Plastic Hinge Region Research Articles

Perilaku Lentur Kolom yang Diretrofit Menggunakan Wire Mesh dan Self Compacting Concrete Akibat Beban Siklik

Results of experimental and analytical study of the flexural behavior of retrofitted columns using wiremesh and SCC concrete due to cyclic loading. The purpose of this study was to analyze the strength of the column retrofitted using wiremesh and SCC due to cyclic loading. The test object consisted of 3 columns with a size of 300x300 mm, consisting of a control column (KK), a total reinforcement column (KR-1) and a reinforcement column in the approximate plastic hinge region (KR-2). From the test results, the flexural strength of the reinforced column is higher than that of the unreinforced column. The rate of increase in strength of KR-1 compared to KK is 46.68% in compression and 37.87% in tension. The rate of increase in the strength of KR-2 compared to the compressive load of KK is 41.71%, and the tensile load is 32.35%.

Cyclic testing of a steel-tube-enabled emulative precast column-to-column connection

Precast systems are increasingly favored in modern construction to meet the growing demands for faster project delivery, cost control, and enhanced quality assurance. Yet, the feasibility of connections between precast elements remains a crucial factor affecting the overall structural performance of these systems. Considering the versatility and dimensional consistency of structural steel sections, this study introduces an emulative column-to-column hybrid connection achieved by using welding-spliced steel tubes, with a view to improving assembly efficiency and on-site quality control. Reversed cyclic loading tests were conducted on five near full-scale column specimens to assess the seismic performance of the proposed connection. Results indicated that this connection method could provide seismic performance comparable to that of the traditional cast-in-place counterpart. Nevertheless, the anchorage of the column longitudinal rebars played a critical role, as inadequate anchorages led to significant reductions in the columns’ lateral capacity. For this reason, increasing the tube thickness was shown to be insufficient as a substitute for proper anchorage detailing. Moreover, it was found that the incorporation of the welded steel tubes shifted the plastic hinge region upward, resulting in a more extended damage zone—a consequence of the localized stiffening effect. Finally, existing equations and methods are employed to evaluate the lateral strength, load-displacement response, and plastic hinge length of the tested specimens.

Retrofitting circular RC columns using UHPC jackets reinforced with stainless steel mesh in the plastic hinge region

Retrofitting circular RC columns using UHPC jackets reinforced with stainless steel mesh in the plastic hinge region

Seismic performance study of plastic hinge region using PVA-ECC composite bridge piers

This study explores the use of high tensile ductility engineered cementitious composites (ECC) to replace the plastic hinge region in conventional reinforced concrete (RC) pier, aiming to enhance seismic performance. Experiments and numerical simulations were performed on a traditional reinforced concrete pier and three composite piers with different replacement heights of ECC in the plastic hinge area. The findings demonstrated that the use of ECC led to a substantial enhancement in the piers' ultimate displacement, displacement ductility factor, and energy dissipation capacity, with improvements of more than 20.3 %, 17.1 %, and 80 % correspondingly. Increasing the replacement height from 300 mm to 400 mm boosted the displacement ductility coefficient by 10 %. Numerical analyses corroborated these findings, indicating a decline in seismic performance with higher axial pressure ratios. At an axial pressure ratio of 0.2, ductility increased by over 1 % for every 100 mm increase in ECC height up to 400 mm, beyond which the increase was less than 1 %. Thus, ECC in the plastic hinge improves seismic performance, with greater enhancement discovered at higher replacement heights within a certain range.

Seismic Performance of the Bridge Piers Reinforced with PP-ECC in the Plastic Hinge Region

Ductility deficiency in reinforced concrete (RC) piers is a substantial factor contributing to earthquake damage in bridge structures. In this study, the conventional concrete in the potential plastic hinge area was substituted with polypropylene fiber-reinforced engineered cementitious composite (PP-ECC), thereby leveraging its high ductility characteristics to explore the seismic performance of RC piers strengthened by PP-ECC. A finite element model was established to discuss the reinforced height, axial compression ratio, longitudinal reinforcement ratio and stirrup ratio on the hysteresis performance by referring to a published paper with a 1/5 scale test specimen. Based on the results of the parameter analysis, an ideal set of configuration parameters was proposed. Subsequently, a full-size simplified mechanical model was established with ideal reinforcement parameters. Time-history and pushover analysis were utilized to test the seismic response. The study indicates that the two analytical methods were largely consistent. The improvement in the displacement and shear force of the strengthened pier gradually decreased with the increase in acceleration amplitude. Time-history analysis reveals a decrease in the enhancement of displacement from 82.26% to 17.98% and a reduction at the bottom reaction from 12.2% to 1.5%. Under the pushover analysis method, the retrofitting level of the top displacement decreased from 77.22% to 11.53%, whereas the improvement level of the bottom shear decreased from 9.62% to 3.69%. These results provide a theoretical basis and reference standard for the application of PP-ECC.

Structural behavior of partially confined circular CFST columns under lateral cyclic loading

The seismic performance of concrete-filled steel tubular (CFST) columns is severely influenced by the failure at the potential plastic hinge zone. This paper proposes a novel confinement technique at the potential plastic hinge region using an inner circular steel tube for the circular CFST columns named partially confined concrete-filled steel tubular (PCCFST) columns. This confinement technique strengthens the plastic hinge region, and hence, the overall structural performance of the columns is enhanced. To verify the effectiveness of the proposed technique, a total of 7 columns: 6 PCCFST and 1 counterpart CFST have been tested under lateral cyclic loadings while subjected to constant axial load. Failure mode, hysteretic behavior, flexural capacity, ductility, and energy dissipation ability of the PCCFST specimens were investigated by varying the diameter and height of the inner circular steel tube. It was seen that the height of the circular inner steel tube has an obvious effect on the cyclic performance of the columns. For the PCCFST columns considered, the maximum lateral strength, ductility, and energy dissipation ability were enhanced by a maximum of ∼ 16 %, 24 %, and 14 %, respectively, when compared with the counterpart CFST column. A new design guideline has been proposed based on the Eurocode and limited experimental data obtained from the present study. A comparison between the experimentally determined maximum lateral strength and the proposed guideline has been made and is found to be in good agreement.

Numerical modeling of beam plastic hinges in steel moment resisting frames including local buckling and stiffness/strength degradation

Plastic hinge formation in beams is the main energy dissipation mechanism in moment resisting frames, but its deformation capacity is limited by the strength deterioration after reaching the maximum moment. Such degradation is highly influenced by the onset of local buckling in the plastic hinge region once a significant portion of the cross-section has reached the yield stress. Numerical models developed to study this effect have shown good accuracy against experimental data, but with high computational costs and the need to calibrate several model parameters. This work proposes a numerical model of a beam plastic hinge that uses only one parameter to reproduce the hysteretic behavior under cyclic loading, degrading simultaneously stiffness and resistance with lower computational cost. The proposed model relies on the discretization of the beam cross-section using uniaxial bars with a prescribed geometric imperfection with buckling degrading strength capability spanning along an assumed plastic hinge length. The Euler-Bernoulli hypothesis is imposed at the ends of the plastic hinge region and elastic beam elements are used to model the beam outside this domain. The model is validated against experimental data from three cyclic loading connection tests reported in the literature. Results show that the model can accurately represent the response of the beam plastic hinge with a low computational cost by adjusting one single model parameter as well as the definition of the nominal information of the beam geometry and material properties, expected plastic hinge length, and standard fabrication tolerances.

Seismic performance of a novel concrete-filled steel tube column to continuous reinforced concrete beam joint with multiple openings in the core region

This study developed a novel concrete-filled steel tube column to continuous reinforced concrete beam joint with multiple openings in the core region, aiming to eliminate field welding and improve construction efficiency. To evaluate the seismic performance of the joint, six full-scale specimens were tested under cyclic loading, which and a series of numerical simulations were implemented upon refined models. The effects of reinforcement ratio, steel tube thickness, and concrete strength on the failure mode and the mechanical performance degradation of the joint were quantitively evaluated. The results indicated that depending on the beam-column flexural capacity ratio, three typical failure modes, i.e., compression bending failure at the column end, shear failure at the joint core region, and flexural failure at the beam plastic hinge region, were observed. Among them, the flexural failure-dominated joint possessed the best energy dissipation capacity and a high ductility coefficient greater than 3.72. Moreover, increasing the thickness of steel tube within the core region can effectively compensate for the reduction of seismic performance caused by multiple openings, and a preliminary value of at least 2.5 times the thickness of column steel tube is recommended. This novel joint configuration exemplifies a balance between structural integrity, construction efficiency, and mechanical performance, rendering it a feasible alternative for frame structure in seismic-prone regions.

Experimental and numerical study on cyclic behavior of precast segmental railway bridge columns with lap-spliced rebar connections using UHPC wet joints

A novel lap-spliced connection with ultra-high performance concrete (UHPC) was proposed to connect precast railway bridge column segments with footings or cap beams. Two 1:3 scaled specimens were tested under cyclic loads. Specimen PC-LS was a precast column with lap-spliced rebar connection and UHPC wet joints. Specimen CIP was a monolithic column as a reference specimen. The test results revealed that the plastic hinge region of the precast specimen shafted to the upper surface of the UHPC wet joint. The failure mode of the precast specimen was exhibited as the crushing of the core concrete and the buckling/fracture of the longitudinal rebars. Specimen PC-LS experienced larger lateral force, initial stiffness, comparable ductility, and energy dissipation compared to specimen CIP. Additionally, the validated finite-element (FE) models considering the bond-slip effect between concrete and reinforcements were developed. The parametric studies were carried out to further investigate the cyclic behavior of specimen PC-LS. Analytical results demonstrated that the variation of the compressive and tensile strength of UHPC showed little influence on the cyclic behavior of the precast segmental column, which indicated that UHPC with natural curing and lower volume content steel fibers could be used as the wet joint. The precast segmental column had similar lateral force and stiffness with the cast-in-place column when the lap splice length was 10 times of the rebar diameter.

Cyclic tensile response and crack closure performance of novel superelastic Ni-Ti SMA cable grid-reinforced engineered cementitious composites

To further improve the tensile and self-healing properties of engineered cementitious composites (ECCs) for their special uses such as harsh environments, plastic hinge regions, and old members strengthening, an innovative high-performance superelastic Ni-Ti shape memory alloy (SMA) cable grid-reinforced ECC (SMACG-ECC) was first proposed and tested in this study. The effects of water-binder ratio, cable grid material, and reinforcement ratio on the cyclic tensile properties and crack closure performance of the proposed SMACG-ECC were systematically examined. Test results revealed that the tensile strength, initial crack strength, ultimate tensile strain, dense crack, crack closure, and self-healing properties of the traditional ECC were obviously improved by being reinforced with the SMACG. Compared with the ordinary steel cable grid-reinforced ECC (SCG-ECC), the proposed SMACG-ECC exhibited approximately 50 % lower first crack strength, similar tensile strength and deformation ductility, but a 53.7 %-75.1 % greater energy dissipation, 75.8 %-80.2 % lower residual strain, and 80.4 %-83.4 % smaller maximum residual crack width. The tensile properties, cracking performance, and self-healing ability improved with the incorporation of SMACG as well as the increase in reinforcement ratio. Notably, most specimens showed satisfactory composite operation with no cable ends slipping during the entire cyclic loading process, with a maximum tensile strain amplitude of 8 %.

Seismic strategy of non-seismically designed reinforced concrete columns retrofitted with steel rods

This paper presents experimental results of combined cyclic load testing on a reinforced concrete (RC) column that was retrofitted with newly designed steel rods. The steel rods were installed around the column longitudinally and then anchored. The proposed steel rods utilize simple components and installation to enhance both the strength and ductility of RC columns. Cyclic lateral load tests were conducted on three specimens: one unreinforced specimen as reference, one specimen with the entire length of the column retrofitted, and one specimen with only the plastic hinge region of the column retrofitted. All specimens were tested under eccentric constant axial load and incrementally increasing lateral loading cycles with eccentricity. The implementation of steel rods resulted in significant improvement in ductility and an up to 60% increase in ultimate loading capacity.

Shaking table test-based numerical study on post-buckling ULCF fracture behavior of partially concrete filled steel tubular piers

Steel structures may undergo local buckling deformation or ultra-low cycle fatigue (ULCF) fracture due to stress concentration under earthquake excitations, and the stress concentration may further develop after buckling deformation, thus leading to ULCF fracture. To investigate the post-buckling fracture behavior of partially concrete-filled steel tube (PCFST) piers under earthquake exactions, a new ULCF analysis method that integrates three fracture indexes of cyclic void growth model (CVGM) was proposed in this study based on a shaking table test of PCFST piers, and then the index for quantifying the buckling deformation of PCFST piers was developed to study the post-buckling ULCF mechanism. Finally, the effect of each design parameter on the ULCF fracture index was analyzed. The results indicate that all three indexes of CVGM can accurately predict the triggering time, crack location, and crack propagation of ULCF fracture after buckling. The failure mechanism of PCFST bridge piers experiencing post-buckling fracture is also revealed, i.e., under repeated lateral loads, the plastic hinge region at the pier bottom bulges, causing an expansion of the plastic region. Meanwhile, the cumulative rate of ULCF damage rapidly increases during the expansion process and slows down after the bulge reaches the maximum stable value until the cumulative damage value meets the fracture condition. In addition, the results of the parametric analyses indicate that the model with high ductility can undergo a greater number of cycles before localized instability failure, and thus is more likely to suffer ULCF fracture first.

Plastic hinge length in reinforced HPFRCC beams and columns

The use of ductile concrete materials such as High Performance Fiber Reinforced Cementitious Composites (HPFRCCs) within plastic hinge regions of structural components has garnered research interest in order to improve the seismic resistance of reinforced concrete structures. While experimental and numerical results appear promising in reducing component damage and probability of system level collapse, accurate nonlinear analysis tools capable of capturing the influence of axial load well into a component’s inelastic regime is needed. In this study, a series of 180 high fidelity numerical simulations of HPFRCC beam–column elements are simulated and used to calibrate new plastic hinge length expressions for concentrated and distributed plasticity models for use in system level structural analysis. The numerical models cover a range of HPFRCC material properties, reinforcement ratios, shear span lengths, and axial load levels. The ability of the newly developed expressions to predict component inelastic rotations are subsequently compared to hinge length expressions in the literature and the inelastic rotations of 47 experimental components. The results of this study provide new insights into the effects of axial load on the plastic hinge behavior of HPFRCC components, significantly improves on the accuracy of past plastic hinge length expressions allowing for more accurate modeling of HPFRCC component responses and system level behavior.

Innovative Methods to Improve the Seismic Performance of Precast Segmental and Hybrid Bridge Columns under Cyclic Loading

This paper investigates the seismic performance of prefabricated segmental bridge columns (PSBCs) with hybrid post-tensioned tendons and energy dissipation (ED) bars under cyclic loading. PSBCs with unbonded and hybrid bonded prestressed tendons and columns incorporating ED bars are designed to improve the lateral strength, energy dissipation, and limit the residual drift. The PSBCs under cyclic loading were investigated using the three-dimensional finite element (FE) modeling platform ABAQUS. The FE model was calibrated against experimental results, with an overall error of less than 10%. The seismic performance of the proposed PSBCs was evaluated based on critical parameters, including lateral strength, residual plastic displacement, and the energy dissipation capacity. The results show that bonding the tendons in the plastic hinge region as opposed to the overall bonding along the column leads to a better cyclic performance. The lateral strength, and recentering abilities are further improved by bonding tendons up to 2/3 of the length in the plastic hinge region, along with 100–300 mm in the footing. It was also found that selecting a longitudinal length of ED bars crossing multiple precast segmental joints and having a circumferential spread of 70–90% of core concrete results in a higher bearing capacity and energy dissipation compared to ED bars crossing the single joint.

Feasibility of using superelastic shape memory alloy in plastic hinge regions of steel bridge columns for seismic applications

AbstractThis paper contributes to the further development of seismic resilient infrastructure by introducing a novel prototype bridge which integrates tubular steel piers with superelastic shape memory alloy (SMA). The proposed bridge pier is composed of a circular steel tube which is bonded to a superelastic SMA tube in regions of high stress. The pier is distinguished by its ability to minimize residual drifts following inelastic deformations induced by cyclic loading. Three‐dimensional continuum finite element (FE) models are utilized to examine its lateral behavior. Experimental data is used to demonstrate the effectiveness of the continuum FE procedure in replicating the cyclic response and capturing both global and localized behaviors. A novel composite material model is proposed to represent the degradation of strength and accumulation of irreversible strains in the cyclic response of superelastic SMAs. An iterative procedure for the calibration of this material is presented. Investigations, employing the calibrated FE procedure, focus on the quasi‐static cyclic response of steel piers with superelastic SMA in the plastic hinge zone, aiming to identify the optimal length of the SMA tube for achieving a self‐centering response with reduced residual deformation. The study is then further expanded to examine the seismic response of a bridge structure incorporating such piers. Development of the FE model for the prototype bridge includes the modelling of the piers using continuum elements, while the superstructure, bearing units, abutment walls, and backfill material are modelled using discrete elements. Nonlinear time history analyses are undertaken to investigate the effects of column wall thickness and materials used in the plastic hinge zones of the piers. Dynamic FE study results indicate that bridges employing such piers are capable of returning to their original position, provided the SMA tube is of adequate length.

Reinforcement methods of an reinforced concrete beam with the circular opening in the plastic hinge region under cyclic loading

Transverse opening in the plastic hinge region of reinforced concrete (RC) beam is generally not recommended due to increased risk of shear failure rather than flexure or flexure-shear failure. However, in recent years, the actual pipeline configuration requirements have posed challenges in arranging such opening in the plastic hinge region of an RC beam member. To address this issue and propose design guidelines, this work examines the mechanical behavior of nine specimens subjected to cyclic loading. The test results are compared with the design methods suggested in other guidelines and research. Additionally, a set of design guidelines and novel reinforcement methods, utilizing Double-square hoop and U-shaped stirrups, are proposed and compared with traditional reinforcement methods for RC beams with circular openings. Three distinct regions for reinforcing beams with transverse circular openings are proposed based on their distance from the column support. In the first region, extending from three times the opening diameter to one beam depth (1H), the opening is reinforced with two inclined U-shaped stirrups on each side and double-square hoops on both faces. The second region (1H to 2H) utilizes one inclined U-shaped stirrup on each side, along with double-square hoops on both faces. Beyond twice the beam depth (2H) in the third region, the opening is reinforced solely with double-square hoops on both faces. The sets of design methods provide valuable insights for future design considerations.

Maximum Drift Demands of Earthquake Damaged Reinforced Concrete Columns Based on Residual Flexure Cracks

Assessment of existing reinforced concrete (RC) structures after an earthquake is a challenging task that must somehow relate qualitative and quantitative observations in the plastic hinge regions and the associated residual deformation capacity of damaged structures. Having an estimate available for the remaining drift capacity will result in more economical and informed decisions regarding demolition or strengthening options. This study aims to develop a practical methodology to estimate the maximum drift demand of an RC column based on the residual crack width. For this purpose, fiber-based frame elements are used to model the RC column considering appropriately concrete behavior in compression and tension stiffening effects. Afterwards, the accuracy and reliability of the proposed methodology are demonstrated by validating the computational approach with two cyclic experimental results from literature and new test data for a one-bay one-story RC frame conducted within the course of this study. A comprehensive parametric study is performed for RC columns with different axial loads, longitudinal and transverse reinforcement ratios, and ground motions to exhibit the stochastic behavior. The study identifies the axial load ratio as the predominant parameter. Key findings include strong correlations between maximum drift ratios and total residual crack widths, as well as maximum compressive strains, with regression analysis yielding equations for accurate drift ratio estimation. Simple predictive models are proposed to estimate the maximum deformation demands based on observed residual crack widths. Residual cracking exceeding 5 mm poses significant risk for the columns with axial load ratios above 0.4, with 90% probability of exceedance 2% drift ratio.

Seismic Behavior of Steel Moment Frame Connections with Repairs in the Plastic Hinge Region

Seismic Behavior of Steel Moment Frame Connections with Repairs in the Plastic Hinge Region

Progressive collapse resistance of local prestressed concrete sub-structures: Numerical analysis and theoretical verification

The local prestressed concrete (LPC) structure is a structural form that combines the prestressed concrete (PC) span with the common reinforced concrete (RC) span, with significant asymmetry. Currently, there is insufficient research on the progressive collapse resistance of LPC structures. To investigate the progressive collapse mechanism of LPC structures, a parametric analysis was conducted by using the finite element software OpenSEES. Based on the failure mode of LPC structures, the proposed method predicted the limit state by considering displacement coordination, force equilibrium, and the influence of the plastic hinge regions. The research showed that LPC structures exhibited a distinct transition action stage (TAS) between the compressive arch action stage (CAAS) and catenary action stage (CAS), which distinguished them from the symmetrical structures. Increasing the strand area could significantly improve the catenary action (CA) of the LPC structure and extend the TAS. Lengthening the PC part also improved CA and allowed the structure to progress into TAS and CAS earlier. By increasing the length of the RC part, the compressive arch action (CAA) could be strengthened, while the duration of CAAS was extended. The theoretical prediction method proposed in this study can effectively predict the ultimate displacement and ultimate resistance of LPC structures.

Study on the hysteretic characteristics of FRP-reinforced concrete shear wall with innovative friction dampers

FRP-reinforced concrete shear walls (FRCWs) are able to achieve satisfactory residual deformation and corrosion resistance compared with steel reinforced concrete walls (SRCWs). However, in the FRCWs, the failure of the plastic hinge region brings great challenges to the post-earthquake repair of the structure. Therefore, this paper designed one SRCW and two FRCWs with innovative friction dampers (FDs) at the feet, and steel truss and steel plate were embedded at the plastic hinge region of the two FRCWs respectively to supplement the weakened shear strength. Then pseudo-static tests were carried out twice before and after repairing the two FRCWs with FDs. Experimental results showed that compared with the SRCW at the same lateral drift, the damage of the FRCW was reduced by installing FDs at the feet, and the energy dissipation capacity was enhanced; the repaired FRCWs with FDs could still have acceptable seismic performance. Subsequently, the Park-Ang damage indices of wall webs of the FRCWs with FDs were calculated, which proved that the FRCWs with FDs could meet the four-level seismic fortification objective. In the end, two orthogonal tests were designed based on the established OpenSees models to evaluate the impact of the damper friction and FRP reinforcement ratio on the seismic behaviours of the FRCWs with FDs. It was recommended to adopt larger longitudinally distributed FRP reinforcement ratio to obtain satisfactory self-centering ability and hysteresis performance of the FRCW with FDs.