International Journal of Civil Engineering最新文献

Abstract

This work introduces a theoretical framework for determining the active non-limit earth pressure of cohesive soil on a base-rotating rigid wall. The framework incorporates the nonlinear Mohr–Coulomb failure criterion, the Duncan–Chang hyperbolic stress–strain relationship, the log-spiral potential failure surface in retained soil, and a horizontal slice method for the earth pressure evaluation. The proposed method allows quantitative determination of displacement-dependent earth pressure and its distribution along the wall back. Practical wall movement in the at-rest state is considered, and the tension crack depth near the soil surface is calculated based on the soil tensile strength cut-off. Analysis results highlight the nonlinear variation of the mobilized soil shear strength vertically, influenced by the nonlinear Mohr–Coulomb failure criterion. As the wall rotation increases, the earth pressure follows a convex parabolic distribution with a tension failure zone near the soil surface and no pressure at the wall base. The resultant of the earth pressure reduces and its application point descends while the tension crack depth expands, though always remaining less than the Rankine’s earth pressure. A practical example shows that the at-rest earth pressure can be up to 1.3 times greater than the active earth pressure, with the resultant application point approximately 5% higher. Parameter study exhibits that the active non-limit earth pressure correlates nonlinearly with the soil ultimate tensile stress and nonlinear coefficient, particularly as wall movement increases. Active non-limit earth pressures vary within 86% across different soil cohesions, and up to 50% under varying ultimate tensile stresses and nonlinear coefficients. Overturning safety factors of the wall in the active non-limit state differ significantly from those in the at-rest state, especially under varying soil cohesions.

Based on the existing research results on prefabricated shear wall vertical bolt connections, the force performance of horizontal bolt joints composed of multiple bolt connections were further examined in this paper. Through the quasistatic load test of two horizontal bolt joint specimens, the hysteresis curve, backbone curve, and stiffness degradation curve of the wall were obtained. The test results show that the specimens’ load-bearing capacity can reach 240–280 kN, with a maximum displacement between 40 and 70 mm, indicating that the force performance and deformation ability of the horizontal joint are good at this size. The overall shape of the hysteretic curve of the specimens is similar to an arch, with a certain pinch effect, and the hysteretic loop is relatively full, indicating good energy dissipation ability. The failure of the specimens reveals that a single bolt connection exists under shear, compression and tension conditions. The force state of the bolt connections in the horizontal joints was divided into four situations: shear state, axial compression state, small eccentric compression state and large eccentric compression state. For each situation, a calculation formula for bolt connections in horizontal joints was proposed and the average relative error is 4.72%, providing a reference for the force calculation of this type of joint.

Coupling beams are used in double-column high-pier bridges to improve the integrity of the two piers. The stiffness of coupling beams has a significant effect on the seismic performance of double-column piers. The seismic behavior of a double-column pier with triple-coupled beams was investigated by cyclic loading test. The failure mode and cyclic response, as well as the shear deformation of a double-column bridge pier, were analyzed to investigate its seismic behavior. The test results, especially after a drift ratio of 1/83, indicated the presence of non-uniform damage characteristics between the coupling beams. Finite element models were developed and parametric analysis was carried out after validation. The focus was on the effects of the variable stiffness of the coupling beam along its height. By analyzing the bearing capacity, ductility, and damage of the double-column piers, the upper flexible and lower rigid coupling beam is a more reasonable arrangement principle. The research results can provide a reference for the innovation design ideas of similar bridge piers.

Abstract

The mechanical properties of connection joints and the fire protection design of steel structures are crucial for ensuring structural safety. The utilization of fire-resistant steel in steel structure joints represents a novel approach to enhance fire resistance. In this study, a test on two welded–bolted hybrid connection joints between fire-resistant steel columns and beams was conducted considering both ambient and elevated temperatures. Through an analysis of the failure modes, load–vertical displacement curves, moment–rotation curves, and load–strain curves of the joints, key parameters such as the ultimate bearing capacity, ductility, and deformation capacity were determined. The test results showed that the ultimate bearing capacity of specimen Joint-2-ET at an elevated temperature is 81.14% that of specimen Joint-1-AT at an ambient temperature. While the temperature increases during fire had little effect on the initial stiffness of the joint, it significantly reduced the rotation capacity and ductility of the joint. A finite element model of the joints was developed using ABAQUS software, and its accuracy was validated by comparing the results with the experimental findings. Additionally, a parametric analysis was conducted to explore the effects of temperature and heating region on the mechanical performance of these welded–bolted hybrid connection joints. The outcomes of this research provide valuable insights for engineering applications involving welded–bolted hybrid connection joints between fire-resistant steel columns and beams.

This study presents an experimental study on cold-formed steel (CFS) composite beams with profiled steel sheeting. Four full-scale composite beam specimens comprising cold-formed double-lipped channel sections, profiled steel sheeting, concrete slabs, and bolted shear connectors were examined. The results show that profiled steel sheeting behaves like tensile reinforcement beside the concrete slab. Of particular interests were thickness and height of CFS beams. The results showed that for higher steel thickness, the failure mode was concrete crushing before CFS beam reached its yielding point. Besides, no failure occurred in the shear connections. By increasing the thickness of CFS from 1.25 to 2 mm, the ultimate loading capacity of composite beams increased almost 45%. This was due to the presence of the profiled steel sheeting and the strong connectors, which prevented sudden slip between the CFS beam and the concrete slab. A comparison between code-calculated and experimentally evaluated degree of shear connection shows that the results are so close. Furthermore, a 3D finite element model was established, and the numerical models were verified against experimental results and the behavior of structures were accurately simulated.

In this study, we propose baffle-type rectangular pipe jacking in the context of the world’s first shallow large-section rectangular pipe-jacking project under a high-speed railway line, with the aim of improving the utilization of underground urban space. We introduce the relevant method of construction as well as safety control technology for ongoing construction in the proximity of pipe jacking in a complex geological and structural environment, and propose techniques of optimization for the continued application of baffle-type rectangular pipe jacking in similar projects. The results showed the following: (1) the maximum value of the surface settlement as the pipe-jacking machine passed through it was 160 mm. But the maximum uplift, maximum settlement, and maximum relative settlement of the D-shape temporary beams were 6.31, −5.78, and 6.71 mm. (2) The theoretical mechanics-based calculations was used to derive the minimum safe distance required to form a stable microarch effect between the roofs of the pipes, and the recommended distance in the project considered in this study was 24 cm. (3) The results of assessments based on multiple measures showed that the proposed pipe-jacking method led to the successful completion of crossing work for high-speed rails that were in use. This means that it is feasible to use rectangular pipe jacking to pass through an operating high-speed rail in composite strata at a shallow depth. We also provide suggestions for applications of the retractable baffle-type rectangular pipe jacking in the future.

An optimization problem is formulated in this study to optimize the total investment in education, apprenticeship, and financial incentive to address the skilled labor shortages in the construction industry. Three separate mathematical models, namely linear programming (LP) models, fuzzy mathematical models, and structural equation models are compared for their accuracy, robustness, and ease of application in solving the optimization problem. LP models are found to be the best fit for solving the optimization problem. Relevant data on construction budget and investment preferences in education, apprenticeship, and financial incentive are obtained through a survey questionnaire from construction firms engaged in commercial and residential construction. The survey response suggests that more apprentices lean toward electrical and plumbing over carpentry due to the higher pay scale in both trade fields, thus reducing the skilled labor shortage in both areas when compared to carpentry. The optimization results indicate that apprenticeship and financial incentives play a significant role in reducing short-term labor shortages. Education, on the other hand, plays a significant role in reducing the labor shortage in the long run. A sensitivity analysis shows different optimal investments for the optimal allocation of labor shortages to be overcome by investments in education, apprenticeship, and financial incentives. A more robust analysis using additional data can be performed in future works to further investigate the relative effectiveness of investments in education, apprenticeship, and financial incentives in reducing skilled labor shortage.

No recent research was found regarding mix design for coating mortars. Those that exist (older ones) have limitations in use or specific materials. They are defined for the use of a certain equipment or specific condition and cannot be applied in other regions. An appropriate mix project needs to have a process that al-lows to obtain adequate proportions of the materials taking into account the different materials and conditions at the application site. Therefore, the aim of this paper is to propose an experimental mix design method for mixed mortars to be used in wall cladding and to study two types of most common aggregates (natural or crushing) through properties from the application sites and material characteristics. The experimental program of this study consisted in characterizing the materials and conducting necessary tests to evaluate the mix design method and how the characteristics of the aggregates influence the mixing design process, as well as the mechanical properties (flexural, compressive strength and pull off strength) and durability indicators (elasticity modulus, water absorption and porosity). We verified that the characteristics of the aggregates interfere with the properties of these composites and that the proposed method was able to capture this and define adequate proportions of the materials according to the exposure conditions. The method generated more economical (less cement consumption) and more sustainable mixed coating mor-tars (reduction of cement and lime in the mixtures, especially with artificial aggregate) without compromising the limiting properties Pull Off (0.390 MPa) and Flexural Strength (2.396 MPa). We conclude that the mix design method allows to optimize the characteristics of the mixed mortars depending on the type/characteristics of the aggregate and the conditions of the application environment.

To study the impact of blasting construction of double-layer superimposed primary support arch cover method, relying on the station construction project of Dalian Metro Line 5, the disturbance of blasting on high-rise buildings, surrounding strata, adjacent pilot tunnels and the arch structure is analyzed based on numerical simulation and field monitoring results. At the same time, research is carried out on the blasting excavation footage of pilot tunnels. The results show that there will be a certain “elevation amplification effect” (EAE) on high-rise buildings during the blasting construction using the method. The peak particle velocity (PPV) of adjacent tunnels decreases gradually with the increase of the distance from the explosion centers. For the adjacent pilot tunnel, the main influence area is within the range of − 5 to 5 m from the pilot tunnel face. For adjacent buildings, the main influence stage is within the range of − 2 to 2 m from the pilot tunnel face. Blasting operations significantly intensify the plastic yield of surrounding rocks around the station. Blasting excavation footage can be used as the optimization parameter in the construction process, and the blasting excavation footage of pilot tunnel 4 can be adjusted from 1.0 to 1.5 m. The formation of the arch structure composed of double-layer superimposed primary support and secondary lining effectively reduces the impact of rock blasting on the whole station and high-rise buildings.

The uniaxial compression tests are conducted on single-fissured sandstone with different angles, and the effect of fissure angle (β) on mechanical properties, acoustic emission (AE) features, crack propagation characteristics, and failure mode of sandstone are studied with the AE monitoring and photographic system. The research results reveal that as the β increases, the uniaxial compressive strength (UCS) exhibits an asymmetric inverted “U” shape and the minimum is only 33.14 MPa when β = 30°, while the elastic modulus increases monotonously from 8.98 to 15.14 GPa. During the loading process, the AE parameters demonstrate obvious stage characteristics, while tension cracks dominate and the shear cracks significantly increase. As β increases, the AE activity gradually shifts to the post-peak destruction stage, and the effect of shear crack on the final failure mode of the specimens becomes more significant. The stress–strain relationship, AE features, and real-time photographic system are sufficient to comprehensively depict the crack evolution process in each stage, and there is a good correlation between each parameter. Increase in β makes the crack initiation stress and its ratio to UCS increase, from 68.74% to 79.92%, which makes it more difficult for crack initiation, and the secondary crack propagation gradually transforms from tension to shear. The macroscopic failure mode of fissured sandstone gradually changes from tension failure to mixed tension–shear failure and finally to shear failure, the angle between the propagation direction of initial cracks and fissure gradually decreases, and the surface spalling zone becomes more obvious.