Steel Tendons Research Articles

Corrosion behavior of ASTM A416 tendon steel in wet conditions under various chloride concentrations

This study examines the corrosion behavior of steel tendons for prestressed concrete (PSC) structures under varying chloride concentrations and [Cl-]/[OH-] ratios. Tendons were exposed to controlled wet conditions, with chloride concentrations ranging from 0.0 to 0.25 mol/L, and [Cl-]/[OH-] ratios from 0.3 to 0.9. Results showed significant corrosion even at low chloride levels, with corrosion current density escalating from "high-risk" to "severe" as chloride concentration increased. The study also found that complete grouting is critical, as tendons exposed to humid environments without proper protection corrode significantly, irrespective of the chloride content. The findings suggest that traditional "critical chloride content" concepts may not apply to PSC tendons, highlighting the need for meticulous grout quality control to prevent corrosion. This research provides essential insights into the factors influencing tendon corrosion, offering guidance for improving PSC durability.

Analysis of bond strength of CFRP cables with concrete using random forest model

The use of carbon fiber-reinforced polymer (CFRP) as an alternative to steel tendons in prestressed concrete is increasingly favored due to its non-corrosive properties. A critical aspect of this substitution is the bond strength required to effectively transfer pre-stressing force. This study investigates the bond strengths of CFRP rods, CFRP strands, and steel strands following ISO 10406 standards. The research comprehensively explores the influence of cable type, cable surface roughness, and concrete strength on bond-slip behavior. Experimental results were augmented using a data augmentation method to enrich the dataset, which facilitated the development of a robust random forest (RF)-based prediction model for bond strength. The RF model achieved strong performance metrics, including a mean absolute percentage error (MAE) of 17.9 % and an R-value of 0.97, underscoring its efficacy in predicting bond strength. Notably, the model highlighted the significant impact of cable surface roughness on bond strength relative to other parameters studied based on the feature importance analysis. This study contributes to advancing the understanding of CFRP's applicability as a steel tendon replacement in prestressed concrete structures. The findings emphasize the importance of surface characteristics in optimizing bond strength, providing valuable insights for structural engineers and material scientists.

Behaviour of yielding mechanical hybrid rockbolts under complex loading conditions

The original “hybrid bolt” was a pragmatic solution to address installation issues in the use of resin grouted rockbolts in heavily fractured ground and the inadequate capacity of friction rock stabilisers. The original hybrid rockbolt involved installing a resin rebar in a friction rock stabiliser. The development of Yielding Mechanical Hybrid Rockbolts has been driven by efforts to eliminate the use of resin in heavily fractured ground. A typical Yielding Mechanical Hybrid Rockbolt consists of a steel tendon mechanically anchored within a friction unit. The bolt is percussion driven by the rock drill and the mechanical anchor is subsequently activated using rotation. This installation process improves the rockbolt resilience to hole closures and avoids issues associated with the use of resin. Yielding Mechanical Hybrid Rockbolts are used in both squeezing and rockburst prone ground conditions.This paper addresses a significant knowledge gap related to the behaviour of Yielding Mechanical Hybrid Rockbolts under multiple quasi-static conditions. A comprehensive experimental program investigated the complete load displacement performance of Yielding Mechanical Hybrid Rockbolts under axial, shear, and a combination of tensile and shear loads. It was observed that the load capacity increases from axial (0°), combined axial and shear (30°), combined axial and shear (60°), and pure shear (90°). The displacement capacity, however, decreases under the same testing conditions. The results are consistent but there is a slightly greater variability as the loading angle increases from 0° to 90°. It was observed that beyond 60° loading angle there is greater variability in the results as the influence of the shear component manifests itself in greater disintegration of the concrete blocks at the shear interface.

Comparative studies on the seismic performances of precast segmental columns with different concrete, reinforcement and tendon materials

In recent years, precast segmental columns cast with ordinary Portland cement (OPC) and reinforced with steel rebars have gained popularity in engineering practices owing to its obvious advantages. However, the use of OPC in the construction associates to significant emission of carbon dioxide. Moreover, the corrosion of steel reinforcements and tendon are unavoidable during the lifetime of the structure, which will significantly lower the structural strength and durability. To overcome these issues, very recently, this study proposes using green and sustainable construction materials, i.e., the geopolymer concrete (GPC), together with basalt fibre reinforced polymer (BFRP) reinforcements and tendons, which possess the characteristics of less CO2 emission and excellent corrosion resistant capability, to construct precast segmental columns (i.e., to construct GPC-BFRP segmental columns) for seismic resistant applications. Experimental studies on the proposed GPC-BFRP and the conventional OPC-steel segmental columns were then performed to examine the performances of the proposed design. However, the comparisons of the experimental results were not strictly fair since the key parameters of the two types of columns, e.g., concrete strength and posttension force, in the experiments could not exactly be the same even though they were designed to be the same. This paper therefore extends the recent experimental study and performs numerical simulations. In particular, the experimentally tested columns were used to validate the three-dimensional (3D) finite element models (FEMs) of the two segmental columns with different materials (i.e., OPC-steel and GPC-BFRP). The validated numerical models are then used to examine the seismic performances of these two types of columns under the same design parameters. Numerical results show that under small earthquakes, two types of columns present almost identical structural responses. Under moderate to severe earthquakes, the two columns also have comparable performances, but GPC-BFRP segmental column presents larger displacement responses and failed earlier because of the smaller BFRP elastic modulus. The results in this study demonstrate the potentials of constructing sustainable and durable GPC-BFRP segmental columns in seismic regions.

Time-Limited Aging Analysis of the Containment of Nuclear Power Plants without Monitoring Tendons

A prestressed concrete containment is the enclosure structure of a nuclear reactor that serves as the last physical barrier of a nuclear power plant (NPP) safety defense system. It plays a key role in the prestress time-limited aging analysis (TLAA) required for operating license extensions for NPPs. Considering prestress containment systems without long-term monitoring tendons in a nuclear power plant, the technical route for prestress TLAAs involves analyzing operating license extension regulations and in-service monitoring technical requirements for prestressed tendons performance. Using tendons based on theoretical calculations of prestress loss in a nuclear power plant and the minimum required value of prestress determined by numerical simulation, the theoretical predictive value can be compared with the minimum required value for prestressed steel tendons. This comparison can be used to evaluate the 20-year life extension of the prestress system and provide a reference for aging and life management of NPPs.

Research on the recovery performance of SMA tendon and the active control effect of adaptive cable dome

Cable dome is a widely used cable-strut tensile structure, and whose form is controllable. The shape and internal force of the structure can be adjusted by adjusting the length of the cable elements to enhance its load-bearing capacity. Shape memory alloy (SMA), as a new type of intelligent material, has excellent driving performance and is widely used in aerospace engineering, biotechnology, and construction engineering. In order to achieve active control of cable elements in cable domes using SMA, this paper conducted uniaxial tensile tests on SMA wires. Based on the test results, this paper designs and manufactures a SMA tendon suitable for active control and establishes a recovery performance model specifically for SMA tendon. Subsequently, tests on recovery performance are conducted to delve into the recovery force and displacement of the steel tendon. Finally, the SMA tendon is connected in series with the steel wire rope to obtain the active control cable elements, which is used to replace the diagonal cable in the Levy cable dome. Apply full span load to the structure, conduct active control tests by heating SMA tendon, record cable stress and node displacement during the test, and compare the results with finite element results and control methods in literature to study the control effect of SMA tendon. The test results show that the SMA tendon has good recovery performance and can be used as the control device of the control cable elements in the cable dome structure. The control effect is stable and reliable. Adjusting length of the diagonal cable can achieve Levy cable dome structural shape adjustment and improve the relaxation phenomenon of the ridge cable.

Corrosion-induced fragility of existing prestressed concrete girder bridges under traffic loads

Italian and European transportation networks include a significant number of existing bridges, built since the early ‘60s, characterised by simply supported prestressed concrete (PC) girders with post-tensioned steel tendons. Corrosion of tendons, which may lead to significant loss of structural capacity, cannot be detected by simple visual inspections and requires advanced and expensive testing by bridge owners. Therefore, procedures aimed at risk-informed prioritisation of advanced inspections and possibly retrofit are needed. The paper presents a study on the fragility of existing PC girder bridges considering traffic loads, accounting for corrosion-induced effects. An automated framework is proposed, aiming at the efficient probabilistic structural assessment of the investigated bridge typology accounting for different critical corrosion scenarios and the influence of knowledge-based uncertainty related to geometric and mechanical properties. To simulate corrosion effects, prestressing steel tendon geometric and mechanical characteristics are modified through a specific algorithm able to estimate variations in flexural and shear bearing capacity of critical cross-sections. To simulate the traffic loads, a simplified analysis is performed by using code-based traffic load models. In the paper, the framework is tested with reference to a dataset of case-study superstructures. The obtained fragility curves are deeply discussed, highlighting the effects of the number of girders and span length on the corrosion-induced increase in fragility. Although the proposed methodology presents some simplifications, it could improve the current practices of risk prioritisation, by supporting transportation authorities in ensuring the safety of the existing bridge stock.

Self-centering concrete-filled steel tubular column-steel beam joint: Experiment and numerical modeling

This paper studied the seismic behavior of a novel self-centering concrete-filled steel tubular column-steel beam (SCSTCSB) joint. The restoring force was provided by the post-tensioned tendons arranged in the CFST columns. Cyclic loading tests were performed on five 1/3 scaled specimens by varying the parameters of steel tendon type, concrete strength (fc), and axial compression ratio (n). The failure modes, hysteresis behavior, stiffness and strength degradation, energy dissipation, post-tensioned tendons response, residual deformation, and strain distribution were studied in detail. The finite element models were established to capture the stress distribution of the joints. In addition, parameter analysis was performed by expanding 17 finite element models. The results show that the ratio of residual deformation to beam rotation angle of the specimens ranged from 0.068 to 0.172. And the proposed joints demonstrated excellent self-centering ability. The self-centering (SC) performance of joints with ordinary steel tendons was better than that of joints with high-strength steel tendons. With the increase of n, the SC performance of the joints intensified at the lower ratio (n from 0.1 to 0.3) and weakened after n = 0.3. The flexural capacity of the joints improved with the increase of axial compression ratio (n), width-thickness ratio (D/t), diameter of steel tendons (d), and assembly part strength (fy,a).

Event identification in acoustic emission from wire breaks in pre-stressing/post-tensioning cables

Steel tendons commonly used in pre-stressed/post-tensioned concrete structural systems can lose cross-section due to corrosion, eventually leading to acoustic emission (AE) events when the stress exceeds the breaking strength of the wires that make up the tendons. Reliable differentiation of wire break AE events from traffic or grout crack events is critical for monitoring large structures, even where the distance between sensors may produce highly attenuated signals. In this paper, the Fuzzy c-means clustering algorithm was employed to differentiate AEs released from breaking wires of steel tendons from a database of 13464 AEs, including wire breaks, environmental and grout crack AEs. Wire breaks and grout crack AEs were collected from axial loading tests of grouted tendons in which the load increased until a wire broke. Environmental acoustic signals were collected from a bridge. Then all the collected AEs were gathered in a database and post-processed to simulate attenuation of up to 20 m from source to sensor. To optimize the speed and reliability of the Fuzzy c-means clustering algorithm, a non-dominated sorting genetic algorithm-II (NSGA-II) was used to find the minimum number of acoustic features needed. The NSGA-II algorithm started with 201 possible acoustic features and found 12 combinations of features that resulted in more than 80% wire break detection accuracy. In contrast, less than 3% of grout cracks and 0% of environmental signals were detected as wire breaks. The proposed method is suitable for deployment in a large sensor network and has sufficiently low-computational requirements for at-the-sensor processing, eliminating the need to send high-frequency sampled data outside the sensor node.

Matched Filter for Acoustic Emission Monitoring in Noisy Environments: Application to Wire Break Detection

Regular inspections of important civil infrastructures are mandatory to ensure structural safety and reliability. Until today, these inspections are primarily conducted manually, which has several deficiencies. In context of prestressed concrete structures, steel tendons can be susceptible to stress corrosion cracking, which may result in breakage of individual wires that is visually not observable. Recent research therefore suggests Acoustic Emission Monitoring for wire break detection in prestressed concrete structures. However, in noisy environments, such as wind turbines, conventional acoustic emission detection based on user-defined amplitude thresholds may not be suitable. Thus, we propose the use of matched filters for acoustic emission detection in noisy environments and apply the proposed method to the task of wire break detection in post-tensioned wind turbine towers. Based on manually conducted wire breaks and rebound hammer tests on a large-scale test frame, we employ a brute-force search for the most suitable query signal of a wire break event and a rebound hammer impact, respectively. Then, we evaluate the signal detection performance on more than 500 other wire break signals and approximately one week of continuous acoustic emission recordings in an operating wind turbine. For a signal-to-noise ratio of 0 dB, the matched filter approach shows an improvement in AUC by up to 0.78 for both, the wire break and the rebound hammer query signal, compared to state-of-the-art amplitude-based detection. Even for the unscaled wire break measurements originally recorded at the 12 m large laboratory test frame, the improvement in AUC still lies between 0.01 and 0.25 depending on the wind turbine noise recordings considered for evaluation. Matched filters may therefore be a promising alternative to amplitude-based detection algorithms and deserve particular consideration with regard to Acoustic Emission Monitoring, especially in noisy environments or when sparse senor networks are required.

Experimental investigation of self-centering beam-to-column connections with different ribbed top and seat angles

This study experimentally investigated the seismic behavior of a novel self-centering beam-to-column connection with the different ribbed top and seat angles. The connections were composed of square concrete filled steel tubular (CFST) column, H-shaped steel beam, angles with or without stiffening rib, and post-tensioned (PT) high-strength steel tendons. Eight half-scale specimens were designed and tested under cyclic loading. The influences of stiffening rib type including plane rib and multi-wave rib, PT tendon distance, and with or without PT tendons upon the performance of the connection were evaluated experimentally. The results show that the connections installed PT tendons exhibited the double linear hysteretic feature with a slight narrow hysteretic loop due to the friction of the components, the connections assembled the angles or ribbed angles took on the fuller and more stable hysteretic loop, and the connections installed the PT tendons and ribbed angles exhibited the double-flag shaped hysteretic curve. The employment of plane or multi-wave ribbed angles significantly increased the initial rotational stiffness and ultimate moment. For the connection combined the PT tendons and ribbed angles, the average residual rotation angle ratio and the maximum equivalent viscous damping ratio reached about 0.095 and 0.07 at the drift ratio of 2%, respectively. The distance of PT tendons did not affect the hysteretic behavior of the connection. The PT tendons could provide the excellent self-centering behavior of the connection.

Repairable Precast Concrete Bridge Columns for Seismic Events

In multispan bridges excited by ground shaking, columns are usually the target ductile members. Although current practice is successful in attaining the no-collapse objective for bridges, columns are usually damaged at displacements associated with this performance level. Minor damage can be repaired, but excessive damage is usually beyond repair. A new design paradigm with minimal damage and repair need is gaining interest. The benefits of such a design can be increased if low-damage technologies are combined with accelerated bridge construction techniques. The main goal of the present study was to develop rein¬forced concrete bridge columns that are fully precast concrete, low damage, and repairable through compo¬nent replacement. To achieve the project objectives, 20 repairable precast concrete alternatives were developed and ranked. Subsequently, the top three candidates were designed at 50% scale, constructed at a precast concrete plant, and tested in a laboratory. The precast concrete columns incorporated different exposed fuses, such as stainless steel bars and steel tendons, advanced materials such as ultra-high-performance concrete, a self-centering mechanism, or an accelerated bridge construction socket connection. A reference cast-in-place concrete column was included for comparison. Each precast concrete column was tested twice. It was found that the repair of the precast ultra-high-perfor¬mance concrete columns with exposed tendons was easy,

Distributed Optical Fiber-Based Monitoring of Smart Passive Anchors for Soil Stabilization

Geotechnical structures, such as piles and anchors, play a critical role in providing stability and support in a wide range of civil engineering applications. Ensuring the integrity and safety of these structures and reliably understanding their structural behavior are of paramount importance. This paper explores the application of distributed fiber optic sensors (DFOS) as a cutting-edge technology for monitoring the performance and health of passive composite anchors for soil stabilization. These anchors comprise a conventional carbon steel self-drilling bar with one or more embedded harmonic steel tendons, cemented within the central cavity of the bar. The system is finalized by an external plate for securing the bar and a protective cover for safeguarding the tendon head. Within this context, DFOS technology offers a non-invasive and cost-effective solution for real-time monitoring of various parameters, such as strain and temperature, along the entire length of the fiber optic cable. This technology enables continuous, high-resolution monitoring data collection, providing a comprehensive understanding of the long-term behavior of this specific geotechnical structure. The capability of DFOS to provide spatially distributed information facilitates the detection of localized stress concentrations and deformation patterns. The paper covers some practical considerations, such as installation techniques, data analysis and preliminary results on recently case study. The limitations and challenges associated with DFOS technology in geotechnical applications will be also discussed, including the need for specialized expertise in interpreting the data, the potential for signal attenuation in long cables and the particular care that these sensors require during cable installation and management.

Stress relaxation of concrete beams caused by creep and shrinkage effects

Shrinkage and creep are two important physical properties of concrete material which cause increase of the deformation of the constantly loaded structure over long period of time, the feature known as rheology. Additional deformation of concrete structures at the end of the design working period (most commonly 50 years) caused by these phenomena is circa three times larger than the value of the immediate elastic deformation (or even larger in some cases). Hence, in accordance with the corresponding European standard, these effects should be taken in account while evaluating the serviceability limit state of concrete structures, and if significant, consideration of these phenomena is also needed for the verification of the ultimate limit state. In concrete material, creep occurs at all stress levels, and is dependent on many parameters, as cement class, concrete grade, relative humidity of the environment, surface of the structure in contact with the ambient air (drying surface), and the age of concrete (after casting) at the loading moment. Shrinkage of the concrete is independent on loading. It is caused by decrease of the pore water content in the hardened concrete, and is predominantly dependent on the ambient relative humidity. Relaxation describes stress reduction at a constant material strain, usually in prestressing steel tendons. In this study, the physical experiments of multiple concrete beams over time with respect to rheological processes are described. Each experimental system consists of two C35/45 beams horizontally bounded by a prestressed steel cylinder. Decrease of these pretension forces in cylinders over time have been monitored (stress relaxation). All together time histories of two forces are documented, based on measurements conducted in interior environment of an agricultural building. The experimental time histories of the pretension forces are then compared with the results of the finite element numerical analyses conducted in ANSYS software. Creep and shrinkage effects of the concrete material have been considered based on the corresponding European standard for design of the concrete structures. The time-histories of the forces in prestressed cylinders obtained from the numerical simulations are then compared with the experimental data, and discussed. It is concluded, that the estimation of the force decrease over analysed time with the creep and shrinkage effects considered according to the corresponding European standard appears to be slightly larger than the experimentally measured decrease of the force value, hence the assumption is more conservative.

Experimental and analytical investigations of prefabricated segmental concrete beams post-tensioned with unbonded steel/FRP tendons subjected to impact loading

Studies of prefabricated segmental concrete beams (PSCBs) under impact loading are extremely scarce, especially those constructed with geopolymer concrete (GPC) and non-corrodible fibre-reinforced polymer (FRP) tendons. This study conducts experimental tests to explore the impact performance of PSCBs made of GPC and post-tensioned with FRP/steel tendons. An analytical model for predicting the impact response of PSCBs is also derived. The test results show that different from monolithic beams, the damage in PSCBs is mainly concentrated around segment joints due to joint openings that led to the beam failure by concrete spalling. The PSCBs with carbon-FRP tendons and steel tendons show similar damage patterns. Under a similar condition, the difference in the displacement response of these two beams is less than 4 %. A similar trend in the generated impact load and reaction force is also observed. These two beams reach the first peak and plateau region of impact load and the maximum reaction force at similar times. Overall, the PSCB with carbon-FRP and steel tendons exhibits comparable impact performances. These results manifest the applicability of carbon-FRP tendons in PSCBs against impact loads, as a feasible and durable alternative to conventional steel tendons. Furthermore, theoretical derivations are conducted to derive a simplified analytical model for predicting the impact response of simply supported segmental beams. This analytical model is based on a mass-spring-damper system and a nonlinear sectional analysis, considering the local response at the impact zone, global elastic and inelastic behaviours of segmental beams, imperfections in segment interfaces, nonlinear behaviours of material properties and strain rate effects. The proposed analytical model can facilitate the analysis and design of segmental beams.

Effects of unbonded prestressing steel tendons and slit dampers on the seismic behavior of precast concrete beam-column joints

This article proposes a novel precast concrete (PC) beam–column joint that uses prestressing steel reinforcement tendons and external steel slit dampers (SSDs) to provide self-centering and energy dissipation capabilities. The SSDs are steel plates cut to a desired shape installed under the beam ends to control their yield through energy dissipation. Three exterior beam–column joint specimens were investigated through quasi-static reversed cyclic loading tests. The specimens included a PC beam–column joint with only an SSD and two PC beam–column joint specimens using unbonded prestressing steel tendons (two in one specimen and four in the other) and an SSD. A fiber-based model using the software Ruaumoko and a code-based design were developed and validated against the experimental results. The test results showed that without the tendon, the specimen was significantly damaged, whereas using unbonded prestressing steel tendons with an SSD endowed the beam–column joint with a higher lateral load capacity of up to 40%. In addition, the ductility improved significantly up to 1.88 times. The developed model and the code-based design were in excellent agreement with the experimental results. Overall, this innovative connection type offers an alternative for seismic-resistant PC structures, and its design enables easy repair after an earthquake.

Mechanics and validation tests of a post-tensioned self-centering brace with adjusted stiffness and deformation capacities using disc springs

Self-centering braces have been developed to reduce the residual deformation of steel frames in earthquakes. The brace has a higher elastic axial stiffness before the activation, which may result in a higher base shear for frame design. This work was aimed to develop a new post-tensioned self-centering brace (PT-SCB) with adjusted stiffness and deformation capabilities such that the brace could be designed based on a specified yield or ultimate frame drift. Combining disc springs and one of the compression members together in the original SCB could achieve new structural characteristics, providing an alternative to tune the axial stiffness and deformation. This work first introduces the mechanics and deformation mechanism of the proposed SCB and performs a parametric study to investigate the effect of disc spring stacks on the hysteretic response of SCBs. A test program is then conducted on cyclic tests of disc spring stacks in different serial and parallel combinations and two PT-SCBs. Each 3800 mm-long brace is composed of high-strength steel tendons, compression steel members, disc spring stacks, and bolted friction device. The hysteretic responses of the new SCB with different design parameters are used to validate the mechanics and ability of the axial stiffness and deformation adjustment.

Bond behavior of flexible braided AFRP tendons in high-performance concrete based on pull-out and beam tests

AFRP tendons are manufactured in both rigid and flexible form, where flexible AFRP tendons could be coiled and utilized as external prestressed tendons with significant curvature. This study investigates the bond behavior of flexible AFRP tendons in high-performance concrete (HPC) by examining the effects of tendon types, tendon diameter, concrete types, and test methods. Results show that pull-out failures are prone to occur in specimens with AFRP tendon, whereas splitting failures are prone to occur in specimens with steel tendon. The bond stresses for AFRP tendons reach maximum value within a slippage range of 4.5–10.5 mm, while for steel tendons, the maximum bond stresses occur within a larger slippage range of 17–44 mm. The bond strength of steel tendons is 1.12–1.26 times higher than that of AFRP tendons. Normal concrete (NC) specimens with splitting failure produced maximum 7.1 % higher bond strength compared to HPC. On the other hand, the pull-out failure is determined by the interlaminar shear strength of AFRP tendons, leading to comparable bond strength between NC and HPC. A 5 % difference in bond strength exists between pull-out tests and beam tests with similar failure modes. For AFRP tendons, changing the diameter from 13 mm to 15 mm increases the bonding strength by +6 % to −17 %, which is basically consistent with the existing research that the bonding strength decreases as the diameter increases. This study presented a formula for AFRP tendon bond strength, considering concrete strength, types, tendon diameter, and test methods. The proposed model outperforms existing ones with an average of 0.99 and a variance of 0.13.

Composite CFST column to H-shaped steel beam joint: Experimental and numerical investigation

Conventional CFST column-to-steel beam connection has excellent collapse-resist capacity, good plastic deformation, and high energy dissipation. However, it makes reconstruction challenging after extreme inelastic deformation in a severe earthquake. This paper proposes a self-centering (SC) composite CFST column to H-shaped beam joint (SCCCB joint) using post-tensioned (PT) tendons. The residual deformation of the splicing column can be greatly reduced under the action of pre-tension tendons. Cyclic loading tests were performed on five 1/3 scale test specimens with the main parameter of axial compression ratio (n = 0.10, 0.12, 0.15, and 0.17) and steel tendon types (with or without cutting processing) to investigate the cyclic behaviour and SC performance. The finite element models were established to capture the stress distribution of the joints. Finally, the seismic and SC performance of the joints were studied by the parametrical analysis including five parameters: width-thickness ratio of steel tube (D/t), diameter, number and spacing of steel tendons (d, ns and s), and connecting diaphragm strength (fy,a). The SC performance can be improved with the increase of ns. The bending capacity of the joints increased with the increase of n, D/t, d and fy,a.

Precast segmental beams made of fibre-reinforced geopolymer concrete and FRP tendons against impact loads

In the open literature, there is no investigation into the impact behaviour of prefabricated segmental concrete beams (PSCBs) cast with low CO2-emission fibre-reinforced geopolymer concrete (GPC), reinforced with non-corrodible basalt fibre-reinforced polymer (BFRP) reinforcement, and post-tensioned with carbon FRP (CFRP) tendons. This research, hence, aims to close this existing gap of knowledge. The primary goals are to investigate the effect of dispersed fibres on the impact response of PSCBs and to compare the performance of CFRP versus steel tendons. The experimental results reveal that the PSCBs fail due to excessive joint openings that lead to concrete spalling and flying concrete debris. The inclusion of dispersed fibres in the concrete postpones crack development, reduces reinforcement strain, and effectively mitigates concrete spalling and stiffness degradation of the beams. While fibres show limited influence on the deflection response of PSCBs, as the deformation of segmental beams is predominantly governed by joint openings with no fibres bridging across the joints, they play a crucial role in preventing severe damage during impact events. The impact response of beams post-tensioned with CFRP tendons is analogous to those with steel tendons. Notably, both the CFRP tendon and BFRP reinforcement remain intact even when the beam fails under impact loads. This implies that CFRP tendons and BFRP reinforcement can be successfully employed in constructing durable and sustainable segmental GPC beams capable of withstanding impact loading. A high-fidelity numerical model of PSCBs made of GPC and FRP tendons and reinforcement subjected to impact loads is also developed, for the first time, to supplement the discussions of experimental findings.