Search Results (104)

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

Prestressed, precast composite panels are a type of building component that combines prestressing technology with composite materials; but, for most of them, it is difficult to balance structural stress performance and assembly efficiency. This paper proposes a series of novel bidirectional, prestressed, prefabricated, composite slabs, aiming to enhance their bidirectional force characteristics and assembly efficiency. By implanting a kind of specially designed concrete movable core rib with the same geometry as the cavity in the hollow-core slab at medium spacing, the transverse stressing performance of the structure is enhanced without affecting the unidirectional structural performance. Then, in the pre-set transverse apertures, several pieces of unidirectional, prestressed, precast hollow-core slabs that are implanted in the core mold are connected in series with high-strength strands and prestressed; finally, we obtain a bidirectional, prestressed, prefabricated composite slab. Two types of slabs (i.e., 3.3 m × 4.5 m and 4.5 m × 4.5 m) are selected and their mechanical behavior is investigated experimentally and by the finite element method, and the results are in good agreement. The proposed bidirectional, prestressed, precast composite slab not only has better overall bearing performance but also improves the structural stiffness and assembly rate, which can greatly improve the economic benefits and is of great significance for the popularization and application of assembled concrete structures. Full article

Unlike traditional building structures, transmission tower foundations endure significant vertical and horizontal loads, with particularly high uplift resistance requirements in complex terrains. Moreover, challenges such as difficult material transport and low construction efficiency arise in these regions. This study, based on practical projects, proposes a novel high uplift resistance prestressed concrete prefabricated foundation (HURPCPF) tailored for transmission line systems in complex terrains. A refined finite element model is developed using ABAQUS to analyze its performance under uplift, compressive, and horizontal loads. Comparative studies with cast-in-situ concrete foundations evaluate the HURPCPF’s bearing capacity, while parametric analysis explores the impacts of foundation depth and dimensions. The results show that the proposed HURPCPF exhibits a linear load–displacement relationship, with uniform deformation and good integrity under compressive and uplift conditions. During overturning, the tilt angle is less than 1/500, meeting safety standards. The design of prestressed steel strands and internal reinforcement effectively distributes tensile stress, with a maximum stress of 290 MPa, well below the yield stress of 400 MPa. Compared to cast-in-situ concrete foundations, the displacement at the top of the HURPCPF’s column differs by less than 7%, indicating comparable bearing performance. As foundation depth and size increase, vertical displacement of the HURPCPF decreases, enhancing its uplift resistance. Full article

This study introduces high-strength non-prestressed steel strands as reinforcement materials into Engineered Cementitious Composites (ECCs) and developed a novel high-strength stainless-steel-strand-mesh (HSSWM)-reinforced ECC with enhanced toughness and corrosion resistance. The bonding performance between HSSWM and an ECC is essential for facilitating effective cooperative behavior. The bond behavior between the HSSWM and ECC was investigated through theoretical analysis. A local bond–slip model was proposed based on the average bond–slip model for HSSWM and ECCs. The results indicated that the local bond–slip model provided a more accurate analysis of the bonding performance between HSSWM and the ECC compared to the average bond–slip model. The effects of the ECC’s tensile strength, steel strand diameter, and transverse strand spacing on local bond–slip mechanical behavior were investigated through FEA. The results showed that the local bond–slip model and FE results aligned well with the experimental data. Additionally, the distribution of bond stress between the HSSWM and the ECC was analyzed using the micro-element method based on the local bond–slip model. A prediction model for the critical anchorage length and bond capacity of HSSWM in the ECC was established, and the accuracy of the model was verified. Full article

The use of carbon fiber reinforced polymer (CFRP) strands as prestressed reinforcement in prestressed concrete (PC) structures offers an effective solution to the corrosion issues associated with prestressed steel strands. In this study, the flexural behavior of PC beams reinforced with prestressed CFRP strands and non-prestressed steel rebars was investigated using finite element modeling (FEM) and artificial neural network (ANN) methods. First, three-dimensional nonlinear FE models were developed. The FE results indicated that the predicted failure mode, load-deflection curve, and ultimate load agreed well with the previous test results. Variations in prestress level, concrete strength, and steel reinforcement ratio shifted the failure mode from concrete crushing to CFRP strand fracture. While the ultimate load generally increased with a higher prestressed level, an excessively high prestress level reduced the ultimate load due to premature fracture of CFRP strands. An increase in concrete strength and steel reinforcement ratio also contributed to a rise in the ultimate load. Subsequently, the verified FE models were utilized to create a database for training the back propagation ANN (BP-ANN) model. The ultimate moments of the experimental specimens were predicted using the trained model. The results showed the correlation coefficients for both the training and test datasets were approximately 0.99, and the maximum error between the predicted and test ultimate moments was around 8%, demonstrating that the BP-ANN method is an effective tool for accurately predicting the ultimate capacity of this type of PC beam. Full article

Prestressed concrete box girders are commonly employed in the development of high-speed railway bridge constructions. The prestressed strands in the girder may corrode due to long-term chloride erosion, leading to the degradation of its flexural performance. To examine the flexural performance of corrosion-affected simply supported prestressed concrete box girders, eight T-shaped mock-up beams related to the girders used in the construction of high-speed railway bridges were manufactured utilizing similarity theory. Seven of the beams underwent electrochemical accelerated corrosion, and then each beam was subjected to failure under the four-point load test method. Measurements recorded and analyzed in detail during the loading process included the following: crack propagation, crack width at various loads, crack load, ultimate load, deflection, and concrete strain of the mid-span section. The results demonstrate that a corrosion rate of just 8.31% has a considerable impact on the structural integrity of the beams, as evidenced by a pronounced reduction in flexural cracks and a tendency towards reduced reinforcement failure. Furthermore, the corrosive process has a detrimental effect on mid-span deflection, ductility, and ultimate flexural bearing capacity, which could have significant implications for bridge safety. This study provides valuable insights for the assessment of flexural performance and the development of appropriate maintenance strategies for corroded simply supported box girders in high-speed railways. Full article

Several prestressing reinforced structures have recently collapsed due to chloride-induced steel corrosion. This study investigates the effect of the corrosion of hot-dip galvanized conventional prestressing steel reinforcement under hydrogen evolution on bond strength in normal-strength concrete. The impact of hydrogen evolution on the porosity of cement paste at the interfacial transition zone (ITZ) is verified through image analysis. The whole surface of prestressing strands is hot-dip galvanized, and their corrosion behavior when embedded in the cement paste is investigated by measuring the time dependence of the open-circuit potential. Concerning the uniformity of the hot-dip galvanized coating and its composition, it is advisable to coat the individual wires of the prestressing reinforcement and subsequently form a strand. It is demonstrated that the corrosion of the coating under the evolution of hydrogen in the cement paste reduces the bond strength of hot-dip galvanized reinforcement in normal-strength concrete. Image analysis after 28 days of cement paste aging indicates insignificant filling of hydrogen-generated pores by zinc corrosion products. Applying an additional surface treatment (topcoat) stable in an alkaline environment is necessary to avoid corrosion of the coating under hydrogen evolution and limit the risk of bond strength reduction. Full article

This study builds a refined finite element (FE) model to research the flexural behavior of a reinforced beam with prestressed CFRP tendons. The precision of the FE model is validated through a comparison with the experimental outcomes. The numerical findings align well with the experimental outcomes, encompassing the failure mode, load-deflection curve, load-strain curves of concrete, steel reinforcements and CFRP tendons. The variances between predicted values and experimental results are within 10%. Leveraging the verified FE model, an extensive parametric study has been carried out to examine the effects of various parameters, including the CFRP tendon prestress, the CFRP tendon diameter, the deviator layout, the anchorage height and the prestressing strand prestress. Leveraging the findings from the parametric study, some refined design recommendations are proposed for practical reinforcement applications: Increasing the CFRP tendon prestress in practical reinforcement designs is recommended; CFRP tendons with larger diameters are recommended for use in practical reinforcement designs; Employing a linear CFRP tendon profile for reinforcement is not considered optimal in practical applications; The prestress loss in the prestressing strands of PC beams should be considered in practice. Full article

To optimally preserve and manage our civil structures, we need to have accurate information about their (1) geometry and dimensions, (2) boundary conditions, (3) material properties, and (4) structural conditions. The objective of this article is to show how imaging and image fusion using non-destructive testing (NDT) measurements can support structural engineers in performing accurate structural evaluations. The proposed methodology involves imaging using synthetic aperture focusing technique (SAFT)-based image reconstruction from ground penetrating radar (GPR) as well as ultrasonic echo array (UEA) measurements taken on multiple surfaces of a structural member. The created images can be combined using image fusion to produce a digital cross-section of the member. The feasibility of this approach is demonstrated using a case study of a prestressed concrete bridge that required a bridge load rating (BLR) but where no as-built plans were available. Imaging and image fusion enabled the creation of a detailed cross-section, allowing for confirmation of the number and location of prestressing strands and the location and size of internal voids. This information allowed the structural engineer of record (SER) to perform a traditional bridge load rating (BLR), ultimately avoiding load restrictions being imposed on the bridge. The proposed methodology not only provides useful information for structural evaluations, but also represents a basis upon which the digitalization of our infrastructure can be achieved. Full article

This paper proposed a novel demountable fabricated joint in frame, which is connected by the prestressed and mortise–tenon connection. The prefabricated components of the demountable structures are designed to be reused, and the joint presented in this paper will promote the sustainable application of prefabricated components in future. The damage process and damage pattern of the internal joints under the horizontal load were analyzed using the refined numerical analysis model based on ABAQUS 6.14. Parametric analyses were conducted simultaneously for five parameters: axial compression ratio, the area and effective initial stress of unbonded prestressed strands (UPSs), the local reinforcement ratio in the core zone of the demountable joint, and the friction coefficient between the interface of concrete. The results showed that the demountable joint exhibits excellent energy dissipation potential under horizontal loads, but the damage was concentrated in the core zone. The deformation of the joint mainly consisted of the self-deformation of the prefabricated components, including bending, bearing and shear, as well as the relative slip deformation between the prefabricated components. The axial compression ratio has a more significant effect on the hysteresis performance compared to the areas of the UPSs and the reinforcement ratio. The initial effective stress of the UPS and the friction coefficient have relatively minor influence on the hysteretic performance of the joint. Finally, this paper recommends the design parameter values (axial compression ratio should not exceed 0.4, area of unbonded prestressed reinforcement should be not lower than As_n=0.₀₂ and not higher than As_n=0.₁, the initial stress of the UPS takes the value of 0.75f_pu) and outlines optimization measures. Full article

This paper deals with the issue of the bond of concrete with the new artificial aggregate Certyd to prestressing steel strands. The solution of the problem is of great importance in the development of the use of lightweight aggregate concrete for prestressed concrete elements. Experimental research on the bond stress–slip relationship of concrete to 15.7 mm non-pretensioned steel strand was carried out. The results of bond stress–slip tests for various embedment lengths (40, 80, 120, 240, 330 and 460 mm) for test specimens made of the same lightweight aggregate concrete mixture, in which the transfer of prestressing force took place at different levels of concrete maturity (after 3, 7 and 28 days of concrete maturing), are presented. Based on the obtained results, an analytical model of the bond stress–slip relationship of lightweight aggregate Certyd concrete to 15.7 mm non-pretensioned steel strand was proposed. The tests presented demonstrated that the lightweight aggregate (Certyd) concrete is suitable for the production of pretensioned concrete elements. Full article

Structural damage in the steel bridge anchorage, if not diagnosed early, could pose a severe risk of structural collapse. Previous studies have mainly focused on diagnosing prestress loss as a specific type of damage. This study is among the first for the automated identification of multiple types of anchorage damage, including strand damage and bearing plate damage, using deep learning combined with the EMA (electromechanical admittance) technique. The proposed approach employs the 1D CNN (one-dimensional convolutional neural network) algorithm to autonomously learn optimal features from the raw EMA data without complex transformations. The proposed approach is validated using the raw EMA response of a steel bridge anchorage specimen, which contains substantial nonlinearities in damage characteristics. A K-fold cross-validation approach is used to secure a rigorous performance evaluation and generalization across different scenarios. The method demonstrates superior performance compared to established 1D CNN models in assessing multiple damage types in the anchorage specimen, offering a potential alternative paradigm for data-driven damage identification in steel bridge anchorages. Full article

This paper introduces a novel type of connection that integrates unbonded prestressed strands (UPS) and mortise-tenon in an assembly frame structure (UPS-MTF). First, the damage process and failure modes of the joints under reciprocating horizontal loads were systematically analyzed using refined numerical models. The recommended values of the design parameters of the joints were derived from the parametric analysis results. Refined numerical modeling results reveal the diagonal compression strut mechanism within the core region of the joint. The diagonal compression struts model assists in establishing the theoretical calculation formula for the skeleton curve of shear stress–strain in the core region. Second, a genetic algorithm (GA) parameter was identified for the restoring force model of the core region to determine the parameters of the hysteresis rules. Finally, a macro-simplified analytical model of the joint was created based on the restoring force model of the core region, and parameter analysis was conducted to verify the applicability of this macro-simplified analytical model. The research results prove that the damaged form of the joint proposed in this paper originates from the shear and relative slip damage between the components in the core region. The axial compression ratio significantly affects the hysteretic performance of the joints, and the upper and lower limit values were identified for the axial compression ratio of the joints. The area and initial effective stress of the UPS exert a minimal effect on the hysteretic performance of the joint. Based on the method proposed in this paper for determining the restoring force model in the core region of the joints, the hysteresis curves obtained from the macro-simplified analytical model closely match the refined numerical analysis model results. This correspondence verifies the applicability of the macro-simplified analytical model. Full article