Search Results (116)

This study aims to enhance the damage controllability and overall seismic resilience of assembled underground structures under earthquake actions. To achieve this, three types of prefabricated roof–sidewall composite joints are proposed based on the design concepts of cogging for force transfer and local strengthening. These include the high-strength bolt–cogging–grouting sleeve joint (HCG), the prestressed steel strand–cogging–grouting sleeve joint (PCG), and the UHPC–cogging–grouting sleeve joint (UCG). Following the principle of positioning joints in regions of low structural stress, four 1/4-scale reinforced concrete (RC) specimens were designed and fabricated, including one cast-in-place (CIP) reference specimen and three precast RC specimens. Quasi-static tests were carried out to systematically evaluate the seismic behavior and internal force distribution of each specimen. Numerical validation was also performed using ABAQUS. The results show that both UHPC and a reasonable application of prestressing can effectively inhibit crack initiation and damage propagation at the joint seams. When the composite joints are positioned outside the plastic hinge region, they provide a reliable load transfer path for the reinforcement. The HCG and UCG joints significantly enhance the load-bearing capacity and energy dissipation capacity of the specimens. Their ductility and energy dissipation both achieve a seismic performance equivalent to that of the CIP specimen. Furthermore, damage in these specimens is predominantly confined to the designated plastic hinge region of the roof. This effectively mitigates shear damage in the roof–sidewall connection zone (RSC). Although the PCG joint improves the initial stiffness of the specimen, its energy dissipation capacity and ductility are reduced. It also causes damage to be transferred to the RSC. This leads to increased shear deformation and premature shear failure in this zone. Consequently, both UHPC and a reasonable application of prestressing can be used for the prefabrication of underground structures. Positioning the joints outside the roof plastic hinge zone can effectively achieve the seismic design goal of “strong joint, weak component”. Full article

The corrosion of prestressed tendons in concrete structures remains a major durability concern, especially for post-tensioned members exposed to aggressive environments. High-strength aluminum alloy (AA) bars exhibit favorable characteristics such as corrosion resistance, low density, and high ductility and may therefore provide an alternative or supplementary prestressing material in durability-oriented structural design. In this study, a bonded post-tensioned T-shaped concrete beam with hybrid prestressing combining prestressed steel (PS) strands and 7075 AA bars was investigated. A refined finite element model was developed by considering the bond-slip relationship between the AA tendons and grout inside corrugated tubes. The flexural behavior of the beam was analyzed through a combination of finite element simulation and sectional theoretical analysis. In addition, a fatigue-life assessment framework was established based on vehicle fatigue loads and material fatigue constitutive models, and the fatigue performance of the proposed hybrid beams was compared with that of conventional prestressed concrete beams. The theoretical predictions agreed reasonably well with the numerical results. Results indicated that partial replacement of PS strands with corrosion-resistant AA bars could alter the governing fatigue failure mode and improve the fatigue durability of prestressed beams under corrosive conditions. These findings highlight the potential of hybrid AA–PS prestressing as a durability-oriented strategy for concrete beams in corrosive environments. Full article

During circumferential tensioning of prestressing strands in U-shaped aqueducts, longitudinal tensile stresses may develop and impair crack resistance. Most existing studies rely on three-dimensional finite element (FE) simulations. Although accurate, FE modeling is time-consuming and unsuitable for rapid scheme evaluation during construction. To overcome this limitation, the U-shaped aqueduct was first simplified as a cylindrical shell and the feasibility of this idealization was verified. An approximate analytical solution was then derived from cylindrical shell theory to predict the longitudinal stress induced by circumferential prestressing. Practical factors, including non-uniform wall thickness, non-equidistant strand spacing, and strand positional deviations, were incorporated to improve engineering applicability. FE results confirm good agreement, with RMSE of 0.055–0.169 MPa and NRMSE of 2.3–19.6%, where the upper bound occurs only in localized regions. The method was further applied to an engineering project to optimize the tensioning scheme. With a rational interval-tensioning procedure, the peak longitudinal tensile stress was reduced by 31.6%. Overall, the proposed approach enables rapid stress estimation and supports preliminary screening and optimization of circumferential tensioning schemes. Full article

The truss transfer story serves as a critical structural zone connecting different structural systems in high-rise buildings. This component incorporates numerous inclined-web trusses, which are prone to cracking and failure under seismic events. To enhance the seismic performance of long-span transfer structures and address the tensile cracking vulnerability of inclined-web trusses in conventional truss transfer stories, this study investigates the seismic behavior of a novel composite system: a prestressed CFRP tendon–steel-reinforced concrete transfer story structure with inclined-web trusses and two specimens of inclined-web truss transfer story frames—with and without prestressed CFRP tendons—were designed and fabricated. These specimens were subjected to horizontal low-cycle reversed loading to examine seismic performance indicators, including crack propagation patterns, failure modes, hysteretic curves, skeleton curves, stiffness degradation, ductility, and energy dissipation capacity. The results demonstrate that incorporating prestressed CFRP tendons into the inclined-web trusses did not alter the failure mode of the steel-reinforced concrete transfer story structure. The primary failure morphology consistently manifested as flexural-shear failure in the bottom chord columns. During the loading process, tensile cracking failure manifested in the inclined-web members of both specimens, with and without prestressing. Crack distribution remained uniform in all cases. The inclined-web trusses incorporating prestressed strands exhibited an 80% increase in cracking load compared to the non-prestressed specimen. Furthermore, the prestressed specimen demonstrated superior resistance to performance degradation and enhanced energy dissipation capacity. Both configurations exhibited significant deformation capacity and satisfactory seismic performance. The prestressed CFRP tendons enhance the crack resistance and deformation capacity of a transfer story structure with inclined-web trusses, providing novel insights for seismic design of truss transfer story structures. Full article

To achieve efficient design and ensure the safety of concrete structures, the use of high-strength concrete, reinforcing steel, and prestressing tendons has been steadily increasing. In this study, for flexural design of prestressed concrete (PSC) structures employing high-strength strands with tensile strengths of 2160 MPa and 2360 MPa, the applicability of the current design-code equation for predicting the strand stress at flexural failure ($f_{ps}$)—which was originally proposed based on studies of conventional strands with tensile strengths of 1860 MPa or lower—was evaluated. Furthermore, an improved prediction equation was proposed. Section analyses based on stress–strain curves obtained from numerous tensile tests of high-strength strands were conducted, and the results were compared with the existing prediction equations specified in ACI 318 and the Korean KDS code. The comparison revealed that, for high-strength strands, the strand stress tends to be underestimated in the tension-controlled region and overestimated in the compression-controlled region. To address these issues, a new prediction equation was proposed that retains the form of the existing equation but incorporates correction factors reflecting the characteristics of high-strength strands. The performance of the proposed equation was evaluated not only for rectangular sections but also for T- and I-shaped sections, and its predictive accuracy was verified by comparing the predicted strand stresses and nominal flexural strengths with those obtained from section analyses. As a result, the proposed prediction equation demonstrated improved accuracy compared with the existing one, while maintaining an appropriate level of conservatism. Therefore, it is expected to enhance design efficiency for PSC structures employing high-strength strands. Full article

Prestressed concrete (PSC) beams are widely used in critical infrastructure but are highly susceptible to corrosion in aggressive environments, which can significantly compromise their structural performance. Accurate prediction of residual flexural capacity is crucial for evaluating the safety and serviceability of corroded PSC elements. This study presents a simplified empirical model for estimating the residual flexural strength of corroded PSC beams, with maximum strand mass loss serving as the key governing parameter. This approach is superior to existing models, which typically rely on average mass loss and fail to capture the localized stress concentrations induced by pitting corrosion. The model was developed from an experimental dataset of 31 corroded beams, covering maximum mass loss up to 90% using exponential regression. An extensive database of 124 test results from 19 independent studies was used for the purpose of verification and comparison with existing models. The proposed model was capable of effectively capturing the degradation trend and providing accurate and conservative predictions, with an average experimental-to-calculated capacity ratio of 1.04 and a coefficient of variation of 8.7%. Its direct reliance on maximum mass loss, which can be indirectly inferred from corrosion-induced crack widths, significantly enhances the practicality and safety of the model for field condition assessments and life-cycle management of PSC structures. Full article

Self-centering structures have emerged as a promising seismic design solution, offering advantages in structural safety, rapid post-earthquake functionality recovery, and life-cycle economy. This paper introduces a self-centering beam–column joint that integrates superelastic shape memory alloys (SMAs) and prestressed steel tendons as restoring components. A numerical model was developed in OpenSees and validated against experimental results, with discrepancies in residual deformation within 10%. The validated model was used for parametric studies on strand area, prestress, and SMA configuration. The results show that the proposed joint sustains a maximum drift of 6% while maintaining nearly zero residual drift (less than 0.2%), and its hysteresis curve exhibits a stable flag-shaped pattern. The equivalent viscous damping ratio exceeds 0.1, confirming excellent deformation and energy dissipation capacities. These findings highlight the joint’s potential for application in seismic-resilient steel frames. Full article

Based on the principle of re-centering with low prestress and energy dissipation through sloped friction (SF) energy dissipators, this study proposes a new hysteresis concept characterized by enhanced post-stiffness and energy dissipation for self-centering prestressed concrete (SCPC) frames. The focus of this research is to compare the seismic performance of SCPC frames utilizing both traditional and novel hysteresis concepts, aiming to provide critical evidence for the advancement of seismic-resilient structures. Nonlinear dynamic time history analyses were conducted under various seismic levels to investigate the impact of the novel hysteretic concept on seismic performance indicators, including inter-story drift, residual inter-story drift, and beam-column damage. Additionally, the influence of energy dissipator configuration and prestress level on the repair costs of structures subjected to the maximum considered earthquake (MCE) was analyzed to elucidate the structural functional recovery capacity. The results indicate that the combination of low prestress and sloped friction energy dissipators significantly reduces internal forces in beams and columns compared to traditional high prestress SCPC frames with conventional friction energy dissipators. The integration of sloped friction energy dissipators and the application of low prestress to post-tensioned (PT) strands effectively dissipate the energy transmitted to the frame during an earthquake, leading to a substantial reduction in structural damage within the SCPC frame utilizing the new hysteresis concept during large earthquakes, thereby facilitating post-earthquake repairs. Full article

The development of wind power aligns with the strategy of low-carbon development and plays a crucial role in the global transition to a green economy. The segmented steel–concrete wind turbine tower offers advantages such as modular fragment prefabrication, prestressed structural enhancement, and integrated intelligent construction. To investigate the structural performance of such towers, this paper established a numerical model based on an existing project. The model was validated against previous experiments and used for parametric analysis. A numerical model of a segmented steel–concrete wind turbine tower was developed to evaluate its overall deformation, stress distribution, and vertical and horizontal joint separation under various conditions. The concrete segment of the tower was numerically simplified, and a comparative analysis of structural performance was conducted between the detailed and simplified models. Based on the simplified model, the effects of the friction coefficient, prestress loss, and contact area on the anti-slip performance of the transition section of the towers were investigated and analyzed. The results indicated that the validity of the modeling approach was confirmed through the existing experimental results. The top displacement of the model incorporating vertical and horizontal joints (Model 1) did not exceed the limit of 1/100 under the safety factor considerations, indicating that the structure could ensure safety. The simplified model (Model 2) showed consistent behavior with Model 1, thereby providing a reliable basis for parametric studies. A reduction in the steel-to-steel friction coefficient, steel strand prestress, and contact area between the steel transition section and the embedded anchor plate resulted in an increase in the horizontal relative displacement between the steel transition section and the embedded anchor plate to varying extents. Notably, a more pronounced increase in displacement was observed under higher loading conditions. Overall, the horizontal relative displacement between the steel transition section and embedded anchor plate under single-loading conditions was below one millimeter in most of the studied conditions, which was relatively small compared to the assembly tolerance of the structure. Full article

Due to the presence of stray current in the subway environment, the durability issues of subway structures differ from those of general structures. This study simulates the combined effects of chloride ions and stray current in the subway environment through electrochemical corrosion experiments, thereby analyzing the corrosion morphology and mechanical property degradation of steel strands and the corrosion-induced cracking of concrete. The experimental results indicate that stray current affects the strength and ductility of steel strands as well as the cracking of concrete. The corrosion difference coefficient μ_c at different positions is greater than 1.6 and the average corrosion degree η_ave is less than 7%. The corrosion morphology gradually changes from non-uniform to uniform corrosion until the η_ave is greater than 12%. The concrete crack width under a stray current of 60 mA is 10.67 times that of cracks under 20 mA after 42 days, which is approximately linearly related to the current intensity. Based on the experimental results, a corrosion-induced crack prediction model for prestressed concrete under stray current is proposed, with the main influencing factors being current intensity, concrete tensile strength, and protective layer thickness. These findings can provide valuable references for the durability analysis of subway structures. Full article

Incorporating Nitinol (NiTi) shape memory alloy (SMA) into concrete structures has gained significant attention in recent years due to its ability to enhance the properties of concrete. This review paper illustrates the history of NiTi SMA and its use in various civil engineering structural applications. A detailed analysis of the existing literature and case studies offers perspectives on the possible applications, benefits, and prospects of utilizing NiTi SMA to reinforce and strengthen elements in concrete structures. The study examined publications on the internal usage of NiTi SMA in concrete and cement-based matrices as an embedded element, including fibers, bars, cables, wires, powder, and strands. In addition, superelastic and shape memory forms of NiTi were considered. It was concluded that the superelasticity of NiTi aided in energy dissipation from impact or seismic events. It also improved the re-centering performance and deformation capacity and reduced residual stresses, strains, and cracks. Conversely, the SMA effect of NiTi helped bridge cracks, recover the original shape, and induced prestressing forces under thermal activation. Full article

The traditional research methods of the notch frequency phenomenon are mainly discussed by experimental observation or the semi-analytical finite element method. In this paper, the notch frequency characteristics of ultrasonic guided waves are simulated by the general finite element method. Firstly, the theoretical dispersion curve of the longitudinal mode in the axially loaded rod is derived by the acoustic elasticity theory, and the finite element simulation is carried out by ABAQUS/Explicit 6.14 to simulate the wave propagation in the seven-wire steel strand. In order to verify the model, laboratory experiments are carried out on three types of prestressed steel strands with diameters of 12.7 mm, 15.2 mm, and 17.8 mm, respectively. Each specimen is gradually loaded from 50 kN to 110 kN in increments of 30 kN. At each loading level, the ultrasonic signal is obtained, and the corresponding notch frequency is extracted from the spectrum. The experimental results confirm the accuracy of the model, and the maximum deviation between the predicted notch frequency and the measured value is 3%. The results show that the proposed method provides a robust and non-destructive means for structural health monitoring in civil engineering applications, and has the potential to be more widely used in complex waveguide structures. Full article

Acoustic emission (AE) technology has been extensively applied in the damage assessment of steel strands; however, it remains inadequate in identifying and quantifying the number of strand fractures, which limits the accuracy and reliability of prestressed structure monitoring. In this study, a test platform based on practical engineering was built. The AE monitoring method using a waveguide rod was applied to identify signals from different numbers of strand fractures, and their acoustic characteristics were analyzed using Fourier transform and multi-bandwidth wavelet transform. The propagation attenuation behavior of the AE signals in the waveguide rod was then analyzed, and the optimal parameters for field monitoring as well as the maximum number of plates suitable for series beam plates were determined. The results show that AE signals decrease exponentially with an increasing propagation distance, and attenuation models for various AE parameters were established. As the number of strand fractures increases, the amplitude of the dominant frequency increases significantly, and the energy distribution shifts towards higher-frequency bands. This finding introduces a novel approach for quantifying fractures in steel strands, enhancing the effectiveness of AE technology in monitoring and laying a foundation for the development of related technologies. Full article

In contrast to brittle normal-strength concrete (NSC), high-performance steel-fiber-reinforced concrete (HPSFRC) provides better tensile and shear resistance, enabling enhanced bridge girder design. To achieve a balance between cost efficiency and quality, reducing conventional reinforcement is a viable cost-saving strategy. This study focused on the flexural behavior of a type of pre-tensioned precast HPSFRC girder without longitudinal and shear reinforcement. This type of girder consists of HPSFRC and prestressed steel strands, balancing structural performance, fabrication convenience, and cost-effectiveness. A 30.0 m full-scale girder was randomly selected from the prefabrication factory and tested through a four-point bending test. The failure mode, load–deflection relationship, and strain distribution were investigated. The experimental results demonstrated that the girder exhibited ductile deflection-hardening behavior (47% progressive increase in load after the first crack), extensive cracking patterns, and large total deflection (1/86 of effective span length), meeting both the serviceability and ultimate limit state design requirements. To complement the experimental results, a nonlinear finite element model (FEM) was developed and validated against the test data. The flexural capacity predicted by the FEM had a marginal 0.8% difference from the test result, and the predicted load–deflection curve, crack distribution, and load–strain curve were in adequate agreement with the test outcomes, demonstrating reliability of the FEM in predicting the flexural behavior of the girder. Based on the FEM, parametric analysis was conducted to investigate the effects of key parameters, namely concrete tensile strength, concrete compressive strength, and prestress level, on the flexural responses of the girder. Eventually, design recommendations and future studies were suggested. Full article

Compared to conventional reinforced concrete (RC) piers, self-centering rocking piers exhibit better seismic resilience and sustain minor damage. However, their construction typically relies on prefabrication. Moving large, prefabricated components can be challenging in mountainous areas with limited transportation access. Therefore, using concrete-filled steel tube (CFST) piers is a practical alternative. The steel tube both serves as a construction permanent formwork and enhances the compressive performance of concrete through confinement effects. To apply CFST self-centering rocking piers in mountainous regions with high seismic intensity, a fast construction system was designed and a 1:4 scale specimen was developed for testing. Lateral cyclic loading tests revealed that the specimen exhibited good deformation and self-centering capabilities, with a residual drift ratio of only 0.17% at a drift ratio of 7.7%. Most of the horizontal displacement was contributed through a rocking gap opening, resulting in minimal damage to the pier itself. The damage was concentrated primarily in the energy-dissipating rebars, while the prestress strands remained elastic, though prestress loss was observed. Full article