Development Of Plastic Hinges Research Articles

Analysis of Factors Affecting the Seismic Performance of Widened Flange Connections in Mid-Flange H-Beams and Box Columns

Following the Northridge and Kobe earthquakes, research has increasingly focused on achieving high ductility in beam-to-column connections. This study investigates the seismic performance of connections featuring widened beam-end flanges in mid-flange H-beams and box columns, an area with limited prior research compared to I-section columns and narrow-flange H-beams. Detailed finite element modeling using ABAQUS 6.1.4 demonstrates that widened beam-end flanges significantly improve bending capacity and ductility by relocating the plastic hinge away from the connection, thereby enhancing seismic resilience. Key findings include the identification of optimal design parameters: flange length ranging from 0.55 to 0.75 times the beam flange width, beam flange cutting length between 0.36 and 0.39 times the beam depth, and flange cutting depth from 0.19 to 0.23 times the beam flange width. These parameters ensure effective plastic hinge development and improved structural performance. This study introduces a novel approach that emphasizes geometric optimization over material-based enhancements, offering a cost-effective and practical solution for improving seismic performance and extending previous research insights.

Seismic behaviour and design of a tall mixed reinforced concrete–steel structure supporting an oil refinery reactor

AbstractThis study investigates the seismic behaviour of a special mixed reinforced concrete-steel structure that supports an oil refinery reactor. The structure is 64.90 m tall and consists of three parts: (a) a reinforced concrete frame basement; (b) a steel braced frame that supports the oil reactor and (c) the steel reactor itself. A three-dimensional model of the structure is created to perform static non-linear (pushover) analyses in order to obtain the capacity curves and understand the overall inelastic behavior of the structure. The results of the pushover analyses reveal that the structure exhibits similar inelastic behavior in both horizontal directions and satisfies the capacity design principles. The structure exhibits limited ductility considering the fact that has been designed with a behavior factor of q = 1.5 and primary damages are expected mainly in concrete members. Subsequently, dynamic non-linear time-history (NLTH) analyses are performed utilizing the three translational components of three seismic motions recorded during past earthquakes. These results involve: (i) the maximum values for displacements, accelerations and base shears; (ii) the maximum stresses at critical points of the oil refining reactor and (iii) the formation of plastic hinges at columns, beams and braces of the structure. Contrary to pushover analyses, NLTH analyses revealed the development of plastic hinges, hence seismic damage, that do not follow the desirable formation pattern. Moreover, the accelerations and displacements observed are expected to cause failure of the piping and mechanical equipment, while local failure of the high-stress areas of the shell of the reactor may be possible. Localized strengthening might be necessary to avoid repair works and downtime after such seismic event.

Cyclic behavior and pushover analysis of large scale two-bay, two-story reinforced concrete frames infilled with walls with openings

This study presents experimental results on the seismic behavior of a large-scale two-bay, two-story RC frame with RC infill walls, including openings typical of low-rise RC row buildings in Taiwan. The test findings indicated that the specimen failed due to the failure of the vertical members of the first story. Specifically, the critical wall segments located between openings and between an opening and a boundary column and short columns resulting from the presence of these openings were shown to be the main contributors to the failure. Based on the observed phenomenon during the test, an analytical model was verified and proposed for the tested specimen’s pushover analysis. The selection of plastic hinges in the analytical model was determined according to the Taiwan Earthquake Assessment for Structures by Pushover Analysis (TEASPA). Pushover analysis performed by commercially available software indicated that the analytical model could well capture the specimen's behavior regarding peak base shear, initial stiffness, displacement of each story, and development of plastic hinges.

Elasto-Plastic Seismic Shear Distributions of Frame-Wall Structures

ABSTRACT In this study, theoretical and numerical methods were used to research seismic shear distributions of frame-shear wall structures under elasto-plastic conditions. The shear distributions of frame-shear walls were analyzed based on a simplified elasto-plastic analysis model of flexural shear. Based on a preliminary project, three groups of 2D models with different stiffness eigenvalues were designed and used to compare the shear distributions of whole structures and frames. The characteristics of the shear distributions of structures and frames and the development of plastic hinges were analyzed, and the rationality of shear adjustment based on Chinese standards was discussed from the perspectives of structural design, seismic performance and collapse resistance. The results revealed obvious differences between shear distributions of structures caused by strong vs. frequent earthquakes. For strong earthquakes, the shear distributions tended to be evenly distributed with respect to height, while the shear force of the bottom story was significantly larger than that of the upper stories. This was mainly caused by the redistribution of plastic internal forces due to the development of plastic hinges. The shear adjustment of the frame usually affected the reinforcement in the beams rather than in the columns, which contradicted the design concept of strong columns – weak beams. Additionally, shear adjustment had little effect on the seismic performance and collapse resistance of structures. This paper suggests that by ensuring the ability of strong columns, weak beams and plastic hinges to rotate, shear force adjustment can be prevented.

Practical Considerations in the Design of Passive Free Piles in Sliding Soil

The stabilisation of shallow translational landslides can be carried out by using large diameter concrete piles, with the aim of increasing the available strength along the slip surface. In the following article, 3D numerical models of a free-head flexible pile embedded into a translational type of landslide are studied. The landslide model has a given inclination angle, β, and a thickness, D, while the reinforced concrete pile has a fixed diameter, d, and a length, D + L, in the perspective of studying the failure modes B1, BY and B2 of free-head flexible piles. In this category of piles, collapse is reached with the formation of plastic hinges. Both the soil and the concrete are modelled with simple constitutive models, such as Mohr–Coulomb for soil and the elastic-perfectly plastic for the concrete pile, in order to carry out the design approaches provided by Eurocode, as well as to highlight some practical aspects of soil–structure interaction during the landslide displacements. The results highlight how the achievement of the shear strength in a flexible free-head concrete pile generally precedes the achievement of the ultimate bending moment associated with the development of plastic hinges. Furthermore, the axial load supported by the pile may itself contribute to the overall strength available along the slip surface.

A Review of Friction Dissipative Beam-to-Column Connections for the Seismic Design of MRFs

The use of friction-based beam-to-column connections (BCCs) for earthquake-resistant moment-resistant frames (MRFs), aimed at eliminating damage to beam end sections due to the development of plastic hinges, has been prevalent since the early 1980s. Different technical solutions have been proposed for steel structures, and some have been designed for timber structures, while a few recent studies concern friction joints employed in reinforced concrete structures. Research aimed at characterizing the behavior of joints has focused on the evaluation of the tribological properties of the friction materials, coefficient of friction, shape and stability of the hysteresis cycles, influence of the temperature, speed of load application, effects of the application method, stability of preload, the influence of seismic excitation characteristics on the structural response, statistical characterization of amplitude, and frequency of the slip excursion during seismic excitation. Studies aimed at identifying the design parameters capable of optimizing performance have focused attention mainly on the slip threshold, device stiffness, and deformation capacity. This review compiles the main and most recent solutions developed for MRFs. Furthermore, the pros and cons for each solution are highlighted, focusing on the dissipative capacity, shape, and stability of hysteresis loops. In addition, the common issues affecting all friction connections, namely the characteristics of friction shims and the role of bolt preload, are discussed. Based on the above considerations, guidelines can be outlined that can be used to help to choose the most appropriate solutions for BCCs for MRFs.

Investigation of loading intensity effect (LIE) on the failure mechanism of shield tunnel subjected to fire

The overload damage seriously threatens the service life of the tunnel structure, and the elevated temperatures under the extreme load of fire pose a more serious threat to the structure. In this study, a thermal–mechanical methodology is proposed to analyze the combined effects of loading intensity and fire on tunnel structures. The methodology is also validated by experimental studies. Impacts of loading intensity effect (LIE) on temperature distribution, deformation development and inner force distribution are discussed respectively. Results indicate that LIE aggravates heat flow invasion, making uneven temperature distribution of the segmental ring. On the other hand, LIE has a direct influence on the development of mid-span deformation of lining segments, and induces the failure of lining segments due to excessive deformation at the initial stage of heating. higher loading intensity induces a higher initial axial stress level of the tunnel structure. It is also found that the failure of the segmental ring can be attributed to the development of plastic hinges originated from the coupled thermo-mechanical effect. The findings not only reveal the combined effects of overload damage and fire on tunnel structures, but also provide valuable insights on fire prevention in case of tunnel fire.

Inertial and kinematic demands of isolated pile-supported wharves in liquefiable soils: Centrifuge tests

Pile-supported wharves in liquefiable soils are prone to severe damage during earthquakes. This study employs seismic isolation techniques to adapt for wharf construction, evaluating their seismic performance under lateral ground deformation due to liquefaction. Experimental and numerical analyses are necessary for confirming the efficiency of the isolation in decreasing the requirements for pile-supported wharves. The study initially tests two pile-supported wharves under geotechnical centrifuge conditions, one reinforced by isolation bearings and the other without. The objective is to simulate the force characteristics of isolated pile-supported wharves in liquefiable soils and to analyze the impact of isolation on reducing the seismic response of these wharves. Subsequent analysis delves into the interaction between inertia and kinematics for two types of pile-supported wharves, providing crucial insights. The development of plastic hinges for two kinds of pile-supported wharves under inertia and kinematics is also analyzed. Quantifiable thresholds are established to study the influence of isolation on the resistance of wharves to seismic disruptions, thus preventing pile-supported wharves damage.

Development of plastic hinges of pile groups subjected to lateral pushover

Development of plastic hinges of pile groups subjected to lateral pushover

Study on plug-pin energy-dissipating joint with integrated mild steel dampers

Plug-pin joints are designed for easy assembly and fast construction. Full-scale experiments were carried out on three exterior beams-to-column joints subjected to reversal cyclic loading. It has been proved from experimental results that the proposed connection not only guarantees structural integrity but also moves the plastic hinge away from the column edge. Based on the experimental results, a novel plug-pin connection with integrated mild steel dampers is proposed. The energy dissipation joint fully adopts a dry connection method, and the joint's ductility is significantly improved by the integrated energy-dissipating steel plates. Finite element models are established to study the effects of different diameters of steel bars and thicknesses of energy-dissipating steel plates on structural response and mechanical properties under low cyclic reciprocating loads. Parameter studies were carried out, and the obtained results indicate that the proposed joints can bear a greater displacement load than that of cast-in-place joints and achieve greater energy dissipation. The maximum bearing capacity of the joint can be improved by increasing the thickness of the energy-dissipating steel plates, but the bearing capacity decline period of the joint will appear in advance under the same order of loading. If designed properly, structures installed with the plug-pin joint will be expected to adjust the order of plastic hinge development, thus achieving better seismic performance.

Cyclic Behavior of T-Shaped Composite Plate Shear Walls–Concrete Filled

This paper presents findings from experiments conducted on four large-scale T-shaped concrete filled composite plate shear walls (C-PSW/CF) specimens subjected to axial force and flexure. A C-PSW/CF is a sandwich type of construction by which concrete (without rebars) is enclosed between steel plates connected by tie bars. One of the walls was subjected to a cyclic wind loading protocol and the other walls were cycled with a seismic loading protocol. Their dimensions were identical, but different axial loads (up to 30% of the crushing load of the infill concrete, Acfc′) were applied. The plastic hinge development was investigated along with the composite behavior and compared with the calculated plastic moment of the corresponding cross section. These tests along with the results on C-shaped wall tests were conducted to establish the development of design guidelines for high-rise core-wall steel buildings having C-PSW/CF as the primary lateral force resisting system.

Experimental and finite element analysis of flexural performance of steel-timber composite beams connected by hybrid-anchored screws

The shear connection between the steel and the timber slab is one of the keys to designing steel-timber composite (STC) beams. By three groups of four-point bending tests and finite element simulations, the effects of hybrid anchorage and filling materials on the flexural performance of STC beams were investigated. Firstly, compared with the STC beam connected by ordinary screws, when epoxy resin and mortar were respectively used as the filling material in the STC beams connected by hybrid-anchored screws, the slip stiffness values were increased by 18.79% and 48.40%, the capacity values were increased by 10.13% and 15.15%, and the maximum end slip values were reduced by 8.77% and 8.97%, respectively, indicating that mortar was more effective. Secondly, due to the strong restraint provided by the filling material and the H-steel flange for the screw tip and head, respectively, double plastic hinges were generated in the screw, and the development of double plastic hinges at both ends of the simply supported STC beam is more significant. Thirdly, finite element analysis showed that the mortar strength (greater than 30 MPa) had little effect on the flexural performance of STC beams connected by hybrid-anchored screws; increasing the number of hybrid-anchored screws can significantly improve the slip stiffness of the connection interface of STC beams and reduce the slip.

Study on Redistribution of Internal Force and Plastic Hinge Development of Mountainous Building Structures with Foundations at Two Different Elevations

This study was conducted to study the redistribution of internal force and the development of the plastic hinge of an MBS with foundations at two different elevations considering the torsional effect. The results indicate that the redistribution of the base shear of MBS is evident at different embedding ends, and the redistribution of story shear on different floors also took place. The redistribution of the shear force of columns is different at the upper- and lower-embedding sides, and the internal force redistribution is more prominent along the slope direction. Consequently, the redistribution of the internal force of MBS should be considered in practical seismic design. Furthermore, the damage of MBS is transferred from the floors above the upper-embedding end to the floors under the upper-embedding end with the increase in the seismic intensity, where the elements at the floors above the upper-embedding end suffer the most serious damage, and the damage is unevenly distributed in the upper-embedding story and the adjacent upper story. The lower-embedding column is more prone to hinge across the slope direction because of the torsional effect. With γintra changes, the redistributions of the shear force of the base, story, and column are different. A larger γintra would result in a weaker redistribution of base shear. The redistribution of the story shear of the 1st floor and its columns along the slope direction shows an increasing-decreasing tendency with the increase in γintra, and the redistribution is the most serious when γintra is 0.4. While across the slope direction, the redistribution of the story shear tends to be weakened as γintra increases. The forming of the plastic hinge of single-frames along the slope direction is related to γintra and γnon, especially the damage of the upper-embedding columns. The torsional effect has a significant influence on the damage of the single-frames across the slope direction. Some measures should be taken to improve the bearing capacity of the upper embedding columns and columns on floors under the upper-embedding end, as well as the drift ductility of the upper-embedding columns.

Rebar Replacement in Severely Damaged RC Bridge Column Plastic Hinges: Design Criteria and Experimental Investigation

This paper presents a procedure for rehabilitating plastic hinges with damaged/fractured weldable longitudinal rebars in severely damaged reinforced concrete (RC) bridge columns and possible improvements regarding connection protection and plastic hinge development. Damaged/fractured longitudinal rebars are replaced with new rebar segments, and the basis of this approach involves connecting intermediate machined parts to the original longitudinal rebars by welding with an off-the-shelf steel equal angle. The proposed rehabilitation design procedure is based on capacity design principles, with equations that define the new geometries and required ductility, and it is validated experimentally on three 1∶6-scale RC circular column specimens. Compared with the original columns, the ductility capacity of the rehabilitated columns increased from 39% to 58%, and the energy dissipation (equivalent viscous damping ratio) increased from approximately 50% to 250%. The base shears of the rehabilitated columns were smaller than those of the original columns owing to the reduction in the rebar area; thus, shear failure was avoided, and the demand on the foundation was reduced. The rehabilitation procedure, by adopting a welding connection that is easily performed on site and concentrates the damage in the new rebar segments, promises to be a quick, simple, reliable, and effective means to improve the ductility and shear capacity of RC bridge columns without using mechanical couplers or changing the column dimensions.

Effect of The Haunch Angle and Stiffener Types on Column-Beam Connection Behaviour Under Static Loading

The strong column-weak beam principle, one of the earthquake resistant building design theories, require the connection area to be strong enough so that the plastic hinge forms in the beam. One of the proposed solutions is to strengthen the column-beam connection zone in steel connection with haunches. This study aims to look at parametrically behavior of column-beam haunched connections under the 100mm vertical displacement controlled loading using the finite element method. To obtain this, a total number of 21 finite elements model with 15, 30, and 45 degrees angles and 6 various stiffener types has been modeled by ABAQUS software. The research later discussed behavior of underlying components of haunch connections models such as the load-displacement curve, bearing capacity, extended end plate bending, stress distribution, and the position of the plastic hinge's development after finite element analysis. The study found that decrease in haunch angle improve the connection's bearing capacity, while in this case, the failure modes and plastic hinges will occur close to the joints which does not meet the code requirements. The article concludes that the 30-degree haunch angle is the most appropriate one in haunch connection and the three parallel and K-stiffeners is the most suitable reinforcement type for the haunched connections.

Performance-Based Design of an Irregular RC Structure with and without Supplemental Damping

Many countries are undertaking changes in earthquake design codes, the main reason for it is that the existing building codes do not specify the performance criteria of individual structural elements under various levels of shaking. Even though some buildings performed well in life safety aspects, many of those failed in safeguarding the building from high extent of structural damage under severe shaking. Retrofitting had also proved to be uneconomical for the buildings to perform better under severe shaking. In the current earthquake codes, the displacements and forces are within the elastic limit i.e., the assumed behaviour is linear. But the response of a structure to the major earthquakes is not elastic. There is a high chance of yielding and the development of plastic hinges in the members. Therefore, it is required to perform the non-linear analysis for assessing the inelastic behaviour of the structure. In the present study non-linear static analysis was adopted to assess the seismic performance of an irregular building in plan with re-entrant corners using the capacity spectrum method. If either the drift limit of the structure or the response of the hinges is exceeding the desired level of performance, the structure is fed with supplemental damping to ensure the required performance. It was observed that the formation of hinges crossed life safety level and entered the collapse prevention state. As the response exceeded the desired level of performance a methodology to calculate the required supplemental damping for the structure is proposed. Depending on the level of safety of the structure, an appropriate supplemental damping value can be obtained from the proposed performance plots.

Generalized Plastic Hinge Method for Failure Analysis of Steel Framed Structures

For steel framed structures with small geometric nonlinearity, the conventional first-order plastic hinge method (FPHM) estimates rapidly the failure mode and ultimate strength of frames according to the proportionality property. However, it ignores the combined action of multiple internal forces on the development of plastic hinge, leading to mistakes in estimating the failure mode and ultimate strength of frames. Though the second-order plastic hinge method (SPHM) and the refined plastic hinge method (RPHM) overcome this problem, they lose the FPHM’s proportionality property and the high efficiency of computation as well. In this paper, the generalized plastic hinge method (GPHM) featuring proportionality property is proposed for steel framed structures to overcome the drawbacks of the conventional FPHM, the SPHM and the RPHM. Firstly, a linearly elastic analysis is performed on the steel framed structure between the formation of any two plastic hinges; then the strength reduction factor is developed by means of the generalized yield criterion (GYC) for modification of the sectional strength of frame component under multiple internal forces during loading process. Secondly, the element bearing ratio (EBR) is defined on the basis of the homogeneous generalized yield function and is in proportion to the loading, so that the position of generalized plastic hinge and the corresponding load increment are determined for each loading step according to this proportional property. Furthermore, the balance vector is developed by means of the GYC and the slope-deflection relation to modify the result of the calculated load increment. Finally, several examples are presented to validate the much higher computational efficiency and accuracy of the proposed method by comparing it with the plastic zone analysis (PZA), the SPHM and the conventional FPHM.

Energy Dissipation Enhanced by Multiple Hinges in Bridge Piers with CFST Y-Shaped Fuses

Concrete-filled steel tubular Y-shaped (CFST-Y) piers are good candidates for meeting the structural and aesthetic requirements of bridges. By using the theoretical and nonlinear static (pushover) analyses, the seismic performances of three types of CFST-Y piers were evaluated at different seismic hazard levels. The theoretical formulas were first proposed to estimate the lateral stiffnesses for piers with different pier–deck connections. Then, the structural ductility with the development of plastic hinges in piers was investigated based on the pushover analyses. The results demonstrate that the structural dimensions, deck mass, shear limit, and stiffness of bearings can remarkably affect the formation of hinges and thereby lead to different energy dissipation patterns to achieve the expected performance in piers. The findings suggest an economic design strategy of piers, using CFST-Y members as energy dissipation fuses with multiple hinges, to achieve low-level seismic performance cost-effectively.

Experimental study on influence of host rock strength on shear performance of Micro-NPR steel bolted rock joints

The development of deep underground engineering has brought new challenges to bolt materials. Micro-Negative Poisson's Ratio (NPR) steel is a new type of bolt material with high strength, high toughness, and super energy absorption. The effect of host rock strength on the shear performance of micro-NPR steel anchoring rock joints was studied by performing an indoor direct shear test . Ordinary Q235 steel bolted joints and unbolted joints were set as the test control groups. The shear force-shear displacement curves, surface failure characteristics, bolt deformation, fracture characteristics , shear strength, and shear energy absorption were all compared and analyzed. The study found that the bolted rock joints have significant ductile failure characteristics under shear load , which effectively improves the brittle failure characteristics of the unbolted rock joints. The ability of the rock to resist the crushing damage of the bolt is continuously enhanced with an increase in the host rock strength, while the damaged area of the grout and rock mass at the opening of the joint surface gradually decreases. The failure area of the Q235 steel bolted joint surface is significantly smaller than that of the micro-NPR steel. Additionally, the equivalent internal friction angle , equivalent cohesion, and peak shear strength of the micro-NPR steel are significantly higher than those of Q235 steel. The higher the strength of the host rock, the greater the bolt peak shear strength of the joint. The bolts undergo local shear deformation near the joint surface, and the bolt deforms into an ‘S’ shape after shearing. The improvement of the host rock strength limits the development of the bolt's plastic hinge to a position far from the joint surface. The shear fracture displacement and shear energy absorption of the bolt decrease with an increase of the host rock strength. The shear energy absorption capacity is at least 3.7 times higher than that of Q235 steel. When the host rock strength is low, the bolt yields in tension and bends at the plastic hinge, at which time tension-bending failure occurs. With an increase of the host rock strength, the bolt undergoes tension-shear failure. The high strength and high ductility of traditional steel are well balanced by the micro-NPR steel, with the tensile and shear resistance of the steel bolt being greatly improved, which allows for large deformation and super energy absorption in the bolt material, which allows for a wide range of applications at deep engineering sites.

Seismic Performance and Design of the Fully Assembled Precast Concrete Frame with Buckling-Restrained Braces

Although precast concrete structures have been widely used in building engineering, their application in moderate- and high-seismic zones is restricted because of poor lateral performance. This study proposed a fully assembled precast concrete frame with buckling-restrained braces (PCF-BRB) to simplify construction and enhance seismic performance. A nonlinear finite element model of the PCF-BRB was established using ETABS to investigate the feasibility of its use in seismic regions. The accuracy and rationality of the analysis model were verified by existing experimental data. Furthermore, the seismic performance, including plastic hinge development, internal force distribution, maximum inter-story drift, and energy dissipation, of the PCF-BRB was evaluated through static pushover analysis and dynamic time history analysis. The analysis results showed that the PCF-BRB has good seismic performance. Finally, this study provided a recommended seismic performance factor for design, namely the stiffness ratio of buckling-restrained braces (BRBs) to the frame (k, defined later) for the PCF-BRB structure. It is recommended that the stiffness ratio range of low-rise PCF-BRB structures should be 1.5 ≤ k ≤ 3.0, and that of high-rise PCF-BRB structures should be 3.0 ≤ k ≤ 4.0.