Compression Shear Tests Research Articles

Mechanical properties of steel fiber reinforced recycled concrete under compression-shear stress state

The continuous urbanization of construction has led to an increasing demand for concrete, resulting in large-scale gravel and river sand mining, which seriously affect the sustainable development of the environment. The waste concrete produced by the demolition of old buildings is processed into recycled aggregate to replace natural aggregate, and then the preparation of recycled concrete can effectively alleviate this problem. This paper investigates the mechanical properties of steel fiber reinforced recycled concrete (SFRRAC) under compression shear conditions, a compression shear test with 99 cubic specimens was designed, with the variation parameters being recycled aggregate concrete replacement rate, compressive stress, and steel fiber content. The failure mode of SFRRAC under compression-shear stress was observed, and the shear force-displacement curve was calculated. Furthermore, a thorough examination was performed to assess the mechanical characteristics of SFRRAC specimens under compression-shear stress. The findings of this study suggest that as the compressive stress increases, the failure characteristics of the specimens shift from exhibiting brittle failure to displaying ductile failure. The shear strength is most sensitive to the change in compressive stress. When the compressive stress reaches 6 MPa, the shear strength can reach 3.41 times that of the direct shear specimen. The shear strength of SFRRAC specimens is composed of the bond strength of concrete, shear expansion strength, and friction shear strength. The incorporation of steel fibers can modify the distribution of shear strength among the individual components. The adverse effect of the recycled aggregate replacement rate on the toughness index of the specimen is mainly concentrated after the peak point. Nevertheless, an elevation in compressive stress and the inclusion of steel fibers can counterbalance this detrimental influence. The shear strength calculation formula of SFRRAC in shear state is put forward, which has a reference value. This study provides an experimental reference and a theoretical basis for further examination of SFRRAC.

On asymmetric failure in additively manufactured continuous carbon fiber reinforced composites

Due to a filament-by-filament and layer-by-layer structure produced by an additive manufacturing (or namely 3D printing) technique, mechanical properties of 3D printed materials diverge considerably from those of carbon fiber reinforced polymer (CFRP) composites made by traditional processes. This study aims to experimentally characterize their mechanical properties through the off-axis tensile, compressive and V-notch shear tests. Advanced imaging techniques, such as digital image correlation (DIC), scanning electron microscopy (SEM) and computed tomography (CT), are used to investigate anisotropic nature of materials and failure mechanisms of the 3D printed CFRP composites. The applicability of conventional failure criteria to the 3D printed CFRP composites, including Tsai-Wu, Tsai-Hill, Hoffman, Maximum Stress, Hashin, Puck and LaRC05, is assessed systematically. The experimental results divulge that the filament-by-filament and layer-by-layer features intrinsic to 3D printed CFRP composites lead to an uneven yet organized distribution of voids. This characteristic contributes on the development of claw mark strain patterns, parallel track inter-fiber failure patterns, and distinct compression failure modes such as delamination and interlayer crack under loading perpendicular to the fiber direction. The voids in the 3D printed CFRP materials are partially responsible for the significant asymmetry when off-axis angle increases. Notably, the conventional failure criteria exhibit limited capability for predicting the off-axis tensile strength accurately. This phenomenon can be attributed to the redistribution of inherent fiber waviness as the fiber encounters tensile loads. Based on the experimental results, the inter-fiber failure as per the LaRC05 is modified to obtain an enhanced failure criterion for predicting the off-axis tensile strength. This study is expected to provide fundamental understanding of structural characteristics and mechanical properties for 3D printed CFRP composites.

Fracture behaviors of sustainable recycled aggregate concrete under compression-shear loading: Laboratory test, numerical simulation, and environmental safety analysis

A series of compression-shear tests were carried out to investigate the shear failure of sustainable recycled aggregate concrete, and shear failure surfaces were scanned by a 3D laser scanner. The effect of recycled coarse aggregate (RCA) replacement rates and normal stresses on the shear strength, failure mode, and fracture morphology were analyzed. Meanwhile, discrete element method was used to study shear behaviors at a mesoscale. Finally, the carbon emission was calculated to evaluate the effect of RCA on the environment. The result shows that the shear strength, cohesion c, and internal friction angle φ all decrease as the RCA replacement rate increases. The shear damage of RAC can be aggravated by increasing the RCA replacement rate. Fractal dimension and joint roughness coefficient of shear failure surface tend to increase with increasing RCA replacement rate and normal stress. In addition, more microcracks can be found in coarse aggregate with the increase in RCA replacement rate, and the increasing normal stress can cause more microcracks. Given the nonlinear development of stress-displacement, a modified nonlinear constitutive model is proposed. Finally, the total carbon emissions of recycled aggregate concrete are calculated considering production, transportation, and construction, the carbon emission of 100% sustainable recycled aggregate concrete is 10.2% less than that of 100% natural aggregate concrete.

Comparison of perlite and pumice effects on the geotechnical properties of saline silty soil

ABSTRACT This research mainly sought to evaluate the sediments of the Urmia lake bed to prevent their erosion and the possibility of improving the problematic saline fine soils in the region by the geo-polymerisation process. For this purpose, perlite and pumice materials, with pozzolanic properties and weight percentages of 3, 5, and 7, were separately mixed with soil, along with the calcium hydroxide (Ca(OH)2) solution as a catalyst with 2%, 5%, and 7%. Then, the samples were cured for one day. Uniaxial compressive strength (UCS), direct shear, and consolidation tests were performed to assess the geotechnical properties of improved soil compaction. The results revealed that, compared to pumice, perlite could improve the behavioural properties of the studied soil. The inclusion of perlite and pumice, along with calcium hydroxide, increased the flexibility of the stabilised soil, as indicated by the brittleness index. Similarly, combining 3% perlite with 2% Ca(OH)2 could increase UCS at failure by 3.27 times. In addition, the mixture of 5% perlite with 7% Ca(OH)2 could enhance the shear strength by 3.3 times. Finally, combining 3% perlite with 5% calcium hydroxide reduced the swelling of the improved soil by 82%, and the consolidation settlement was decreased by 64% on average.

Static and dynamic strength properties of highly structured clay-rich diatomite in Shengzhou, China

Diatomite is a widespread geological substance found in coastal and lake areas worldwide. Although diatomites are increasingly used in geotechnical engineering construction, a significant knowledge gap exists regarding their mechanical responses to static and dynamic loadings, particularly in high-speed railway projects. This study investigates the static and dynamic behaviors of diatomites through extensive experiments, considering both natural and remolded states. It focuses on representative diatomite specimens obtained from the Shengzhou region in China, an area intersected by the Hang-Shao-Tai high-speed railway. The results of uniaxial compression and undrained triaxial shear tests show that the structural degradation of diatomite significantly impacts its stress-strain responses, failure patterns, and mechanical parameters under static and dynamic loading conditions. The structural effects of natural diatomite tend to degrade as the confining pressure level increases, resulting in corresponding changes in its mechanical parameters. Undrained triaxial shear tests conducted on natural diatomite reveal that the inclinations of the shear band closely correspond to those predicted by the Mohr-Coulomb solution. Additionally, we present a modified hyperbolic-type model to evaluate the damping ratio of diatomites. Furthermore, a power-law model based on Hardin's formula was used to predict the maximum shear modulus of diatomites under varying stress levels and void ratios. Microstructural and chemical analyses were conducted using scanning electron microscopy and X-ray diffraction to gain insights into the observed structural effects at the microscale.

Investigation on mechanical behaviors and energy characteristics of deep-buried marble in a hydraulic tunnel in Southwest China

Shear behavior of rock is of great significance to the stability of deep-buried rock in transportation geotechnical engineering. A series of direct shear tests are carried out on deep-buried marble with different size and shape to focused on the mechanical properties and size shape effects of deeply buried marble, which have been less studied previously. The results show that the size and shape of the specimen have a relatively small impact on the trend of shear stress-shear displacement curve. The failure morphology at the front and rear surfaces shows a significant normal stress effect. Some properties of specimens with different sizes and shapes increase with increasing normal stress, but the dilation angle generally decreases with the increasing normal stress. With the increase of the shear plane size of intact specimen, the cohesion decreases gradually while the internal friction angle increases steadily. The difference value in peak strain between axial compression and direct shear tests is relatively small while it is huge for the peak compression and peak shear strength. The results in this study are beneficial for further understanding the shear mechanics, energy evolution process and size effects of deep-buried rock in transportation geotechnical engineering.

Wavelet technique and FEA for modal identification in damaged URM shear walls

In existing masonry buildings, the structural capacity with respect to horizontal actions is due to the in-plane response of shear walls, usually evaluated in terms of effective stiffness and drift capacity. The objective of this work is to provide first results to the damage sensitivity in diagonal cracking of URM shear walls and a study methodology based on vibration tests to assess the structural health of existing masonry buildings. The state of pre-existing discontinuities caused by previous damage events or material degradation may play a role in the in-plane response of shear walls. For this, an experimental campaign was carried out on three typologies of UnReinforced Masonry (URM) walls, simulating different damage situations, subjected to Shear-Compression (SC) and vibration tests in order to correlate the structural behaviour with changes in modal parameters. From the vibrational response acquired during the SC test, the modal parameters related to the pre-damage and post-damage condition were identified using the Continuous Wavelet Transform identification technique. The experimental results are then used to implement a Finite Element Model (FEM) with a 2D homogenization approach to simulate the behaviour of URM walls. A parametric study through FEM analysis is carried out in order to investigate the change in modal parameters for different damage configurations and for triggering strut mechanisms.

Estimating the macro strength of rock based on the determined mechanical properties of grains and grain-to-grain interfaces

Obtaining complete rock cores is exceptionally challenging in certain extreme environments, such as deep earth and deep space; consequently, it is difficult to obtain the macro strengths of rock, which are the key indexes for engineering design, via standard rock mechanical tests. This research indicates that by determining and leveraging the mechanical properties of grains and grain-to-grain interfaces, the rock macro strength can be effectively estimated. Nanoindentation tests were first conducted to determine the elastic modulus of the mineral grains and their interfaces. Subsequently, symmetrical and anti-symmetrical four-point bending tests were executed to establish the statistical law governing interfacial tensile and shear fracture toughnesses. Furthermore, by employing the Dugdale–Barenblatt model and considering the oblique angular distribution of interfacial cracks, the corresponding tensile strength, shear strength, and friction parameter were derived. These meso‑mechanical parameters were then inputted into the 3D Finite-Discrete Element Method to estimate rock macro strength. And the numerical results were then compared with the results of standard uniaxial compression, direct tension, Brazilian splitting, and direct shear tests. The consistency observed between the predictions and experimental results attests to the validity of the proposed method.

Uncovering Failure and Cracking Behaviors of Double-Flawed Sandstone Under Compressive-Shear Loading Using Digital Image Correlation (DIC) Technique

The coalescence of flaws provides valuable insights into the failure behaviors of rock masses, which is a critical issue in rock engineering. In this study, a series of compressive-shear tests were conducted on sandstone specimens containing double flaws. The failure and cracking behaviors of specimens with different geometric configurations under various loading conditions were analyzed using the digital image correlation (DIC) technique. The strain and displacement fields effectively demonstrate crack propagation and coalescence, accompanied by the axial load–displacement curve. The results revealed the effect of eccentric and overlapping distance of double flaws on the compressive-shear bearing capacity. The relative displacement method (RDM) was applied to analyze the crack characteristics in this study. Based on the relative displacement behaviors of the cracks, five typical types of crack modes were identified, including tensile mode, shear mode, mixed-I mode, mixed-II mode, and mixed-III mode. Both wing cracks initiated from flaw outer tips and anti-wing cracks generated from flaw inner tips were classified as a tensile mode or mode-I, dominated by normal relative displacement. In contrast, the secondary cracks were categorized as either shear mode or mode-III, which are dominated by tangential relative displacement. The geometry configurations of flaws affected both the coalescent mode and cracking path, which in turn influenced the failure mode of specimens. This study identified and summarized eight types of coalescent modes between double flaws. The findings presented in this paper contribute to a better understanding of the failure behavior of rock masses containing flaws subjected to compressive-shear loads.

Deformation and Strength of Unsaturated Loess—Hydraulic Coupling Effects under Loads

The volumetric change in unsaturated loess during loading causes serious damage to the foundation and structure, accompanied by changes in hydraulic conditions. Therefore, quantifying the change in the load effect of loess under hydraulic coupling is of great significance for revealing the mechanism of hydraulic interaction. This study conducts isotropic compression and undrained shear tests on unsaturated compacted loess, simultaneously introducing the strength parameter η to enhance the Glasgow coupled model (GCM). The objective is to elucidate the hydraulic and mechanical coupling mechanism, where saturation increases under mechanical effects lead to strength degradation. The results show that saturation increases under mechanical effects improve the compressibility of the sample, and saturation has a direct impact on the stress–strain relationship. The increase in water content and confining pressure increases the trend of the critical state stress ratio M decreasing, and the strain softening trend increases. The compression of volume during shear tests increases the saturation, changes the hydraulic characteristics of loess, and affects the deformation and strength of loess. The modified GCM improves the applicability and prediction accuracy of unsaturated loess under the same initial state. The research results are of great significance for revealing the hydraulic and mechanical behavior of loess.

Experimental Study of the Mechanical Properties of Full-Scale Rubber Bearings at 23 °C, 0 °C, and -20 °C.

In this study, the effects of ambient temperature on the horizontal mechanical performance of isolated rubber bearings were investigated using high-speed reciprocating loading methods. A comprehensive series of 54 experimental trials are performed on the full-scale (900 mm-diameter) isolation rubber bearings, encompassing a range of temperatures (-20 °C, 0 °C, and 23 °C), shear pressures (50%, 100%, and 250%), and frequencies (0.20 Hz, 0.25 Hz, and 0.30 Hz). Because the compression-shear tests were conducted at high velocities and pressures (specifically, vertical compressive stress of 15 MPa), the equipment used in these tests was capable of generating substantial inertial and frictional forces. Appropriate correction methodologies for the precise determination of mechanical performance metrics for bearings are presented. Then, a comprehensive investigation of the effects of various loading conditions on the characteristic strength, post-yield stiffness, horizontal equivalent stiffness, and equivalent damping ratio of LRB900 (lead-core rubber bearings 900 mm-diameter) and LNR900 (linear natural rubber bearings 900 mm-diameter) is conducted. The empirical results show a discernible relationship between these characteristics and ambient temperature as the number of loading cycles increases, except for the equivalent damping ratio. Finally, empirical fitting formulations incorporating the influence of ambient temperature are presented for each performance indicator. These formulas are intended to assist designers in performing seismic design analyses by allowing them to take into consideration the effects of ambient temperature comprehensively.

Dynamic characteristics of stone masonry walls before and after damage: Experimental and numerical investigations

Seismic behavior of masonry walls has been heavily investigated, especially by means of laboratory experiments employing cyclic tests to determine the mechanical parameters and seismic capacity. Nevertheless, the dynamic properties of the tested walls often remain unknown, even though the nature of the seismic response is dynamic and profoundly affected by the structure's dynamic properties. This paper presents an investigation on the dynamic properties of three different masonry wall panels in healthy and damaged states, and examines if damage quantification via tracking the changes in dynamic properties is feasible. Ambient vibration and impact measurements are used for the dynamic identification of wall panels, before and after they are tested in reversed-cyclic in-plane shear-compression tests. The natural frequencies, damping ratios, and mode shapes of the walls are determined and compared to each other. Moreover, the damage progression and its effect on the dynamic features of the URM wall panel is investigated using a discrete element model of the benchmark wall that is validated in terms of the force-displacement response and damage pattern of the wall. The results of the study indicate that changes in natural frequencies and mode shapes are traceable, although it is difficult to infer damage quantification relationships from these changes. The outcomes of this study also highlight that numerical models verified with the nonlinear quasi-static behavior do not necessarily match the wall's dynamic behavior, and that more research is required to update nonlinear numerical models. Overall, the results contribute to the knowledge regarding the dynamic characteristics of masonry walls in healthy and damaged conditions, and to quantify the damage in masonry walls as well as the changes in their dynamic properties.

DLP printed 3D gyroid structure: Mechanical response at meso and macro scale

Rapid prototyping (RP) technology enables the fabrication of complex geometries, making lattice structures increasingly popular. Lattice structures, known as cellular materials, have garnered significant attention over the past two decades due to their ability to optimise mass distribution in components. These structures excel in mechanical properties, catering to energy absorption (bending-dominated structures) and structural performance (stretch-dominated structures). In this paper, we investigate the behaviour of stretch-dominated lattice structures using periodic surface models, specifically focusing on sheet-based Gyroid cells, to allow for a more efficient macroscale modelling. We study cells and scaffolds of different sizes, considering various triply periodic minimal surface thicknesses and relative densities ranging from approximately 0.2 to 0.65. We explore load applications in directions different from the unit cell's principal axes and analyse the strain rate effect on both bulk and cellular material. The lattice structures are manufactured using epoxy resin and digital light processing (DLP) technology. In the range of relative density investigated, both in quasi-static and dynamic conditions, a linear trend is observed for Young's modulus and compression yield strength. To extend the quasi-static results to the dynamic regime, we employ a more generalized normalization technique. This approach divides Young's modulus and compression yield strength by the behaviour of the base material at a specific strain rate, facilitating the correlation of mechanical properties across the two loading regimes. Based on experimental findings, we implemented and calibrated a bi-linear material model for describing, in macroscale, triply periodic minimal surface (TPMS) Gyroid structures. The model coefficients are parameterized with respect to relative density. In addition, the presented material law was compared with that proposed by Gibson-Ashby. Furthermore, we evaluated the anisotropy of both the base material and the unit cell. The first one is done by testing the 3D printed samples in directions different from the printing one, the latter by using the Zener factor. The anisotropy evaluation confirmed the isotropic behaviour of the unit cell within the range of relative density and test conditions investigated. Finally, we perform linear elastic 3D macroscopic and mesoscopic model simulations for combined shear-compression tests using the implemented bi-linear material model and the anisotropic stiffness matrix (obtained through the homogeneous formulation) for the macroscale, and the base material for the mesoscopic one. The results demonstrate the suitability of the proposed equivalent material model for studying the TPMS Gyroid structure in the elastic regime, both in quasi-static and dynamic states. This allows for an efficient FE modelling process of complex lattice structures.

Experimental Study on the Mechanical Properties of Nylon Fabric-Reinforced Elastomeric Isolators (N-FREIs)

In recent decades, carbon fiber, glass fiber, polyester and Kevlar fiber have been utilized to replace the steel shims in conventional steel-reinforced elastomeric isolators (SREIs). This study chose nylon fabrics owing to their extreme low cost, low elastic modulus and good adhesion to rubber, and nine nylon fabric-reinforced elastomeric isolators (N-FREIs) were manufactured with different design parameters. Compression and compression shear tests were, respectively, conducted to investigate the mechanical properties together with their influential factors of the N-FREIs. Results show that the vertical load-carrying capacity of the isolator is high enough to sustain a compressive stress of 10[Formula: see text]MPa without visible damage. The compressive stiffness of N-FREI is much smaller than that of SREI, and the vertical damping ratio under cyclic compression reaches up to 7%. In the compression shear tests, the shear stiffness of the isolator first decreases and then increases as the shear strain increases within 300%, and the equivalent damping ratio varies between 9% and 14% for different sizes of the isolator. Additionally, due to the flexibility and extensibility of the low modulus nylon fabric, both vertical and horizontal stiffness decrease a bit with an increase in the number of fabric layers. Finally, a formula for calculating the horizontal stiffness of N-FREI is proposed, it provides a comprehensive mathematical model to predict the behavior of the N-FREI under horizontal shear conditions.

Experimental characterization of a polydicyclopentadiene thermoset, study of protective metal-polymer and polymer-metal two-layer structures

Multilayer structures are frequently used for military impact protection applications. For low-velocity impacts, they can be made from a wide variety of materials, including metallic and polymeric materials. One proposes to investigate the impact resistance of two-layer structures composed of polydicyclopentadiene thermosetting resin (P-DCPD) combined with DP450 steel or AA2024-T3 aluminum. Structures are subjected to debris impacts of 125 J at 10 m/s. Polymer stacking order is evaluated, highlighting the importance of P-DCPD to be the first layer impacted. To understand and validate these experimental results, the behaviors of DP450, AA2024-T3 and P-DCPD are studied. Experimental tests (quasi-static tension and compression, dynamic compression and Iosipescu shear tests) are carried out to characterize P-DCPD and validate material behavior laws. Finite element simulations using LS-Dyna software are used to validate and explain experimental impact results.

Utilization of Nano Silica and Plantain Leaf Ash for Improving Strength Properties of Expansive Soil

This study investigates the effect of nanosilica and plantain leaf ash on the sustainable stabilization of expansive soil. This study conducted various strength tests, including Unconfined Compressive Strength (UCS), direct shear, and California Bearing Ratio (CBR) tests, to analyze the enhancement of mechanical properties by adding nano silica and plantain leaf ash. Scanning Electron Microscopy (SEM) analysis was conducted to investigate the interaction mechanism between the soil and the combination of nano silica and plantain leaf ash. Three different combinations of plantain leaf ash were utilized, ranging from 5% to 15%, alongside nano silica ranging from 0.4% to 1.2%. The reinforced soil’s compressive strength, shear strength, and bearing capacity were assessed through UCS, direct shear, and CBR tests. The results demonstrated significant improvements in compressive strength, up to 4.6 times, and enhancements in cohesion and frictional angle, up to 3.3 and 1.6 times, respectively, at 28 days. Moreover, the addition of nano silica and plantain leaf ash led to increased bearing capacity and reduced soil swelling potential, contributing to the overall stability and strength improvement in expansive soil. The SEM test results demonstrate that maximum bonding and compaction occur when 1.2% nano silica and 15% plantain leaf ash are added to the soil.

Influence of polyether ether ketone (PEEK) viscosity on interlayer shear strength in screw extrusion additive manufacturing

The excellent properties of polyether ether ketone (PEEK) have made it applicable for high-performance components in aerospace, electrical, chemical, and biomedical industries. Material extrusion (MEX) additive manufacturing (AM) of PEEK using fused filament fabrication (FFF) predominantly uses modified PEEK filament. Fused granulate fabrication (FGF) systems conventionally employ injection moulding and extrusion grades which are not specifically formulated for MEX AM. There is a limited amount of research on the use of these grades for MEX AM using PEEK. This study evaluated different viscosity PEEK grades at various extruder temperatures to optimise interlayer strength and therefore determine the best grades of PEEK for FGF. Compression shear testing (CST) was used to study this property as it represents a mostly shear loading condition i.e., without bending, compared to other conventional shear testing methods, whilst also being easier to fabricate. PEEK crystallinity is corelated to the interlayer strength and was evaluated using differential scanning calorimetry (DSC), Raman spectroscopy and X-ray diffraction (XRD). The highest interlayer strength of 17.70±0.58 MPa and the lowest crystallisation degree of 29.7±1.3% (Raman) was achieved by VESTAKEEP L4000G PEEK, printed at the highest extruder temperature (420°C). This grade had the highest viscosity or the lowest melt volume-flow rate (MVR). In contrast with lower MVR grades, the high MVR grade VESTAKEEP L2000G, achieved a higher increase in bond strength and crystallinity with higher extruder temperatures. At lower MVR, the crystallinity was found to decrease from 33% to 30% with increasing extruder temperatures, along with an increase in melting temperature. This behaviour was attributed to a change in crystalline morphology possibly caused by the long residence time and high processing temperature of FGF.

Achievement of high-strength Al/CFRP hybrid joint via high-speed friction stir lap joining and laser texturing pretreatment parameters variation

This paper presents the achievement of a high-strength Al/CFRP hybrid joint through a high-speed friction stir lap joining process, combined with variations in laser surface texturing pretreatment parameters. The study examined the impact of laser surface texturing parameters by varying the depth, interval distance and width of the laser texture. By adjusting laser texturing parameters, the softened PA66 was fully infused into the textured grooves on the aluminum surface, leading to a significant reduction in interfacial voids and cracks in Al/CFRP. The preliminary tensile shear test showed that the hybrid joint broke at the CFRP base material, indicating that the laser texturing exhibited excellent Al/CFRP interface strengthening ability. Further compression shear tests were applied to reveal the actual interfacial load-carrying performance for comparison. The maximum shear strength of 25.5−1.34+0.7 MPa was achieved at a joining speed of 3000 mm/min. Additionally, a mathematical model was proposed to assess the strengthening impact of laser texturing parameters, considering micro-texture geometry and interfacial defects. The tearing of PA66, detachment of carbon fibers, and the breakage of carbon fibers were the three primary types of fracture modes identified at the Al/CFRP interface. The joining mechanism revealed that both mechanical interlocking and the chemical bonding of Al-O-C contributed to the increase in joint shear strength. This study presents a credible method for producing high-strength Al/CFRP lightweight structures.

Degradation mechanisms of concrete cold joint surfaces under sulfate cycles and varying pouring intervals

In concrete structures, particularly in arid and saline environments, the cold joint surface often serves as a primary entry point for erosion damage, thus dictating the lower limit of structural durability. This study investigates the erosion and damage mechanisms of cold joint concrete under such conditions, focusing on specimens with varying pouring intervals (0.25 d, 0.5 d, 1 d, 7 d, and 28 d). These specimens underwent 0, 30, 90, and 150 sulfate dry‒wet cycles, with their degradation assessed through compression‒shear tests. The findings reveal a logarithmic relationship between the cold joint surface adhesion and the pouring interval, and similarly, there is a logarithmic relationship between the internal friction angle and the pouring interval. Shorter intervals correspond to a higher rate of decrease in both adhesion and internal friction angle, while longer intervals result in lower, eventually stabilizing, values of these properties. Scanning Electron Microscopy analysis indicates that inherent defects in the cold joint surface expedite sulfate penetration into the concrete. As the number of sulfate cycles increases, ettringite formation in the cracks leads to their expansion and interconnection, diminishing the shear resistance of the cold joint surface. The study shows that the pouring interval significantly influences corrosion resistance, with its effects becoming more pronounced after a threshold of sulfate cycles (approximately 90). Shear strength is found to be more susceptible to sulfate erosion compared to compressive strength, with a faster degradation rate. After 80 to 110 erosion cycles, the adhesion corrosion resistance drops to 75%, while the compressive strength remains above this threshold.

Developing a New Constitutive Model of High Damping Rubber by Combining GRU and Attention Mechanism.

High damping rubber (HDR) bearings are extensively used in seismic design for bridges due to their remarkable energy dissipation capabilities, which is critical during earthquakes. A thorough assessment of crucial factors such as temperature, rate, experienced maximum amplitude, and the Mullins effect of HDR on the mechanics-based constitutive model of HDR is lacking. To address this issue, we propose a deep learning approach that integrates the Gate Recurrent Unit (GRU) and attention mechanism to identify time series characteristics from compression-shear test data of HDR specimens. It is shown that the combination of GRU and attention mechanism enables accurate prediction of the mechanical behavior of HDR specimens. Compared to the sole use of GRU, this suggested method significantly reduces model complexity and computation time while maintaining good prediction performance. Therefore, it offers a new approach to constructing the HDR constitutive model. Finally, the HDR constitutive model was used to analyze the impact of experienced maximum amplitudes and cycles on following processes. It was observed that maximum amplitudes directly influence the stress-strain relationship of HDR during subsequent processes. Consequently, a solid foundation is laid for evaluating the responses of HDR bearings under earthquakes.