Quasi-static Cyclic Tests Research Articles

Study of a new type of steel slit shear wall with introduced out-of-plane folding

The steel slit shear wall (SSSW), made by cutting vertical slits in a steel plate, is increasingly used for the seismic protection of building structures. In the domain of thin plate shear walls, the out-of-plane buckling together with the potential fracture developed at slit ends at large lateral deformation may result in degraded shear strength and energy dissipation, which is not desirable in view of seismic design. To address this issue, the present study proposed a new type of SSSW made by intentionally introducing initial out-of-plane folding into the originally flat slitted plate. Quasi-static cyclic tests on three SSSWs with different amplitudes of introduced out-of-plane folding were conducted to study their shear strength, elastic stiffness, energy dissipation capacity and buckling behavior. By introducing proper amplitude of out-of-plane folding into the SSSW fracture at slit ends was eliminated, plumper hysteretic behavior was obtained and there was nearly no strength degradation. A method to estimate the shear strength and elastic stiffness of the new SSSW was also proposed.

Steel Structures Research Update: Self-Centering Column Base Connections with Friction Dampers

Recent work on a self-centering column base connection with friction dampers is highlighted. This research is a collaborative effort by Senior Researcher Massimo Latour and Professor Gianvittorio Rizzano from the University of Salerno, Italy, and Professors Aldina Santiago and Luis Simões da Silva of the University of Coimbra, Portugal. The Salerno-Coimbra team has developed an alternative self-centering column base solution to minimize initial costs and economic losses. Specific objectives are to limit damage and residual drifts, with connection components that are easy to repair or replace if needed. The self-centering column base has been validated through quasi-static cyclic testing and pseudo-dynamic testing. The self-centering connection has also been investigated through numerical time-history analyses of moment-resisting frames comparing conventional, fixed column bases to self-centering column bases. Some highlights of the research are presented.

Behavioral Evaluation of Modular ICH RC Columns through Quasi-Static Cyclic Tests

Owing to the recent expansion in sizes of wind turbines, the required height for the wind turbine tower is increasing. Therefore, new types of structures are needed to fulfill this requirement. In this study, a modular Internally Confined Hollow Reinforced Concrete (ICH RC) column was suggested for a wind power tower, and quasi-static test was performed to evaluate its bending performance. One single body specimen (SP-S) and two modular specimens (SP-MP, SP-MF) applying different connection methods were fabricated. The specimens were designed and manufactured while considering the numerical analysis and conditions of the testing laboratory. The test was conducted by controlling the displacement according to the drift ratio. The experimental results of moments, lateral loads, displacements, dissipation energy, ductility, etc. for each specimen were compared with those of numerical modeling. Consequently, plastic hinges were found at the bottom of the column and connection part for SP-S and modular specimens, respectively, which is due to the rigidity change at the connection of the modular specimens. Therefore, the result of energy dissipation was 40% higher in the case of the modular specimens than that of SP-S whereas the lateral force and moment in the case of the modular specimens were smaller than those of SP-S. In terms of displacement and energy ductility, modular specimens exhibited 50% higher results than those of SP-S. For the future work, it is necessary to enhance the performance of the connection part to apply the modular ICH RC structure to a wind turbine tower.

Composite behavior in RC buildings retrofitted using buckling-restrained braces with elastic steel frames

Seismically retrofitting reinforced concrete (RC) building with a combination of buckling-restrained braces (BRBs) and elastic steel frames offers a practical solution that provides additional lateral stiffness and energy dissipation capacity. However, the available methods to vertically distribute the BRB sizes based on equivalent linearization do not consider the additional stiffness due to the composite behavior between the RC frame and the elastic steel frame, which may lead to an overly conservative estimate of the BRB stiffness demands. This study proposes a retrofit design method incorporating the composite behavior. Numerical models considering the detailed composite behavior are developed and calibrated against quasi-static cyclic loading tests, and a simplified evaluation method is proposed. A four-story RC school building is used as a benchmark model, and the proposed retrofit design method is validated using nonlinear response history analysis. The analysis results suggest that taking the composite behavior into account by using the proposed retrofit design method more accurately estimates the lateral stiffness of the retrofitted structure and leads to a more economic retrofit.

Application of Linear Viscoelastic Continuum Damage Theory to the Low and High Strain Rate Response of Thermoplastic Polyurethane

BackgroundUnderstanding the mechanical response of elastomers to applied deformation at different strain rates and temperatures is crucial in industrial design and manufacture; however, this response is often difficult to measure, especially at high strain rates (e.g. > 100 s− 1), and more predictive methods to obtain constitutive relationships are required.ObjectiveThe objective of the research described in this paper is to develop such methods.MethodThe paper outlines a novel approach combining quasi-static monotonic tests in tension and compression, quasi-static cyclic tests in tension, and high strain rate tests in compression, with dynamic mechanical analysis and time-temperature superposition. A generalized viscoelastic model incorporating continuum damage is calibrated.ResultsThe results show that a model calibrated using data from quasi-static compression and dynamic mechanical analysis can be used to adequately predict the compressive high strain rate response: hence, this paper provides an important step in the development of a methodology that avoids the requirement to obtain constitutive data from high strain rate experiments. In addition, data from FE models of the dynamic mechanical analysis experiments are provided, along with a discussion of data obtained from tensile and cyclic loading.ConclusionsThe paper demonstrates the effectiveness of ‘indirect’ predictive methods to obtain information about high rate behaviour of low modulus materials.

Development of a new hexagonal honeycomb steel damper

This paper presents a new metallic damper called hexagonal honeycomb steel damper (HHSD) for damage mitigation in structures subjected to earthquake excitations. The HHSD is composed of steel plates having several hexagonal and welded to the top and bottom anchor plates. The damper takes the advantages of hexagonal honeycomb geometry and steel material capability to dissipate seismic energy. The quasi-static cyclic test was performed experimentally and numerically on a series of specimens to evaluate the robustness of the HHSD. A three-dimensional finite element analysis of HHSD was carried out and verified with the experimental results. The results showed that the HHSD has low yield displacement, stable hysteretic behavior, a good range of ductility and high-energy dissipation capability. Additionally, the constitutive formulas of the damper are also derived based on the obtained results. Furthermore, it is found to have lightweight and inexpensive with ease of implementation as a potential alternative for new structures or seismic retrofitting of the existing structures.

Experimental and numerical study performed on seismic behavior of irregular external SRC joints in the main plant of CAP1400 NPP

The main plant of steel reinforced concrete (SRC) structure is proposed for CAP1400 nuclear power plant (NPP) in high seismic zone, which not only has better mechanical properties than reinforced concrete structure plant, but also has lower maintenance cost than steel structure plant. The irregular SRC joints are inevitably appeared in the main plant due to the limitations of power generation technology and equipment. In this paper, quasi-static cyclic tests were carried out on three 1:4 reduced scale irregular external SRC joints to discuss the seismic performance of the joints in the NPP, mainly including the damage pattern, hysteretic behavior, load carrying capacity, stiffness degradation and ductility. In addition, the detailed 3D finite element (FE) models were established, in which the bond-slip behavior between the shaped steel and concrete was considered by using the developed software to add a huge number of non-linear spring elements, and the FE models were verified by the test results. Then, the parametric study on seismic performance of irregular external SRC joint was carried out, and the influence of each parameter on the seismic performance of the irregular external SRC joint was analyzed. Finally, the effective and economical reinforcement measures were proposed, and verified by the FE method.

Experimental evaluation of self-centering hybrid coupled wall subassemblies with friction dampers

Post-tensioned hybrid coupled wall system has desirable seismic characteristics including self-centering capability and tolerance for large nonlinear displacements with limited damage. In this study, the behavior of concrete coupled wall subassemblies with post-tensioned steel coupling beam was experimentally evaluated. In this system, the coupling beam is not embedded into the walls, and the coupling of the concrete walls is accomplished by post-tensioning the steel coupling beam to the walls using unbonded post-tensioning strands. Steel angles and friction dampers were used at the beam-to-wall connection region for energy dissipation. In the first series of tests, a friction damper with different values of the clamping force was tested under two different loading frequencies. In the second series, seven quasi-static cyclic tests were conducted on 2/3-scale subassemblies of the post-tensioned hybrid coupled wall system. The test specimens included a control specimen without energy dissipation device, a specimen with steel angles and four specimens with friction dampers. In addition, one of the tested specimens with dampers was re-tested to investigate the structural behavior and residual capacity of the system during a strong aftershock. The test parameters included the type of energy dissipation device, the initial stress of post-tensioning strands and the amount of damper normal force. The test results show that the subassemblies equipped with friction dampers exhibit excellent lateral stiffness, strength, ductility and energy dissipation and are capable of withstanding large nonlinear cyclic deformations up to the drift of 8%, without residual displacements and without significant damage to the system. Whereas the subassembly equipped with steel angles provide lower energy dissipation capacity and because of the low-cycle fatigue fracture of angles, energy dissipation and load carrying capacities of the specimen decrease significantly.

Experimental study of a steel damper with X-shaped welded pipe halves

In this paper, a new steel damper named X-shaped pipe damper (XPD), is proposed and examined. The proposed damper is made through welding two oppositely positioned pipe halves to form a X-shaped core, and connecting the X-shaped core to side plates with fillet welds or circumferential welds. The XPD damper provides the lateral resistance and energy dissipation behaviors initially through flexural bending of pipe plates, and latter through the tensile stretching at composite pipe halves. Theoretical derivations of initial stiffness and yielding properties were conducted, and the nonlinear working mechanisms and seismic performance were investigated through cyclic quasi-static tests. Effect of welding methods and pipe configurations on the stiffness, strength, ductility and energy absorption efficiency of the XPDs were studied. The XPDs can presented similar lateral load resistance with only half pipe usage than dual pipe dampers. The XPD specimens all presented stable and pump hysteretic loops, and had a steady strength increase after yielding until fracture failure. The circumferential weld XPDs displayed higher initial stiffness, strength and better deformation ability than the fillet welded ones, but also possessed fatigue fracture potential at the heat affecting zones under fatigue cyclic protocols. Based on the obtained results, the application field and improving suggestions for the XPDs are discussed.

Experimental investigation of the in-plane cyclic behaviour of calcium silicate brick masonry walls

The material and structural performance of calcium silicate (CS) brick masonry has received relatively little attention in the past, although this material is often used for the construction of low-rise buildings in Central and Northern Europe. Upon the occurrence of induced seismicity in the north of the Netherlands, an extensive testing programme has been conducted since 2014 at Delft University of Technology. The paper presents the outcomes of eight quasi-static cyclic tests performed within this program on CS brick masonry walls under vertical and lateral in-plane loads. Different dimensions, boundary conditions and applied pre-compression loads were considered. Overall, the tests allowed to characterise the in-plane behaviour of CS brick masonry walls. The results confirmed the influence of the shear ratio (i.e. the ratio between the effective height and the length of the wall) on the wall response in terms of prevailing failure mode, initial stiffness, force and deformation capacity, energy dissipation. Besides, the experimental outcomes stressed the difficulty in estimating the effective stiffness and near collapse drift capacity. Additionally, an empirical equation is proposed to predict the peak lateral force. The equation, calibrated against the tests presented in this paper, was validated against an extended dataset of tests performed on CS masonry walls. The equation, which does not need any input of material parameters and is applicable irrespectively of the expected failure mode, can be used to estimate the force capacity of CS masonry walls when no or limited data on the material properties are available.

Cyclic testing of moment-shear force interaction in reinforced concrete shear wall substructures

Previous quasi-static cyclic tests of shear walls, which routinely used an incremental lateral displacement test protocol with a constant axial load, failed to reflect the character of moment-shear force interaction of prototype buildings. To study the effect of the moment-shear force interaction on the seismic performance of shear walls, three identical 2-story shear wall specimens with different loading patterns were constructed at 1/2 scale, to represent the lower portion of an 11-story high-rise building, and were tested under reversed cyclic loads. The axial force, shear force and bending moment were simultaneously applied to simulate the effects of gravity loads and earthquake excitations on the prototype. The axial force and bending moment delivered from the upper structure were applied to the top of the specimens by two vertical actuators, and the shear force was applied to the specimens by two horizontal actuators. A mixed force-displacement control test program was adopted to ensure that the bending moment and the lateral shear were increased proportionally. The experimental results show that the moment-shear force interaction had a significant effect on the failure pattern, hysteretic characteristics, ductility and energy dissipation of the specimens. It is recommended that moment-shear force interaction should be considered in the loading condition of RC shear wall substructures cyclic tests.

Experimental Seismic Performance of Partly-Sliding Partition Walls

ABSTRACT Plasterboard partition walls typically used in commercial buildings are especially sensitive to earthquakes, with the onset of cosmetic damage initiating at small values of interstorey drift. The most common partition wall systems are constructed of gypsum board attached to either steel or timber framing which is fixed directly to the floor system at the top and bottom interfaces. This study investigates the seismic performance of a novel partly-sliding steel-framed partition system examined in the past and used by industry, with minor modifications incorporated within the partition detailing. This novel system involves removing top track anchors within the proximity of wall intersections, thus allowing the tracks to ‘bow’ out at these locations. In this study three full-scale specimens were subjected to quasi-static cyclic testing; two identical plane specimens and the third including a doorway. The specimens were built in a y-shape and angled at 30° to the direction of applied loading, which allowed bi-direction behaviour to be examined. The specimens included an acoustic/fire sealant. The progression of damage in a partition can be categorized by three sequential damage states associated with distinct levels of repair: superficial damage requiring cosmetic repair (damage state 1 (DS1)), damage requiring local repairs or replacement of only portions of the partition assembly (damage state 2 (DS2)), and severe damage requiring complete removal and replacement of the wall (damage state 3 (DS3)). Damage was first observed as cracking of the wallboard at the wall ends, at external junctions, and propagating from the corners of the door opening. The onset of DS1 and DS2 occurred simultaneously at a median in-plane drift of 0.29%. DS3 was not observable until the linings had been removed at the end of the tests. In addition to providing drift capacities, the force-displacement behaviour is also reported, the dissipated energy was computed, and the parameters of the Wayne–Stewart hysteretic model were fitted to the results. The specimen with the door opening behaved significantly different to the plane specimens: damage to the doorway specimen began as cracking of the wallboard propagating from the corners of the doorway following which the L- and Y-shaped junctions behaved independently, whereas damage to the plane specimens began as cracking of the wallboard at the top of the L-junction and wall system deformed as a single unit. The results suggest that bi-directional behaviour is important even if its impact cannot be directly quantified by this experiment. Damage to sealant implies that the bond between plasterboard and sealant is important for its seismic performance, and careful quality control is advised, as defects in the bond may significantly impact its ability to withstand seismic movement.

Seismic behaviour of Taiwanese timber complex brackets subjected to out-of-plane loading

The Taiwanese Dieh-Dou-type complex brackets used in traditional timber buildings are commonly believed to sustain both in-plane and out-of-plane loadings of the main frame during seismic events. From past statistical investigation, single-tier, double-tier and triple-tier asymmetric bracket designs were chosen as test subjects. A series of quasi-static cyclic tests was applied to full-scale specimens to evaluate their seismic behaviour when subjected to out-of-plane loading. The test specimens generally exhibited significantly higher resistance when all horizontal members sustained compression. The Gong members functioned like braces and subsequently led to enhanced resistance. However, when the global structure was subjected to tension, the joints of Gong, purlin support and purlin members were more likely to be pulled out. The counter-resistance force observed from the tension side resembled that of rigid-body rotation. The triple-tier specimen sustained more serious damage than the other two types, where the middle Dou member was more prone to split due to stress concentration. The proposed bi-linear semi-rigid spring models were in good agreement with the test results, so the general assumptions made were valid.

Eccentric steel brace retrofit for seismic upgrading of deficient reinforced concrete frames

The paper presents a simplified static force-based procedure for seismic retrofit design of RC frames using internal eccentric steel braces (ESBs), connected to long beam at distance of L/8 from beam ends, to enhance seismic resistance of the frame. The technique uses the linear static procedure given in ASCE 7-16 for calculation of appropriate design base shear for frame analysis, and the AISC 360-16 seismic provisions for preliminary design of steel braces. Response modification factor R was derived based on simplified kinematics of rigid frame response and flexure hinging of link beam, to reduce the elastic base shear force for lateral load analysis of frame and design of steel braces. This shifts plastic hinges from columns, and reduces joint shear deformation, by means of capacity protected braces and beam shear. The procedure was used for the preliminary design of ESB retrofitting technique for a two-story RC frame, employing hollow box steel sections. Quasi-static cyclic tests were performed on both as-built and ESB retrofitted portal frame panels under multiple-levels of lateral displacements demands. The tests performed on frames were analysed to understand the damage mechanism and retrieve the essential seismic response properties: force–displacement capacity curves, hysteretic cyclic response and hysteretic damping, and to establish performance-based story drift limits. The experimental data was used to calibrate finite element based nonlinear numerical models in SeismoStruct. Nonlinear static pushover analysis of considered two-story ESB retrofitted frame was carried to quantify structure ductility and response modification factors. The preliminary design was verified through nonlinear time history analysis (NLTHA) for both design base earthquakes and maximum considered earthquakes. Proposed seismic design of ESB retrofit for multi-stories RC frames having three to six stories has been presented and verified through NLTHA. It indicates the promising behaviour of ESB retrofit technique as well as the efficiency of the proposed simplified design procedure.

Roles of pile-group and cap-rotation effects on seismic failure mechanisms of partially-embedded bridge foundations: Quasi-static tests

Pile foundations, especially partially embedded in soils, are vulnerable parts of bridges under seismic loadings. In this study, to investigate seismic failure mechanisms of partially-embedded reinforced concrete (RC) pile-group foundations, a series of quasi-static cyclic loading tests were conducted on 1 × 1, 2 × 2 and 2 × 3 pile-foundation specimens in sand. Observed hysteretic behavior and pile damage were recorded, along with pile curvature distributions. Then, numerical models based on the Beam-on-Nonlinear-Winkler-Foundation (BNWF) approach were developed and validated by test data. The failure process of each specimen was reached, characterized by the sequence and locations of plastic hinges on piles. Combining the test and numerical results, seismic failure mechanisms of all partially-embedded pile specimens with different layouts are revealed: side piles yield before center piles, each pile forms two plastic hinges, and pile heads yield before underground portions. Special attentions are paid to the roles of cap rotation and pile-group effect (PGE) on the failure mechanisms. The results reveal that the existence of PGE leads to lower lateral loads and greater displacements at different limit states such as the first yielding and ultimate states etc., while the impact of cap rotation only increases corresponding lateral displacements at these limit states.

Response of Self-Centering Mass Plywood Panel Shear Walls

The rocking behavior of self-centering mass plywood panel (MPP) walls was investigated with and without the use of supplementary energy dissipation systems. Two energy dissipation systems were tested. The first system used a kinematically expanding hysteretic damper (KE-HD), whereas the second system used slip friction connections (SFCs). The reviewed energy dissipating systems were used in a self-centering system comprising one unbonded posttensioned (PT) hold-down rod on each side of the MPP walls. The cyclic performance of the PT and the hybrid MPP specimens was investigated through a series of full-scale quasi-static cyclic tests. The test results demonstrated the viability of the investigated energy dissipaters in self-centering MPP rocking systems. Results further indicate that hybrid specimens with SFC dissipate more energy and provide higher strength than those with KE-HDs, however, with higher residual drift.

Performance and optimum design of replaceable steel strips in an innovative metallic damper

In this study, a high efficiency metallic damper with replaceable steel strips and the adjustable construction is proposed for framed structures. The proposed damper uses bolted steel strips as the energy dissipation fuses, which can be adjusted or replaced after failure without affecting the connecting part. The steel strips participate in the load bearing and energy dissipation through an in-plane bending mechanism. In addition, to exert the load bearing and achieve the potential plasticity fully, the steel strips are desired to yield simultaneously and dissipate energy throughout the entire section. In this paper, the primary configuration design method was provided through a theoretical derivation. Further, the nonlinear performance of the proposed fuse strips was evaluated through a series of quasi-static cyclic tests. The influence of the configuration dimensions was investigated through the experimental study and corresponding finite element analyses. The results indicate that the strips successfully exert their potential energy dissipation with pump hysteresis loops. The fuse strips can better participate in the energy dissipation through bending-dominated working mode, and the bending moment strength of the steel strip is mainly controlled based on the width of the central region. The configuration of the transition region greatly affects the failure mode, the plasticity distribution, and the deformation capability. Based on the test data and the numerical simulation investigations, some primary design guidance for the fuse steel strips is suggested.

Stiffness and Strength Estimation of Damaged Unreinforced Masonry Walls Using Crack Pattern

ABSTRACT After an earthquake, the residual stiffness and strength of structural elements are typically estimated based on a qualitative visual inspection of cracks that is prone to error. In this paper a new approach is proposed to automatically estimate the updated stiffness and strength of damaged unreinforced masonry walls by characterization of crack patterns by a mathematical index. It is shown that structural and textural fractal dimensions of a crack pattern reflect the extent of cracking and the type of cracking or crushing, i.e., whether the cracks pass through joints or whether bricks have been damaged and crushed. Using results of six quasi-static cyclic tests on unreinforced brick masonry walls with different failure modes at various drift ratios, it is shown that the structural and textural fractal dimensions of the crack patterns are an accurate predictor of the stiffness and strength degradation. This procedure seems therefore a promising approach for replacing the traditional assessment methods that are based on visual inspection and engineering judgment by an analytical procedure based on image processing that can eventually be completely automated.

Experimental evaluation of seismic performance of unbonded prestressed reinforced concrete column

Unbonded prestressed reinforced concrete column (UBPRC column) has become an attractive approach in the field of bridge seismic design due to its superior self-centering behavior. Unbonded prestressing bar in a UBPRC column functions as a self-centering element and longitudinal mild reinforcement functions as an energy dissipator. Quasi-static cyclic test was carried out in this study to compare the seismic performance of reinforced concrete column (RC column), UBPRC column and fully prestressed concrete column (FPC column). The result shows that the UBPRC column has higher post-yield stiffness and smaller quasi-static residual displacement, but lower energy dissipation capability than the RC column. The FPC column suffers from the least quasi-static residual displacement, but has the lowest energy dissipation capability, the least ultimate displacement and the most severe prestress loss. The quasi-static residual displacement and residual crack width of the UBPRC column are around 66% and 73% of those of the RC column, respectively. The failure patterns of the RC column and the UBPRC column are similar, while the failure pattern of the FPC column is similar to that of a rocking column. The self-centering behavior of the three columns was analyzed and quantified using a self-centering index, which can be recommended for use in the seismic design of bridge columns.

Seismic Performance of Precast Concrete Columns with Improved U-type Reinforcement Ferrule Connections

This paper proposes a new kind of U-type reinforcement ferrule (URF) connection for the assembly of precast concrete (PC) components, which has a good fault-tolerance ability and low cost of construction with a simple post-grouting process. The modified connection features welded U ferrules, which can increase the bonding mechanism and internal stress transmission in the spliced region. A series of quasi-static cyclic tests were performed on URF-connected PC columns with different welding patterns. Comprehensive comparisons were performed on the load-bearing capacity, the plastic energy dissipation ability, the internal force transmission, the column ductility and the stiffness. The results indicated that PC columns with welded URF connections can ensure better lateral resistance than the cast-in-place concrete column. The weld type and length influence the connection performance, and the 15d-welded and full-length welded URF connections presented better connection performance and were suggested for the assembly of PC columns. Then, finite element analyses were performed to further reveal the working and failure mechanisms and the affecting mechanism of some working parameters. Parametric simulations indicated that the increase in the axial load ratio and the concrete strength in the postcast region had a slight but limited effect on improving the lateral resistance of the column connection.