U-shaped Steel Plate Research Articles

Experimental study on the seismic performance of prestressed wood joints with buckling-restrained rods

Adding energy dissipaters to prestressed wood joints with reinforced beam-column interfaces is the main way to improve their seismic performance. In this paper, three quasistatic tests for beam-column edge joints with buckling-restrained rods (BRRs) were performed, and the effects of different reinforcements for beam-column interfaces and BRR connection methods on the stiffness, bearing capacity, energy dissipation, and self-centering performance of the joints were analysed. First, for BRRs connected with steel supports, the core member exhibited significant multi-wave deformation; for BRRs connected with steel pins, the slippage of the steel pins can easily lead to bending failure of the BRR end. Second, after adding BRRs, the bearing capacity of the joints increased by 24.8% on average, the final degradation rate of the secant stiffness decreased by 13.8% on average, and the equivalent viscous damping ratio at 0.03 rad drift increased by 17.3% on average. Third, compared with the joint reinforced by the combination of the U-shaped steel plate and screws, the skeleton curve of the joint reinforced by the combination of the flat steel plate and screws had little difference, but the final prestressing loss and residual drift were reduced by 14% and 74%, respectively. It was recommended to use the simpler reinforcement combining the flat steel plate and screws to improve construction efficiency. Finally, compared with steel pins, BRRs connected with steel supports were more conducive to improving the seismic performance of joints at large drifts. Among them, the equivalent viscous damping ratio increased by 29.3% on average. This study can give designers flexibility when selecting the interface reinforcements and BRR connection methods. These research results highlight the good seismic performance of prestressed wood joints with BRRs, which is conducive to further promoting the application of prestressed wood structures.

New reinforcements combining a steel plate and screws to enhance beam-column contact surfaces for prestressed timber joints

ABSTRACT The beam-column contact surface of joints in prestressed timber frames is one of the key factors determining structural performance. In this paper, a new reinforcement combining a steel plate and screws was proposed, and the effect of the reinforcements on the performance of joints was investigated by quasistatic tests for 5 beam-column edge joints. First, compared with the conventional joint, the joints reinforced by the steel plate and screws had an average increase in capacity of 25.8% and an average reduction in the degradation rate of the secant stiffness of 14.5%, which were beneficial for resisting repetitive loading. Then, the rate of the final prestressing loss and residual drift of the joint reinforced by the flat steel plate and screws were reduced by 20.5% and 85.7%, respectively, compared with those of the conventional joint. The enhancement effect of the reinforcement combining a U-shaped steel plate and screws was difficult to realize due to the susceptibility to the initial clearance. Finally, the mechanical mechanism of the new reinforcement was clarified, and a method for calculating the compression zone height of the beam in joints with the reinforcement was suggested, which improved the calculation accuracy by 13.7%.

Experimental evaluation of a U-shaped steel plate as a seismic fuse

This paper evaluates experimentally the cyclic response of a novel U-shaped steel plate proposed to dissipate seismic-induced energy through a unique mechanism called scissor bending. The cyclic behaviour of the U-shaped plate, including hysteresis response, plastic mechanism, strength and stiffness, ductility and energy dissipation capacities are examined. Four U-shaped steel plates varying in thickness are tested under cyclic loading. Furthermore, a mechanics-based method is proposed to estimate the stiffness and yielding strength of the fuse. The finite element model of the specimens is developed to reproduce their hysteretic behaviour and verify the stiffness and yielding capacity of the fuse. The results confirm that the proposed U-shaped steel plate demonstrate stable hysteretic behaviour and exhibit appreciable deformation ductility and energy-dissipating capacities. The U-shaped plate can be used as a seismic fuse in the design of frame structures.

Experimental and Numerical Study of Strengthening Prestressed Reinforced Concrete Beams Using Different Techniques

This study aimed to evaluate the static response of prestressed reinforced concrete beams strengthened in their flexure and shear properties using different strengthening techniques, steel plates, and externally bonded woven carbon fiber fabric (WCFF). The experimental work involved testing twenty large-scale prestressed reinforced concrete beams with a length of 3000 mm, and cross-sections measuring 400 mm in height and 200 mm in breadth were cast in the factory and tested in the laboratory. Four beams without prestressing served as the reference beams; two unbonded pre-tensioned beams served as the control beams, and the remaining fourteen beams were strengthened with steel plates and externally bonded woven carbon fiber fabric (WCFF). Eight of the beams were strengthened with 4 mm thick steel plates and tested under a monotonically increasing load with manual readings recorded. The remaining six beams were strengthened with 0.5 mm thick WCFF and tested under a monotonically increasing load with manual readings recorded. The variables considered included the strengthening techniques (FRP composite sheets, steel plates), the types of strengthening (slices, U-shaped), and the flexural and shear capacities of the strengthened beams. All the implemented strengthening techniques yielded enhancements in both the flexural and shear strength outcomes of the beams compared to their respective controls. The most significant increase in load capacity, whether in terms of ultimate load or first crack load, for the prestressed concrete beams’ flexure properties occurred when strengthening with U-shaped steel plates. Additionally, the greatest reduction in deflection at the point of reaching the maximum load for the prestressed concrete beams, in terms of their flexure properties, was observed when strengthening with U-shaped steel plates. Similarly, the maximum load increase for the prestressed concrete beams, in terms of their shear properties, was achieved through strengthening with U-shaped woven carbon fiber fabric wrapping. Furthermore, a finite element model was created to simulate various experimental specimens. The finite element model’s results exhibited harmony with the experimental results, affirming the efficacy of the presented finite element model.

Research on Reinforcement Technology of Existing Frame Structure with Externally Attached U-Shaped Steel Plate Sub-Structure

With the improvement of building technical requirements and the updating of standards, the demand for the reinforcement of existing buildings is increasing. In order to solve the problem regarding the low economic applicability of the traditional seismic retrofit method, this paper proposes a seismic retrofit method for an externally attached U-shaped steel plate sub-structure that follows the concept of “reinforcing while using”, is composed of a U-shaped steel plate and herringbone channel steel, and can meet the needs of multiple retrofits. Based on the results of a pseudo-static test, the mechanical properties of one unreinforced frame and three reinforced frames with different specifications for the U-shaped steel plate sub-structure were comparatively studied, and the effectiveness and rationality of the reinforcement method were analyzed. The results show that the externally attached U-shaped steel plate sub-structure has good deformation and energy dissipation capacity and can effectively improve the horizontal bearing capacity of an existing frame without changing the original failure mode. The bearing capacity of the three reinforced frames was 1.43, 1.89, and 2.57 times that of the unreinforced specimen. The initial lateral stiffness of the frame also increased significantly, namely, to 1.41, 2.02, and 2.08 times that of the unreinforced specimen, and the stiffness degradation rate decreased. The seismic performance of the original frame was greatly improved.

Study of U-shape steel-encased composite beams with variable sections under negative bending moments

To reduce steel consumption and improve the negative moment bearing capacity of composite beams, a new type of composite beam with an external U-shaped steel plate was proposed in this paper. Static load tests of three scaled simply supported composite beams were completed, and the failure patterns, load–displacement curves, strain distributions, and slip of the new composite beams under negative bending moments were researched. The results showed that the new composite beam under negative bending moments underwent typical flexural failure with excellent ductility (ductility coefficient of 6.2), wherein the embedded steel plate played a key role in the loading process of the composite beams, contributing more than 50% of the flexural load capacity. On the basis of the experiments, finite element models were established in ABAQUS to investigate the influence of different construction parameters, including the material strength, thicknesses of the external steel plate and the embedded steel plate, and reinforcement ratio. Finally, design formulas were derived according to the simplified plasticity theory to calculate the flexural capacity of the proposed composite beam for engineering practice, which achieved close agreement with the experiments, with an average relative error of 3.5%.

Comparative study on the seismic behaviour of assembled composite walls with vertical joint rigid connections and ductility connections

To investigate the efficient dry connection type of fully assembled composite (FAC) walls, two novel vertical joint connection types, including rigid connections (box connections) and ductile connections (U-shaped plate connections), are proposed. In the experiment, three specimens were constructed and tested under in-plane reversed cyclic loading, including specimens with box connections (FAC-B) and U-shaped steel plate connections (FAC-U) and a specimen with a horizontal cast-in-place assembled composite (CAC) wall as the reference specimen. In the reversed cyclic loading test, the failure mode, hysteretic behaviour, bearing capacity, stiffness degradation and energy dissipation capacity were obtained. The test results indicated that the failure mode of all specimens was shear failure. In addition, a finite element model (FEM) of FAC-U is subsequently established and validated to further investigate the seismic performance of the plate thickness, concrete strength, compression ratio and block strength on the bearing capacity and ultimate displacement.

Study on Seismic Behavior of Spliced Outer Sleeve Beam–Column Joints with U-Shaped Steel Plates

Study on Seismic Behavior of Spliced Outer Sleeve Beam–Column Joints with U-Shaped Steel Plates

Experimental characterization of the mechanical behaviour of U-shaped dissipative devices

Energy dissipation devices are used in earthquake engineering in order to reduce the negative effects of ground-motions on structures, thus limiting damage to structural and non-structural components. Different technologies have been proposed to this aim, i.e. viscous fluid dampers, friction-based dampers, hysteretic dampers, etc. Among the different solutions available the present paper focuses on a specific type of hysteretic dampers, U-shaped dissipators. They were first proposed in the 70s and to date have found limited application in the design practice, mainly in buildings with structural walls, exploiting the relative displacement between adjacent walls to dissipate energy.The paper presents the results of an experimental campaign aimed at characterizing the mechanical behaviour of energy dissipators with linear movement, based on U-shaped steel plates. Different configurations were designed and tested, imposing displacement cycles of increasing amplitude. The paper discusses the observed energy dissipation capacity and the stability of the hysteretic cycles.

Test of Novel Self-Centering Energy Dissipative Braces with Pre-Pressed Disc Springs and U-Shaped Steel Plates

ABSTRACT To control the residual displacement of the structure after strong earthquakes, this paper develops and validates a novel brace, i.e. the self-centering energy dissipative brace with pre-pressed disc springs and U-shaped steel plates (SCEDB-U). The pre-pressed disc springs are used for recovering nonlinear deformation and the U-shaped steel plates are used for dissipating energy. Initially, the configuration and working principle are described in detail. Then the analytical equations governing the cyclic behavior of the brace are derived. To confirm the concept, the large-scale bracing specimens are designed and manufactured for the quasi-static cyclic loading tests. In the tests, the varied parameters included the plate width of the U-shaped steel plates and the pre-pressure magnitude of the stacked disc springs. Besides, the high-fidelity three-dimensional finite element (FE) models of SCEDB-U are established. According to the experimental data, the SCEDB-U has typical flag-shaped hysteresis, which is characterized by excellent self-centering capability and stable energy dissipation ability. It also indicates that increasing the plate width of U-shaped steel plates can effectively improve the energy dissipation capacity, but may induce residual displacement; increasing the pre-pressure magnitude of disc springs could improve self-centering ability. The numerical results are in good agreement with the experimental data; hence, the FE models can be further utilized for parametric analysis, initial design and optimization.

Experimental study on multi-cellular L-shaped CFST slender columns under biaxial eccentric compression

Multi-cellular L-shaped concrete-filled steel tubular (MCL-CFST) column is an improved L-shaped CFST column, which is composed of multiple rectangular steel tubes welded by U-shaped steel plates and then filled with concrete. The global stability capacity of MCL-CFST slender columns is vital for engineering applications. However, few investigations have been carried out on the stability performance of the MCL-CFST slender columns. This paper mainly focuses on the global stability performance of MCL-CFST slender columns. Firstly, six hinged supported MCL-CFST slender columns were designed and tested under biaxial eccentric loading. The load-displacement curves, failure modes, strain development and second-order effects of MCL-CFST slender columns were reported. Then, a refined finite element (FE) model of the MCL-CFSTs was established and verified by experimental results. Moreover, based on the validated FE model, the effects of eccentricity, column height and sectional dimension on the stability performance of MCL-CFSTs under eccentric loading were investigated, and the bending resistance curves Mx/Mxu-My/Myu in two directions under various parameters were obtained. These results can provide valuable references for engineering practice.

Flexural behavior of precast concrete beams in-span assembled with bolt-steel plate joints

The assembly of precast concrete structural components is primarily concentrated at the splicing joints of the components. Wet connections involving additional stirrups and detailing cause casting difficulties and possibly deficient joints. Herein, a new type of precast beam in-span assembled with bolt–steel plate joints (PBSPB) is proposed. A significant unique feature is the discontinuous longitudinal reinforcement in the midspan, where the U-shaped steel plate covers the web and tensile zone of the concrete beam. The steel plates and bolts are used to connect the two assembled short beams to resist both flexure and shear owing to the external effects. To investigate the effects of the steel-plate thickness and span–depth ratio on the flexural behavior of beams, a static behavior test was conducted on six PBSPBs and one cast-in-situ beam. The failure mechanisms of the PBSPBs and cast-in-situ beam were examined and compared with regard to the crack propagation, load–displacement characteristics, and strain responses. All the PBSPBs exhibited excellent performance with limited cracks under identical conditions; only minor damage was observed, which consisted of small amounts of concrete spalling and edge warping of the steel plates. Finite-element analysis (ABAQUS) models of the proposed PBSPBs were developed to verify the ultimate load and damage situations of each specimen, a simplified flexural-capacity calculation formula for the PBSPB was developed, and the theoretical results were consistent with the experimental results. The results indicated that the new precast concrete beams had favorable flexural capacities. The beam with thicker steel plates in the span had a higher strength owing to the higher stiffness. Increasing the span–depth ratio increased the ultimate load and barely affected the failure mechanism.

Analysis of flexural capacity of a novel straight-side U-shaped steel-encased concrete composite beam

This paper proposes a novel straight-side U-shaped steel-encased concrete composite beam (SUSCCB). The SUSCCB is constituted by encasing the top sections of the U-shaped steel plates directly into the concrete flange, with the composite action generated through perfobond connections consisting of reinforcement bars transversely passing through perforations in the encased top sections of the steel plates. It is engineered to overcome the shortcomings of the existing varus or valgus U-shaped steel-encased concrete composite beams (USCCB), for which the installation of shear connectors can be complex and costly to achieve because of the numerous required welds. The main objective of this paper is to study the flexural behavior of the proposed SUSCCB and develop a method for calculating its flexural capacity. A finite element model (FEM) is developed and validated against available USCCB experimental results. After, the validated FEM is used to conduct a parametric study of the SUSCCB. The flexural behavior is assessed from the strain distribution, stress analysis, and load–deflection curves. Results show that the flexural performance of the SUSCCB is superior to that of a traditional USCCB, and that its flexural capacity can be calculated through the simplified plastic theory. Lastly, the analytical flexural capacity of the SUSCCB is derived. The analytical values show close agreement with results from the numerical simulations.

Experimental and Numerical Study on Flexural Performance of a Novel Steel-Encased Concrete Composite Beam

This paper presents a novel configuration of high strength U-shaped steel-encased concrete composite beam (HUCB) in which shear studs connect concrete and U-shaped steel at top flanges and bottom plate. The junction surface of upper slab and lower portion is strengthened by evenly distributed inserted circular rebar. Two steel reinforcements are arranged in the composite beam along the longitudinal direction to reduce the deformation of encased concrete and provide adequate bending capacity under fire condition. Based on the flexural experiments of five specimens, the test failure pattern, load-deflection relation curves, sectional strain distribution at different height and ultimate flexural performance of the HUCB were obtained and are reported in this research. The experimental results show that the HUCB has high ductility and excellent flexural performance. According to test results of five specimens, new calculation formulae were presented to theoretically analyze the flexural capacity of the HUCB. The theoretical analysis values of flexural capacity according to the proposed calculation formulae are consistent with the test results of all specimens. A three-dimensional finite element model is also established to investigate structural performance of the proposed novel composite beam. Test results of five specimens verify the accuracy and validity of finite element analysis results. Parametric studies of the HUCB under positive bending moment are carried out to further analyse the influence of concrete compressive strength, yield strength of U-shaped steel plate and flange width of concrete slab on the flexural performance of the proposed new composite beam.

Numerical Simulation of Corroded Reinforced Concrete Beam Strengthened by a Steel Plate with Different Strengthening Schemes

This paper proposes 3D nonlinear finite element (FE) models to predict the response of corroded reinforced concrete (RC) beam strengthened using a steel plate. Five FE models are developed based on the tests carried out by the authors in a previous investigation, in which three models are used to simulate the corroded RC beams with different schemes. The FE models use the coupled damaged‐plasticity constitutive law for concrete in tension and compression and consider the bond‐slip between the corroded tensile steel bar and concrete. The cohesive element is also used to model the cohesive bond between the steel plate and concrete. The FE results of load‐deflection and the crack distribution are compared with the test data. The FE results are consistent with the test results. The influence of the thickness of the steel plate, the thickness, and location of the U‐shaped steel strip on the bearing capacity of the strengthened corroded beam is analyzed through FE models. The results show that the thickness of the steel plate on the bottom surface should not exceed 4 mm for the flexure‐strengthened and combined strengthened beams with a 10% corrosion rate. It is most reasonable to improve the bearing capacity using the 3 mm and 2 mm of thick U‐shaped steel strips for the shear‐strengthened and combined strengthened beams, respectively. The most reasonable location of the U‐shaped steel plate is at the end of the steel plate for beams with a 10% corrosion rate.

Dissipative connections with U-shaped steel plate for braces of concentrically braced frames

In concentrically braced frames, braces-to-adjacent member connections are suitable locations for the dissipation of seismic energy. If the implementation of dissipative connections does not compromise the global lateral stiffness of the structure, the compression braces can then be protected from buckling, while the structural ductility is increased and the action effects reduced. Furthermore, an efficient use of dissipative connections allows reducing the cost of post-earthquake interventions. In this paper, an innovative dissipative connection for braced frames is proposed, consisting of a steel plate bent to a U shape and connecting the brace to the adjacent column. In this connection, energy dissipation is obtained through the inelastic flexural deformation that takes place in the plate. This paper presents experimental results on the isolated U-connection and on single-storey concentrically braced frame (real scale) including the U-connection. Besides considering several variations on the geometry of the U-shape plate, the tests considered both monotonic and cyclic loading. The results highlight the efficiency of the U-connection to dissipate the energy input through inelastic deformations. On the other hand, the cyclic tests show however that the connection is potentially sensitive to fatigue, as the deformation capacity is significantly reduced with repeated loading and increasing stress amplitude, requiring thus specific attention in practical design situations.

Testing of seismic dampers with replaceable U-shaped steel plates

This research focused on a new type of seismic damper consisting of replaceable U-shaped steel plates. To investigate behavior of the damper, seven specimens were tested. The test parameters varied in these specimens included geometries and materials of the U-shaped steel plates and the loading protocols. Test results show that the specimens exhibited stable hysteretic behaviors and satisfactory energy dissipating capacities. In addition, this research provided clear evidence that the damper is robust and tolerant to the ruptures in the U-shaped steel plates. Some specimens continued to dissipate significant amounts of hysteretic energy even after formation of the visible ruptures in the U-shaped steel plates. Moreover, this research demonstrated that the damper repaired through replacement of the U-shaped steel plates following a severe earthquake remained satisfactory in a subsequent earthquake. Further, this paper presents the equations for estimating yield strength and ultimate strength of the damper. It was found that the derived equations provide reasonable predictions and can be used for future design.

Improving Seismic Behavior of MRFs by U-shaped Hysteretic Damper Along Diagonal Brace

This paper presents seismic assessment of a U-shaped hysteretic damper as an enhancement system, in moment resisting frames. The proposed system is consisted of a damping box at the middle of a diagonal brace. The box includes U-shaped steel plates welded to the side plates. When a transverse load, like earthquake, is exerted to the building, relative displacement between the stories forms and will be transmitted to the braces where energy dissipation will be achieved by adding a displacement-dependent U-shaped damper. For this purpose, the system is applied to a 2D 2-span 3-story frame to which by applying eight different earthquake records, far-field, near-field and mid-field, seismic response are evaluated. The responses are the roof displacement, inter-story drifts, root mean squared of roof displacement and base shear. Result verification is carried out via calibrating characteristics of this damper with an experimental work on a somewhat similar device conducted at the University of Toronto. The results showed that by using this system, the roof maximum displacement decreased 38.9, 40.0 and 37.1% and the maximum base shear decreased 36.5, 28.5 and 39.5% respectively under near-field, mid-field and far-field records, averagely. Similar results were observed in inter-story drifts and roof displacement RMS.

Parametric study of anti-explosion performance of reinforced concrete T-shaped beam strengthened with steel plates

Parametric studies are performed to investigate the influence of the weight and position of explosive charges, reinforcement lengths of steel plates, and reinforcement methods, such as pasting steel plate on the bottom of reinforced concrete T-shaped (RCTS) beam, pasting steel plate on both sides of web plate, pasting U-shaped steel plate on the web of RCTS beam, fully packaged the beam with steel plate and pasting steel plate on the top and bottom of RCTS beam, on the dynamic behavior of the RCTS beam under blasting load by numerical simulation method. Numerical results show that the failure modes of the RCTS beam are closely related to the weight and position of explosive charges. With the increase of explosive charges, the deformation modes of the beam are changed from elastic deformation to tension bending deformation, and finally the flexural shear failure is occurred. With the height increase of vertical direction of explosion, the failure patterns of the beam are changed from bending shear to tensile bending. Changing the explosion positions from the mid-span to the end of the beam, the damage positions are also changed with the moving of explosive. The damage modes of the beam and the positions, where the cracks are formed, have a strong dependence on the position and the weight of explosive charges due to the local effect of blasting load. Compared with the ordinary RCTS beam, the initiation time of cracks of the RCTS beam strengthened with steel plates is delayed and the growth speed of the cracks is also significantly reduced. The crack distributions of the beam strengthened with steel plates are mainly concentrated on the reinforced area. Moreover, the number of the formed cracks is also reduced and the compressive stresses of concrete in the compression zone of the beam strengthened with steel plates are lowered down. Among the reinforcement methods in the present study, the best reinforcement method to improve anti-explosion performances of the beams is the beam strengthened with steel plates on the top and bottom of it. The optimal size of reinforcement length of steel plate is about 80cm by comparing the different reinforcement lengths of steel plates in the same explosion case. To some extend, this study could provide some basis for evaluating anti-explosion performances and scheme design of structural strengthening of the beam.

NMIT Arts & Media Building—Innovative structural design of a three storey post-tensioned timber building

The NMIT Arts & Media Building in Nelson, New Zealand is the first in a new generation of multi-storey timber structures. It employs a number of innovative timber technologies including an advanced damage avoidance earthquake design that is a world first for a timber building. Aurecon structural engineers are the first to use this revolutionary Pres-Lam technology developed at the University of Canterbury.This technology marks a fundamental change in design philosophy. Conventional seismic design of multi-storey structures typically depends on member ductility and the acceptance of a certain amount of damage to beams, columns or walls. The NMIT seismic system relies on pairs of coupled timber shear walls that incorporate high strength steel tendons post-tensioned through a central duct. The walls are centrally fixed allowing them to rock during a seismic event. A series of U-shaped steel plates placed between the walls form a coupling mechanism, and act as dissipaters to absorb seismic energy. The design allows the primary structure to remain essentially undamaged in a major earthquake while readily replaceable connections act as plastic fuses.With a key focus on sustainability the extensive use of timber and engineered-wood products such as laminated veneer lumber (LVL) makes use of a local natural resource, all grown and manufactured within an 80km radius of Nelson.This IstructE award winning project demonstrates that there are now cost effective, sustainable and innovative solutions for multi-storey timber buildings with potential applications for building owners in seismic areas around the world.