Pseudo-static Test Research Articles

Mechanical Properties of New Dry-Type Beam-Column Bolt Connection Joint

Beam–column assembled joint connections are crucial for realizing the industrialization of buildings through prefabrication. This paper focuses on the mechanical properties of a new dry-type high-strength bolt connection joint used in prefabricated buildings. The structural performance properties examined include bearing capacity, stiffness, failure mode, energy dissipation capacity, and deformation performance, all of which are tested through a pseudo static test involving low-cycle repeated loading. The test results show that the failure of the new dry-type beam–column connection joint is through plastic failure, with full hysteretic curve and good energy dissipation performance. The results provide a foundation for the analysis of assembled structural framework systems based on different forms of dry-type connection joints.

Experimental Investigation of the Seismic Performance of a Novel Bolt-Assembled Precast Panel Building Structure

In this study, the authors investigated the behavior of the proposed bolt-assembled precast panel building (BPPB) system under the simulated seismic loading through a large experimental campaign. A pseudo-static test was carried out on a two-story half-scale building specimen constructed by many individual precast components which were properly joined together with bolted connections. The results show that the building specimen had the good seismic performance with high bearing capacity, comparable energy dissipation capacity and perfect structural integrity. The crack pattern and failure mode of the building specimen are different from those of traditional cast-in-situ concrete structures and equivalent cast-in-situ precast concrete structures. The final damage was concentrated in the bolted joint zones, a shear failure occurred in the edge of concrete panel near the bolt holes. It results in that the traditional design approaches of concrete shear wall cannot be applied to this new system. Therefore, the design philosophy and design formulas were proposed for the bolt-connected precast concrete panels to ensure the ductility of the panels and further improving the seismic performance of the BPPB system. The design theory of the bolt-connected precast concrete panels was validated by the successful prediction of the building specimen’s flexural capacity.

RESEARCH ON THE SEISMIC BEHAVIOR OF FRAME STRUCTURES WITH T-SHAPED STEEL REINFORCED CONCRETE COLUMNS AND STEEL BEAMS

To study the seismic behavior of frames with T-shaped steel reinforced concrete columns and steel beams, a pseudo-static test of a 1/3 scaled, 3-story 2-bay specimen was carried out. The main results such as the failure pattern, hysteretic and skeleton curves were obtained. The ductility, energy dissipation capacity and degradation of stiffness and strength of the specimen were analyzed. Numerical simulations were conducted with the fiber model to study the effects of different design parameters such as the axial compression ratio, steel ratio and concrete strength on the seismic performance of the frame. It was demonstrated that the specimen exhibited a beam-hinge failure mode under the condition of horizontal cyclic loading. The specimen had good ductility and energy dissipation capacity and it met the seismic design requirements of strong column-weak beam, strong shear-weak bending and strong joint-weak pole. The axial compression ratio has great influence on the performance of the specimen after yielding. With the increase of the axial compression ratio, the strength and ductility of the structure will decrease. It is necessary to control the axial compression ratio in a reasonable range in the design. The steel ratio mainly affects the initial stiffness and ultimate strength, while its increase can effectively improve the seismic performance of the frame. The increase of concrete strength can increase the ultimate strength of the structure, but reduce the ductility slightly. It is of great significance to consider concrete strength comprehensively in the design. The research results can provide reliable support for the design of this kind of structures.

Experimental Study on Seismic Performance of Prefabricated Joints of Underground Utility Tunnel

In order to study the seismic performance of underground utility tunnel prefabricated joints anchored by button-head reinforcement, pseudo-static tests were carried out on two full-scale underground utility tunnel prefabricated joint specimens. The failure mode, bearing capacity, energy dissipation, and other seismic performance of the joints were analyzed. The results show that the bearing capacity, energy dissipation and other seismic performance parameter of these specimens can meet the seismic design requirements. However, the damage in the core area of the joint is severe under the pseudo-static loading. Therefore, when the button-head reinforcement is applied to practical engineering, necessary reinforcement measures should be taken to ensure that the joint has good seismic performance.

Research on pseudo-static cyclic tests of precast concrete shear walls with vertical rebar lapping in grout-filled constrained hole

In this paper, the seismic behaviors of four precast shear wall specimens and one cast-in-place shear wall specimen are investigated by pseudo-static test method. For the precast shear wall specimens, a new type of assembled rebar lap splices with prepared grout-filled holes and constraining spiral hoops were applied. Different vertical rebar lap splice positions and different rebar lap lengths at the horizontal assembly joints of the precast specimens were designed and fabricated in order to compare their seismic behaviors with the cast-in-place specimen. The geometric size and rebars of four precast specimens are totally same as those of the cast-in-place specimen. By analysis of test results including the load-lateral drift hysteresis curves, crack propagation and rebar strains, the failure modes, bearing capacity, hysteretic characteristics, ductility, rigidity degeneration and energy dissipation of all specimens were obtained and compared. The test results show that the precast concrete shear walls with horizontal assembly joints by this kind of rebar connection have good seismic behaviors and could be equivalent to the cast-in-place shear walls on the conditions of specified construction details.

Contrast Experimental Analysis of Seismic Performance of Steel Beam Node and Rectangular Steel Tube Recycled Concrete Beam Node

The context makes pseudo-static test of two square steel tube recycled concrete column - steel beam nodes and two square steel tube recycled concrete column-rectangular steel tube recycled concrete beam nodes, taking axial compression ratio and beam column linear stiffness ratio as experimental parameter, and studies the characteristics and mechanisms of destruction, hysteresis curves, ductility and stiffness degradation and other seismic performance. The results showed that, compared with the steel beam joint, hysteresis curve of rectangular steel tube recycled concrete beam nodes are fuller, its energy dissipation capacity is relatively strong, its displacement ductility factor can reach 4.32, but the beam joint only can reach 3.51, so its ductility and deformation capacity are pretty good, the degree of stiffness degradation is smaller. As we can know, the seismic performance of rectangular steel tube girder recycled concrete beam node is better than that of steel beam node, it is worthy of further promotion applications.

Snap back testing of unbonded post-tensioned concrete wall systems

Unbonded Post-Tensioned (UPT) precast concrete systems have been shown to provide excellent seismic resistance. In order to improve understanding of the dynamic response of UPT systems, a series of snap back tests on four UPT systems was undertaken consisting of one Single Rocking Wall (SRW) and three Precast Wall with End Columns (PreWEC) systems. The snap back tests provided both a static pushover and a nonlinear free vibration response of a system. As expected the SRW exhibited an approximate bi-linear inertia force-drift response during the free vibration decay and the PreWEC walls showed an inertia force-drift response with increased strength and energy dissipation due to the addition of steel O-connectors. All walls exhibited negligible residual drifts regardless of the number of O-connectors or the post-tensioning force. When PreWEC systems of the same strength were compared the inclusion of further energy dissipating O-connectors was found to decrease the measured peak wall acceleration. Both the local and global wall parameters measured at pseudo-static and dynamic loading rates showed similar behaviour, which demonstrates that the dynamic behaviour of UPT walls is well represented by pseudo-static tests. The SRW was found to have Equivalent Viscous Damping (EVD) between 0.9-3.8% and the three PreWEC walls were found to have maximum EVD of between 14.7-25.8%.

Experimental and numerical investigations on mechanical behaviour of spatial beam to side column connection with T-stub

The prediction of the behaviour of spatial beam to column joints relies on experimental and numerical tests that provide accurate information for the mechanical characterization of the joints. This study focused on the seismic behaviour of semi-rigid beam to side column space joints which connected with T-stubs. Beam to side column joints in the steel frame structures were considered as research objects to perform a spatial pseudo-static test on two joint models of a spatial subdivision, with end column as the load mode. The models of spatial beam to side column connection with T-stub implemented in the ABAQUS which takes into account the non-linear geometrical and material behaviour, non-linear contact and slip. Based on the experimental and numerical results, analyses were conducted on the deformation characteristics, plasticity status and failure modes of the joints, as well as the strengths, rotational stiffness, hysteretic characteristics, ductility coefficients, and energy dissipation properties of different joints. The results indicate that under the action of a spatial load, the relevant mechanical properties of the spatial semi-rigid joints were affected to varying degrees.

Seismic damage mitigation of bridges with self-adaptive SMA-cable-based bearings

Residual drifts after an earthquake can incur huge repair costs and might need to replace the infrastructure because of its non-reparability. Proper functioning of bridges is also essential in the aftermath of an earthquake. In order to mitigate pounding and unseating damage of bridges subjected to earthquakes, a self-adaptive Ni-Ti shape memory alloy (SMA)-cable-based frictional sliding bearing (SMAFSB) is proposed considering self-adaptive centering, high energy dissipation, better fatigue, and corrosion resistance from SMA-cable component. The developed novel bearing is associated with the properties of modularity, replaceability, and earthquake isolation capacity, which could reduce the repair time and increase the resilience of highway bridges. To evaluate the super-elasticity of the SMA-cable, pseudo-static tests and numerical simulation on the SMA-cable specimens with a diameter of 7 mm are conducted and one dimensional (1D) constitutive hysteretic model of the SMAFSB is developed considering the effects of gap, self-centering, and high energy dissipation. Two types of the SMAFSB (i.e., movable and fixed SMAFSBs) are applied to a two-span continuous reinforced concrete (RC) bridge. The seismic vulnerabilities of the RC bridge, utilizing movable SMAFSB with the constant gap size of 60 mm and the fixed SMAFSBs with different gap sizes (e.g., 0, 30, and 60 mm), are assessed at component and system levels, respectively. It can be observed that the fixed SMAFSB with a gap of 30 mm gained the most retrofitting effect among the three cases.

Experimental Study on the Seismic Behaviour of Reinforced Concrete Bridge Piers Strengthened by BFRP Sheets

With the continuous development of the ductility capacity concept for seismic design of bridges, the ductility capacity of many existing bridges does not meet the requirements of the current code for seismic performance because of the low reinforcement ratio and reinforcement corrosion of reinforced concrete (RC) piers. Because of their superior mechanical properties and low price, basalt fibre‐reinforced polymer (BFRP) sheets have potential application in the seismic retrofits field of existing bridges. To study the seismic strengthening effect of RC pier columns, scaled specimens with standard reinforcement ratios, with low reinforcement ratios according to the past code and with corroded reinforcements, were designed and manufactured and then wrapped and pasted with BFRP sheets on the plastic hinge areas. Pseudostatic tests were conducted to verify the seismic performance of the strengthened and unstrengthened specimens. Experimental results showed that the ultimate flexural capacity, deformation capacity, and energy dissipation capacity of strengthened RC pier columns were superior. Especially for strengthened specimens with low reinforcement ratios or corrosion reinforcement, their seismic performance could rival than that of columns with standard reinforcement ratios, which showed the advantage of BFRP sheets in the seismic retrofitting of existing bridge piers.

Experiment study on hysteretic behaviour of arch truss

The research carries pseudo-static test on 6m-span spatial arch truss specimen with three centers under vertical circle loading, and analysis on their failure process. The hysteretic loops, skeleton curves and stiffness deterioration is obtained. The experimental results showed that the failure of arch truss specimens starts buckling and cracking of lower chord, then the members gradually formed local cracking in this region, and finally the midspan with the greatest force cracking leads for the truss to form geometrical mechanism and collapse; When the structure fails, many members enter the plastic stage. The overall plastic deformation is large and the energy consumption performance is good.

Experimental investigation on seismic behaviour of self-heat-preserving shale masonry walls

Perforated blocks made of shale as the matrix material were designed and constructed with holes drilled in a dense rectangular arrangement as a way of improving thermal insulation while retaining seismic performance. Compressive tests of single blocks and masonry prisms were conducted to determine their strength rating. Pseudo-static tests on masonry walls with and without openings were then conducted to evaluate seismic behaviour. It was found that the dense hole arrangement and the thin brittle walls improved thermal insulating properties but decreased ductility. To improve the seismic performance of the shale masonry walls, horizontally reinforced binding bands at 1/3 and 2/3 heights of the masonry walls and structural columns were applied and these indeed enhanced both the ultimate bearing strength and ductility. The experimental results indicate that this type of perforated block could be used for the construction of houses in earthquake-prone zones.

Plastic hinge analysis of long-span rigid frame bridge

The formation and development of plastic hinge have a great influence on the seismic response of long-span rigid frame bridges. Therefore, it’s especially important to study the development process of plastic hinges under ground motion. Based on the OpenSees software, the elastic-plastic finite element model of long-span rigid frame bridge is established, the influence of pier design parameters on plastic hinge is studied from the perspective of IDA analysis. Meanwhile, the advantages and disadvantages of lumped plastic hinge and distributed plastic hinge are discussed in two groups of bending failure pier of “Pseudo-static test on bridge pier of chengdu-lanzhou railway”. The results show that the accuracy of distributed plastic hinge element simulation is higher than lumped plastic hinge; and with the increase of pier height and longitudinal reinforcement ratio, the PGA with plastic hinge in the section will increase for the first time.

Experimental research on resilient performances of Fe-based SMA-reinforced concrete shear walls

Earthquake-resilient structural system is a new kind of seismic vibration control structure, which has the characteristics of rapid recovery or with only a small amount of repair after earthquake. Using superelasticity of shape memory alloys (SMAs) can effectively increase the resilient performance of reinforced concrete (RC) shear wall structures, which have a wide application prospect in the seismic field of civil engineering. A pseudo static test of six Fe-based SMA-reinforced concrete shear walls is performed in the paper, aiming at investigating the influences of different SMA reinforcement ratio and steel stirrup ratio on their resilient performances and seismic capacities. By using the concept of the resilience-force-ratio at balance positions of the shear walls, resilient performances (e. g., deformation recoverability) of shear walls can be well represented. The experimental numerical results show that the resilient performances of SMA-RC shear walls can increase 21.7% compared with the ordinary steel reinforced ones, and the resilient performances of SMA-RC shear walls can be effectively improved by placing SMA reinforcements with an appropriate ratio. The steel stirrup ratio and SMA reinforcement ratio in the edge member have a great influence on the resilient performances of the shear wall structures.

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.

Study on the performance of lead rubber bearing considering vertical force correlation

To study the vertical force correlation of the lead rubber bearing, the pseudo static test of the bearing has been carried out, and the test shows that when the vertical force is small, the pre-yield stiffness and the yield shearing force of the bearing are increased with the increase of vertical force, while the post-yield stiffness is decreased with the increase of vertical force. When the vertical force is increased to a certain extent, the bearing parameters may be stable. The bearing parameter has been identified by the least square method, and then, the quantitative relation between the bearing parameter and the vertical force could be obtained. The calculation model and the motion equation of the isolation structure under the multi-dimensional earthquake excitation have been established, and the parameter iteration of bearing obtained from the test has been used for solving the motion equation, from which the seismic response of an isolation structure has been made available when the vertical force of the bearing is considered. The calculation of engineering examples shows that the displacement of the isolation layer will increase after the consideration of the vertical force correlation of the bearing, and the displacement of the upper structure will have a larger overall shifting.

End web stiffeners for connecting ductile replaceable links

The ability to restore the integrity of structural lateral systems that utilize steel links to inelastically deform in earthquakes can be improved through the use of replaceable links. Replaceable links can be removed when damaged, especially when isolated from the gravity carrying system, and can provide engineers greater design freedom with respect to structural stiffness and strength. To ensure that ductile inelastic deformation is isolated to the effective length of the replaceable link, robust connection details capable of sustaining large cyclic deformations are needed. An integrated numerical and experimental research program was performed to evaluate a bolted end plate connection detail which utilized fillet welds, instead of full joint penetration welds, between the links and end plates in an effort to simplify fabrication. Continuum finite-element methods were used to evaluate various end stiffener options to shift flange plastic strains caused by link deformation away from the welds. The results from that study informed the selection of cases evaluated in large-scale experiments. Cyclic pseudostatic tests were conducted to experimentally demonstrate the performance of the selected end-stiffener configurations. Results from the experimental investigation showed that ductile inelastic deformation within the effective length of the links can be achieved using a bolted end plate connection with fillet welds between the shear link and end plate by utilizing end stiffeners placed parallel to the web. Design recommendations for incorporating the end stiffeners are outlined based on the data and experiences gained.

Shear behavior of precast concrete wall structure based on two-way hollow-core precast panels

In this study, a new precast concrete shear wall system based on two-way hollow-core precast panels (TWHCPP) is proposed. Considering that the ductility of a shear wall is strongly related to its shear behavior, the shear behavior of the newly proposed system was investigated. First, pseudo-static tests were performed for one cast-in-place shear wall specimen and three TWHCPP shear wall specimens. Test results indicate that the cast-in-place shear wall specimen experienced diagonal tension failure and its axial load carrying capacity decreased abruptly when the peak strength was attained. In contrast, the TWHCPP shear wall can effectively avoid such brittle failure and can sustain the vertical and lateral loads at the limit state. Second, a numerical simulation method for the TWHCPP shear wall was proposed and applied to the three TWHCPP shear wall specimens. The predicted strengths and failure mechanisms show good agreement with the experimental results. Finally, a shear strength estimation method was proposed for the TWHCPP shear wall system. Compared to the experimental results, the method yields conservative estimations; thus, it can be a suitable approach to the TWHCPP shear wall design.

Seismic behavior of confined masonry walls subjected to freeze-thaw cycles

This paper presented a systemic research evaluating the seismic behavior of confined masonry walls subjected to different freeze-thaw cycles (FTC). The seismic behavior of frost-damaged confined masonry walls was related to the mechanical properties of the frost-damaged masonry material. Thus, the mechanical properties of the frost-damaged masonry material were investigated firstly. Then, pseudo-static tests were conducted with four levels of frost-damage on confined masonry wall specimens. The visual damage, failure patterns, hysteresis behavior, bearing and deformation capacity, strength degradation, lateral stiffness degeneration and energy dissipation capacity were analyzed. Results showed that with an increasing number of FTC, the compressive strength, elastic modulus and Poisson’s ratio of the masonry material decreased whereas the strain at peak stress increased. Moreover, with an increasing number of FTC, the peak load, strength attenuation coefficient, lateral stiffness and energy dissipation of the specimens gradually decreased whereas the cracking displacement and ultimate displacement gradually increased. After 120 FTC, the peak load were lower by 38.9%, the ultimate displacement increased by 12.4% and the cumulative energy dissipation of the wall specimens decreased by 72.6%. Finally, the formula for shear bearing capacity for confined masonry walls under FTC was derived based on the results of mechanical property and pseudo-static tests.

Experimental investigation on the lateral structural performance of a traditional Chinese pre-Ming dynasty timber structure based on half-scale pseudo-static tests

Existing ancient Chinese timber buildings are frequently subjected to seismic or strong wind loads throughout their lifetime, hence their lateral structural performance can undergo significant changes. It is essential to employ tests in the laboratory to study these variations to protect these existing timber buildings. In this paper, a single-layer model of a timber building with a geometrical ratio of 1:2 was fabricated according to the pre-Ming dynasty construction method. Six pseudo-static tests were conducted under three levels of vertical loads. The timber structure displayed visible rocking characteristics during the tests, and the column feet and mortise-tenon joints were the weak links in the structure. The features of hysteresis curves, envelope curves, strength reduction, energy dissipation, and lateral stiffness of the timber structure were obtained, and their variations associated with loading courses were discussed. Moreover, a simplified restoring force model was built for this type of timber structure.