Search Results (20)

To address the research gap in gas blast resistance of composite precast assembled utility tunnels, this study investigates structural damage evolution and the mechanisms influencing parameters through validated numerical simulations. A three-dimensional numerical model, incorporating the Karagozian & Case (K&C) concrete damage model and tie-break contact algorithm, was developed using LS-DYNA. The first validation against composite precast concrete slab explosion tests confirmed the model’s reliability, with displacement peak errors below 10%. The second validation focuses on the blast resistance test conducted on an underground utility tunnel, revealing an error margin of less than 10%. Results indicate that the utility tunnel exhibits a progressive failure mode of “joint cracking-interface damage-midspan cracking” under explosive loads, with stiffness degradation observed in joint regions at a loading pressure of 700 kPa. Increasing the normal strength of the interface to 5 MPa suppresses 90% of interface delamination, whereas completely neglecting interface strength results in a 9.0% increase in midspan displacement. Concrete strength shows minimal impact (<2.5%) on displacement under high loading conditions (≥0.9 MPa), and increasing the reinforcement ratio from 0.44% to 0.56% reduces displacement of the roof slab by 10.5%. These findings of address the research gap in the gas explosion response of composite precast assembled utility tunnels and could have significant implications for enhancing the disaster resistance of urban underground spaces. Full article

To study the fire resistance of castellated composite beams with semi-rigid restraints, temperature rise tests with constant loads were performed on two full-scale castellated composite beams with circular holes and semi-rigid restraints to compare the influence of whether stiffeners were set or not under semi-rigid restraints on the fire resistance of castellated composite beams. The results indicate that during the fire, the primary failure mode of castellated composite beams with semi-rigid restraints is the buckling failure of the web and lower flange in the negative moment zone at the beam end. Composite beams with stiffeners exhibited less buckling of the web and lower flange than those without stiffeners; for steel beams without stiffeners, the web and lower flange show overall lateral instability. Following the fire, the composite beams initially exhibit downward vertical deformation. After 5–10 min, when the web temperature is around 500 °C, it matures upward to the initial position. After 50 min, when the temperature of the web is around 800 °C, it starts to deform downward continuously. During the cooling stage, the end plates at the lower flange of the steel beam and the steel column show a separation phenomenon. By comparing the joint deformation and the mid-span displacement, the fire resistance performance of semi-rigid restrained castellated composite beams is better than that of hinged and rigid restraints. Numerical simulation analyses were carried out on the castellated composite beams. The simulation results showed a high degree of consistency with the test results, which effectively validated the accuracy and reliability of the proposed finite-element model. Full article

To ensure the connection performance of precast concrete square piles, a screw clamping and welding joint connection is applied to the solid square piles. By conducting full-scale bending performance tests on six solid square pile specimens with cross-sectional side lengths of 300, 450, and 600 mm, including pile bodies, screw clamping joints, screw clamping, and welding joints, the bending load-bearing capacity, deformation capacity, and failure characteristics of the screw clamping–welding joint connection are compared and studied. The results show that the bending failure mode of the pile body specimens is shear failure in the flexural shear section and concrete crushing in the compression zone of the pure bending section; the bending failure mode of the screw clamping joint specimens are the pull-out of steel bar heads at the joint end plate; the bending failure mode of the screw clamping and welding joint specimens are concrete crushing in the compression zone of the pure bending section, steel bar breakage in the tension zone of the flexural shear section, and pull-out of steel bar heads at the end plate. It is worth noting that no significant damage occurred at the joints. The cracks in the pure bending section of the bending specimens mainly develop vertically and are evenly distributed, while some cracks in the flexural shear section develop obliquely towards the loading point, with branching. Compared to the pile body specimens, the cracking moment of the joint specimens is up to 16% higher, the ultimate moment is within 15% lower, and the maximum mid-span deflection is within 25% lower, indicating that the provision of anchorage reinforcement can increase the stiffness and cracking moment of the specimens. Full article

Thousands of multi-span, simply supported beam bridges with short or medium spans have been built in China. They often suffer from problems of cracks in the link slabs over piers, and the deterioration and damage of deck expansion joints at abutments. To address these problems, one approach is to retrofit them by converting the simply supported box beams into continuous structures over the piers and jointless bridges over the abutments. This paper discusses the design methodology and details for retrofitting the Jinpu Bridge in Zhangzhou, Fujian, China, from a simply supported bridge into a semi-integral bridge, in which semi-fixed dowel joints are used to connect the superstructure and the substructure, including piers and abutments. Simultaneously, the finite element software is used to calculate the internal forces and displacements of the structure. The analysis reveals an 11.1% reduction in the maximum positive moment at the midspan of the main beam in the semi-integral bridge compared to the simply supported bridge. However, the shear forces at the interior pier increase by 6.4%. According to the response spectrum analysis, the maximum longitudinal displacement of the semi-integral bridge’s main beam is 11.6 mm, reduced by 80.1% compared to the simply supported bridge under a dead load and earthquake effects. The maximum bending moment and shear force on the pier of the semi-integral bridge are 984.7 kN·m and 312.6 kN, respectively, both below their ultimate bearing capacities. The maximum displacement at the top of the pier is 7.7 mm, which is below the allowable 52.4 mm displacement. The calculated results conform to the design requirements specified by the code. Full article

In recent years, prefabricated components have been widely used in the construction of substation superstructures, while cast-in-place foundations remain the primary method for substation foundations. This paper presents and evaluates a novel prefabricated foundation design aimed at enhancing construction efficiency and load-bearing performance. The foundation features a modular design, with each module weighing only half that of a cast-in-place foundation of the same size, significantly improving construction convenience and transportation efficiency. The load-bearing performance of the foundation was validated through static load tests and finite element modeling. The results indicate that the foundation demonstrates excellent ductility, with flexural failure as the primary mode, characterized by multiple cracks across the mid-span and complete yielding of longitudinal reinforcing steels. Further parametric analysis shows that increasing the plate thickness ratio (λ) improves the ultimate bearing capacity of the foundation significantly. Additionally, enlarging the cross-sectional size of the shear key or increasing the strength of the wet joint material enhances overall structural synergy, reduces local deformation, and improves load distribution efficiency. Overall, the sensitivity order of factors influencing the bearing capacity of the new prefabricated foundation is plate thickness ratio (λ) > wet joint strength > shear key cross-sectional size. Full article

Transfer learning techniques for structural health monitoring in bridge-type structures are investigated, focusing on model generalizability and domain adaptation challenges. Finite element models of bridge-type structures with varying geometry were simulated using the OpenSeesPy platform. Different levels of damage states were introduced at the midspans of these models, and Gaussian-based load time histories were applied at mid-span for dynamic time-history analysis to calculate acceleration data. Then, this acceleration time-history series was transformed into grayscale images, serving as inputs for a Convolutional Neural Network developed to detect and classify structural damage states. Initially, it was trained and tested on datasets derived from a Single-Source Domain structure, achieving perfect accuracy (1.0) in a ten-label multi-class classification task. However, this accuracy significantly decreased when the model was sequentially tested on structures with different geometry without retraining. To address this challenge, it is proposed that transfer learning be employed via feature extraction and joint training. The model showed a reduction in accuracy percentage when adapting from a Single-Source Domain to Multiple-Target Domains, revealing potential issues with non-homogeneous data distribution and catastrophic forgetting. Conversely, joint training, which involves training on all datasets except the specific Target Domain, generated a generalized network that effectively mitigated these issues and maintained high accuracy in predicting unseen class labels. This study highlights the integration of simulation data into the Deep Learning-based SHM framework, demonstrating that a generalized model created via Joint Learning utilizing FEM can potentially reduce the consequences of modeling errors and operational uncertainties unavoidable in real-world applications. Full article

An experiment was conducted on a prestressed concrete (PC) composite girder bridge with steel truss webs to investigate its flexural performance. The mechanical characteristics and failure modes of a PC composite girder bridge with steel truss webs was clarified. Finite element (FE) analysis was carried out, and the influence of the girder height-to-span ratio and eccentric loading effect on the flexural performance of a composite beam bridge with a steel truss web was discussed. The method for calculating the cracking bending moment, the bending moment at the rebar yield stage, and the ultimate bending moment of a PC composite girder with steel truss webs was proposed. Key findings include that, in both the elastic and cracking elastic stages, the strain of the bottom and top conforms to the plane-section assumption. Throughout the loading process, there was no occurrence of joint failure or local buckling failure in the steel truss webs; the composite girder ultimately fails due to excessive deformation, indicating that the overall mechanical performance of the composite beam is good. The deflection and stress in the mid-span section decrease with an increasing height-to-span ratio, and there are significant impacts of eccentric loading on deflection and stress. Compared with the results of the FE analysis and test, the calculation methods of the cracking moment, reinforcement yield moment, and ultimate moment of PC composite girders with steel truss webs presented in this paper have a high accuracy. Full article

This study investigates the structural performance of assembled rib-plate bridge abutments (ARBAs) with two different connection methods: bull leg bolt and flange connections. In addition, we explored the bending and shear performance of the connection parts and related areas to assess the damage characteristics and modes of these ARBAs. Utilizing model testing, a numerical analysis was conducted to define the force performance of the ARBA, with reference to a cast-in-place rib-plate abutment. The research results indicate that the bearing capacity and deformation capacity of the cap part of the assembled ribbed slab abutment model with cow leg connections are lower than those of the cast-in-place structure. When the structure fails, a 45° diagonal crack develops from the cross-section at the mid-span joint to the connection between the rib slab and the cap, until the concrete protective layer at the joint is crushed, exhibiting a shear failure mode. The bearing capacity of the assembly rib plate type abutment cap connected by the flange plate is basically the same as that of the cast-in-place structure, and the deformation capacity is weaker than that of the cast-in-place rib plate type abutment. The expansion of structural cracks is consistent with that of the rib plate type abutment connected by the cow leg. When the flange plate at the mid span is damaged, the contact surface between the flange plate and the concrete is pried off, resulting in the inability of the structure to continue bearing, exhibiting a shear failure mode. Through numerical simulation, taking the stress performance of the integral cast-in-place ribbed slab abutment as a reference, the assembled ribbed slab abutment connected by the flange plate is basically consistent with the integral cast-in-place ribbed slab abutment in terms of ultimate load, concrete damage, and steel reinforcement skeleton stress, and the connection device has not yet reached the yield state. The ultimate displacement is slightly weaker than that of the integral cast-in-place ribbed slab abutment. By comparison, it can be seen that the ultimate bearing capacity of the assembled ribbed slab abutment connected by the flange is basically the same as that of the cast-in-place ribbed slab abutment, and the stress performance can reach an “equivalent cast-in-place”, making it the preferred solution for the assembled abutment structure. The finite element parameter analysis of the flanged ARBA revealed that the thickness of the stiffening ribs, the number of bolts, and length of the flange plate anchoring steel plate were proportional to the ultimate load-bearing capacity of the prefabricated ARBA. In the case of no change in the structural damage mode, considering the economic benefits and load-bearing capacity of the structure, the following parameter combinations of the flanged ARBA are recommended: a thickness of 30 mm of the stiffening ribs, the number of bolts is 12, and a length of 50 cm of the length of flange plate anchoring steel plate. Full article

Beam–column connection zones are high regions of interest in reinforced concrete (RC) structures, which are expected to respond elastically to seismic loads. Using carbon fiber-reinforced polymers (CFRP) to improve these connections, performance is critical in retrofitting deficient RC frames because existing slabs may pose numerous limitations in the design and wrapping of CFRP sheets in joints. The main aim of this research is to develop a new design for flange-bonded CFRP retrofit of frames, including slabs, for the relocation of plastic hinges of the connection area toward the beam and to develop beam–column joint capacity and building stability in cases of subjection to dynamic loads. The performance of these proposed retrofittings was explored both experimentally and numerically. Two full-scale fabricated interior RC joints of a real moment-resisting frame with moderate ductility were subjected to monotonic loads before and after retrofitting, and the results were used to detail the numerical progress and verify of the beam–column connection. Moreover, a parametric study was conducted on CFRP sheets’ optimal thickness to examine its influence on plastic hinge relocation in the connection region. Results show that the retrofitting method can efficiently relocate the plastic hinge to the mid-span of the beam, which, in turn, leads to improved capacity and achievement of the RC frame and guarantees better structural safety a lower cost. Full article

The joint form plays a vital role in the rapid assembly of precast bridge decks for steel–concrete composite bridges. Existing research primarily focuses on studying the shear performance of joints through direct shear tests, which is insufficient to fully reflect the mechanical behavior of joints under the constraint of prefabricated bridge deck panels during actual vehicular traffic. Considering situations such as vehicle loads and external forces acting on precast bridge decks, this study investigates the shear performance of epoxy joints under constraint through an improved shear test. The influence of constraint force, shear key details and interface defects on the shear performance of epoxy joints is investigated. The results reveal that the shear test method employed in this study can realistically reflect the shear performance of epoxy joints in precast bridge decks. Both active and passive constrained epoxy joint specimens exhibited no interface cracks, and their failure modes were identified as shear failure between mid-span supports. Compared with passive constraint, the shear-bearing capacity of epoxy joint specimens under active constraint was increased by 86.1~130.6%. Among the epoxy joint specimens with depth–height ratios of 15/110, 25/110, 35/110 and 45/110, the joint with a depth of 35 mm demonstrated the highest shear strength. Furthermore, the shear performance of epoxy joints significantly deteriorated when the interface defects exceeded 30%, resulting in the failure mode transforming from shear failure to interface failure. Full article

To study the mechanical properties of steel–concrete joints during construction, the Mao Port Bridge in Shanghai is used as a case study. The mechanical properties of the bridge and the joint under the construction conditions were studied based on the site construction monitoring results, the finite element calculation of the entire bridge and the refined model of the joint. The results show that the finite element analysis of the bridge and the stress analysis of the joint during the construction phase agreed with the measured values, the end of block 0# of the main span remained in compression during construction and the compressive stresses varied in a zigzag pattern with the progress of construction. The lifting of the mid-span steel beam is a critical construction condition where the side spans of the girders are stretched upwards by 20.9 mm and the main spans are stretched downwards by 32.3 mm. When the steel beam was lifted, the joint was compressed as a whole. At the joint, the longitudinal stresses in the steel structure gradually decreased from the front bearing plate to the joint face, while the longitudinal stresses in the concrete structure gradually increased. Full article

A hybrid girder bridge adopts a steel segment at the mid-span of the main span of a continuous concrete girder bridge. The critical point of the hybrid solution is the transition zone, connecting the steel and concrete segments of the beam. Although many girder tests revealing the structural behavior of hybrid girders have been conducted by previous studies, few specimens took the full section of a steel–concrete joint due to the large size of prototype hybrid bridges. In this study, a static load test on a composite segment to bridge the joint between the concrete and steel parts of a hybrid bridge with full section was conducted. A finite element model replicating the tested specimen results was established through Abaqus, while parametric studies were also conducted. The test and numerical results revealed that the concrete filling in the composite solution prevented the steel flange from extensive buckling, which significantly improved the load-carrying capacity of the steel–concrete joint. Meanwhile, strengthening the interaction between the steel and concrete helps to prevent the interlayer slip and simultaneously contributes to a higher flexural stiffness. These results are an important basis for establishing a rational design scheme for the steel–concrete joint of hybrid girder bridges. Full article

The excessive deflection of large-span cantilever cast prestressed concrete (LCCPC) box girders has always been a complex problem to be solved in bridge engineering. To analyze the effect of shear deformation at segmental joints on the deflection of LCCPC box girders, comparison tests were carried out on three prestressed concrete (PC) I-girders with joints and a PC I-girder without joints, and a finite element simulation method of segmental joints was proposed based on the tests. Subsequently, finite element analysis was conducted on a test girder and the Assistant Shipping Channel Bridge of Humen Bridge (a PC continuous rigid frame bridge with a main span of 270 m) using this method. The experimental and theoretical analysis results showed that the effect of the shear deformation at joints compared to the deformation at midspan of the girder specimens was negligible. Deformation at midspan of the specimens would not significantly increase, even if shear rigidity at the joints was significantly reduced or there were more joints in the girder specimen. The effect of shear deformation at segmental joints on the deflection of LCCPC box girders was quite small and thus insignificant. Full article

Fire in a tunnel will deteriorate the mechanical properties of the tunnel. For fabricated tunnels formed by splicing prefabricated components through joints, under the high temperature of a fire, the rapid degradation of the bearing capacity of the joints can easily lead to tunnel damage. In this study, a new type of joint (bolt-pin joints (BPJ)) for prefabricated frame tunnels is proposed. To investigate the fire resistance of the new joint and the other three fabricated frame tunnel joints (including mortise joints (MJ), bolt-mortise joints (BMJ), and pin joints (PJ)), a three-dimensional solid model of four types of fabricated frame tunnel joints is established using the finite element calculation software ABAQUS. According to the standard European HC curve, the heat transfer characteristics of the joint model are analyzed, the temperature distribution law of the joint under fire is studied, and the flexural bearing performance and deformation characteristics of the joint before and after the fire are discussed, as well as the influence of the initial axial force on the flexural bearing capacity and the opening of the joint under fire. The analysis result shows that the vertical peak load of the BPJ is higher than that of the other three joints at room temperature. Under the combined action of the pin and bolts and the tongue groove, the vertical peak load of the joints can be effectively increased and the midspan vertical displacement can be reduced. The decrease degree of the vertical peak load of the MJ and BMJ under fire exposure is greater than that of the other two joints, and the opening of the BPJ is 19 mm, which is much smaller than that of the other three joints. When the initial axial force is increased, the openings of the four joints under fire exposure are reduced, the vertical peak loads of the PJ and BPJ are increased, and the vertical peak loads of the MJ and BMJ are not significantly increased. Overall, the BPJ demonstrates better fire resistance. Full article

Based on the paucity of studies on the analysis of the coupled vibration response of the train-track-overhead System, in this article, finite element software ABAQUS was integrated with multi-body dynamics software, Universal Mechanism (UM), to construct a joint simulation model of the train-track overhead system under a railway line, with the focus on the investigation of the influence of different track irregularity levels, speeds and damping coefficients on the coupled vibration response of the vehicle-track-overhead system. The findings demonstrate that the response of the train body is sensitive to track irregularity, which primarily impacts the safety index of train operation. The results also suggest that the level of track irregularity should be rigorously regulated above AAR5 during construction. The train-track-overhead system functions well and satisfies the overhead system’s design requirements when the train travels through the reinforced line at a speed of no more than 60 km/h. When the train speed is 100 km/h, the vertical acceleration exceeds the limit for the “I” overhead system. There is a possibility of excessive lateral acceleration of the train body and excessive lateral force of the wheel and rail when the train speed is greater than 60 km/h, which endangers the safety of the driver. While it has little effect on the mid-span and vertical displacements, the damping factor of the bridge has a substantial impact on the vertical acceleration and mid-span acceleration of the vertical and horizontal beams. The study’s findings provide useful guidance. Full article