Reverse Cyclic Loading Research Articles

Seismic behavior and restoring force model of GFRP-RC beam-column interior joints

In this paper, the beams-column interior joint in the concrete frame structure was taken as the main research object. First, four joints reinforced with GFRP (glass fiber reinforced plastic) bars were used to analyze the influences of reinforcement ratios under reversal cyclic loading. Then, the failure mechanism of the joints with GFRP bars was analyzed based on the damage of concrete and the bars. Finally, the corresponding restoring force model was proposed to show the bearing capacity and deformation characteristics of joints. The results show that the seismic behaviors of the GFRP-RC (glass FRP reinforced concrete) joints are good due to the high drift ratio, which can reach to about 6%. The energy dissipation of the joints mainly comes from the compression damage of the concrete. Compared with steel reinforced concrete, the high ultimate drift rate increases the range of concrete involved in energy consumption, which makes up for low energy consumption of GFRP bars. The stiffness degradation of the skeleton curve is related with the damage of concrete and the surface damage of the reinforcement. Besides, the damage of the bars was concentrated on the surface of the rib marks. The four-stage hysteretic model proposed in this paper can better reflect the seismic behaviors of joints. This study aims to provide research basis for the researches of GFRP-RC structures from the component level to the structural level.

Experimental Evaluation of Steel Bracings and Metallic Yield Damper as Retrofit Techniques for Severely Damaged RC Building Frames

ABSTRACT The concentrically placed hollow circular steel bracings and hybrid metallic yield dampers as structural retrofitting techniques for severely damaged reinforced concrete (RC) portal frames are evaluated under reverse-cyclic load conditions. In addition, the efficiency of a specially designed coupler-box assembly to retrofit severely damaged columns of the model frame by reconnecting the buckled or ruptured longitudinal reinforcing bars at the plastic hinge locations is evaluated under similar load conditions. Competency of the proposed techniques is assessed by comparing the hysteresis behavior, performance index parameters, and failure mechanism of the retrofitted frames with the native-tested conventional bare frame. The lateral load and deformation capacities are significantly enhanced in the retrofitted frames with a comprehensive increase of 2.0 times in the braced frame and 2.5 times in the damper-equipped frame compared to the conventional bare frame. A stable and symmetric post-yield behavior is noticed in the retrofitted frames until a lateral drift of 3.5% and 6% in braced and damper-fit frames, respectively, which is even higher than the collapse prevention drift level specified in FEMA codal guidelines.

Predicting the Influence of Shear on the Seismic Response of Bridge Columns

In the seismic design and evaluation of bridges, a method is required for determining the shear strength of reinforced concrete columns to avoid brittle shear failures. In addition, detailed design and evaluation often require predictions of the complete hysteretic response of bridge columns to accurately model the nonlinear dynamic response of the bridge. Predictions of the shear strength of columns using the provisions of the AASHTO Specifications are compared with the reversed-cyclic loading test results of shear-critical columns. It is found that the Simplified Procedure results in very conservative predictions of the seismic shear strength. The General Procedure provides conservative and more accurate predictions of the seismic shear strength. It is suggested that the AASHTO reduction factor on the concrete contribution resisting shear for low compressive axial load levels be removed. Nonlinear finite element analysis predictions are made for a selection of rectangular and circular columns tested in reversed-cyclic loading and are compared with the experimental results. The ability of nonlinear finite element analysis to predict the reversed-cyclic loading responses of columns with a wide range of variables and having different failure modes is demonstrated.

Comparison of the simulated seismic behavior of small- and large-scale cripple walls: PEER-CEA Project test programs

As part of the Pacific Earthquake Engineering Research Center (PEER)-California Earthquake Authority (CEA) project, experimental programs were performed at UC San Diego and UC Berkeley, with the former focusing on small-component testing and the latter focusing on large-component testing. During the small-component testing program, a suite of 28 cripple wall-only specimens was tested under quasi-static reverse cyclic lateral loading with variations in exterior finishes, retrofit condition, cripple wall height, anchorage condition, boundary conditions, vertical load, and loading protocol. In the large-component testing program, cripple wall-first story specimens, load path connections, and combined materials in occupied stories were tested. The more easily performed small-component specimens facilitate comparison with the large-component specimens to allow the assessment of their potential to emulate large-scale specimen behavior, with a particular interest in cross-comparing their global hysteresis and physical damage evolution. This cross-comparison among small- and large-scale specimen test results is intended to offer best practices for the future design of cripple wall seismic retrofits in residential housing, with a particular interest in: (1) supporting the realistic design of small-component specimens that may capture the response of large-component specimens and (2) to qualitatively determine where the small-component tests fall in the range of lower- to upper-bound estimation of strength and deformation capacity for the purposes of numerical modeling. Data from both test programs were utilized in the PEER-CEA project to assist with validating numerical modeling tools, which in turn were used to generate seismic loss models capable of quantifying the reduction of loss achieved by applying state-of-practice retrofit methods as identified in FEMA P-1100 Vulnerability-Base Seismic Assessment and Retrofit of One- and Two-Family Dwellings. The objective of this article is to present an overview of the small- and large-component testing programs and key results pertaining to exterior finishes, boundary conditions, the FEMA P-1100 retrofit, and cripple wall height.

Experimental investigation of lateral resistance of CFS walls with rigid diagonal bracings

In this study, monotonic and reversed-cyclic loading tests were conducted on six diagonally reinforced cold-formed steel (CFS) shear walls sheathed with a gypsum board (GYP) and a magnesium crystal board (MCB), respectively, to evaluate the effects of sheathing panels and different types of diagonal bracings on the shear capacity, lateral stiffness, ductility, and energy dissipation capacity of CFS shear walls. The results revealed that the stiffness of the skeleton, the sheathing material, the performance of the screw connections, and the construction of the splice of the wall panels have a distinct effect on the shear performance of the wall. The cooperative work effect of the rigid and strap bracings was excellent, and the ultimate strength and lateral stiffness of the wall were effectively improved by using an extra steel strap bracing. The shear performance of the wall sheathed with the MCB was higher than that of the wall sheathed with the GYP. When a flat steel strap was used to connect the panel splices, the torsion of the flat steel strap reduced the overall performance of the wall panels. This should be considered in practical engineering applications.

Seismic behavior of steel-sheathed cold-formed steel shear walls with reinforced end columns

In this study, we investigated six full-scale, steel-sheathed, cold-formed steel shear walls (CFS-SWs), three of which were CFS-SWs with reinforced end columns (CFS-SW-Rs), under reversed-cyclic loading and analyzed their damage modes and mechanical properties. Tests were conducted to compare the seismic performance between the CFS-SWs and CFS-SW-Rs and investigate the effects of the horizontal steel bands and aspect ratio on the seismic behavior of the CFS-SWs, and the effects of the thickness of the steel plates, and the aspect ratio on the seismic behavior of CFS-SW-R. According to the results, CFS-SW-Rs exhibited better seismic performance than CFS-SWs. Specifically, the CFS-SW-R benefited from the high strength and stiffness of the square steel tube end columns that could effectively restrain the thin steel plate, such that the tension band formed by the thin steel plate could be fully expanded. In addition, the shear capacity of CFS-SWs was improved by increasing the number of horizontal steel bands and the aspect ratio, the shear capacity of CFS-SW-Rs was also improved by increasing the aspect ratio and thickness of the sheathing plate.

Seismic behavior of RC columns strengthened with near-surface-mounted aluminum alloy bars and CFRP wraps

This paper proposed a near-surface-mounted (NSM) strengthening technique by using aluminum alloy (AA) bars and carbon fiber-reinforced polymer (CFRP) wraps to improve the seismic behavior of square reinforced concrete (RC) columns. Eight strengthened concrete columns with square cross sections of 250 mm × 250 mm and 1600 mm shear span were tested under axial compression and reversal cyclic loading to investigate the effects of NSM reinforcement ratios (0.36–1.29%), layers of CFRP wraps (0 and 3), and axial compression ratios (0.1 and 0.4) on the seismic behavior. The failure mode, hysteretic response, load-bearing capacity, ductility, stiffness degradation, and energy dissipation capacity of those column specimens were analyzed. Results indicated that the lateral load-bearing capacity, stiffness, and cumulative energy dissipation capacity increased with the increase of the NSM reinforcement ratio. The CFRP wraps in the NSM technique can provide hoop confinement to avoid the buckling failure of NSM AA bars, and improve the seismic behavior by mitigating spalling of concrete. When increasing the axial compression ratio from 0.1 to 0.4, the lateral load-bearing capacity and cumulative energy dissipation capacity increased significantly, while the stiffness degradation became obvious. In addition, three-dimensional (3D) finite element (FE) models were developed and verified by comparisons in the deformation and lateral loads at characteristic points, as well as the strain distribution along NSM AA bars. The verified FE models can be used to analyze the damage of concrete and the stress distribution at the interface between epoxy and concrete.

Performance of a prestressed efficiently prefabricated beam-column connection.

Analyzing the seismic performance and flexural capacity of beam-column joints is crucial in structural design phase. The purpose of this paper is to investigate the seismic performance and flexural capacity of precast prestressed efficiently fabricated frame (PPEFF) joints. Reverse cyclic load tests and flexural capacity analysis are conducted. The damage modes, hysteresis curves, skeleton curves, stiffness degradation, ductility, and energy dissipation capacity of five PPEFF joint specimens with different reinforcement rates of the energy-dissipating bars and shear reinforcement are obtained. The results show that the damage pattern of the specimen is ideal, i.e., the plastic hinge region at the end of the beam is severely damaged, whereas the remainder of the beam is slightly damaged. Increasing the reinforcement rate of the energy-consuming steel bars enhances the load capacity, energy dissipation capacity, and initial stiffness of the joint but reduces the ductility performance. The maximum change in ductility was 5.31 for the reinforcement rate of energy-consuming steel bars ranging from 0.38% to 0.59%. In addition, the flexural capacity of the PPEFF joint is evaluated, considering the influence of the shear steel on the yielding and ultimate states. An equation of the flexural capacity is derived. A good agreement is observed between the experimental and calculation results, verifying the correctness of the proposed flexural capacity equation.

Seismic performance evaluation of unconfined dry stacked block masonry structure

Dry stacked block masonry is getting popularity and has auspicious future both in developed and developing countries. In this research work, it was aimed to appraise the seismic performance of unconfined dry stacked block masonry structure built with Hydraform blocks. The experimental work included the construction of a full-scale typical building and testing by using quasi-static reverse cyclic loading. The seismic parameters and behavior studied in this research work, include the force–deformation relationship, ultimate ductility factor, response modification factor, displacement amplification factor, energy dissipation, stiffness degradation, and structural performance levels. The visual assessment and analyses of the test data was scrutinized to construe and elucidate the damage patterns, and local and global behavior of the structure. Based on the results, the unconfined dry stacked block masonry structures can easily withstand against low to moderate seismic actions. The tolerance of self-interlocking blocks, in sliding and rotation in out-of-plane direction, enables it to act as energy dissipating devices and mitigates the chances of brittle shear failure.

Experimental seismic performance evaluation of brick masonry cavity-wall buildings

A full-scale single room cavity-wall brick masonry structure is tested under quasi-static reverse cyclic loading to evaluate its seismic behavior at the Earthquake Engineering Center, University of Engineering and Technology in Peshawar, Pakistan. The materials and techniques used in the specimen are typical of those found in the northern areas of Pakistan affected by the Kashmir earthquake of 2005. The results are presented in the form of force-deformation hysteresis loops and envelope curves. The three performance levels, namely immediate occupancy (IO), life safety (LS), and collapse prevention (CP) have been established. They correspond to story drift levels of 0.031%, 0.448%, and 0.600% respectively. Careful observation of the damage mechanism revealed the structure behaved predominantly in a flexure rocking mode.

Behaviour of Hybrid Fibre-Reinforced Ternary Blend Geopolymer Concrete Beam-Column Joints under Reverse Cyclic Loading.

Beam–column joints are extremely vulnerable to lateral and vertical loads in reinforced concrete (RC) structures. This insufficiency in joint performance can lead to the failure of the whole structure in the event of unforeseen seismic and wind loads. This experimental work was conducted to study the behaviour of ternary blend geopolymer concrete (TGPC) beam-column joints with the addition of hybrid fibres, viz., steel and polypropylene fibres, under reverse cyclic loads. Nine RC beam-column joints were prepared and tested under reverse cyclic loading to recreate the conditions during an earthquake. M55 grade TGPC was designed and used in this present study. The primary parameters studied in this experimental investigation were the volume fractions of steel fibres (0.5% and 1.0%) and polypropylene fibres, viz., 0.1 to 0.25%, with an increment of 0.05%. In this study, the properties of hybrid fibre-reinforced ternary blend geopolymer concrete (HTGPC) beam-column joints, such as their ductility, energy absorption capacity, initial crack load and peak load carrying capacity, were investigated. The test results imply that the hybridisation of fibres effectively enhances the joint performance of TGPC. Also, an effort was made to compare the shear strength of HTGPC beam-column connections with existing equations from the literature. As the available models did not match the actual test results, a method was performed to obtain the shear strength of HTGPC beam-column connections. The developed equation was found to compare convincingly with the experimental test results.

Glass-box model representation of seismic failure mode prediction for conventional reinforced concrete shear walls

The recent surge in earthquake engineering is the use of machine learning methods to develop predictive models for structural behavior. Complex black-box models are typically used for decision-making to achieve high accuracy; however, as important as high accuracy, it is essential for engineers to understand how the model makes the decision and verify that the model is physically meaningful. With this motivation, this study proposes a glass-box (interpretable) classification model to predict the seismic failure mode of conventional reinforced concrete shear (structural) walls. Reported experimental damage information of 176 conventional shear walls tested under reverse cyclic loading was designated as class types, whereas key design properties (e.g., compressive strength of concrete, axial load ratio, and web reinforcement ratio) of shear walls were used as the basic classification features. The trade-off between model complexity and model interpretability was discussed using eight Machine Learning (ML) methods. The results showed that the decision tree (DT) method was a more convenient classifier with higher interpretability with a higher classification accuracy than its counterparts. Also, to enhance the practicality of the model, a feature reduction was conducted to reduce the complexity of the proposed classifier with higher classification performance, and the most relevant features were identified, namely compressive strength of concrete, wall aspect ratio, transverse boundary, and web reinforcement ratio. The ability of the final DT model to predict the failure modes was validated with a classification rate of around 90%. The proposed model aims to provide engineers interpretable, robust, and rapid predictions in seismic performance assessment.

Experimental research and finite element analysis on seismic behavior of square reinforced concrete columns with four interlocking spirals

The seismic performance of square reinforced concrete columns confined by an innovative transverse reinforcement configuration composed of four interlocking spirals and outer square stirrups were investigated experimentally and numerically. Five composite specimens were tested under quasi-static reverse cyclic loading. The experimental results indicated that compared with conventional single spiral reinforced square composite column (SSRSCC) the newly developed interlocking multi-spiral reinforced square composite column (IMSRSCC) even with a slightly lower volumetric confinement ratio exhibited superior seismic performance in ultimate bearing capacity, energy dissipation and delaying the degradation of strength and stiffness. Moreover, a detailed three-dimensional finite element model considering the bond-slip behavior between concrete and steel reinforcement was developed and validated through a comparison with experimental results. The stress development and confining mechanism of transverse reinforcement of IMSRSCC was explored and the effects of the main design parameters on the seismic performance of IMSRSCC were also discussed through parametric studies.

Retrofit of External Beam-Column Concrete Joints with Diagonally Crossed Reinforcement: Experimental and Analytical Investigations

AbstractExperimental research was carried out regarding the flexural behavior under cyclic reversal loading of six full-scale external beam-column concrete joints cast with plain concrete in the pr...

PERFORMANCE OF RCC FRAME WITH SPECIAL CONFINING REINFORCEMENT ON SLOPE

Earthquake is a natural disaster that occurs when the Earth's crust moves suddenly. Every year, hundreds of earthquakes strike various parts of the globe. According to previous research, buildings that are built on sloped terrain are the most susceptible to earthquakes. This is attributable to the different heights of the columns on the ground floor. By changing the height of the column at the base of a 2-D Conventional RCC Frame and a Special Confined RCC Frame, an experimental investigation was carried out in this study. The parameters like load verses deflection, crack width and stiffness degradation was used to draw comparison between the Conventional RCC Frame and Special confined RCC Frame under Reverse Cyclic Loading by using Push and Pull Jack. Hysteresis curve clearly shows that Special Confining reinforcement provided for the column throughout the span because of columns with varying stiffness provides additional strength and performance against lateral force by dissipating energy. The ductility of Short column improved at initial stage, meanwhile the displacement of the Special confined RCC frame with short column also improved due to ductile reinforcement which leads to reduction in failure rate and arrest the sudden failure of the short columns in the frame as that is physically visible from the crack pattern.

Experimental investigation of initially damaged beam column joint retrofitted with reinforced UHP-HFRC overlay

The present experimental study investigates the effectiveness of ultra-high-performance hybrid fiber reinforced concrete (UHP-HFRC) overlay for retrofitting the initially damaged reinforced concrete beam column joint (BCJ). Eight control BCJ specimens are tested under quasi static reverse cyclic loading. The ‘Park and Ang’ damage indices are calculated for four distinct damage states, i.e., complete, severe, moderate and slight from the load displacement curve of the control specimen. Each set of specimens were subjected to reverse cyclic loading to achieve their respective damage states. Each damaged specimen is then retrofitted using the wire mesh as reinforcement in the UHP-HFRC overlay. The retrofitted specimens using reinforced UHP-HFRC overlay exhibited the improvement in the load-carrying capacity, ductility, drift capacity, energy dissipation, equivalent viscosity damping, stiffness retention at higher drift, and lower strength degradation for a given damage level. However, the performance of the retrofitted BCJ specimens significantly depends upon the initial damage state of the BCJ. The improvement in the performance of the retrofitted specimen gradually decreases as the initial damage state of BCJ shifted from slight to complete; nevertheless, the performance of all the retrofitted samples is better than the controlled specimen.

Influence of the Loading Protocol and Loading Rate on the Characteristics of Timber Nail Joints

Nail joints are one of the key components that control the lateral performance of light wood frame shear walls. In previous experimental studies, researchers have used different loading rates, which failed specimens from less than a minute to more than an hour, to study the characteristics of nail joints. Moreover, there have been different loading protocols used for testing of timber nail joints or shear walls. Although some efforts have been made to address this subject, it is still unclear how the loading protocol and loading rate may influence the performance of nail joints. In this study, a total of 96 nail joints tests were carried out under monotonic and reversed-cyclic loads at three different loading rates, and under three different loading protocols (ISO, CUREE and SPD). The results of the test revealed that the loading rate did not have a noticeable effect on the mechanical properties of nail joints, while the loading protocol did influence those properties. Especially, protocols with larger cumulative damage demands lead to lower ultimate displacement and ductility of nail joints.

Reverse Cyclic Loading Effect on RCC Wall‐Floor Slab‐Deep Beam Connection

High‐rise structures are more vulnerable when subjected to lateral loading. Generally, the shear walls function as the main lateral load resistant system in high‐rise structures. In the case of high‐rise structures with an open ground story, the shear wall‐floor slab‐deep beam acts together as a rigid jointed frame connection to withstand gravity and lateral force induced by external loadings like earthquakes and wind. The wall‐floor slab‐deep beam connection will be subjected to a higher concentration of stresses, which is a more vulnerable area in any high‐rise structure. Hence, it is necessary to design this connection with more ductility. This article presents the experimental investigations carried out to study the behavior of three different reinforcement detailing in RCC wall‐floor slab‐deep beam connections, such as (1) 90° bend up bars connection as per Indian Standard Code (Conventional connection), (2) U‐hooks connecting the core region as per Euro code 2, and (3) proposed U‐hooks with additional reinforcement in the core region transverse to the beam orientation. The additional reinforcement is provided at a distance of 50 mm from the face of the shear wall. The parameters considered for this study are load‐carrying capacity, energy dissipation, ductility, and stiffness. The results were then compared with that of the conventional connection. It was found that the proposed U‐hook with additional reinforcement performed better than that of the conventional connection and type 2 connection.

The RC samples with infill walls strengthened with steel truss wires

Infilled walls are frequently used to create interior spaces in the reinforced concrete (RC) buildings and to provide heat and sound insulation. However, under earthquake loads, the infill walls resist the load and displacement demands that occur in and out-of-plane. Severe damages of masonry infill walls in many the reinforced concrete frames have been observed after the 2011 Turkey/Van-Ercis earthquake. It is aimed to strengthen the horizontal and vertical joints of the infill walls in order to increase the contribution of the infill wall to RC frame and to restrict the out-of-plane movement of the walls caused by the earthquake in the buildings. In this study, five RC frames used in the experimental works have been produced with various structural defects, 1/5 scale, two-story and one-bay. Two of these RC frames were filled with autoclaved aerated concrete blocks and brick wall. Other two samples were strengthened by adding truss elements to horizontal joints of infill walls. In order to determine the seismic contribution of these strengthening works, reference sample was tested as bare frame. All test samples were tested under reverse cyclic lateral loading and constant vertical loading. For the strengthened and non-strengthened samples with infill walls, the main damage occurred in the infill walls of the 1st storey at the experimental study. As a result, the sample with strengthened infill brick wall, and autoclaved aerated concrete block wall showed a significant increase in the lateral load-carrying capacities, initial stiffness, and the cumulative energy consumption capacity at the end of test.

Seismic Performance of a Full-Scale Precast Concrete L-Shaped Column Frame Structure with a Grouted Connection

Precast concrete frame structure with nonrectangular columns are becoming attractive to researchers and engineers owing to advantages such as avoiding column protrusion from walls and saving space. This paper presents the experimental investigation of a full-scale precast concrete frame structure with L-shaped columns (PCFS) subjected to reverse cyclic loading. The precast connection adopted grouted anchor connection. As a comparison and benchmark, one full-scale monolithic sample (RCFS) was also tested. The results indicates that the greater steel ratio in the grouted anchor connection region leads to a high local stiffness of the elements, which contributed to delaying occurrence of the first crack at the grouting holes. The failure mode, lateral load capacity, stiffness degradation, load-carrying capacity degradation, energy-dissipating capacity, ductility and interlayer residual deformation were compared between two specimens. PCFS specimen exhibited comparatively better hysteretic behavior, energy-dissipating capacity, residual deformation-resisting capacity and ductility. For RCFS and PCFS specimens, the peak load difference was within 7%. About 15% increases in ductility were observed for PCFS specimen compared with RCFS specimen. The test results would provide reference for the application of the precast concrete structure with nonrectangular columns in the new residential buildings.