Search Results (102)

The composite primary structures of railway vehicles endure not only mechanical loads including tension, compression, bending, and torsion, but also external impacts, such as by the crushed stone in ballast. In the present study, the low-velocity impact response of preloaded hybrid composite laminates with different thicknesses is examined using a finite element method based on a progressive damage model. The hybrid plate consists of carbon fiber-reinforced unidirectional and woven prepregs. The progressive damage model, based on the 3D Hashin model, is validated by experiments on hybrid laminate, and further compared with the post-impact appearance obtained from CT scans. Preloading, considered to be tensile, compressive, or shear, corresponds to different positions in a bending beam with flanges and a web. Finally, the effects of impact energy, preloading, thickness, and impact angle on the dynamic response are analyzed, with an emphasis on new results and failure mechanism analysis comparing the influence of preloads under a given impact energy and different thicknesses. Full article

Multi-cavity double steel plate–concrete composite structures are composed of two layers of steel plates, accompanied by steel flanges, diaphragms, and a core of concrete. Thanks to their exceptional mechanical attributes, these structures have gained widespread adoption in the field of wind power engineering. The outer steel plates exert a notable confinement on the concrete filling. Nonetheless, there remains a lack of a constitutive model specifically tailored for concrete under confinement within the field of multi-cavity double steel plate–concrete composite structures. To bridge this gap, our research endeavor involved the creation of approximately 2000 shell–solid finite element models, leading to the derivation of a constitutive model for compressed confined concrete within such structures through regression analysis. Initially, theoretical evaluations were conducted to pinpoint the structural parameters potentially influencing confinement behavior. Thereafter, Abaqus shell–solid finite element models were formulated, and their accuracy was corroborated through experimental validations. By systematically adjusting parameters in batch modelling, regression analysis was conducted. Consequently, a constitutive model tailored for uniaxial compression of concrete in multi-cavity double steel plate–concrete composite structures (MDSCCS) was formulated. According to the results, the strength of confined concrete in MDSCCS can be enhanced by up to 23% under typical configurations, as observed in the benchmark model MDSCCS-1. The proposed regression-based confinement model demonstrates a prediction error of less than 15% in 97.8% of the 1342 finite element models that successfully converged in batch simulations. Full article

The finite-element model was developed using ABAQUS to investigate the hysteretic properties of space joints. This study examined the effects of axial compression ratio, T-plate stiffness, column wall thickness, and bolt-preload on the joint’s hysteretic behavior. The model was verified by comparing the failure modes, hysteresis curves, and skeleton curves of the specimens with the test results of the relevant literature, ensuring the reliability of the research. The results reveal three primary failure modes: beam flange buckling, T-plate buckling, and column-wall buckling; increasing the thickness of the T-plate web or column wall significantly enhances joint stiffness and mitigates brittle failure. Specifically, the stiffness of T-plate 1 has a substantial impact on joint performance, and it is recommended that its web thickness be no less than 18 mm. In contrast, variations in the thickness of T-plate 2 have negligible effects on seismic performance. Increasing the column wall thickness improves the bearing capacity and stiffness of the joint, with a recommended minimum thickness of 12 mm, which should not be less than the flange thickness of the steel beam. While an increase in the axial compression ratio reduces the bearing capacity and stiffness, it enhances the energy dissipation capacity and ductility of the joint. Notably, variations in bolt-preload were found to have minimal influence on joint performance. These findings provide valuable insights for optimizing the design of unilateral bolted joints in steel structures to improve seismic resilience. Full article

The dynamic behavior of three-layer composite beams, consisting of concrete slabs and steel beams, is influenced by the structural configuration of each layer as well as the shear connectors. The interlayer shear stiffness in three-layer composite beams governs their global dynamic behavior, while interlayer slippage-induced localized vibration effects represent a key limiting factor in practical applications. Based on the dynamic test results of steel–concrete double-layer composite beams, the feasibility of a finite element solid model for composite beams, which accounts for interlayer shear connectors and beam body characteristics, has been validated. Utilizing identical modeling parameters, an analytical model for the inherent vibration characteristics of three-layer steel–concrete composite beams has been developed. This study encompasses two types of composite beams: concrete–steel–concrete (CSC) and concrete–concrete–steel (CCS). Numerical simulations and theoretical analysis systematically investigated the effects of interface shear connector arrangements and structural geometric parameters on dynamic performance. Research indicates that the natural frequency of steel–concrete three-layer composite beams exhibits a distinct two-stage increasing trend with the enhancement in interlayer shear stiffness. For CSC-type simply supported composite beams, the fundamental vertical vibration frequency increases by 37.82% when achieving full shear connection at both interfaces compared to the unconnected state, while two-equal-span continuous beams show a 38.06% improvement. However, significant differences remain between the fully shear-connected state and theoretical rigid-bonding condition, with frequency discrepancies of 24.69% for simply supported beams and 24.07% for continuous beams. Notably, CCS-type simply supported beams display a 12.07% frequency increase with full concrete-to-concrete connection, exceeding even the theoretical rigid-bonding frequency value. Longitudinal connector arrangement non-uniformity significantly impacts dynamic characteristics, while the transverse arrangement has minimal influence. Among structural parameters, steel flange plate thickness has the most significant effect, followed by concrete slab width and thickness, with steel web thickness having the least impact. Based on the observation that the first-order vertical vibration frequency of three-layer composite beams exhibits a two-stage decreasing trend with an increase in the span-to-depth ratio, it is recommended that the span-to-depth ratio of three-layer steel–concrete composite beams should not be less than 10. Full article

This study investigates a novel steel grid shear wall (SGSW) structure with lightweight and discrete lateral-resistance members, focusing on its structural behavior in lateral resistance. By comparing the characteristics of the thin steel plate shear wall, the mechanism of the steel grid components in both the tension zone and compression zone was briefly described. The formulas of lateral-resistant capacity and initial stiffness of the SGSW were derived through the static equilibrium method. Then, the influence laws of the span–height ratio, steel member spacing and section size of the steel members on the lateral-resistant performance of the SGSW were determined through a parametric analysis. In addition, the accuracy of the calculation formula was validated. The results showed that the strains of the steel grid components in different positions were all the same when the bending stiffnesses of the edge members were significantly large. The lateral-resistance capacity of the SGSW increased with the span-to-height ratio, while it decreased as the spacing between the steel components increased. Compared with the effects of web height, web thickness and flange width, increasing the flange thickness exhibited the best effects on improving the lateral capacity. As the flange thickness increased from 7 mm to 13 mm, the lateral-resistant capacity showed an improvement of 35.45%. Additionally, the formula derived in this study demonstrated high accuracy and reliability, with the error not exceeding 8% between the formula calculation and the simulation results. 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

In view of the fact that the specification does not specify the calculation model for the temperature gradient of the concrete box-shaped arch rib without wing plates, and there is also a lack of relevant research on the temperature model of this type of arch rib, this paper carries out research on the impact of sunshine temperature on a section of concrete box arch rib without a flange plate based on the 355 m Shuiluohe Bridge. Firstly, a temperature experiment of the arch rib without flange plates was conducted. According to the experimental data, the temperature distribution and changing rules of the arch rib cross-section were analyzed. Then, according to the measured temperature data, a calculation mode of the vertical temperature gradient of the arch rib was proposed and compared with the specification. Finally, in view of the most disadvantageous phases of the arch rib in the construction process, the influence of different gradient modes on the structural mechanical behavior was analyzed by means of a simulation model. The results show that along the span from the springing to L/2, the maximal temperatures of the top plate, web plate and bottom plate gradually increase. The temperature gradient of the box’s top plate is the largest, that of the web plate is the second largest, and that of the bottom plate is the smallest. The vertical temperature difference of the key section of the arch rib gradually increases from the springing to L/2, and the maximal temperature difference of the section at L/2 is 16.3 °C, which is 4.2 °C higher than that of the springing section. The vertical temperature gradient proposed in this paper is a four-fold nonlinear model. Compared with the temperature gradient distribution range specified in the specification, the vertical temperature gradient in this article has a wider distribution range in the cross-section height, and the temperature varies more quickly along the cross-section height. The temperature gradient model proposed has more adverse effects on the mechanical behavior of the structure. The temperature gradient model proposed in this paper not only fills the gap in the specification but also provides suggestions for the design and construction of bridges. Meanwhile, the temperature distribution model of this type of arch rib also lays a theoretical foundation for the further development of corresponding thermal insulation materials for concrete surfaces or new concrete materials. Full article

This study investigates the bending performance of web-embedded double inverted T-shaped steel–concrete composite beams (WDTSCBs) through experimental testing and finite element analysis (FEA). A novel composite beam structure was developed, where double inverted T-shaped steel beams are interconnected by slotted web plates and embedded in concrete flanges, aiming to enhance load-bearing capacity and ductility. Four WDTSCB specimens, utilizing C40 concrete and Q345qB steel, were tested under static loading to analyze failure modes, load-deflection behavior, and crack development. The experimental results were validated by FEA in ABAQUS, achieving an error margin of less than 5%. The findings indicate that WDTSCBs exhibit superior flexural performance compared to traditional composite beams, with higher bending resistance and reduced steel consumption. These results provide valuable insights into the design and optimization of steel–concrete composite structures, promoting their application in civil engineering. Full article

A precast concrete segmental box-girder bridge (PCSBGB) is one of the most popular styles of Accelerated Bridge Construction (ABC). To address some common challenges (low durability, poor integrity, and construction inconvenience) in PCSBGBs, this paper proposes a precast ultra-high-performance concrete (UHPC) segmental box-girder bridge (PUSBGB). In comparison to conventional PCSBGBs that use three-dimensional prestress, the PUSBGB adopts only one-dimensional (longitudinal) prestress. In addition, the thickness of the bottom/top plate and web of the UHPC box-girder are relatively thin, and as a result, the self-weight is significantly reduced. Considering the fact that the thickness of box-girder is thinner than the NC structure, the shear lag effect and risk of girder cracking may correspondingly increase when a PUSBGB is adopted in a long-span bridge. Thus, it is of essential necessity to explore the flexural behavior of a PUSBGB. In this work, a specimen with a scale (1:4) associated with a field bridge (a 102 m long simply supported PUSBGB with externally unbonded tendons) is fabricated and experimentally investigated. The mechanical behaviors of the PUSBGB are discussed, including the failure mode, the crack distribution pattern, the longitudinal strain of the UHPC plate, and the variation of tendon strain. It is found that in the elastic stage, the top slab of the UHPC box girder exhibits a significant shear lag effect, and this phenomenon is even more obvious after cracking. With the development of the cracks, the effective flange width is decreased (with a minimum value of 0.76), and the second-order effect is kept the same before the dominant crack appears (the reduction factor is around 0.95). Moreover, four existing code equations, e.g., ACI 440, ACI 318, ASSHTO, BS 8100, used to predict the stress in the externally unbonded tendons are examined. Furthermore, a finite element analysis (FEA) of the field bridge is conducted, and the theoretical calculation demonstrates that the flexural resistances of the proposed PUSBGB can comply with the design requirements of Chinese code under the ultimate limit states (ULSs). Full article

In order to solve the problems of high production cost and complex control of the inverted arch of an unsupported prestressed concrete composite slab, a flange truss high-ductility concrete composite slab floor is proposed to change the structure and pouring material to meet the requirements of no support during construction. The crack distribution and bending performance of the flange truss high-ductile concrete composite slab floor (CRHDCS) under different structures are clarified through the test and numerical analysis of four different rib plate structure floors. According to the analysis results, the calculation formulas of the cracking moment and short-term stiffness before cracking are modified, and the equivalent short-term stiffness formula of a single web member of the “V” truss to this kind of bottom plate is established. The results show that, unlike the short-term stiffness-change law of typical concrete composite slabs after cracking, the short-term stiffness of the designed bottom plate in this paper includes a short-term increase stage. The numerical simulation results are the same as the experimental ones; the maximum error is 10%. The maximum errors between the modified cracking moment and the short-term stiffness calculation formula are 6% and 8%, respectively. The influence rates of removing flange plate, truss-inverted binding, and adding rib plate on the cracking bending moment of foundation structure are −81.5%, 11.0%, and 22.2% respectively, and the influence rates on short-term stiffness are −87.6%, −1.5%, and 37.5% respectively. Full article

Adjacent existing box girder bridges should be spliced in the long-span bridge expansion project. A type of integral splicing composite structure for connecting the adjacent flange plates is designed herein. The mechanical characteristic of the integral splicing composite structure is tested using a local full-scale model, and a refined simulation model is also proposed for the optimization of the integral splicing composite structure. The loop bar in the joint connection segment and the application of Ultra-High-Performance Concrete (UHPC) material can guarantee the effective connection between the existing flange plate and the splicing structure. The embedded angled bar can delay the interface debonding failure and interface slip. The UHPC composite segment below the flange plate (segment CF) can bend together with the existing flange plate. In this study, an innovative integral splicing composite structure for a long-span bridge extension project is proposed and verified using both a local full-scale model test and finite element simulation. The adaptation of UHPC material and loop bar joint connection form can meet the cracking loading requirements of the splicing box girder structure. By proposing a refined simulation model and comparing the calculation result with the test result, it is found that the flexural performance of the integral splicing composite structure depends on the size of the composite segment below the flange plate (segment CF). Increasing the width of segment CF is beneficial to delay the interface debonding failure, and increasing its thickness can effectively delay the cracking load of the flange plate. Finally, the scheme of segment CF with one side width of 200 cm and a minimum thickness of 15 cm can improve the flexural resistance of the spliced structure and avoid the shear effect caused by the lane layout scheme and the location of the segment CF end. Through the research in this paper, the reasonable splicing form of a long-span old bridge is innovated and verified, which can be used as a reference for other long-span bridge splicing projects. Full article

This study investigates the mechanical behavior of cover-plate reinforced connections in steel frames with I-section columns and middle- or wide-flange H-beams, addressing gaps in current design standards. Finite element analyses validated by experimental data were employed to explore the effects of cover-plate geometry—shape, length, and thickness—on seismic performance. Results demonstrate that cover plates improve load-bearing capacity and ductility by relocating plastic hinges outward from joint regions. Specifically, cover-plate connections increased ductility by 25%, yield moment by 15%, and initial rotational stiffness by 7% compared to non-reinforced connections. The shape of the top cover plate had minimal impact on mechanical behavior. The cover-plate length and thickness significantly influenced seismic ductility and load-bearing capacity. The cover-plate thickness should be at least 0.3 times the beam flange thickness (not less than 6 mm) while ensuring the combined thickness of the cover plate and beam flange does not exceed the column flange thickness. These recommendations address the conservatism of existing standards, balancing material efficiency and seismic performance. Optimal cover-plate lengths of 0.7 to 0.9 times the beam depth were also identified. These findings provide practical guidelines for designing resilient steel frame connections in seismic regions. Full article

In view of the application status and technical challenges of steel–wood composite joints in architecture, this paper proposes an innovative connection technology to solve issues such as susceptibility to pry-out at beam–column joints and low load-bearing capacity and to provide various reinforcement methods in order to meet the different structural requirements and economic benefits. By designing and manufacturing four groups of beam–column joint specimens with different reinforcement methods, including no reinforcement, structural adhesive and angle steel reinforcement, 4 mm thick steel sleeve reinforcement, and 6 mm thick steel sleeve reinforcement, monotonic loading tests and finite element simulations were carried out, respectively. This research found that unreinforced specimens and structural adhesive angle steel-reinforced joints exhibited obvious mortise and tenon compression deformation and, moreover, tenon pulling phenomena at load values of approximately 2 kN and 2.6 kN, respectively. However, the joint reinforced by a steel sleeve showed a significant improvement in the tenon pulling phenomenon and demonstrated excellent initial stiffness characteristics. The failure mode of the steel sleeve-reinforced joints is primarily characterized by the propagation of cracks at the edges of the steel plate and the tearing of the wood, but the overall structure remains intact. The initial rotational stiffness of the joints reinforced with angle steel and self-tapping screws, the joints reinforced with 4 mm thick steel sleeves, and the joints reinforced with 6 mm thick steel sleeves are 3.96, 6.99, and 13.62 times that of the pure wooden joints, while the ultimate bending moments are 1.97, 7.11, and 7.39 times, respectively. Using finite element software to simulate four groups of joints to observe their stress changes, the areas with high stress in the joints without sleeve reinforcement are mainly located at the upper and lower ends of the tenon, where the compressive stress at the upper edge of the tenon and the tensile stress at the lower flange are both distributed along the grain direction of the beam. The stress on the column sleeve of the joints reinforced with steel sleeves and bolts is relatively low, while the areas with high strain in the beam sleeve are mainly concentrated on the side with the welded stiffeners and its surroundings; the strain around the bolt holes is also quite noticeable. Full article

The failure mode of thin-walled C-channel beams typically manifests as premature local buckling of the compression flange, leading to insufficient utilization of material strength in both the flange and the web. To address this issue, this study adopts the approach of increasing the number of bends to reinforce the flange and adding V-shaped stiffeners in the middle of the web to reduce the width-to-thickness ratio of the plate elements, thereby delaying local buckling and allowing for greater plastic deformation. However, the challenge lies in the irregular cross-sectional shape and complex buckling patterns. Therefore, this paper aims to explore a suitable cross-sectional form to expand the application of stainless steel members. Subsequently, three-point bending tests were conducted on the optimally designed stainless C-channel beam with folded flanges and mid-web stiffeners. The finite element simulation results were compared and analyzed with the experimental results to validate the model’s effectiveness. After verifying the correctness of the finite element model, this study conducted numerical parameterization research to investigate the effects of the shear span ratio, complex edge stiffeners, web height–thickness ratio, and V-shaped stiffener size on the shear performance of stainless steel folded flange C-beams. The results show that changing the shear span ratio has a significant impact on the shear capacity and vertical deflection deformation of components; increasing the web height–thickness ratio can enhance the shear capacity of the component; elevating the V-shaped stiffener size can slightly improve the shear capacity of components; and for the stainless steel C-shaped beam with folded flanges and intermediate stiffening webs, adding edge stiffeners cannot remarkably promote the shear capacity of the component. Full article

When traditional joint structures are used to widen multi-span continuous concrete box girder bridges, excessive lateral deformation often occurs at the girder ends, typically leading to the squeezing and cracking of seismic blocks by the girder webs. To address these technical challenges, this paper investigates a new type of slide-rail lateral joint structure that can create a longitudinal sliding effect between two bridge decks of the old and new bridge box girders, thereby effectively reducing the lateral deformation at the girder ends. First, this paper employs the finite element method to conduct a numerical analysis of a real-world bridge widening project, exploring the working mechanism and application feasibility of this novel connection method. The results show that, in the case study, if the traditional joint method is used, the lateral displacement at the girder ends can reach up to 40 mm after three years of widening. However, when the slide-rail joint structure is employed, the lateral displacement at the girder ends is limited to no more than 6 mm. This demonstrates that the new joint method can indeed effectively address the issue of excessive lateral deformation at the ends of the widened structure. Second, given that the slide-rail lateral joint structure is a relatively precise engineering structure, this paper examines the lateral load transfer mechanism under loads such as wheel loads and foundation settlement differences. It discusses the load-bearing characteristics of various components, including square steel pipes, lateral connection rebars, concrete flange plates, and embedded rebars. Finally, through a parameter sensitivity analysis, it is found that the torsional stiffness of the square steel pipes is a critical parameter for ensuring the load-bearing capacity of the structure. Therefore, it is recommended to set the wall thickness of the square steel pipes to 5 mm. Based on these research findings, this paper theoretically demonstrates that the new slide-rail lateral joint structure can effectively solve the technical challenges encountered during the lateral joint widening of multi-span long-span concrete continuous box girder bridges, providing a new solution for this field. Full article