Post-tensioned Steel Research Articles

Lateral Performance of Self-Centering Steel–Timber Hybrid Shear Walls with Slip-Friction Dampers: Experimental Investigation and Numerical Simulation

An innovative self-centering steel–timber hybrid shear wall (SC-STHSW) system is proposed in this paper. The SC-STHSW system is composed of two subsystems: the posttensioned (PT) steel frame, and the infill light-frame wood shear wall. Slip-friction dampers are used as connectors between the frame and shear wall. A reversed cyclic loading experiment was conducted to investigate the failure modes, hysteretic characteristics, and the loss of posttensioning force in the system. The working mechanism of the subsystems and the interaction between them were explored. Experimental results revealed that the peculiar flag-shaped hysteretic behavior is available in the SC-STHSW system. Under the coupled effects of the PT technology and the slip-friction dampers, the energy dissipation behavior of the system was transferred from the plasticity in primary structural members to the frictional dissipation in the dampers, and the residual deformation of the system was controlled effectively. A detailed numerical model was developed to predict the hysteretic performance of the SC-STHSW system. The model was validated by comparing the experimental and numerical results. This work supports the application of the innovative steel–timber hybrid structural system in practical engineering.

Flexural Performance of Unbonded Posttensioned Rectangular Concrete Filled FRP Tube Beams

Abstract This paper experimentally investigates the effect of using the posttensioning (PT) steel strands on the flexural performance of rectangular concrete filled fiber-reinforced polymer (FRP) t...

Multiscale Analysis of the Influence of Steel Fiber Reinforcement on the Shear Strength of Post-Tensioned Dry Joints

In this work we follow a multiscale methodology to characterize the structural performance of post-tensioned steel fiber-reinforced concrete dry joints. At the material level, we use an experimentally validated lattice-particle model whose input parameters are the properties of the different phases themselves (i.e., mortar, aggregates, fibers) and mixing information. This model is used to obtain the mechanical properties used in the structural-level simulations of the joints in terms of constitutive laws. The structural analyses are performed using the concrete damage plasticity model, which allows us to quantify the effect of fiber addition on the shear strength of the dry joints and their ductility. Our simulations agree well with other macroscopic models in the case of plain concrete and show, once again, that the American Association of State Highway Transportation Officials (AASHTO) code overestimates the nominal shear capacity of multiple-keyed joints. Regarding the fiber addition, we observe that it promotes an important increase in the shear capacity, but the prestress level is still more relevant in this sense. Based on our simulations, we propose an updated shear capacity estimate accounting for the fiber volume fraction. Finally, a clear increase in the ductility of the joint is observed when the fiber volume content is increased.

Seismic performance of bridge with unbonded posttensioned self-centering segmented concrete-filled steel-tube columns: An underwater shaking table test

As one of the prefabricated structures, precast segmented bridges can be used to shorten construction time, reduce traffic delays, improve quality control, and minimize environmental impact. Despite the numerous advantages of segmented pre-fabricated rapid assembly technology, it is not widely used in high seismic hazard zones nor applied to complex water-abundant situations because of the lack of knowledge on its seismic performance. Through experimental and numerical studies, researchers have studied the seismic performance of such type of column under quasi-static testing. The behaviors of the column or bridge under desired strong ground motions (GMs) have been rarely investigated. This paper presents the major findings of an underwater shaking table testing program conducted on a 1/4 scaled single-span bridge with novel self-centering segmented concrete-filled steel tube columns. This study focuses on the performance of the bridge subjected to different GMs under 4 water conditions, which are with water at a height of 1.2 m, 1.5 m, 1.8 m, and without water. The bridge model incorporated two post-tensioned precast self-centering segmented concrete-filled steel tube (PSCFST) single columns with fixed and sliding supports connected to a single span steel box-girder superstructure. The internal unbonded PT tendons are installed at the center of the segment section, and external energy dissipation (ED) bars are installed on the outside of the bottom segment. The bridge model was then subjected to a sequence of natural and artificial GMs with different amplitudes. The well-designed PSCFST bridge demonstrated a desirable seismic performance, and no significant damage was observed. Concerning the overall response of the structure, the maximum drift ratio reached 2.14%. Moreover, a maximum residual drift of 0.09% was observed after the tests, which indicates that the test model demonstrated a desirable self-centering capability after a sequence of GMs. The cumulative energy dissipation and equivalent viscous damping ratio of the bridge were calculated. A comparison is made for the seismic performance of the bridge especially in terms of the displacement and acceleration of the whole structure under the cases of with and without water.

Self‐centering steel–timber hybrid shear wall with slip friction dampers: Theoretical analysis and experimental investigation

SummaryAn innovative self‐centering steel–timber hybrid shear wall (SC‐STHSW) system is proposed as a promising structural solution for earthquake‐resilient buildings. The SC‐STHSW is composed of posttensioned (PT) steel rocking frame and infill light‐frame wood shear wall. The PT steel frame provides self‐centering capability, whereas the infill wood shear wall improves the lateral stiffness and the load resistance. Meanwhile, friction dampers are assembled into the connections between the steel frame and the infill wall to provide energy dissipation. Theoretical analysis and cyclic loading test were conducted to comprehend the load‐resisting behavior of the proposed SC‐STHSW system, and closed‐form solutions of the moment, shear, and axial force distribution along the length of the steel beam were formulated. Moreover, a nonlinear finite element model was developed, and the model was further used to verify the derived theoretical formulas. Results showed that the SC‐STHSW system was able to undergo large interstory drift without the development of plastic zones in the steel frame members, which resulted in very small residual deformation. The presented experimental and numerical results aim to provide a practical structural solution for high‐performance earthquake‐resilient buildings.

Moment–rotation response of post-tensioned self-centring beam–column connection

In order to overcome common problems such as low stiffness, insufficient ductility and enormous residual displacements in beam–column connections, a steel beam–column connection equipped with high-strength strands was developed. These so-called post-tensioned (PT) steel connections consist of high-resistance strands passing parallel to the beam web and through drilled holes in the column flange and the top and bottom beam angles, which act as energy dissipation elements. The displacement and rotation of connections in earthquake events is a problem that can be avoided by a self-centring feature of steel PT connections. In this research, the cyclic response of PT beam–column steel connections with stiffeners connected to the top and bottom beam angles was investigated. Different stiffener geometries and thicknesses were examined and numerical models were simulated using Abaqus software. The results showed that installation of stiffeners on the top and bottom beam angles had a direct effect on the gap opening of the beam–column interface and reduced the relative rotation. Under large applied drifts, primary elements of the connection experienced large deformation and failure. Thus, by equipping angles with stiffeners, all of the induced stresses and damage will be concentrated in the stiffeners. In all the models equipped with stiffeners, the behaviour of beam reached the plastic phase and the minimum value of Mmax/Mpn was almost 1·1. Failure of the angles was also delayed and the primary elements of the connection (beam and column) remained undamaged.

Experimental evaluation of self-centering hybrid coupled wall subassemblies with friction dampers

Post-tensioned hybrid coupled wall system has desirable seismic characteristics including self-centering capability and tolerance for large nonlinear displacements with limited damage. In this study, the behavior of concrete coupled wall subassemblies with post-tensioned steel coupling beam was experimentally evaluated. In this system, the coupling beam is not embedded into the walls, and the coupling of the concrete walls is accomplished by post-tensioning the steel coupling beam to the walls using unbonded post-tensioning strands. Steel angles and friction dampers were used at the beam-to-wall connection region for energy dissipation. In the first series of tests, a friction damper with different values of the clamping force was tested under two different loading frequencies. In the second series, seven quasi-static cyclic tests were conducted on 2/3-scale subassemblies of the post-tensioned hybrid coupled wall system. The test specimens included a control specimen without energy dissipation device, a specimen with steel angles and four specimens with friction dampers. In addition, one of the tested specimens with dampers was re-tested to investigate the structural behavior and residual capacity of the system during a strong aftershock. The test parameters included the type of energy dissipation device, the initial stress of post-tensioning strands and the amount of damper normal force. The test results show that the subassemblies equipped with friction dampers exhibit excellent lateral stiffness, strength, ductility and energy dissipation and are capable of withstanding large nonlinear cyclic deformations up to the drift of 8%, without residual displacements and without significant damage to the system. Whereas the subassembly equipped with steel angles provide lower energy dissipation capacity and because of the low-cycle fatigue fracture of angles, energy dissipation and load carrying capacities of the specimen decrease significantly.

Experimental investigation of self-centering steel reinforced concrete coupled wall panels with replaceable energy dissipaters

Resilience of structures is already the new issue and challenge in the field of earthquake engineering. In order to enhance the restorability of concrete wall panels and further use them in steel moment frames, a novel self-centering steel reinforced concrete coupled wall panels with replaceable energy dissipaters is presented in this paper. For this purpose, subassembly tests of the coupled walls with frame beams as boundary were carried out. Four full-scale specimens were tested under cyclic lateral loads. The initial prestress of post-tensioned (PT) steel bars and configuration of energy dissipaters were varied to investigate their impacts on lateral responses of the walls. The failure process, load-displacement relation, energy absorption capacity, residual deformation and force of PT steel bars were also investigated. Test results show that the three-stage nonlinear response is characterized by the sequential failure process of wall rocking, yielding of energy dissipater and yielding of PT steel bars. The initial prestress of PT steel bars greatly affects the initial stiffness, rocking load and residual deformation of the walls. Failure of the walls is mainly concentrated on the energy dissipaters. With the increase of energy dissipaters in quantitative terms or in type terms, the capacity of energy absorption is accordingly improved, but self-centering capacity is accordingly weakened.

ABAQUS modeling for post-tensioned reinforced concrete beams

Finite element analysis (FEA) using ABAQUS software was performed to investigate the behavior of post-tensioned concrete beams. This study is an attempt to examine the concrete damage behavior using a concrete damaged plasticity (CDP) model in ABAQUS, as well as the effect of an external post-tensioning (EPT) steel rod system. Concrete is a well-used material in many architectural and civil structures, with behavior exhibiting different characteristics in compression and tension; it also shows an inelastic-nonlinear behavior. These properties of concrete make modeling or simulation of the material difficult. In reinforced concrete, there is particular difficulty with respect to the bond-slip relationship between concrete and steel. However, in this paper the finite element analysis for concrete beams through ABAQUS simulation has been carried out with some assumptions, including perfect bond of steel and concrete and the CDP model for concrete property. In comparing analysis and experimental results, the simulated tensile deformations are similar to actual crack patterns in tests and the analytical responses such as strength, deflection, and stress of external rods are in good agreement with the measured responses.

Investigation on Seismic Performance of Bidirectional Self-Centering Reinforced Concrete Frame Structures by Shaking Table Tests

This paper presents an experimental study on the seismic performance of a bidirectional self-centering reinforced concrete (RC) frame structure. In the structure, the column-base joints, which were installed with external mild steel (MS) dampers, could uplift freely and the beam-column joints could open effectively under earthquake excitations. Angle steels and MS dampers were installed at the beam-column joints in the structural X and Y directions, respectively. During the gap opening of the joints, unbonded posttensioned (PT) steel wires, which passed through the plastic ducts inserted in the RC beams and columns, provided the structure with the ability to return to pre-earthquake positions, and the yielding MS dampers and angle steels dissipated the seismic energy. A 1/2-scale two-story model structure was designed and constructed. Shaking table tests were performed on the structure under four different types of earthquake excitations with increasing seismic hazard levels. The test results indicated that the self-centering RC frames installed in both the directions showed satisfactory seismic performance, with only slight damage to the main structure after extreme earthquakes. The natural frequencies of the self-centering frames installed in both the directions degraded progressively, mainly because of the prestress loss of the PT steel wires and the yielding of the MS dampers. The structure showed desirable self-centering ability with very small residual deformation under ground motions of all hazard levels. The structural deformation was mainly concentrated at the column-base and beam-column joints, and hence, damage to the concrete beams and columns was considerably alleviated. In addition, the residual gap opening of the joints was minimal.

Progressive collapse assessment of friction damped post-tensioned steel frames based on a simplified model

Post-tensioned energy-dissipating (PTED) connections for steel frames have drawn great research attention on account of their good seismic performance. Few studies focus on the progressive collapse of friction damped post-tensioned (FDPT) frame structures. The progressive collapse of FDPT frames exhibits a complex three-dimensional mechanical behavior that is quite different from that of traditional frame structures. In this work, a simplified 3D PTED connection model was first established and then used to investigate the progressive collapse behavior of FDPT frames. The influences of material strength, initial PT force, friction force, and axial and bending stiffness of beams on the collapse behavior of FDPT were studied. Finally, the dynamic response of FDPT frames was compared with that of traditional frame structures (TF).

Seismic retrofit of RC buildings using self-centering PC frames with friction-dampers

This paper presents the seismic upgrade of existing reinforced concrete (RC) structures by using a self-centering post-tensioned pre-cast concrete frame with friction dampers (SC-PC-FD). The effectiveness of the retrofit is investigated through conducting cyclic loading tests on a single story RC frame before and after the retrofit. The experimental results are used to validate the numerical modeling of the test specimens. A performance-based seismic design procedure is proposed based on a genetic algorithm (GA) to determine the story-wise distribution of the damper friction capacity and the area of post-tensioning steel. Three-, five-, and eight-story RC framed structures are used as case study models for evaluating the effectiveness of the retrofit technique. Non-linear time-history response analysis (NLTHA), incremental dynamic analysis (IDA), and fragility analysis are conducted to investigate the seismic performance of the retrofitted structures. Results of the nonlinear time-history analyses show that the retrofit reduces the maximum inter-story drift ratio (MIDR) and the residual drift of the model structures. IDA and fragility curves show that the collapse capacities of the model structures are increased after the retrofit and the retrofitted buildings have lower probabilities of reaching the design limit states compared to the un-retrofitted ones.

Assess the Effectiveness of SMA on Response of Steel Connection with PT Strands

Using the post-tensioned (PT) elements can significantly plummet the persistent damages and the relevant costs to post-earthquake repair and maintenance, facing earthquake hazards. Rooted in a PT self-centering steel connection, the deformation and residual drift of the main members are limited to the linear elastic branch derived from existence of steel strands by omitting the gap between beam-column connections. The shape memory alloys (SMA) material has super elastic property according to the conversion of austenite to martensite phases due to changes in the temperature and stress. In this research, a nonlinear behavior of PT steel connection with top-and-seat angles was analyzed due to vulnerability of the connection during the cyclic loading, so that the connection was equipped with stiffened angles and SMA material in order to improve seismic behavior of the steel connection. The results illustrated that the using the equipped angles with SMA property flourish a logical performance in the steel connection under cyclic loading, by which the connection witnesses an appropriate energy dissipation (ED) capacity and dramatically effect on initial stiffness.

Strengthening of pre-damaged concrete cylinders using post-tensioned steel straps

The effectiveness of an innovative post-tensioned steel strapping strengthening solution for enhancing the behaviour of pre-damaged plain concrete cylinders was investigated. To achieve this, 24 cylinders of diameter 100 mm and height 200 mm were subjected to axial compression; 18 of these specimens were initially subjected to compressive load in unconfined conditions to produce three different damage levels. These pre-damaged specimens were then repaired and strengthened using different strap spacings and number of confining layers of straps. The results showed that the post-tensioned steel straps were extremely effective at enhancing the strength of the pre-damaged specimens, by up to 313%. The strapping also increased the axial deformability of the pre-damaged cylinders up to values of 2·64–2·95%. However, the effectiveness of the repair solution varied with the pre-damage level. The results of this work should contribute towards the development of more rapid and effective strengthening solutions for damaged reinforced concrete structures.

Shear behaviour of post-tensioned inter-module connection for modular steel buildings

In modular steel buildings the inter-module connections are key to the successful site installation of modules and the overall structural behaviour of the assembled building. The existing connection details such as site welding typically require external access during site install, which is not always possible or practical. Post-tensioned bolted steel connections are an enticing solution because they minimise the requirement for site work, allowing for easier internal assembly. However, the existing shear force-displacement model for inter-module connections is inadequate, and the initial load-slip behaviour is not accurately predicted. In this study, a new post-tensioned bolted steel connection is proposed and the prototypes are manufactured. The shear force-displacement and load-slip behaviours are investigated experimentally. The proposed connection is shown to have good initial stiffness in shear, which can be well controlled by the parameters of preload and slip factor. In addition, numerical simulation is conducted and the influence of the preload and slip factor on the load-slip behaviour is investigated. An improved empirical model is developed, and its application is demonstrated for the proposed connection.

A Study on Coupled Wall System with Post-tensioned Steel Truss Coupling Beams: Concept and Performance Evaluation

In order to improve the seismic behavior of coupled shear wall structures, a new type of post-tensioned steel truss coupling beam (PSTCB) is developed in this paper. The PSTCB is composed of chord members, two diagonal buckling-restrained energy dissipaters and diagonally placed post-tensioned tendons. The energy dissipaters are expected to serve as fuses and can be quickly repaired after earthquake. Furthermore, the residual drift of the coupling beam can be reduced by the application of post-tensioned tendons in the diagonal direction. In the PSTCB, the post-tensioned tendons are anchored at outer ends of the wall piers. According to the Chinese code, an 11-story coupled wall structure was designed and the numerical model was developed in PERFORM-3D software. The seismic behaviors of the hybrid coupled wall system with PSTCBs (HCW-P), the hybrid coupled wall system with replaceable steel truss coupling beams and concrete coupled wall system with reinforced concrete coupling beams were evaluated and compared under maximum considered earthquake. Results showed that the HCW-P can achieve excellent lateral strength, stiffness, and ductility as well as reduce the residual displacements of the structure after earthquake.

Ductility and stiffness of slender confined reinforced high-strength concrete columns under monotonic axial load

This paper presents an investigation based on tests results of high-strength concrete (HSC) columns externally confined with post-tensioned steel straps, subjected to monotonic axial load. The parameters of the tests were eccentricity ratio (ei/es = 0, 1), load eccentricity (e = 25 mm, 50 mm), slenderness ratio (λ = 16, 24, 32) and confining volumetric ratio (ρv = 0.09, 0.25, 0.50). This paper is served as a continuation of a previous paper conducted by Ma et al. (2014b), which focuses on the ductility and stiffness analysis. The results show that the confinement of post-tensioned steel straps is beneficial to HSC columns but confining efficiency reduced drastically with the increase of column slenderness. Two ductility models were proposed to predict the ultimate ductility for slender confined HSC columns with the consideration of important parameters. The proposed models are simple and easy to apply but adequately accurate estimation is guaranteed. It is believed that the proposed ductility models can aid structural engineers in the designing a ductile structure especially in the seismic region. The confinement has no significant effect on the flexural stiffness of HSC columns.

Improving the seismic performance of post-tensioned self-centering connections using SMA angles or end plates with SMA bolts

Cyclic performance of self-centering post-tensioned (PT) steel beam-column connections has been investigated numerically by introducing stiffened angle connection, shape memory alloy (SMA) angle connection and SMA bolted end plate connection. Results show that stiffened angle connection can significantly improve the seismic performance in terms of moment capacity (up to 40% increase), post-decompression stiffness (up to 58% increase) and energy dissipation capacity (up to 67% increase) compared to the corresponding connections with top and seat angles by accumulating permanent strain in the angle and stiffener. On the other hand, SMA angle connection has robust self-centering behavior which eliminates the need for replacement of energy dissipating element at the end of a strong earthquake. The limit states of other structural components, such as bolts and beam flanges, can be higher due to stress concentration which has been demonstrated in this study by presenting plasticity index (PI) and rupture index (RI) of the bolts. The use of an SMA bolted end plate connection can remove damage or residual deformation in connection components where the SMA bolts are responsible for energy dissipation and PT strands help re-center the connection. A full factorial analysis has been conducted by considering four important parameters such as end plate length, gage length, SMA bolt diameter, and pretension forces in the bolts to evaluate the seismic performance of this connection. A prediction equation has been presented to estimate the connection response and verified through further finite element analyses.

Parametric study of hexagonal castellated beams in post-tensioned self-centering steel connections

The effects of important parameters (beam reinforcing plates, initial post-tensioning, and material properties of steel angles) on the behavior of hexagonal castellated beams in post-tensioned self-centering (PTSC) connections undergone cyclic loading up to 4% lateral drift have been investigated by finite element (FE) analysis using ABAQUS. The PTSC connection is comprised of bolted top and bottom angles as energy dissipaters and steel strands to provide self-centering capacity. The FE analysis has also been validated against the experimental test. The new formulations derived from analytical method has been proposed to predict bending moment of PTSC connections. The web-post buckling in hexagonal castellated beams has been identified as the dominant failure mode when excessive initial post-tensioning force is applied to reach greater bending moment resistance, so it is required to limit the highest initial post-tensioning force to prevent this failure. Furthermore, properties of steel material has been simulated using bilinear elastoplastic modeling with 1.5% strain-hardening which has perfectly matched with the real material of steel angles. It is recommended to avoid using steel angles with high yielding strength since they lead to the yielding of bolt shank. The necessity of reinforcing plates to prevent beam flange from local buckling has been reaffirmed.

Numerical Investigation on the Cyclic Behavior of Post-tensioned Steel Moment Connections with Bolted Angles

Post-tensioned (PT) steel frames have recently been introduced to resist lateral load and to provide self-centering capability. In these frames, high strength steel strands that run parallel to the beam web, have been used to provide moment resisting and restoring force. Also, the top and seat angles have been used to provide suitable energy dissipation capacity. In this paper, ten interior connections of these frames are designed such that we could numerically investigate the effects of angle and strand parameters on their stiffness, moment and energy dissipation capacity, as well as on their self-centering capability. Also, it is aimed to determine the effects of angle parameters on the amount and distribution of plastic deformation in the column and beams. To validate the numerical results, two of these specimens are considered to be the same as experimentally tested PT connections that are available in the literature. The results showed that our numerical results are in good agreement with the experimental ones. Also, PT connections will have appropriate strength and stiffness along with excellent energy dissipation capacity and ductility, if the number of strands and angle thickness be chosen properly. In story drifts corresponding to the design based earthquake, the column and beams are remain elastic and the PT connection returns to its plump position after unloading (self-centering capability). Upon applying a story drift corresponding to the maximum considerable earthquake, these connections are able to retain their special characteristics (such as self-centering capability and ductility). At this story drift, minor yielding occurs in the column panel zone and in the beams at the end of reinforcing plates.