Displacement Ductility Factor Research Articles

Experimental and numerical investigation of the cyclic behaviour of coupled balloon-type CLT shear walls with high-capacity base connections

Mass timber buildings have gained global popularity due to the increasing availability and affordability of mass timber products and an increasing awareness of the sustainability of timber construction. This paper presents an experimental and numerical study on coupled balloon-type cross-laminated timber (CLT) shear walls with the aim of overcoming the capacity limitations of platform CLT shear walls. Using self-tapping screws to create innovative hold-down solutions, three two-storey coupled CLT shear walls were cyclically tested and the results demonstrated that the proposed coupled wall systems could achieve significantly higher lateral strength (over 400 kN) and initial stiffness (up to 14 kN/mm) compared to platform CLT shear walls in literature. The cyclic test results were used to validate a finite element CLT shear wall model in CLTWALL2D. The calibrated model was then used to run a parametric study of a series of balloon-type CLT shear walls up to twelve storeys (42 m) in height. This study provided evidence that coupled balloon-type CLT shear walls with high-capacity screwed connections have the potential of reaching high strength and stiffness with the displacement ductility factor μ = 2–4.

Local scour effects on seismic behavior of pile-group foundations in cohesionless soils: Insights from quasi-static tests

Local scour has been reported as a common phenomenon for pile-group foundations in marine, coastal, and riverine sites, while its effects on the seismic behavior of pile-group foundations are yet to be well documented. This paper reported a pair of quasi-static cyclic loading tests on 2 × 3 scoured pile-group foundation specimens, one in global scour and the other in local scour, to understand the influence of local scour on the seismic behavior, particularly in terms of soil-pile interaction features and failure mechanisms. Test results indicate a flexural failure mode for both specimens. Local scour does not change the order of limit states but postpones the occurrence of concrete cover cracking and rebar yielding due to the reduced lateral stiffness of the locally scoured piles. Moreover, local scour rarely changes the aboveground damage regions at the top of outer piles (one time the side length of squared pile section, D), but significantly aggravates and deepens the underground damage regions at outer piles (from 4 ∼ 5D for global scour to 3.7 ∼ 6D for local scour). Besides, local scour reduces the displacement ductility factor from 2.50 to 1.25 for the Easy-to-Repair limit state, resulting in adverse impacts on pile-group foundations in general.

Seismic performance evaluation of plastered cellular lightweight concrete (CLC) block masonry walls

The current research presents a novel and sustainable load-bearing system utilizing cellular lightweight concrete block masonry walls. These blocks, known for their eco-friendly properties and increasing popularity in the construction industry, have been studied extensively for their physical and mechanical characteristics. However, this study aims to expand upon previous research by examining the seismic performance of these walls in a seismically active region, where cellular lightweight concrete block usage is emerging. The study includes the construction and testing of multiple masonry prisms, wallets, and full-scale walls using a quasi-static reverse cyclic loading protocol. The behavior of the walls is analyzed and compared in terms of various parameters such as force–deformation curve, energy dissipation, stiffness degradation, deformation ductility factor, response modification factor, and seismic performance levels, as well as rocking, in-plane sliding, and out-of-plane movement. The results indicate that the use of confining elements significantly improves the lateral load capacity, elastic stiffness, and displacement ductility factor of the confined masonry wall in comparison to an unreinforced masonry wall by 102%, 66.67%, and 5.3%, respectively. Overall, the study concludes that the inclusion of confining elements enhances the seismic performance of the confined masonry wall under lateral loading.

Strength reduction factor spectra for SDOF systems with structural fuses

Highly ductile replaceable fuses can greatly improve the performance of structures and mitigate seismic damage. A fused structure refers to a dual system that generally includes the primary structural system and the fuses acting in parallel. Few studies have thoroughly investigated the strength reduction factors of dual systems or their nonlinear response behaviors; instead, a restoring force model was adopted to represent the performance of the whole system while ignoring the interactions between the primary structure and fuses. This paper separates the two components and considers their interaction. The behavior of the primary structure and structural fuses is assumed to be similar to elastic-perfect plastic. Two parameters, the yield displacement ratio (α) and the initial stiffness ratio (β), are introduced to describe the relationship between the fuses and the primary structure. Based on a dual system, the dimensionless governing equation of motion is derived. The strength reduction factor spectra with a known displacement ductility factor (μ) are then calculated under two groups of selected ground motions. The influences of α, β, and μ are investigated statistically. The strength reduction factor spectra of the fused structure can be expressed by the four-stage predictive model developed by Newmark and Hall for traditional structures, but the spectral shape and two plateau values are closely related to α, β, and μ. These two plateaus are crucial for the spectral shape of the four-stage model. Finally, a simplified equation is proposed to estimate the strength reduction factors of dual system considering α and β with equivalent μ.

Confinement detailing of concrete encased steel concrete composite columns

Steel concrete composite construction is now gaining popularity in our country. Concrete-encased steel columns have several advantages, but like RC columns, there is a need to ensure adequate concrete confinement so that it has sufficient ductility under seismic loads. This study investigates the confinement of the concrete based on the detailing of the transverse reinforcement. The ductilities of a typical encased section that satisfies the minimum reinforcement criteria and a highly confined section with special detailing are compared. A nonlinear 3D finite element model is developed in ABAQUS for this purpose. The confined stress-strain curve for M30 grade of concrete is carefully incorporated in the special confined section. The interaction between structural steel and concrete is modelled with an 'embedded region' interaction tool available in the ABAQUS library. Based on the eigen mode of the section, the initial geometric imperfection was given. The significant increment in displacement ductility factor, plastic hinge rotation and drift ratio are observed for a special confined encased column. A parametric study has been carried out by varying the parameters; the axial load ratio, steel contribution ratio, steel width to depth ratio and transverse reinforcement spacing. It was observed that structural section aspect ratio (steel width to depth) and transverse reinforcement spacing significantly affect the ductility of the section. The plastic hinge rotation and drift ratios were also calculated for different sections.

Seismic behavior of RC cross-shaped column under combined torsion loading: Experiment and simulation finite element

The seismic behavior of the reinforced concrete (RC) cross-shaped columns under the combined action of compression, bending, shear, and torsion were studied by experiment and numerical simulation. The effects of torsion-bending ratio (T/M) and axial compression ratio (n) on the seismic indexes, i.e., failure modes, skeleton curves, hysteretic curves, strength, ductility and stiffness were studied. Experimental results suggested that the T/M ratio determines the failure modes of RC cross-shaped section columns. Both the damage length and crack angle increase with the raise of the T/M ratio. The displacement ductility factor and elastic–plastic drift ratio are higher than 3.0 and 0.02, respectively, indicating that the RC cross-shaped columns exhibit good ductility and deformation capacity under combined torsion loading conditions. The normalized shear-displacement hysteretic model and the torque-twist angle hysteretic model were established. Based on the experimental results, as well as the finite element model for RC cross-shaped columns under combined torsion, was proposed. The results derived from the hysteretic models and finite element simulation are in good agreement with the experimental results.

Seismic Behavior of Box Steel Bridge Pier with Built-In Energy Dissipation Steel Plates

Based on the design concept of earthquake-resilient structure, a new-type of box-shaped steel piers with embedded energy-dissipating steel plates was proposed. Quasi-static tests of 6 box-shaped steel pier specimens under variable axial pressure and cyclic horizontal loading were carried out. By analyzing the failure mode, load-displacement hysteretic curve, skeleton curve, displacement ductility coefficient, stiffness degradation characteristics, strength degradation coefficient, and cumulative hysteretic energy, the effects of setting energy-dissipating steel plate, axial compression ratio, and thickness of energy dissipation steel plates on the seismic performance of new-type steel piers were discussed. Finite element models of steel bridge piers were established and compared with the test results. The analysis results using FEM agree well with the test results. Results show that the setting of energy-dissipating steel plates can effectively improve the ductility, deformation capacity, and energy-dissipating capacity of box-shaped steel piers, and effectively delay buckling deformation and cracking of wall plates. The steel plate near the bolt hole of the wall plate at the root of the new-type of box-shaped steel piers is easy to crack due to stress concentration, resulting in a rapid reduction of the maximum bearing capacity of the specimens. With the increase of axial compression ratio, the bearing capacity, energy-dissipating capacity, and earthquake-resilient capacity of the specimens increase. The smaller the thickness of the replaceable energy-dissipating steel plates, the smaller the bearing capacity and faster the stiffness degradation of the specimens become, while the ductility and energy-dissipating capacity of the specimens are improved. The axial compression ratio and the thickness of the energy-dissipating steel plate have relatively little effect on the strength degradation of the specimens. In order to facilitate the popularization and application of the new-type steel piers, formulas were also established to calculate the bearing capacity and displacement ductility factor of the new-type of box-shaped steel piers.

Effect of material uncertainty on the performance of bridge's pier-bent cap joints under cyclic loading

The current article deals with an investigational study on the bridge's pier-bent cap assemblies exposed to cyclic loading. In the study, four types of concrete are used—conventional reinforced concrete (CRC), fibre reinforced concrete (FRC), self-compacting concrete (SCC), and fibre reinforced self-compacting concrete (FRSCC)—to investigate the assemblies' behaviour using the concrete materials in the specified structural component. All the bridge element samples (8) are scaled down to one-twenty seventh for experimental purposes and correct performance results. The pier-bent cap subassemblies were exposed to cyclic loading tests to evaluate their crack generation pattern and resistive capability under seismic actions. The results are analysed as hysteresis behaviour, envelope pattern, stiffness behaviour, energy dissipation, and failure pattern. The study's findings are inspiring as the FRSCC outperformed the CRC in all the results along with ultimate strength, displacement ductility factor, and stiffness behaviour with 46%, 71%, and 74% improvements, respectively.

Experimental Study on the Shear Behavior of Reinforced Highly Ductile Fiber-Reinforced Concrete Beams with Stirrups

The aim of this study is to improve the shear behavior of reinforced concrete (RC) beams with stirrups by using highly ductile fiber-reinforced concrete (HDC), which is a fiber-reinforced cement-based composite material with tensile-strain-hardening properties. Twelve reinforced HDC (RHDC) beams and three RC beams with stirrups were tested under a concentrated load. The experimental parameters involved the shear span to effective depth ratio, stirrup ratio, and longitudinal reinforcement ratio. The results revealed that the mode of failure of RHDC beams, which exhibited better ductility than RC beams, included diagonal compression, shear compression, diagonal tension, and flexural shear failure. RHDC beams exhibited stable multiple crack propagation behavior and satisfactory integrity, thus showing that HDC effectively restricted the development of shear cracks and improved the damage resistance of beams. Compared with RC beams, the shear strength, displacement ductility factor, and deflection-clear span ratios corresponding to the peak load and ultimate deflection increased by up to 30.5%, 44.9%, 150.0%, and 148.0%, respectively. RHDC beams exhibited higher residual strength and deformation capacity than RC beams, thus indicating that HDC significantly improved the brittle shear failure mode. Specimens H-1 and H-2 exhibited the largest improvement in shear strength and displacement ductility factor, respectively, compared with RC beams. The shear strength of RHDC beams increased as the shear span to effective depth ratio decreased. For RHDC beams with the same shear span to effective depth ratio, the shear strength increased with the increase in the longitudinal reinforcement ratio and stirrup ratio under shear compression failure.

Experimental Study on Seismic Behavior of PC Walls with Alveolar-Type Horizontal Joint under Pseudo-Static Loading.

There are many horizontal joints on precast concrete (PC) wall panel structures, which certainly has a significant impact on the seismic behavior of structures. This paper proposes a novel alveolar-type horizontal joint, which has advantages of convenient and rapid assembly. Six precast concrete wall specimens with alveolar-type joints were designed and constructed, and they were weakly connected by spliced rebars anchored into grouted sleeves to meet the requirements of structural performance. The pseudo-static loading tests on these specimens were conducted to investigate the effects of influencing factors, such as the axial compression ratio, the thickness of wall (interface contact area), and the addition of a vertical grouted sleeve connection at the horizontal joint, on the seismic performance of PC walls. Analyses and comparisons were conducted in terms of the cracking propagation pattern, failure modes, force–displacement hysteretic curves, skeleton curves, bearing capacity, ductility factors, and energy dissipation of PC walls. It was concluded that the axial compression ratio and adding grouted sleeve connection had a significant influence on the cracking mode of PC walls, whereas the impact of the wall thickness was slight. The shear capacity and energy dissipation capacity of specimen dramatically enhanced by increasing the axial compression ratio or adding grouted sleeve connection. The PC wall exhibits good ductility after adding the vertical grouted sleeve connection at a horizontal joint. However, the ductility factor increases firstly and then decreases in the enhancement of the axial compression ratio. The reduction in wall thickness has remarkable impacts on the shear strength and energy dissipation capacity of specimens, but the influences on ductility were not significant. The prediction method for calculating the shear capacity of PC walls with alveolar-type horizontal joints was proposed based on the experimental data, and these calculated results are in good agreement with the experimental results.

Experimental hysteretic behavior of high strength concrete columns confined by butt-welded closed composite stirrups

Six specimens of high strength concrete columns with butt-welded closed composite stirrups were tested under cyclic lateral loads, to study the structural performance (deformation) and hysteretic characteristics of the columns. The influences of the axial compression ratio and the volume-stirrup ratio were considered. According to the regression analysis of the test results, it was determined that the unloading stiffness and strength degradation rate under repeated loading conditions are mainly dependent on the two parameters of the “displacement ductility factor” and “axial compression ratio”. According to the test results, the skeleton curves were determined by the section layer and the statistical regression analysis methods. By considering the influence of axial compression ratio and the volume-stirrup ratio to the hysteretic characteristics of high strength concrete columns confined by butt-welded closed composite stirrups, the shear force-lateral displacement restoring force model was established. The results show that the axial compression ratio has a great influence on the strength degradation of the columns. As the axial compression ratio increases, the strength degradation of the columns occurs faster. On the other hand, the volume-stirrup ratio has a reverse effect on the strength degradation of the columns, with the increase of the volume-stirrup, the strength degradation of the column is observed gradually and slowly. The stiffness degradation of the columns increases as the axial compression ratio increases while the volume-stirrup ratio decreases.

Experimental and Numerical Investigation of Seismic Performance of UHPC Thin‐Walled Short Piers

Rigid frame bridges with different heights of adjacent piers are inclined to crack the main girder at the pier‐beam connection. This cracking occurs due to a significant difference in thrust stiffness between tall and short piers. This problem can be resolved by applying ultra‐high performance concrete (UHPC) materials. Thus, in the present paper, the seismic performance and failure behavior of UHPC thin‐walled short piers were tested under low‐frequency cyclic loads. Based on previous studies, the test was conducted using a proposed experimental model, where the effects of longitudinal reinforcement ratio, stirrup reinforcement ratio, and axial load ratio were considered. The failure mode, ultimate bearing capacity, stiffness, displacement ductility factor, and other performance parameters were analyzed. It was found that the specimens present the bending‐shear failure mode. Also, the load‐bearing capacity of the UHPC thin‐walled piers was significantly improved by increasing the longitudinal ratio of the thin‐walled short piers, while the contribution of the stirrup ratio was limited. In addition, compared with traditional short piers, the ductility of UHPC thin‐walled short piers increased by 53.36%, and the thrust stiffness decreased by 23.73%, indicating that UHPC thin‐walled short piers have more efficient seismic performance than RC short piers. Note that, in the present paper, UHPC thin‐walled short piers’ internal behavior was also analyzed by establishing a finite element model. The analysis proves that the numerical results are consistent with the experimental data, which is promising to better understand the failure behavior.

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.

Design guideline for extended pile shaft incorporating nonlinear pile-soil interaction

Equivalent fixed-based cantilever approach is commonly used for seismic performance-based design of pile foundations supporting marine and bridge structures. In this method, prior knowledge of parameters such as equivalent length of fixity, depth-to-plastic hinge and equivalent plastic-hinge length is essential for reliable assessment of ductility capacity. Available recommendations for these parameters have resulted in contradicting conclusions due to numerical simplifications and/or experimental limitations. In this study, basic concepts of strain wedge model are employed to provide guidelines for the estimation of the key parameters by incorporating nonlinear behavior of the soil-pile system. A set of dimensionless design charts is produced based on an analytical approach covering a range of practical values of soil and pile properties. Finally, the performance of the proposed analytical model in assessing the local curvature ductility of a bridge system induced by an imposed displacement ductility factor is demonstrated through two examples.

Flexural behavior of hybrid GFRP-reinforced concrete-steel double-skin tubular beams

The hybrid GFRP-concrete-steel double-skin tubular beams (DSTBs) are composed of the outer GFRP tube, the inner steel tube and the sandwich concrete between both tubes. They have attracted the attention of researchers owing to the high ductility, lightweight, corrosion resistance and convenient construction. However, there are few studies on the reinforced DSTBs under bending load compared with the unreinforced DSTBs. Eight circular cross-sectional composite beams are tested in this paper to investigate the flexural behavior, including five reinforced DSTBs, two unreinforced DSTBs and one solid reinforced concrete GFRP tubular beam. The main parameters include the longitudinal steel reinforcement ratio, the inner steel tube diameter, the GFRP tube thickness, and the concrete strength. The results show that all the composite beams exhibit ductile flexural failure, and the average displacement ductility factor of the reinforced DSTBs is 3.85. The arrangement of longitudinal steel bars significantly enhances the bearing capacity and reduces the mid-span deflection of the composite beam, and it is recommended to use a reasonable low steel ratio for the excessive steel reinforcement is adverse to the ductility. Increase of the inner steel tube diameter greatly improves the flexural capacity on premise of ensuring the stiffness and ductility. The outer GFRP tube provides moderate hoop confinement on the compressive concrete in the pure bending members, which limits the increasing extent of the flexural capacity. Reasonable confinement stiffness is suggested for the reinforced DSTBs to avoid insufficient or excessive constraint. Besides, concrete with sufficient compressive strength is recommended to be used in the hybrid DSTBs for it increases both the flexural capacity and the initial stiffness of the beam.

Effective stiffness and period-dependent seismic response modification factors for flexure-dominated fully-grouted reinforced masonry rectangular shear walls

The wall effective elastic stiffness, displacement ductility, and seismic force modification factors are important force-based seismic design (FBD) parameters for reinforced masonry (RM) shear walls. The effective stiffness, ke of reinforced masonry shear walls (RMSW) is crucial in computing the natural period and thus the elastic forces, and essential also in computing the displacements corresponding to the design seismic forces. This study analyzes previously reported test results of forty-three flexure-dominated fully-grouted rectangular RMSWs subjected to quasi-static cyclic load to evaluate the FBD parameters adopted by Canadian and American standards. In this study, based on the experimental results of 43 tested walls, a new stiffness reduction factor is proposed considering the effect of axial stress, vertical reinforcement ratio, and horizontal reinforcement ratio. Moreover, the seismic force modification factors are compared to the Canadian and US codes. The results showed that ductility related reduction factors should be dependent on the wall natural frequency and there is a room to relax the current proposed code values. In addition, incremental dynamic analysis was performed using a simplified numerical model to study the effect of dynamic loading on response modification factors and stiffness characteristics of the walls.

Optimal ductility enhancement of RC framed buildings considering different non-invasive retrofitting techniques

Existing RC framed buildings lack significant ductility, especially when they have been built with pre-code criteria. Improving their ductile capacity can help to prevent them from the brittle collapse mechanism and to reduce the seismic damage expected. This paper aims to investigate the enhancement of the ductile response behaviour of RC framed buildings considering different non-invasive retrofitting techniques. To do so, a pre-code RC framed school located in the Spanish province of Huelva has been selected as a case study. Five non-invasive retrofitting techniques have been tested: FRP wraps and steel jackets in columns, steel beams and plates under RC beams and single steel braces. They have been selected so that they can be easily implemented in the building. Some of them have been studied in detail in previous works and others have been included for further research in this paper. In order to compare the results obtained, the most typical technique in the seismic retrofitting of RC framed buildings, the addition of X-bracings in bays, has also been tested. Most previous studies on the seismic retrofitting of RC buildings are focused on validating a method based on artificial models. This paper compares the different techniques in terms of the capacity improvement and the damage reduction, performing analyses in detail and adding them in an existing RC building. A sensitivity analysis has been carried out to determine the influence of each technique in the building’s ductile capacity considering the finite element method. Nonlinear static analyses have been performed to obtain the capacity, the displacement ductility factor (μ) and the behaviour factor (q) of each model defined. The damage expected has been determined considering the ductile and fragile failure of the elements according to the Eurocode-8 (EC8) requirements. To analyse the suitability and the efficiency of each solution, a benefit/cost ratio has been obtained taking into account the ductility improvement and the damage reduction with regards to the retrofitting costs. The results have shown that the best benefit has been obtained with the addition of steel braces. However, the optimal solutions have been single braces and steel jackets due to their combination between benefit and cost. It has been observed that the solutions that increase the stiffness of the joints have had a higher improvement due to the key role that joints have in the resistant capacity of RC structurers. Also, it has been obtained that the values of the fundamental periods have been reduced, when adding the retrofitting elements and materials, up to 30% owing to the increase of the stiffness of the system. Finally, it must be highlighted that a detailed analysis of the behaviour of the whole building must be conducted in order to avoid additional rotation effects and shear forces that could worsen the building’s seismic behaviour.

Experimental in-plane seismic strengthening of masonry infilled reinforced concrete frames by engineered cementitious composites (ECC)

The present study aimed to evaluate the performance of engineered cementitious composites (ECC) retrofit technique for unreinforced hollow clay brick masonry infill wall in non-ductile reinforced concrete (RC) frames subjected to in-plane cyclic loading (quasi-static loading). To this aim, the mechanical properties of ECC and masonry elements were tested. Then, four 1/3-scale, one-story, single-bay RC frames were fabricated. Among these specimens, one frame was tested without infill wall (BF), one frame with unretrofitted infill wall (IF-E0), and specimens IF-SF-E20 and IF-DF-E20-2 were retrofitted by using an overlay ECC on the masonry infill wall on one side and both sides, respectively. The retrofitted specimens provided higher lateral load capacity, stiffness, and energy dissipation capacity up to 215%, 32%, and 102%, respectively, compared to the unretrofitted specimen. Further, the proposed strengthening technique prevented brittle premature failure in the masonry infill walls and partially maintained the integrity of unreinforced infill walls. Also, the obtained backbone curves of specimens were idealized. Based on the results, the displacement ductility factor of the retrofitted specimens decreased up to 50%, but also the force reduction factor and the overstrength factor of them increased up to 19 and 68%, respectively. At the end of the paper, a simplified analytical method is proposed to calculate the peak strength of retrofitted masonry infilled RC frames. The results obtained from this method were close to the experimental results.

Numerical simulation of the influence of bond strength degradation on the behavior of reinforced concrete beam-column joints externally strengthened with FRP sheets

Limited information is known about the effects of bond strength degradation during installation on the bond's quality and performance between fiber-reinforced polymer (FRP) reinforcement and substrate material. This research study's primary focus is to investigate the efficiency of the external FRP composites in rescuing the structural performance and controlling the mode of failure of the reinforced concrete (RC) beam-column joint with different bond strength degradation percentages nonlinear finite element analysis (NLFEA). Firstly, the RC beam-column model was validated against the published experimental results and then was expanded to consider the effect of the degradation percentages in bond strength between concrete and FRP composite (0 % (Fully bond), 10 %, 20 %, 30 %, 40 %, 50 %, 60 %, 70 %, 80 %, 90 %, and 100 % (control or un-strengthened joint). The structural performance was evaluated in terms of failure mode, stress distribution, pulling and pushing ultimate load capacity and corresponding displacement, horizontal load-displacement hysteretic loops, horizontal load-displacement envelopes, displacement ductility, energy dissipation, stiffness degradation, and equivalent hysteretic damping factor. The NLFEA results showed that the FRP strengthening technique with bond strength degradation percentages less than 30 % enhanced the cyclic performance (higher load capacity, larger horizontal displacement, higher displacement ductility, higher energy dissipation, and slower secant stiffness degradation). Also, the utilized FRP method with bond strength degradation percentage less than 30 % performed well in eliminating any surface debonding or buckling in the FRP composite because of the proper lateral support provided for the strengthening sheets. Finally, the bond strength degradation percentage less than 30 % could significantly enhance the deficient joints' seismic performance under strong beam-weak column conditions by changing its behavior to a more ductile one, including the beam flexural hinging. Moreover, the relocation of a plastic hinge in the beam provided more lateral strength for the joint specimens.

Experimental Study on the Behavior of Existing Reinforced Concrete Multi-Column Piers under Earthquake Loading

When a seismic force acts on bridges, the pier can be damaged by the horizontal inertia force of the superstructure. To prevent this failure, criteria for seismic reinforcement details have been developed in many design codes. However, in moderate seismicity regions, many existing bridges were constructed without considering seismic detail because the detailed seismic design code was only applied recently. These existing structures should be retrofitted by evaluating their seismic performance. Even if the seismic design criteria are not applied, it cannot be concluded that the structure does not have adequate seismic performance. In particular, the performance of a lap-spliced reinforcement bar at a construction joint applied by past practices cannot be easily evaluated analytically. Therefore, experimental tests on the bridge piers considering a non-seismic detail of existing structures need to be performed to evaluate the seismic performance. For this reason, six small scale specimens according to existing bridge piers were constructed and seismic performances were evaluated experimentally. The three types of reinforcement detail were adjusted, including a lap-splice for construction joints. Quasi-static loading tests were performed for three types of scale model with two-column piers in both the longitudinal and transverse directions. From the test results, the effect on the failure mechanism of the lap-splice and transverse reinforcement ratio were investigated. The difference in failure characteristics according to the loading direction was investigated by the location of plastic hinges. Finally, the seismic capacity related to the displacement ductility factor and the absorbed energy by hysteresis behavior for each test were obtained and discussed.