Flange Cover Plate Research Articles

Design theory of self-centering column foot joint with dog bone weakened flange cover plate

Basing on the concept of post-earthquake repairability, plastic damage control, and self-centering, this study introduces a novel self-centering column foot joint with dog bone weakened flange cover plate (FCP) for prefabricated steel structure. The method and design theory for the target yield load and initial stiffness of the new joint were established. Parametric research was conducted using finite element simulation to assess the influence of the dog bone weakened FCP thickness, initial cable force, and axial compression ratio on the bearing performance of the new joint, thereby verifying the above method and theory. The results reveal the accuracy of the proposed method for determining the target yield load and initial stiffness, and provide practical design guidance for the new joint. The design theory values of the new joint and the simulation values demonstrate an error within 10%, which satisfies the engineering accuracy requirements. The corresponding procedures and suggestions for the design theory of this new joint were finally provided. Based on design theory, the overall plastic damage concentrates on the dog bone weakened FCP, successfully controlled by the new joint design, ensuring minimal damage to the main structure and demonstrating good bearing capacity and self-centering performance.

Numerical investigations of earthquake resilient beam‐to‐column joints with replaceable BRFCPs using different restraint plates

AbstractA replaceable buckling‐restrained flange cover plate (BRFCP) was previously proposed to improve seismic performance of beam‐to‐column joints. Quasi‐static tests were conducted to investigate the seismic performance of beam‐to‐column joints using three different formats of restraint plates for BRFCP: no restraint plate, separated restraint plate, and integral restraint plate. The test results showed that both separated and integral restraint plates restrained the core plate buckling under compression and increased the beam‐to‐column joints load resistances. This paper first validates finite element models (FEMs) using test results. Then the validated FEMs are used to investigate influences from different BRFCP design parameters (such as core plate thickness, restraint plate thickness and length, restraining gap size, and restraint plate blot prestress force) to the beam‐to‐column joint load–drift hysteretic responses. Finally, the paper proposes a design range of each investigated design parameter and a BRFCP design procedure.

Experimental investigations of beam-column joints with replaceable BRFCPs using sliding restraint plates

This paper proposes a replaceable buckling-restrained flange cover plate (BRFCP) for steel beam-column joints with cantilever beam segments, in which a sliding restraint plate (SRP) with slotted holes is used to constrain the core plate buckling deformation and simultaneously control the restraint plate without significant damage. First, theoretical analyses and design considerations were presented for this joint. Second, cyclic loading tests were conducted on five joints with different BRFCP configurations, including different formats of restraint plates (discontinued or sliding restraint plates), filling plates (discontinued or sliding filling plates), and restraining gaps with different sizes. The test results showed that the damage of the proposed joint was visually observed only on the replaceable core plates and was not observed at any other structural components. The SRP can effectively constrain the buckling deformation of the core plate in comparison to the discontinued restraint plates; thus, the proposed joint showed more stable force–deformation hysteresis. The continuity of the filling plates and the restraining gap size had little influence on the overall hysteretic response of the joint. However, a larger restraining gap caused larger stress in the restraint plates. Finally, numerical models of the test joints were established in ABAQUS and validated by the test results, which can serve as a reference for further research.

Seismic Performance of Earthquake Resilient Steel Frame Joints with Replaceable Buckling-Restrained Flange Cover Plates

ABSTRACT This paper proposes replaceable buckling-restrained flange cover plates to improve the seismic performance and resilience of steel frame joints. Five full-scale specimens were designed and tested under cyclic loads to investigate the hysteretic performance. The investigated parameters were the core plate thickness (affecting strength ratio α and thickness-gap ratio β) and restraining plate configuration (affecting restraining length ratio λ and restraining plate disconnected position ratio ψ). Numerical models were established using ABAQUS and verified through comparisons with experimental data and phenomena. The results show that the proposed joint can achieve the expected target of buckling-restraint and damage control.

Experimental study of plate-buckling type earthquake-resilient prefabricated steel beam-column joints with replaceable double flange cover plates

The damage control and post-earthquake repair of beam-column joints is a hot research topic in the seismic field. Therefore, a new type of earthquake-resilient prefabricated steel beam-column joint with replaceable double flange cover plates (RFCP-ERPSJ) was proposed. The yield load of this joint can be controlled by the buckling or slip of plates, so it can be divided into plate-slipping type and the plate-buckling type. Considering that the yield load of the plate-buckling type RFCP-ERPSJ is stable, firstly, a practical design procedure and design theory of the newly plate-buckling type joint is proposed in this paper. Then, to study the seismic performance and post-earthquake repairability of this RFCP-ERPSJ, a total of 6 full-size specimens are designed and subjected to a low-cycle reciprocating loading test and constant-amplitude low-cycle fatigue test. The effects of the thickness of FCPs, the material strength of FCPs, dog-bone width, amount of FCPs connecting bolts, and bolt spacing at the middle row on the seismic performance and energy dissipation performance of the joint are studied. The experimental results are also compared with the theoretical results. The research showed that the plastic hinge of the joint could be concentrated on the replaceable FCPs, so as to protect the beams and columns. By replacing damaged FCPs and bolts, the repaired joint had the same performance as the original joint. After comparison, the theoretical yield load is in good agreement with the experimental yield load. Besides, the small thickness and dog-bone width of FCPs can reduce the load carrying capacity and energy dissipation capacity of joints, and improving the material strength of FCPs will reduce the ductility of joints and increase the risk of plastic damage to the beams and columns. If the amount of FCPs connecting bolts is reduced, the specimens mainly dissipate energy by the slip of FCPs, and the load carrying capacity will descend. Excessive bolt spacing at the middle row will reduce the load carrying capacity and energy dissipation capacity.

Seismic performance of steel-PEC spliced frame beam

In this paper we propose a novel form known as the steel-PEC spliced frame beam (SPSFB), which is intended to maintain the advantages of the PEC beam while reducing the consumption of steel. In the SPSFB, an independent H-beam (mid-portion beam) is replaced by the PEC beam with a thinner flange. The PEC and stub beams are connected by web bolts, a welded flange, and a girth welded flange cover plate to improve flexural capacity. Low cycle loading tests were conducted on five SPSFB specimens testing the variables of the concrete strength, the length of the stub beam, and the length of flange-plates. Two failure modes were observed, and the related seismic behavior was investigated. When the damage occurred at the bottom of the PEC beam, higher grade concrete was correlated with better seismic performance. When the damage occurred at the bottom of the stub beam, setting an appropriate length of stub beam and flange-plate can improve the hysteretic capacity and further reduce steel consumption. Based on elastic and plastic analysis, the bearing capacities and deformation were calculated. The calculated results agreed well with the experimental results.

Buckling performance evaluation of steel cellular beams strengthened with flange cover plate

Buckling performance evaluation of steel cellular beams strengthened with flange cover plate

Seismic performance of joint for H-beam to CFST column with field-bolted flange-splicing

A novel shop-welded joint for H-beam to concrete-filled steel tubular column with field-bolted flange splicing used in prefabricated steel structure is proposed. Four full-scale specimens were tested under cyclic loads, and the effects of bolt diameter, beam flange cover plate, widened beam flange at the end, and the flange thickness on the seismic performance of joints were studied by experiments and numerical simulation. The seismic performance of the shop-welded joint is compared to that of traditional welded joints. According to the results, the beam flange thickened by welding cover plate and widened by welding plate at the beam end can improve the yield resistance, ultimate resistance, stiffness, ductility, and energy dissipation capacity of the joint, while the bolt diameter and the flange thickness did not make significant influences. The shop-welded joints could be regarded as rigid. Adding cover plate, widening beam flange, or increasing column base flange thickness can effectively reduce the beam end stress and avoid brittle failure of welds under rare earthquakes. Simplified formulas for the yield and ultimate loads of the shop-welded joint were proposed.

Experimental study of earthquake-resilient high ductility prefabricated opening-web steel channel beam-column joint

In order to improve the construction efficiency and precision of prefabricated steel structures, and effectively protect the main members of the structures in the earthquake, a new form of joint was proposed in this study. This new earthquake-resilient high ductility prefabricated opening-web steel channel beam-column joint (HDPSJ) was designed on the basis of the concepts of modular construction, damage control and buckling restraint. A total of six joint specimens were tested under low-cycle load to study the seismic properties and post-earthquake restoration properties of the new joint, and the curves of hysteresis, skeleton and strain, and the energy dissipation ability of specimen were obtained. This paper mainly studied influences of the thickness of the flange cover plate (FCP), the weakened degree of FCPs and the quantity of bolts connecting the FCP on the seismic properties and restoration properties of joints. U-shaped web connecting plate (UWCP) was applied to this type of joint to restraint the buckling of FCPs. The results show that the HDPSJs have excellent bearing capacity, ductility and post-earthquake repair capacity, and the indexes of the restored joints are still up to the seismic standards; the yield load of the joint principally depends on the thickness of FCP. The slip of FCP is mainly determined by the number of flange connecting bolts; the UWCP can effectively improve the ductility of the joint. The hysteretic property of the joint is stable during the low-cycle constant amplitude load, which shows the joint also has the function of a damper.

Cyclic loading tests of self-centering prestressed prefabricated steel beam-column joint with weakened FCP

Earthquake-resilient structures are an ideal new direction for seismic design of structures. In recent years, earthquake-resilient structures have gradually become a research hotspot in seismic field. Based on the idea of damage control, this paper proposes a self-centering prestressed prefabricated steel beam-column joint (SPPSJ) with dog bone weakened flange cover plate (FCP). By designing three sets of test specimens for cyclic loading test, the thickness of the dog bone weakened FCP and the pretension of the cable were studied, and the hysteresis curve, skeleton curve and cumulative energy dissipation curve of the joint were obtained. Then, the reliability of the test results is verified by numerical analysis. Finally, the design proposals of SPPSJ are put forward, which is convenient for the popularization and use of SPPSJ. The results show that: The SPPSJ has good bearing capacity, seismic performance and self-centering capacity after earthquake, which can effectively dissipate energy through plastic deformation of FCP, and realize post-earthquake resetting of the joint through prestressed cables. On the premise of the same load-bearing capacity, it can obtain that the SPPSJs with dog bone weakened FCP have better energy dissipation performance and lower requirement cable pretension, which makes the prestressed cable maintain high safety factor during the loading process. There is a certain range of correspondence between the thickness of the dog bone weakened FCP and the cable pretension. When the yield load ratio of the dog bone weakened FCP to high-strength bolts on web connection plates and the cables is about 3/7, the energy dissipation capacity and self-centering capacity of the SPPSJ can reach the best balance.

Low-cycle reciprocating loading test of Earthquake-resilient prefabricated steel frame with double FCPs

As an important component, the mechanical properties of the prefabricated beam-column steel joints have an effect on the mechanical mechanism of the whole frame structure system. According to the concept of replaceable post-earthquake and plastic damage control, the earthquake-resilient prefabricated beam-column steel joint with double flange cover plates (ERPBJ with double FCPs) has been proposed. To investigate the overall performance of the new steel frame with the new joint, four frame specimens are designed, and low-cycle reciprocating loading test and low cycle fatigue test had been carried out on them. The influence of the number of bolts, width of weakened dog-bone, post-earthquake repairability and different loading protocols have been studied. The failure mode, hysteretic curve, skeleton curve, the displacement ductility coefficient, the equivalent viscous damping coefficient have been obtained. The study results shows that the new earthquake-resilient prefabricated steel frame (ERPSF) with double FCPs have the advantage of controlling the damage positions. The plastic damage occurs on the replaceable FCPs, which ensures the structural performance, and the main structural components don not undergo plastic deformation. The decrease of the number of bolts will make the slip of FCPs more obvious, which will lead to the failure to fully utilize the bearing capacity of the FCP and reduce the ultimate load of the frame, but will improve the ductility and energy dissipation capacity of the frame. The behavior of ERPSF with double FCPs is stable under low cycle fatigue loading test and many repair tests, which indicates that the ERPBJ with double FCPs can be used as a damper in the frame structure system.

Experimental study of earthquake-resilient prefabricated composite joint with T-shape connector

Based on the idea of damage control, a new type of earthquake-resilient prefabricated composite joint (ERPCJ) with the T-shape connector has been proposed. On the premise of considering the composite action of concrete slab and beam-column joint, the seismic behavior, post-earthquake recoverability and failure mode of concrete slab under different loading protocols are studied. By changing the connection mode between flange cover plate (FCP) and beam, the influence of the relative slip between FCP and beam on the bearing capacity and energy dissipation capacity of the specimen are also studied. The low frequency cyclic loading tests and low cyclic fatigue tests of six specimens show that the basic and repaired specimens of the prefabricated composite joints with recoverable functions show good seismic behavior. The plastic damage of steel joint is concentrated on FCP, while the main structural members such as beam and column still maintain elasticity. The collaborative work of T-shape connector with foams, concrete slab and the gaps between concrete slab and column can reduce the plastic damage of concrete slab. The main reason of concrete slab damage is the strong squeezing effect between concrete slab and T-shape connector in negative moment zone. Whether FCP can slip or not can make a great difference in the bearing capacity and energy dissipation capacity of the joint. The damage and deformation of FCP are small when FCP and beam can slide relatively, but the bearing capacity and energy dissipation capacity of the joint are low. The bearing capacity and energy dissipation capacity of the joint are high when FCP and the beam cannot slip relatively, but FCP will cause serious plastic damage and even fracture.

Seismic behavior of assembled beam-column joints with C-shaped cantilever section

A kind of assembled steel beam-column joint with C-shaped cantilever section was proposed. The influences of the lengths of cantilever sections and cover plates on seismic performance of the joints were discussed through low-cycle reciprocating loading tests and numerical simulations. Then the sensitivity analysis of key parameters such as thickness and width of flange plate,bolt number and cover plate's length were carried out. The results show that the joint consumed energy through warping deformations of end plate and the friction slippages between flange of beam, C-shaped cantilever section and cover plate. By reasonably increasing the lengths of C-shaped cantilevers section and cover plates, it can ensure that the joints have high bearing capacities, while significantly improving energy dissipation capacities of the joints. Parameter analysis showed that increasing thickness of the flange plate can effectively improve the stress concentration at root of the cantilever section. Reducing width of flange plate has a great impact on bearing capacity and initial stiffness of the joint with the maximum drop amplitude of 13.1% and 18.9%, respectively.

Cyclic loading tests of earthquake-resilient prefabricated steel cross joints with different FCP connections

Prefabricated steel structure has been promoted in construction for its advantages in the greening, industrialization and informatization of buildings. Meanwhile, the earthquake-resilience of steel structures has become a research hotspot in the field of international seismic engineering. In this paper, five earthquake-resilient prefabricated steel beam-column cross joints (ERPCJs) were studied by the low-cyclic loading tests. The influence of flange connecting bolts number, flange connection forms, bolt distance of middle row and bolt hole forms on the seismic performance, failure mode and other key performance indexes were studied. The tests results show that ERPCJs with reasonable parameters have outstanding bearing capability and seismic behavior. The beams of each specimen were damaged slightly or basically free from damage. Also, earthquake-resilient requirement could be quickly achieved by replacing connecting plates and high-strength bolt groups. Reducing the connecting bolts could make the joint fully utilize the sliding friction of flange cover plates (FCPs) to dissipate energy, and enhance ductility and rotation of the joint, but it could reduce joint’s initial stiffness and ultimate bearing capability at the same time. The smaller bolt distance of middle row has little effect on the yielding load of the joint, but can improve joint’s ultimate bearing capability. Besides, slotted holes on the cantilever beam can avoid the stressconcentration resulting from the compression of bolt rods and bolt hole walls, as well as can also effectively realize sliding energy dissipation of the FCPs.

Cyclic loading tests of an earthquake-resilient prefabricated steel frame with open-web steel channel beams

Based on the ideas of damage control and energy dissipation by sliding, this paper puts forward an earthquake-resilient prefabricated steel frame with two open-web steel channel beams (OWSCBs). To study its seismic performance and post-earthquake repair performance, the low frequency cyclic loading tests and low cyclic fatigue tests were carried out on five specimens, and several seismic behavior indicators such as the hysteretic curve, the slip curve, the strain analysis curve and the skeleton curve of frames were obtained. The influence of the thickness of the flange cover plate (FCP), the number of connecting bolts in the FCP and the residual deformation on seismic performance of prefabricated steel frames before and after restoration were mainly investigated. The results show that there are two main failure modes of the specimen, one is FCP friction sliding and the other is local buckling deformation of FCP dog-bone weakened section, while the main components such as beams and columns are still in the elastic stage. The repaired specimens have the same experimental phenomena and seismic performance as the initial specimen, which indicates that the functional restoration of prefabricated steel frame structures can be realized by repairing beam-column joint connecting devices. The repair process of the specimen with residual story drift went well, and this specimen still showed good mechanical and seismic performance after repaired. The overall bearing capability of the specimens decreases obviously with the thickness of the FCP decreasing. The decrease in the number of the connecting bolts in the FCP will reduce the critical sliding load of the FCP, which will lead to the slippage of the FCP in advance and reduce the overall bearing capability of the specimens.

Experimental study of earthquake-resilient prefabricated opening-web steel channel beam-column joint with double FCPs

In order to facilitate floor assembly and pipeline paving, this paper puts forward a new kind of prefabricated opening-web steel channel beam-column joint with double flange cover plates (POWSCBCJ) which is based on the design concept of plastic damage concentration and replaceable damage components. Six quasi-static reciprocating loading tests were carried out on four joints, and the hysteretic curves, skeleton curves, slip curves and strain curves of each specimen were obtained. The effects of thickness of flange cover plate (FCP), the quantity of connecting bolts and the bolts spacing of FCP and other parameters on the seismic performance and post-earthquake repairable performance of the joint are mainly investigated, and the post-earthquake repairable function, and fatigue performance of the joint under low-cycle reciprocating load are evaluated. Experimental study shows that this kind of joint has good bearing capacity, seismic performance and low-cycle fatigue performance. The joint can transfer the plastic hinge to the replaced FCP by strengthening the flange of the cantilever beam and weakening the FCP, so as to protect the major components such as beams and columns, and the joint function can be quickly repaired by replacing the energy dissipation components after earthquake; the repaired joint also has good bearing capacity and seismic capacity. Each design parameter has great influence on the bearing capacity and energy dissipation capacity of the joint.

Experimental study of an earthquake-resilient prefabricated opening-web steel channel beam-to-column joint with flange cover plates

Post-earthquake structural repair combined with prefabricated steel structures is an important aspect of repairing buildings damaged by earthquakes and has been extensively studied by earthquake engineering scholars. Based on the concept of plastic damage concentration and replaceable damage elements, and considering the convenience of floor assembly and pipeline pavement, an innovative earthquake-resilient prefabricated opening-web steel channel beam-to-column joint (POWSCBCJ) with flange cover plates (FCPs) was proposed in this paper. By varying four influencing parameters and applying three loading protocols, eight low-frequency cyclic loading tests were carried out on eight full-scale specimens of a new type of earthquake-resilient POWSCBCJ. The seismic behavior and earthquake-resilient performance were evaluated by varying parameters such as the thickness of the FCPs, bolt spacing in the middle row, width of the dog-bone reduced sections, number of bolts, and loading system. The experimental results show that the thickness of the FCPs is the main factor affecting the yielding load and bearing capacity of the joint. In addition, an appropriate number of connecting bolts on the FCP and the bolt spacing in the middle row are conducive to improving the energy dissipation ability of the specimen. At the same time, the hysteretic performance of the joint is stable during the process of equal amplitude loading, indicating that it can be used as a damper.

Influence of bolts on seismic performance of earthquake-resilient prefabricated sinusoidal corrugated web steel beam-column joints

Earthquake-resilient structures have been widely recognized and applied in the seismic field of prefabricated steel structures due to their excellent performance. The prefabricated sinusoidal corrugated web steel beam-column joint (PSCWJ) with the earthquake-resilient design concept has been previously proposed. To study the impact caused by the bolt parameters on the seismic behavior of the new PSCWJ, five specimens were designed, with varying the number of flange connecting bolts, type of bolt holes, and interval between the middle bolts. A low cycle reciprocating load test and the finite element (FE) simulations were conducted on the specimens to determine the failure mode, energy dissipation capacity, ductility, hysteretic curves, sliding curves, strain curves, skeleton curves, and other main indexes on seismic performance. And the study indicates that the PSCWJ has excellent bearing capacity and seismic performance, the new prefabricated joint can realize the dual energy dissipation by buckling and sliding of the flange cover plate (FCP), and the number of flange connecting bolts directly determines the sliding load of FCPs. A rational interval between middle bolts can control the buckling load of FCPs and provide the joint with a satisfactory bearing capacity. The setting of slotted hole can increase the rotation and energy dissipation capacity of the joint. Further, the energy dissipation performance of the repaired specimens is stable under the low frequency constant amplitude loading, thereby ensuring that the PSCWJ can be used as a damper.

Development and experimental investigation of hybrid precast concrete beam–column joints

In this study, an innovative type of hybrid beam–column joint using energy dissipated connection plates and I–shaped steel connectors to connect beams and columns was developed. Five interior beam–column specimens including a monolithic specimen and four hybrid precast joints, were tested under reversed cyclic loading to evaluate the seismic behavior of the connections. Test variables were the hybrid connection forms, flange cover plate, and steel fiber concrete usage. During the test, the hysteresis curves and cracking patterns were recorded. The seismic indicators, such as stiffness degradation, strength, energy dissipation, and ductility were determined. The test results revealed that the hybrid joint with the energy dissipated connection plates and steel fiber concrete failed in a typical flexural mode, exhibited stable hysteretic responses, and showed satisfactory seismic performance. The strength and cumulative energy dissipation of the proposed joint were higher by 46.6% and 230.9%, respectively, when compared with the monolithic specimen. The proposed hybrid connection could effectively transfer the plastic hinges to the connection region, reduce the damage and mitigate the stiffness deterioration due to the energy dissipated connection plates and the tensile deformability of the steel fiber. Therefore, the hybrid beam–column joints had superior performance to resist seismic loading. The developed seismic beam–column joints give a viable alternative for the precast concrete moment–resisting frames due to easy construction.

Experimental study of earthquake-resilient prefabricated beam-column steel joint with L-shaped plate

The research of prefabricated steel structure have become a hot topic in international structural engineering, which accelerates its promotion and application. Based on the idea of damage control, an earthquake-resilient prefabricated beam-column steel joint (PBCSJ) has been proposed, which can make the plastic damage occur at the flange cover plate (FCP) by reasonable design of the FCP thickness, middle bolts interval and other parameters. It is ensured that no plastic damage occurs at the main components such as beams and columns. Thus, joint can be repaired by replacing the connection devices to restore its use function. In this article, four specimens are designed, and the quasi-static loading tests and the numerical simulations are conducted to the four specimens and two repaired specimens. The impact on the seismic performance caused by the FCP thickness, FCP connecting bolts number, beam gap and other parameters, as well as the post-earthquake resilience are emphatically investigated. The failure mode, hysteretic curves, skeleton curves and other main performance indexes are obtained. The study shows that: PBCSJ can dissipate energy through the FPC plastic deformation; the thickness of FCP has a relatively big influence on the joint bearing capacity and energy dissipating performance; the decreasing number of FCP connecting bolts would cause the FCP sliding; the insufficient gap of beams would cause the local plastic damage due to the extrusion of the beams. In addition, the joint before and after the repairing would have excellent bearing capacity and energy dissipating performance. The results of the refined finite element (FE) analysis basically match the test results, and can be used as an important tool for the performance study of such type of joints.