Post-tensioned Tendons Research Articles

Cyclic loading test of self-centering precast segmental concrete high-speed railway bridge columns with UHPC-filled duct connections

Precast concrete high-speed railway (HSR) bridge columns are attractive for standardized HSR bridges, but their applications are rare partly due to a research gap in their lateral behavior. Traditional under-reinforced HSR bridge columns have huge lateral stiffness and poor drift capacity, which means that their prefabrication is not a simple separation-assembly process and requires special research. This study aims to develop a novel self-centering precast segmental concrete (SPSC) HSR bridge column, which is designed to have five major improvements including adopting large-diameter deformed bars as energy dissipation (ED) bars, inter-locking multi-hoops, unbonded post-tensioning (PT) tendons, a cast-in-situ ultra-high performance concrete (UHPC) layer at the bottom joint, and UHPC-filled duct connections. A 1/6 scaled cyclic loading test was conducted on three specimens to validate prefabrication feasibility and assess seismic behavior. The research results show that inter-locking multi-hoops can enable the developed bridge columns to have ductile flexural failure and a drift capacity of up to 5 %. The bridge columns have increased lateral stiffness and strength as well as decreased ductility. UHPC-filled duct connections can cause the strain amplification of ED bars at the bottom joint. The bottom joint opening dominates lateral deformation while the influence of joint sliding can be neglected. The bridge columns have good ED capacity and the equivalent hysteretic damping ratio of about 20 % at the drift ratio of 5 %. The bridge columns have the excellent self-centering capacity to control residual drift ratio in an allowable range before flexural failure. The acceptable drift ratios are suggested to be 3.5 % and 4.0 %, respectively, for the SPSC HSR bridge columns without and with PT force.

Reinforcement determination for anchorage zones of post-tensioned concrete beams

In post-tensioned concrete beams, the high concentrated compressive forces are transmitted to the concrete zones at the beam ends through the anchorage devices. As a result, they can burst and split if the concrete is not adequately reinforced. The paper determines the reinforcement in anchorage zones with axially loaded post-tensioned tendons using the linear elastic analysis method, which involves computing the state of stresses as linearly elastic, and the equilibrium-based plasticity approach method as strut-and-tie models to provide prestressing force paths as a truss structure. Some numerical models are also analyzed to clarify the present methods.

Seismic Performance of an Earthquake Resilient Self-Centering Precast Reinforced Concrete Rocking Wall with External SMA Rods

ABSTRACT This research aims to propose an alternative way to provide a recentering force to a precast unbonded post-tensioned reinforced concrete rocking wall (RW) using shape memory alloy (SMA) bars. The physical and mechanical properties, such as fatigue, corrosion resistance, and large damping capacity, qualify the SMA to be at the forefront of materials used in structural engineering applications. In this study, the SMA bars replace the post-tensioned tendons to minimize the permanent deformation resulting from the system’s exposure to the lateral loading coming from the seismic events. The SMA bars are attached externally to the wall and fixed with the base to facilitate the installation process and reduce the repairing time if a failure occurs under unexpected events. The proposed system shows that the SMA rods can play the same role as the PT tendons to minimize the residual displacement while also providing an acceptable level of energy dissipation to the system.

Structural behaviour of 2D post-tensioned precast beam-column sub-assemblages subjected to column loss scenario

Many previous studies have investigated alternative load path (ALP) mechanisms of 2D reinforced concrete (RC) beam-column sub-assemblages under column removal scenarios. However, how precast and prestressed RC structures respond under a column loss scenario receives far less attention, as evident from a lack of published test data. Herein, five 2D post-tensioned precast RC sub-structures subjected to a middle column loss scenario were tested by multi-point quasi-static loading. In all the specimens, individual precast members such as beams and columns were joined together through wet connection. The study focused on investigating the combined effects of post-tensioned tendon (PT) and wet connection on load-resisting mechanisms and the influence of basic parameters such as unbonded and bonded PT, T-beam effect, and boundary conditions. The test results indicated that both unbonded and bonded parabolic-shaped PT significantly enhanced compressive arch action (CAA) and catenary action (CA) beyond basic flexural capacity, and also changed the plastic hinge mechanism in the precast beams. The specimen with unbonded PT could provide greater residual capacity than bonded PT, but the former was severely damaged by fracture of normal reinforcement and crushing of concrete rather than fracture of the tendon. In addition, the effects of T-beam and boundary conditions are discussed in detail. Finally, new design criteria for precast and post-tensioned concrete structures under column removal scenarios are proposed for structural engineers to take advantage of high-strength tendons and avoid failure at critical locations by precast joints.

Experimental evaluation of a locally prestressed precast concrete wall under repeated loading histories: Seismic performance and repairability

Seismic damage and residual deformation of buildings usually lead to high repair costs and business downtime. To develop more repairable structures, the locally prestressed precast concrete wall (LPPW) has been proposed, which allows the post-tensioning (PT) tendons and dissipaters to be easily replaced. This paper conducted quasi-static tests on the LPPW to investigate the influence of the height of the upper anchorage points of the PT tendons and to evaluate the seismic performance of the LPPW under repeated loading and post-repair loading. The test results showed that the decrease in the anchorage height of the PT tendons increased the post-yield stiffness and prestress losses of the LPPW. The seismic performance of LPPW was retained well under repeated loading in terms of the bearing capacity, energy-dissipating capacity, and self-centering capacity. The post-repair LPPW restored most of the original seismic performance, validating the excellent repairability of LPPW. Moreover, a parametric analysis was conducted using the numerical mode validated through the experimental results. The analysis revealed that the drift ratio corresponding to the yielding of the PT tendons decreased with a lower anchorage point height; increasing the axial compression ratio enhanced the bearing capacity and reduced the drift ratio at the ultimate state of the LPPW; enlarging the cross-sectional area of dissipaters positively affected the bearing capacity, energy dissipation, and shear-weight ratio of the LPPW.

Progressive collapse analysis of precast reinforced concrete beam-column assemblies with different dry connections

Beam-column joints using dry connections usually experience severe damage under large deformations, causing precast concrete (PC) frames with dry connections to become highly vulnerable to progressive collapse. Hence, this study conducted a static pushdown test adopting uniformly distributed loading on four PC beam-column assemblies using dry connections and one reinforced concrete (RC) substructure to investigate the collapse-resisting behavior under the middle-column removal scenario. The tested dry connections included top-and-seat angle connection (TA), strengthened top-seat angle connection (STA), and two refined connections with unbonded post-tensioning tendons (UPTA and UPSTA, respectively). Results showed that compared with specimen RC, the resistance of specimen TA at the beam flexural and compressive arch action (B-CAA) and catenary action (CA) stages dropped by 41% and 27%, respectively, due to the buckling of steel angles and endplates (B-CAA) and the fracture of steel angles and bolts (CA). Specimen STA had a 7% greater resistance of B-CAA because of the strengthened steel angles. However, the ductility decreased, with the displacement of rebar fracture decreasing by 37%, leading to a 30% resistance reduction of CA. The unbonded post-tensioning tendons dramatically improved the structural integrity, contributing to 52% and 97% increase in the resistance of the CA of UPTA and UPSTA, respectively. Further numerical analyses indicated that the restraint gaps reduced the initial stiffness of the collapse responses, and a good rebars welding anchorage condition could remarkably improve the resistance in the B-CAA and CA stages. An improved joint was proposed based on UPTA and rebar welding anchorage to improve deformation capacity while retaining reasonable collapse resistance. Finally, the resistance contributions from different mechanisms and components were identified through a developed calculation procedure.

3D response simulation of a bridge with a posttensioned base rocking steel pier under sequential loading of traffic loads, braking force, and earthquake excitations

AbstractThis paper presents finite element (FE) investigations of the seismic response of a bridge incorporating a base rocking steel pier. The pier consists of a circular steel tube, circular end plates, posttensioned (PT) tendon(s), and supplemental energy dissipation devices, and is configured to rock at its interface with the foundation. The main characteristic of such a pier is its ability to ensure small residual drifts after undergoing inelastic deformations during cyclic loading. The system has a tendency to close the gap due to the presence of superstructure dead load (DL) and tendon posttensioning force. Using experimental data, the calibration of the FE procedure is done at the material, component, and global system levels. The FE model of a prototype bridge is developed with the rocking pier modelled by continuum elements while superstructure, bearing units, abutment walls and backfill material modelled by discrete elements. The analysis procedure includes the application of one or two earthquake excitations, traffic loads, and braking force. The varied parameters are the diameter‐to‐thickness ratio of the column, presence of a PT tendon, addition of supplemental energy dissipaters (EDs), base plate dimensions, height of ED chairs, and ED strength. The results of dynamic FE studies demonstrate that a bridge utilizing such a pier has the potential to undergo consecutive earthquakes without sustaining significant damage and return to its original position without requiring abutment component stiffness and strength.

Experimental study of a post-tensioned precast concrete beam-column joint with energy dissipaters and partially-precast slabs

A post-tensioned precast concrete beam-column joint (PPED-PPS) with energy dissipaters and partially precast slabs was investigated in this paper; this joint was mainly composed of a precast column, a partially precast beam, four partially precast slabs, and energy dissipaters. The precast column and partially precast beam were assembled together by using post-tensioned tendons. Two batches of PPED-PPS specimens were designed and tested to investigate the seismic performance of the PPED-PPS in the following cases: failure of energy dissipaters, repeated loading and post-earthquake repairs. The experimental results illustrated that the PPED-PPS exhibited significant reductions in energy dissipation capacity and bearing capacity at a larger drift ratio after repeated loading and failure of the energy dissipaters. The partially precast slabs showed a series of interconnected cracks at larger displacement, extensively reducing the energy dissipation capacity and bearing capacity of the PPED-PPS specimen. By recasting the damaged slabs and replacing the energy dissipaters with new ones, an effective post-earthquake repair method for the PPED-PPS was implemented. Notably, the post-earthquake repair method did not increase the elastic deformation demands of post-tensioned tendons in the PPED-PPS.

Pull-out test of carbon-fiber composite cable (CFCC) tendon for an internal anchorage

An internal strengthening system involving the embedding of a post-tensioned prestressing tendon in a wedge-shaped anchorage of an existing concrete member was developed previously. The previous study confirmed the adequate load capacity of the prestressing tendon for the internal strengthening technique. The tendons used in the previous investigation were steel-rigid bar and steel-wire cables. These steel tendons are prone to corrosion under severe environmental conditions, such as bridge deck slabs sprayed with deicers. Carbon fiber composite cables (CFCC) are occasionally employed as tendons in prestressed concrete bridges. This study focused on the non-metallic material and examined the load capacity of CFCC tendon in internal strengthening systems to achieve the feasibility of the technique under corrosive environment. The main concern of the novel strengthening system was the anchoring system of the CFCC in the internal wedge. In general, both ends of the CFCC tendon can be gripped with external fasteners and be provided a tensile force using a hydraulic jack. In an internal prestressing system, a CFCC end must be anchored without any external fastener. It is preferable to simply fix the CFCC in a small wedge anchor made of existing concrete. This study focused on developing a CFCC anchoring method in a wedge-shaped hole and examined the tensile load capacity of the CFCC tendon fixed in the anchorage. The end of the CFCC tendon was reversely twisted to improve the pullout resistance by increasing the diameter of the cable. To examine the load-bearing capacity of the developed CFCC tendon, a mock-up reinforced concrete (RC) block with an internal wedge-shaped anchorage was used. A CFCC tendon equipped with a reverse-twisted tip was inserted into a wedge-shaped hole filled with high-strength grout. A pull-out test of the CFCC tendon was conducted to examine its load-bearing capacity. The test results revealed that the CFCC tendon with a reverse-twisted tip embedded in the anchorage exhibited adequate load-bearing capacity. This study confirmed that the post-tensioned prestressing system using the CFCC tendon is appropriate for strengthening RC members having the thickness of at least 200 mm, such as bridge deck slabs.

Experimental Assessment of Resilient Controlled Rocking Masonry Walls with Replaceable Energy Dissipation

In recent years, several studies have been conducted to evaluate the seismic response of controlled rocking masonry walls (CRMWs) that depend on unbonded post-tensioning (PT) tendons. The current paper describes the quasi-static cyclic testing of proposed controlled rocking masonry walls that omit PT but incorporate externally attached energy dissipation (ED-CRMWs). The proposed external energy dissipation (ED) is a flexural yielding device, named a flexural arm, that is bolted to the wall through a special steel hollow block to allow simple and fast replacement after an earthquake. As such, this wall system overcomes the limitation of internal ED devices (e.g., unbonded axial yielding bars) of being unreachable and unreplaceable after damage due to yielding or fracturing. In addition, the paper reports the retesting of the proposed controlled rocking wall after being repaired and subsequently compares the performance to that of the original wall in order to evaluate the wall resilience following seismic events. The experimental results are discussed in terms of the failure modes and damage pattern, force–displacement response, wall lateral load capacity, residual drifts, displacement ductility, and ED capacity. The results show that using a special hollow steel block at strategic locations produced a high displacement capacity of 5.0% drift without strength degradation and preserved the intended self-centering with residual drifts of less than 0.2% until at least 3.7% lateral drift. The flexural arm also had significant ductility capacity, where the walls reached 5.0% drift without buckling or fracturing of the arms. Both the original and the repaired walls exhibited limited and localized damage at the wall toes, thus positioning the proposed ED-CRMWs as a resilient system for masonry construction. Finally, the paper presents design recommendations that could be considered for introducing ED-CRMWs with flexural arms in future relevant standards.

Design procedure and seismic response of low-damage self-centering precast concrete frames

The seismic design procedure of the low-damage self-centering precast concrete (LDSCPC) frame is proposed. Its effectiveness was verified by nonlinear dynamic analysis based on the OpenSees model, and the seismic response of the LDSCPC frame was studied. The results show that the difference between the designed base shear and the average base shear obtained by nonlinear dynamic analysis is approximately 2.5%. The peak strain of the longitudinal reinforcement in each story of the beam is significantly lower than the yield strain, and the precast beam of the LDSCPC frame can meet the design requirements according to the structural reinforcement. The displacement response of the LDSCPC frame under frequent earthquakes is similar to the displacement response of the reinforcement concrete (RC) frame. Under rare earthquakes, the average of the maximum drift of the LDSCPC frame meets the code limit of 0.02 rad, and there is almost no residual displacement. The limit state of post-tensioned (PT) tendons will appear much later than the limit state of drift. The seismic vulnerability analysis results show that the metallic yield dampers of the LDSCPC frame can reduce the failure probability of IO and BR performance levels by 4.58% and 7.54%, respectively, which can effectively reduce the displacement response of the structure.

Review of experimental investigations on seismic performance of precast segmental bridge columns in seismic regions

Due to the fast construction and low interference, precast segmental bridge columns have gained increasing attention for use in non-seismic regions. However, their applications in seismic areas remain scarce due to their ambiguous dynamic performance. To estimate the seismic performance of PSBCs, existing quasi-static cyclic tests and shaking table tests are gathered and reviewed in this study. According to the structural details and material property at the joints, the PSBCs are categorized as 11 types based on the connection type, namely grouted splice sleeve couplers (GSSCs), grouted corrugated duct connections (GCDCs), wet joint connections (WJCs), mechanical bar splice connections, socket connections (SCs), unbonded post-tensioned tendon connections (UPTCs), partial precast columns (PPCs), hybrid connections (HCs), high-strength steel bars (HSBs), high-performance concrete (HPC), and external dissipators (EXDs). Based on the experimental results, the failure reason of each connection types are discussed and the effective structural details are suggested. And also, the PSBCs are divided into those with ductile and resilient connections according to the damage levels, residual drift ratios, displacement ductility coefficients, equivalent viscous damping ratios and effective stiffness parameters. With the achievements in this research, the application of PSBCs is expected to be promoted in medium-to-high seismic regions.

Reliability of the grouting of tendons under consideration of uncertainties under on-site conditions

This paper contributes to the body of knowledge from German research work Deutscher Ausschuss für Stahlbeton and from author’s experiences, to improve the reliability of cable ducts grouting. The complete and reliable filling of post-tensioned tendons with grout is necessary to protect the prestressing steel against corrosion and for bond between prestressing steel and the concrete structure, which is in both limit states applied. Diagnostics of bridges built in the last century showed the cases of faulty grouting of cable ducts. These faults are cause of corrosion prestressing steel often. Based on these diagnostics, bridges are after 35 to 70 years of service life demolished, although service life of these bridges was to 100 years declared. In the studied research work were investigated the effects of individual components, procedures and conditions of the grout and results of grouting investigated. Tests have been performed both on the experiment cable ducts and the real structures. Based on this paper, certain principles have been recommended that aim to prevent grouting faults and to improve the reliability of the grouting. In these recommendations are suggestions of controls of grouting included.

Infrared thermography detection of grouting defects in external post-tensioned tendon ducts under construction hydration heat excitation

Most duct grouting defects are caused during the construction period, and its existence will seriously affect the safety performance of the structure. Timely detection and remediation during the construction period will reduce the high inspection and maintenance costs and the probability of structural failure later. This study proposed an approach for detecting grouting defects in external post-tensioned tendon ducts using infrared thermography (IRT) under the hydration heat of duct grouting material. IRT semi real-time detection of four different grouting defect specimens was performed indoors in the first 48 h after grouting completion to validate the proposed approach. Results showed that grouting defects with 0%, 40%, and 70% grouting compactness in high-density polyethylene ducts could be identified simultaneously from 12 h to 21.5 h after grouting completion, while defects in galvanized steel pipes (GSP) could also be identified after improving the emissivity and reflectivity of the pipe surface. Furthermore, grouting compactness could be quantified by the distance between the half maximum contrast, and PCA-based image preprocessing could reduce the quantitative error of grouting compactness detection. In addition, the detection in high temperature environment should be avoided because the rise in ambient temperature would reduce the identification ability of grouting defects. IRT technique could guide the grouting construction of external tendon ducts in actual engineering because of its ability to efficiently identify grouting defects during the hydration heat release stage of grouting material.

Parametric Study on Steel–Concrete Composite Beams Strengthened with Post-Tensioned CFRP Tendons

A sustainable environment can be achieved by strengthening the existing building to avoid new construction and by replacing the construction materials with long-lasting sustainable materials such as a fiber-reinforced polymer (FRP). Using post-tensioned (PT) FRP systems has proven to be an effective technique in strengthening the structure and decreasing cracks and deformability. In this study, a 3-D finite element model was built to investigate the flexural behavior of composite beams strengthened with external PT FRP tendons. Limited research studied the use of FRP tendons to enhance the structural behavior of composite beams. This paper represents a comprehensive study of the effect of several parameters that control the design of the FRP tendons. Parameters such as PT level, tendon material, tendon length, degree of shear connection (DOSC), and tendon profile shape were considered under loading. The 3-D model’s correctness is validated using published experimental data. It was observed that of all FRP materials, carbon FRP is the best type for upgrading the beam strength, and it was recommended to use a 30 to 40% PT level. In addition, applying external PT over the full length of the beam increases the ultimate load capacity significantly. However, due to the difficulty of construction, it was recommended to use 90% of the beam span length since the difference in beam capacity does not exceed 5%. Finally, adding PT tendons with a trapezoidal and parabola profile to composite beams significantly increases the yield load and the beam capacity.

Electrochemical Assessment of Galvanized Steel Corrosion in Alkaline Sulfate Solution

Corrosion of steel prestressing strand in bonded post-tensioned bridge tendons have been associated with elevated concentrations of sulfate ions in deficient grout that can develop due to grout segregation [1]. Previous research indicated that the early presence of elevated sulfate ion concentration in the deficient grout in contact with the embedded steel can impair steel passivity. Metastable pitting was observed for steel in saturated calcium hydroxide solutions with sulfate ion concentrations greater than 1,300 ppm and pitting was observed in solutions above 20,000 ppm [2-4]. In addition to steel strand corrosion, galvanized steel ducts in direct contact with the deficient grout with elevated sulfate ion concentrations were also observed to have severe localized corrosion [1]. Galvanized steel in alkaline solutions, such as in cement pore water, have been characterized to have greater resistance to chloride-induced corrosion with chloride threshold concentrations as much as 2.5 times greater than carbon steel [5]. Information relating to sulfate concentrations is less available. Electrochemical testing including the electrochemical noise (EN) technique was conducted to identify the role of early sulfate ion presence on corrosion of galvanized steel.EN provides a test method to assess the corrosion modality without the influence of an external excitation that can affect the electrode surface and electrolyte chemistry (such as metal oxidation and oxygen reduction) [6-7]. The testing aims to identify the corrosion mitigation characteristics of the galvanized steel such as zinc activity and protective barrier surface oxide layers in presence of sulfate ions as well as combined cases with chloride ion contamination below reported threshold concentrations for galvanized steel. In the testing here, steel specimen were exposed to alkaline solutions simulating pore solutions with pH 12.6 with varying sodium sulfate levels and sodium chloride. Supplemental electrochemical experiments included the steady-state condition (open circuit potential, linear polarization test, and electrochemical impedance spectroscopy). References K. Lau, and I. Lasa. "Corrosion of prestress and post-tension reinforced-concrete bridges." Corrosion of steel in concrete structures. Woodhead Publishing, 2016. 37-57. DOI: https://doi.org/10.1016/B978-1-78242-381-2.00003-1.S. Permeh, K. K . Krishna Vigneshwaran, K.Lau., and I.Lasa. “Corrosion of Post-Tensioned Tendons with Deficient Grout. Part 3: Segregated Grout with Elevated Sulfate and Vestigial Chloride Content.” Corrosion 75 (2019) pp.848-864.S. Permeh, K. Lau, M. Duncan, and R. Simmons. “Initiation of localized steel corrosion in alkaline sulfate solution.” Materials and Structures, 54 (2021), pp.1-17.S. Permeh, K. Lau, M. Duncan, and R. Simmons. “Identification of steel corrosion in alkaline sulfate solution by electrochemical noise.” Materials and Corrosion, 72(2021), pp.1456-1467.S. Yeomans. Galvanized steel reinforcement in concrete. Elsevier, 2004.S. Permeh, and K. Lau. "Electrochemical Behavior of Steel in Alkaline Sulfate Solutions with Low Level Chloride Concentrations." ECS Meeting s. No. 10. IOP Publishing, 2021.K. Lau, S. Permeh. “Assessment of durability and zinc activity of zinc-rich primer coatings by electrochemical noise technique.” Progress in Organic Coatings, 167(2022): 106840.

(Digital Presentation) Bipolar Electrochemical Impedance Spectroscopy for Corrosion Monitoring of Steel Reinforced Cementitious Structural Components

Bipolar electrochemical impedance spectroscopy (BPEIS) was previously explored as a potential nondestructive method for detecting corrosion of steel in post-tensioned tendons which are used as reinforcing structural elements in segmental bridge construction. The tendons are composed of a grout-filled cylindrical plastic duct that contains high-strength steel strands. A proof of concept was demonstrated by experiments performed on tendons with passive and corroded strands and through finite-element simulations of the indirect impedance response1. Further work showed that bipolar impedance was sensitive to local corrosion in field tendons if the measurement is obtained near the corroding region2. This work further scrutinizes BPEIS as a corrosion monitoring method for reinforced cementitious structural components with direct comparison between corrosion damage estimates and actual metal loss.Bi-polar electrochemistry is a noncontact method in which a conducting material placed within an electric field induced by two feeder electrodes is indirectly polarized while maintaining charge neutrality such that the conducting material forms two poles, a positively charged pole which acts as the anode and negatively charge one that acts as the cathode. If the electric field is applied between the feeder electrodes under alternating current, the poles fluctuate between anode and cathode extremes corresponding to the direction of the induced field. Under such polarization conditions, the opportunity to assess the electrochemical impedance between the feeder electrodes is provided. The measured impedance includes the interfacial impedance of the feeder electrodes, the conducting material interface impedance, and the impedance of the conductor itself which can be assumed to be negligible. By placing two reference electrodes between the feeder electrodes, the interfacial impedance of the feeder electrodes can be eliminated from the measurement, thus allowing one to obtain an impedance reflective of the electrolyte impedance between the reference electrodes and the impedance of the conducting material interface.A finite element model is used to relate the measured impedance response to the impedance of the steel and cement interface and therefore the corrosion rate. The ability to accurately monitor the corrosion rate will be assessed by comparing the estimated corrosion damage obtained by integration of periodic estimates of corrosion rate to the actual damage. The role of a corrosion product layer, reinforcement geometry, and electrode configuration to the sensitivity of the measurement to corrosion rate will be described.[1] Alexander, C. L., & Orazem, M. E. (2020). Indirect electrochemical impedance spectroscopy for corrosion detection in external post-tensioned tendons: 1. Proof of concept. Corrosion Science, 164, 108331.[2] Alexander, C. L., & Orazem, M. E. (2020). Indirect impedance for corrosion detection of external post-tensioned tendons: 2. Multiple steel strands. Corrosion Science, 164, 108330.

Experimental investigation of a locally prestressed precast concrete wall

AbstractThe posttensioned (PT) tendons in a prestressed precast wall (PPW) may suffer yielding or damage under rare earthquake events, increasing the potential demand for their maintenance and renewal. A locally PPW (LPPW) with PT tendons arranged only in the lower stories was developed in this article to facilitate the replacement of the PT tendons. Quasi‐static tests were conducted to investigate the seismic performance of the LPPW with and without additional energy dissipaters. The test results demonstrated that the LPPW featured a stable hysteretic response and an excellent self‐centering capacity. The dissipaters effectively improved the energy dissipation capacity of the LPPW and preserved its self‐centering capacity. Numerical studies were further performed to address the influence of the layout of the PT tendons and dissipaters. The numerical results showed that reducing the height of the upper anchorage points of the PT tendons could increase the bearing capacity and postyielding stiffness of the LPPW. The concrete contact force at the base joint could be reduced by about 40% by moving the dissipaters from center to edge regions of the cross‐section of the wall.

Structural behavior of full‐scale precast posttensioned girder with substandard transverse reinforcement–experimental and analytical study

AbstractRapid expansion of developed cities create problems mainly attributed to traffic congestions. Recently, Bangkok has faced rapid growth and the expanded neighborhoods require convenient public transport to be linked with central Bangkok and other parts of Thailand. Monorails can be an exceptional alternative to conventional skylines and subways thankfully to their excellent climbing abilities, lower noise, shorter constructions periods, and their capabilities to be adapted within limited spaces. Recently, Mass Rapid Transit Authority adopted monorail system to facilitate public in Bangkok's expanding neighborhoods. A four‐span continuous posttensioned girder system has been proposed for the straddle monorail system. Current study focuses on the structural response of full‐scale precast posttensioned (FPP) end girders in the proposed monorail system. Results suggested that the girder remained undamaged under service load while exhibiting a linear load versus vertical deflection response. Failure under ultimate load was accompanied by crushing of concrete, buckling of compression longitudinal bars and posttension tendons at the midspan. Further, experimental rosette strains suggested that concrete strains remained well below the ultimate of strains in the vicinity of high shear zones of the girder. Therefore, these results augment that the proposed design practice is safe against shear and the proposed girder can safely be used as the end girder in four‐span straddle monorail system. Nonlinear analysis of the girder was performed using advanced tool for engineering nonlinear analysis by adopting its built‐in constitutive laws for concrete and steel reinforcement. Predicted analytical response of FPP was in good agreement with experimental results in terms of load‐deflection curves, crack patterns, and failure mode.

Analysis and experimental testing of a self-centering controlled rocking wall with buckling-restrained braces at base

A new self-centering controlled rocking wall (CRW) with buckling-restrained braces (BRBs) at the base (SC-CRWBB) is proposed to improve the energy dissipation and self-centering capacities of CRWs. The SC-CRWBB was established by adding unbonded posttensioned tendons (UPTs) at the center and BRBs at two corners of a CRW. The quasi-static test results demonstrated that the proposed SC-CRWBB achieved a satisfactory seismic performance. Structural damage was concentrated in the BRBs, while a few cracks occurred in the surface between the CRW and mortar layer and between the BRBs and CRW. Then, a finite element model (FEM) of the test specimen was created in ABAQUS software to study the influence of the initial stress of the UPTs and sectional area of the BRB core plate on the residual deformation and lateral carrying capacity of the SC-CRWBB. Finally, an analytical method for the investigation of SC-CRWBBs was validated against the test and FE analysis results.