Quasi-static Cyclic Tests Research Articles

Seismic Performance of a Rocking Precast Concrete Cladding Panel System under Lateral Cyclic Displacement Demands

ABSTRACT This paper experimentally investigates the seismic performance of an innovative ‘rocking’ precast concrete cladding panel system. Quasi-static cyclic loading tests were conducted on a sub-assembly of three ‘rocking’ panel pairs attached to a 3D steel structure, with and without sealant in the vertical joints between adjacent panels. The sub-assembly included a flat panel pair, an L-shaped panel pair and an oblique corner panel pair. Although the loading was applied in a single direction, the alignments of the panel pairs allowed scrutinizing their in-plane, out-of-plane and bi-directional performances. The test results validated the low-damage attributes of the novel cladding system, which was able to accommodate large cyclic drifts with minor physical damage to the panels and their connections with the structures. Up to a cyclic drift of 4.0%, the only forms of damage observed were tearing of the sealants in between the panel pairs, dislocation of backer rods behind some sealants, dislodgement of a grout piece, and loosening of a nut supporting a corner panel. All these forms of damage are minor and repairable, which can be avoided by making some minor changes to the details of the system.

Seismic behavior of Chuan-dou timber frames with different infilled walls

The Chuan-dou timber frame is a structural system that is most suitable for natural factors such as local topography and climatic environment, and used by the people in southwestern China after thousands of years of production and life. In this study, a standard frame of a typical two-story Chuan-dou timber structure in southwestern China was used as a prototype, and three Chuan-dou timber frame models with a scale of 1:2 were designed and produced. The models were one Chuan-dou timber frame without infilled walls (PWF), one Chuan-dou timber frame with infilled wooden panels (WWF), and one Chuan-dou timber frame with infilled brick walls at the bottom and infilled plasterboard at other parts (BWF). Through a quasi-static cyclic test, the force–deformation characteristics, failure modes, stiffness degradation behavior, and energy dissipation capacity were investigated. The results showed that PWF had good deformation property, but its stiffness and ultimate load carrying capacity were low. Compared with PWF, the lateral strength and stiffness of WWF and BWF were effectively improved, but the compatible deformation capability of the brick wall and the frame was poor due to the weak connection between them. In addition, increasing the connection capacity between the column foot and ground to restrict the sliding of the column foot could be a proper way to improve the deformation and energy dissipation capacity of timber frame.

Seismic Performance of Precast Concrete Frame with Innovative Assembly Pattern

ABSTRACT A novel precast concrete (PC) frame with an innovative assembly pattern and optimised connection locations was proposed and evaluated. The PC column components were connected by extrusion sleeves and/or U-type reinforcement ferrules to realise cost-effective, efficient, and reliable assembly. Quasi-static cyclic loading tests and finite element analyses were conducted on a cast-in-place (CIP) frame and three PC frames with different connection types. The PC frames exhibited higher lateral stiffness and load bearing capacities than the CIP frame, as well as similar energy dissipation capacities. The PC frames employing the extrusion sleeve connections in the beam exhibited the best seismic performance.

Fixation of intraoperative proximal femoral fractures during THA using two versus three cerclage wires - a biomechanical study

BackgroundIntraoperative proximal femoral fractures (IPFF) are relevant complications during total hip arthroplasty. Fixation using cerclage wires (CW) represents a minimally-invasive technique to address these fractures through the same surgical approach. The goal of treatment is to mobilise the patient as early as possible, which requires high primary stability. This study aimed to compare different cerclage wire configurations fixing IPFF with regard to biomechanical primary stability.MethodsStandardised IPFF (type II, Modified Mallory Classification) were created in human fresh frozen femora and were fixed either by two or three CW (1.6 mm, stainless steel). All cadaveric specimens (n = 42) were randomised to different groups (quasi-static, dynamic) or subgroups (2 CW, 3 CW) stratified by bone mineral density determined by Dual Energy X-ray Absorptiometry. Using a biomechanical testing setup, quasi-static and dynamic cyclic failure tests were carried out. Cyclic loading started from 200 N to 500 N at 1 Hz with increasing peak load by 250 N every 100 cycles until failure occurred or maximum load (5250 N) reached. The change of fracture gap size was optically captured.ResultsNo significant differences in failure load after quasi-static (p = 0.701) or dynamic cyclic loading (p = 0.132) were found between the experimental groups. In the quasi-static load testing, all constructs resisted 250% of the body weight (BW) of their corresponding body donor. In the dynamic cyclic load testing, all but one construct (treated by 3 CW) resisted 250% BW.ConclusionsBased on this in vitro data, both two and three CW provided sufficient primary stability according to the predefined minimum failure load (250% BW) to resist. The authors recommend the treatment using two CW because it reduces the risk of vascular injury and shortens procedure time.

The Seismic Performance Analysis of Semi-rigid Spatial Steel Frames Based on Moment-Rotation Curves of End-plate Connection

With their efficiency and high ductility for energy consumption, end-plate connection steel frames (EPCSFs) are commonly used in high seismicity areas. With the aim to realise high-efficiency calculation of EPCSFs performance, this study proposes a simple and accurate model in OpenSees software for the end-plate connection (EPC) with a behaviour captured by nonlinear rational springs. Previous EPC test study and design criteria are summarised and provides a reasonable failure mode of the connection. In light of the summary, the moment-rotation curve model of the spatial connection is developed according to the component method. Three 1/4-scale specimens with EPC of the quasi-static cyclic test are carried out to verify the model accuracy and study the failure mode in the EPCSFs. According to the failure criteria, the mechanical characteristics and deformation of the specimen are studied. The bearing capacity, stiffness degradation, and plastic energy dissipation of the test specimen and OpenSees analytical model are also analysed and compared. The failure modes of the test specimens are consistent with the optimal ones of the EPCs, which satisfy the design criteria of ‘strong column, weak beam’. The specimens perform well in the hysteresis characteristics and provide stable lateral stiffness and high ductility, with a mean ductility coefficient of all specimens is approximately μ = 5.086. This model supplies an accurate prediction of EPCSFs performance for significant savings on computational cost, and is thus extraordinarily useful for daily design by seismic performance analysis.

Confined hollow concrete block masonry buildings: An experimental approach for vulnerability assessment

This paper presents experimental study on the response of a sustainable structure 3.65 x3.05x3.35 m, made with confined hollow concrete block masonry (CHCBM). The model was tested under quasi-static cyclic test to assess the response against seismic load and to determine the potential vulnerability. Based on test data, envelope curves and bilinear idealized curves were drawn according to both Magenes–Calvi and Elnashai methods. Different performance levels i.e. Immediate Occupancy (IO), Life Safety (LS) and Collapse Prevention (CP) were evaluated based on both methods. Damage pattern and force-deformation behavior of CHCBM building was compared with models of the similar configuration and loading conditions. Similarly values of Response modification factor (R), Displacement Ductility (µD) and Displacement amplification factor (Cd) were calculated and compared with the previously tested models and it confirmed that CHCBM building was ductile and structurally integrated under earthquake loading.

Cyclic behavior of coupled steel plate shear walls with different beam-to-column connections

In a coupled steel plate shear wall system, the interaction between two steel plate shear wall piers provided by the coupling beams improves the overturning capacity of the structure. Quasi-static cyclic tests were conducted on three 1/3 scaled specimens to investigate the inelastic behavior with several different features. Each specimen had a different coupling beam-to-column connection, namely, a welded moment connection, a bidirectional bolted connection, and a cantilever endplate connection. The hysteretic behavior, envelope curves, ductility, and strength and stiffness degradation of the specimens were studied. The experimental results demonstrate that the introduction of concrete-filled square steel tubes is effective in resisting the demands imposed by the web plates and that the coupled steel plate shear wall system has the characteristics to provide good seismic performance. The specimen that had welded moment connections suffered weld fracture of the coupling beam-to-column connections while the coupling beams of the two other specimens had ductile shear yielding followed by tearing and fracture of webs. The strength and stiffness degradation of three specimens were similar and stable. Finite element models were developed to simulate the nonlinear behavior of the specimen that had welded moment connections and to study the benefits of employing modified connections with wing plate and reduced-beam section configurations. The modeling showed that wing plate and reduced-beam section connection could reduce demands at the critical welds and delay weld fracture. The connection type was found to have little influence on the internal force of the columns or the overall system behavior.

Experimental study and numerical model of the seismic behavior of reinforced concrete beams in an artificial corrosion environment

The corrosion of reinforcement materials induced by chloride attacks is the primary reason for the deterioration of the seismic performance of reinforced concrete (RC) structures. In this paper, 12 RC beams with different corrosion levels, shear span to depth ratios and stirrup ratios were subjected to accelerated corrosion tests in an artificial climate as well as quasistatic cyclic loading tests, and the corrosion form, failure process, bearing capacity, deformation capacity, energy dissipation capacity, stiffness and strength degradation of corroded RC beams were investigated. The results showed that the artificial climate corrosion method could simulate the uneven corrosion form of steel bars in a natural environment; the corrosion of steel bars would intensify the shear failure characteristics of specimens; the degradation rates of the bearing capacity and deformation capacity of corroded RC beams with different shear span to depth ratios and stirrup ratios are significantly different; and the degradation degree of bearing capacity of specimens with a high shear span to depth ratio is 3.58 times higher than that of specimens with a low shear span to depth ratio. Subsequently, a numerical modeling method for corroded RC beams based on SFI-MVLEM was proposed, empirical formulas for the stiffness coefficient of the corroded dowel were determined based on experimental data, and the bond-slip deformation was simulated by the infinitesimal algorithm and zero-length fiber section element. The proposed model was accepted to numerically simulate 12 corroded RC beams in this paper, and the average values of the bearing capacity error and energy consumption error of the simulation results were 10.07% and 13.09%, respectively, indicating that the proposed model had good accuracy and could be adopted to predict the residual seismic performance of corroded RC beams.

Shear-compression tests on stone masonry walls strengthened with basalt textile reinforced mortar (TRM)

Textile Reinforced Mortar (TRM) composites are one of the most effective techniques to prevent failure and ensure seismic protection of unreinforced masonry in earthquake-prone areas. Aiming at assessing the suitability of this technology for irregular stone masonry walls, this study describes quasi-static cyclic shear-compression tests carried out on limestone masonry walls, typical of the UNESCO historical district of Lyon and of the Beaujolais region (France). Four medium-scale panels were tested: one unreinforced, one plastered, and two strengthened by a basalt textile externally bonded with a lime mortar (BTRM), either with or without transversal connectors and wall-to-foundation anchors. The mechanical characterization of the BTRM was carried out to highlight the dependence of the overall behaviour of walls on the characteristics of the reinforcement. Digital Image Correlation (DIC) was used to thoroughly capture damage development over the wall surfaces. Test outcomes demonstrate the effectiveness of BTRM in enhancing the shear strength and the displacement capacity of the wall. The results also show the key role of connectors and anchors and the non-negligible contribution of the mortar matrix, allowing to investigate the reliability of the design formulations provided by the current guidelines.

Seismic Performance of a Full-Scale Two-Story Bolt-Connected Precast Concrete Composite Wall Panel Building Tested on a Shake Table

A novel bolt-connected precast concrete wall panel structural system has recently been proposed for low-rise buildings in rural areas. The system features replaceable distributed bolt-connections adjoining walls, floors, and connecting columns fixed in base, enabling the whole system to be demountable and remountable. Previous quasi-static cyclic push-over test results showed an unfavorable punching shear failure of bolted joints without fully mobilizing the strength of the wall panels. Therefore, the connections were strengthened by using high-strength bolts and adjusting the positions of bolts. In order to evaluate the seismic performance of the precast system with the improved connections, incremental dynamic shake table tests were performed on a full-scale two-story building. Seismic demands and capacities of the precast building with connecting columns fixed in base (Model I) and without fixed-base constraints (Model II) were compared. The experimental results highlighted the high capacity of the improved precast system against beyond design-basis earthquakes with a peak ground acceleration of up to 0.8 g. Only slight to moderate damage was observed in terms of cracks at the edges of the door/window openings, similar to those on a cast-in-place structure, followed by cracks on concrete at connections. Although Model I showed higher lateral stiffness and lower seismic fragility, seismic energy was dissipated more evenly throughout the whole structure of Model II, which was proven well suited for low-rise buildings. Insight was given to explain the improvements on the bolt connections and the reinforcing effects of the connecting columns to provide references for the potential application of the proposed precast system.

Lateral force-displacement response of rat-trap bonded masonry

Rat-trap bond (RTB) masonry is one of the most economical, fast, and energy efficient construction technique for brick masonry buildings. Many developing countries including India, Nepal, Sri Lanka and Pakistan have constructed large number of buildings using this technique. However, structural stability and performance validation are as important as the economy in any construction project. Therefore, this study presents the results of in-plane quasi-static cyclic load tests on three wall specimens constructed in RTB. The pre-compression load was adjusted to simulate the load condition of a typical two storey building. The key parameters evaluated include stiffness, ductility, damping, energy dissipation, force-displacement behaviour, lateral strength, etc. The experimentally obtained results were also compared with the existing research of similar nature on conventional masonry as well as with the results predicted by various empirical equations. The comparison indicates that the lateral strength and stiffness of rat-trap masonry is significantly less than those of conventional masonry because of the reduced effective thickness, while other properties like ductility, damping and energy dissipation do not show any significant variation.

Experimental Investigations on the Lateral Cyclic Response of Post-Tensioned Rocking Steel Bridge Piers

This paper presents the results of a series of unidirectional quasi-static cyclic tests on 1/3-scale post-tensioned rocking steel bridge column specimens designed to rock at the interface with the foundation. The objective was to examine the effects of column diameter-to-thickness ratio, base plate, and energy dissipaters and their locations on the lateral cyclic behavior of the system. Site-specific cyclic displacement loading protocols were developed by performing time-history analyses of the pier. Emphasis was placed upon the sources of lateral response degradation including elastic restoring force reduction, local buckling, and energy dissipater failure. Strain distribution at the rocking plane and along the height, local bulging of the column, and uplift profile are discussed. The influence of multiple loading on the lateral response was also investigated. A component testing program was conducted to characterize the cyclic loss of post-tension force due to wedge seating in a typical industry monostrand anchorage system. The column test results demonstrate that a stable and robust self-centering response can be achieved with minimal damage to the column and most of the hysteretic energy is confined within the replaceable elements.

Cyclic Shear Performance of Reinforced Concrete Columns Strengthened by External Steel Rods

This study presents a strengthening method for reinforced concrete (RC) columns. The proposed method, which consists of a pair of steel rods, two reverse-threaded couplers, and four corner blocks, is feasible and straightforward. A quasi-static cyclic loading test was performed on the columns externally strengthened by the steel rods. It was found that the corner blocks and the external steel rods with a low prestress level effectively confined the concrete on the compression side of plastic hinges, which eventually induced flexural failure with a ductility higher than three in the strengthened columns. In addition, an analytical approach to predict the shear strength and ultimate flexural strength of the externally strengthened columns was applied. The comparison of analytical and experimental results showed that the analytical approach provided highly accurate predictions on the maximum strength and the failure mode of the externally strengthened columns. It is expected that the application of the proposed method will improve the seismic performance of damaged or deteriorated RC structures, thereby increasing their lifespan expectancy and sustainability.

In-plane cyclic behaviour of RC frames strengthened with composite sandwich panels

This paper presents an experimental study about the development of a sustainable and multifunctional composite sandwich panel for the rehabilitation of reinforced concrete (RC) buildings from the 1960s to the mid-1980s. For this purpose, the cyclic behaviour of representative RC frames was assessed by performing in-plane quasi-static cyclic tests on three different specimens: (i) a bare RC frame (individual behaviour of the frame); (ii) an RC frame with masonry infill wall (representative of target buildings); and (iii) an RC frame strengthened with an innovative sandwich panel formed by outer wythes in recycled steel fibre reinforced micro-concrete and polystyrene core layer. The results show that, in comparison with the traditional masonry infill wall solution, the proposed rehabilitation solution significantly improved the cyclic performance of the RC frame, reaching higher levels of load carrying capacity (395% vs. 349% increase) and energy dissipation (700% vs. 524% increase). Moreover, the sandwich panel has maintained its structural integrity with low level of damage in its internal load-bearing layer for high values of lateral drift (up to 2.1%).

Experimental and numerical investigation of assembled multi-grid corrugated steel plate shear walls

The aim of this study is to develop an assembled multi-grid corrugated steel plate shear wall (CoSPSW), which can significantly increase the out-of-plane pre-buckling stiffness and be suitable for factory standardization. The proposed shear wall comprises several corrugated steel plates which are embedded in small grids enclosed by the longitudinal- and transverse-connecting stiffeners, frame beams and columns. To verify the seismic behaviour of the multi-grid CoSPSW, three 1:3 scale-specimen quasi-static cyclic tests were performed and demonstrated that the multi-grid CoSPSW can sustain a better energy dissipation capacity. Numerical analysis was conducted to investigate the seismic behaviour and the parameter optimization of the proposed shear wall. Based on the validated finite element model, parametric studies included the effects of the corrugated profile, corrugated steel plate layouts (vertical, transverse, and 45° oblique corrugated), and connecting stiffener parameters, which revealed the trapezoidal corrugated steel plate and the horizontal and vertical layouts in the small grids showed a higher buckling capacity and initial lateral stiffness. Both of the experimental results and the numerical analysis showed that the energy dissipation capacity and out-of-plane stiffness of the multi-grid CoSPSW was further improved compared to the ordinary CoSPSW by setting the longitudinal- and transverse-connecting stiffeners.

Research on the specially-shaped corrugated steel plate shear walls with horizontal corrugation

A specially shaped corrugated steel shear wall (S-CSSW) system was proposed for the application of steel residential buildings. The proposed shear wall system featured a main shear wall with small section concrete filled steel tube (CFST) boundary columns and horizontally corrugated shear plates and side short pier CSSWs in the perpendicular direction. Quasi-static cyclic tests were performed on the S-CSSWs with and without reinforcing beams to investigate the shear strength, failure modes and hysteretic responses. Finite element simulations were introduced to further study the shear bearing mechanisms of S-CSSWs for a comparison with traditional flat plate shear walls with similar wall configurations. An additional parametric simulation was performed to investigate the influence of the corrugated plate width on failure modes. Results indicated that the proposed S-CSSWs possessed good ductility. Compared with the flat plate shear walls, the proposed shear walls had higher initial stiffness and elastic shear strength. The width of the corrugated shear panels was an important factor influencing the failure modes and lateral bearing abilities and needed to be carefully controlled to avoid early buckling occurring ahead of the shear yielding mode. Some design remarks are concluded regarding the design of the corrugated shear panels and stiffening beams.

Seismic performance of T-shaped precast concrete superposed shear walls with cast-in-place boundary columns and special boundary elements

The seismic behaviors of three full-scale T-shaped precast concrete superposed shear wall specimens with cast-in-place boundary columns and special boundary elements and two those of T-shaped cast-in-place shear wall specimens for reference were investigated using quasi-static cyclic loading test. In this study, a novel vertical joint of superposed wall panels and special boundary elements was designed differently from that obtained using additional overlapped connecting steel bars. The failure mode, strength, hysteresis feature, ductility, energy dissipation capacity and stiffness degradation of each specimen were compared. The influence of different connecting methods of vertical joint, boundary elements and axial compression load ratios on the seismic behavior of T-shaped superposed shear walls were analyzed. The test results show that the T-shaped superposed shear walls with boundary columns and an axial compression load ratio of 0.2 exhibited seismic performances close to that of the reference T-shaped cast-in-place shear wall, and the T-shaped superposed shear walls with special boundary elements and an axial compression load ratio of 0.4 exhibited seismic performances equivalent or even superior to that of the reference cast-in-place specimen in the loading direction along the web axis. The T-shaped superposed precast concrete shear wall specimen with the new connecting method of vertical joint exhibited higher strengths, deformation capacities and energy dissipation capacities than that of the T-shaped superposed precast concrete shear wall specimen with the traditional overlapped connecting method. Furthermore, the shear strength of all the specimens calculated by the formulas recommended in the Chinese code JGJ 3–2010 were smaller than the tested peak load.

Loading protocols for seismic performance evaluation of buckling-restrained braces in RC frames

The selection of a proper loading protocol for seismic performance evaluation of structural dampers poses quite a challenge at the very first step of quasi-static cyclic tests. Existing loading protocols for buckling-restrained braces (BRBs) are mainly developed on the basis of the seismic responses of BRB-steel frame systems. However, the behavior of a BRB in reinforced concrete frames (RCFs) differs markedly from that in the steel frames. In this study, a set of loading protocols were constructed to provide a reference for seismic performance assessment of BRBs in RCFs. The methodology for the development of loading protocols was illustrated and a series of BRB-RCFs varying in building heights and story shear resisted by BRBs were designed. An extensive analytical investigation of seismic responses of BRBs under far-field, near-fault, and long-duration earthquakes was systematically evaluated and quantified. Based on the rainflow counting method, the control parameters in terms of numbers of cycles, amplitudes, and residual core strains were determined to construct loading sequences. The effectiveness of the proposed loading protocols was discussed and verified through comparisons with existing loading sequences and time-history analysis results of a validated BRB-RCF model. It is indicated that the proposed loading protocols can conservatively reflect the actual seismic damage demands with a reasonable agreement.

QUASI-STATIC CYCLIC TESTS ON THE HYSTERETIC BEHAVIOR OF BUCKLING-RESTRAINED BRACES WITH A T-SECTION CORE

An all-steel assembled buckling-restrained brace is proposed, in which both the core and the restraining members are made of section-steel. The brace has the advantages of assembly, replaceable core, easy fabrication, low cost and can be used for strengthening existing members. The steel core is composed of two angle steels and stiffening plates to form a T-shaped section. The restraining members are formed by bolting plates and angle steels through mat strips. Quasi-static cyclic tests for six specimens were carried out to investigate the hysteretic performance, seismic performance and failure modes. The effects of adding filler plates in the core, the gap between the core and the restraining members, the spacing between the two angle steels of the core, and the stopper configuration on the hysteretic performance were analyzed. The results show that the actual performance of the brace was basically consistent with the design performance. The brace specimens exhibited stable hysteretic performance. Adding filler plates in the middle of the core shows little influence on the hysteresis performance. An excessive gap between the core and the restraining member and excessive spacing between the two steel angles of the core reduced the hysteresis performance. The hysteretic performance of the braces with middle stoppers were better than the brace with end stoppers. The analysis of the seismic performance of the specimens shows that the braces have satisfactory ductility and cumulative plastic deformation capacity, which can be used as dampers in structures. By analyzing the failure modes, the stress concentration of the welding at the end of the stiffening plates will make the failure position move from the yielding segment to the stop of the weld. The middle stopper of the core can reduce the adverse effects of friction.

Seismic behavior of RC columns internally confined by CFRP strips

During past decades fiber-reinforced polymer (FRP) sheets have been externally bonded to structural elements to increase their axial, shear, or bending capacity. FRP bars also have been widely used to replace the steel reinforcements in columns subjected to a harsh environment. In this study, carbon fiber-reinforced polymer (CFRP) strips were used as the transverse reinforcement for concrete columns. Although FRP bars have already been used as the transverse reinforcement in concrete columns, the efficiency and feasibility of CFRP strips have not been investigated. CFRP strips are flexible; therefore, they can be easily shaped as spirals to confine the concrete core of columns. The efficiency of CFRP strips for the confinement of the concrete core was examined through a series of quasi-static cyclic tests on four full-scale columns that had similar size and longitudinal reinforcements. One of the columns was selected as the reference, and steel spirals transversally reinforced it. CFRP strips transversally reinforced the other three columns with different widths and spacing. The obtained results showed that the number of cracks in the CFRP-confined columns was less than the reference column. The length of cracks in the CFRPconfined columns was also relatively shorter. Besides, the CFRP-confined columns had a larger ultimate load, effective yield strength, and displacement ductility ratio compared with the reference column.