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This study aims to establish a strain instanton equation and damage factor evolution law for gypsum specimens by considering damping. First, damping energy is calculated based on the single-degree-of-freedom vibration model, and the instantaneous strain equation is obtained based on the stress balance equation. Second, the dissipation energy is divided into damping and damage energies, and a damage-factor correction algorithm is obtained. Third, cyclic loading and unloading tests were performed at different loading rates and stress amplitudes to verify the accuracy of the strain equation. Finally, the specimens' magnitude curves and crack characteristics were monitored using moment–tensor acoustic emission simulations. The factors influencing the damping energy and strain equations, energy and damage evolution laws of the specimens, and damage patterns of the specimens at different loading rates were analysed. The results show that the instantaneous strain equation and the modified damage factor considering the damping effect can effectively reflect the deformation law and damage state of the specimens. In contrast, the damage to the specimens in the lower limit of the variable stress experiment was lower than that in the lower limit of the constant stress experiment. As the loading rate increases, the damage energy density of the specimen decreases, and the damage factor within a single cycle gradually decreases. As the loading rate increases, the number of crack events in the model increases significantly, size becomes more uniform, and sequentially exhibits dense and sparse distribution patterns, percentage of shear cracks decreases significantly, number of mixed cracks increases significantly, brittle behaviour of the specimen becomes obvious, and a complete damage state is attained known as the 'crushed' state. This study provides a theoretical reference for damage assessments of viscoelastic–plastic materials subjected to perturbing loads. [ABSTRACT FROM AUTHOR]

This study investigated the effectiveness of carbon fibre-reinforced polymer (CFRP) materials in strengthening the diagonal tension members of steel-truss bridges. Monotonic tensile and cyclic loading tests were performed on CFRP-strengthened specimens with variations in the CFRP-bonding range on the flanges. This study focused on the strengthening methods A and B, which were proposed to address insufficient CFRP anchoring near gusset plates by bonding CFRP sheets to both sides of the flanges of the diagonal tension members. The results of the monotonic tensile loading tests indicated a significant increase in tensile stiffness and substantial improvements in yield strength (27%) and ultimate load-bearing capacity (51%) when the strengthening methods A and B were employed. Delamination of the bonded CFRP sheets was effectively delayed, occurring only after the steel yielded, owing to the use of a ductile adhesive (polyurea putty). On the other hand, the cyclic loading tests demonstrated a significant enhancement in the load-bearing capacities (33% for tensile, 32% for compressive) of the strengthened specimens. Moreover, the energy dissipation capacities of the specimens strengthened by methods A and B exhibited linear increases, with 12% and 14% higher values respectively than those of the non-strengthened specimen. Although the stiffnesses (tensile and compressive) of the strengthened specimens decreased in each loading loop, the strengthening methods A and B maintained the stiffness values at approximately 35% higher than those of the non-strengthened specimen. [ABSTRACT FROM AUTHOR]

Large‐scale fatigue testing is very important to the research on scale effects, which occur in large cyclic loaded structures, such as wind turbine towers. However, such experimental testing has a very high energy consumption. As an efficient alternative, this paper presents a new resonant testing facility for large‐scale specimens under cyclic bending loads. The facility works as a 4‐point bending test, in which the specimen is supported in the nodes of its first normal bending mode, where theoretically no reaction forces occur. Two counter‐rotating imbalance motors with excitation frequencies near resonance generate a harmonic force acting on the specimen. Experimental trial fatigue tests on a steel pipe as a specimen were carried out, in order to validate the new testing setup. A great decrease in the support forces was reached by placing the supports at the normal mode nodes. Additionally, the behavior of the support forces under varying positions and excitation frequencies was also investigated. In summary, the resonant testing method combined with the supports at the normal mode nodes offers an efficient and energy‐saving testing setup for large‐scale fatigue tests. Highlights: A resonant testing facility for large‐scale bending fatigue tests was developed and tested.Supports were placed in the nodes of the specimen's first normal bending mode.The influence of the support positions on the support forces was investigated.A significant reduction in support forces was achieved. [ABSTRACT FROM AUTHOR]

Cold-rolled ribbed steel bar welded mesh (CRWM) is used to speed construction and improve the quality of the reinforcing. However, the seismic performance of such RC walls is uncertain. The current study assessed the seismic efficacy of these walls by analyzing the effects of different combinations of axial and cyclic lateral loading in a large-scale experimental program. The walls were built with boundary elements at the ends and two layers of mesh placed into the web of the walls. The seismic parameters comprise a force-displacement hysteresis curve, concrete and rebar strains, dissipated energy, and stiffness. The experimental findings show that the axial load had a significant effect on the deformation capacity, strength, and failure mode of the wall. Except for walls with flexural failure, the study revealed that the use of such mesh had a detrimental effect on the cyclic performance of other specimens. In walls exhibiting flexural failure modes, such as C15, the use of CRWM slightly improves ductility compared to the ASCE 41-17 proposed model. The use of such mesh in walls with any type of shear failure mode had a significantly negative influence on the seismic performance of the walls. Among shear failure modes, sliding shear failure is particularly adverse. In such failures, the vertical rebars are subjected to deformation perpendicular to their direction. Because of their brittle nature, they cannot accommodate this deformation and are prone to fracture. Moreover, a comparison of the experimental backbone curve of the walls and the numerical model proposed by ASCE 41-17 revealed that the ASCE model tended to overestimate the effective stiffness of walls with axial loads of less than 10% fc′Ag. Practical Applications: The structural integrity of buildings is critical in seismically active areas. This study looks into the use of cold-rolled ribbed steel bar welded mesh (CRWM) in the web of reinforced concrete special structural walls, a technique used in Turkey and China that is also being considered in Iran. Because of a lack of performance data, current building codes, such as ACI 318-19, do not include provisions for CRWM in seismic systems. Our research attempts to fill this gap, which provides empirical data from large-scale experimental tests to evaluate the cyclic performance of walls with CRWM under various axial loads. The findings provide important insights into the behavior, strength, and ductility of such walls, allowing for a better understanding of their use in earthquake-prone areas. The findings are intended to inform and potentially influence building codes and practices, advocating for the use of CRWM where it can improve construction efficiency and seismic resilience. This research not only helps to optimize structural designs but also helps to develop safer, more cost-effective building strategies in seismically active areas. [ABSTRACT FROM AUTHOR]

This paper aims to introduce a highly efficient computational model compared to the current cycle-by-cycle simulation strategy to compute the viscoelastic responses of asphalt concretes and pavement structures under large numbers of load cycles. An explicit constitutive relation for viscoelastic solids in multiple time scales was developed based on the temporal homogenization. The original initial-boundary value problem was divided into a global part in the slow time scale and a local part in the fast time scale. Two simulation studies were presented to validate the computational accuracy and efficiency of the proposed model: (1) a cylindrical asphalt concrete subject to a uniaxial cyclic compression load, and (2) a pavement structure subject to a locally cyclic loading. The laboratory test results and field measurements were compared with the modeled responses to validate the models before comparing with the reference solutions. Results indicate that the temporal homogenization-based viscoelastic model saves considerable computational cost and maintains a satisfactory accuracy. The absolute values of relative error of the modeled responses between the time homogenization and reference solutions are lower than 1% and 4% for the cylindrical asphalt concrete and pavement structure under locally cyclic loadings, respectively. Based on the proposed computational approach, only 4 min are needed to model the response of a cylindrical asphalt concrete subject to 104 repeated load cycles under a uniaxial compression load. The computational time is reduced from 7 h of the reference solution to 38 min of the temporal homogenization solution to model 103 load cycles of a viscoelastic pavement structure. Practical Applications: This study introduces a highly efficient computational model to compute the viscoelastic responses of asphalt concretes and pavement structures under large numbers of load cycles. Multiple time scales were applied to an explicit constitutive relation of asphalt concretes to obtain the formula of global and local initial-boundary value problems. Its computational accuracy and efficiency were verified by comparing the temporal homogenization-based solutions with the testing results and reference solutions for a cylindrical sample and a pavement structure. It is the basis for the long-term pavement performance prediction after including the fatigue damage analysis in the present temporal homogenization framework. By successfully implementing a mechanistic framework for the long-term pavement performance prediction, the pavement design can more rely on the material inherent properties instead of using redundant empirical transfer functions. It is promising that the local calibrations of the current empirical performance transfer functions can be minimized as the proposed pavement long-term performance predictions depend on the material inherent properties and constitutive models. [ABSTRACT FROM AUTHOR]

Red mudstone is a problematic soil that is easily subjected to weathering, disintegrating, and swelling. In this study, a series of large-scale cyclic triaxial tests were performed to investigate the cumulative deformation behavior of red mudstone clay mixed with weathered red mudstone gravel as an improved coarse-grained red mudstone soil (IRMS). The influences of compaction moisture content and confining pressure were investigated. The cyclic loading was applied from 25 to 225 kPa with an increment of 25 kPa and 1,000 or 2,000 cycles for each stage at a frequency of 2 Hz. The experimental results indicate that the strains at the onset of failure are approximately 1% for the optimal moisture content (OMC) with the number of cycles N = 14,000–16,000, and the strains are approximately 1% for the moisture content 2% dry of OMC with N = 12,000–14,000, while the strains exceed 10% for the moisture content 2% wet of OMC with N = 3,000–4,000. The cumulative strain decreases with increasing confining pressure from 20 to 50 kPa, but the influence becomes more significant under higher dynamic stress. A prediction model is proposed for the evolution of cumulative strain under cyclic loading. The IRMS could be used as a construction material for railway subgrade with proper control of field compaction moisture content. [ABSTRACT FROM AUTHOR]

Under earthquake excitations, reinforced concrete (RC) columns could be subjected to lateral drift reversals and a combination of axial forces, bending moments, and torsional effects. This paper investigates the behavior of glass fiber-reinforced polymer (GFRP)-RC columns under seismic-simulated loading, including torsion, which has not been studied previously. Seven large-scale circular GFRP-RC column-footing connections were cast and tested under various combined reversed cyclic loading configurations to examine the effects of torsion-bending moment ratio (tm), transverse reinforcement ratio, and concrete compressive strength. The test results revealed that increasing the tm reduced the lateral load capacity and deformability of the GFRP-RC column, but resulted in a more symmetric torque-twist relationship. Increasing the transverse reinforcement ratio mitigated core damage and provided additional support (for example, spiral turns) for torsion-induced tensile stresses. Moreover, increased concrete compressive strength bolstered torque capacity and torsional stiffness, while, under a tm of 0.4, it resulted in decreased twist capacity. When torsion was present, increasing the concrete compressive strength had an insignificant impact on the bending-shear response, differing from findings for GFRP-RC columns subjected to seismic loading without torsion. [ABSTRACT FROM AUTHOR]

In the present study, shear-friction tests were conducted under cyclic loading to investigate in-plane shear transfer across a thin and long interface between new and existing concrete slabs. For shear reinforcement across the interface, concrete shear keys and steel shear plates were used in combination with adhesive anchors (that is, post-installed reinforcing bars). Test results showed that the shear behavior of the thin slab interfaces was significantly affected by the types and details of interface reinforcements. The concrete shear keys and shear plate effectively restrained relative slip across the interface during the initial behavior and increased the peak strength, while the adhesive anchors contributed to the peak strength and post-peak residual strength. Failure modes were concrete failure around the concrete shear keys (that is, local crushing and shearing-off) and in the anchorage zone of the shear plate (that is, cracking and spalling-off). The nominal shear strengths of the thin slab interfaces were calculated by summing the shear-friction strength of adhesive anchors, local crushing strength around concrete shear keys, and shear yield strength of shear plates. The predicted strength agreed with the test results. Based on the results, design considerations of shear transfer across an interface between thin concrete slabs were discussed. [ABSTRACT FROM AUTHOR]

With an emphasis on the combined degradation of railway track geometry and components, an improved numerical approach is proposed for predicting the track geometrical vertical levelling loss (VLL). In contrast to previous studies, this research unprecedentedly considers the influence of unsupported sleepers (US) configuration on VLL under cyclic loadings, elasto-plastic behaviour, and different operational dynamic conditions. The nonlinear numerical models are performed adopting an explicit finite element (FE) package, and their results are validated by field data. The outcomes are iteratively regressed by an analytical logarithmic function that cumulates permanent settlements, and by a power function factor, which innovatively extends the response of US on VLL over a long term. Results shows that at 3 million cycles (or 60 MGT) the worst configuration for 20-ton axle load is at 5 US with 5-mm gap (5,51%), whereas for 30 and 40-ton axle loads is at 5 US with 2-mm gap (1.23% and 0,89%, respectively). This indicates that the axle load affects considerably the VLL as expected, however, the US condition plays an important role to accelerate it. Based on this study, the acceptable configuration of US can be specified for a minimum effect on VLL (thresholds) and, therefore, supports the development of practical maintenance guidelines to prolong the railway track service life. [ABSTRACT FROM AUTHOR]

In the implementation process of carbon capture and storage (CCS), the geomechanical problems arising from the cyclic injection of carbon dioxide into the formation cannot be ignored. To clarify the influence of cyclic loading on the geomechanics properties of reservoir rocks, cyclic loading tests were carried out on rocks in sandstone reservoirs with the RTR‐2000 Rock Mechanics Test System, and the evolution of compressive strength, elastic modulus, and Poisson's ratio parameters was analyzed, which revealed the law of the geomechanical deterioration and damage evolution of sandstone reservoirs under cyclic loading. The results show that under the same cyclic load, when the number of cycles is increased to a certain degree, the influence on the peak strength is small. As the number of cycles increases, the modulus of elasticity of rock appears to be increasing and then decreasing, whereas a rapid increase in Poisson's ratio and a slow increase in Poisson's ratio occur with the increase in the number of cycles. Under the same number of cycles, the peak strength of the core gradually decreased with the increase of the maximum cyclic stress. When the cyclic load was smaller than the yield stress of the core, the effect of cyclic loading on the strength of the core was small, and when the cyclic load was larger than the yield stress, the effect of cyclic loading on the strength increased significantly. With the increase of cyclic load, the modulus of elasticity showed a tendency to increase and then decrease, and Poisson's ratio had a tendency of decreasing and the overall degree of change was small. [ABSTRACT FROM AUTHOR]

Numerous geotechnical applications are significantly influenced by changes of moisture conditions, such as energy geostructures, nuclear waste disposal storage, embankments, landslides, and pavements. Additionally, the escalating impacts of climate change have started to amplify the influence of severe seasonal variations on the performance of foundations. These scenarios induce thermo-hydro-mechanical loads in the soil that can also vary in a cyclic manner. Robust constitutive numerical models are essential to analyze such behaviors. This article proposes an extended hypoplastic constitutive model capable of predicting the behavior of partially saturated fine-grained soils under monotonic and cyclic loading. The proposed model was developed through a hierarchical procedure that integrates existing features for accounting large strain behavior, asymptotic states, and small strain stiffness effects, and considers the dependency of strain accumulation rate on the number of cycles. To achieve this, the earlier formulation by Wong and Mašín (CG 61:355–369, 2014) was enhanced with the Improvement of the intergranular strain (ISI) concept proposed by Duque et al. (AG 15:3593–3604, 2020), extended with a new modification to predict the increase in soil stiffness with suction under cyclic loading. Furthermore, the water retention curve was modified with a new formulation proposed by Svoboda et al. (AG 18:3193–3211, 2023), which reproduces the nonlinear dependency of the degree of saturation on suction. The model's capabilities were examined using experimental results on a completely decomposed tuff subjected to monotonic and cyclic loading under different saturation ranges. The comparison between experimental measurements and numerical predictions suggests that the model reasonably captures the monotonic and cyclic behavior of fine-grained soil under partially saturated conditions. Some limitations of the extended model are as well remarked. [ABSTRACT FROM AUTHOR]

The out‐of‐plane response of prefabricated (precast) concrete shear walls (PWs) are usually neglected in the structural designs. However, because of the relatively low stiffness and inevitable deformation of slabs, the out‐of‐plane behavior of PWs could influence the in‐plane response by causing premature failure or stability problems and affect the overall structural performance. This issue becomes significant when single‐row connections are employed because the neutral axial is shifted toward the compression side and the out‐of‐plane capacity is altered accordingly. In this study, PWs with grouted steel sleeve splices were tested under reciprocating cyclic loading. Both single‐row and paired connections were considered in test program. It was shown that all PWs suffered bending failure dominated by yielding of reinforcement at the bottom, and their load‐carrying capacity, stiffness degeneration trends were similar to the monolithic (cast‐in‐place) reference walls. Under the normalized compression of 0.12, the ductility of the prefabricated walls was 2.62 and 3.07, which was comparable to that of the reference cast‐in‐place wall (2.72). For the case that axial compression was not applied, the hysteresis curve of the PW with single‐row connection exhibited significant pinching. Nonetheless, the load‐carrying capacity of these walls did not exhibit significant drop at the end of the tests due to the lower axial compression, exhibiting high level of deformability. For both load cases, PWs with paired connection exhibited higher energy dissipation than the single‐row connected specimens. [ABSTRACT FROM AUTHOR]

Expanded polystyrene (EPS) particle-based lightweight soil, which is a type of lightweight filler, is mainly used in road engineering. The stability of subgrades under dynamic loading is attracting increased research attention. The traditional method for studying the dynamic strength characteristics of soils is dynamic triaxial testing, and the discrete element simulation of lightweight soils under cyclic load has rarely been considered. To study the meso-mechanisms of the dynamic failure processes of EPS particle lightweight soils, a discrete element numerical model is established using the particle flow code (PFC) software. The contact force, displacement field, and velocity field of lightweight soil under different cumulative compressive strains are studied. The results show that the hysteresis curves of lightweight soil present characteristics of strain accumulation, which reflect the cyclic effects of the dynamic load. When the confining pressure increases, the contact force of the particles also increases. The confining pressure can restrain the motion of the particle system and increase the dynamic strength of the sample. When the confining pressure is held constant, an increase in compressive strain causes minimal change in the contact force between soil particles. However, the contact force between the EPS particles decreases, and their displacement direction points vertically toward the center of the sample. Under an increase in compressive strain, the velocity direction of the particle system changes from a random distribution and points vertically toward the center of the sample. When the compressive strain is 5%, the number of particles deflected in the particle velocity direction increases significantly, and the cumulative rate of deformation in the lightweight soil accelerates. Therefore, it is feasible to use 5% compressive strain as the dynamic strength standard for lightweight soil. Discrete element methods provide a new approach toward the dynamic performance evaluation of lightweight soil subgrades. [ABSTRACT FROM AUTHOR]

Lithological layering makes coal mechanically heterogeneous and strongly controls the pore fluid diffusivity. Localized elastic deformation and high pore pressure favor the dynamic failure of coal. The effects of lithological layering and fluid diffusivity on the nucleation of coal dynamic failure were investigated by performing undrained triaxial cyclic loading tests on fully saturated coal of lithological layers. The porous layer in coal provides the dominant sites for fluid storage. The pore fluid in the regional porous layer of coal is strongly compacted, forming high pore pressure due to undrained fluid caused by the barrier effect of the neighboring tight layer. Excited by the mechanical disturbance of periodic mining, the regional pore pressure decomposes mineral grains of the porous layer, resulting in significant radial and volumetric dilation. Moreover, asynchronous deformation occurs among different lithological layers and results in resistance at the layer interface, causing tensile cracks. Different fluid enrichment zones coalesced into a large pore overpressure zone by these tensile cracks. On the microscale, with the maximum stress level (σmax) increase from 0.7σST to 0.9σST, the primary pores' porosity of after loading increased from − 3.74 to 19.61% relative to the porosity before cyclic loading, while the porosity of secondary pores increased from 53.78 to 1573.23%, indicating that the pore fluid in the large pores is compacted more significantly. On the one hand, the high pore pressure formation in the secondary pores weakens the coal strength. On the other hand, such a porosity increase in coal enlarges the fluid storage volume and enhances the regional fluid diffusivity for more gas energy accumulation. The enlarged pore overpressure domain and the corresponding reduction in coal strength contribute to the nucleation of coal dynamic failure. Highlights: The regional pore pressure decomposes mineral grains of the porous layer. The pore overpressure causes significant radial and volumetric dilation of coal. Incongruous radial strain in different layers produces tensile crack. Tensile cracks coalesce fluid enrichment zones into a large pore overpressure zone. Pore overpressure in secondary pores weakens coal strength and enlarges porosity. [ABSTRACT FROM AUTHOR]

To investigate the fracture behavior of slope rock masses under reservoir water fluctuation, several groups of constant-amplitude-cyclic loading tests and acoustic emission (AE) tests were conducted on two types of sandstone rocks, i.e., red sandstone and cyan sandstone, under both dry and saturated conditions. The variation in mechanical parameters, failure pattern and AE characteristics with water saturation and cyclic loading were systematically explored. The laboratory results show that water saturation causes: i) a notable reduction in peak stress (53.98% for red sandstone and 20.70% for cyan sandstone); ii) a considerable increase in failure strain (8.03% for red sandstone and 13.27% for cyan sandstone); iii) an elevated level of AE activity during cyclic loading phase; and iv) a significant enhancement in the occurrence of tensile failure. The statistical analysis of experimental AE waveform data demonstrates a discernible clustering of AE waveforms with low dominant frequency (L-type waveform) and those with high dominant frequency (H-type waveform). Dry rocks under cyclic loading exhibit the prevailing dominance of H-type waveforms, while saturated rocks display a shift towards the predominance of L-type waveforms. Moreover, both water saturation and cyclic loading contribute to the occurrence of L-type waveforms, which are closely associated with tensile failure in rocks. Based on this, cyclic loading is believed to substantially accelerate strength degradation and catastrophic fracture of rocks. Fracturing and AE characteristics investigated in this work likely shed light on accessing the stability of reservoir slopes experiencing recurrent external loads. [ABSTRACT FROM AUTHOR]

The article discusses the use of rubberized concrete in reinforced concrete columns and its performance under axial and cyclic loads. The addition of crumb rubber to the concrete reduces its compressive strength and load capacity but improves its displacement ductility and damping ratio. The study suggests that rubberized concrete can enhance the performance of concrete columns under cyclic loading and delay the onset of earthquake damage. The article provides a technical analysis of various parameters and their implications for the seismic performance of rubberized concrete. [Extracted from the article]

This present research conducted an experimental study on the influence of different earthquake damages on the seismic performances of aged reinforced concrete (RC) beam-column joints retrofitted with basalt fiber-reinforced polymer (BFRP) sheets under cyclic loadings. Six beam-column joints included one benchmark specimen, one uncorroded specimen retrofitted with BFRP sheets, and four earthquake-damaged corroded specimens with the corrosion rates of 0% and 9% retrofitted with BFRP sheets. Test results demonstrated that the seismic performances of earthquake-damaged corroded specimens effectually improved after retrofitting with BFRP sheets, and the retrofitting effectiveness was significantly affected by the earthquake-damaged levels. The bucking of stirrups, spalling and crushing of concrete of retrofitted specimens were effectually postponed, while the ductility of corroded and uncorroded specimens under the earthquake damages increased after retrofitting with BFRP sheets. The total cumulative energy dissipation and final stiffness of retrofitted specimens considerably improved with the maximum increase of 22.3% and 14.3% comparing to those of benchmark specimen, respectively. Besides, the models for predicting the shear strength of RC beam-column joint cores considering the influences of earthquake damage, reinforcement corrosion, and FRP retrofitting were proposed. [ABSTRACT FROM AUTHOR]

Suction bucket jackets have been used as foundations for offshore wind turbines in intermediate water depths where layered soil stratigraphies are often encountered. Although suction installation in layered soils has been studied, experimental data on the in-service response is scarce. During installation in stratigraphies containing a low permeability layer underlain by a high permeability layer, suction is transferred to the underlying layer when the pressure at the lid invert is sufficient to uplift the low permeability plug. This suction-transfer mechanism also affects the in-service response, albeit the load-sharing mechanism is not well understood. This paper presents data from centrifuge tests of suction buckets subjected to constant amplitude and varying amplitude cyclic vertical loading in two stratigraphies—a sand with an overlying clay layer and in a sand with a sandwiched clay layer. These experiments show that tensile stresses exceeding the vented tensile resistance can be withstood without significant uplift of the bucket in both stratigraphies, even under a zero mean stress. Plug uplift was shown to have an important effect on the amount of stress transferred to the skirts, with the load-sharing mechanism depending on the stratigraphy. Additionally, the load-sharing mechanism and the bucket in-service resistance was shown to depend on the effectiveness of the clay in sealing the soil plug within the bucket, with a more effective seal resulting in higher tensile resistance and therefore better performance. A limiting loading condition was not identified in the sand with a sandwiched clay layer, with the data indicating that the suction pressure to cause plug uplift during cyclic loading may be much higher than during suction installation. [ABSTRACT FROM AUTHOR]

Compressive cyclic loads induce a progressive failure in rock materials, and the long-term stability can not be guaranteed by the strength under monotonic load. To this end, the present study aims at establishing an elastoplastic fractional fatigue damage model for predicting the accumulative deformation of rock materials in a unified framework. A fractional-order plastic flow rule is introduced to describe volume transformation of rock sample from compression to expansion, eliminating the need for plastic potential functions. And a hardening function with an equivalent plastic shear strain is adopted. Concerning the fatigue effects, the progressive deterioration of material due to cyclic loads is intricately linked to microstructural degradation, depicted by a convolution law. In the context of creep deformation, loading cycle serves as an equivalent time measure, connecting the plastic deformation with the fatigue damage. In order to verify the accuracy, the proposed model is numerically implemented by a returning mapping procedure simulate the mechanical responses of three types of rocks in both uniaxial and triaxial cyclic tests. Comparative analysis with associated fatigue model is also provided to evaluate the accumulative deformation and damage evolution of concerned rocks. • A fractional-order fatigue damage model for predicting the accumulative deformation of rocks is established. • The continuous progression due to cyclic damage is linked to microstructure degradation by a convolution law. • The model is numerically implemented by a returning mapping procedure considering the plastic and damage effects. • The accuracy is validated by comparison with experimental data of different types of rocks in cyclic tests. [ABSTRACT FROM AUTHOR]

Cellulosic fiber board (CFB) is a lightweight form of sheathing that contains 94% post-consumer recycled materials. The viability of CFB sheathed shear walls as an alternative to Oriented Strand Board (OSB) walls is the focus of this study. A total of 23 walls and 10 connection samples were tested under cyclical loading to determine their overall behavior and capacity. The walls consisted of 2.44 m high by 3.66 m long CFB and OSB sheathed walls with and without openings. The design capacity of each wall was calculated and compared to the experimental results. For the walls with openings, the effects of blocking and strapping on their behavior were also evaluated. It was found that CFB is a viable alternative to OSB; however, some adjustments to the current design values and processes are required as the current procedure results in safety factors that are significantly lower than those for OSB walls. [ABSTRACT FROM AUTHOR]

For an offshore photovoltaic helical pile foundation, significant horizontal cyclic loading is imposed by wind and waves. To study a fixed offshore PV helical pile's horizontal cyclic bearing performance, a numerical model of the helical pile under horizontal cyclic loading was established using an elastic–plastic boundary interface constitutive model of the clay soil. This model was compared with a monopile of the same diameter under similar conditions. The study examined the effects of horizontal cyclic loading amplitude, period, and vertical loads on the horizontal cyclic bearing performance. The results show that under horizontal monotonic loading, the bearing capacities of a helical pile and monopile in a serviceability limit state are quite similar. However, as the amplitude of horizontal cyclic loading increases, soil stiffness deteriorates significantly, leading to greater horizontal displacement accumulation for both types of piles. The helical pile's bearing capacity under horizontal cyclic loadings is approximately 60% of that under monotonic loading. With shorter cyclic loading periods, horizontal displacement accumulates rapidly in the initial stage and stabilizes over a shorter duration. In contrast, longer cyclic loading periods lead to slower initial displacement accumulation, but the total accumulated displacement at stabilization is greater. When vertical loads are applied, the helical pile exhibits more stable horizontal cyclic bearing performance than the monopile. [ABSTRACT FROM AUTHOR]

This paper discusses the iteration of a seismic retrofit solution for shear-deficient end regions of 19 reinforced concrete (RC) moment-resisting frame (MRF) T-beams located in a 12-story RC MRF building in downtown Los Angeles, California. Local strengthening with externally bonded (EB) fiber-reinforced polymer (FRP) fabric was chosen as the preferred retrofit strategy due to its cost-effectiveness and proven performance. The FRP-shear-strengthening scheme for the deficient end-hinging regions of the MRF beams was designed and evaluated through large-scale cyclic testing of three replica specimens. The specimens were constructed at 4/5 scale and cantilever T-beam configurations with lengths of 3.40 m or 3.17 m. The cross-sectional geometry was 0.98 × 0.61 m with a top slab of 1.59 m in width and 0.12 m in thickness. Applied to these specimens were three different retrofit configurations, tested sequentially, namely: (a) unanchored continuous U-wrap; (b) anchored continuous U-wrap with conventional FRP-embedded anchors at the ends; and (c) fully closed external FRP hoops made of discrete FRP U-wrap strips and FRP through-anchors that penetrate the top slab and connect both ends of the FRP strips, combined with intermediate crack-control joints. The strengthening concept with FRP hoops precluded the premature debonding and anchor pullout issues of the two more conventional retrofit solutions and, despite a more challenging and labor-intensive installation, was selected for the in-situ implementation. The proposed hooplike EB-FRP shear-strengthening scheme enabled the deficient MRF beams to overcome a 30% shear overstress at the end-yielding region and to develop high-end rotations (e.g., 0.034 rad [3.4% drift] at peak and 0.038 rad [3.8% drift]) at strength loss for a beam that, otherwise, would have prematurely failed in shear. These values are about 30% larger than the ASCE 41 prescriptive value for the Life Safety (LS) performance objective. Energy dissipation achieved with the fully closed scheme was 108% higher than that of the unanchored FRP U-wrap and 45% higher than that of the FRP U-wrap with traditional embedded anchors. The intermediate saw-cut grooves successfully attracted crack formation between the strips and away from the FRP reinforcement, which contributed to not having any discernable debonding of the strips up to 3% drift. This paper presents the experimental evaluation of the three large-scale laboratory specimens that were used as the design basis for the final retrofit solution. [ABSTRACT FROM AUTHOR]

This research introduces a novel gusset plate damper designed to safeguard structures from intense seismic activity and enhance the performance of X-braced frames. The damper includes a grooved plate with multiple parallel steel strips, and cross braces segmented into four parts by the central grooved plate. Both sides of each brace segment, a set of strips is embedded within the gusset plate, oriented perpendicular to their corresponding brace axis. The X-braced frames equipped with grooved gusset plate damper (GGPD) were subjected to cyclic loading both experimentally and numerically. The experimental results demonstrated that the proposed system exhibits robust seismic performance. Employing ABAQUS, the calibration results demonstrated excellent agreement between the experimental and numerical outcomes, affirming the accuracy of the finite element method in predicting the cyclic behavior and fracturing patterns of this innovative system. Additionally, the study delved into the local buckling and the necessity of incorporating stiffeners for the grooved plate damper along their edges, evaluating their impact on the main characteristics of the new damper. The findings revealed that when appropriately reinforced at its edges, the proposed damper demonstrates excellent behavior and stable hysteretic curves. Moreover, decreasing the width-to-thickness ratios of steel stiffeners in the GGPD resulted in wider hysteresis loops. Findings indicated that a width-to-thickness ratio of 7 yields favorable outcomes for design parameters, including lateral elastic stiffness and ultimate strength. [ABSTRACT FROM AUTHOR]

This work presents in situ transmission electron microscopy observations of dislocation activities and associated fatigue properties in a cross‐sectional sample of a Cr–Au bilayer on a polyimide substrate under cyclic loading. Dislocation structures in the Au layer are observed to evolve into a geometrically necessary boundary parallel to the Cr–Au interface, which significantly impedes dislocation motion and plays a crucial role in enhancing the fatigue resistance of the studied sample. While a comparison to the damage in a conventional blanket film testing geometry reveals some differences in the accumulation of plastic flow, the findings can provide insights into the underlying mechanisms governing fatigue in nanostructured multilayer materials on polymer substrates. [ABSTRACT FROM AUTHOR]

ABSTRACT The simulation of the soil–structure interface (SSI) under cyclic loading is critically important in geotechnical engineering. Numerous studies have been conducted to explore the cyclic behaviors exhibited at the SSI. However, existing model evaluations primarily rely on direct comparisons between experiments and simulations, with limited analysis focused on specific behaviors like accumulated normal displacement and stress degradation under cyclic loading. This study proposes and adapts six SSI models, including three nonlinear incremental models and three elastoplastic models. These models incorporate nonlinear shear modulus, critical state theory, and particle breakage effects to enhance their capability to capture SSI behaviors. Utilizing optimization‐based calibration for a fair comparison, the model parameters are fine‐tuned based on the experimental data. Comprehensive assessments including global comparisons and specific behaviors like accumulated normal displacement and stress degradation are carried out to evaluate the models' performance. The results indicate that all models effectively replicate the typical behaviors of SSI systems. By incorporating the particle breakage effect, the models can represent both the reversible and irreversible normal displacements under cyclic loading with better performance. The irreversible normal displacement remains stable and is solely influenced by the soil properties rather than the stress level. Moreover, the models successfully capture the stress degradation under constant normal stiffness caused by the irreversible normal displacement. [ABSTRACT FROM AUTHOR]

This paper investigates the seismic performance of thin-walled stiffened steel square box columns, modeling bridge piers subjected to unidirectional cyclic lateral loading with a constant axial load, focusing on local, global, and local-global interactive buckling phenomena. Initially, the finite element model was validated against existing experimental results. The study further explored the degradation in strength and ductility of both thin-walled and compact columns under cyclic loading. Thin-walled, stiffened steel square box columns exhibited buckling near the base, forming a half-sine wave shape. The research also addresses discrepancies from different material models used to analyze steel tubular bridge piers. Analysis using a modified two-surface plasticity model (2SM) yielded results closer to experimental data than a multi-linear kinematic hardening model, particularly for compact sections. The 2SM, which accounts for cycling within the yield plateau and strain hardening regime, demonstrated enhanced accuracy over the multi-linear kinematic hardening model. Additionally, a parametric study was conducted to assess the impact of key design parameters—such as width-to-thickness ratio (Rf), column slenderness ratio (λ), and magnitude of axial load (P/Py)—on the performance of thin-walled stiffened steel square box columns. Design equations were then developed to predict the strength and ductility of bridge piers. These equations closely matched experimental results, achieving an accuracy of 95% for ultimate strength and 97% for ductility. [ABSTRACT FROM AUTHOR]

Cast‐in‐suit stairs and precast stairs were damaged seriously during many earthquakes in recent years. Stairs with new sliding support were put forward in order to avoid the failure of stairs, landing slab in the half floor was divided into two parts and sliding support was placed between stair beam and landing slab. Down‐scaled model of stairs with new sliding support was produced, and reversed cyclic loading test was conducted to investigate the failure mode, hysteretic behavior, ductility, stiffness degradation and energy dissipation. The failure mode was crushing damage of frame column and stair components remained intact. The new sliding support had good working properties and landing slab separated from stair beam under the pull condition. In addition, seven finite element models of staircase were developed to investigate the seismic performance of staircase, and seven finite element models of frame structure were developed to investigate the effect of stairs on the seismic performance of main structure. Lateral stiffness of the staircase was asymmetrical affected by common stairs, so torsional deformation of staircase was large, and stairs with new sliding support had no effect to the lateral stiffness of staircase. Compared with frame structure, the natural period of vibration decreased approximately by 5% and the first vibration mode also changed direction when common stairs was considered, the natural period of vibration and the first vibration mode were not change when sliding support was adopted. Stairs were not damaged and did not affect the seismic performance of main structure when new sliding support was used. [ABSTRACT FROM AUTHOR]

The effect of cyclic loading is an essential factor leading to progressive soil strength degradation. Therefore, a comprehensive analysis of the pile‐soil system behavior under cyclic loading is required to ensure the stability of pile group. There is room for improvement in the inherent constraint of the conventional numerical model in terms of approximating the soil resistance distribution along the pile by point loads at element nodes, necessitating a specific element that integrates considerations of pile group effect and cyclic loading within a unified framework. This study aims to develop a newly specific type of element for efficiently predicting nonlinear behavior within the pile‐soil system, addressing simulations involving nonlinear pile‐soil interaction, pile group effect, and cyclic loading. Modified element formulations based on soil stiffness matrices and soil resistance vectors specifically address pile group effect and consider parameters that influence pile behavior under cyclic lateral loading. The numerical solution procedure with Newton‐Raphson iteration allows the calculation of pile responses in geometric and material nonlinear analyses. The validation of the proposed method includes several examples, comparing it with existing numerical solutions and experimental tests of single piles and pile groups under cyclic loading. These comparisons further support the consistency of the proposed method with measured data and validate its accuracy in considering group effect and cyclic loading. The parametric study illustrates the ability of the proposed method to capture cyclic loading parameters while considering the influence of the number and magnitude of load cycles, the cyclic load direction, and the installation methods. [ABSTRACT FROM AUTHOR]

The soft soil foundations of gravity wharves are subject to the wharf weight and wave forces, and the deterioration of the wharf soil foundation strength under such cyclic loading affects the structural safety of gravity wharves. This study investigated the weakening characteristics of soft soil strength. Undrained triaxial tests were conducted on undisturbed saturated soft soil specimens under isotropic consolidation conditions, and a dynamic finite element model of the wave-gravity-structure-soft-soil-foundation interaction was established. The results indicated that the shear modulus of the soil was related to the effective confining pressure and shear strain; this relationship was fitted using the Van Genuchten equation. As the internal friction angle of the soft-soil foundation decreased, its stability decreased nonlinearly, the strength decreased, and the sliding failure surface expanded. Simply increasing the riprap layer thickness had a limited effect on the overall wharf stability. These findings will guide the design of gravity wharves with foundations on soft soils in port areas that are subjected to intense wave actions. [ABSTRACT FROM AUTHOR]

In order to study the deformation and damage characteristics of the limestone specimens with high strength and brittleness under constant amplitude cyclic loading, the deformation and the acoustic emission (AE) characteristics were analysed, and the relationship between them was sought. The damage variables under different amplitude cyclic loading were defined by AE counts. The results showed that the radial deformation of the limestone specimens was more sensitive and unstable than the axial deformation. The concept of apparent residual strain was proposed to describe the specimen deformation characteristics, and it resulted that the radial apparent residual strain produced at higher stress state would recover at lower stress state. The limestone specimens showed obvious Kaiser effect and Felicity effect under cyclic loading. When the upper limit of the cyclic loading was close to the peak stress of the specimen, the AE counts generated in unloading sections were almost the same as that in the loading sections. The damage was increased as the amplitude and the stress level increased and the unloading process at higher stress level would also lead to the aggravation of damages. Specimens would absorb more energy under cyclic loading than under uniaxial loading. Reasonable driving parameters should be controlled in underground excavation practice, to ensure that the stress level of surrounding rock mass in a periodic stress state is located before peak stress and such that to limit the occurrence of rock burst to a certain extent. [ABSTRACT FROM AUTHOR]

During the cyclic injection and extraction process in underground storage wellbores, the cement sheath undergoes loading and unloading stress cycles. In this study, we investigated the mechanical properties of latex-modified cement stone (LMCS), widely used in oil and gas wells, through uniaxial and triaxial cyclic loading and unloading tests. The aim of the study was to determine the effect of various loading conditions on the compressive strength and stress–strain behavior of LMCS. The results show that the stress–strain curve of LMCS exhibits a hysteresis loop phenomenon, with the loop intervals decreasing throughout the entire cyclic loading and unloading process. As the number of cycles increases, the cumulative plastic strain of the LMCS increases approximately linearly. Under uniaxial cyclic loading and unloading conditions, the elastic modulus tends to stabilize. However, under triaxial conditions, the elastic modulus increases continuously as the number of cycles increases. This result provides data for engineering predictions. Furthermore, a comparison of the uniaxial and triaxial cyclic loading and unloading of LMCS shows that its cumulative plastic strain develops rapidly under uniaxial conditions, while the elastic modulus is larger under triaxial conditions. These findings provide a valuable reference for constructing underground storage wellbores. [ABSTRACT FROM AUTHOR]

The accuracy of the constitutive model affects the precision of the finite element analysis. Four advanced sand constitutive models—the DM04 model, the SANISAND-MS model with memory surface (MS), the SANISAND-Sf model with semi-fluidized state (Sf), and the SANISAND-MSf model with both memory surface and semi-fluidized state—are examined in this article based on a comparison of simulation and experiment results of element tests. First, four constitutive models are implemented in OpenSees, and the constitutive models are calibrated based on the cyclic loading experiments of Karlsruhe fine sand. After that, the advantages and disadvantages of four constitutive models under different test conditions are analyzed. Finally, the finite element model of the LEAP-UCD-2017 (Liquefaction Experiments and Analysis Project, University of California Davis, 2017) centrifuge test is established to evaluate the performance of the four constitutive models for solving boundary value problems. It is found that the SANISAND-MSf model can well reproduce the undrained cyclic properties. [ABSTRACT FROM AUTHOR]

Shaft-surface friction pairs in marine equipment endure considerable wear and corrosion in seawater, particularly under cyclic loading. A friction and wear test bench was employed to replicate the conditions faced by ship stern shafts and bearings in seawater. The study aimed to assess the tribological performance of three types of polyphenylene sulfide (PPS) materials: pure PPS, PPS reinforced with 30% glass fiber (30% GF in PPS matrix), and PPS reinforced with 30% carbon fiber (30% CF in PPS matrix), against 316L stainless steel under varied lubrication conditions. Results demonstrate that all PPS variants exhibit minimal friction force and wear loss in seawater, with 30% CF in the PPS matrix displaying the least friction and wear characteristics. Friction force fluctuates within a 2.5 ~ 5 N range, and wear loss is 0.027 g. However, due to the uneven bonding of glass fiber (GF) within the PPS matrix, the addition of GF did not significantly enhance the materials’ anti-friction properties and wear resistance. The predominant wear mechanism involves severe three-body abrasive wear caused by GF detachment from the friction pairs surface. Additionally, the study explores carbon fiber’s resilience to cyclic loading, the lubricating effect of seawater mixed with carbon fiber debris, and the transfer mechanism of polymer films. These findings highlight synergistic anti-friction and wear-resisting effects between carbon fiber, seawater, and polymer transfer films, offering valuable insights for selecting effective shaft friction pairs materials in challenging seawater conditions. [ABSTRACT FROM AUTHOR]

To date, the traffic-induced dynamic behavior of geosynthetic-encased stone column-supported embankments (GESC) under traffic cyclic loads accompanied by embankment consolidation has not been well studied. Three-dimensional (3D) coupled mechanical and hydraulic modeling is performed using FLAC3D, which considers the fluid flow during the lifespan of three stages: (1) embankment construction (EC): (2) consolidation (C) under embankment surcharge; and (3) cyclic loading (CYC). During the simulation, excess pore pressure, stress concentration, settlement, and lateral displacement are monitored, and the total settlement and lateral displacement could be easily obtained by accumulating the components of the three stages. Parametric analyses are conducted on the reinforcement forms and cyclic loading characteristics that include the dynamic stress amplitude and loading frequency. The ordinary stone (OSC) and GESCs could reduce the settlement and lateral displacement during each stage by improving the strength of the foundation and accelerating drainage consolidation; however, GESCs outperform the columns without geoencasement. In addition, the stress concentration ratio under embankment filling decreased with the increase in the dynamic stress amplitude and loading frequency, which led to the increase in the percentage of the cyclic loading-induced settlement to total settlement. [ABSTRACT FROM AUTHOR]

This study investigates the fatigue behavior of cold-finished mild steel subjected to electrochemical hydrogen charging under controlled conditions. Samples were subjected to hydrogen charging at constant time in a fixed electrolyte pH, after which the samples underwent fatigue testing under constant loading condition with fixed frequency. The primary objective was to assess the impact of varying hydrogen permeation levels on the number of cycles to failure. The experimental results revealed a complex relationship between hydrogen concentration and fatigue life. Initially, as hydrogen permeation increased, the number of cycles to failure substantially decreased, demonstrating the detrimental effect of diffused hydrogen on the fatigue resistance of samples. This decline in fatigue life was attributed to hydrogen embrittlement (HE) and hydrogen-enhanced decohesion (HEDE) phenomena, which collectively facilitate crack initiation and propagation. However, at high hydrogen concentrations, an unexpected increase in the number of cycles to failure was observed suggesting the existence of a threshold hydrogen concentration beyond which the fatigue mechanisms may be altered, potentially due to a saturation of hydrogen-related defects and mechanisms such as hydrogen-enhanced localized plasticity (HELP). The discovery from this research has significant implications for the material's application in hydrogen-rich environments, such as those encountered in the energy and transportation industries. [ABSTRACT FROM AUTHOR]

Vertically loaded anchors (VLAs) are widely used as mooring foundations in marine environments. Their working conditions typically involve deep-sea seabed, frequently subjected to cyclic loads induced by wind, waves, and currents. Therefore, understanding the mechanical properties of VLAs under cyclic loading is essential for ensuring the safety of mooring systems. This paper summarizes the current research status on the mechanical properties of VLAs under cyclic loading, analyzing the mechanisms by which cyclic loads affect these properties. Additionally, it reviews and summarizes the research methods applied to studying VLAs under cyclic loading, discussing the issues inherent in various methodologies. Finally, it provides an outlook on future research into VLAs under cyclic loading, laying the groundwork for subsequent studies on the bearing mechanisms of novel VLAs, such as the double-plate vertically loaded anchor (DVLA), under cyclic loading. [ABSTRACT FROM AUTHOR]