plastic interlayer displacement angle was 1/20, which indicated high collapse resistance capacity of the steel frame. Furthermore, the finite element analysis was conducted to simulate the behavior of traditional-style frame structure. Test results agreed well with the results of the finite element analysis.

Experimental Verification of Vertical Joints in an Innovative Prefabricated Structural Wall System

In order to verify the viability of the new-type vertical joints (composed of high-strength bolts, connecting steel frames, embedded limbic steel frames, and steel sleeves) in an innovative prefabricated structural wall (IPSW) system, low-cyclic reversed loading tests (pseudo-static tests) were performed on two H-shaped test specimens fabricating from precast web wall panel and precast flange wall panels joined together through the novel vertical joints. On the basis of the loading procedure and test data, the global behavior (including failure modes, lateral stiffness, ductility, and energy-dissipating capacity) and the local performance (including the stress distribution in the connecting steel frames and the relative slippages between the connection components) of the test specimens were detailedly discussed and presented. The research results demonstrated that the connectors were strong enough for maintaining the web wall panel and flange wall panels work together as an entirety to resist lateral seismic force, no slippages occurred on the contact interfaces between the connecting steel frame and embedded limbic steel frame throughout the loading procedure, and the vertical shear stress at the midpoint of the connecting steel frame (close to zero) was far smaller than that at its lower end (still much less than its yield strength). This experimental research confirms the viability and reliability of the new-type vertical joints, although the configurations of the precast wall panel as well as the vertical joints need indispensable improving to optimize the seismic performance of the entire test specimen.