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The deterioration of the US transportation highway network and the onset of new technologies in the freight industry are expected to cause changes in the axle load magnitude and distribution, further exacerbating the reduction in the service life of flexible pavements. In this study, a reviewed framework to incorporate roughness-induced dynamic wheel loading into tire–pavement contact stress prediction is presented. The response to nonfree-rolling conditions, usually overlooked, was considered. State-of-the-art numerical models were used to account for pavement unevenness, vehicle dynamics, and 3D and nonuniform contact stresses. In this framework, for a given target international roughness index, an artificial multitrack roughness profile was converted into a dynamic loading profile based on the mechanical properties of a Class 9 vehicle. Upon discretization of the dynamic loading profile into a finite number of loads based on percentile distributions, a 3D finite element model of a dual-tire assembly was used to predict the contact stress distribution over a rigid surface. The performed numerical simulations allowed us to analytically quantify the variation of vertical and in-plane contact stress distribution. Hence, changes in the stress/strain field distribution and peak values under various axle loading scenarios were determined. The findings reveal that disregarding the effect of road roughness and vehicle maneuvering could result in considerable underestimation of the net forces and contact stress distribution developed at the tire–pavement interface. These considerations are particularly impactful on in-plane contact stresses, which, in turn, are associated with near-surface distresses. Practical Applications: The distribution of contact stresses at the tire–pavement interface influences the likelihood of failure near the surface and is greatly affected by driving behavior (braking, cornering, and acceleration). Truck electrification is likely to modify driving behavior due to the instant torque availability provided by electric powertrains, and the incorporation of battery packs is likely to alter the distribution of axle loading. The impact of these variables on the applied load to a pavement system could be further exacerbated by road conditions. In that regard, this paper aims to quantify the changes in the contact stress distribution when roughness, driving behavior, and axle loading are compounded. Because these considerations are not taken into account by current pavement analysis procedures, pavement engineers can use the results to assess the importance of each parameter on load characterization, a controlling variable on the prediction of pavement responses. [ABSTRACT FROM AUTHOR]

Hanging sleepers, which result from the differential settlement of the ballast layer, are a prevalent issue that leads to the rapid degradation of track components that include the ballast, sleeper, fastener, and rail. A novel type of sleeper, the wedge-shaped self-leveling sleeper (WSS), was proposed as a solution to the hanging sleeper problem. The WSS leverages the train's dynamic loading and the gravity of the ballast to naturally allow the ballast particles to fill the gap between the ballast and the sleeper. This paper focuses on the dynamic performance of the WSS from different aspects, which include wedge angles (30°, 45°, and 60°), sleeper materials (concrete and plastic), and the number of WSS to replace regular sleepers in the transition zone. A series of numerical modeling [which coupled multibody simulation (MBS) and discrete-element methods (DEM)] were conducted to design, optimize, and test the WSS. The results reveal that a concrete WSS is well-suited to address the problem of hanging sleepers in transition zones. The WSS with a 45° angle demonstrated superior performance compared with other types of WSS. Importantly, the WSS could reduce vibrations in the vehicle and track, even when dealing with hanging sleepers. Due to the self-leveling function, the WSS shows significant promise for applications in transition zones, which could reduce the frequent need for track geometry maintenance. [ABSTRACT FROM AUTHOR]

Mechanically stabilized earth (MSE) retaining walls have been successfully implemented in numerous applications, particularly where dynamic loads such as earthquake and traffic loading are prevalent. However, using MSE walls as foundations for high-speed train track systems remains uncertain, and their performance under high-speed train loading is inconclusive. This paper extensively investigates the behavior of MSE walls under various high-speed train loading conditions, addressing key considerations, challenges, and findings. The study focuses on evaluating wall performance in terms of horizontal displacement, settlement behind the facing, tensile load and displacement of reinforcement elements, and wall amplification characteristics. The performance of the wall is also assessed by examining the influence of the cement asphalt mortar layer. The total axle load and loading duration are identified as critical design parameters for high-speed train loading, and an empirical equation is developed to estimate horizontal wall displacement based on these parameters. [ABSTRACT FROM AUTHOR]

Accurate prediction of the dynamic response of a structure is crucial for its system identification, reliability analysis, and health monitoring. However, uncertainties in physics-based models and parameters may cause a significant discrepancy between predictions and actual responses. The neural network–augmented physics (NNAP) model aims to address this issue by augmenting physics-based models with deep-learning models trained by real data. While promising, such an approach has yet to be applied to large multi-degree-of-freedom (MDOF) structures under response-dependent forces. This paper presents a novel method incorporating modal truncation into the NNAP model for more accurate prediction of the dynamic responses of nonlinear MDOF systems. The proposed NNAP-m uses modal truncation to describe a physics-based model by lower-dimension coordinates and augments it with a neural network representing phenomena with more significant epistemic uncertainties. This hybrid modeling approach relies on information about mode shapes and natural frequencies to improve prediction capability. The proposed method is successfully verified using a numerical example of the Lysefjord bridge structure exhibiting nonlinear behaviors, including the interaction between wind loads and dynamic responses. The proposed approach is expected to provide accurate response predictions of real-world structures using measurement data and to promote the development of physics-based deep-learning approaches for complex structures with large DOFs. [ABSTRACT FROM AUTHOR]

This paper presents the results of a laboratory investigation into the response of stone column–improved soft clay under dynamic traffic load conditions. Six reduced-scale model tests were performed with vertical traffic load composed of three consecutive stages: initial static load, cyclic load, and postcyclic load. The principal parameters were comprehensively investigated, such as loading frequency (1, 3, and 5 Hz), bearing stratum, and reinforcement conditions. The results show that dynamic settlement of a floating geosynthetic-encased stone column (F-ESC) increases rapidly with the increase in the time of cyclic loading at high loading frequency (5 Hz), accounting for 36.8% of total settlement. The geogrid encasement showed great benefits to the settlement improvement of stone columns under traffic loading. High-frequency traffic load generally decreased the bearing capacity and load transfer efficiency of F-ESC. Excess pore-water pressure (EPWP) is sensitive to the load frequency, and the value in F-ESC under the 5 Hz cyclic load is 1,420.5% larger than that under 1 Hz cyclic load. Rapid increase and accumulation of EPWP may cause significant foundation settlement at high loading frequency. The end-bearing geosynthetic-encased stone column shows a high strain increment ratio (up to 96.2%) under cyclic loads, which should be duly considered in the selection and design of reinforcement materials. [ABSTRACT FROM AUTHOR]

The structural integrity of steel trusses and I-beams is of vital importance for preventing the potential collapse of steel bridges when subjected to extraordinary forces. Thus, identifying damage to I-beams, which cannot be noticed in typical inspections, based on their measured response, would enable early damage detection, and would trigger the necessary mitigation measures to restore the structural integrity of the bridge. This investigation built a vast database of structurally damaged cantilever I-beams, in which openings of various degrees and locations were placed along the beams to emulate reductions in stiffness. Both damaged and undamaged I-beams were modeled using Abaqus software, facilitated by Python scripting. Three deep-learning algorithms were trained, validated and tested with the healthy and damaged I-beam cases: long short-term memory (LSTM), a LSTM-based autoencoder, and multivariate time-series transformers (MTTs), for which the input data consisted of acceleration responses recorded at specific points on the top flange of both undamaged and damaged I-beams subjected to harmonic dynamic loads. To enhance adaptation for field monitoring data, random normal noise was introduced into the acceleration responses before running the machine learning (ML) damage identification algorithms. The three algorithms demonstrated exceptional ability to accurately distinguish between the damaged and the undamaged I-beams. Furthermore, the location of the damage on the beam was identified by the LSTM and MTT algorithms, which had the best accuracy for damage localization. Finally, a comparative analysis of the three algorithms was conducted to clarify the optimal quantity of data points required to attain reliable results. [ABSTRACT FROM AUTHOR]

Wide-base tires (WBTs) have been gradually adopted for trucks to improve fuel economy and driving comfort. This study aims to investigate the impact of WBTs on flexible pavement responses as compared to dual tires (DTs) coupling the effects of multiaxle and dynamic loading. A semi-analytical finite element model (SAFEM) was developed to simulate pavement responses under dynamic moving loads with high efficiency and good accuracy. The model was validated by comparing simulation results with field measurements from the instrumented section in the Long-Term Pavement Performance (LTPP) database. The influence of tire type, axle configuration, and pavement roughness was analyzed in terms of four critical pavement responses: longitudinal tensile strain at the bottom of asphalt layer, transverse tensile strain on pavement surface, near-surface shear strain, and compressive strain at the top of subgrade. The analysis results show that pavement responses induced by dynamic loads conform to normal distribution, and the variation of pavement responses increases linearly with that of dynamic loads. WBTs cause greater pavement damage than DTs in general. Among four pavement distresses, the highest damage ratio is observed for top-down cracking and the least one is for near-surface rutting. The damage ratios vary with axle configuration or speed rather than pavement surface roughness, especially for top-down cracking. The study emphasizes the impact of pavement roughness, tire type, and axle configuration on pavement responses. [ABSTRACT FROM AUTHOR]

This article provides a comprehensive state-of-the-art review of research on bridge deck fatigue under moving wheel loads and compares it to conventional fixed-point pulsating load fatigue. An overview and a brief history of the evolution of this test method from around the world are provided. The effect of key parameters on fatigue life and performance under moving loads are discussed, including loading magnitude and stress ratio, loading footprint, boundary conditions, loading eccentricity, loading frequency, dynamic effect and impact, reinforcement layout, slab thickness, crack control, concrete strength, and environmental exposure conditions. The fatigue accumulation rule and the incremental step (staircase) rolling load method are discussed. Cracking and failure mechanisms in slabs under rolling loads are presented and compared. It is clearly demonstrated that fixed-point pulsating fatigue loads inadequately simulate fatigue damage, stiffness degradation, and cracking patterns induced by rolling loads. For example, one rolling load cycle is shown to be equivalent to 80–1,800 pulsating load cycles. Varying the magnitude of the rolling load (dynamic effect) further reduces the fatigue life. Decreasing the spacing of the transverse rebar and compression reinforcement both can increase susceptibility to crack initiation, potentially reducing fatigue life. Environmental factors, particularly moisture intrusion, drastically reduced fatigue life. A conversion factor of stiffness degradation from pulsating to equivalent rolling load fatigue is proposed. Finally, recommendations for future work in this field are proposed. [ABSTRACT FROM AUTHOR]

Seismic retrofitting of existing bridges has been in practice for years to meet the stringent seismic requirements set forward by revised design codes. For retrofitting, however, bridge piers are often prioritized while less attention is given to the bridge foundations, which are equally prone to damage under seismic loadings. The current work presents a series of experimental studies in assessing the performance of 2 × 2 pile groups reinforced with micropiles in terms of head-level stiffness and damping under low-to-high levels of static and dynamic loadings, encompassing the influence of loading-induced soil nonlinearity. Practical micropiles inclinations of 0°, 5°, and 10° with respect to the vertical are studied. Experimental results reveal that the head-level stiffnesses of pile groups reinforced with micropiles, contrary to the general expectations, become smaller than the pile group without micropiles at higher levels of applied loading. To elucidate the governing mechanism for such experimentally obtained results, three-dimensional nonlinear finite-element analyses were carried out. Results from the numerical analyses support the experimental results, suggesting that the presence of micropiles may not always increase the head-level stiffness of soil–foundation systems, particularly at higher levels of applied loading where the soil nonlinearity generated at the vicinity of piles and micropiles governs the overall head-level stiffnesses. [ABSTRACT FROM AUTHOR]

The utilization of a mechanically stabilized earth wall (MSE wall) is prevalent due to its stability and cost-effectiveness compared to conventional earthwork construction methods. In addition, the railway transportation infrastructure has played a vital role in connecting Thailand's numerous regions. The behavior of a 6-m-high MSE wall constructed on a hard ground foundation, which was reinforced with high-density polyethylene on one side and a metallic strip on the other side, was studied in this research. The purpose of this MSE wall is to support the railway structure under dynamic train loads at 100, 150, and 200 km/h. The three-dimensional finite-element method was used to simulate and investigate the behavior of the MSE wall in terms of lateral displacement, settlement, and strain of reinforcement materials. The findings of the study demonstrate that there is a positive correlation between train speed and both lateral displacement and settlement. This relationship is most pronounced at the top of the MSE wall, which is primarily attributable to the influence of surface waves. The MSE wall's behavior under the influence of dynamic train loads was most prominently displayed by the surface waves, which were a curved wavefront at 150 km/h and a Mach cone at 200 km/h. The settlement profile increased when the speed of dynamic train loads increased. The impact of velocity fluctuations on the strain of the reinforcement material was insignificant. Due to the hard ground foundation, the behavior of the MSE wall on both types of reinforcement materials exhibited similar tendencies. Moreover, it was observed that the maximum tension lines closely follow the bilinear coherent gravity method with a standard distance of 0.3H from the facing, where H represents the equivalent height of the MSE wall. [ABSTRACT FROM AUTHOR]

The vehicle dynamic load can greatly affect the service life of pavement. To study the vehicle dynamic load accurately and conveniently under different pavement characteristics and driving conditions, a multibody dynamics method was employed to establish a three-dimensional (3D) vehicle dynamics simulation model of a six-axle heavy vehicle (the most typical heavy vehicle on an expressway). Experimental tests of vehicle component parameters and axle spindle loads were performed to provide simulation parameters and to validate this vehicle dynamics model, respectively. The validation results showed that the accuracy and robustness of the dynamics model were satisfactory. Based on the validated model, the effects of International Roughness Index (IRI) and vehicle speed on the dynamic load coefficient (DLC) were explored. The DLC increased by about 80% when the speed or IRI changed from 30 km/h or 1.184 m/km to 70 km/h or 3.551 m/km , respectively. To better evaluate the effect of dynamic load, the relationship between the DLC of the vehicle and the vehicle speed and IRI is proposed according to simulation results. This relation equation can quickly and accurately study the DLC of this heavy vehicle under different IRI pavements and driving speeds. Because the vehicle dynamics model is convenient for studying the dynamic load under different conditions, this method is recommended in vehicle–pavement coupled analysis. [ABSTRACT FROM AUTHOR]

Concrete is obviously affected by the loading strain rate, and concrete exists in the state of shear multiaxial stress in practical engineering. Studying the dynamic response of concrete under multiaxial shear states facilitates comprehensive analysis of its actual failure behavior under complex loading conditions, thereby establishing an experimental foundation for precisely formulating dynamic constitutive models of concrete. Therefore, in this study, five axial compression ratios (0, 0.138, 0.207, 0.276, and 0.414 fc) and four strain rates (10−5/s , 10−4/s , 10−3/s , and 10−2/s) were considered. A servohydraulic machine for compression and shear was applied to conduct experimental research on the shear multiaxial dynamic mechanical properties of concrete. Different failure patterns and shear mechanical characteristic values of concrete under different loading conditions were obtained from the experiments. The following conclusions were mainly drawn through comparative analysis: as the axial compression ratio increases, oblique cracks are gradually formed in the parallel shear direction of the concrete, accompanied by a small amount of concrete spalling. The strain rate parameter has no significant influence on the apparent failure pattern of concrete in the parallel shear direction; moreover, as the axial compression ratio increases, the ranges of increase in shear stress and residual stress for concrete under different strain rates are 357.02% to 291.65%. The increase of strain rate gradually leads to a decreasing trend of shear stress for concrete under the influence of the axial compression ratio; as the strain rate increases, the range of increase in shear stress for concrete under different axial compression ratios is 21.08% to 33.81%. Overall, the increase of axial compression ratio leads to a decreasing trend of shear stress for concrete under the influence of strain rate. Based on the compression-shear relation and the principal stress space, the combined dynamic failure criterion of plain concrete is proposed by considering the effect of strain rate, and the corresponding stress mechanism is analyzed. The research results are of great significance to the development and application of concrete engineering. [ABSTRACT FROM AUTHOR]

Structural systems are vulnerable to dynamic loading and need special protection while facing extreme conditions. This study proposes an integrated structural control and health monitoring (ISCHM) system to enhance the safety and performance of building structures subjected to seismic loading. The system encompasses a semiactive controller based on reinforcement learning (RL) as well as a real-time damage identification (RTDI) system for structural health monitoring. The controller uses Deep Q -Networks (DQNs) to operate a semiactive control device and suppress the dynamic vibrations. The DQN controller was integrated with the RTDI system proposed in the preliminary phase of the project. The damage information provided by the RTDI was used to train the DQN controller and optimize the control policy in different damage conditions. The performance of the ISCHM system was evaluated through the numerical example of a building structure with variable viscous dampers installed between adjacent floors. OpenAI Gym and Keras were used to create a custom environment, define the DQN agent, simulate the interaction between the agent and environment, and train the agent while exploring the environment. The smart structure equipped with the ISCHM system was subjected to earthquake loading and the performance was compared with conventional semiactive control alternatives including skyhook and Lyapunov controllers. The results show the effectiveness of the proposed ISCHM system especially in the presence of damage. The ISCHM system can enhance the episode score by up to 58%. [ABSTRACT FROM AUTHOR]

The tall building design process typically goes through a time-consuming iterative procedure to ensure the cost efficiency of the proposed structural system, especially in the conceptual design stage where the layout is designed. Despite that, this procedure does not guarantee to yield an optimal layout. Consequently, an automated layout optimization procedure will result in a more economical and sustainable design. This paper presents a novel multiobjective lateral load resisting system (LLRS) (i.e., shear walls) layout optimization framework provided for dynamically sensitive tall buildings subjected to a wind load time history. The developed framework relies on an artificial neural network (ANN) surrogate model for constraints and objective function evaluation to reduce the computational time of the optimization process. The adopted surrogate model is built based on an automated finite element models-generated database using MATLAB code via the Open Application Program Interface of the ETABS software. The ANN surrogate model proved its efficiency in capturing complex variations in the structural response with a correlation coefficient that ranges between 90% and 98%. A nongradient optimization algorithm (NSGA-II) is adopted to identify the optimal shear wall layout to resist the applied dynamic wind load. In order to reduce the number of optimal layout solutions on the Pareto front, a pruning algorithm is used to limit the optimal solutions to 24 layouts. This will enable designers to use the direct selection method to choose an appropriate layout that fits the project's objectives. Also, a case study building is presented where the optimized results are analyzed and discussed in the numerical example to verify the effectiveness of the proposed optimization framework. [ABSTRACT FROM AUTHOR]

Due to the unique conditions of the Wudong subvertical coal seam, damage to the underground roadway occurs frequently during the coal mining process. With the increase in mining depth, the energy and incidence of microseismic events increase significantly, showing characteristics of zoning and grading along the strike. Therefore, the damage to the underground roadway of the Wudong coal seam was studied with a focus on dynamic load disturbance. The results showed that the underground roadway damage exhibits asymmetric characteristics, with significant sinking on the north shoulder and various degrees of bulging on both sides of the roadway. The existing support scheme in the mine could not effectively control the deformation and damage to the rock surrounding the underground roadway under the action of dynamic loads. Therefore, the asymmetric support scheme with the high prestressed anchoring long and short anchor cable network was proposed to provide targeted reinforcement for the underground roadway, which has been shown to effectively mitigate the deformation of the surrounding rock. Eventually, considering the characteristics of microseismic event distribution and the observed increase in the rock damage with the increase of the seismic source energy, a segmented and asymmetric support scheme was suggested to tactically support the underground roadway. The findings of this study could potentially improve the ground safety of underground roadways under similar mining conditions. [ABSTRACT FROM AUTHOR]

The dynamic behaviors of subgrade soil are usually investigated by use of continuous loading mode in most studies; however, the dynamic loading induced by traffic loading is composed of cyclic loading and intermittent periods. Moreover, the existence of cyclic deviator stress, cyclic confining pressure, and shear stress has been already observed in the stress field induced by traffic loading. Recognizing this, intermittent cyclic loading was applied to saturated soft clay for this study. The impacts of cyclic deviator stress, cyclic confining pressure, and drained condition during intermittent periods on the deformation behaviors of soft soil were analyzed. The variations in strain increment were similar in all cases: as the number of loading stages increased, the strain increment decreased, and the difference in strain increment was more significant in the first loading stage although it could be ignored in subsequent loading stages. Furthermore, the strain increment increased with increasing cyclic stress ratio (CSR) and decreased with increasing cyclic confining pressure. Moreover, the dissipation of excess pore-water pressure induced during the cyclic loading period resulted in the increase of accumulated axial strain under intermittent partially drained conditions, while the recovery of specimen deformation during intermittent period led to the decreasing of accumulated axial strain under undrained conditions. In addition, an empirical formula of accumulated axial strain under intermittent cyclic loading was established, and the calculated results were consistent with the measured data. [ABSTRACT FROM AUTHOR]

The adverse effects of the frequent reservoir earthquakes (REs) and the severe degradation of the hydrofluctuation belt (HFB) on the long-term stability of bedding bank slope since the Three Gorges Reservoir Area (TGRA) impoundment were considered fully in this paper. Under such complex conditions, the dynamic response pattern and instability mechanism of typical bank slopes were investigated systematically by using a method of combining field survey, laboratory shaking table (ST) model test, and Universal Distinct Element Code (UDEC) numerical exploration. The research shows that the degradation forms of the HFB of typical bank slopes in the key field survey of the TGRA can be arranged into four types: erosion (denudation), corrosion (suffosion), avalanche (collapse), and slip (flow). The dynamic response of slope shows obvious characteristics of "surface effect" and "elevation effect," and the cumulative displacement (CD), damping ratio (DR) and natural frequency (NF) of slopes show a trend of gradually increasing, and increasing and decreasing, respectively. Meanwhile, the "S–type" cubic function and "Steep rise type" exponential function can be used to characterize the cumulative damage degree (CDG) of slope at the excitation stages of microseisms—small seisms and strong seisms, respectively. Subsequently, the dynamic evolvement process for cumulative damage and unstable failure of slope considering the impact of degradation of rock mass in the HFB was obtained, and there are good agreement between the model test and numerical exploration results. Furthermore, fully considering the influence of slope height (SH), slope angle (SA), thickness of bedding plane (TBP), dip angle of bedding plane (DABP), dynamic load amplitude (DLA), dynamic load frequency (DLF), height of water level of the HFB (HWHB), degradation range of the HFB (DRHB), and degradation shape of the HFB (DSHB), the CD of slope subjected to continuous excitation of multiple seismic loads increases in the form of exponential function, the dynamic stability coefficient (DSC) of slope decreases slowly first and then drops sharply, and the response degree of slope deformation and sliding velocity is obviously different. Especially, the sensitivity level of every preceding factor to the dynamic stability of slope based on the orthogonal analysis method (OAM) is in the order of DLA > DRHB > SA > SH > DLF > HWHB > DSHB > DABP > TBP. [ABSTRACT FROM AUTHOR]

Red clay is commonly used as filler for roadbed or subgrade, but it always leads to engineering problems of uneven settlement and strength decay under cyclic dynamic loading because of its engineering characteristics such as high water content, high plasticity, and poor compaction. It is essential to assess the dynamic characteristics of undamaged red clay in the small-strain range, but few relevant researches are reported. In this study, the small-strain dynamic property of undisturbed red clay from Guiyang, Southwest China, was investigated. Multistage dynamic triaxial shear tests were performed to analyze the development of the skeleton curve (σd–ɛd), the maximum dynamic modulus of elasticity, the maximum dynamic shear modulus, and the maximum dynamic damping ratio in the small-strain range of undisturbed red clay with different confining pressures, consolidation stress ratios, loading frequencies, and water content ratios. Moreover, under the small-strain conditions, the small-strain dynamic deformation mechanism of the specimens with isobaric consolidation and anisotropic consolidation was analyzed. In addition, some empirical prediction models for the dynamic constitutive relationship, dynamic elastic modulus, and dynamic damping ratio of undisturbed red clay under small-strain range test conditions were proposed. Results indicate that the skeleton curve of undisturbed red clay showed softening behavior when the dynamic axial strain ɛd > 1.0%, the center of the hysteresis curve, shifted positively along the coordinate axis with the increasing confining pressure and the loading number. The undisturbed specimens exhibited mainly two types of deformation under small-strain test conditions, including axial compression deformation when the consolidation ratio Kc was 1.0 and bulging deformation when the Kc was 1.5 and 2.0. The proposed models could be used to predict the skeleton curve, dynamic elastic modulus, and dynamic damping ratio of the undisturbed red clay in the small-strain range. [ABSTRACT FROM AUTHOR]

Bond failure is a crucial element in ascertaining the failure mechanisms of reinforced concrete (RC) structures. The investigation pertaining to the dynamic loading's impact on bond efficacy remains a lacuna within scholarly discourse. Therefore, 138 eccentric pull-out half-beam specimens have been fabricated to probe the intricate degradation mechanisms underlying the bond-slip phenomena between concrete and reinforcement when subjected to high-temperature transients. Initially, a series of experiments were conducted on half-beam specimens possessing different reinforcement diameters and embedded lengths. Subsequently, the transient temperature changes within the bond segment were recorded, and this was pursued by the execution of eccentric pull-out tests. Second, the bond stress-strain curves under transient temperature were measured. The experimental findings revealed that the bond strength peaked at 101°C and showed an upward trend up to 302°C. Beyond this temperature, however, the bond strength exhibited a decline. Specifically, at a target temperature of 400°C, the bond strength increased by 18.1% and 9.3% compared to values at 20°C and 200°C, respectively. In contrast, it decreased by 23.2% and 41.3% in comparison to values at 600°C and 800°C. Additionally, as the reinforcement diameter increased, there was a decrease in bond strength, while the ultimate failure force increased. Finally, a methodology for evaluating bond strength under dynamic temperature was introduced, and a semiempirical constitutive model was formulated, taking into account the interplay between different heating rates. The constitutive model underwent validation through temperature computations, proposing a bending moment calculated methods, thus affirming its accuracy under fluctuating temperature scenarios. [ABSTRACT FROM AUTHOR]

Analytical approaches to determine the long-term settlement of shallow foundations subjected to dynamic cyclic loading with a large number of cycles (millions) are presented. The approaches use the high-cycle accumulation (HCA) model to calculate the permanent strain caused by the cyclic loading and are conceptionally similar to conventional settlement analyses. The incorporation of a threshold strain amplitude, below which no accumulation of deformations occurs, in the HCA model is discussed. It is demonstrated that the simple analytical approach, which does not require numerical calculations, gives results very similar to more complex finite-element simulations. [ABSTRACT FROM AUTHOR]

Understanding fundamental track behaviors under dynamic load conditions is important to optimize design practices and achieve high-quality track performance. The American Railway Engineering and Maintenance-of-Way Association provides recommended practices to estimate trackbed pressures, which are primarily based on the Talbot equations. The Talbot methodology for computing crosstie-ballast (CT-B) interfacial pressures may "not" be valid for modern railroad design due to several factors, including the sensitivity of pressure measuring equipment, the presence of uneven support conditions, and the implementation of jointed rails in testing different wheel loadings, which contributed to overestimation of pressure readings as a result of impact loading. However, modern railroad infrastructure has been designed with a smooth track layout and well-supported rails as well as incorporating rolling stock equipped with smooth wheels, particularly in high-speed train operations. This study proposes a new approach to estimate the pressures at the CT-B interface, which was developed using measured in-track CT-B interfacial pressures taken from an active mainline. The data from the in-track measurements were filtered by using a signal processing tool and analyzed to develop basic equations to predict interfacial pressures as a function of basic train characteristics, including train speed, wheel loads, and wheel spacing, assuming no impact loading from wheel defects. To validate the efficacy of the square wave theory, the predicted pressures were compared with the data obtained from in-track tests. Further, a method to estimate dynamic pressures of a moving train at the CT-B interface was developed using square wave theory. By representing the vehicles of a train as a periodic square waveform, the dynamic CT-B interfacial pressures can be predicted for an unlimited number of locomotives and cars for smooth track geometry, smooth wheels, limited rail surface roughness, and well-supported track. [ABSTRACT FROM AUTHOR]

In this paper, results of a flow visualization study on the flow around a square cylinder with corner chamfering are presented. The corners of the test cylinders were chamfered with each corner forming a triangle with chamfer dimension b. Experiments were conducted for b/Bo ratios of 0.05, 0.1, 0.2, and 0.3 where Bo is the side dimension of the uncut square cylinder. The flow structures, particularly the vortex shedding mode and mechanism around the uncut as well as chamfered square cylinders, were investigated in order to deduce the effect of corner modification. All the studies were conducted at a Reynolds number value of 2,100 (based on Bo) on both stationary and oscillating cylinders. For oscillating cases, a special mechanism was built to oscillate the cylinders (forced oscillation) at desired amplitudes and frequencies. Results indicates that corner chamfering brings notable changes in the near-wake flow structures of a square section cylinder both in stationary and oscillating conditions. In view of aerospace structures with similar geometries, the present results carry considerable practical significance. Many engineering structures carry square section geometry, such as buildings, bridge pylons, and so on, and are subjected to fluid flows. Flow around them can induce certain static and dynamic loads on these structures due to which eventually, they can fail if not designed properly. Flow-induced loads majorly depend on the body geometry. For square section cylinders (structures), corner shape is found to be a crucial factor that decides the nature of the flow field developed over them. This is because a properly designed corner shape can significantly bring down hydrodynamic/aerodynamic loads imposed on structures, ensuring structural safety. In this study, the corners of a square section cylinder are chamfered, and influence of this corner shape is studied through flow visualization. Flow visualization enables qualitative (mainly) as well as quantitative analysis of the flow field developed on the cylinder with different degrees of corner chamfering. This study brings out the effectiveness of corner chamfering in influencing the flow around a square cylinder, which represents an engineering structure in real world scenarios. [ABSTRACT FROM AUTHOR]

Seamless expansion joints for small- and medium-span bridges attract engineers due to their acknowledged integrity (durability), driving comfort and noise attenuation. Traditional asphalt plugin joints are easy and cheap to install, but they are hindered by premature failures frequently observed in situ. Comparatively, polyurethane (PU) possesses good durability and toughness and excellent chemical resistance, etc. The purpose of this study is to identify the proper PU material and devise a new seamless expansion joint. As such, the mechanical properties of three PU materials were tested, including initial setting time, tensile strength, rupture strain, hardness, wheel rutting, adhesion to pavement, water absorption, and aging. The appropriate mass ratio was identified to be polyol/isocyanate = 100/105. Subsequently, monotonic tensile/compressive, vertical loading and low-cycle fatigue tests were performed on the four full-scale expansion joints. It revealed that the rate-dependent behavior rendered the PU material suitable for seamless joints, as it was softer to accommodate the low-rate longitudinal deformation and was stiffer to sustain the high-rate vehicle loadings. Furthermore, the inclined angle between the PU and pavement would ameliorate the strain status and is recommended for practical use. Experimental and numerical results were synthesized into a proposed alternative polyurethane-based design that reduces the vertical displacement and circumvents the possible early failures under the effect of dynamic traffic loading. [ABSTRACT FROM AUTHOR]

This paper presents a new discretize-then-optimize (DTO) method for dynamic force inversion in a two-dimensional (2D) linear elastic, damped solid based on Runge–Kutta (RK) explicit time integration. Previous literature on DTO modeling for force or material inversion has predominantly focused on inversion methods based on Newmark implicit time integration. However, because implicit time integration may not be suitable for a problem with a large number of degrees of freedom [e.g., third-dimensional (3D) wave problems], there is a need to study an alternative DTO force-inversion formulation that centers around the RK explicit time integration, leveraged by a diagonal mass matrix. This paper attempts to fill this gap and present the full detail of the new RK-DTO formulation for dynamic force inversion. Our computational examples demonstrate that the new RK-DTO inversion simulator effectively reconstructs moving dynamic forces on the upper surface of the solid. It excels in efficiency when dealing with a higher number of degrees of freedom (DOFs) and maintains accuracy even with increased DOFs and observation durations. A smaller sensor spacing enhances the accuracy of the inverted force profile in the RK-based inversion. The presented inversion method can effectively identify the profiles of dynamic moving loads even when measurement data include noise or when the values of material properties are not deterministic. [ABSTRACT FROM AUTHOR]

Pile foundations supporting high-rise buildings are generally subject to cyclic loading because of dynamic loading. The corrosion of steel materials in pile foundations is another major concern, especially for piles in a marine environment. In this study, a series of cyclic and static loading tests on model piles made of fiber-reinforced polymer (FRP) and seawater–sea sand concrete (SSC) and ended in a rock socket were reported. Three structural configurations (FRP tube–confined, FRP rebar cage–reinforced, and centered FRP rebar–reinforced) were adopted for the model piles. Strain along the depth of the piles was measured using fiber Bragg grating (FBG) optic sensors and an advanced distributed optical sensing technique known as optical frequency domain reflectometry (OFDR). Strain distribution, axial cyclic stiffness, and shaft friction mobilization of the piles under static and different modes of axial cyclic loading were analyzed and explored in detail. The test results indicated that the FRP tube–confined model pile showed higher confinement and cyclic capacity and lower stiffness degradation, leading to relatively more stable behavior. A high level of cyclic loading can cause microcracks to form and grow within the pile material, thereby decreasing pile stiffness. The strain profile of all the piles along the depth appeared to follow a similar trend, and fluctuations at certain points led to failure. Cyclic stiffness showed gains initially when cyclic load conditions were below a certain threshold level but degraded when loading was increased beyond it. Moreover, shaft resistance gradually increased with cycles, causing higher mobilization in the upper portion of the socket. The experimental results have provided the first systematic study on the performance of the FRP-SSC composite model piles ended in rock sockets under axial cyclic and static loadings. This will contribute to development of a potential predictive method for pile settlement and capacity for the better design of rock-socketed piles. [ABSTRACT FROM AUTHOR]

Active mass dampers (AMDs) have been used to suppress vibration of structures subjected to dynamic loading. Generally, controller design of AMD requires an identified numerical model of the structure. However, unmodeled dynamics and system uncertainties could lead to mediocre control performance. In this study, a novel controller synthesis method of AMD named direct excitation with machine learning (DEML) is proposed and verified. In DEML, the AMD on top of the structure generates trivial excitation with sufficient bandwidth. Then the corresponding structural acceleration response is collected and used for training a controller formulated in an artificial neural network. Accordingly, the associated controller can be realized and implemented to generate control force from the structural acceleration response directly. Seismic control performance of the controller synthesized by DEML was verified numerically in which 9-story and 27-story building models were considered. Moreover, shake table testing of an AMD on top of a 3-story structural specimen was conducted to further validate the effectiveness of the proposed DEML. Experimental results demonstrate that the controller synthesized by DEML achieves competitive seismic control performance compared with a conventional linear-quadratic Gaussian controller. [ABSTRACT FROM AUTHOR]

This study comprehensively describes the viscoelastic behavior of high-elasticity modified asphalt mixtures under varying strain conditions. The commonly used sigmoidal model, which relies on a single parameter (dynamic modulus) to depict viscoelastic behavior, has limitations. In this research, by utilizing the dynamic modulus master curve and the Kramers–Kronig relationship, master curve models developed for the phase angle, storage modulus, and loss modulus enable a more comprehensive understanding of the materials' viscoelastic response functions. Dynamic modulus tests were conducted on the high-elasticity modified asphalt mixtures using the simple performance tester (SPT) at various temperatures (5°C, 15°C, 25°C, 40°C, and 55°C) and frequencies (0.1, 0.5, 1, 5, 10, 20, and 25 Hz). The results indicate that the master curves of the phase angle, storage modulus, and loss modulus, established using the dynamic modulus master curve and Kramers–Kronig relationship, are well-fitted, demonstrating that the method feasibly can be used to draw the master curves for each viscoelastic parameter. Additionally, mathematical models based on the Kramers–Kronig relationship were developed to explain the correlations among parameters under dynamic loading conditions, and the accuracy of the master curve models for various parameters was validated. This deeper insight into material responses under varying loading conditions and temperatures can help researchers better model and predict the mechanical performance of pavements. [ABSTRACT FROM AUTHOR]

In this study, the fractal characteristics and energy dissipation behavior of gas-bearing coal are explored under both dynamic and static loads. Multifactor coupling mechanical tests are conducted using visualized static and dynamic loading experiment systems. The effects of impact velocity, axial compressive stress ratio, and initial gas pressure on energy dissipation and fragmentation characteristics of gas-bearing coal are analyzed. An internal correlation between the debris fractal and the energy dissipation density is clarified considering the fact that debris distribution has prominent fractal characteristics in the log–logarithmic coordinates. It is discovered that the fractal dimension experiences exponential growth with the strain rate in the impact velocity group, while showing that it rises linearly in the gas pressure group. There exists a critical axial compressive stress ratio that causes the formation of the debris fractal segment in the axial compressive stress ratio group. The debris fractal dimension change with the energy dissipation density is divided into two stages, and it is found that the dissipated energy value and its ratio decrease with the rise of initial gas pressure; debris fractal exhibits a quadratic decreasing relationship to the density of energy dissipation. Furthermore, by considering the dimension of the strain rate, the relationship of the aforementioned three indicators are uniformly quantified and compared. The research results reinforce the fundamentals of gas-bearing coal dynamics and provide a theoretical reference for further research on gas composite dynamic disasters in mines. [ABSTRACT FROM AUTHOR]

The bonding performance between a thin overlay and the pavement is an important basis for good performance of asphalt pavement. To research the effect of interlayer bonding on the fatigue life of thin overlays, three-point bending fatigue test was carried out on the double-layer beams with interlayer (DLBI). The equivalent fatigue life obtained by the Weibull distribution function was used to analyze the influence of stress ratio, loading frequency, immersion times, and freeze–thaw cycles on the fatigue life. The results suggest that the fatigue performance of DLBI was affected significantly by stress ratio, loading frequency, immersion times, and freeze–thaw cycles. The higher the loading frequency, the greater the effect of the stress ratio on the fatigue performance of the DLBI. The lower the stress ratio, the greater the effect of the loading frequency on fatigue performance of the DLBI. The fatigue life of the DLBI declined by 31.4% and 24.7% after 6 immersion days and five freeze–thaw cycles, respectively. The damage to DLBI caused by one freeze–thaw cycle was equivalent to that caused by 4 days of immersion. Models that take into account four kinds of environment factors to equivalent fatigue life prediction based on 50% failure probability and 5% failure probability, respectively, are proposed, with the equivalent fatigue life method. Taking the equivalent fatigue life as the indicator, the DLBI crack length expansion model is obtained, and the axle load conversion coefficients considering the influence of dynamic loads and adverse seasons factors are calculated. A method is proposed to judge the fracture of double-layer beams. [ABSTRACT FROM AUTHOR]

This paper reports the influence of delay time on the index and engineering properties of geopolymer-, cement-, and lime-treated expansive soil. Locally available expansive soil was treated with different doses of slag-based geopolymer, cement, and lime. The index and engineering properties like Atterberg's limits, free swell index, grain-size distribution, compaction properties, and unconfined compressive strength (UCS) were evaluated at delay periods of 0, 6, 12, 24, 48, 72, and 168 h. Further, the mineralogical characteristics and microstructure of the stabilized materials were examined using X-ray diffraction (XRD) and scanning electron microscopic (SEM) images. It was observed that with an increase in delay time, the plasticity and swelling characteristics of the treated soil reduced with improvement in the soil grain size along with the formation of hydration and geopolymeric compounds. The delay in compaction results in the decline of the compacted density and UCS. The formation of hydrated products and flocs during the delay period caused loose packing under dynamic loading and affects the mechanical properties. A significant improvement in plasticity and engineering properties of the expansive soil was observed with geopolymer stabilizers. Thus, it is noteworthy to consider geopolymers as a new generation eco-friendly stabilizer for treating expansive clays for geotechnical constructions. [ABSTRACT FROM AUTHOR]

Pier columns, as primary bridge supports, are vulnerable to extreme loading demands resulting from fire, vehicle collisions, and blasts. The combined effects of these demands may cause significant strength reduction, extensive damage, and potentially collapse. Although the response of bridge columns subjected to independent or combined vehicle impact and air blast has been widely investigated, the cumulative effects of fire in conjunction with these dynamic loads have received limited attention. Consequently, this study presents a unique and advanced multistep finite-element modeling approach using LS-DYNA to simulate the response of isolated round reinforced concrete bridge columns subjected to fire prior to and after a vehicle collision and subsequent air blast. The developed modeling approach incorporates uncoupled implicit heat transfer analyses and explicit structural analyses and was validated against published fire, impact, and blast test results. A parametric study that investigated the effects of various column diameters and fire exposure scenarios on performance was completed, considering fire occurring before or after impact and blast. Column performance was assessed based on damage levels, residual load capacities, and lateral displacements. Study findings enhance the understanding of bridge column performance under this combination of hazards, provide insight into improving bridge resiliency, and could potentially have practical implications for the design and maintenance of bridge columns. Specifically, the study reveals that fire prior to impact and blast was a more critical load sequence for larger column diameters that could potentially remain in service in their final damage states while being repaired. Moreover, the study indicated that for the same fire duration and column diameters, residual capacities and displacements corresponding to half-surface-area exposure were slightly lower than those exposed to fire on the full surface area, a finding that could be beneficial in many practical applications where protective techniques and tools could be implemented. [ABSTRACT FROM AUTHOR]

Rerounding is a technique for remediating excess deflection in thermoplastic pipe. A pneumatic device vibrates along the vertical axis and pushes against the inside crown and invert to restore the original pipe shape and redistribute the surrounding backfill. A systematic evaluation of the method was justified because rerounding is routinely used by contractors to remediate deflected thermoplastic pipes, and it has not been investigated outside of a few previous reports. Three 900-mm and two 450-mm corrugated high-density polyethylene (HDPE) pipes were installed in various bedding and backfill materials. Test pipes were intentionally installed with substantial deflection (10% or more) and then rerounded. The pipe conditions were measured and monitored by collecting profiles, measuring vertical deflections, and monitoring soil pressure, soil stiffness, backfill characteristics, and pipe corrugation depth before and after rerounding. The data from the deflection, soil stiffness, corrugation, and soil pressure monitoring confirmed the following: (1) during rerounding, soil particles migrated and soil pressure was redistributed; fine material from the crown and springline moved down toward the haunch area, at least in the well-graded aggregate backfill; (2) it is difficult to successfully reduce deflection in corrugated HDPE pipes in well-graded aggregate backfill; (3) installing the pipes with excess deflection proved a significant challenge, as all the pipes required much effort to reach sufficient deflection. It proved necessary to create a device to hold the pipe in a deflected state during backfilling; (4) rerounding successfully reduces deflections for pipes in sand backfill; and (5) test pipes backfilled with Ohio Department of Transportation (ODOT) Type-3 backfill were easy to reround, but a change in environmental conditions and/or dynamic loading may create a change in the stress path leading to excessive deflection and reversal of the effects of rerounding. [ABSTRACT FROM AUTHOR]

This paper explores the utilization of the excess capacity of monopiles supporting offshore wind turbines (OWTs) by deploying hybrid and colocated wave and current marine energy concepts. However, there is a lack of guidance in literature and standards relating to the evaluation of natural frequency and foundation damping for monopile-supported wind turbines in shared anchoring configurations. The work presented here represents one of the first studies quantifying the dynamic characteristics of simulated colocated and hybrid energy systems sharing the anchoring capacity of OWT monopiles. A 3D finite-elements numerical model is developed and used to perform dynamic simulations of the OWT monopile. The hybrid system is modeled as a marine hydrokinetic device represented by an annulus plate installed around the monopile perimeter, providing additional mass participating in system damping and vibration while inducing additional loading due to drag forces on its perimeter. For a colocated system, tension forces from the mooring lines of a wave hydrokinetic device are first computed by ANSYS-AQWA then these forces are applied to the monopile in the 3D numerical model. The dynamic analyses are first performed to calibrate the numerical model parameters using data from three existing OWT projects (i.e., Burbo Bank, Walney 1, and Gunfleet Sands). Results from a parametric study varying diameter and length of the monopile, demonstrated the effect of the added mass in the hybrid configuration, as well as the influence of the tension forces of the mooring lines in the colocated configuration on the natural frequency and foundation damping. Results indicate that the simulated hybrid and colocated systems do not alter the natural frequency of the system; however, the foundation damping of the hybrid system is approximately 1.5 to 2 times higher than that of the monopile supporting only the wind turbine tower. Results also demonstrated the minimum obtained natural frequency (f1,dmin) for a combination of diameter, length, and relative densities (i.e., DP = 5 m, LP = 38 m, and DR = 25%–100%) is higher than the minimum frequency of the dynamic loading caused by the passing blades (f3P,min = 0.25 Hz) while the maximum obtained natural frequency (f1,dmax) is lower than the maximum frequency of the 3P dynamic load (f3P,max = 0.65 Hz). As such, for the cases analyzed herein, f1,d falls within the frequency range of the 3P dynamic load, and the system operates in-between the two frequency zones of soft–stiff and stiff–stiff. To ensure operational natural frequency within the soft–stiff zone in these cases, reducing the dimensions of the tower would be necessary. [ABSTRACT FROM AUTHOR]

Double-beam systems have found many applications in civil and mechanical engineering. Extensive works of research have been conducted on the investigation of double-beam systems in which some have studied the vibration characteristics of general double-beam systems without considering the effect of axial load, whereas others investigated the vibration and buckling of axially loaded double-beam systems with classical boundary conditions. A few previous studies have considered a general axially loaded double-beam system, but none of them have provided a general solution to calculate the critical buckling load of the system with arbitrary boundary conditions. In the present study, free vibration and buckling of an axially loaded double-beam system, which was composed of two nonidentical beams with generalized boundary conditions, were analytically studied by using the Euler–Bernoulli beam theory. A semianalytical method was proposed to calculate the natural frequencies and mode shapes of the system, and an explicit formula was derived to determine the critical buckling load of the system. Parametric investigations were performed to study the influences of the connecting stiffness of the interlayer and axial loads on the dynamic characteristics and critical buckling load of the system. Results show that the proposed method can be used for free vibration and buckling analyses of generalized double-beam systems subjected to axial loads. [ABSTRACT FROM AUTHOR]

The uncertainties related to the inherent properties of pavement subgrade subjected to the dynamic effect of vehicular and earthquake loading were studied extensively using probabilistic analysis. The dynamic effect of the loading on pavement was modeled using lower bound shakedown analysis. Pavement subgrade was considered to be purely cohesive and was assumed to fail through the Mohr–Coulomb yield criterion. The soil spatial variability was simulated using random fields, which were represented in the form of finite-element random variables using the Karhunen–Loéve expansion method. The effect of parameter uncertainty was investigated using stochastic results such as the mean, coefficient of variation, and failure probability of the structure using the Monte Carlo simulation technique. The effect of dynamic loading of vehicles was studied by varying the period of vehicular movement. The dynamic shakedown was analyzed using two different methods. Seismic waves were generated using modified pseudodynamic approach. The combined effect of moving vehicles and earthquake was studied to determine the worst-case scenario. It was found that the generation of seismic waves affects the direction and frequency of the moving vehicle, which reduces the effect of shakedown on pavements due to vehicular load. The worst-case scenario was found to be the pavements with period ratio of 0.06 for a deterministic analysis, whereas it was 0.48 for a probabilistic analysis. [ABSTRACT FROM AUTHOR]

Pendulum tuned mass dampers (PTMDs) are one of the most commonly used devices for high-rise structures to control large-amplitude vibrations due to dynamic excitations. In practice, the damper of PTMD usually connects the tuned mass to the location below the top floor rather than to the top floor, which is different from the case using a conventional tuned mass damper (TMD). Therefore, the classical optimal parametric formulas derived from the structure-conventional TMD model are not applicable to design the optimal parameters of PTMDs. In this paper, the simplified mechanical model of the structure-PTMD system is updated to consider the damper connection in practice. The fixed-points theory is employed to analytically derive the optimum design formulas for the PTMD by introducing the effect of modal shape. Moreover, the control effectiveness of the PTMD using the proposed method is studied. The control performance and robustness of the PTMD designed by the proposed method are compared to those designed by the classical optimum formulas under various dynamic loads. Finally, with the help of the performance degradation index (PDI), the control performance degradation of PTMD designed by classical formulas is quantified. The results show that the proposed optimal parameters have considerable differences from classical formulas. Through designing a PTMD on a multi-degree-of-freedom (MDOF) structure, the proposed optimum design is demonstrated to be more effective and robust than the classical formulas. To design a large mass ratio PTMD, the control performance degradation from the damper connection in practice is significant and should be seriously considered. [ABSTRACT FROM AUTHOR]

Evaluation of pavement deflection bowl using nondestructive testing (NDT) is an ideal method for assessing the structural capacity of individual layers of a pavement system. However, the cost of modern NDT equipment and the complexity involved in the back-calculation process makes it difficult for the road agencies to back-calculate individual layer properties and evaluate the in situ condition of existing pavements. This study developed low-cost equipment (LCE) for evaluating the pavement deflection bowl under static loading conditions and to correlate the results with the deflection bowl observed under dynamic loading on same pavement combinations. The study also analyzed the deflection bowl parameters through an understanding of the load distribution evaluated using linear elastic software. The moduli of the individual pavement layer were back-calculated using back-calculation software and correlated with the deflection bowl parameters. The study concluded that the deflection bowl under dynamic loading was only 0.65–0.75 times that of the deflection bowl under static loading. The difference of deflection measured at radial distances of 0 and 450 mm of the deflection bowl correlated well with the base-layer modulus, and the difference of deflection measured at radial distances of 300 and 600 mm correlated well with the subbase-layer modulus. Based on the deflection bowl data collected from nine test sections, it was found that emulsion-treated base layers exhibited 40%–60% higher moduli values than the conventional base layers during the monsoon season. Low-volume roads with dense surface mixes 30 mm thick exhibited significantly improved structural performance compared with that of low-volume roads with open-graded surface mixes 20 mm thick with a 6-mm seal coat. [ABSTRACT FROM AUTHOR]

Concrete and steel are typical rate-dependent materials. Therefore, the dynamic behavior of reinforced concrete (RC) members is inevitably affected by the loading rate. To study the effect of the loading rate on the behavior of RC beam–column joints (BCJs), a dynamic test was carried out on RC BCJs. Cyclic loading with various loading rates was applied to the column end of RC BCJs to simulate horizontal earthquake excitation. The final crack morphology and the first principal stress contour plots of BCJs indicate that dynamic loading can promote the shear effect in the core region of RC BCJs. The lower the shear span ratio is, the higher the loading rate and the more obvious the effect. Experimental results show that the yield strength and ultimate strength of BCJs are approximately linear with the logarithm of the loading rate. There is no obvious effect of the loading rate on the yield, ultimate, and failure displacements of the BCJ, but the shear angle of the core region is approximately linear with the logarithm of the loading rate. In addition, the effects of the loading rate on the stiffness degradation, ductility, and energy dissipation capacity are studied. [ABSTRACT FROM AUTHOR]

The perceived and observed differences in the dynamic behavior between wheeled and tracked military vehicles should be considered when applying appropriate dynamic load effect values for bridge design and assessment. Based on available test data, tracked military vehicles appear to impose less severe dynamic load effects when compared with wheeled vehicles under similar crossing conditions. In exploring a range of crossing conditions, a review of test data was used to make a general comparison of the dynamic loading amplification between tracked and wheeled military vehicles. To expand the range of crossing conditions tested for an instrumented bridge, additional data were collected for an artificially induced roughness of the bridge surface. By combining the test results from previous studies with the results from this testing program, the relative dynamic loading amplification between tracked and wheeled military vehicles can be quantified for situations with similar crossing conditions. Given this comparison, it may be appropriate to use a dynamic load allowance (DLA) of as low as 70% of the code-specified DLA for wheeled vehicles when evaluating the capacity of bridges subjected to military tracked traffic. This is especially relevant when considering maneuver options for main battle tanks during military combat operations. [ABSTRACT FROM AUTHOR]

The identification of two-dimension distributed dynamic loads using partial structural responses is still challenging. In this paper, a method is proposed to identify the gradually varying spatial distribution functions and the time histories of time-space decoupled two-dimension distributed dynamic loads using partial structural responses. First, due to the properties of good decorrelation and energy compression by discrete cosine transform (DCT), two-dimension DCT is used to expand the spatial distribution functions with fewer coefficients than those by other transform such as discrete wavelet transform (DWT) in previous identification approaches. Under given DCT coefficients, the load time histories and structural responses are identified by the Kalman filter with unknown input (KF-UI). Then, the DCT coefficients are evaluated based on minimizing the errors between the estimated and measured structural responses. Finally, the spatial distribution function is reconstructed by the inverse two-dimension DCT with the estimated optimal DCT coefficients, and the load time history is identified by KF-UI accordingly. The novelty of the proposed method is that fewer DCT coefficients are involved to expand the gradually varying two spatial dimensions, which simplifies the difficulty of estimating many coefficients using partial structural responses. Numerical examples of identifying different dynamic loads verify the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

In aerospace load simulation loading systems, due to the coupling between the loading system and the system under testing, surplus forces and poor loading accuracies remain to be key issues. To solve this, this paper introduces a new intelligent dynamic force loading algorithm. First, based on the mechanical geometry and fluid theory of the system, a nonlinear mathematical model that can describe the system more accurately is established. By combining the mechanical structure and mathematical model of the system, it is found that the surplus force caused by external disturbances has the greatest impact on the force loading accuracy. The causes of the surplus force are then analyzed and the solutions provided. To improve the force loading performance and eliminate excess force on the controller, an intelligent dynamic force loading algorithm is proposed. This new control algorithm ensures that the surplus force caused by an external disturbance can be suppressed to within the required range in a short time as well as improve the controller performance and dynamic force loading accuracy of the system. Finally, the algorithm is applied to an aerospace air rudder load simulator and its performance is compared with the three other classical control algorithms. The results show that the proposed intelligent control algorithm can attain better accuracy in dynamic force loadings and can attain a control accuracy that meets technical requirements. The load simulator and digital controller involved in this paper are applied in a Chinese Aerospace Research Institute. The load simulator is currently used for testing and product acceptance of the institute's servo products. Because the control algorithm proposed in this paper meets the requirements of technical indicators and product performance testing requirements, it has been recognized by the institute and has been put into practical use. The technical experts of the institute have verified the experimental results and believe that its control accuracy and loading performance are better than those of the original old load simulator. [ABSTRACT FROM AUTHOR]

The performance of a structure is primarily determined by its material characteristics under different loading conditions, strain rates, and temperatures. In the present work, the plastic flow response of a homogenized AT61 magnesium alloy was constitutively analyzed under a wide variety of quasi-static and dynamic strain rates. The quasi-compression test was conducted at 25°C–250°C with strain rates from 10−4 to 10−1 s−1. The dynamic loading of AT61 alloy was performed on a split Hopkinson pressure bar (SHPB) apparatus under a strain rate of 1,000–4,000 s−1. The material shows hardening behavior throughout the strain rate regime, whereas the plastic flow stress significantly reduces with an increase in deformation temperature. At a very high strain rate, the accumulated energy around the cracks is attributed to the dynamic recrystallisation with the onset of adiabatic temperature rises in the materials. A phenomenological Johnson-Cook (JC) model was also calibrated and used for numerical simulation in ABAQUS/Explicit to predict the material flow response. It was observed that a strong correlation exists between experimental and numerical results. [ABSTRACT FROM AUTHOR]

The document is a closure to a study on the performance of geogrid-reinforced rubber-coated ballast and natural ballast mix under direct shear conditions. It addresses concerns and suggestions raised by discussers regarding residual friction angle, stress-dilatancy behavior, and the correlation between particle breakage and peak friction angles. The writers clarify the use of crumb rubber from scrap tires and present empirical relationships for peak and residual friction angles. They also evaluate stress-dilatancy behavior and correlations between peak friction angles and particle breakage. The document does not address the effects of dynamic loading, environmental impacts of polyurethane binder, or end-of-life scenarios for rubber-coated ballast, as these were beyond the original paper's scope. [Extracted from the article]

This article discusses the performance of geogrid-reinforced rubber-coated ballast and natural ballast mix under direct shear conditions. The study evaluates the abrasion, impact, and weathering resistance of rubber-coated ballast compared to natural ballast. The authors highlight the omission of residual friction angle data and recommend its inclusion for a more comprehensive analysis. Additionally, the article suggests addressing the impacts of dynamic loads and environmental considerations related to using recycled rubber in the coating process. [Extracted from the article]

Traditional soil mechanics idealizes geomaterials as being in a dry or fully water-saturated state. However, there is a zone between the ground surface and the groundwater table, where the soil is unsaturated, which means the pore space is filled with air and water. This zone is affected by environmental changes during wetting and drying seasons through precipitation, evaporation, or evapotranspiration. The influence of water content, for instance, the degree of saturation, on the characteristics of soil under dynamic loading i.e. at small to intermediate strains, for example, small-strain shear modulus (Gmax), modulus degradation [G(γ)], and damping ratio [D(γ)] remain of interest in the geotechnical community due to the practical relevance of the problem. This study attempted to cover the existing gaps in the dynamic characteristics of soil with different degrees of saturation. Therefore, Hostun sand (HS) was mixed with 30% Amberger kaolin (AK) and compacted to Proctor density at the optimum water content. They were saturated in a special saturation cell applying back pressure. Then, the saturated samples were dried to different degrees of saturation. Resonant column (RC) tests were carried out on the prepared samples to determine the effect of the degree of saturation on Gmax, G(γ), and D(γ). Of note, in this series of tests, suction was not strictly controlled; however, the necessary volume change corrections were performed via various noncontact transducers. To describe the experimental observations and to evaluate the impact of the degree of saturation on Gmax, G(γ), and D(γ), the soil water characteristic curve (SWCC) of the adopted mixture was determined. The results showed a significant increase of Gmax with the degree of saturation following an S-phaped curve. Based on the new data, previous models to predict Gmax were inspected under a significantly wider range of the degrees of saturation and suction. In addition, the effect of the degree of saturation on the intermediate strain characteristics of the adopted mixture [G(γ)/Gmax] and D(γ) was evaluated, where modulus degradation was found almost unaffected by Sr while a moderate increase of damping ratio with Sr was observed. [ABSTRACT FROM AUTHOR]

Current evaluation of bumps at bridge approaches is limited in scope and performance, and varies in practice at different state DOTs. This study intends to propose a general criterion specifically for bridge approach bump classification and develop a formula for dynamic load allowance (IM) estimation for bridges in Oklahoma. A total of 98 bridges in Oklahoma were studied using recently developed sub-mm 3D laser imaging technology that simultaneously collected inertial profiles, sub-mm 2D/3D images, and right-of-way images at highway speeds for roughness and distress analysis. A three-level criterion that evaluates maximum roughness within an approach or departure slab is established to classify approach bumps into Good, Fair, and Poor conditions. The threshold defined in the criterion considers both the field crew's sensation during data collection and the surface distresses that cause or are associated with different levels of International Roughness Index magnitudes. The development of the formula for bridge IM estimation is based on the established criteria while incorporating the influences of bumps from approach slab and bridge deck. The results of evaluating approach bump and IM of 98 bridges demonstrate the ability of using sub-mm 3D laser imaging technology to evaluate bridge approach bumps and bridge IM in an efficient and effective manner. [ABSTRACT FROM AUTHOR]

This study investigates the working mechanism and seismic behavior of the Combined Viscous-Steel Damping System (CVSDS) considering the longitudinal wave-passage effect. In the CVSDS, the operational status of the fluid viscous damper (FVD) and the steel damper (SD) can be switched by the fuse–lock device (FLD), which is triggered by the output force of the FVD. The configuration and working mechanism of CVSDS are introduced in detail. A test model is manufactured and examined by cyclic tests to verify its fusing–locking function during cyclic motions. The numerical model of CVSDS is proposed based on the experimental result. The fusing–locking behavior and seismic reduction effectiveness of CVSDS installed in a long-span bridge is analyzed, in which the wave-passage effect is considered. The results show that the fuse–lock function under dynamic loading can be achieved by the proposed FLD. The occurrence condition of the locking mechanism activation depends on the viscous damping force. The traveling wave will induce a delay of the locking time, cause large locking intervals between CVSDSs installed at different positions, and lead to a larger required moving capacity of the CVSDSs. The mitigation effectiveness of CVSDS is significantly reduced due to the wave-passage effect. [ABSTRACT FROM AUTHOR]

The design of footbridges has begun to receive more attention in recent years due to cases in which undesirable vibrations occurred. The utilization of passive energy dissipation systems to control bridge responses has become popular as a remedy for this matter. This paper proposes the use of inerters to mitigate pedestrian bridge vibrations, and explores their potential. This is done by presenting a topology and sizing optimization methodology for pedestrian bridges equipped with fluid viscous dampers and inerters. Planar truss-like bridges are examined, loaded under dynamic and static loads. All constructive elements' sizes (including dampers) serve as continuous design variables. The objective is to minimize a cost function of the bridge. The optimization process is constrained by demanding responses of interest not to exceed allowable values, along with global and local buckling. A first-order gradient-based optimization algorithm is adopted to lessen the computational effort. Lastly, a discretization postprocess is offered to lead to discrete designs of relevant design variables, such as steel cross sections. The results shed light on the advantages of combining inerters in pedestrian bridges. [ABSTRACT FROM AUTHOR]

Ground improvement (GI) techniques have shown promise in effective liquefaction mitigation, but the physical mechanisms governing their three-dimensional (3D) response during dynamic loading are not yet fully understood. To evaluate the 3D performance of one GI technique, the rammed aggregate pier (RAP), in-situ site characterization, full-scale field test data, and calibrated baseline constitutive soil model parameters are combined to model the 3D fully coupled hydromechanical response of natural (unreinforced) and improved (reinforced) soil profiles. To the authors' knowledge, this contribution represents the first 3D model of a columnar-reinforced soil profile being calibrated using full-scale field testing. The field observations from the comprehensive ground improvement testing (GIT) program in New Zealand and insights from two-dimensional (2D) finite-difference analyses using constitutive model parameters calibrated against the field measurements were used. The developed 3D models were subjected to dynamic loads simulating the excitation generated by a vibroseis truck at one of the in-situ test sites of the GIT program, as well as unidirectional and bidirectional earthquake ground motions from the Canterbury Earthquake Sequence events. The 3D simulations showed that the improved soil profiles experienced reduced excess pore pressures and reduced dynamically induced shear strains compared to the natural, unreinforced soil models. The developed 3D finite-element predictions were compared and validated vis-à-vis the field observations of the GIT program. Compared to 2D analyses, 3D analyses provide a more accurate description of actual field conditions, and, for instance, it was observed that multidirectional shaking has a significant effect on liquefaction triggering, particularly for natural soil profiles. Finally, it was shown that soil densification around the installed pier elements and the lateral earth pressure increase within the densified soil and are the primary ground improvement mechanisms contributing to the reduction of dynamically induced shear deformations and excess pore pressure generation during earthquake shaking. It was also found that the permeability and shear stiffness of the installed RAP piers did not have a significant influence on the pore pressure response and shear strains developed along the centerline of the improved area. [ABSTRACT FROM AUTHOR]

A bounding surface plasticity p − y model is used to examine the internal energy responses of a laterally loaded pile in static and dynamic simulations. The model response is first compared with those observed in physical centrifuge tests, including monotonic and cyclic loading, in a normally consolidated fine-grained soil. Then, the model is used to examine hypothetical static and dynamic situations. The monotonic load capacities determined by the model and an upper-bound limit analysis method are in agreement with that inferred from the physical test. The work done by external loads in static conditions is principally balanced by the plastic work in the p − y springs and the elastic strain energy in the structural pile elements, which are comparable in the cases examined. The numerical model is capable of reproducing accurately the observed test structural responses as well as the characteristics of plastic energy dissipation. In a dynamic free-vibration simulation, the pile is highly damped as a result of the significant plastic energy dissipation. The simple work-hardening elastic–plastic p − y model is theoretically sound, applicable to arbitrary loading histories, and requires the same level of effort to use as traditional p − y methods. An easy-to-use p − y model facilitates an efficient analysis of piles exposed to arbitrary lateral loadings. The implementation, use, and interpretation of results are familiar to engineers experienced in traditional p − y methods associated with piles founded in normally consolidated fine-grained soils. Energy balance equations demonstrate its theoretical soundness and provide insight into the accuracy of the numerical solution strategy. The calibration of the model parameters is accomplished with data available from standard site surveys and laboratory mechanical tests. Suggested typical model parameters are provided. The model is useful to those interested in computing the response of piles to loading conditions for which there are specific displacement service condition limitations. In the offshore oil production industry, typical applications would include the following: anchors to prevent pipeline walking as a result of thermal cycles, the design of conductors supporting wellhead control equipment, an evaluation of the dynamic response of riser bases exposed to dynamic environmental loads, and the design of foundation anchor piles for fixed or floating structures. [ABSTRACT FROM AUTHOR]