Post-tensioned Research Articles

Optimization of relative-span ratio in rocking steel braced dual-frames

Controlled rocking concentrically steel braced frame (CR-CSBF) is an earthquake-resisting system that is effectively capable of reducing structural damage after earthquakes and causes resilience in the structure. Post-tensioning (PT) strands and fuse members are two important elements in CR-CBSFs to provide frame self-centering and energy dissipation, respectively. This study firstly purposes to evaluate the nonlinear response history analysis with five different relative-span ratios (A/B = 1.5, 2.0, 2.5, 3.0, 3.5). Various amounts of four parameters consist of the yield strength and modulus of elasticity of the fuse, the initial force of the PT cable, and the gravity load on the rocking column are also considered as design valuable factors in the analysis. Additionally, it is considered to involve the influence of frame height with 3-, 6- and 9-story and earthquake different characteristics. The second aim of the study is to investigate about optimizing the seismic response of CR-CSBFs, in order to determine the optimal A/B for each height of structures. In addition to previous valuable research, this study has taken a more innovational approach and aims to complement them. A statistical multi-objective optimization methodology is used to distinguish the design of the spanning ratio required to minimize the peak story drift ratio (PSD), peak roof displacement (PRD), peak roof acceleration (PRA) and peak base shear (PBS), which are considered seismic response demand factors. The results demonstrate that the optimal relative-span ratio or A/B for the three-story controlled rocking concentrically steel braced dual-frame is equal to 1.5, and for the six- and nine-story frames is equal to 3.5.

Seismic performance of precast concrete wall with vertical energy‐dissipating connection

SummaryA precast concrete wall with vertical energy‐dissipating connection (PCWVEC) was proposed in which X‐shaped metal dampers (XMD) with better energy‐dissipating capacity were installed along the vertical connections between precast wall panels, and the pore‐forming grouted lap‐sliced connector was adopted for the longitudinal steel bars between wall panels and floors. Lateral cyclic loading tests were carried out on two full‐scale specimens, including an assembled monolithic concrete wall (PCWVEC1) and unbonded post‐tensioning (PT) concrete wall (PCWVEC2), where the longitudinal steel bars at wall toes were replaced by PT tendons to provide the self‐centering capacity and bearing capacity. The seismic behavior of PCWVEC was experimentally investigated including failure mode, wall panel and XMD deformation, bearing capacity, ductility, strain, and energy‐dissipating capacity. The test results showed that XMDs used as vertical connection can effectively transfer the internal force and dissipate energy well. The average peak load of specimen PCWVEC2 was smaller than that of specimen PCWVEC1 about 13.67%. In addition, the finite element analysis (FEA) model of specimen PCWVEC2 was established, and the FEA results match well with the test results. Based on a parameter study, specimen PCWVEC2 with proper design parameter can have the same strength, energy‐dissipating capacity, and better self‐centering capacity.

Progressive collapse resistance of post-tensioned concrete beam-column assemblies under a middle column removal scenario

Post-tensioning technology is widely used in engineering practice. Recent researches showed that post-tensioned (PT) beam-column assemblies are able to enhance the structural capacity against progressive collapse triggered by a column removal scenario (CRS), but the influence of various parameters of post-tensioning on progressive collapse resistance is not fully illustrated. To fill this gap, high-fidelity numerical models are built using LS-DYNA to analyze structural behaviour of a reinforced concrete (RC) beam-column assembly and a PT concrete counterpart under middle CRS based on a referenced experimental program. Each assembly consists of a two single-bay beams, a middle joint and two enlarged side column stubs. The referenced RC assembly is mainly used to calibrate the boundary conditions to the assemblies. The model of PT assembly is validated through the comparisons of global resistance, failure pattern as well as the stress development of post-tensioning tendons with experimental data. Thereafter, the PT model is further used to investigate the effects of magnitude of prestressing and tendon profile on the overall response of PT specimens under middle CRS. Results indicate that the ability of PT tendons to enhance structural resistance is mainly because the total area of reinforcement is increased regardless of the prestressing magnitude, and straight and parabolic tendon profiles result in similar structural resistance but different failure modes.

Incorporation of Stress Time Dependence into Failure Projection Modeling of Corroding Bridge Post-Tensioning Tendons

Post-tensioning (PT) has evolved to become an important technology for designing long span bridge structures. However, tendon failures resulting from wire/strand corrosion have been reported as early as 2 y post construction. In response to this, a recent study introduced and evaluated an analytical modeling approach that projects corrosion-induced wire and strand fractures and tendon failures, given statistics that characterize wire corrosion rate. This past modeling effort assumed that tensile stress in tendons was constant with time at 63% of the guaranteed ultimate tensile strength (GUTS); however, in actuality this stress decreases with time over an assumed 10,000 d (approximately 27 y) from an initial value of about 70% of GUTS to a long-term value in the range 60% to 63% of ultimate at mid-span for a simply supported beam as a consequence of long-term concrete creep and shrinkage and strand relaxation. The present study builds upon this model by incorporating this time dependence of tendon stress into the failure projection modeling. Results are discussed within the context of better understanding bridge tendon integrity issues and corrosion related failure concerns.

NONLINEAR FINITE ELEMENT MODELING OF POST-TENSION RC AND RC BEAMS STRENGTHENED WITH NSM FRP RODS

The post-tensioned (PT) reinforced beams can provide a fast construction advantage through precast and cast-in-situ structural elements. However, due to the excessive increase in load capacity, especially when it comes to girder of bridges, the strengthening using Fiber-reinforced polymer (FRP) might be a solution. Near-surface mounted (NSM) is one of the methods used in strengthening cases, especially in the case of non-degraded concrete cover. Furthermore, very few researchers visited this area experimentally, which consider cost-effective. In this paper, two finite element models using the Abaqus program validated experimental results for both Post-tension beam and strengthening of the beam using NSM separately as preliminary models for combining both systems. PT reinforced concrete beam subjected to four-point bending loading as well as reinforced concrete beam strengthened with NSM using FRP bars subjected to two-point bending loading examined and validated through a 3D non-linear finite element (FE) model to be compared by the experimental results. This FE model considered the non-linear constitutive properties of concrete, yielding of steel, and the bond between strand, concrete, and FRP bars at NSM. The models were targeting the strengthening of existing Post tension girder beams of existing bridges structures. These modeling results showed a reasonable agreement with the tested beam results in terms of failure modes, the load capacity, load-deflection curve, and cracking behavior.

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.

Experimental Investigation of Hysteretic Performance of Self-Centering Glulam Beam-to-Column Joint with Friction Dampers

In this study, friction dampers (FDs) were placed at the top and bottom of a post-tensioned (PT) self-centering glulam (SCG) beam-to-column joint to dissipate earthquake energy. PT tendons were installed in two externally elongated slots at the centroid of the beam to provide the system with self-centering capacity so that the system can return to its original position after an earthquake. Theoretical and experimental analyses of the beam-to-column joint were performed to investigate the effects of various design parameters, such as the total clamping forces applied to the FDs and initial forces of the PT tendons, on the hysteretic performance of the FD-SCG joint under cyclic loading. During the tests, the backbone members (glulam beam and column) and main connecting members (PT tendons and FDs) were measured to always be within the elastic limit range. Both the theoretical and experimental results indicated that under low initial PT forces and clamping forces, the energy is dissipated primarily by FDs; in contrast, under high PT forces and clamping forces, some energy is dissipated by the glulam materials, owing to the occurrence of minor local damage in the specimen, in the direction perpendicular to the grain. Moreover, the FD-SCG joint can be suitably designed to achieve the desired stiffness, load capacity, self-centering ability, energy dissipation capability, and expected overall system response.

NUMERICAL STUDY ON ANCHORAGE ZONES OF POST-TENSIONED SLAB CONSIDERING ANCHORAGE DEVICE

The integrity of Post-Tensioned (PT) concrete slabs is highly dependent on the design of the anchorages zone and the anchorage system used. Using new anchorage devices may require much experimental testing, particularly when we need to examine several parameters. This research aims to numerically investigate the stresses at anchorage zones when using a new anchor device. To that aim, a 3D finite element model for the slab and the anchor device was established using a finite element program. The numerical modelling technique and parameters were verified using the results of experimental work from literature. Anchorage device transversal ribs, ties around the device, and reinforcement in the end block slab were examined to study their effect on the end block stresses. It was found that the studied parameters have a considerable impact on the behaviour of the end block. Also, numerical modelling was successful in studying anchorage zones stresses when using new anchorage devices.

A Theoretical Study of Estimating the Elastic Responses of Framed Self-Centering Wall Structures under Lateral Loading

The framed self-centering wall (FSCW) structure is a newly-emerged special type of seismic-resistant system. However, the related studies rarely concern the theoretical investigation of the FSCW structures subjected to lateral loading, which is of great importance for seismic design of the FSCW structures. In view of this, the analytical model of the FSCW structures is firstly developed, then the fundamental equations that govern the elastic responses of FSCW structures under lateral loads are formulated and the corresponding analytical solutions are derived. Meanwhile, the developed analytical model is validated by the finite element method, which shows that the developed model has a good reliability in predicting the elastic responses of FSCW structures sustaining lateral loading. Utilizing the proposed method, the effects of the post-tensioned (PT) tendon and dampers on the behaviors of the FSCW structure under lateral loading are investigated. Moreover, a comparative study of mechanical performance between the FSCW structure and conventional structures under lateral loading is conducted. The results show that, in terms of the lateral displacement and shear force responses of the frame, the mechanical performance of the FSCW structure subjected to lateral loading generally falls in between those of the conventional frame-shear wall structure and the moment-resisting frame structure.

Probabilistic seismic vulnerability and loss assessment of a seismic resistance bridge system with post-tensioning precast segmental ultra-high performance concrete bridge columns

Precast segmental ultra-high performance concrete (UHPC) columns with post-tensioned (PT) tendons can effectively protect the compression toe from damage and enhance energy dissipation (ED) capacity of column compared to conventional segmental concrete columns. Extensive experiments and numerical studies have been carried out to explore the cyclic response of segmental UHPC columns in the existing literature; however, the effect of such novel columns on the seismic safety of bridge structures has not been thoroughly understood. This study aims to numerically assess the seismic fragility and seismic life-cycle loss of bridge structures supported by the precast segmental UHPC columns. For comparison, the seismic performance of the same bridge with monolithic reinforced concrete (RC) piers are also evaluated. Here, three-dimensional (3D) numerical models are generated to simulate these two bridge types. A performance-based earthquake engineering (PBEE) framework is used to evaluate and compare their seismic performance. The segmental UHPC column model is validated with the previous experimental studies. The validated model is combined into the whole bridge. Numerical results showed that the precast segmental UHPC bridge experiences similar peak acceleration and larger peak displacement in comparison to the monolithic RC bridge. The segmental UHPC bridge pier experiencing lower residual deformation can effectively reduce the damage probability and life-cycle loss of a bridge compared to the conventional monolithic RC pier. Under the design event (2475-year return period) and maximum considered event (5000-year return period), the expected losses of the segmental bridge in the lifetime were approximate 92% and 84% of that of the monolithic bridge, respectively. The segmental UHPC bridge has a noticeable economic benefit when such a bridge is constructed in regions of high seismicity.

Seismic performance of steel frame with a self-centering beam

Self-centering moment-resisting frames are capable of returning to their original plumb position after a severe earthquake, having sustained no or only slight structural damage. In this paper, a steel frame composed of a self-centering I-beam is proposed, with its capacities for self-centering and inelastic deformation provided by post-tensioned (PT) strands and energy dissipating (ED) elements, respectively. Based on an analysis of its mechanical properties, an experiment involving this self-centering frame under cyclic loading was conducted to investigate its load transfer mechanism, bearing capacity, hysteretic behaviour, ductility, energy dissipating capacity and self-centering capacity. The results agree well with the theoretical analysis, and it can be concluded that its force-displacement hysteretic curve has a typical flag shape. The plastic deformation of the specimen is concentrated on the ED elements, which can be replaced easily after an earthquake. As the gap-opening of the anchorage plate occurs, the PT strands and ED elements provide the bending stiffness for the structure. When the story drift is loaded to 4%, the skeleton curve does not have a descending section, which means that the structure still has sufficient bearing and deformation capacities. The analysis of the residual story drift and the equivalent viscous damping coefficient shows that the frame has good energy dissipating and self-centering capabilities. A finite element model is established with OpenSees to simulate the seismic behaviour of the self-centering frame. Using the model, the seismic performance of the frame is analysed in terms of its structural parameters, including the section area of the PT strands, initial stress on the PT strands and section area of the ED elements.

Prosopis juliflora fibre reinforced green building plaster materials — An eco-friendly weed control technique by effective utilization

Abstract The use of eco-friendly materials are now becoming the field of interest in construction industry to ensure sustainability and healthy living. Gypsum plasters are eco-friendly building materials but are brittle in nature and hence reinforcement of these plasters using fibres has been found to be beneficial at its post tensioning stage. In this present work the control of harmful ecological impact of Prosopis juliflora invasive species by their effective utilization in building plaster is proposed. To assess the performance of this environmental friendly building plaster using Prosopis juliflora fibres the physical properties such as setting time, temperature rise and density were measured. Furthermore the Prosopis juliflora fibres were subjected to various chemical treatments (NaOH, KmnO4 and distilled water) and the effect of these treatments on the interaction of fibre with gypsum plaster was evaluated in terms of mechanical strength characterization. Based on the observed results the enhancement in flexural strength of the plaster was observed coupled with the transformation of brittle failure to ductile failure. The toughness of the composites were also much enhanced with the addition of the fibres.

Rocking response of self-centring wall with viscous dampers under pulse-type excitations

self-centering wall (SCW) is a lateral resistant rocking system that incorporates posttensioned (PT) tendons to provide a self-centering capacity along with dampers to dissipate energy. This paper investigates the rocking responses of a SCW with base viscous dampers under a sinusoidal-type pulse considering yielding and fracture behaviour of the PT tendon. The differences in the overturning acceleration caused by different initial forces in the PT tendon are computed by the theoretical method. The exact analytical solution to the linear approximate equation of motion is also provided for slender SCWs. Finally, the effects of the ductile behaviour of PT tendons on the rocking response of a SCW are analysed. The results demonstrate that SCWs exhibit two overturning modes under pulse excitation. The overturning region with Mode 1 in the PT force cases separates the safe region of the wall into two parts: region S1 with an elastic tendon and region S2 with a fractured tendon. The minimum overturning acceleration of a SCW with an elastic-brittle tendon becomes insensitive to excitation frequency as the PT force increases. After the plastic behaviour of the PT tendon is considered, the minimum overturning acceleration of a SCW is increased significantly in the whole range of the studied wg/p

Cyclic Behavior and Simplified Design Method of Hybrid Rocking Columns with External Energy-Dissipators

In recent years, hybrid rocking columns incorporating post-tensioned (PT) tendons and energy dissipation devices become prevalent on account of the superior self-centering capacity. In this paper, the simplified analysis method based on interface section analysis is employed to conduct parametric analyses on the hybrid rocking columns with external buckling-restrained devices, which are adopted as the external energy-dissipators. The effects of four parameters including the aspect ratio, the initial PT force, the area of PT tendons and the area of energy-dissipators are investigated. Furthermore, a simplified design method for hybrid rocking columns with external energy-dissipators is proposed using the parametric analysis results. In the design procedure, the performance index [Formula: see text] is employed considering the requirement of residual drift. The efficiency of the design method is verified by a numerical design example to show the application. The results show that the design objectives of lateral force and residual drift can be achieved through a small number of iterations.

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...

Performance of double skin FRP-concrete-steel self-centered segmental bridge piers subjected to forward-directivity near-fault ground motion

This paper investigates the damping energy and behavior of a proposed damage-resistant self-centering unbonded post-tensioned (PT) bridge pier system for accelerated bridge construction. The system is investigated with and without the addition of external energy dissipaters using two piers. The cross-section of each pier was a double-skin consisting of two tubes: outside glass fiber reinforced polymer (GFRP) tube and an inside steel tube. Self-consolidating concrete (SCC) was poured in between. The piers system has the benefits of accelerating construction using segments, self-centering capability due to rocking, and high energy dissipation from the steel bars. The piers were tested under ascending intensities of scaled ground motions. A near-fault pulse-like motion was chosen to examine the velocity impact effect on the piers. After being subjected to a series of ground motions of up to 250% of the design earthquake (DE), the piers had self-centering capability with almost no residual drift and no noticeable damage. The peak drift was 8.85%. The rocking motion reveals a complex induced dynamic behavior, in which a small change in the system can cause chaotic and butterfly effects. Hence, the energy of the system was investigated to better comprehend the dynamic behavior of rocking under forced vibrations. Two analytical models were developed to simulate the static and dynamic behaviors of the self-centering unbonded post-tensioned bridge piers.

A Case Study on Two-Span Post-Tensioned Concrete Bridge Decks with Different Span Lengths and Investigation on Prestressing Tendons with Comparisons

Post-Tensioned (PT) concrete system is one of the widely used bridge superstructure types because of its better load capacity performance. By increasing load carrying capacities on conventional reinforced concrete structures, PT is considered as an advanced technology in engineering. The aim of this paper is to study on finite element analysis of two-span PT concrete bridge decks with different span lengths. For three different span lengths, two-span bridge decks were investigated. To reduce the self-weight of the deck, at mid spans, deck section was used as voided section and at diaphragm regions, section was used as filled. Two-dimensional Finite Element (FE) deck models were created by frame elements. The FE software package Midas Civil was used. Permanent, transient and time-dependent loading types were considered. Boundary conditions were defined with their real mechanical properties. To balance the deck section stresses, prestressing tendons were used. By iterations, PT tendons layout and types were studied. Interaction between span lengths and PT tendons areas was investigated. Also, different effects on PT tendons were studied and relevant comparisons were submitted. The “best” tendon using was examined for the investigated deck sections. Concluded that optimization on PT tendon areas at bridge deck sections is possible by investigating the main effects on it. Results show that a good optimization enables us to have the optimal PT tendon using with lower cost.

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.

Experimental and numerical study of low-damage self-centering precast concrete frame connections with replaceable dampers

A kind of low-damage self-centering precast concrete (LDSCPC) frame connection with replaceable dampers was proposed. Precast components with embedded steel connectors were assembled by unbonded post-tensioned (PT) tendons, and the modular energy dissipation devices made them have great upgrading and expanding capacity. Based on the cyclic load tests of three specimens of LDSCPC frame joint and one specimen of RC frame joint, the influence of initial PT force, location of PT tendons and contribution of dampers on the mechanical performance of LDSCPC joint and the significant difference with RC joint were studied. The test results showed that the load-displacement behavior of the LDSCPC joint presented two-stage characteristics, with the excellent self-centering ability and stable mechanical properties. The stress level of the precast beam of the LDSCPC joint at 3% chord rotation could reach the stress level that of the RC joint at 0.25% chord rotation, and only a few 0.08 mm wide cracks appeared on the concrete surface. The precast components were at lower stress levels and had excellent low damage characteristics. The elaborate solid-element FE model was established, and the results of numerical simulation proved the behavior and characteristics of the LDSCPC joint in the experiment. The parametric study related to the damper was carried out, and some design comments and suggestions were also made.

Seismic Response of Post Tensioned Hybrid Shear Walls with External Energy Dissipating Reinforcement (EEDR)

ABSTRACT A major limitation with conventional post-tensioned (PT) shear wall in seismic areas is its low energy dissipation, which is tackled by placing additional mild steel reinforcement at the intersection of the wall and the foundation, called internal energy dissipating reinforcement (EDR). While the behavior of hybrid walls with internal EDR is satisfactory, the replacement of them post-yielding (i.e., after an earthquake) poses a major concern. Therefore, in this study, a new simple arrangement is proposed with external-energy-dissipating-reinforcement (EEDR) to facilitate its easy placement and replacement. This proposed system is expected to enable convenient rehabilitation of the wall after an earthquake and will keep it ready for next seismic shock. A detailed numerical study has been conducted to examine the feasibility of the proposed configuration. The proposed model depicts rocking behaviour with sufficient self-centering and energy dissipation. Having external EDR in the hybrid PT shear wall resulted in an increase in energy dissipation but keeping the strength and stiffness of the wall nearly unaffected. This study has highlighted the effectiveness of proposed external EDR system without significantly compromising the performance of a hybrid PT shear wall during an earthquake.