Plastic Hinge Relocation Research Articles

Experimental investigation and seismic vulnerability assessment of low flexural strength rectangular bridge piers retrofitted with ultrahigh-performance concrete jackets

Effectiveness of an innovative retrofitting technique using ultrahigh-performance concrete (UHPC) jackets was investigated, for “as-built” bridge piers with low flexural strength. Cyclic loading test was performed on the pier specimens, two of which were retrofitted with a mono-wide-strip UHPC (W-UHPC) jacket, and the other two were with a multi-narrow-strip UHPC (N-UHPC) jacket. Their seismic responses were compared, regarding damage evolution, hysteretic behavior, skeleton curve, ductility and energy dissipation. The piers with the W-UHPC jacket exhibited a higher lateral strength, but were prone to plastic hinge relocation. Comparatively, N-UHPC jacket improved the piers’ ductility and smeared concrete damage. Nevertheless, guaranteeing the tight contact between the N-UHPC jacket and the shaft was crucial. Both W- and N- UHPC jackets mitigated residual drift and concrete damage, and thereby enhancing the piers’ seismic resilience. Four enhancing mechanisms from the UHPC jackets are discussed, namely passive confinement effect, cross-section enlargement effect, gap-opening effect, and interface-opening effect. Alongside, 3D solid and 1D fiber-based finite element (FE) models are constructed to represent the piers’ nonlinear static push-over (SPO) and cyclic responses, respectively. Finally, seismic vulnerability of the retrofitted piers was evaluated by generating structure-specific fragility curves.

Plastic hinge relocation in exterior reinforced beam–column joint and compliance issues to seismic design guidelines—A review

AbstractThe current recommendations for the design of monolithic reinforced concrete beam–column joints allowed for the provision of transverse reinforcements at the joint to avoid brittle shear failure of the joint during seismic events but neglected the effect of plastic hinge penetration in the joint leading to bond deterioration and shear failure, especially for external frames. In this paper, previous studies conducted by different authors using the seismic design recommendations are reviewed for failure modes and the effectiveness of the code recommendations to avoid joint failure. Various retrofitting strategies to upgrade nonseismically designed beam–column joints are also reviewed. Methods of plastic hinge relocation in beam–column joints of new construction were proposed and verified with numerical simulation. This study contributes to knowledge by highlighting areas of concern in current design guidelines and a call for further research on code compliant exterior beam–column joint for better seismic performance.

Seismic Repair of Circular Reinforced Concrete Bridge Columns by Plastic Hinge Relocation with Grouted Annular Ring

ABSTRACT Modern seismic design practice for bridge structures involves the implementation of capacity design principles which localize plastic hinges in columns, while protecting against other modes of failure. The resulting structures are capable of reliably sustaining far greater deformations than their predecessors; however, despite their initial resilience, the formation of plastic hinges can result in buckling and rupture of longitudinal steel, typically leading to the structure’s demolition and reconstruction. Replacement is deemed necessary since the inelastic strain capacity of reinforcing bars severely diminishes once buckling occurs, rendering the structure vulnerable to collapse in future earthquakes. Recent research demonstrates the feasibility of a repair technique in which the previously damaged region is strengthened such that future inelastic action occurs at a new location, although there are presently a limited number of tests on which to base reliable design recommendations. Results of an experimental program are presented in this paper, in which six extensively damaged columns are repaired using the plastic hinge relocation technique and retested. The proposed repair strategy consists of a grouted annular ring composed of conventional materials (i.e. steel rebar, a steel sleeve, and concrete or grout). The results substantiate plastic hinge relocation as a viable repair option for columns with buckled and fractured longitudinal bars and serve to expand the existing data set considerably. A novel analytical model which accurately predicts the behavior of the repaired column is also presented.

Retrofitting external RC beam-column joints of an ordinary MRF through plastic hinge relocation using FRP laminates

This paper presents the results of experimental and numerical investigations on flange and web -bonded FRP retrofitting schemes for external RC joints of moment resisting frames. Two, identical full-scale external joints are designed and constructed according to ACI318M-11 requirements for ordinary moment resisting frames. Quasi-static cyclic loading tests are then carried out on the specimens and some seismic performance parameters including strength, ductility, energy dissipation and stiffness are evaluated and compared. Numerical analyses are also carried out to study the effects of FRP overlay length on required number of plies for plastic hinge relocation and joint strength. It is found that successful relocation of plastic hinge away from the face of the column into the beam is possible with appropriate number of FRP laminate plies and overlay length. It is also found that as the length of the FRP laminate over the beam flange increases, the joint strength is enhanced; however, larger number of plies would be required for plastic hinge relocation.

Experimental study of earthquake-resilient prefabricated sinusoidal corrugated web beam-column joint

The functional structure of earthquake-resilient has become a frontier issue in the field of structural seismic performance. For researching the performance of seismic and post-earthquake resilience of earthquake-resilient prefabricated sinusoidal corrugated web beam-column joint (PSCWJ) previously proposed by the author, the low frequency cyclic loading test and the finite element (FE) numerical verification have been carried out on eight specimens in this paper. The hysteretic curve, skeleton curve, strain variation curve, ductility, energy dissipation and other seismic performance indexes of this joint have been obtained. The impact of weakend form, thickness and strength of the flange cover plate (FCP), and the gap between beams on the joint seismic performance as well as the post-earthquake repair performance have been investigated. The results indicate that: the reasonably designed joint does well in bearing capacity, ductility and energy dissipation capability; the quick repair of joint can be realized by installing a new connection device, and the repaired joint can still meet the seismic performance requirements; the FCP weakened by a straight dog-bone profile is better for the joint plastic development and the relocation of plastic hinge at the beam end; the gap properly set between beams can effectively promote the rotation capability of the joint; the yield load of joint is directly decided by the thickness and the strength of the FCP.

Plastic hinge relocation in reinforced concrete beam–column joint using carbon fiber–reinforced polymer

Reinforced concrete buildings with moment-resisting frames comprising beam–column joints (without joint shear reinforcement) designed prior to introduction of seismic codes are shear deficient when subjected to seismic loading, thereby mostly fail in shear at the core of the beam–column joint. However, those designed to the new seismic codes may fail by flexural hinging at the interface of the beam–column joint due to the yielding of the beam reinforcement at the location of highest stress demand (usually the beam–column joint interface). The shear failure has been precluded through the provision of transverse reinforcement at the joint in new design and the use of carbon fiber–reinforced polymer retrofitting in old buildings. Plastic hinge formation at the interface of the beam–column joint is critical because of its penetration into the joint and its effect on bond deterioration. In this study, eight corner-external beam–column joint specimens of 1/3 scale of a typical moment-resisting frame, made without transverse reinforcement, were tested for monotonic and reversed cyclic test under displacement-controlled regime. The control specimens failed by flexural hinging at the beam–column joint interface. The experimental results have been validated using the finite element model. The specimens were retrofitted with unidirectional carbon fiber–reinforced polymer of different layers and different length. After retrofitting, the plastic hinge was relocated to the curtailment end of the carbon fiber–reinforced polymer. The relocation of the plastic hinge resulted in higher load capacity and ductility.

Plastic hinge relocation in reinforced concrete beams using Cu-Al-Mn SMA bars

Self-centering earthquake resistant systems have attracted the attention of researchers because of their promising potential in controlling seismic residual drifts, and, therefore, reducing the associated repair costs. The use of Ni-Ti superelastic shape memory alloy (SMA) constitutes a considerable portion of this research. Cu-Al-Mn superelastic SMA has been recently developed to eliminate the high cost of Ni-Ti SMA, as well as, to have better machining characteristics. This paper explores the use of Cu-Al-Mn SMA bars to relocate the plastic hinge of concrete beams through an experimental–numerical study. The cyclic performance of four beams was examined. The first was reinforced with steel bars and the remaining three were reinforced with combination of SMA and steel bars. The location of the SMA bars was different for each of the examined beams. The beams were loaded such that the moment diagram is zero at midspan and maximum at the ends to simulate the expected seismic moments. Results of the experimental–numerical investigation confirmed the recentering capability of SMA RC beams. Relocating the plastic hinge, by placing Cu-Al-Mn SMA bars away from the beam ends, improved the strength, rigidity, and energy dissipation.

Anisotropic Damage Plasticity Model for Concrete and Its Use in Plastic Hinge Relocation in RC Frames with FRP

In an RC frame, relocating plastic hinges in the beam away from the column face is suggested to increase ductility of the frame. This can be achieved through flange-bonded FRP retrofit of the joint. Relocating the plastic hinges further into the beam, shortens the effective length of the beam.As the effective length of the beam is reduced, ductile flexure failure in the beam may switch to a brittle shear failure, resulting in a decrease in ductility of the frame. The consequences and limits of plastic hinge relocation are therefore important issues in need of evaluation. To achieve this, in this paper, an accurate numerical model is first developed for simulating the complex behaviour of concrete and its interaction with steel and FRP materials. For this purpose, anisotropic damage plasticity model for concrete is developed. Damage plasticity model simulates irreversible plastic deformation besides material degradation (crack). After verifying the accuracy of the developed software through comparison with experimental results, response of full-scale RC frames with different beam clear length/effective height ratios is evaluated to find advantages and drawbacks of the flange-bonded retrofitting scheme for relocating plastic hinges. The results show that for beam clear length/height ratios<6, the frame cannot achieve the 0.02 code-required inelastic drift and the ductile flexural failure in the beam changes to an undesirable brittle shear failure. Also, the results indicate that for clear length/height ratios between 6 and 9, bending moment at the face of the column may increase by up to 60% depending on the length of FRP overlay, therefore, columns should be controlled, and if necessary, be retrofitted for the increased moment.

Rapid repair and replacement of earthquake-damaged concrete columns using plastic hinge relocation

A rapid repair and replacement method is developed for earthquake-damaged concrete columns. Headed steel bars enclosed in a carbon fiber-reinforced polymer (CFRP) shell filled with non-shrink concrete are used to relocate the column plastic hinge. The method employs a steel collar with steel studs to increase bond of the column to non-shrink concrete within the CFRP shell. Two columns were damaged under quasi-static cyclic loads and were repaired with this method. The first column required epoxy injection of the cracks to restore stiffness; the second column was completely severed from the cap beam before repair to simulate replacement of a column with unrepairable damage. The plastic hinge was successfully relocated, the lateral force and displacement capacity were restored, and failure of the repaired columns included concrete crushing and steel bar fracture. This is an accelerated bridge construction method that could be used to repair columns with repairable damage as an emergency repair, replace columns with unrepairable damage, or construct new bridges.

Plastic hinge relocation in concrete structures using the double-slotted-beam system

Several plastic hinge relocation techniques were proposed in the past few decades to avoid the congestion of the transverse steel at the joint, avoid strain penetration into the joint, and maintain the strong-column weak-beam behavior. The challenging aspect of these designs is the level of accuracy in predicting the center of rotation of the beam element, which is a necessary component in the seismic design of reinforced concrete frames. In this research, a newly developed concrete beam-column connection called the double slotted beam (DSB) was developed and used to relocate the plastic hinges in concrete frames, with a high level of accuracy in controlling the location of the center of rotation. Two vertical slots made at the top and bottom fibers of the beam member were introduced in the DSB system to control the location of the center of rotation. The plastic hinge was relocated by moving the vertical slots away from the face of the column. Experimental evaluation of large-scale DSB connections with and without relocated vertical slots showed the excellent performance of the system in achieving high drift capacities, non-tearing action, minimal concrete damage, and reduced bond deterioration in the joint.

Development of a ductile steel bridge substructure system

Described in this paper is the evaluation of a series of design concepts which attempt to improve the inelastic cyclic response of steel bridge substructures. The bridge system under consideration consists of hollow circular steel piles welded to steel cap beams. Described first is the motivation for the use of this type of structure, followed by a discussion of the research methods which include large scale reversed cyclic testing supplemented by finite element analysis. Next, the performance of the current as-built system, the fillet welded connection, is evaluated. This connection is shown to perform poorly with little inelastic deformation capacity prior to failure. A variety of alternative connections are then proposed and evaluated. These alternative connections include modified weld detailing and plastic hinge relocation approaches. Alternative weld detailing focuses on the complete joint penetration weld with reinforcing fillet welds. The plastic hinge relocation alternatives include a gusseted connection, a reduced column section, and the recently proposed grouted shear stud (GSS) connection. Alternative weld details produce only slight improvement in performance. Of the plastic hinge relocation concepts, the grouted shear stud (GSS) connection offers the most promising approach to improve inelastic cyclic response.

Plastic Hinge Relocation Methods for Emulative PC Beam–Column Connections

AbstractVarious plastic hinge relocation methods were studied to improve the earthquake resistance of emulative precast concrete (PC) beam-column connections using PC U-shell beams. The present study used two strengthening methods (hooked bars and headed bars) and a weakening method (reduced beam bar section), to relocate the plastic hinge zone of beams away from the weak beam-column joint. Five full-scale test specimens including a conventional reinforced concrete (RC) specimen were tested to evaluate the earthquake resistance. The test results showed that the used relocation methods significantly decreased that bond-slip of beam flexural bars and joint shear cracking. As a result, the energy dissipation capacity significantly increased, compared to those of the conventional RC specimens and PC specimens without relocation methods. On the basis of the test results, design recommendations are suggested for plastic hinge relocation design of emulative PC beam-column connections.

Plastic Hinge Relocation in Reinforced Concrete Frames as a Method of Improving Post-earthquake Fire Resistance

Post-earthquake fire (PEF) presents a risky situation to buildings that have been partially damaged in a prior earthquake, particularly in urban areas. As most standards ignore the possibility of fire after earthquake, buildings are not adequately designed for that possibility and thus PEF is a high-risk load needed to be scrutinized further, codified and become part of a routine design. An investigation based on sequential analysis inspired by FEMA356 is performed here on a two story RC frame, at the Life Safety performance level and designed to the ACI 318-08 code, after it has been subjected to a spectral PGA of 0.35g. The results show that structures previously damaged by the earthquake and exposed to PEF are considerably more vulnerable than the structures, which have not been damaged previously. A method of strengthening using Carbon Fiber Reinforced Polymer (CFRP) wraps is introduced in order to relocate plastic hinges away from the column faces towards the beams. This method increases the structural load carrying capacity, and thus reduces the potential damage from a potential earthquake, improving the fire resistance. The results show a considerable improvement in the PEF resistance of the frame.

Reducing the potential seismic damage of reinforced concrete frames using plastic hinge relocation by FRP

Due to its distinct properties, Fibre reinforced polymer (FRP) has become the product of choice in many retrofitting applications of existing reinforced concrete structures. Relocation of potential plastic hinges using FRP can greatly improve the seismic resistant capacity of reinforced concrete structures and results in lower damage levels comparing to un-retrofitted frames if subjected to similar earthquake excitations. The aim of the current study is to quantify the effect of plastic hinge relocation on the potential damage of a reinforced concrete frame subjected to different seismic levels based on current seismic designs. The paper presents the reduced damage indices and quantifies the positive change on the damage states of the frame. The limitation of the technique is also discussed.

On the effect of plastic hinge relocation in RC buildings using CFRP

Relocation of nonlinear inelastic hinges away from the column faces towards the beams using externally bonded carbon fibre reinforced polymer (CFRP) is suggested as a promising method for retrofitting of reinforced concrete (RC) joints. This approach would also prevent the formation of undesirable brittle joint failure. In order to investigate the effects of this type of retrofit in the seismic performance of RC buildings, a numerical investigation pertaining to strengthening of an 8-storey intermediate RC frame using CFRP was conducted. The retrofit strategy focused on the relocation of the plastic-prone region away from the column faces and out into the beams. To pursue this objective, composite sheets were applied at the top and bottom sides of the plastic hinge regions of beams increasing the bending moment resistance. The additional flexural stiffness generated by the composite materials at the beam to column connections is calculated by a comparison of the moment-rotation of CFRP retrofitted and original joints obtained from the finite element analysis. A rigorous seismic assessment of the retrofitted frame was implemented using the nonlinear pushover procedure and the capacity spectrum approach. The analysis results indicate that a rehabilitation design as described combined with the strong-column weak-beam design philosophy would improve the seismic performance of structures significantly.

Repair of Reinforced Concrete Bridge Columns Containing Buckled and Fractured Reinforcement by Plastic Hinge Relocation

AbstractThis paper describes a new repair technique that involves the use of plastic hinge relocation to restore strength and deformation capacity of RC bridge columns. Summarized is the overall repair concept and experimental results that include the reversed cyclic testing of three large-scale bridge columns that were previously damaged, repaired using the proposed methodology, and then subsequently retested. To date, two different repair alternatives were executed using unidirectional carbon fiber sheets in the hoop and longitudinal directions, the latter anchored into the RC footing with 30-mm-diameter carbon fiber anchors. A method for predicting the force-displacement responses of columns repaired in this manner was also developed and found to give reasonable results. Also included in this paper are design considerations, which are carried out in the steps needed to design a repair system to relocate the plastic hinge in a column containing buckled longitudinal reinforcement. The responses show that...

Numerical Investigation on the Hysteretic Behavior of RC Joints Retrofitted with Different CFRP Configurations

The strengthening of beam-column joints in RC structures is considered an effective approach for improving their seismic resistance and overall performance. This paper presents a numerical investigation into the effectiveness of carbon fiber-reinforced polymer (CFRP) sheets in enhancing the seismic performance of RC joints under combined axial and cyclic loads. For this purpose, a case-study joint subassemblage was retrofitted using three different retrofitting configurations (L-shaped, web bonded, and flange bonded), all commonly used for external strengthening with composite materials. Following the verification of the nonlinear numerical model against the existing experimental data, the analysis outcomes of the retrofitted specimens were compared with those of the control specimen in terms of the tip beam load distribution versus tip beam displacement, energy dissipation, and plastic hinge relocation. Compared with the results of the original joint, the results of the retrofitted joints confirmed an improved load-carrying capacity for all strengthening schemes. However, some configurations led to a decrease in the ductility and dissipated energy. It was shown that the L-shaped and flange-bonded retrofitting schemes could relocate the plastic hinge from the column face toward the beam. This represents a good outcome because it can potentially eliminate the possibility of joint core brittle failure.

Plastic hinge relocation in RC joints as an alternative method of retrofitting using FRP

The efficiency of fiber reinforced polymers (FRPs) in enhancing the performance of deficient reinforced concrete (RC) joints has been investigated in recent years. Relocating plastic hinge from the column face toward the beam is an effective method of upgrading RC beam–column joints. This retrofitting approach might also prevent the formation of undesirable brittle joint failure. In this paper, the numerical results of analysing three FRP retrofitted RC joints are compared in order to investigate the effectiveness of FRP composites in improving the performance of the beam to column joints through the relocation of the plastic hinges away from the joint core. Different configurations of FRP application, including a novel retrofitting scheme at beam–column joints, are assessed and the efficiency of each composite architecture in relocating the plastic hinge is discussed. The results show that the newly proposed configuration is not only capable of relocating plastic hinges and improving the load carrying capacity of the joints but is also capable of preventing the typical interface failure.