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Traumatic brain injury (TBI) is a significant public health burden, and the development of advanced countermeasures to mitigate and prevent these injuries during automotive, sports, and military impact events requires an understanding of the intracranial mechanisms related to TBI. In this study, the efficacy of tissue-level injury metrics for predicting TBI was evaluated using finite element reconstructions from a comprehensive, multi-species TBI database. The database consisted of human volunteer tests, laboratory-reconstructed head impacts from sports, in vivo non-human primate (NHP) tests, and in vivo pig tests. Eight tissue-level metrics related to brain tissue strain, axonal strain, and strain-rate were evaluated using survival analysis for predicting mild and severe TBI risk. The correlation between TBI risk and most of the assessed metrics were statistically significant, but when injury data was analyzed by species, the best metric was often inconclusive and limited by the small datasets. When the human and animal datasets were combined, the injury analysis was able to delineate maximum axonal strain as the best predictor of injury for all species and TBI severities, with maximum principal strain as a suitable alternative metric. The current study is the first to provide evidence to support the assumption that brain strain response between human, pig, and NHP result in similar injury outcomes through a multi-species analysis. This assumption is the biomechanical foundation for translating animal brain injury findings to humans. The findings in the study provide fundamental guidelines for developing injury criteria that would contribute towards the innovation of more effective safety countermeasures.

Railway bridges are a critical part of the railway infrastructure system and the majority of these bridges are approaching their expected design lifespan. These bridges need to be maintained effect...

In this article, a new damage indicator is presented that can detect a (partial) load path failure for a multiple load path structure, based on variable amplitude strain response measurements by fiber optic Bragg grating sensors. Many (aircraft) structures have multiple load paths where after a (partial) failure of a load path the remaining structure can carry the limit load without catastrophic failure or too severe impact on the operational characteristics of the whole structure, until the structure is repaired, replaced, or modified. The damage indicator is defined as a ratio of the strain response summation of the current strain time variation measured at fiber Bragg grating (FBG) sensors and a reference strain time variation measured at the same FBGs. For application in real structures with varying loads and environmental conditions, it should be insensitive for the load time variation as well as temperature. The FBG strain response due to a load variation can be easily computed by means of a finite element analyses. In this way, an optimal number, location and orientation of strain sensors can be derived for complex structures. A test was performed on a box-shaped structure representative of a typical aircraft structure to validate the damage indicator, showing that the damage indicator is able to detect a damaged load path at an early stage of failure with few sensors per load path. From finite element analyses, the damage size can even be determined from the damage indicator value for a known damage scenario, making it a level 3 structure health monitoring system.

The behavior of reinforced concrete (RC) deep beams strengthened with near-surface-mounted carbon fiber-reinforced polymer (NSM-CFRP) reinforcement around cutouts is examined in this study. The study comprised experimental testing, numerical simulation, and strut-and-tie modeling (STM). Three different NSM-CFRP strengthening solutions around the cutouts were developed using STM. The investigated parameters included the amount and orientation of NSM-CFRP reinforcement. The NSM-CFRP solutions fully restored the original shear strength, except in two cases where only 93 % and 94 % of the capacity were restored. Finite element (FE) models were developed to simulate the nonlinear behavior of the tested beams. The strength predicted by the FE models were insignificantly different from those measured experimentally. The nonlinear deflection response, CFRP strain response, and crack patterns predicted numerically were in good agreement with those obtained from the tests. The STM tended to provide a conservative prediction for the nominal strength of the tested beams.

Boundary layer ingestion (BLI) concepts have become a prominent topic in research and development due to their increase in fuel efficiency for aircraft. Virginia Tech has developed the StreamVane™, a secondary flow distortion generator, which can be used to efficiently test BLI and its aeromechanical effects on turbomachinery. To ensure the safety of this system, the complex vanes within StreamVanes must be further analyzed structurally and aerodynamically. In this paper, the induced strain of two common vane shapes at three different operating conditions is computationally determined. Along with these predictions, the aerodynamic damping of the vanes is calculated to predict flutter conditions at the same three operating points. To achieve this, steady computational fluid dynamics (CFD) calculations are done to acquire the aerodynamic pressure loading on the vanes. Finite element analysis (FEA) is performed to obtain the strain and modal response of the StreamVane structure. The mode shapes and steady CFD are used to initialize an unsteady CFD analysis, which acquires the aerodynamic damping results of the vanes. The testcase used for this evaluation was specifically designed to overstep the structural limits of a StreamVane, and the results provide an efficient computational method to observe flutter conditions of stationary systems.

Low-velocity impact (LVI) events in carbon fiber reinforced plastic (CFRP) structures are a major concern as they result in barely visible impact damage which can reduce the strength and stiffness of impacted structure. Detection of such impact events in terms of location and severity will be a significant milestone for aerospace structural health monitoring applications. This can result in well-targeted inspection programs thereby reducing the time and cost of periodic inspections. One of the easy and efficient ways of getting the impact response of a structure is through strain measurement. LVI event monitoring using fiber Bragg grating sensors has evolved as an attractive choice in recent years along with various soft computing algorithms and advanced signal processing techniques. Machine learning techniques such as artificial neural networks and support vector machine are widely used to localize impact events. Getting information regarding the ensuing damage due to LVI event from the strain response is not straight forward as it could involve estimation of intermediate parameters like energy/force of impact, which are further related with probable damage size. This paper demonstrates least square support vector regression-based algorithm to localize impact event in terms of $X$ - and $Y$ -coordinates and its energy on a CFRP plate-like structure and its comparison with other algorithms cited in the literature.

It is still an issue to identify the vehicle weight for bridges with multi-T-girders which is essential in bridge operation management. In this study, a vehicle weight identification method is proposed for bridges with multi-T-girders. To consider the load transverse distribution effect, first the separation variable method is adopted to separate the spatial influence surface function of vehicle load into the product of two single-valued functions. Then the procedures of the vehicle weight identification method are proposed using the measured strain responses of the T-girders caused by the passing vehicle accordingly. A numerical example of a bridge with five T-girders and an experimental example of a bridge with two T-girders are conducted to verify the feasibility and effectiveness of the proposed method. Furthermore, the performance of the proposed method is compared with the typical existing method in which the load transverse distribution effect is not considered.

Many benefits can be derived from in situ monitoring of the growth, load response, and condition of human bone. In particular, bone monitoring offers opportunity to advance understanding and designing of osseointegrated mechanical components fixated into bones such as artificial joints and more recently osseointegrated prosthetic limbs. In this study, a bio-compatible wireless inductive strain-sensing system is proposed, which is designed to monitor the growth and strain response of bone-hosting implants. Thin-film circuit fabrication methods based on lithography are adopted to develop a conformable wireless strain sensor designed as a passive resistive–inductive–capacitive circuit. Two forms of strain sensing are designed into the thin-film sensor. First, parallel-plate capacitors fabricated from metal electrodes and a polyimide dielectric layer are introduced to modulate bone strain onto a resonant frequency of the thin-film sensor. A second resonant frequency is introduced in the sensor design to measure circumferential bone growth using a highly nonlinear titanium-resistive element, whose resistance exponentially increases well after 1000 µε under monotonic increasing hoop strain. To ensure the possibility for implantation in animal subjects in future study, the thin-film sensing system is fabricated using mainly bio-compatible polymers (e.g. polyimide) and metals (e.g. titanium and gold). Fabricated prototypes inductively coupled using an impedance analyzer are experimentally tested. Results reveal linear response of the first resonant frequency to low levels of strain with a sensitivity of 4.555 Hz per unit microstrain. The second resonant frequency is sensitive to the resistive fuse with nonlinear fuse behavior initiated above 1000 µε and impedance phase increasing exponentially thereafter.

The technical feasibility of commercial gas production from microbially enhanced coalbed methane (MECBM) reservoirs can be divided into two broad categories: microbial treatment procedures and reservoir suitability. At this time, studies investigating the changes in reservoir-scale properties of coal as a result of bioconversion are lacking. This paper, first of a two-part series, presents the experimental work aimed at investigating the changes in sorption-induced strain response of coal to helium and methane flooding as a result of bioconversion. The strain and its variation, critical to producing methane after bioconversion, were established for coal treated for three periods, 15, 30 and 60 days. The results indicated a softer coal post-bioconversion which, in turn, resulted in inelastic strain with initial helium injection. However, past this initial compression, the bioconverted coal behavior was similar to untreated coal during continued helium injection/depletion. Methane flooding resulted in decreased sorption-induced shrinkage post-treatment, the decrease in Langmuir pressure and volume constants becoming larger with continued treatment. The observed results were used to understand the changes in coal structure for production of biogenic coalbed methane (BCBM) from depleted CBM reservoirs, recharged with methane using the bioconversion technology. The second part presents a detailed analysis of the experimental results to evaluate the behavior and performance of BCBM reservoirs.

In elite ice hockey, concussions occur from a variety of impact sources with different compliances, such as player-to-player collisions, impacts on the ice, boards, and glass. The effectiveness of ice hockey helmets to manage an impact under varying compliance conditions is currently unknown. The objective of this research was to determine the effect of striker compliance on ice hockey helmet performance. Striking caps of different compliance were used to impact a helmeted and unhelmeted Hybrid III headform at three locations. The headform kinematics was measured in linear and rotational acceleration, rotational velocity. The linear and rotational time histories were then used as input to a finite element model of the human brain to determine maximum principal strain response. Helmeted conditions produced significantly lower linear and rotational acceleration, and rotational velocity for the three levels of compliance at the three impact locations. The reductions through the use of a helmet were higher at low compliance in comparison to the other compliance conditions. Considering player-to-player collisions are the most common source of concussion in adult ice hockey, and also the most compliant, these data support the development of helmet technologies that can mitigate impacts under higher compliance conditions to reduce the risk of brain trauma.

Purpose To measure the ex vivo pressure-induced strain response of the human optic nerve head and analyze for variations with glaucoma diagnosis and optic nerve axon damage. Methods The posterior sclera of 16 eyes from 8 diagnosed glaucoma donors and 10 eyes from 6 donors with no history of glaucoma were inflation tested between 5 and 45 mm Hg. The optic nerve from each donor was examined for degree of axon loss. The posterior volume of the lamina cribrosa (LC) was imaged with second harmonic generation and analyzed using volume correlation to calculate LC strains between 5 and 10 and 5 and 45 mm Hg. Results Eye length and LC area were larger in eyes diagnosed with glaucoma (P ≤ 0.03). Nasal-temporal EXX and circumferential Eθθ strains were lower in the LC of diagnosed glaucoma eyes at 10 mm Hg (P ≤ 0.05) and 45 mm Hg (P ≤ 0.07). EXX was smaller in the LC of glaucoma eyes with 25% axon loss than in glaucoma eyes with milder damage (P = 0.004, 10 mm Hg). Conclusions The stiffness of the LC pressure-strain response was greater in diagnosed glaucoma eyes and varied with glaucomatous axon damage. Lower LC strains in glaucoma eyes with milder damage may represent baseline biomechanical behavior that contributes to axon loss, whereas greater LC strain and altered radial LC strain variation in glaucoma eyes with more severe damage may be caused by glaucoma-related remodeling.

A dent is a common type of defect that occurs during pipeline service. A dented region on a pipe usually creates a strong stress concentration that may become a threat to the safety and integrity of the pipeline. Therefore, such issues are major concerns for pipeline managers. To investigate the strain history behaviour of a dented steel pipeline subjected to increasing internal pressure, a full-scale experimental burst test was performed, and a nonlinear finite element method was used to compare the numerical and experimental results in this study. The paper first discusses the test specimens and test results. Then, the finite element numerical results are verified using the experimental measurement results. Subsequently, the strain behaviour at measurement points and the deformation behaviour of the test pipes were analysed in detail. Furthermore, a sensitivity analysis of strain in the axial and circumferential directions from the dent centre was performed. Deformation analysis reveal that an outward convex phenomenon occurred in axial shoulders on both sides of the dent when the Pipewall Yield Pressure reached. Test results and finite element analysis show that the strain in the dented regions changes rapidly and sharply with a large range, which can easily lead to fatigue under operation pressure for an unconstrained dent.

This paper aims to investigate the seismic behavior of blind bolted end plate composite frames between square or circular concrete filled steel tubular (CFST) columns and steel beams. Two composite frames were tested under a constant axial load on the CFST columns and a lateral cyclic load on the frame. Each specimen composed of CFST columns and steel beams was selected to represent a plan frame in an assembly building. Failure pattern of the type of frames was analyzed to comprehend the structural response. The seismic resistance ability of the blind bolted CFST frames was also estimated in terms of hysteretic curves, ductility and energy dissipation etc. The effect of column section type and end plate type on the type of semi-rigid CFST frames was studied. The test results showed that at the same steel ratio of the column section, the bearing capacity and energy dissipation of square CFST frame were higher than those of circular CFST frame at ultimate state. Strain response of main members in each CFST frame was also estimated. The internal force analysis of the test CFST frames with semi-rigid connections was discussed and evaluated the effect of the bending moment distribution. It was concluded that the novel typed CFST frames exhibited excellent seismic performance and structural internal force redistribution. The experimental studies will be useful for design and application of the blind bolted CFST frames in fabricated steel structure building.

Extending blades of wind turbine in service is the most effective method for increasing energy production. Adhesively bonding technology increases less mass and has simpler operation process, which is more suitable for extending blades in service. But unsteady aerodynamic loads on the blades due to stochastic turbulent inflow may lead to fatigue damage and even failure. This paper presented a study on strain response and fatigue life of adhesively bonded extended composite wind turbine blade suffering unsteady aerodynamic loads. Firstly, a loading method that applies periodic distributed aerodynamic loads on the blade was proposed to accurately simulate the unsteady distributed loads on the real extended blades in service. Secondly, strain response behaviors to unsteady aerodynamic loads and strain distribution behaviors in the adhesively bonded area were revealed. Finally, fatigue damage was predicted with unsteady aerodynamic load spectrums, rainflow cycle-counting algorithm, Goodman diagram and Miner's linear superposition principle. Based on the findings obtained from this study, the feasibility of adhesively bonding technology for extending blade was affirmed and a few potential future directions of study were addressed to reduce the risk of adhesively bonded structures.

A dent is a typical defect found in oil and gas pipelines and poses a significant threat to their safety and integrity. In this study, the buckling behavior and limit strain capacity of pipelines with kinked dents under bending moment loads were investigated. First, four-point bending tests of full-scale pipelines with kinked dents were conducted in a laboratory, and the critical buckling load and strain response of the pipelines during buckling failure were tested. The test results revealed that the existence of kinked dents, specifically those with large depths, could weaken the bending resistance of the pipelines. During the buckling process of the pipeline, a considerable compressive strain was generated at the bottom center of the dent, which was considerably higher than the strain value at the corresponding position of the intact pipeline. However, the strain at both axial sides of the dent gradually changed from compressive strain at the initial bending stage to tensile strain after buckling failure. Then, nonlinear finite element (FE) models of buckling failure for pipelines with kinked dents under bending moment loads were developed, and the reliability of the FE models was verified through comparison with the test results. In addition, a parametric sensitivity study was conducted to determine the effect of parameters, such as dent depth, dent angle, diameter-to-thickness ratio of the pipe, and yield ratio of the pipe steel, on the compressive strain capacity of the pipeline. Finally, based on a large number of FE simulation results, a model for predicting the buckling compressive strain capacity of pipelines with kinked dents was developed, which can be used for evaluating buckling instability failure of pipelines with kinked dents subjected to bending moment loads.

Experiments were performed in this study to investigate the influence of damage caused by low-velocity impact (LVI) and shear after impact (SAI) behavior of grid stiffened composite panels . Two positions were subsequently impacted with the same energy and the mechanical response curves were analyzed. Significant stiffener/skin debonding of specimens can be observed even if the impact points were far away from the stiffener . The SAI experiments were conducted with a comparison of shear on virgin specimens. The results demonstrated that the buckling modes of grid stiffened stiffener were the superposition of local buckling and global buckling. According to the strain response and failure modes, the delamination propagation after stiffener fracture was the trigger leading to the failure and the stress concentration near the impact point changed the failure path of skin.

Recent advances in concrete technology and construction have promoted an increasing utilization of concrete in fatigue-critical structures, such as wind turbine towers. While research into concrete fatigue is not a new topic and has been going on for several decades, a large majority of this research has primarily been focused on the determination of concrete fatigue capacity. However, understanding and advancing concrete fatigue behavior (e.g., fatigue stress vs. strain response) has received limited attention, even though this is also crucial, especially considering the inherently nonlinear behavior of concrete. To address this knowledge gap and further advance our understanding of concrete fatigue behavior, an experimental investigation consisting of uniaxial compressive fatigue testing of concrete cylinder specimens until failure was undertaken, and axial strains were recorded throughout the duration of fatigue loading. The behavior and evolution of concrete axial strains, including the rate of accumulation of strains, through the fatigue loading process were extensively analyzed and are reported. Additionally, the influence of key parameters, such as peak stress levels and number of cycles to failure, on peak strain evolution were investigated and are described. Magnitudes of peak axial strain at the end of the stable strain accumulation phase, as well as at failure, are also reported, and recommendations are made for estimating strain magnitudes at these critical junctures when conducting fatigue analysis and design. The results will help advance the understanding of concrete axial strain behavior under compressive fatigue loading. The results also provide guidelines for estimating the magnitudes of concrete strains under fatigue loads, which in turn will be beneficial to designers, as it allows them to also consider structural performance during the analysis and design of fatigue critical concrete structures.

Background: In this study, piezoelectric sensors were embedded into concrete structures to monitor dynamic response. The embedded piezoelectric sensors had sensitive frequency and linear response. Objective: In the experiment, two loading conditions were applied to the concrete cantilever beam and concrete frame. The dynamic properties could be monitored using the embedded sensors and the damage could also be identified.

The collapse mechanics and ultimate strength of a stiffened plate with pitting damage are investigated experimentally with specimens with circular shaped holes representing the pits in the plate. A series of compressive tests has been conducted to investigate the effect of pitting corrosion, including the initial imperfections. The pit location, pit diameter and pit depth are examined to determine the influence of the pitting on the ultimate strength. The experimental results of load-displacement relationship, the strain response and the ultimate strength under compressive loads are analysed. The ultimate strength reduction is related with the degree of pitting or volume loss.

This paper focuses on comparative evaluation of pavement responses and performance under accelerated loading facility (ALF), Model Mobile Load Simulator 3(MMLS 3) and Asphalt Pavement Analyzer (APA) tests, in terms of rut depth, strain response, seismic stiffness and contact stress. Test slabs extracted from the ALF test lanes were trafficked with the MMLS3 under comparable environmental conditions at a laboratory in Virginia Tech. Some small specimens were cut from the slab for APA tests at VTRC. It is found that the monitored parameters yielded by the MMLS 3 test were comparable to the related full-scale ALF test results in terms of intrinsic material characteristics and pavement performance. It is concluded that MMLS 3 is an effective, economic and reliable trafficking tool to characterise rutting and fatigue performance of pavement materials with due regard to the relative structures. The APA test is not suitable to assess the fatigue resistance of pavement material, but is an efficient and effective ...

The collapse mechanics and ultimate strength of crack damaged stiffened plates are investigated by testing stiffened plates with an initial crack. A series of stiffened plates with initial distortions and with a crack are subjected to in-plane compression until achieving their ultimate strength. The crack position, length and the angle between the crack and longitudinal stiffener are changed for determining the influence of the crack on the plate ultimate strength. The ultimate strength and the strain response of the panels are reported. Finally, the ultimate strength reduction related with the presence of the crack and the failure mode are discussed for establishing a damage tolerant procedure for the design of ship structures.

The development of all-steel tube-in-tube buckling controlled brace (TinT-BCB) is presented. The efficiency of the TinT-BCBs is evaluated experimentally and numerically. The cyclic behavior and fracture life of TinT-BCBs was first investigated through physical testing, followed by FE-based simulations revealing the inherent correlation between fracture and peak cyclic strain in load-bearing braces. The cyclic strain in plastic zones was recorded up to 0.02 strain range during the cyclic tests, enabling the study to use the recorded strain in verifying the FE simulation models. The strain response of plastic zones was captured by the FE simulation up to fracture in conventional large-size braces. The paper concludes that (1) the TinT-BCB, developed based on the buckling-controlling concept, has demonstrated stable and symmetrical cyclic response, with global and local buckling controlled up to 0.035–0.04 story drift ratio; (2) the TinT-BCB is proven to be effective in elongating cyclic fracture life of conventional CBF from 2% SDR to 3.5–4% SDR by adding simple buckling controller. The cost for adding the buckling controller is low in comparison with the substantially increased lateral strength and energy dissipation capacity; and (3) the efficiency of the TinT-BCB in improving overall cyclic behavior in general and elongating fracture life of braces in particular is attributed to its ability in controlling highly concentrated strain in plastic zones of conventional braces. By spreading the concentrated strain demand throughout the entire length, the buckling controller is shown to reduce excessive peak strains in conventional braces by 7–8 times.

This study aims to analyze the dynamic response characteristics of the serviced asphalt pavement subjected to the real random vehicle loads. Fiber Bragg Grating (FBG) sensors were embedded within four types of asphalt pavements to establish pavement structural information monitoring system. Then the spatial-temporal distribution of dynamic response were obtained by data analysis. The influences of speed, axle load and temperature on the pavement response as well as the response comparison among four types of asphalt pavements were investigated. The results show that low speed, large axle load and high temperature may cause large pavement damage. The order of strain response magnitude at the bottom of asphalt layer is: Structure II > Structure III > Structure I > Structure IV. FBG measuring technology is quite reliable and beneficial for dynamic response monitoring and performance evaluation of the asphalt pavement.

Cartilage metabolism—both the synthesis and breakdown of cartilage constituents and architecture—is influenced by its mechanical loading. Therefore, physical activity is often recommended to maintain cartilage health and to treat or slow the progression of osteoarthritis, a debilitating joint disease causing cartilage degeneration. However, the appropriate exercise frequency, intensity, and duration cannot be prescribed because direct in vivo evaluation of cartilage following exercise has not yet been performed. To address this gap in knowledge, we developed a cartilage stress test to measure the in vivo strain response of healthy human subjects’ tibial cartilage to walking exercise. We varied both walk duration and speed in a dose-dependent manner to quantify how these variables affect cartilage strain. We found a nonlinear relationship between walk duration and in vivo compressive strain, with compressive strain initially increasing with increasing duration, then leveling off with longer durations. This work provides innovative measurements of cartilage creep behavior (which has been well-documented in vitro but not in vivo) during walking. This study showed that compressive strain increased with increasing walking speed for the speeds tested in this study (0.9–2.0 m/s). Furthermore, our data provide novel measurements of the in vivo strain response of tibial cartilage to various doses of walking as a mechanical stimulus, with maximal strains of 5.0% observed after 60 minutes of walking. These data describe physiological benchmarks for healthy articular cartilage behavior during walking and provide a much-needed baseline for studies investigating the effect of exercise on cartilage health.

This study outlines the experimental investigation of the steel tube columns filled with selfcompacting concrete under axial compression. The effect of the stiffening arrangements and the concrete strength on the properties of the concrete-filled steel tube columns having stiffeners of different geometric dimensions has been investigated. The failure modes, ultimate loads, stiffness, ductility and strain response of the concrete-filled steel tube columns during the experiment have been analyzed. The results imply that the local buckling of the steel tubes can be delayed by the stiffeners. Moreover, the specimen with the four-sided stiffening arrangement possesses higher stiffness and better ductility as compared with the two-sided one. The test results also demonstrate that the proposed stiffening schemes can improve the ultimate compressive capacity. The predicted ultimate loads have been compared using the existing codes, and the modified formula has been proposed. A good agreement between the theoretical and the experimental results is observed.

The beam-column connection, called ‘Que Ti’, is the key component of historic Tibetan timber buildings to transfer shear, compression and bending loads from one structural element to another. This kind of connections can reduce the internal forces and improve the structure’s ability to resist earthquakes. Its structure is very complicated and there is little information about the behaviour of this kind of semi-rigid connections. In this paper, a temperature-based response sensitivity method is proposed to identify the connection stiffness of the ‘Que-Ti’ in typical historical Tibetan buildings from temperature and strain response measurements. The semi-rigid connection is modeled as two rotational springs and one compressive spring. The temperature is treated as a measurable input and the thermal loading on the structure can be determined from the temperature variation. The numerical results show the method is effective and reliable to identify both unknown boundary conditions and the connection stiffness of the structure accurately even with 10% noise in measurements. A long-term monitoring system has also been installed in a typical historical Tibetan building and the monitoring data are used to further verify the proposed method. The experimental results show that the identified stiffnesses by the proposed method are consistent with that by finite element model updating from ambient vibration measurements.

This study presents a simple method which can estimate displacement using measured strain response of simply supported girder b ridges. The basic concept of the present method is derived from a relation between displacement and strain, and is generalized by intro ducing analytical tool. Static and dynamic laboratory test are conducted on simply supported plate which is designed to respond dynamically similar to actual bridges to experimentally verify the present method, and displacement and strain are measured at the midpoint of specimen. Displacement es timated by using measured strain is well agreed with measured one. This study demonstrates that the present method is suitable for estimating di splacement of real simply supported bridge, in which the installation of a displacement transducer at the fixed reference point is difficult.Keywords: Simply supported girder bridge, Displacement, Displacement estimation method, Displacement-strain relationship, Strain 1 정회원 , 씨티씨주식회사 전무이사교신저자

In order to investigate the actual strain response of asphalt pavement under real condition, three types of asphalt pavement sections with typical surface structures are built. The effects of axle configuration, axle load, speed and testing temperature on strain response of asphalt pavement were analysed through in situ dynamic loading. Experimental results indicate that the strain response at the bottom of the asphalt surface layer increases with increasing axle load and temperature, but decreases with the rise of speed. On the other hand, the temperature exerts different influence levels on pavement sections with different structures. It is also concluded that the tandem axle load could lead to a greater strain response than that of single axle load. Applying the analysis of variance, the effects of pavement surface temperature, axle load, speed and their double interactions are studied as well. Finally, the paper proposes prediction models of the strain response at the bottom of asphalt layer b...

The strain sensors that are used to evaluate structural members have a limited lifespan and thus have shown limitations to perform long-term structural health monitoring (SHM). This study presents a convolutional neural network (CNN)-based strain prediction technique that allows for structural safety evaluations in case of absence or defect of strain sensors. In the proposed method, CNNs were used to establish a relationship between the dynamic structural response and the strain response measured in the structure. A number of dynamic structural responses and the structural member’s strain response that are measured before the strain sensor malfunctions are used as input data and output data, respectively, to train the CNNs. The trained CNNs can estimate the strain and evaluate the structural safety even when the later strain measurement response cannot be used. Dynamic acceleration and displacement responses are used as input data in the two CNNs presented in this study, called CNN_A and CNN_D respectively. A numerical study of a beam-like structure and an experimental study which includes shaking table tests on a reinforced concrete frame specimen were conducted to confirm the validity of the strain predictions by the proposed method with CNN_A and CNN_D. The strain prediction performance of the proposed CNNs is compared in these applications. This study also examines the proposed technique’s strain prediction performance according to the amount of data used to train the CNNs. In addition, this study discusses influences of variations in the number of locations for measuring the dynamic structural responses that are used as the CNNs’ input data on the strain prediction performance.

Tunnel anchor is a relatively new type of anchor for suspension bridges. Loading tests on a scale model in site are generally considered to be the most direct way to evaluate the bearing capacity of the tunnel anchor system. The response of the anchor body has received minimal attention and involves only a few or no measuring points, because the anchor plug does not undergo elastoplastic failure in a model test. This article intends to explore the relationship between the strain response of the anchor and the state of the surrounding rock. Optical fiber strain sensing technology based on adjustable wavelength optical time domain reflectometry (i.e., TW–COTDR) was applied to the scale model test of Baotaping Bridge tunnel anchor. The strain distribution and evolution of the entire anchor body were determined by optical measurements during overload. In the elastic and plastic stages of the anchor system, the strain around the anchor body linearly decreased from back to front, except for the top arch and the bottom plate at the end. The anchor strain–load curve was nonlinear, similar to the displacement–load curve, but unrelated to concrete damage, which signaled that plasticity began to appear in the anchor system. Therefore, the strain response of the anchor body can be used as an alternative to determine bearing capacity of the anchor system, especially when the displacement is too small to observe.

The structural fatigue damage caused by vortex-induced vibration (VIV) is one of the most important failure reasons for flexible cylinders in offshore engineering applications. Helical strakes are often employed to reduce the VIV of slender marine structures. Based on a previous experimental investigation, this paper further investigates the effects of the yaw angle on the VIV fatigue damage of a yawed flexible cylinder with or without helical strakes in a uniform flow. Four yaw angles (α= 0°, 15°, 30° and 45°) are considered. The rain-flow counting (RFC) procedure and the Miner-Palmgren hypothesis are adopted to calculate the fatigue damage of the flexible cylinder. The influence of the yaw angle on the strain response, fatigue damage distribution and maximum fatigue damage of the flexible cylinder are investigated and discussed. The fatigue damage levels in the cross-flow (CF) and in-line (IL) directions of the flexible cylinder are obviously reduced by helical strakes. The VIV fatigue damage of the smooth cylinder is nearly independent of the yaw angle, while that of the straked cylinder is extremely sensitive to the yaw angle. As the yaw angle increases from 0° to 45°, the fatigue damage of the straked cylinder caused by VIV increases several orders of magnitude.

This work first numerically investigates on the effect of the application of cyclic remote loads on the local stress/strain response of a peripheral stent. For this purpose, three stents of identical geometry, but different material properties (linear elastic, elastic-plastic and Nitinol material), were modelled and subjected to uniaxial and multiaxial proportional cyclic loads. The local response under uniaxial loads is non-proportional only for the case of Nitinol stent, while it happens for all the materials when multiaxial loads are applied. This paper also aims to evaluate how the use of different multiaxial fatigue criteria may affect the fatigue assessment for Nitinol peripheral stents. The same stent model was subjected to different proportional and non-proportional multiaxial cyclic loads and the results were interpreted using the standard von Mises and three approaches based on the concept of critical plane. The results showed that the von Mises is the most conservative criterion.

In this study, a series of shaking table tests of a ten storey concrete suspended structure equipped with viscous dampers were carried out to evaluate the dynamic responses and vibration damping performance of suspended structures. The effects of link types between the primary structure and suspended floors and different seismic excitations on the response of suspended structure models was verified. The responses include the damping ratio, the frequency, maximum relative displacements, accelerations and maximum strains of the suspended structures. Test results showed that the damping ratio and the frequency of suspended structures installed with dampers (called damping suspended structure) are adjusted compared with a conventional suspended structure with rigid-bar links (conventional suspended structure). Maximum relative displacements of the primary structure of the damping suspended structure were distinctly smaller than those of the conventional suspended structure. However, the maximum relative displacement between the primary structure and the suspended floors of the damping suspended structure was significantly larger than that of the conventional structure, indicating that the swing of the suspended floor can help dissipate seismic energy. The peak acceleration and acceleration amplification factors of the damping suspended structure were less than the conventional suspended structure. Moreover, the peak acceleration response of the damping suspended structure was slightly behind the conventional suspended structure. The damping suspended structure certainly had a considerable and stable reduction for strain response, and the maximum strain response was decreased by 42.3%&ndash, 72.7% for the damping suspended structure compared with the conventional suspended structure.

The importance of uniaxial compression test (UCT) of rocks will never be overemphasized as it plays a vital role in understanding the mechanical properties of rocks for use in civil, mining, and petroleum engineering. Strain response of rocks to external loading is small; it requires a precise instrument to capture the strain with reasonable accuracy. The conventional method is associated with system compliance error, limited precision, and bedding error. Several methods were devised to alleviate these errors. This study embodies the existing strain measuring instruments during UCT of rocks, their principles, features, accuracy, merits, and demerits are correctly scrutinized. The paper serves as a powerful tool that enables the selection of a suitable instrument accordingly. It is hoped that the study will encourage more exploration in the area.

This paper presents a Finite Element Analysis(FEA)-based design of a health monitoring system for a structurally complex long-span bridge. The system consists of Bridge Weigh-in-Motion(BWIM), damage detection function and thermal behavior monitoring. To determinate the sensor position for BWIM, the strain response in the floor system is analyzed. Besides, FEA simulations are performed to grasp the damageable parts during an earthquake. Based on the analysis, a sensor arrangement for the bridge is proposed.

The hot-mix asphalt (HMA) dynamic modulus (E*) is a fundamental mechanistic property that defines the strain response of asphalt concrete mixtures as a function of loading rate and temperat...

Long-gauge fiber Bragg grating (FBG) strain response is characterized by sensitivity to local damage and obtaining global behavior (e.g., deflection, natural frequency) of structures, and can be measured with high-accuracy and high sampling frequency. Recent research about performance assessment of engineering structures using long-gauge FBG sensors is reviewed in this paper. Firstly, description of long-gauge FBG sensing technique is presented. Secondly, assessment methods of structural local behavior using long-gauge strain response are classified into two types (time domain-based and frequency domain-based method). Time domain-based methods are those methods which directly use long-gauge strain to identify local damage of structures. Frequency domain-based methods are those methods which extract frequency features (e.g., modal macro-strain) of structures for damage identification. Thirdly, assessment methods of structural global behavior using long-gauge strain response are summarized. These methods include calculating deflection of structures from long-gauge strain response, extraction of natural frequency from dynamic strain time-history, and calculating displacement mode shape from modal macro-strain. Finally, suggestions on the selection of methods for performance assessment of engineering structures are proposed and some challenges are discussed.

The results of an experimental study of the cyclic axial stress-strain response of rectangular concrete columns confined with a combination carbon-fiber-reinforced polymer (CFRP) jacket and CFRP anchors are presented and discussed. The test variables include aspect ratio of the column section, area of CFRP wraps, and area and configuration of the CFRP anchors. It was found that adding CFRP anchors improves the confinement effectiveness of the CFRP jackets, leading to substantially enhanced envelope stress-strain response and ductility of axial failure. Furthermore, changing the anchor configuration while maintaining the total anchors’ cross-sectional area does not produce a noticeable effect on the envelope stress-strain curve. The cyclic part of the stress-strain response of the CFRP-anchored specimens is similar to that of the companion specimens confined with CFRP sheets without anchors. Based on the results of this study, analytical expressions are derived for predicting the stress-strain curv...

Composite timber beams strengthened by U-shape steel sections and carbon fiber–reinforced plastic (CFRP) are studied experimentally in this paper. Specimens with various strengthening, i.e., steel only, CFRP only, and a combination of the two, were considered under three-point flexural tests. Failure, displacement and strain response, ductility, bending capacity, and structural efficiency were evaluated for the present tested models. Dramatic enhancement of the capacity in addition to improved deflection and ductility were gained for the strengthened beams relative to the plain specimens, indicating the effectiveness of the reinforcement on the flexural strength of such composite beams.

This paper presents an experimental investigation into a self-designed single-layer cylindrical explosion containment vessel (CECV) and a new multi-layer CECV composed of single-layer CECV and aluminum foam sacrificial inner lining subjected to non-uniformly distributed internal blast loading. Based on the experimental results, the characteristics of the blast loading acting on the inner wall of the vessel and the strain response of the vessel shell are analyzed through theoretical analysis and numerical simulation. The analysis results show that the pole of the ellipsoidal end cap is the most dangerous position of the vessel when subjected to internal blast loading produced by a cylindrical charge at the geometric center of the vessel. At the same time, the analysis results confirm the possibility of nonlinear modal coupling to cause strain growth in a CECV. For the multi-layer CECV composed of single-layer CECV and aluminum foam sacrificial inner lining, analysis results demonstrate that the inner lining has a certain protective effect on the CECV as a whole, but may play a counteraction on the cylindrical shell portion of the vessel. This study can guide the design and safety assessment of explosion containment vessels.

Strain has a high sensitivity to structural damage and can be used for damage diagnosis of marine risers in engineering. Considering the structure and boundary conditions of the top tensioned riser, it can be simplified to the Euler-Bernoulli beam element, and the strain equation on the riser wall is derived. The element Root-Mean-Squared Strain(RMSS) difference is proposed as the damage index parameter of the riser. The finite element software ANSYS is used to simulate the element strain response of the 1000m length top tensioned riser in the South China Sea with different damage locations, damage degree and sea state parameters, and the RMSS difference curve is drawn. The results show that the RMSS difference has high sensitivity to the riser structure damage, and the damage position of the riser can be effectively identified in many different situations.

The Federal Highway Administration conducted controlled loading tests on the U.S. Route 23 Test Road in hot weather conditions in Ohio, including two dual and two wide-base configurations. This paper is to reveal the influence of tyre configuration on pavement and provide some suggestions on tyre configuration from the perspective of reducing pavement damage. The raw strains were adjusted to common temperature, lateral offset distance and nominal speed for consistent comparison. MEPDG fatigue cracking and rutting models were used to predict damage brought by different tyres to pavement sections. The results indicate that newer generation of wide-based tyres with wider interface with pavement could be road-friendly, inducing similar or even less damage than the conventional dual tyres. At the same time, certain conventional dual tyres, which are commonly used in the current market, might cause larger damage to the pavement than other tyres in certain environmental and loading conditions.

This research is focused on a comparison of classic and strain experimental modal analysis (EMA). The modal parameters (the natural frequencies, the displacement mode shapes (DMSs) and the damping) of real structures are usually identified with classic EMA, where the responses are measured with motion sensors (e.g. accelerometers). Strain EMA is a special approach in the field of EMA, where the responses are measured with strain sensors. Classic EMA is the preferred method, but strain EMA offers advantages that are important for particular applications: for example, the direct identification of strain mode shapes (SMSs), which is important in the vibration-fatigue and damage-identification models. The next advantage is that strain EMA can sometimes be used, for experimental/geometrical reasons, where classic EMA cannot. There are also drawbacks: for example with strain EMA only, the mass-normalization of the DMSs and SMSs cannot be performed. This study researches the theoretical similarities and differences of both EMA approaches. Furthermore, the accuracy of both approaches for the case of a free–free supported beam and a free–free supported plate is investigated. Classic and strain EMA were performed with a piezoelectric accelerometer and the piezoelectric strain gauges, respectively. The results show that the accuracy of strain EMA results (the natural frequencies, DMSs and the damping) is comparable to the accuracy of classic EMA.