KSCE Journal of Civil Engineering最新文献

The conventional reinforced concrete beam exhibits limitations in terms of bearing capacity, intricate construction procedures, and substantial labor requirements. In response to these challenges, a novel approach featuring an Angle Steel Skeleton (ASS) for concrete reinforcement has been proposed. In this study, four concrete beam specimens along with two beam-column joint specimens were meticulously prepared for static loading tests and low-cycle loading tests. The bending performance of the innovative structure, Angle Steel Skeleton-Reinforced Concrete Beam (ASSB), was comprehensively analyzed through static loading testing. Furthermore, formulations were developed to calculate the stiffness and bearing capacity of ASSB. Employing the finite element method, an examination was conducted to elucidate the influence of factors such as shear span ratio, concrete strength, and angle steel strength on the bearing capacity of concrete beams. Building upon the aforementioned investigations, the seismic performance and mechanical response of Angle Steel Skeleton-Concrete Beam-Column Joints (ASSJ) was investigated through low-cycle loading tests. An in-depth analysis was conducted to establish the correlation between the axial compression ratio and steel skeleton stress. Results from the research indicate that the adoption of ASS in lieu of steel cages results in a substantial enhancement in the ultimate bearing capacity of concrete beams, ranging from 29% to 36.6%. Additionally, there is a twofold increase in energy dissipation capacity, accompanied by a 14% increase in ductility. Notably, ASSJ specimens exhibit superior seismic performance, particularly in low-intensity seismic zones.

Mat foundations have been widely used as foundations of mobile offshore platforms such as jack-up rigs and installation platforms. Throughout the service period, the mat bears coupled multi-dimensional loads transferred from the superstructure and directly from the environment. Evaluating the bearing capacity of the mat is the premise of offshore platform design. However, there are few studies on the bearing capacity of commonly used irregularly shaped mats under multi-dimensional load conditions. Looking at two types of A-shaped mats on cohesive soil, uniaxial bearing capacities are calculated using the finite element method (FEM) in this study. The centrifuge test was performed to verify the FEM results. Effects of the length-to-width aspect ratio of the foundation on bearing capacities are discussed. The V-H, V-M, and V-H-M failure envelopes of mats with unlimited and zero tension interfaces are obtained. Studies have shown that the uniaxial bearing capacities change monotonously with aspect ratio increases, and that the bearing capacity of a rectangular A-shaped mat is higher than that of a trapezoidal A-shaped mat. The V-H-M envelope with unlimited tension interface condition is ellipsoid-shaped, while that with zero tension interface is scallop-shaped. With the capacity expressions established in the paper, it is possible to quickly check the bearing state of the mat under a given V-H-M load condition, and then assess the safety of the engineering operation.

In order to explore the dynamic response and damage state of the steel square tubular structural component under blast-loading, A few experiments of near-field explosions are conducted respectively on five steel square tubes, Among them, two are hollow, one is wrapped with glass fiber-reinforced plastic (GFRP) on the front surface, and others are the one being infilled with C30 and the other with C70 concrete. It can be concluded from the analysis on the deformation and strain of the tubes that, at the same explosive mass, when the standoff distance of the steel square tube is lengthened from 48.5 mm to 68.5 mm, the maximal depth of deformation on the front surface is lessened by 37.5%, deflection by 42.1% and residual strain by 66.7%. As wrapped with GFRP, the maximal deformation is reduced by 17.0%, deflection by 30.8% and the residual strain is decreased by 69.5% respectively, the approach by wrapped with GFRP on the tube can improve the performance of blast resistance. While being infilled with concrete, the deformation of the tube is greatly reduced. Moreover, the deformation is decreased with the increment of the compressive strength of the concrete. Specifically, when the components are infilled with C30 and C70 respectively, the residual strains are decreased by 91.3% and 69.1% respectively.

The mechanical properties of shallow expansive soil are crucial to expansive soil engineering. However, few effective test methods have been available to measure the in-situ mechanical properties of shallow expansive soil. This paper attempts to test the effects of water content and fissures on the mechanical properties of shallow expansive soil under a natural state by in-situ CBR and resilience modulus tests. The evolution characteristics of shrinkage fissures in expansive soil were recorded and observed. The fissure connectivity coefficient is used to express the degree of fissure development and the integrity of soil structure. The CBR strength and resilience modulus of expansive soil increase first and then decrease with the decrease of water content and the increase of fissure development degree, and reach the peak near the optimal water content. It is effective to use the inverse hyperbolic sine function to fit the relationship between soil mechanical parameters, water content, and fissure connectivity coefficient. When the water content is higher, the influence of water content on soil mechanical properties is great. When the water content is lower, fissures are more developed, and the influence of fissures on soil mechanical properties is dominant.

This study addresses the critical role of shaft friction of pile in the interaction with expansive soil under varying moisture content. A simplified estimation method is proposed, capturing the non-linear correlation between the interface relative displacement between the soil and pile and unit skin friction and during water infiltration. The approach integrates soil-pile displacement, interface shear strength parameters, and soil matric suction fluctuations. Tests on Nanyang expansive soil include a laboratory model with water infiltration, constant volume swelling, direct shear for interface shear strength, and a filter paper method for SWCC determination. Initial water content of 21% shows an increases swelling pressure more than 24% and 27%. Increasing soil water content reduces soil matric suction. Due to lower soil matric suction, cohesion, friction, and soil interface shear strength decreased. After the passage of the infiltration duration (specifically, 200 hours), ground heave peaks at 10.7 mm, potentially affecting pile axial forces. As matric suction diminishes, the pile’s shaft friction reduces, transferring more weight to the pile base, leading to settlements. Experimental data validate the proposed shaft friction estimation method. The approach aligns with previous studies and laboratory models, providing a comprehensive understanding of soil-pile interaction in changing moisture conditions.

The influence of water content and dip angle conditions on the pre peak energy accumulation characteristics of coal rock assemblages and their mechanism of action are crucial for studying the stability of high dip angle coal seams. The results indicate that water content changes the peak strength turning point. The accumulated energy before the peak gradually decreases from 0° to 60° and increases at 60° to 90°. As the inclination angle of the interface increases, the pre peak energy accumulation decreases. As the water content increases, the proportion of coal components gradually increases, while the proportion of rock components gradually decreases, and the energy accumulated before the peak of coal components is greater than that of rock components. The energy reduction rate gradually increases from 0° to 60° and decreases from 60° to 90°. When the inclination angle of the interface is 0° ∼ 30°, 30° ∼ 60°, and 90°, the main mechanism affecting its stability is the combined effect of water weakening, water weakening, and interface slip, as well as the uneven deformation of the coal rock interface.

To investigate the degradation mechanism of the performance of CFRP-concrete bonded interface under fatigue loading, double shear tests with the adhesive layer thickness and stress level as the variables were conducted. The results indicate that under fatigue loading, varying thicknesses of the interface adhesive layer result in different interface failure modes. The strain variations of the CFRP fabric in static and fatigue tests exhibited similar trends, with an increase in bonding thickness leading to higher ultimate load or fatigue cycles. With an increase in the thickness of the adhesive layer, the initial stiffness of the interface decreases, leading to improved deformation performance of the interface. During the second stage of damage development, a thicker adhesive layer led to slower interface damage progression. Under fatigue loading, when the specimen is in the stable crack propagation stage at the interface, a decrease in the load level and an increase in the thickness of the adhesive layer lead to a reduction in the rate of crack propagation. The proposed crack propagation rate model effectively predicted the interface crack propagation process and fatigue life. Finally, the damage and failure process of the interface under fatigue loading was simulated using Fe-safe software, and predictions for its fatigue life were made.

To reveal the impact of erosion environment and age on the strength and deterioration of solidified soil exposed to salty soil, two types of solidified soil, soda residue-ground granulated blast furnace slag-carbide slag solidified soil (S20G10) and cement solidified soil (C10), were eroded by salty soil prepared with kaolin mixed with Na₂SO₄, MgSO₄ or seawater. The unconfined compressive strength tests, X-ray diffraction and scanning electron microscopy analysis were conducted. The results showed that 1% MgSO₄ erosion resulted in the most significant reduction in strength. After 28 days of erosion, the strength was approximately 66% to 68% of the standard curing sample. The strength initially increased and then decreased with the erosion age. Numerous needle-like ettringite or thamuasite were generated in the samples, which led to a loose microstructure and decrease in strength. Sample S20G10 showed stronger erosion resistance than sample C10. The bearing capacity of solidified soil exposed to MgSO₄ erosion exhibited an initial increase followed by a decrease with erosion age. When considering erosion deterioration for 50 years, it was necessary to increase the pile diameter by 1.1 to 1.7 times if the bearing capacity of the mixing pile was equal to the allowable bearing capacity.

Riverbank erosion is a significant and distinct problem in the floodplains of alluvial rivers in North East India. The Barak River has experienced an alarming increase in bank erosion rate over the last few decades, resulting in embankment breaches and biodiversity loss, but there is a dearth of field studies to evaluate riverbank fluvial erosion. This study aims to assess the river bank erosion and Vulnerability Assessment of the Barak River in India using an in-situ submerged Jet Erosion Test (JET). The riverbank erosion was estimated for a span of the riverbank on one side of the stream using the excess shear stress equation and impinging jet theory. Data was collected using a JET along the riverbank to determine the erodibility parameter of the bank soil. The results show that the spatial variation in erosion parameters of river banks varies significantly, which is dependent on the specific location. Annual bank erosion was computed using measured erodibility parameters and stage record data, which shows the bank erosion of the Barak River will occur in many places, particularly at the critical area. The measured bank erosion was compared with the observed satellite imagery map for the 2000–2020. This study shows that JET results should be used with caution; further, the findings can be helpful in planning river training and management strategies for vulnerable areas and may serve as a model for similar alluvial river studies.

The seismic response of structures is pivotal in ensuring their safety and resilience against earthquakes. While traditional methods rely on elastic response spectrum to predict seismic behavior, accurately estimating the elastic-plastic response, particularly in structures equipped with intricate dissipative devices, remains challenging. This paper explores a novel self-centering variable friction energy dissipation brace (SCVFB) system that addresses this challenge. Through finite element analysis, the elastic-plastic displacement response spectrum and the strength discount factor spectrum are obtained. By subjecting a five-story frame with SCVFBs to seismic testing through elastic-plastic time-history analyses, a comparison of the results with those predicted by spectral methods is conducted. Remarkably, the results from both approaches are closely aligned, confirming that the seismic response of structures equipped with SCVFBs, as evaluated via spectral methods, offers valuable insights for structural design.