Displacement-controlled Cyclic Loading Research Articles

Experimental investigation of EBROG and bore-epoxy anchorage methods used for interior RC beam-column joints strengthened with CFRP sheets

In severe earthquakes, the energy dissipation and ductility capacities of the structures depend on the performance of the beam-column joints where the load transfer is performed. Experiences in past earthquakes have shown that damage occurs in the beam-column joints that do not have sufficient strength and rigidity. In particular, the shear failure observed in deficient detailed joints has caused the collapse of many structures. Joints are effectively retrofitted with carbon fiber reinforced polymer (CFRP) sheets to increase the earthquake safety of the structures. However, the debonding problem experienced in CFRP sheets significantly affects the efficiency of the applied retrofit and the earthquake behavior of the member. In this study, the retrofit of reinforced concrete beam-column joints with deficient shear strength was carried out with CFRP sheets by using externally bonded reinforcement on grooves (EBROG) and bore-epoxy anchorage methods. These two retrofit methods were applied to effectively utilize the full capacity of CFRP sheets by delaying the debonding. Six ½ scaled reinforced concrete (RC) interior beam–column specimens without transverse reinforcement in the joint core were constructed. One reference and five retrofitted joints were subjected to displacement-controlled cyclic loading. The shear failures in the specimens were delayed until advanced displacement levels. The use of EBROG and bore-epoxy anchorage methods improved the yield load of the specimens by 32 % to 69.05 % compared to the reference specimen. Additionally, significant increases were observed in the initial stiffness, load-carrying, and energy dissipation capacities of the retrofitted specimens up to 68 %, 64 %, and 104 %, respectively. The ductility of the retrofitted specimens increased by approximately 7 % to 26 %. The EBROG and bore-epoxy anchorage methods proved to be highly successful in preventing the early debonding of CFRP sheets. In specimens strengthened with EBROG and bore-epoxy anchorage methods, the displacement values at which the FRP sheets began to debonding approximately doubled. It was concluded that EBROG and bore-epoxy anchorage methods were more effective than the externally bonded reinforcement (EBR) method in improving the overall structural performance of the joints.

Seismic Performance of Cementitious Grout Filled Coupler and Sleeve Connections in Precast Wall Panels under Cyclic Lateral Loading

This study investigated the seismic performance of cementitious grout filled coupler and sleeve connections in precast wall panels under cyclic lateral loading. The effectiveness of these connections in enhancing the seismic performance of precast concrete walls was evaluated. In many countries, grouted coupler connections are the preferred option, whereas sleeve connections were more commonly utilized in India due to the belief that a greater portion of the dowel being grouted enhances structural stability. Tests were conducted on full scale precast wall panels to study the behaviour of connections by applying a displacement-controlled cyclic lateral loading and the results were discussed. The experimental study revealed that the cementitious grout filled coupler connection exhibited better seismic performance and was recommended for precast wall panel connections over the grouted sleeve connection. Compared to the grout filled sleeve connection, the specimen with an unbonded segment demonstrated an 8% rise in energy dissipation, while the specimen with a grouted coupler connection displayed a 55 % increase.

Very low-cycle fatigue failure behaviours of pipe elbows under displacement-controlled cyclic loading

In this study, quasi-static very low-cycle fatigue tests were conducted on pipe elbows at room temperature to investigate the effects of the pipe thickness, internal pressure, and material on the failure behaviours under large-amplitude cyclic loads. Three types of elbow specimens comprising two different materials and two different pipe thicknesses were used in the tests. Elbow specimens were subjected to displacement-controlled, fully reversed, in-plane mode cyclic bending with and without internal pressure. All specimens failed due to through-wall cracking of which the location and orientation depend only on the pipe thickness regardless of the internal pressure and elbow material. For thin-walled elbows of Schedule 40, the axial crack at flank was developed, whereas for thick-walled elbows of Schedule 160, the circumferential crack at intrados. The number of cycles to failure decreased with increasing internal pressure in thin-walled elbows. However, the effect of internal pressure on the number of cycles to failure was negligible in thick-walled elbows. Regardless of internal pressure level, stainless steel elbows were more resistant to failure, compared with carbon steel elbows of identical dimensions. Finally, the strain-based evaluation model considering the void growth and shrinkage effect was applied to predict fatigue failure location and cycles. Two parameters in the model, the multi-axial fracture strain locus and void shrinkage ratio, were determined from monotonic tensile test data and the fatigue life curve of the material. The predicted crack initiation site and orientation were consistent with experimental finding. For all cases, the predicted failure cycles were less but overall close to experimental data.

Ratcheting assessment of pressurized elbow pipes using the visco-plastic Chen-Jiao-Kim hardening rule frameworks

In this study, the ratcheting responses of pressurized long and short radius 90° elbow pipes made of 304L austenitic stainless steel under displacement-controlled cyclic loading is evaluated mainly using the Chen-Jiao-Kim (CJK) kinematic hardening rule at room temperature. Visco-plastic flow rule and isotropic hardening are introduced into the CJK model to better reflect the time-dependent behavior and cyclic hardening characteristics of the 304L stainless steel material. The model is implemented employing the user material subroutine (UMAT) in the ABAQUS finite element software. The predictions show that the maximum ratcheting strain occurs at the flank of the long and short radius 90° elbow pipes. The influence of internal pressure, cyclic loading, and bending radius on the ratcheting responses of the elbow pipes is respectively investigated. It is found that the predictions of the CJK model are very nearly the same as the test data. In addition, the ratcheting responses of two long radius elbow pipe specimens under force-controlled cyclic bending are evaluated. Further, the C-TDF (The Committee of Three Dimensional Finite Element Stress Evaluation) combined with CJK model and Linear Matching Method (LMM) is respectively used to determine the shakedown and ratcheting boundaries of the pressurized long and short radius 90° elbow pipes under displacement-controlled and force-controlled bending. The comparison with the test data in this study shows that the shakedown and ratcheting boundaries determined by LMM, divides the shakedown and ratcheting zone well.

Load-carrying and energy-absorbing performance of honeycombs with different cross sections under cyclic loading

Honeycombs, characterized by advantages including large compressive deformation and controllable deformation, have been widely used in energy-absorbing components. The loading process of honeycombs is generally influenced by recovery after unloading in application environments. Expounding the load-carrying and energy-absorbing performance of honeycombs under cyclic loading is critical for the practical engineering application of honeycombs. Honeycombs with four different cross sections were selected to compare their deformation process and load-carrying performance under cyclic loading by conducting quasi-static compression tests and displacement-controlled cyclic loading and unloading tests. On this basis, influences of the cyclic loading on the energy-absorbing performance of honeycombs were revealed. It is shown that cyclic loading does not change the four-stage characteristics of the displacement-force curve of honeycombs while to some extent influences the load-carrying capacity of honeycombs. Under cyclic loading, the honeycombs have larger plateau force and plateau force efficiency and exhibit better stable load-carrying capacity and uniformity. Moreover, evaluation of the energy-absorbing performance of honeycombs based on the total energy absorption index has some limitations, which takes the energy absorption of structures in each stage into account. In view of this, the effective energy absorption was proposed to accurately evaluate the energy-absorbing performance of honeycombs. It is found that honeycombs exhibit better energy-absorbing performance under cyclic loading. The research achievements provide theoretical support for application of honeycombs in fields including mines and underground spaces.

Experimental and analytical investigations of steel shear buckling-inhibited energy dissipation devices

This study presents the development and cyclic performance assessment of steel buckling-inhibited shear yielding devices (St-BISYDs). These devices consisted of thin steel plates as the main energy dissipating elements and modular built-up restrainers as the buckling inhibition mechanism. St-BISYDs are designed to achieve a shear strain of at least 20% without buckling to maximize the energy dissipation potential by minimizing the heat-affected zone (HAZ) and using the bolted connections. Ten specimens with two geometric configurations, namely, hourglass and rectangular, steel plates were experimentally tested under quasi-static displacement-controlled cyclic loading. The proposed restrainers greatly enhanced the cyclic performance of St-BISYDs and helped the St-BISYDs to reach the target shear strain level without significant strength and stiffness degradation under cyclic loading. An analytical study is conducted to predict the force-deformation characteristics of St-BISYDs. Experimental results of the tested specimens are also compared with other similar energy dissipation devices. Further, nonlinear modeling parameters are proposed for the force-deformation response of St-BISYDs which can be directly used in the design practices.

Steel rigid beam-to-column connections strengthened by buckling-restrained knee braces using round steel core bar dampers

This paper presents an innovative application of buckling-restrained knee braces (BRKBs) for spreading plasticity at the beam ends of rigid moment connections. A slender knee brace configuration consisting of a steel core bar and tube buckling restrainer is proposed. The benefit of adopting a steel bar is that it enables the downsizing of the knee brace connections between braces and beam flanges. The advantages of tube buckling restrainers include relatively simple implementation for ease of construction and reduced weight compared to mortar-filled buckling restrainers. Displacement-controlled cyclic loading tests were conducted to examine the spreading of the plasticity behaviors of rigid moment connections using the proposed BRKBs. Structural performance metrics such as hysteretic behavior, strength capacity under a given loading, and strain distributions at beam flanges were measured and analyzed in detail. Additionally, the optimal parameters for the proposed BRKBs were determined through an extensive numerical study. The results revealed that the optimal parameters of the proposed slender BRKBs significantly improve load-bearing capacity and reduce stress concentrations in the vicinity of the rigid beam-to-column connections. As a result, the plastic region on the beam is spread both inside and outside the knee brace area. Based on the research conducted thus far, it was determined that the proposed BRKB is a viable option for spreading plasticity along beams in rigid beam-to-column connections.

Concrete cone breakout behavior of anchor groups in uncracked concrete under displacement-controlled cyclic tension load

Post-installed anchors can offer a low-invasive and practical solution to connect strengthening elements with the existing reinforced concrete structure in seismic retrofitting applications. Such a connection formed with multiple-anchor groups is faced with several challenges due to high demands and structural or architectural features. In the framework of a performance based design, the displacement and hysteretic behavior is more important than the forces acting on the anchor groups. In this context, the primary aim of this work is to investigate the performance of anchor groups under static and cyclic tension load with emphasis on the behavior of different geometric anchor configurations, concentric loading, eccentric loading, and the behavior of the individual anchors within the group. Tests were conducted on single anchors and anchor groups under static and displacement-controlled cyclic loading. The experimental program, experimental setup are described, and the experimental results are presented and discussed in detail in this paper.

Model pile behavior in calibration chamber under very large number of cycles of axial loading in saturated clay

ABSTRACT The results of a series of displacement-controlled cyclic axial loading tests of model pile in saturated kaolinite clay, carried out in a calibration chamber, are presented. An instrumented pile-probe was used to investigate the evolution of local skin friction and excess pore water pressure during cyclic loading. After a brief description of the experimental setup and the testing procedure, the tests results are presented concerning the response of the probe during installation, initial monotonic axial loading, cyclic loading up to large numbers of cycles (105 cycles) and post-cyclic monotonic axial loading. During cyclic loading, an initial degradation phase of local skin friction followed by a stabilization phase is observed. Generation of excess pore water pressure occurs during the 60 first cycles followed by a dissipation phase. Parametric study showed that, for initial monotonic loadings, maximum tip resistance and local skin friction are proportional to stress level. Furthermore, excess pore water pressure generated during cyclic loading depends both on initial stress level applied to the clay specimen and cyclic displacement amplitude. A peak value of local skin friction resistance has been observed during post-cyclic monotonic loadings.

Experimental investigation of moment resisting frames with perforated shear link

This paper focuses on the application of a new shear link in moment-resisting frames by perforating the web at the mid-span of the beam. Typically, in moment-resisting frames the plastic hinges are formed at the end of the beams adjacent to the beam-column connections. Seismic codes specify a minimum length for the beams that are part of the moment-resisting frames to ensure those beams are flexure-critical, and their plastic hinges are formed at their ends. The use of shear fuse in the mid-span of seismic beams enables the designers to violate the minimum span-to-depth ratio requirement and facilitates the replacement of the damaged parts of the perforated web moment resisting frames subjected to strong ground motions. In this study, a new shear link is proposed in the mid-span of the beam through perforating the web, resulting in a different plastic mechanism in structural beams. Two single-bay perforated web moment resisting frames with a beam span-to-depth ratio less than that required by seismic code provisions are tested. The specimens are subjected to a displacement-controlled cyclic loading. The test results are compared with those of a conventional moment-resisting frame with identical material and geometrical properties. Based on the test results, the new proposed perforated web moment resisting frames provides sufficient strength and stiffness with stable cyclic hysteresis loops. Besides, this frame is proposed in the rehabilitation of existing buildings for its ease of construction and providing shear fuse in the middle of the beam.

Analysis of Cyclic Response of Bucket Foundations Based on Simplified Kinematic Hardening Model

The response of bucket foundations for offshore wind turbines subjected to cyclic loading in saturated clay is explored through three-dimensional finite element numerical analyses. In the analyses, nonlinear cyclic hysteretic behavior of clay under undrained condition is modeled through a simple kinematic hardening constitutive model embedded in ABAQUS. The finite element model is validated against published in situ tests of bucket foundations under quasistatic cyclic loading in Bothkennar clay. The computed results agreed generally with those from in situ tests. The behavior of bucket foundations with different aspect ratios under displacement-controlled cyclic loading mode is investigated. Then, the evolution of foundation displacement with increasing number of cycles is studied subjected to wind and wave combined loading. The results show that, for the cycles of low-amplitude rotation, dimensionless moment-rotation curve is approximately elastic; however, the curve engenders obvious hysteresis loop, whose shape is influenced by soil-sidewall interface condition, during high-amplitude cycles. Under thousands of loading cycles, for bucket foundations of low aspect ratio, the oscillatory displacement component is smaller; however, the residual component will accumulate gradually until the serviceability rotation is exceeded. For foundations of high aspect ratio, the oscillatory component is relatively larger, but the accumulation rate of residual displacement decreases gradually.

One-period stability analysis of polygonal sweeping processes with application to an elastoplastic model

We offer a finite-time stability result for Moreau sweeping processes on the plane with periodically moving polyhedron. The result is used to establish the convergence of stress evolution of a simple network of elastoplastic springs to a unique cyclic response in just one cycle of the external displacement-controlled cyclic loading. The paper concludes with an example showing that smoothing the vertices of the polyhedron makes finite-time stability impossible.

Evaluation of local friction and pore-water pressure evolution along instrumented probes in saturated clay for large numbers of cycles

To investigate local friction mobilization along piles subjected to cyclic axial loadings, a calibration chamber experiment is presented based on the implementation of instrumented probes in specimens of saturated clay. Typical results obtained with a piezo-probe are presented, allowing not only tip resistance and local friction to be measured, but also the local pore-water pressure developed on the probe shaft. In addition, specific piezometers installed in the clay specimen allow a good picture to be obtained of the pore-water pressure field around the probe during installation and loading. After installation of the probe, a succession of monotonic and cyclic displacement-controlled loading phases is applied. Upon displacement-controlled cyclic loading of the piezo-probe up to a very large number of cycles (105 cycles), an initial degradation of local friction is observed followed by a subsequent reinforcement, which continues until the end of the cyclic sequence. The friction evolution is related to the evolution of the pore-water pressure measured during cyclic loading. In particular, the influence of the cyclic loading sequence on the post-cyclic static friction resistance is evaluated. A comparison is finally made with the results obtained with another type of probe, showing a good consistency between both types of results.

Investigation on seismic behavior of bridge piers with thin-walled rectangular hollow section using quasi-static cyclic tests

This study aims to investigate the seismic behavior of thin-walled rectangular hollow reinforced concrete (RC) bridge piers through quasi-static cyclic tests. For this purpose, two identical 1:12 scale specimens were designed and tested under different loading protocols. One specimen was subjected to displacement-controlled cyclic lateral loading with a constant axial load, and the other to the same lateral loading history, but with a variable axial load. The behavior of both specimens was evaluated in terms of the damage progression and failure mode, concrete crack width, hysteretic response, backbone curve, and residual displacement. The results revealed that both specimens experienced a mixed flexure-shear damage progression from the first crack through collapse. Flexural cracks were first observed in the flange surfaces, followed by the development of shear diagonal cracks in both web surfaces. Meanwhile, both specimens exhibited stable hysteretic behavior. Then, concrete spalling and longitudinal bar buckling were concentrated at the corners of the flanges due to the shear lag effect. Eventually, both specimens collapsed as a result of the flange local compression buckling. In addition, the specimen under a variable axial load collapsed much severer than the one under a constant axial load. Ultimate drifts of the specimens under a constant or variable axial load were 2.25% and 2%, respectively. This experiment provides valuable dataset for validating advanced numerical modeling techniques for thin-walled rectangular hollow RC piers, especially the data points in the collapse stage.

Influence Mechanism of Steel Diagonal Braces on Mechanical Behavior of Steel Truss-RC Tubular Column Hybrid Structure

ABSTRACT This paper aims to investigate the influences of steel diagonal braces (SDB) on the deformation performance and seismic behavior of steel truss-RC tubular column hybrid structures. Firstly, the vertical deformation performance of the structures with and without SDB was compared through finite element analysis. Then, pseudo-dynamic tests were carried out to investigate the seismic behavior of a 1/8-scaled substructure with SDB, and hysteretic curves were obtained by applying a subsequent displacement-controlled cyclic loading. The test results indicated that adding SDB is an effective approach to decrease the deflections of steel truss and enables to improve the lateral stiffness and lateral bearing capacity of the steel truss-RC tubular column hybrid structure. In addition, numerical modeling of the specimen with SDB was built on the basis of the refined finite element program. The comparisons between the finite element analysis and test results indicated that the FE modeling approach is reasonable to predict the seismic behavior of this type of hybrid structure.

A Review on Pull out Test on Exterior Beam-Column joint

Conventional concrete loses its tensile resistance after the formation of multiple cracks. However, fibrous concrete can sustain a portion of its resistance following cracking to resist more loading. Use of the headed bar can offer a potential solution for these problems and may also ease fabrication, construction, and concrete placement. There have been many catastrophic failures reported in the past earthquakes, with Turkey and Taiwan earthquakes occurred in 1999, which have been attributed to beam–column joint failures. To achieve this performance level, special steel reinforcement details are required in the beam–column joint region of reinforced concrete framed structures. The experimental work carried out on four different arrangements of reinforcement of beam column joints. The aim of the research is to investigate the pull-out behavior such as strength, failure mode, and crack patterns of different arrangements of reinforcement in exterior beam column junctions. The transverse reinforcement of a joint reduces stresses by improving the confinement of concrete. All joints were tested by using reversed cyclic loading. In the first arrangement, the beam bars are extended in the column for distance Ld + (10xDia) from the inner face of column. This research studies the experimental behavior of full-scale beam-column space (three-dimensional) joints under displacement-controlled cyclic loading. Eleven joint specimens, included a traditionally reinforced one (without adequate shear reinforcement), a reference one with sufficient shear reinforcement according to ACI 318, and nine specimens retrofitted by ferrocement layers, were experimentally tested to evaluate a retrofit technique for strengthening shear deficient beam column joints.

Strengthening of seismically deficient exterior beam-column connections using embedded steel bars

Several techniques for improving performance of reinforced concrete (RC) beam-column (BC) connections have been developed in last two decades, but these techniques have been criticized for being labourintensive and susceptible to premature de-bonding. To overcome these shortcomings, a novel technique utilising embedded steel bars has been developed in this study for strengthening seismically deficient RC BC connections. This technique involves drilling holes within the joint core. After the drilled holes are cleaned, they are partially filled with epoxy. Finally, steel bars are inserted in the epoxy-filled holes. Two exterior BC connections were constructed and loaded under displacement-controlled cyclic loading. The first specimen was a control specimen designed in accordance with the pre-1970s building codes to represent BC connections requiring strengthening. The second specimen was strengthened with eight 8 mm steel bars embedded within the concrete core in the joint area and epoxied to maintain the bond between the concrete and the steel bars. The strengthened specimen had superior performance compared to that of the control specimen in terms of joint shear stress, normalised principal tensile stress demand and stiffness degradation. The results show that shear stress of the joint was enhanced by about 8% whereas the enhancement in the principal tensile stress demand was 24% compared to that of the control specimen. The results showed that the proposed technique is capable in upgrading the seismic performance of seismically deficient RC BC connections.

Experimental behavior of full-scale exterior beam-column space joints retrofitted by ferrocement layers under cyclic loading

A majority of the traditional reinforced concrete frame buildings, existing across the Middle East, lack adequate confinement in beam-column joints, or in other words, are shear deficient because they were constructed before the introduction of seismic codes for construction. This research studies the experimental behavior of full-scale beam-column space (three-dimensional) joints under displacement-controlled cyclic loading. Eleven joint specimens, included a traditionally reinforced one (without adequate shear reinforcement), a reference one with sufficient shear reinforcement according to ACI 318, and nine specimens retrofitted by ferrocement layers, were experimentally tested to evaluate a retrofit technique for strengthening shear deficient beam column joints. The studied variables were the number of layers, orientation angle of expanded wire mesh per layer, and presence of steel angles in the corners of joint specimen prior to wrapping with ferrocement layers. The experimental results showed that proper shear reinforcement for the test joints, according to ACI 318, enhanced the behavior of the specimen over that of the traditionally reinforced specimens without adequate shear reinforcement. The joints retrofitted by ferrocement layers showed higher ultimate capacity, higher ultimate displacement prior to failure (better ductility), and they did not suffer heavily damage as observed for the traditionally reinforced one. Increasing the number of ferrocement layers for retrofitted specimens led to improving performance for such specimens compared to the traditionally reinforced ones in terms of enhancing the ultimate capacity and ultimate displacement. Specimens retrofitted by ferrocement layers reinforced by expanded wire mesh of 60° orientation angle showed slightly better performance than those of 45° orientation angles. Retrofitting using steel angles in addition to ferrocement layers improves the seismic performance of the specimens, achieves better stability for stiffness degradation, attains higher capacity of the dissipated energy, and reduces the vulnerability of joints to excessive damage. Based on the experimental work in this study, it is recommended to retrofit beam-column joint specimens by two ferrocement layers in addition to steel angles as stiffeners taking the orientation angle of expanded wire mesh into consideration.

Optimum engineered infilled frames and the influence of openings

An engineered infilled structural building frame with adjustable strength is proposed. The infill wall has a frictional sliding fuse at mid-height, which can be regulated for a certain sliding strength. Previous experimental and analytical studies have shown that greater fuse strength leads to higher strength but lower ductility for the infilled frame. This paper discusses optimising the fused infill panel. The modification factors and expected strengths of infills with different fuse strengths were calculated and compared. To complement the study on fused infill panels, the influences of an opening were investigated experimentally. Two one-third scale single-storey single-bay concrete infilled steel frames having a frictional sliding fuse were tested by displacement-controlled cyclic loading. The specimen with a door opening at the centre was compared with the specimen with solid infill.

Study on size effect of RC and rehabilitated exterior beam-column connections under cyclic loading

Beam-column connection is one of the vital structural parts, whose behaviour during earthquake is very critical. An experimental programme was undertaken by considering three types of exterior RC beam-column connections with three different sizes of geometrically similar specimens in each type. The specimens were tested under displacement-controlled cyclic loading. Depending on the level of damages, rehabilitation strategies were applied appropriately. The studies were repeated for all the rehabilitated specimens and observed that the rehabilitated specimens could successfully restore their load-carrying capacity. Further, the experimental results from specimens of different sizes revealed the existence of a significant size effect, which could approximately be described by the size effect law previously proposed by Bažant. The size effect was further observed to be more prominent with the increase in brittleness of specimens. Energy dissipation per unit volume (eN) of the D-region was also correlated with drift angle for different specimen sizes. The variation of ultimate stress with relative deflection was also studied. The nominal principal tensile stresses were evaluated at the beam-column connections for all the specimens. It was observed that eN as well as variation of stress with relative deflection and magnitudes of nominal principal tensile stresses also exhibited the existence of size effect.