Post-tensioned Connections Research Articles

Multi-factor analysis and optimization on seismic behavior of precast pier-footing socket connection considering different connection parameters

Accelerated bridge construction technology, with its various connection methods, has experienced extensive global usage. Common methods include post-tensioned, cast-in-place joint, sleeve, and socket connections. Each method has its advantages and limitations, such as the energy dissipation issue in post-tensioned connections and the on-site challenges of cast-in-place joints. Precast pier-footing socket connections have emerged as a promising solution due to their rapid construction and durability. However, previous research has predominantly focused on the minimum embedded length, overlooking critical factors such as grouting material strength, shear key configuration, and axial compression ratio during service. Furthermore, existing studies often isolated individual factors, neglecting their interconnected effects. This study addressed these gaps by testing two specimens and analyzing thirty-eight models through experimental and numerical methods. The results indicated that an embedment depth of at least 1.0 times the diameter (bc) of the precast pier was recommended. Furthermore, to ensure optimal seismic performance, it was essential to enhance the stiffness of the footing sidewalls beyond this depth. Additionally, while shear keys improve bending resistance, their effectiveness decreases with greater embedment depth (>1.5 times the diameter). This study highlights the importance of considering the interplay of multiple factors to ensure project safety and cost-effectiveness.

Bolt-free post-tensioned connection for steel-framed modular buildings and design for optimal preloading

This paper introduces a novel bolt-free preloaded column-to-column connection, termed the ‘AJ connection’, for steel-framed modular buildings. The AJ connection is classified as a post-tensioned inter-module connection, and modules are connected vertically by preload, using specially designed couplers and high-tensile steel rod bolts (SRB) within the columns. The AJ connection enables easy assembly and disassembly processes of modular buildings by inducing preload on top of the modules using a torque or impact wrench, thus improving construction speed and reusability. The paper also establishes a design method, not previously attempted in the literature, to determine the minimum necessary preload for the connection. The primary aim of this method is to design against potential failures by gap-opening and slip between modules, commonly associated with existing post-tensioned inter-module connections. The effectiveness of the suggested method is verified through numerical simulations using FE joint models that have been calibrated against monotonic loading test results. Furthermore, the study investigates the adverse effects of gap-opening and slip at the connection on the performance of the beam-to-column joint and the SRBs within the columns. The findings indicate that (i) minimising the difference between the flexural stiffness of the floor and ceiling beams reduces the impact of gap-opening, and (ii) the rotation of the coupler caused by plate bearing due to slip prior to gap-opening affects the induced preload in the SRBs and leads to premature gap-opening at the connection.

Investigation on Seismic Behavior of a Novel Precast Shear Wall System with Different Infill Wall Constructions

Construction industrialization addresses various challenges in the traditional construction industry, enabling building structures to conserve resources and enhance energy efficiency while reducing emissions. Precast shear walls involve the factory-based production of components, followed by transportation to a construction site for assembly. The method of connecting these components is crucial for precast concrete shear wall systems. Common connection methods include lap-spliced connections, post-tensioned connections, welded connections, bolted connections, and sleeve connections. However, challenges such as construction precision and technology proficiency have limited their application. In response, a novel precast concrete shear wall system utilizing angle steel connectors has been proposed. These angle steel connectors enhance the shear resistance of horizontal joints between precast concrete shear walls and the foundation, providing provisional support for specimen positioning and installation. Presently, the seismic performance of this innovative precast shear wall system under the combined actions of cyclic horizontal loads and axial pressure or tension has been extensively investigated. In practical engineering applications, precast concrete shear wall systems are often accompanied by infill walls. However, there is limited research on the seismic performance of precast concrete shear wall systems with infill walls. To address this gap, this study designed and fabricated two novel precast concrete shear walls with different infill wall constructions. One specimen featured an infill wall composed of a single wall panel, while the other had an infill wall consisting of two panels. Pseudo-static tests were conducted on both specimens under constant axial compression. Subsequently, the seismic performance and force mechanism of the two specimens were compared with the novel precast concrete shear walls without infill walls. The test results demonstrated that the specimen with two infill wall panels exhibited superior overall performance compared to the one with a single continuous infill wall panel. Furthermore, it was observed that, during the loading process, the edge columns of specimens with infill walls provided the majority of the increased load-bearing capacity, while the infill walls made a limited contribution to the overall load-bearing capacity of the structures.

Improving the Seismic Performance of Steel Frames under Mainshock–Aftershock Using Post-Tensioned Connections

In this study, the seismic responses of moment-resisting steel frames (MRSFs) with welded and post-tensioned connections under 28 artificial seismic sequences (mainshock–aftershock) are compared. For this aim, the mainshock are scaled at different ground motion intensity levels as a function of the spectral pseudo-acceleration corresponding to the fundamental period of vibration of the structure Sa(T1), whereas different intensity levels of the aftershocks are used for a percentage of the peak maximum acceleration of the mainshock. The seismic performance comparison of both structural systems is computed for the maximum, residual inter-story drift and hysteretic energy demands. The results show that post-tensioned frames significantly reduce the structural demands, especially in the case of residual inter-story drifts and hysteretic energy in comparison with moment-resisting steel frames with welded connections. The reductions in the structural response tend to be larger as the intensity of the aftershock tends to increase. Therefore, it is concluded that the use of post-tensioned connections is a great alternative to mitigate the seismic response of buildings subjected to seismic sequences.

Progressive collapse resistance and uncertainty analysis of post-tensioned steel frames

Post-tensioned (PT) steel frames with prestressed strands and replaceable energy dissipation angles demonstrate enhanced resilience during earthquakes compared to traditional steel frames. This study aimed to investigate the collapse resistance of PT steel frames in the different column removal scenarios. A macro model of a typical PT connection was developed using OpenSeesPy, a python library for the OpenSees finite element software framework. The model was validated by experimental results and applied to a six-story, four-bay office building. The collapse resistance mechanism of the building was analyzed in detail through a static pushdown nonlinear analysis, considering the edge column and middle column removal scenarios on the ground floor. A probabilistic analysis was conducted, incorporating uncertainty modeling and sensitivity analysis, to determine the effect of parameters on the collapse resistance of the structure. The collapse fragility functions corresponding to different structural performance levels were developed by the Latin hypercube sampling method with random pushdown analysis under the edge column removal and middle column removal scenarios, respectively. The uncertainty analysis results indicated that the PT steel frame investigated in this work has good collapse resistance.

Seismic performance of RC frames with self-centering precast post-tensioned connections considering the effect of infill walls

This paper presents the seismic performance evaluation of self-centering precast post-tensioned concrete (SCPPTC) frames with infill walls. The SCPPTC connection system consists of all-steel bamboo-shaped energy dissipaters (SBED) and prestressed tendons, which provide energy dissipation capacity and self-centering capability, respectively. Using modeling parameters calibrated with experimental tests, nonlinear numerical models of SBED, SCPPTC connection, infill walls, and 2D SCPPTC frames were developed in OpenSees, to compare the performance of the structures with different types of infill wall layouts. Nonlinear static pushover and incremental dynamic analysis (IDA) were performed to study the effect of infill walls on the overall response of SCPPTC frames, in terms of stiffness, strength, maximum interstory drift ratio,θmax, the maximum residual interstory drift ratio, θr,max, and the normalized post-tensioned force. Using the IDA results, the study also developed fragility curves and estimated the collapse margin ratios. The results demonstrated that the shear strength of the SCPPTC frame was improved from 4.19% to 12.2%, and the initial secant stiffness of the SCPPTC frame was augmented from 22.9% to 88.3% with increasing filling rate. The totally infilled SCPPTC frame (SCPPTC-ToI) exhibits a 19.86% lower θmax than that of pilotis-infilled SCPPTC frame (SCPPTC-PiI) under rare earthquakes, and the maximum prestress of SCPPTC-ToI was also 7.14% lower than that of SCPPTC-PiI. With the increase in filling rate, θr,max increased by a maximum of 120.45%. The pronounced soft layer led to the highest failure and collapse probabilities of SCPPTC-PiI among all SCPPTC frames at the same performance level.

Experimental study on seismic behavior of a new precast shear wall system with angle steel connectors

The mechanical behavior of the connections between the wall panels and the foundation determines the seismic performance of precast concrete shear walls. The post-tensioned connection, sleeve connection, lap-spliced connection, welded connection, and bolted connection are the most common today. However, they frequently have some shortcomings, such as the need for skill-trained workers, concealed work, engineering precision, high cost, and remarkable damage to horizontal joints. In order to overcome the shortcomings, a new precast reinforced concrete shear wall system with angle steel connectors was proposed and designed. Angle steel connectors were used to improve the shear resistance of the horizontal joints between the precast RC shear wall and the foundation, as well as to provide temporary support for specimen positioning and installation. Meanwhile, the angle steel connector can provide tensile resistance under extreme conditions such as a typhoon or strong earthquake. In order to investigate the seismic behavior of the new precast shear wall system, a full-scale precast RC shear wall specimen with angle steel connectors was built. Meanwhile, three full-scale precast RC shear walls with integral cast-in-place connections, grouting sleeve connections, and lap-spliced connections were designed and built to compare and investigate their seismic performance and mechanism. The results showed that the new precast shear wall system with angle steel connectors had improved seismic performance and deformation capacity. At the same time, the upward movement of the main crack was conducive to improving the bearing capacity of the shear wall. When compared to the grouting sleeve connection, it significantly reduced the amount of concealed work and made the construction quality easy to ensure. The seismic performance of the specimen with lapped steel bars and angle steel connectors was better than that of the specimen with grouting sleeve connection and cast-in-place specimen. The new precast shear wall system with angle steel connectors proposed in this study is well suited for use as a seismic resistance of building structures.

Aplicación del Método de Elementos Discretos para la simulación de una conexión viga-columna basada en un sistema auto-centrante.

At present, the beam-column connection system through a self-centering post-tensioned connection is currently an alternative to improve the seismic behavior in reinforced concrete buildings; by allowing its elements to have a linear behavior (no damage) in the face of displacements produced by seismic actions. This paper deals with the numerical modeling of the seismic behavior for a self-centering connection based on the Discrete Element Method (MED) is presented, with the aim of validating the hysterical response of the numerical model with an experimental test of the literature. The results demonstrated the horizontal distortions in the column, which are the product of the numerical simulation of the model subjected to a load that increases over time with 4 different stiffness coefficients. In addition, the hysteretic graph is presented as a result of the numerical simulation of the model, with an adequate stiffness coefficient and normal damping, subject to a cyclic load that is reversed as a function of time. The movement of the connection is controlled by the horizontal distortions of the column, achieving an approximate reproduction of the hysterical behavior expected in this type of connection. With the results shown, a simple bilinear hysteresis law is proposed, which allows its simplified use for its application in the modeling of reinforced concrete buildings with self-centering connections.

Punching Shear Strength of Post-Tensioned Transfer Slab-Column Connections

Punching Shear Strength of Post-Tensioned Transfer Slab-Column Connections

Seismic strengthening of existing RC buildings with external cross-laminated timber (CLT) walls hosting an integrated energetic and architectural renovation

In this study a timber-based integrated solution is presented to solve at once common issues affecting typical reinforced concrete (RC) existing buildings, such as seismic and energy performances, providing an eco-friendly alternative to steel external bracing systems. Cross-laminated timber (CLT) walls are provided perpendicularly to the external façades as strengthening elements while interposed CLT slabs are foreseen at each floor level to host new architectural units together with a new envelope. While the connections to the foundations and to the existing RC frames are provided respectively with steel brackets and axial-connectors distributed along the height of the building, a post-tensioned connection, between CLT panels (PT-CLT connection), is implemented in the system to guarantee resistance to horizontal actions acting parallel to existing façades with consequent structural independence and architectural freedom. On this regards a first look at the findings of an experimental campaign carried on the Technical University of Munich are presented. A numerical model is developed with finite element software characterizing each type of connector for linear and non-linear analyses. Modal analyses with response spectrum are performed to verify structural elements and connectors, while pushover analyses with target displacement checks are performed to assess the obtained seismic improvement. Finally, the preassembled architectural components that allow to renovate the envelope and the provided assembly procedure are revealed.

Improved performance-based plastic design method for post-tensioned connection systems

Performance-based plastic design (PBPD) was initially proposed as a method for retrofitting existing structures. The PBPD method gradually became a general approach for designing new structures. This method is a direct method to obtain design base shear and leads to design structures being more economical compared to traditional methods. PT connections were developed after the Northridge earthquake. The self-centering could restore the connection to its original position without damage to the beams and columns. High-strength post-tensioned cables are used to restore the structure to its initial position in PT connections. Also, energy dissipaters (for example, top and bottom angles) are used to increase ductility. In this study, a proposed relationship between the ductility (µ), period (T), and response reduction factor (R) is presented for structures with pinching or flag-shaped behavior, and the effect of the parameters on R has been investigated. Also, a new design approach for structures with PT-steel connections with top-and-bottom angles is presented. The results show that R primarily depends on the post-yield stiffness ratio (α), the yield stress ratio (or energy dissipation) (β), ductility (µ), soil type, etc. Nonlinear time-history analysis indicates that designed models based on the proposed approach satisfy drift limits. The results show that the proposed relationship can be quite suitable for designing PT connections using the PBPD approach.

Seismic behaviour of post-tensioned beam-to-column connection using slender energy-dissipating rectangles

An alternative way to decrease the peak response and provide higher robustness against the loss of post-tensioned (PT) force in self-centering structures is to provide them with stiffness degradation and pinching behaviour. In this study, an innovative PT connection using slender steel rectangles as energy-dissipating elements is proposed. Cyclic tests on five specimens considering the effect of thickness, width and number of steel rectangles, and the initial stress of the PT strands were carried out. The results demonstrate that the connections have acceptable seismic response despite stiffness degradation and pinching behaviour of the energy-dissipating steel elements. Specimens with a smaller width of steel rectangles exhibited typical three-plastic-hinge buckling. Smaller thickness of the steel segments would change the buckling behaviour to a multi-wave out-of-plane mode, which is difficult to predict and design for. The energy-dissipating capacity can be increased by increasing the number of steel rectangles while the re-centering capacity remains unaffected. In addition, a verified phenomenological hysteretic model for slender steel rectangles was developed and implemented into OpenSees as a material, which may facilitate further numerical investigations.

Performance of a Ductile Hybrid Post-Tensioned Beam-to-Column Connection for Precast Concrete Frames under Seismic Loads: A Review

The performance of precast concrete frame structures against seismic loads mainly depends on the beam-to-column connection. A ductile hybrid connection consists of unbonded post-tensioning steel and bonded reinforcement bars, both of which provide overall moment resistance to the frame. Post-tensioning steel acts as a restoring force which brings the structure back to its initial position upon unloading. Mild steel acts as an energy dissipator which yields in tension and compression. To evaluate the performance of precast frame structures, the structural engineer requires extensive knowledge of the complex nonlinear behavior of the connection. Standardization to mass produce is one of the benefits of precast construction, but with standardization in design there is severe risk. All previous earthquakes have clearly shown that continuous repetition of accepted practice without proper engineering review can lead to disaster. It is important to understand how different parameters of the connection influence the behavior and performance of the frame against seismic loads. The present study helps structural engineers and researchers with a detailed review of hybrid post-tensioned connections. This review is focused mainly on precast beam-to-column connections, studies on the development of hybrid connections, performance evaluations of hybrid connections, and the performance evaluation of precast frames with hybrid connections.

Experimental and analytical investigation of improved behavior of existing steel connections by adding self-centering capabilities

This study presents a new post-tensioning configuration for enhancing the seismic performance of existing steel bolted connections. The nonlinear behavior of the proposed post-tensioned connection was investigated through experimental and analytical programs. Different post-tensioning strand configurations were installed on top-and-seat angle connections with different strand length, strand number, and initial post-tensioning force. Data from the tested post-tensioned connections showed a significant improvement in the nonlinear behavior when compared to their non-post-tensioned counterparts. This improvement was achieved by increasing the overall stiffness and strength in addition to providing self-centering capabilities that could limit the residual drifts for the retrofitted moment-resisting frames after a strong earthquake. An analytical representation of the proposed connection is presented and modified considering the effect of the strand relaxation. The derived analytical equation accurately represented the response of the post-tensioned beam-to-column connection in terms of the moment-rotation relationship and it could be used for the analysis and design of post-tensioned connections subjected to large deformations . • Providing self-centering capability for existing steel bolted connections. • Increasing connection stiffness and strength by installing post-tensioning strands. • New post-tensioning configuration for retrofitting steel semi-rigid connections.

Implementing posttensioned connections only in some floors of steel moment frames

The studies conducted on self-centering seismic-resistant systems have largely eliminated ambiguities related to designing these types of structures. However, they have not been used well enough due to the executory differences of the structures mentioned above with those having common welded connections. The need for a specialized workforce and equipment to create posttension and install energy-dissipating elements in implementing self-center systems has made a difference in the cost of their implementation compared to conventional welding structures. The present study aims to improve the seismic behavior of steel moment frame through posttensioned energy dissipating (PTED) connections in some floors. In this regard, several states of posttensioned connections on different floors of 3 and 6-story frame are modeled by csiPerform-3d Software, and time history is used for analysis. The PF coefficient was used to evaluate the seismic performance of the frames and the PEF parameter is used to evaluate the efficiency of the pattern of setting posttensioned connections in the floors. Performing a total of 280 time history analyses on 18 frames indicates that using posttensioned connections in some floors leads to good performance while economically saving so that the seismic performance of some frames can improve more than that of the posttensioned connections-based frame performance in all floors if the best floors for setting these connections are selected. Accordingly, the use of PTED connections in all floors results in increasing 15.9% in the performance of the three-story frame, while the performance of the structure is upgraded 17.1% when PTED connections are used only in the first two floors. In addition, the results indicate that using the posttensioned connections in the lower floors of frames can improve their seismic performance and the one in the upper floors leads to a reduction in seismic performance of the frames. Accordingly, in case of using PTED connections in the two end floors of the 6-story frame, the performance of the frame reduced by 37.6%, and the frame performance reduced by 29.4% when PTED connections were used in the last three floors.

A closer look at numerical simulation of self-centring steel plate shear walls

Unstiffened steel plate shear walls (SPSWs) are one of the most efficient lateral resisting systems in conventional steel structures. The essential characteristics of SPSWs, including high initial stiffness, great ductility and low compression resistance, make them desirable for implementation in self-centring structures that aim to eliminate or effectively reduce residual drift under earthquake load. In this work, a numerical simulation of a self-centring SPSW based on the strip model published by the American Institute of Steel Construction was conducted and an attempt was made to modify the method to match experimental results more accurately. It was found that the compression resistance of shear wall strips, realistic pinching behaviour and energy dissipation of bolts in post-tensioned connections are key aspects for developing a reliable simulation of a self-centring frames with SPSWs. Neglecting any of these issues can distort evaluation of the self-centring capability and the dissipated energy in the frame. In addition, deterioration in the shear wall material due to web plate tearing needs to be considered in the modelling to achieve more realistic assessments of the ultimate stiffness and strength of the system under significant seismic loads.

Multi-stage Performance Upgrade of Steel Moment Frames by Post-tension Connections

Numerous studies have been conducted on self-centering seismic lateral force resisting systems, the consequences of which have resulted in removing many ambiguities regarding the use of such systems in retrofitting the existing frames. The present study evaluated the new approach of improvement of multi-stage performance using such systems. Due to the significant costs of running the whole retrofit project in one stage, as well as some issues such as the impossibility of stopping the use of all floors in some of the existing buildings, multi-stage improvement can be considered as a good suggestion. In this regard, a part of the floors are retrofitted in the first stage and the next stage of improvement are then implemented by spending less budget and time. Accordingly, the execution of the first stage leads to an enhancement in the frame performance to an appropriate extent. In addition, the measuremets taken in the stage are a part of final retrofit project. In the present study, PUF and PEF coefficients were introduced and utilized to select the most appropriate pattern for applying post-tensioned connections in different floors. After analyzing frames, a model was proposed for the multi-stage improvement of each frame by selecting the appropriate pattern using post-tensioned connections in the floors. In the first stage of the suggested plan, for 3-, 6-, and 10-story frames the performance improvements were 15.3, 11.4, and 8.5%, respectively.

Component-based model for posttensioned steel connections against progressive collapse

A component-based method for the estimation of the posttensioned (PT) steel frame against progressive collapse is proposed and presented in the current paper. A mechanical model of PT steel connections is developed and benchmarked with experimental data of a PT beam-column substructure from literature. The developd mechanical models of four PT connections are able to capture the initial elastic stiffness, decompression load, and residual stiffness under lateral loading. Then, analysis of a reduced-scale three-storey two-bay PT steel frame is carried out with sufficient accuracy by incorporating the proposed joint model into the frame analysis. The proposed method is then applied to assessing progressive collapse of a one-storey two-bay PT frame under middle column removal scenario, and is verified against existing experimental and ANSYS finite element results. Three resistance mechanism for progressive collapse of the PT frame are evaluated, which consists of angle flexural mechanism, beam compression arching action and strand tensile catenary action. Finally, parameter analyses of the PT frames are conducted to investigate the effects of the connection details on the behavior and resistance of progressive collapse. The proposed model can be used to predict the quasi-static behavior of PT frames under monotonic vertical loading conditions with satisfactory accuracy.

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 and analytical investigation on post-tensioned beam-to-CFST column connection using wedge-shaped devices

A post-tensioned (PT) beam-to-column connection using wedge-shaped devices (WSDs) and concrete-filled square steel tubular (CFST) column is proposed in this study. The WSD is designed to eliminate the gap between the nut on the energy-dissipating (ED) bar acting as “fuse” and the end plate of the beam when the ED bars yield during an earthquake. Cyclic tests were carried out on four 2/3 scaled specimens to investigate the mechanical behaviour and seismic behaviour of the connection considering the effect of the initial PT force, the area of ED bars and the use of WSDs. Findings demonstrate that the connections using WSDs exhibited desired flag-shaped hystereses before the bottom of the U-shaped surface on the wedge contacted with the ED bar. All the specimens were able to recentre while the structural elements behaved elastically after each cyclic loading and the “fuses” were replaced after each test. Besides, the self-centring behaviour was insensitive to the initial PT force and the size of ED bars. Smaller amount of energy dissipation and initial rotational stiffness were observed after the bottom of the U-shaped surface contacted with the ED bar. Moreover, simplified equations were developed to predict the mechanical behaviour of the PT connection and showed good correlation compared with the experimental results, which can be used in a non-linear structural analysis program.