Post-tensioned Tendons Research Articles

(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.

Explainable machine learning based efficient prediction tool for lateral cyclic response of post-tensioned base rocking steel bridge piers

This study presents a novel explainable machine learning (ML) based predictive model for the lateral cyclic response of post-tensioned (PT) base rocking steel bridge piers. The PT rocking steel bridge pier comprises a circular tube with welded circular base plate that is pre-compressed to its base by means of gravity loads and/or a PT tendon. The input factors were column diameter, column diameter-to-thickness ratio, column height-to-diameter ratio, cross-sectional area of tendon-to-column ratio, tendon initial post-tensioning ratio, dead load ratio, base plate thickness, and base plate extension. Response variables were column residual drift, column shortening, ratio of degraded stiffness to initial stiffness, maximum lateral strength to uplift force ratio, and lateral strength reduction ratio. Nine ML techniques that range from the simplest to advanced techniques were used to generate the predictive models. Several statistical performance indices are computed for the evaluation of the models. The results showed that the simplest white-box models are inadequate to capture the relationship between the input factors and the response variables. The comparative analysis of the examined models showed the superior prediction performance of the proposed xgBoost based model with a maximum coefficient of determination, agreement index, Kling-Gupta efficiency, and lowest error. The results also demonstrated that the optimized xgBoost model can be used to predict the lateral cyclic response of the rocking steel bridge piers efficiently and accurately. In addition, the unified model agnostic Shapley Additive exPlanation (SHAP) framework was employed to explain the outputs of xgBoost model and analyze the significance of the factors and their interaction on the predicted response quantities. Finally, the optimized best predictive model is used to develop a simple and user-friendly web-based prediction tool that facilitates the rapid and efficient lateral cyclic response prediction of post-tensioned base rocking steel bridge piers.

Risk-Based Selection of Inspection Method for External Post-Tensioning System of Bridges

The increasing complexity associated with the maintenance of bridges with post-tensioning tendons, along with growing public awareness to ensure higher levels of safety in bridges, has put additional pressure on the designers and the owners to find innovative solutions to ensure safe as well as economically viable solutions. Risk-based inspection and maintenance helps in finding such solutions and, thus, it is gaining more importance in the field of infrastructure management. Within the framework of current risk-based inspection methodologies, it is normally assumed that the method by which the inspection is performed is known beforehand. However, the selection of the inspection method by itself should be given importance and viewed as the first key step for any inspection. The lack of quantitative data in the initiation step makes this selection uncertain and the decision making rather subjective. Despite recent release of comprehensive reports and other publications on condition assessment of bridges with post-tensioning systems, a quantitative approach and a decision-making framework for the selection of the inspection method and associated protocol are still missing, and the inspection strategy and methods are determined purely by the experience of the inspector or the owner. In this paper, a simple and structured risk-based selection methodology is presented that can bridge the existing knowledge gap. The proposed methodology uses a statistical approach to quantify the likelihood of the inspection error utilizing a variety of applicable NDE (Non-destructive Evaluation) methods. To give the methodology both accuracy and practicality, the specifications for the national bridge inventory (SNBI) condition rating was incorporated in this methodology and the accuracy of the inspection methods are measured against determining the correct SNBI condition. Application and effectiveness of the proposed methodology are demonstrated using a case study inspection conducted earlier by the authors. The results, in this case, converged to the selection of one of the NDE methods, which consequently was accepted by the bridge stakeholders.

Effects of Uniform Load on Externally Post-tensioning Composite Beams under Multiple Degrees of Shear Connection

Composite beams (steel and concrete) are used widely as the main structural elements in flexure in bridges and buildings. Such structures' design life would be decreased if the loads increased or if environmental deterioration could occur. Such modifications can reduce the strength of these members and therefore need to be considered for replacement or retrofitting.The current study presents an evaluation of the effect of shear connection with its different degrees from partial to full for the composite beams strengthened with post-tensioning tendons. It is known by design that the use of partial shear connection in composite beams requires that the sliding capacitance of the shear connectors shouldn’t be less than the maximum slip so that the composite section can reach the ultimate design load. The degree of shear connection over which the composite section is designed, as well as the span length of the beam, are the most important factors governing the maximum slip limit. This study was performed using numerical modelling by the finite element analysis method to simulate the bending behaviour of composite steel beams under uniform loading cases which were strengthened with three shapes of tendons profiles. The results of two finite element models have been compared with experimental results obtained from previous literature related to the same topic. This comparison was made to ensure the efficiency, effectiveness, and accuracy of the model used, using ANSYS Workbench Software.

Feasibility Analysis of Post-Tensioned Beam for Industrial Building: A Review

Abstract: In recent years, due to corrosion and the constant demand for increased traffic flow, there is an eagerly need for an efficient system that can be used to repair or strengthen bridges and structures with steel-concrete composite sections. There have been so many strengthening techniques used to prevent such serious structural problems. One of these most useful techniques, which has successfully proven effective in repairing and strengthening structural members, is to use the externally post-tensioned tendons technique. The various study has also provided a recently completed experimental program on scaled bridge composite steel and concrete beams strengthened with external post-tensioning tendons to explore the fundamental cyclic loading behavior. This article summarizes the design of Post-Tensioned Beam for industrial building and a comparative study between PT Beam and RCC Beam based on a literature survey. We are analyzing such structure in our research having a large span. Manual design of PT Beam for three different span lengths without any intermediate supports and manual design of RCC Beam. We are doing a comparative study of PT Beam and RCC Beam based on the results. This report is based on a study of PT Beam that will aid future research and advances in the construction industry. Keywords: Post-Tensioning Beam, RCC Beam, Industrial Building

Simplified Method for Lateral Distribution Factor of the Live Load of Prefabricated Concrete Box-Girder Bridges with Transverse Post-tensioning

Transverse post-tensioning arrangement in prefabricated prestressed concrete (PC) box-girder bridge can effectively improve the transverse connection's performance to avoid stress concentration. The number of transverse post-tensioning tendons and the transverse post-tensioning force are crucial factors determining the live load's lateral distribution. Four prefabricated PC box-girder model tests were carried out to calculate the lateral distribution of the live load. Based on experimental results, the recommended values of the reduction factors of contact interfaces considering the effective longitudinal transfer length of transverse post-tensioning were given, and a simplified method of lateral distribution factor was proposed. The proposed simplified method results were compared with the PCI code, experiments, finite element method, articulated plate method, and rigid-plate method. The results showed that the lateral distribution factor calculated by the simplified method agreed with the results of experiments and the finite element method. The average relative differences were less than 8%. In comparison, the relative differences were more than 15% for the PCI code, articulated plate method, and rigid plate method. Thus, the proposed method could meet the engineering application and be adopted to calculate the lateral distribution factor of bridges with transverse post-tensioning.

Review of Electrochemical Testing to Assess Corrosion of Post-Tensioned Tendons with Segregated Grout

Post-tensioned (PT) construction incorporating bonded tendons with cementitious grouts has been used for highway bridges. The tendon duct and the encapsulating grout materials provide barrier corrosion protection for the embedded high-strength steel strand. Although generally used in good engineering practice, cases of PT tendon corrosion have been documented relating to inadequate detailing for joints and development of grout bleed water. Recently, in the past several years, unexpected severe localized strand corrosion has related to the segregation of thixotropic grouts. In the latter case, thixotropic grouts (that have been developed to mitigate grout bleeding) formed physical and chemical deficiencies that have been characterized to have high moisture content and elevated sulfate ion concentrations. The early presence of elevated sulfate ion concentrations in the deficient grout hinders stable steel passivation. The corrosion mechanism can be complicated due to the compounding effects of physical grout deficiency, moisture content, pore water pH, and the presence of sulfate ions. There remains interest to reliably assess corrosion of PT tendons with deficient grout. A review of electrochemical techniques and test methods used in earlier research by the authors to identify the role of sulfates on localized steel corrosion in alkaline solutions is presented. It was evident that different testing methods can reveal various aspects of the corrosion of strands in the deficient PT grout. The open-circuit potential and linear polarization method could differentiate corrosion activity between hardened and deficient grout environments but did not reveal the development of localized corrosion. Electrochemical impedance spectroscopy was useful to identify grout deficiencies by the differentiation of its bulk electrical properties. Potentiodynamic polarization and electrochemical noise technique were used to identify metastable and pitting in alkaline sulfate solutions representative of the deficient grout pore water.

Failure Forecasting of Corroding Bridge Post-Tensioned Tendons

Post-tensioning has evolved to become an important design and construction method for reinforced concrete bridges. However, corrosion-caused tendon failures on such structures have occurred and these, in turn, compromise integrity. In response to this, a previous research program developed an analytical methodology that projects the progression of wire and strand fractures and bridge tendon failures based upon corrosion rate statistics for wires. A remaining challenge, however, is to better understand the effectiveness and accuracy of existing technologies for in situ bridge tendon condition assessment, as well as the development of new and improved approaches. The present research builds upon this need by establishing quantitative relationships between the extent of corrosion damage to wires and strands and residual tendon strength. Most analyses are based upon a mean corrosion rate of 0.075 mmpy (3.0 mpy) with standard deviation 0.3, 0.4, or 0.5. As a forewarning of a pending tendon failure, the present study identifies the percentage of wire/strand section loss at 1 y and 5 y prior to failure. A recommendation is made regarding the establishment of a test facility for evaluating/qualifying existing and new technologies for nondestructive corrosion assessment of bridge tendons.

Numerical investigation of the lateral load behavior of core and coupled rocking walls

During last few decades, the researchers have developed new structural systems which have no or minor damage after being hit by severe events like earthquake. Development of self-centering wall having alternative energy dissipation mechanisms was one of these achievements. A wide variety of rocking wall systems, such as jointed walls, hybrid walls, precast walls with end columns (PreWEC), and PreWEC core wall systems, are proposed and studied. This paper describes an analytical investigation of the lateral load behavior of two new types of hybrid rocking wall systems. Core rocking wall is achieved by merging four single hybrid rocking walls and coupled rocking wall is accomplished by coupling two rocking walls using embedded reinforced concrete beams. The concept of coupling hybrid rocking walls using embedded reinforced coupling beam is emerged from previous coupled conventional shear walls studies. As single rocking wall system, in coupled and core rocking wall, post-tensioning tendons are used as a mean to provide self-centering force, and mild steel bars are used to dissipate energy. The nonlinear behavior of the wall is due to the gap opening at the base joint. Three-dimensional finite element model of each system was developed. The stress distribution, crack propagation, and critical sections of these systems are investigated. The effect of spalling concrete cover in the toe region due to rocking action is explained. In addition, the reduction in stiffness and lateral load resisting capacity of the systems due to cracks is monitored. Finally, the lateral load behavior of single rocking walls is compared to that of core and coupled rocking wall systems.

Unbonded Post-Tensioned Structural Masonry Wall with Rubber Interface for Limited-Damage Systems

Unbonded post-tensioned (UPT) tendons have been used in structural masonry walls to enhance the self-centering capability of the walls. However, the lateral displacement capacity of masonry walls with UPT tendons can be compromised by early crushing of the compression toes. To prevent toe crushing, this research study employed rubber pads underneath the bottom corners of a full-scale one-story wall. This concept was investigated by subjecting the wall sequentially to free vibration and quasistatic tests, which minimized damage to the masonry and reduced the strength degradation of the wall with increasing lateral drift. Two major damping components were identified: one is due to the instantaneous impact of the wall on the foundation base, and the other is due to the inelastic action occurring within the rubber pads during the continuous phase of rocking motion. Using the test results, a procedure is presented for designing masonry walls with rubber pads and UPT tendons.

Capacity of concrete structures with corroded reinforcement and prestressing tendons

The main degradation mechanism for concrete structures is corrosion of the reinforcement and prestressing tendons. Management of structures with such degradation requires detailed understanding of their remaining strength and safety and if necessary, make a decision regarding repairs or replacement of the structure or components. Some simplified methods for estimating the residual capacity of concrete structures do exist, primarily based on a reduction of the flexural capacity equal to the percentage of the corroded area. In this paper, a more physical understanding and description of the influence of corrosion on the strength is investigated, based on a reduction of the area of the reinforcement and prestressing tendons both due to uniform corrosion and pitting corrosion. The results of these models are successfully compared to experimental results of concrete beams with corrosion. Particularly corrosion of post-tensioned tendons is a concern for concrete structures. Some disturbing examples of collapse of concrete bridges have been seen as a result of such corrosion. The paper highlights the importance of the significant strength loss of the reinforcement as a result of corrosion itself, but also the loss of ductility due to possible hydrogen embrittlement and hydrogen induced stress corrosion cracking. The paper also suggests sulphate reducing bacteria as a possible explanation to corrosion issues related to corrosion of post-tensioned tendon structures where no chloride is found. The aim of the paper is to propose a method to calculate a lower bound estimate of the remaining capacity of concrete beams with corrosion damage to reinforcement and to the prestressing tendons.

Progressive collapse mechanisms of post-tensioned reinforced concrete frames considering effect of infill walls

This study numerically investigates progressive collapse mechanisms of post-tensioned RC frames under column removal scenarios by using the finite element method. The primary objective of this study is to investigate the influences of infill walls on mechanical behavior of post-tensioned (PT) frames against progressive collapse. Three experimental conventional reinforced concrete (RC) frames are modified into PT reinforced concrete frames: PT bare frame, PT full infilled frame and PT partial infilled frame. The numerical study was performed and the applied vertical load, horizontal displacement, failure process, load redistribution mechanisms, and re-centering capacity of PT frames are investigated under middle column pushdown scenario. Parametric analyses are conducted to study influences of material properties, arrangement of PT tendons, and magnitude of PT forces. The results show that masonry infill walls enhance the resisting capacity; however, change the failure modes and reduce the re-centering capacity of the PT frames against progressive collapse. The presence of the opening reduces the contribution of the infill walls. The PT bare frame have better resilience performance compared with the conventional bare frame. The bed joints, strength of masonry bricks, arrangement of PT tendons and magnitude of PT force greatly influence the progressive collapse resisting capacity of PT frames. Finally, a preliminary design method is proposed to predict the progressive collapse resisting capacity of PT frames with good accuracy and efficiency.

Research on seismic behavior of unbonded post-tensioned concrete wall with vertical energy-dissipating connections

An unbonded post-tensioned (PT) concrete wall system with vertical energy-dissipating connections (UPTW-VEC) is proposed that consists of precast wall panels, several X-shaped metal dampers (XMD), mild steel energy-dissipating bars (ED bars) and PT tendons. In this wall system, the precast wall panels are assembled through XMDs along the vertical joints and ED bars along the horizonal joints to provide the energy-dissipating capacity. The PT tendons installed at the wall toes are used to provide the self-centering capacity. In addition, each wall toe is protected by a steel jacket from the concrete corners spalling or crushing. Firstly, the hysteretic behavior of XMD was studied experimentally. Then, the seismic behavior of the unbonded post-tensioning concrete wall with different parameters were investigated experimentally based on four specimens. It was shown that the wall panels were resilient after tests and the cracks were only observed near the embedded plate in wall panels. In addition, a simplified analysis method was proposed, and the theoretical results matched well with the experimental results. Finally, the finite element analysis (FEA) model of UPTW-VEC was established. Following validating through the experimental results, a parametric study was conducted to investigate the influence of critical parameters on the seismic behavior of UPTW-VEC.

Electrochemical Behavior of Steel in Alkaline Sulfate Solutions with Low Level Chloride Concentrations

Localized corrosion of steel strand in deficient PT grout have been attributed to the accumulation of grout bleed water and more recently to grout segregation with elevated sulfate concentrations [1-4]. Testing of steel in sulfate alkaline solution and grout with high sulfate concentration showed higher corrosion activity and impairment of passive film development. Anodic polarization results showed that in the alkaline solution (pH 12.6), early fixed sulfate presence could be aggressive by disrupting passive film development. Also, electrochemical noise results showed numerous distinct noise events in solutions with >1,300 ppm SO4 2- that were characteristic of metastable pitting and pitting. Pitting events were sustained in solutions above 10 g Na2SO4/L H2O) [5]. Furthermore, chloride ions have often been associated with strand corrosion and limits are specified in material and building specifications [6]. However, even though strand corrosion in segregated grout in field case studies did not coincide with high chloride concentrations [1]. Testing in grout with low-level chloride concentrations (below conventional threshold values) resulted in elevated corrosion rates in presence of the sulfate ions and indicated that the sulfate presence in the grout may reduce its chloride-ion binding capacity. It was posited that there are synergic effects of sulfate ions and vestigial chloride ions in segregated grout that can promote corrosion activity.The electrochemical behavior of steel in simulated grout pore solutions was investigated to elucidate the effect of low level chloride ions in alkaline sulfate solutions on steel corrosion. The electrochemical noise (EN) technique relating to corrosion of metals in aqueous solution has been developed over the past 50 years and was used here to provide a useful mean to elucidate the localized corrosion behavior of steel subjected to alkaline sulfate solutions with low level of chloride concentration. In the testing here, steel specimen were exposed to alkaline solutions simulating pore solutions with pH 12.6 with varying sodium sulfate levels and low level of sodium chloride. Supplemental electrochemical experiments included the steady-state condition (open circuit potential and linear polarization test) and potentiodynamic polarization tests. References Permeh, K.K. Krishna Vigneshwaran, K. Lau, “Corrosion of Post-Tensioned Tendons with Deficient Grout,” Florida Department of Transportation, Final Report, Contract No. BDV29-977-04, October 20, 2016.K. Krishna Vigneshwaran, S. Permeh, M. Echeverría, K. Lau, and I Lasa. “Corrosion of Post-Tensioned Tendons with Deficient Grout. Part 1. Electrochemical Behavior of Steel in Alkaline Sulfate Solutions.” Corrosion 74 (2018) pp.362-371.Permeh, K.K. Krishna Vigneshwaran, M. Echeverría, K. Lau, and I Lasa. “Corrosion of Post-Tensioned Tendons with Deficient Grout. Part 2. Segregated Grout with Enhanced Sulfate.” Corrosion 74 (2018), pp.457-467.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.Permeh, K. Lau, M. Duncan, and R. Simmons, “Identification of Steel Corrosion in Alkaline Sulfate Solution by Electrochemical Noise” Materials and Corrosion, April 2021.DOI: 10.1002/maco.202112347K. Lee, J. Zielske, An FHWA special study: post-tensioning tendon grout chloride thresholds, Federal highway, Final Report, Contract No. FHWA-HRT-14-039, April 2014.

Design of the River Dee Bridge, Aberdeen, UK

The River Dee Bridge is a 270 m long concrete box girder bridge constructed as part of the Aberdeen Western Peripheral Route. The detailed design commenced in 2014, with construction finishing in late 2018. The bridge has a mainspan of 120 m and was built using the balanced cantilever construction method. This paper focuses on the design challenges encountered during the detailed design of this structure, particularly associated with the tight geometrical constraints imposed by environmental and aesthetic considerations on the foundations and the superstructure. The post-tensioned tendon design, which was particularly challenging for this relatively narrow and shallow box section, is also discussed.

Post-tensioned tendons for enhancing the seismic behaviour of base-isolated monopole transmission towers

The seismic performance of monopole transmission towers under the near-fault earthquake excitations are evaluated in this paper and some innovative solutions are presented to enhance their seismic behaviour. To this purpose, two benchmark concrete transmission towers are selected as case studies. The towers differ in the used materials, which are high-performance and ultra-high-performance concretes. In order to improve the tower performance under seismic actions, an isolation system with and without tendon elements are installed. The tendon gross-sectional area, effective length, and post-tensioning force are considered as three important factors, which affect the behavior of the structure equipped with isolation system. The tower top acceleration and displacement responses are evaluated and used to identify the optimal ranges of the above-mentioned design parameters. Accordingly, detailed finite element models are built in OpenSees environment in order to conduct non-linear time-history analyses under some near-fault ground motions. The results of the analyses show that the application of the isolation system may improve the displacement response of the tower, but it may cause an increase of the acceleration responses due to the impact of the isolators with their external boundary. In contrast, the addition of the tendon elements with proper characteristics improves the overall responses of the isolated towers.

Performance evaluation of self-centering rocking shear walls: Part 1 — Quantification of structural damages

Self-centering rocking shear wall (SCRSW) is an innovative structural system which is designed to achieve low damage after strong earthquake shaking. In this paper, an effective damage quantification method is developed to quantify the damages of SCRSWs. The procedure is applied in the performance evaluation and damage quantification for 24 SCRSWs. An equation of the critical parameter β in the damage model is proposed. The results show that increasing stirrup reinforcement ratio, self-centering parameter and concrete strength can reduce the damage developed in SCRSWs effectively, while higher prestress in post-tensioned (PT) tendons tends to increase the damage. An empirical equation between the critical parameter β and structural features is proposed. The critical parameter is then used to quantify the damage index (DI) of SCRSW. The result shows that the proposed β can be used to evaluate and quantify the damages developed in SCRSWs efficiently and accurately.