Abstract:In practical application, arranging stiffeners on a section is a common method used to enhance the stability of structural members. This study focuses on investigating the effects of cold-formed stiffeners on the mechanical properties of high-strength steel tubular columns and evaluating the cost effectiveness of these stiffened columns. An axial compression analysis model for cold-formed stiffened steel tubular columns was established by using finite element ABAQUS software. The study explored the optimal stiffening configuration by investigating the influence of stiffening shape, the number of stiffeners, stiffening spacing and stiffening size on the mechanical performance of Q355 steel pipe columns. Furthermore, the reduction in steel consumption for high-strength Q690 cold-formed stiffened steel pipe columns was analyzed when their ultimate bearing capacity was equivalent to that of ordinary Q355 steel pipe columns. The results show that the addition of cold-formed stiffeners significantly improves the axial compression bearing capacity of steel pipe columns. Interestingly, the improvement in bearing capacity remains consistent even as the number of stiffeners increases. Notably, using a single semicircular arc stiffener yields favorable results in enhancing member bearing capacity. The spacing between cold-formed stiffeners has minimal effects on the overall stability of the members. It is recommended that the radius of the stiffener arc twice the thickness of plate. When achieving equal bearing capacity, the steel consumption for cold-formed stiffened Q690 steel pipe column is about 35% lower than that of Q355 steel pipe columns.

Abstract:The steel pipe piles in the deep-water trestle are flexible yet highly sensitive to faults. Currently, there lacks a simplified calculation method that comprehensively account for the pile’s deflection at the top, with considering the combined effects of geometric initial defects, construction loads, and water flow load. This deficiency makes it challenging to address the non-linear behavior of steel pipe piles in deep water, thus posing safety risks. To address this issue, the water flow load was simplified to an inverted triangle distribution load, and elastic stable equilibrium differential equations for the steel pipe pile, both below and above the water surface, were respectively adopted to derive a theoretical calculation formula for pile deflection with considering geometric nonlinearity. Building upon this foundation, steel pipe piles of varying lengths were selected as the research object to explore the influence of geometric initial defects and nonlinearity on pile deflection. Through theoretical deviation, the theoretical formula was further simplified for derivation, making it more practical for engineering applications. The analysis results show that with considering geometric nonlinearity, the simplified model yields significantly different load flow calculations compared with models that neglect geometric nonlinearity. This is more in line with the flexible structure’s response to water loads. Consequently, our study provides valuable support and practical technology for managing water load impacts and lateral control of steel pipe piles in steel trestle structures during their operational life.

Abstract:To investigate the shear behavior of a new curved girder with a rectangular grouted tubular flange and corrugated web (CG-RGTF-CW), four reduced-scale specimens, including one straight girder and three curved girders, were designed and fabricated for shear bearing capacity tests. Through these tests, data on buckling modes, ultimate loads, load-strain curves and load-displacement curves of all specimens were obtained. The test results show that the corrugated webs of both the curved girder with small curvature and the straight girder exhibited similar failure modes. Interestingly, the density of the corrugated web influenced the buckling mode of the curved girder. To further investigate the shear behavior of these new girders, a finite element (FE) model was constructed. The reliability of the FE model was verified using experimental results. Using the presented FE model, the effects of several parameters on shear behavior were examined. These parameters included corrugated web thickness, girder curvature, folded sub-plate width, corrugation angle, depth of inclined fold and web constraints. The results show that girder curvature has minimal effect on the shear buckling performance of the corrugated web, while the web height-to-thickness ratio has remarkable influence on the buckling modes of the corrugated web and the shear bearing capacity of the new girder. Additionally, the rectangular grouted tubular flange exhibited robust web restraint capabilities, contributing to shared shear force absorption with the web.

Abstract:To study the impact of different restraint methods and the connection structure between concrete piers and caps on the seismic performance and various indicators of bridge pier specimens, three experimental setups were designed: one featuring a prefabricated square steel tube confined concrete pier (SYP-GT4 specimen), another with a square steel tube confined integral cast-in-place concrete pier (SYZ specimen), and a third with a square section integral cast-in-place concrete pier (SFZ specimen). The pseudo-static test was carried out on the pier caps using displacement loading method, and the failure processes and modes of the specimen were closely observed. Various characteristics, including failure modes, load-displacement hysteretic curves, load-displacement skeleton curves, ductility, energy dissipation and other relevant parameters of the piers were analyzed. The results show that all three concrete pier specimens exhibited similar failure modes, characterized by integral failure due to compression and bending. Notably, SYZ specimens outperformed SFZ specimens with a 46.5% increase in horizontal peak load, superior hysteretic energy dissipation capacity, and better ductility, indicating that integral bridge piers constrained by square steel tube demonstrate superior seismic performance compared to cast-in-place concrete piers. Furthermore, when comparing SYP-GT4 specimens to SYZ specimens, they exhibited a similar horizontal peak load value, a 24.1% increase in displacement ductility coefficient, minimal residual displacement, and enhanced deformation recovery capabilities. The hysteresis curve showed a fuller spindle shape without obvious pinching. The connection structure has little effect on the degradation of strength and stiffness, and their seismic performance is similar.

Abstract:To address the pressing demands of industrialized construction and to broaden the application of two prominent structural systems, namely, the steel frame-steel plate wall structure and the steel frame structure with concrete-filled steel tube columns, in high-intensity regions, a high-intensity area affordable housing construction project was taken as a prototype. This involved seismic design based on frequent earthquake response spectra and supplemented by elastic dynamic time history analysis. At the same time, a comparative analysis of the elastic-plastic seismic performance of these two structural systems under rare earthquake scenarios was conducted. The results show that the steel frame-steel plate wall structure system exhibits a bending-type lateral deformation pattern, with plastic hinges predominantly forming at the beam and column ends near the steel plates during earthquakes. Conversely, the steel frame structure with concrete-filled steel tube columns displays a shear-type lateral deformation pattern, with plastic hinges primarily forming at the beam ends on intermediate floors. Furthermore, both structural systems meet the prescribed seismic design requirements, rendering them suitable for application in high-rise civil buildings within high-intensity areas.

Abstract:Due to assembly technology requirements and the introduction of connection seams, the numerical simulation and analysis of prefabricated concrete structures face new challenges. The trade-off between computational efficiency and simulation accuracy becomes increasingly apparent. Based on the general finite element software ABAQUS, in this study a multi-scale modelling approach is used to simulate and analyse the seismic performance of monolithic precast concrete frame structures. Firstly, the correctness of the interface connection method for multi-scale units is validated using experimental data from monolithic precast concrete beam and column substructure. Then, static pushover analysis and dynamic elastic-plastic time-history analysis are performed on the multi-scale model featuring a monolithic precast concrete frame structure. Subsequently, the seismic response and damage of this model are compared with those of a cast-in-place concrete frame structure. The results show that multi-scale modeling effectively improves calculation accuracy and reduces calculation costs. It aptly replicates the failure characteristics of monolithic precast concrete frame structure and overall seismic performance. Compared with the cast-in-place structure, the monolithic precast frame structure exhibits lower lateral stiffness and superior ductility under unidirectional static forces. When subjected to a rare 7-degree earthquake, their seismic performance remains comparable, with a modest 3.8% increase in maximum top-floor displacement. Furthermore, this study underscores the applicability of the multi-scale modelling method in the analysis of prefabricated concrete structures.

Abstract:Through the analysis of various beam-column connected joints,this study reveals that the new connection method, featuring a lower bolted-through diaphragm and an upper welded external plate, enhances the catenary mechanism and improves the resistance to continuous collapse. The analysis employs ABAQUS software to conduct a comprehensive examination of failure modes, load-displacement curves, and resistance mechanisms under varying span-to-height ratios, span ratios and locally weakened sections of this joint. This study introduces a novel joint design aimed at enhancing collapse behavior and establishing a foundation for the design of structures with improved resistance to continuous collapse.

Abstract:In the field of fabricated structures, ensuring the connection reliability between precast frame beams and columns is of paramount importance and represents a current research focus. This paper introduces a prefabricated frame joint centered around a core area consisting of a precast concrete-filled steel tube. The precast concrete beam connects with the steel component via the core area, and cast-in-place steel fiber self-compacting concrete is employed at the beam end to establish the connection between the precast concrete beam and the precast core area. To assess feasibility, a new type of frame joint is designed and compared with a conventional cast-in-place frame joint. Hysteretic behavior of the joint is examined, and differences in ductility, strength, stiffness degradation, energy dissipation capacity, and moment-curvature of plastic hinge region between the two types of joints are analyzed and compared. The results show that both specimens exhibited a plastic hinge failure mode, but the new joint’s steel components, steel tubes, and column reinforcement remained unyielded. Furthermore, the new joints demonstrated slightly superior ductility, energy dissipation capacity, and bearing capacity when compared to the cast-in-place joint. This suggests that the assembled joint can at least meet the requirements of the cast-in-place joint.

Abstract:Semi-rigid joints have a significant influence on the internal forces and deformations of transmission towers. However, in traditional transmission tower structure optimization, semi-rigid joints are often oversimplified as hinge joints. To accurately evaluate the true response of transmission towers and rationally optimize their structures, this study focuses on transmission towers with semi-rigid connections. A finite element model for such towers is established using spring elements to simulate the moment-rotation relationship of semi-rigid joints. Furthermore, an optimization mathematical model and design scheme for transmission towers with semi-rigid connection are proposed, resulting in the development of a discrete optimization method for these structures. The optimization results show that the proposed method effectively reduces the consumption of steel in transmission towers while satisfying structural stress and deformation constraints, leading to cost savings and favorable economic benefits in engineering projects.

Abstract:To study the creep characteristics of interbedded rock mass when considering the effect of time-dependent deformation. This paper proposes a non-constant viscoelastic plastic five-element model considering stress and strain thresholds. The model can simultaneously describe the instantaneous elastic strain, viscoelastic creep, linear viscoplastic creep and nonlinear viscoplastic creep (accelerated creep) of the rock, and derives its creep equation under the three-dimensional stress state. Based on the ABAQUS finite element software, the development of the UMAT subroutine was completed, and the applicability of the model was verified by comparing the indoor creep test of the rock with the numerical simulation results of the model. The results show that the results of the creep test are consistent with the results of the numerical calculations. The non-constant viscoelastic-plastic novelty model can not only accurately describe the decelerated creep and steady-state creep processes, but also can better describe the accelerated creep process of rocks. This verifies the applicability and effectiveness of the model.

Abstract:This paper proposes a moment-rotation tri-linear backbone curve model for reinforced concrete (RC) shear walls. Equations for predicting key points on the backbone curve are provided. The calculated sectional effective stiffness and ultimate drift ratio are compared with experimental results from 105 RC shear walls. The Modified Ibarra-Medina-Krawinkler (ModIMK) material in OpenSees software that considers the strength and stiffness degradation is used to define the hysteresis rules. Numerical simulation and analysis of low-cycle reciprocating tests on reinforced concrete shear walls are carried out, and the simulation results closely align with the test results. When compared to a model that considers the bending-shear coupling effect (SFI), our hysteretic model effectively predicts the response of the frame shear wall during earthquake events. Furthermore, dynamic incremental analysis (IDA) shows that our model can accurately predict the collapse behavior of shear walls during earthquakes, with inter-layer drift ratios during collapse being smaller than those in the fiber mode.