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Optical fiber sensors are the most promising technique in monitoring physical and chemical variables of civil structures. For the brittle material characteristics, a bare sensing fiber is prone to breakage under the shear or torsional action existed in the construction and operation. To guarantee the survival and long-term service of the sensors, the packaging measure is particularly significant. This treatment generates an intermedium layer between the sensing fiber and the monitored structure, which leads to the strain of the host material not entirely transferred to the sensing fiber for a portion of strain loss in the transferring path. To correct the error and improve the measurement accuracy, strain transfer theory is developed to establish the quantitative strain relationship between the sensing fiber and the host material. A state-of-the-art review on strain transfer theory of optical fiber based sensors developed for civil structures is addressed. It aims to demonstrate the advance, the application and the challenge of strain transfer theory and provide scientific guidance for the better understanding of the multi-layered sensing model and the theoretical instruction for the optimum design, calibration and measurement accuracy enhancement of optical fiber sensors.

Because of the rapidly increased traffic weight and severe service environment (i.e. temperature and humidity) in recent years, a great number of newly paved pavement structures suffer from prematu...

A continuous bridge in high-speed railway is close to several known faults in China. Those faults, respectively at different distances from the bridge site, will produce different ground motions with the different ratios of vertical component to the horizontal component at the bridge site. It is necessary to identify the influence of vertical ground motions on the seismic responses and vulnerabilities of the track-bridge system. This paper solved this problem by carrying out an incremental dynamic analysis (IDA) and a further seismic fragility analysis on a widely used continuous bridge in China. The results show that the damage probabilities of most bridge and track components increase along with the increase of vertical part in ground motions. This trend is significant for the sliding layer of track part in the longitudinal direction and the piers of bridge part in any direction, however, insignificant for the bearings of bridge part in any direction. Moreover, this trend is more significant for the track part across the girder gap due to the different seismic responses of adjacent bridges. The seismic design of track-bridge system should rigorously take the vertical part of ground motions into account.

A photonic-assisted multi-functional radar system for simultaneous distance and velocity measurement and high-resolution microwave imaging is proposed and experimentally demonstrated by using a composite transmitted microwave signal of a single-chirped linearly frequency-modulated (LFM) signal and a single-tone microwave signal. In the system, the transmitted signal is generated via photonic frequency up-conversion based on a single integrated dual-polarization dual-parallel Mach-Zehnder modulator (DPol-DPMZM), whereas the echo signals scattered from the target are de-chirped to two low-frequency signals using a microwave photonic frequency mixer. By using the two low-frequency de-chirped signals, the real-time distance and radial velocity of the moving target can be measured accurately according to the round-trip time of the echo signal and its Doppler frequency shift. Compared with the previous reported distance and velocity measurement methods, where two LFM signals with opposite chirps are used, these parameters can be obtained using only a single-chirped LFM signal and a single-tone microwave signal. Meanwhile, high-resolution inverse synthetic aperture radar (ISAR) imaging can also be realized using ISAR imaging algorithms. An experiment is performed to verify the proposed multi-functional microwave photonic radar system. An up-chirped LFM signal from 8.5 to 12.5 GHz and an 8.0 GHz single-tone microwave signal are used as the transmitted signal. The results show that the absolute measurement errors of distance and radial velocity are less than 5.9 cm and 2.8 cm/s, respectively. ISAR imaging results are also demonstrated, which proves the high-resolution and real-time ISAR imaging ability of the proposed system., 16 pages, 9 figures

This study investigates the effects of horizontal ground motion incident angle on a high-speed railway continuous bridge (HSRCB). To that end, incremental dynamic analyses (IDA), seismic vulnerability analyses and seismic risk assessments were conducted on a three-span HSRCB subjected to a set of ground motions under five incidence angles θ (0°–90°). The analysis was developed only from the perspective of PGA and the results showed that the longitudinal waves (θ = 0°) only caused seismic responses in the longitudinal direction, while the waves in other directions, especially in the transverse direction, caused a coupling response both in longitudinal and transverse directions for some components, such as the sliding layer and CA mortar layer. The longitudinal seismic damage of the sliding layer and CA mortar layer under the transverse waves should receive more attention in seismic design since the exceeding probabilities and seismic risk probabilities under various incident angles θ are as high as the calculated value for θ = 0°, and with a variation within 5.95%. The maximum variation of the longitudinal response and probability for track parts was within 10.59% under various incident angles, with a significant difference in the transverse response and probabilities in response to different incident angles. In addition, the responses of bridge structure components were more sensitive to the incident angles in comparison with the track parts. Finally, results indicate that the risk probabilities are at a maximum when the ground motions fall within horizontal orientations of 67.5°–90° at the bridge longitudinal axis.

When an earthquake occurs, due to the high operation speed of the train group, there is still a long distance from braking to stopping, so it needs a large number of bridge spans to calculate the integrated dynamic response, which leads to a large amount of calculation of the train-track-bridge (TTB) system under a seismic event. In order to reduce the amount of calculation, this paper proposed an efficient model called closed-loop model for simply supported railway bridge. The proposed model is realized by coupling the head and end of the rail-slab-bridge system through the utilization of pseudo-element. Simulation comparison of TTB response with and without seismic excitation between conventional TTB model and efficient model indicates that, under the premise of ensuring calculation accuracy, the efficient model shows the advantage of fewer degrees of freedom (DOF) of model and higher computational efficiency. For instance, under El Centro earthquake excitation, the time cost of proposed model is only 6% of conventional model. Meanwhile, six seismic events with different acceleration amplitudes are imposed on the efficient model, and the results of car-body acceleration, wheel-rail force, and wheel load reduction ratio are gathered and discussed; it can be concluded that, except Trinidad earthquake, for other earthquake samples investigated in this paper, with acceleration amplitude larger than 0.8 g, the train operation is at the risk of derailment.

When solving structural dynamic problems, the displacement algorithm needs only calculating and storing structure’s displacements in the main calculation process, which makes the displacement algorithm have advantages over multivariable algorithms in calculation efficiency and storage requirements. By using a novel approach based on dimensional analysis firstly given by the first author, a one-parameter family of two-step unconditionally stable noniterative displacement algorithms, referred to as the CQ-2x method, is developed. Compared with other unconditionally stable noniterative multivariable algorithms such as the representative KR- α method, the proposed method has advantages in several aspects. The CQ-2x method is unconditionally stable regardless of stiffness hardening or stiffness weakening, while the KR- α method is only conditionally stable in case of stiffness hardening. The CQ-2x method needs only one solver within one time step, while the KR- α method needs two solvers within one time step, which makes the CQ-2x method show higher efficiency. Numerical examples are presented to demonstrate the potential of the proposed method.

Artificial seismic waves can be easily generated by software, and needs identification if they can be used to evaluate the seismic vulnerability of general bridges. A finite element model of a (48+80+48)m continuous girder bridge in a high-speed railway was built by OpenSEES software, and was calculated by an incremental dynamic analysis (IDA) using both the artificial waves and actual waves. The seismic fragility curves for major structural components under the artificial waves and actual waves were developed assuming lognormal distributions for both the demand and capacity of bridge structure, and then compared with each other. The comparison results show that there is a perfect consistency between the seismic responses under both the artificial waves and actual waves for most components. Although the seismic responses of sliding layer under the actual waves are slightly different from those under the artificial waves, the largest error of damage exceeding probability between them is still acceptable. Therefore, the artificial waves can be used to evaluate the seismic vulnerability for the continuous girder bridges in a high-speed railway under earthquakes.

A nonlinear train-track-bridge system (TTBS) considering the random track irregularity and mass of train is discussed. Based on the Karhunen–Loéve theory, the track irregularity is expressed and input into the TTBS, and the result of random response is calculated using the point estimation method. Two cases are used to compare and validate the applicability of the proposed method, which show that the proposed method has a high precision and efficiency. Then, taking a 7-span bridge and a high-speed train as an example, the calculation results of random response of the nonlinear and linear wheel-rail model are compared, and the results show that for the bridge and rail response, the nonlinear and linear models are almost the same. Finally, comparing the calculated probability distribution results with the test results, it shows that the method can be applied to the prediction of actual response range.

A specially shaped corrugated steel shear wall (S-CSSW) system was proposed for the application of steel residential buildings. The proposed shear wall system featured a main shear wall with small section concrete filled steel tube (CFST) boundary columns and horizontally corrugated shear plates and side short pier CSSWs in the perpendicular direction. Quasi-static cyclic tests were performed on the S-CSSWs with and without reinforcing beams to investigate the shear strength, failure modes and hysteretic responses. Finite element simulations were introduced to further study the shear bearing mechanisms of S-CSSWs for a comparison with traditional flat plate shear walls with similar wall configurations. An additional parametric simulation was performed to investigate the influence of the corrugated plate width on failure modes. Results indicated that the proposed S-CSSWs possessed good ductility. Compared with the flat plate shear walls, the proposed shear walls had higher initial stiffness and elastic shear strength. The width of the corrugated shear panels was an important factor influencing the failure modes and lateral bearing abilities and needed to be carefully controlled to avoid early buckling occurring ahead of the shear yielding mode. Some design remarks are concluded regarding the design of the corrugated shear panels and stiffening beams.

A built-up type specially shaped corrugated steel shear wall (BS-CSSW) that can be concealed within enclosure walls was proposed for applications in residential buildings. Quasi-static tests were performed on two specially shaped corrugated steel shear wall specimens (S-CSSW and BS-CSSW) and refined finite element simulations were conducted. With the verified modeling method, a parametric study was performed on BS-CSSWs with different wall configurations and interior column positions. The results indicated that the corrugated shear plates in the S-CSSW underwent premature elastic buckling, thus leading to a sudden drop in strength upon buckling and low strength levels after buckling. Shear panels in the BS-CSSW successfully entered the shear yielding mode and remained in a stable in-plane shearing state until reaching 2% drift. The BS-CSSW had higher elastic and plastic strength levels, better ductility, slower stiffness reduction, lower out-of-plane plate deformation and a wider hysteretic relationship than those of the S-CSSW. The position of the interior columns primarily influenced the slenderness of the side and interior corrugated panels and affected the strength development modes. The BS-CSSWs had separate bearing modes between lateral loads and axial loads and could withstand high axial load conditions with little influence on shear strengths.

This study investigated the seismic performance of simply supported girder bridges with a span length of 32 m. Those bridges were a common part in China’s high-speed railway system and used spherical bearings to connect girders and piers. First, a finite element model of the scaled bridge with a geometrical similarity ratio of 1:8 was established by OpenSees. Second, five seismic damage states of fixed bearings and piers were defined based on the deformation failure criterion. Finally, an incremental dynamic analysis and a pseudo-dynamic test were performed to evaluate the effects of friction-based fixed bearings on the seismic response and damage state of bearings and piers. Results show that the sliding of friction-based fixed bearings effectively restricts the force transmitting between piers and girders, and reduces the seismic damage of piers. Those bearings with a small friction coefficient lead to a large relative displacement between piers and girders, while those bearings with a large friction coefficient cause a large seismic force exceeding the yield load of piers. Therefore, an appropriate friction coefficient of friction-based fixed bearing should be determined to achieve an optimal seismic performance of bridge according to the specific conditions of bridge and ground motion inputs.

The durability, robustness, and long-term stability of optical-fiber-based sensors applied to practical engineering have always been challenging problems. Refer to the sensors embedded in asphalt pavements, the situation becomes serious and feasible sensors with enhanced function are in high demand. Therefore, an improved design to configure the quasi-distributed and distributed optical fiber sensors and FBG-based point sensors for monitoring the three-dimensional information of multilayered asphalt pavements is needed. The in-field data declare that the transversal, longitudinal, and vertical deformations of the tested urban asphalt pavement are mainly affected by temperature. The M-shape strain profile induced by heavy vehicles can decrease to the regular state in approximately 30 min after unloading. The tested asphalt pavement presents good structural performance to bear the tensile strain and permanent deformation. The high survival ratio and the good robustness of the proposed sensors against the harsh construction and operation environment validate the feasibility and reliability for the long-term monitoring. Improved design proposals on the construction scheme of asphalt pavement are also addressed to control the strain of the established asphalt concrete course in relatively low level.

In practical application, fast search is necessary for space-based radar to avoid collision. The rapid and efficient selection of the parameter in radar is always a hard pot. In this paper, a parameter optimization algorithm that minimizes the search time is proposed. In the proposed method, a novel optimization objective function, which synthetically integrates the influence factors of search area, beam irradiation surface and “residence time”, is defined. The proposed method is of both theoretical and practical value. The experimental simulation verified the effectiveness and the efficiency of the proposed optimization method.

To realize the reliable and long-term strain detection, the durability of optical fiber sensors has attracted more and more attention. The packaging technique has been considered as an effective method, which can enhance the survival ratios of optical fiber sensors to resist the harsh construction and service environment in civil engineering. To monitor the internal strain of structures, the embedded installation is adopted. Due to the different material properties between host material and the protective layer, the monitored structure embedded with sensors can be regarded as a typical model containing inclusions. Interfacial characteristic between the sensor and host material exists obviously, and the contacted interface is prone to debonding failure induced by the large interfacial shear stress. To recognize the local interfacial debonding damage and extend the effective life cycle of the embedded sensor, strain transfer analysis of a general three-layered sensing model is conducted to investigate the failure mechanism. The perturbation of the embedded sensor on the local strain field of host material is discussed. Based on the theoretical analysis, the distribution of the interfacial shear stress along the sensing length is characterized and adopted for the diagnosis of local interfacial debonding, and the sensitive parameters influencing the interfacial shear stress are also investigated. The research in this paper explores the interfacial debonding failure mechanism of embedded sensors based on the strain transfer analysis and provides theoretical basis for enhancing the interfacial bonding properties and improving the durability of embedded optical fiber sensors.

As for structures with rubber bearings during earthquakes, some firstly damaged bearings and the other normal bearings form a typical spring-friction isolation system. Furthermore, a rough contact surface, due to the stochastic damage of bearing, and the around smooth contact surfaces form a convex distribution of friction coefficient. This paper attempts to analyze seismic responses of a spring-friction isolation system with a theoretically and linearly convex friction distribution, in which the friction coefficient gradually decreases with the distance from the center. The results show that such friction distribution inevitably increases the structural relative displacement and possibly enlarges the structural acceleration and residual displacement under earthquakes. The convex pattern of friction distribution should be avoided in practical engineering, since it reduces the seismic isolation efficiency.

The Multangular Pyramid Concave Friction System (MPCFS) is introduced in this study. Different from the conventional Curved Surface Slider (CSS), the concavity of the MPCFS is designed as a multangular (mostly triangular or rectangular) pyramid, and the slider is removed from the isolator. While maintaining the virtues of the CFS, the MPCFS can provide greater vertical sustaining capacity with a more stable friction force. When combined with a cross uplift restraint, the MPCFS offers numerous virtues such as increased uplift stability, a greater initial yielding force, and resonance-dodge ability during near-fault earthquakes (variable frequency). Frequency-sweeping and acceleration time-history numerical investigations are conducted on a four-storey building model using the MPCFS. The revised State-Space Method (SSM) is expanded from two-degrees-of-freedom to multi-degrees-of-freedom as to accommodate more complex analysis such as dynamic analysis of high-rise, multi-storey structure installed with MPCFS. The simulation result verifies the merits of the MPCFS, indicating that the MPCFS, viewed as a beneficial complement to the existing well-established isolation techniques, may be a promising tool for the seismic isolation of high-rise, and super high-rise buildings in near-fault earthquake prone zones.

Considering the mechanical effects and the different paths for transferring deformation, optical fiber sensors commonly used in civil engineering have been systematically classified. Based on the strain transfer theory, the relationship between the strain transfer coefficient and allowable testing error is established. The proposed relationship is regarded as the optimal control equation to obtain the optimal value of sensors that satisfy the requirement of measurement precision. Furthermore, specific optimization design methods and priority design parameters of the classified sensors are presented. This research indicates that (1) strain transfer theory-based optimization design method is much suitable for the sensor that depends on the interfacial shear stress to transfer the deformation; (2) the priority design parameters are bonded (sensing) length, interfacial bonded strength, elastic modulus and radius of protective layer and thickness of adhesive layer; (3) the optimization design of sensors with two anchor pieces at two ends is independent of strain transfer theory as the strain transfer coefficient can be conveniently calibrated by test, and this kind of sensors has no obvious priority design parameters. Improved calibration test is put forward to enhance the accuracy of the calibration coefficient of end-expanding sensors. By considering the practical state of sensors and the testing accuracy, comprehensive and systematic analyses on optical fiber sensors are provided from the perspective of mechanical actions, which could scientifically instruct the application design and calibration test of industrialized optical fiber sensors.

The high-speed railway in China has to pass through the site surrounded by several known faults. Different earthquake mechanics of those faults and propagation paths cause different ground motions, including different peak ground accelerations (PGA), durations and characteristic periods, acting on the high-speed railway bridges. However, the previous seismic vulnerability analysis mainly aimed at the influence of PGA instead of characteristic periods on the seismic fragilities of bridge structure rather than track–bridge system. By taking a typical and common continuous bridge recommended in Chinese criterion as example, the effects of the uncertain characteristic periods of ground motions on the seismic responses and fragilities of track–bridge system were analyzed based on a numerical method. The results indicate that the probabilities exceeding any damage state of most components, including the bridge and track parts, increase with the characteristic period of ground motions. The uncertain characteristic periods of ground motions should be fully considered for the seismic design of track–bridge system, especially when the uncertain characteristic periods change around a small value. In the seismic vulnerability analysis, the uncertain of the designed characteristic period of ground motions should be developed by considering the different earthquake mechanics of several known faults surrounding the bridge site and the complex propagation paths of ground motion waves through different soils. Using a constant characteristic period of ground motions only considering the soil profile at the local site of bridge possibly leads to an unsafe result in the current criterion.

In this paper we investigate the performance of composite frames composed of circular concrete-filled steel tubular (CFST) columns connected to steel-concrete composite beams subjected to a constant axial load and a cyclic lateral load. Seven single-story and single-bay in-plane frames were fabricated and tested. The effects of the slenderness ratio (λ), the axial compression ratio (n), and the beam-to-column linear stiffness ratio (k) on the seismic performance of the composite frame were studied. The experimental results, including damage development and stiffness degradation, load-deformation responses, energy dissipation capacity and ductility are discussed. It was found that these composite frames exhibited satisfactory seismic performance. Furthermore, a finite element (FE) model was developed and validated by comparisons with the experimental results, considering both material and geometrical nonlinearity for confined concrete and steel. The results obtained from the FE modeling were in good agreement with the experimental results in terms of failure modes, load-displacement hysteretic curves, and skeleton curves.

Many Coulomb friction-based devices have been used for seismic isolation of modern civil structures. Aiming at a practical problem that if the friction action could be scaled in a shaking table model test, a base isolation system using Coulomb friction was numerically scaled in different ways by considering the gravity distortion, friction distribution and other influence factors. The seismic responses back calculated from the scaled models were compared with those of the full-scale model to evaluate the accuracy of scale theory for such a Coulomb friction action. The above numerical results show that the scale theory is still applicable for the uniform and non-uniform friction distribution patterns with nonlinear characteristics. The gravity distortion and uneven friction distribution are the most important factors, causing the errors of scale theory for the Coulomb friction system. However, the unallowable errors, caused by the un-scaled gravity acceleration on common shaking tables, can be avoided by reasonably changing the friction coefficients at the scaled friction interface. And other unallowable errors, caused by the uneven friction distribution, can be prevented if the specific positions with different friction coefficients for the full-scale model are proportionally moved with the scaled contact surface.

Modular steel construction (MSC) comprises off-site manufactured modules that are assembled on-site. When joining two modules together, double-layer wall systems and grouped columns are present at the junction regions, and different fire-proof measures are induced for critical walls and columns in modular steel buildings. In this study, experimental studies on the fire resistance of critical columns, load-bearing walls and non-load-bearing walls in a modular steel building were conducted to obtain the practical fire resistance performance . Temperature developments across the wall and column sections were measured and analyzed to determine the fire damage developments. The fire resistance ratings (FRRs) of different fire-proof measures were evaluated. The double-layer partition wall system and the load bearing wall system failed by the integrity failure criterion. The wall specimens all experienced the fall-off failure of fire side gypsum boards and severe ablation of the mineral wool insulation. The grouped columns with one layer of gypsum board and mineral wool insulation also experienced early gypsum board failure and a short fire-resistance rating. Based on the test results and literature reviews, suitable thermal properties for gypsum boards and mineral wool insulation were determined. The failure modeling methods for gypsum boards and mineral wool insulation were also defined. The established FE models can effectively predict the temperature developments across the section of wall and grouped column specimens. This paper provided useful fire test data for the fire proofing design of structural walls and columns in modular steel buildings, and offered rational thermal modeling methods for structural components considering the failure of commonly used fire proofing materials.

Bridges are common features of high-speed railway infrastructure. However, the performance of such bridges under seismic scenarios has not been well studied. To quantify possible damage levels of bridge components under different intensities of earthquake excitation, a 1/12-scale bridge specimen was constructed and tested using shaking tables. The experimental results of this investigation showed that not all bridge components were damaged when subjected to earthquake with the intensity of 0.20 g. A finite element (FE) model of the prototype bridge was also established and validated by the experimental results with consideration of similarity relationships. Finally, parametric studies involving different intensities of earthquake excitation were carried out by the validated modelling approach to study the damage levels of high-speed railway components under more severe earthquakes (i.e. 0.30 g, 0.40 g and 0.50 g). The results could be applied to quantify the levels of damage of the main components of high-speed railway bridges when subjected to earthquake intensities no greater than 0.50 g. Moreover, the numerical results showed that the shear reinforcement, fixed bearing and the pier installed with the fixed bearing were more vulnerable to earthquake excitation than the shear studs, slide layer, and cement asphalt mortar layer investigated in this study.

We report on the observation of the electromagnetic focusing effect of zero orbital angular momentum (OAM) after introducing the multi-grade OAM concept. It performs the same feature in the central area around the focal point, while the typical Airy disk is transformed into a vortical cloud pattern beside the central area. Quantized focusing phenomena are exhibited based on the periodicity of the OAM. These results were verified by simulation and experiments. Our method achieves an optical focusing theory through OAM manipulation, which can be applied in imaging, photoetching, and communication. Furthermore, it also provides an opportunity for energy harvesting from natural OAM materials.

Fatigue performance of RC plate girder was experimentally investigated. A corrosion-fatigue life assessment approach of railway RC girders under combined carbonation and train loads was proposed. The proposed approach was applied to an 8 m-span RC plate girder in an existing heavy-haul railway bridge, and the effects of annual freight volume, train axle weight, and carbonation environment level on corrosion-fatigue life were analyzed. Results indicate that annual freight volume, train axle weight, and carbonation environment level have a significant impact on corrosion-fatigue life, which can decrease the remaining corrosion-fatigue life by up to 48.71%, 91.11%, and 60.90%, respectively.

In order to meet the requirements of shake tables, frequency filtration of seismic input is usually performed before tests. Aiming to study the error of seismic analysis caused by filtering, the artificial seismic waves before and after filtering with four different waveforms were synthesized in this paper. Based on a spring-friction isolation system, the effects of filtering on seismic responses with various spring constants, friction coefficients and envelope functions were investigated. The results show that the maximum acceleration of the pure friction system is not affected by filtering while the error of maximum relative displacement caused by filtering can reach 60% and decreases with the increment of the friction coefficient. For the spring-friction system, the friction coefficient corresponding to a smaller structural seismic response is exactly the most unfavorable friction coefficient for filtering error and hence needs more attention during shaking table tests. Filtering errors based on different waveforms have the same tendency despite some slight differences owing to the different responses.

The displacement at the terminals of ultra-high-voltage (UHV) post electrical equipment is a critical parameter in the seismic design of flexible conductor interconnected systems. Considering the rotational stiffness of the flange, this work proposed a method to estimate the terminal displacement of the UHV post electrical equipment and validated the model with shaking table tests. The first-order frequency coefficient and mode participation coefficient of the equipment were obtained using the model with different parameter values. Then, the fitting curves of the frequency coefficient and mode participation coefficient were determined. Additionally, the method to obtain the maximum seismic terminal displacement of the UHV post electrical equipment was proposed using a spectrum analysis with fitting curves. Numerical examples were performed in this work, and the maximum terminal displacements of the examples were validated by finite element analyses.

In response to long-term operation of prestressed concrete railway bridges, the girder body will arch because of creep, which may influence the running stability of high-speed trains. Usually, the deformation of the rail-bridge system under the creep effect is calculated by a finite element model with the rail geometry deformation input as additional irregularity. The original irregularity is superimposed to the coupled system of the train and bridge to calculate the dynamic response of the system. However, such a strategy is time-consuming and cannot accurately integrate the uncertainty of the original rail irregularity. This paper presents an analytical formula for predicting the rail deformation caused by concrete creep. The rail deformation caused by the bridge upper arch can be quickly predicted by the creep amplitude of the bridge. The creep deformation of the rail is applied as an irregularity excitation to the train-track-bridge coupled system (TTBCS). In addition to creep irregularities, original random irregularities also exist on the track. The Karhunen-Loeve expansion method is adopted to represent the random track irregularity that considers creep deformation. The results achieve good agreement with the initial samples. Subsequently, the TTBCS model is established to analyze the dynamic responses of different train speeds and different bridge creep deformations using a stochastic dynamic analysis method. This method achieves very high agreement with the Monte Carlo method, and the error rate of the mean bridge displacement calculated by both methods under the same working conditions was only 0.0351%. Finally, the upper probability limit value of the creep of the bridge is put forward: at a speed of a high-speed train of 350 km/h, the creep upper arch limit is only 7 mm. These probability limits at different train speeds have guiding significance for the design, maintenance, and repair of the actual medium–high-speed railway concrete supported beam bridge.

The influence of track irregularity and deck deformation on the running safety of high-speed railway (HSR) trains is investigated, with emphasis placed on those caused by the creep of continuous prestressed bridges. A bridge model is established with CRTS II ballastless track to account for a train-track-bridge (TTB) system. The creep effect is calculated by the finite element software MIDAS/Civil. The accuracy of the numerical simulation is confirmed by comparing the numerical predictions with field measurements. Considering the stability index of the moving train, the deformation threshold for safe operation of the train is determined. The results show that the initial prestressing stress has a great impact on the residual deformation of the bridge, but the deformation of the rail is less affected by the stiffness of the fastener. Creep irregularity has a great influence on the comfort of the moving train, but does not affect its running safety. When the creep amplitude is greater than 4[Formula: see text]mm, the increase in the amplitude of the creep irregularity has a greater effect on the acceleration of the car body.

Dynamic response analysis of a nonlinear train-track-bridge system under earthquakes is a time-consuming task. In this paper, a fast computing strategy is proposed to reduce the simulation time by solving the shortcomings of classical time integration algorithms in the computation of the coupled system. The core of the strategy focuses on completely explicit computational processes and unconditional stability. Based on the loosely coupling scheme, the model of the train-track-bridge system is divided into two parts, namely, the train substructure established using multibody dynamics and the track-bridge substructure established using the finite element method. Track-bridge substructure and train substructure are separately integrated by the unconditionally stable explicit algorithm, CQ3, and its degenerate form, respectively. The interaction of the two substructures depends on wheel-rail forces. The track-bridge substructure is further decoupled to describe its nonlinear behavior and to improve the speed of solving algebraic equations. The proposed strategy not only avoids the complex iterative process of the nonlinear train-track-bridge system but also eliminates the limitation of the integration time step caused by the minimum natural period of the track-bridge substructure. This paper first simulates the dynamic response of a train under a sinusoidal displacement excitation and extends the simulation strategy to analyze the vibration of the coupling system under an earthquake. The applicability, efficiency, and accuracy of the strategy are illustrated through three numerical analyses. The strategy proposed in this paper provides a convenient and greatly computationally efficient option for simulating the nonlinear dynamic response of a large-scale train-track-bridge system.

The responses and damages of cold-formed steel (CFS) structures under near-fault ground motions are not clear currently, which are important for seismic design of CFS structures. This paper investigates the effects of near-fault ground motions on a 6-story CFS building. Three groups of records were chosen from the same events and different stations. The mean damage index of the first-story wall increases by 6.9 ∼ 18.7% and 34.3 ∼ 53.4% under the near-fault (no-pulse) and near-fault (pulse-like) records, respectively. The effects of near-fault earthquakes should be considered, and the Park-Ang seismic damage index is more appropriate for the seismic design of CFS buildings.

Mortise–tenon joints (MTJs) have been playing a crucial role in traditional timber structures to resist service and earthquake loading. In the present work, an experimental study was carried out to...

Multiply-supported non-structural components (NSCs) can be vulnerable under strong multi-directional earthquake excitations. To date, this topic has not been explored much, not to mention considered in design provisions. Seismic analyses of NSCs with multiple attachments were mostly performed numerically and with simplified assumptions. Experimental investigation is scarce. The goal of this study is to describe the seismic behaviour of a multi-supported NSC under multi-directional excitations through experiments. Large-scale testing was implemented to study the development of acceleration from the ground to the NSC, which would otherwise be too small to detect in a small-scale setup. The influence of the vertical component of the excitation on the response of the NSC is displayed. The interaction between the primary structure and the NSC was showcased through its influence on the response of both the primary structure and the NSC. For the first time, seismic response of a multi-supported NSC is expressed using physical experiments, thus accounting for its interaction with the main structure. The seismic demand for multiply-supported NSCs specified in current design provisions is also evaluated.

The seismic vulnerability of skewed bridges has been known since the past few decades. Previous research has found that skewed bridges are more prone to girder unseating than a straight bridge due to the in-plane rotations of the bridge girder which were found to be aggravated by pounding between adjacent spans and abutments. A good understanding of the pounding between girder and abutments of a skewed bridge is crucial for the integrity of the bridge. Most of the past research was performed mainly numerically and without considering movable abutments. Very limited experimental work has been done, and none has incorporated movement of abutments as the surrounding ground moves during earthquakes (movable abutments), influence of girder-abutment pounding, and skew angle at the same time. This study aims to close the knowledge gap through a series of shake table tests performed on a straight bridge, 30° and 45° skewed bridge with abutments on either side of the bridge structure. Abutment movement was considered by subjecting the bridge-abutment model to uniform ground excitations. The results show that ignoring pounding effects could significantly underestimate the bending moments at the piers by up to 1.94 times and the transverse relative displacements by up to 3.43 times. The NZTA recommendation for the seat length was severely inadequate to accommodate for the large displacements of skewed bridges, especially in the transverse direction.

The fixed bearings of high-speed railway continuous bridges were vulnerable during earthquakes, since they transferred most of the seismic force between the superstructure and the piers. A type of friction-based fixed bearing was used and would slide during strong earthquakes. The influence of this sliding friction action on the seismic vulnerability curves of different components in the track-bridge system was analyzed in this article. Results show that the sliding friction action of the fixed bearings can protect other components from severe damage under earthquakes. This phenomenon is more significant when the friction coefficient on the friction-based fixed bearings is reduced. However, it increases the seismic relative displacement of the fixed bearings themselves. Finally, a sufficiently large displacement capacity and an appropriate friction coefficient between 0.2 and 0.3 are almost the best combination for the friction-based fixed bearings, which can effectively protect all components of the track-bridge system, including the track structure, piers, piles, and friction-based fixed bearings themselves.

Cold-formed lipped channel columns (CFLCCs) have been widely used in light gauge steel constructions. The distortional buckling is one of the important buckling modes for CFLCCs and the distortional buckling critical load depends significantly on the rotational restrain stiffness generated by the web to the lipped flange. First, a simplified explicit expression for the rotational restraint stiffness of the lipped flange has been derived. Using the expression, the characteristics of the rotational restraint stiffness of the lipped flange have been investigated. The results show that there is a linear coupling relationship between the applied forces and the rotational restraint stiffness of the lipped flange. Based on the explicit expression of the rotational restraint stiffness of the lipped flange, a simplified analytical formula has been derived which can determine the elastic distortional buckling critical stress of the CFLCCs subjected to axial compression. The simplified analytical formula developed in this study has been shown to be accurate through the comparisons with results from the distortional buckling analyses using the ANSYS finite element software. The developed analytical formula is easy to apply, and can be used directly in practical design and incorporated into future design codes and guidelines.

In order to evaluate the seismic vulnerability of a railway bridge, a nonlinear finite element model of typical three-span continuous beam bridge on the Sichuan-Tibet railway in China was built. It further aimed at performing a probabilistic seismic demand analysis based on the seismic performance of the above-mentioned bridge. Firstly, the uncertainties of bridge parameters were analyzed while a set of finite element model samples were formulated with Latin hypercube sampling method. Secondly, under Wenchuan earthquake ground motions, an incremental dynamic method (IDA) analysis was performed, and the seismic peak responses of bridge components were recorded. Thirdly, the probabilistic seismic demand model for the bridge principal components under the prerequisite of two different kinds of bearing, with and without seismic isolation, was generated. Finally, comparison was drawn to further ascertain the effect of two different kinds of bearings on the fragility components. Based on the reliability theory, results were presented concerning the seismic fragility curves.

Wuhan Leishenshan/Leishenshan (“Leishenshan” for short) hospital is a makeshift emergency hospital for treating patients diagnosed with the novel coronavirus-infected pneumonia (NCIP). Engineering construction uses modular composite building finished products to the greatest extent, which reduces the workload of field operations and saves a lot of time. The building information model (BIM) technology assists in design and construction work to meet rapid construction requirements. Besides, based on the unmanned aerial vehicles (UAVs) data analysis and application platform, digitization and intelligence in engineering construction are improved. Simultaneously, on-site construction and overall hoisting were carried out to achieve maximum efficiency. This article aims to take the construction of Leishenshan Hospital as an example to illustrate how to adopt BIM technology and other high-tech technology such as big data, artificial intelligence, drones, and 5G for the fast construction of the fabricated steel structure systems in emergency engineering projects.

The seismic isolation efficiency of different friction-based devices needs verification by shaking table test, but faces problems in scaling before the test due to their frictional nonlinearity. To solve the scaling problems, a simplified civil structure, isolated by a self-centering spring-friction device, was numerically scaled in different ways considering the effect of friction action. The seismic responses of the scaled models were scaled back to those of the prototype and compared with the seismic responses of the prototype. The scaling problems and solutions were validated by a shaking table test on simply supported bridges using friction pendulum bearings (FPBs). The results show that both the unscaled gravity on a shaking table and the unscaled non-uniform friction distribution cause an inaccurate friction force in the structural motion equations of scaled models, and thus causing the scaling errors. One new and valid solution, i.e. changing the friction coefficient and scaling the non-uniform friction distribution to keep an accurate friction force for the scaled models, is put forward to avoid the scaling errors thoroughly. Another new solution shows that an increasing peak ground acceleration (PGA) can increase the other forces, while weakening the ratio of inaccurate friction force in the structural motion equations of the scaled models, which therefore reducing the scaling errors of acceleration and relative displacement responses, but not the scaling errors of residual displacement responses. In addition, the time-varying friction, the interface separation and collision of bearings, and other complex factors are found to cause scaling errors and need further investigation.

The system fragility method was used to evaluate the seismic structural systems and seismic mitigation devices for a cable-stayed bridge with three super-tall towers. Firstly, a three-dimensional numerical model of a four-span cable-stayed bridge with middle-tower height of 332 m was simulated using OpenSEES, which accounted for the material and geometric nonlinearities; 80 actual ground motions were chosen for conducting time history analysis. Secondly, the fragility curves of the components and the system were derived using general fragility theory and Product of the Conditional Marginal theory, respectively. Then, three longitudinal seismic structural systems were evaluated. Finally, under the optimal seismic structural system, the optimal parameters of the longitudinal fluid viscous damper and cable restrainer were obtained using the response surface method, and the mitigation effects of the fluid viscous damper and the cable restrainer with optimal parameters were compared using fragility curves. The results show that different structural systems and mitigation devices have significant influence on the damage control of displacement and stay cable force. The super-tall tower cable-stayed bridge with a partial constraint system of the consolidated middle tower and floating side towers has the lowest damage probability; and the longitudinal fluid viscous damper and cable restrainer can achieve a certain mitigation effect, however, the fluid viscous damper has better effect. Therefore, the partial constraint system and fluid viscous damper should be used in the longitudinal direction of the multiple super-tall-tower cable-stayed bridge.

This study presents an analytical method to describe the geometry status of the track of a high-speed rail (HSR) line when the bridges are subjected to different types of lateral deformation. In this study, the longitudinal continuous ballast-less track, which is widely used in the HSR line, was adopted as the standard track laid on the bridge. By considering a sufficient length of the track extended beyond the bridge, the influences of the bridge deformation on the geometry changes of the track were evaluated. Based on the Ritz method, the energy functionals for the rail, slab, and base plate of tracks were established, and the expressions of the track deformations were analytically obtained. Considering the compatibility of deformation of each component of the track, the deformation of every track component was analytically solved. Moreover, a finite element (FE) model was established to validate the proposed analytical mapping model. The results obtained from both the FE model and the analytical mapping model were found to be in good agreement. Moreover, the contributions of the material parameters of the track components to the track geometry were further evaluated and discussed. The results indicated that the longitudinal continuous ballast-less track exhibited significant effects on the mapping relationship between the deformations of the track and the bridges. The shear grooves contributed significantly to the mapping rail deformation. The contributions of the lateral blocks could not be neglected. The contributions of the stiffness of the cement asphalt layer and the sliding layer to the mapping rail deformation were also noticeable.

A shear key is installed on a seismic isolation bearing to resist long-term service and small earthquake loads. In the event of a large earthquake, the shear key is cut off to allow for the sliding of a bearing that isolates and dissipates the earthquake's energy. A scale in the bearing will satisfy the shaking table test's demands, however, the bearing will undergo disturbance when cutting off the shear key, including friction variability, gravity distortion, spring and viscous damping. In order to solve the problem prior to a real shaking table test, a simplified single-degree-of-freedom isolation system (SDOFS) can be numerically scaled. In this case, seismic responses are generated from scaled models and then compared with those of the prototype model. Response errors found during comparison demonstrate that friction variability and gravity distortion lead to significant inaccuracies in the scaled models. However, acceleration and displacement errors can be reduced by increasing the strength of the shear key. Moreover, such acceleration and relative displacement errors can also be reduced by increasing peak ground acceleration (PGA). These conclusions have been validated through the adoption of a real shaking table test.

Studying the applicability of existing bridge and track systems of high-speed railway in near-fault areas is crucial and urgent, because the current seismic design methods seldom consider the characteristics of the near-fault ground motion. By comprehensively considering the uncertainties in ground motion and structural parameters, a large-sample analysis method for near-faults area was proposed. In addition, an integrated finite element model for beam bridge-track system of high-speed railway was used to calculate the seismic response of the structure under the action of near-fault ground motion. The over-limit state and applicability of seismic response of key components and systems were predicted and evaluated. The analysis results indicate that the statistical characteristics of structural seismic response and over-limit state tend to be stable with increasing number of samples. Under the near-fault ground motion: (i) the piers of high-speed railway are hard to yield (ii) bearings are damaged severely, and (iii) the piers have insufficient shear capacity and the characteristics of structural seismic damage are not in accordance with the concept of ductility design. The sliding layer of the track structure is severely damaged by the transverse and longitudinal ground motions, while the CA mortar layer and fastener are mainly damaged by the transverse ground motion. The applicability of bearings, the anti-shearing behavior of piers, and the inter-layer structure of tracks make it difficult to achieve the goal of the near-fault fortification against ground motion.

The uneven distribution of rolling friction coefficient may lead to great uncertainty in the structural seismic isolation performance. This paper attempts to improve the isolation performance of a spring-damper-rolling isolation system by artificially making the uneven friction distribution to be concave. The rolling friction coefficient gradually increases when the isolator rolls away from the original position during an earthquake. After the spring-damper-rolling isolation system under different ground motions was calculated by a numerical analysis method, the system obtained more regular results than that of random uneven friction distributions. Results shows that the concave friction distribution can not only dissipate the earthquake energy, but also change the structural natural period. These functions improve the seismic isolation efficiency of the spring-damper-rolling isolation system in comparison with the random uneven distribution of rolling friction coefficient, and always lead to a relatively acceptable isolation state even if the actual earthquake significantly differs from the design earthquake.

A complex yet realistic nonuniform rolling friction force distribution of a spring-rolling isolation system could lead to great complexity in determining its seismic response. This paper investigates the isolation performance of a spring-rolling isolation system assuming that the rolling friction force gradually and linearly increases with the relative displacement between the isolator and the ground. A series of ground motions with different characteristics were applied to this system. The analysis results show that the considered concavely distributed friction force is capable of dissipating the earthquake energy, and it is also able to modify the structural natural period. These merits combined help to improve the isolating efficacy of the spring-rolling isolation system compared with scenarios with uniform distribution pattern, and more importantly lead to a relatively optimum isolation state, avoiding a sudden amplification of the structural seismic response, regardless of the input motion characteristics.