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An iron–carbon electroplated long period grating (LPG) fiber sensor to monitor the passivation, initiation, and propagation of the pitting corrosion of steel bars is characterized in simula...

Seismic resilience of critical infrastructure, such as liquefied natural gas (LNG) storagetanks, is essential to the safety and economic well‐being of the general public. This paper studiesthe effect of different ground motions on large LNG storage tanks under four different siteconditions. Key parameters of structural design and dynamic analysis, including von Mises stressof outer and inner tanks, tip displacement, and base shear, are analyzed to directly evaluate thesafety performance of the large LNG tanks. Because the size of an LNG tank is too large to performany experiments on a physical prototype, Smoothed Particle Hydrodynamics‐Finite ElementMethod (SPH‐FEM) simulation is used as a feasible and efficient method to predict its seismicresponse. First, the accuracy of the SPH‐FEM method is verified by comparing sloshing frequenciesobtained from theoretical formulation to experimental results and SPH‐FEM models. Then, theseismic response of a real‐life 160,000 m3 LNG prestressed storage tank is evaluated with differentliquid depths under four site classes. Simulation results show that the tip displacements of the LNGtank at liquid levels of 25% and 50% under site class IV are nearly identical to that of 75% and 100%under site class II. In addition, the maximum von Mises stress of the inner tanks exceeds 500 MPain all four site classes and jeopardizes the structural integrity of large LNG tanks. As a result,optimization of structural design and the establishment of an early warning system are imperativeto the safety of LNG tanks at high liquid levels.

Most current studies on the seismic responses of transmission towers are performed using two or three translational components of ground motion as earthquake inputs. In this study, a novel ...

In this paper, an innovative approach is developed to consider the impacts of dynamic effect and deterioration on the seismic performance analysis of reinforced concrete (RC) frame structur...

Independent component analysis (ICA) has the potential to identify anomalies in structural health monitoring (SHM) data due to its non-Gaussian data-processing ability. In order to addition...

In the dynamic characteristic analysis of high-speed railway bridges, free-vibration responses after a train passes are valuable for modal identification. However, distinguishing between fr...

The evaluation of stationarity, such as the widely used steady-state response assessment in stepped-sine testing, is a critical issue in structural dynamics. Stepped-sine excitation is a cr...

This paper proposes a strain-based performance warning method for bridge main girder monitoring using the long-term data obtained for varying load conditions, i.e., the variations in temper...

Many engineering systems, from subsea pipelines to space structures, from moving vehicles to stationary skyscrapers, are subject to unwanted vibration excitations. Often vibration control can be considered as a problem of energy dissipation and vibration damping. The aims of this issue are to accumulate, disseminate, and promote new knowledge about vibration control, especially for topics related to energy dissipation methods for vibration damping. Topics in this issue reflect the start-of-the-arts in the field of vibration control, such as inerter dampers and pounding tuned mass dampers (PTMDs). This special issue also reports other types of new energy dissipation devices, including a multi-unit particle damper, a nonlinear eddy current damper, and layered dampers. Also reported in this issue are structural elements with innovative designs to dissipate energy. In addition, this special issue also reports two research studies on the dynamic responses of a structural foundation and an earth-retaining structure. Though most papers in this special issue are related to passive methods, one paper reports a semi-active vibration control via magnetorheological dampers (MRDs), and another two papers report active vibration controls using piezoelectric transducers and inertial actuators, respectively.

In recent studies, spectral matching is the most commonly proposed method for selecting earthquake records for time-history analysis of structures. However, until now, there have been no serious investigations of the effects of coordinate values on the scaling of ground motions. This paper investigated the influence of using arithmetic and logarithmic values of response spectra in spectral matching procedures (i.e., ASM and LSM methods) on the results of nonlinear structural time-history analysis. Steel moment resisting frame structures of the 3-, 9-, and 20-stories, which represent low-, medium-, and high-rise buildings, respectively, were used as examples. Structural benchmark responses were determined by calculating the arithmetic mean and median of peak interstory drift ratio (PIDR) demands based on the three record sets developed by the American SAC Steel Project. The three record sets represent seismic hazard levels with 50%, 10%, and 2% probabilities exceeded in 50 years, and their average acceleration spectra were also taken as the target spectrum. Moreover, another 40 record components for selection were scaled both by ASM and LSM methods. The seven components whose spectra were best compatible with the target spectra were selected for the structural time-history analysis. The scale factors obtained by the LSM method are nearly larger than that of the ASM method, and their ranking and selection of records are different. The estimation accuracies of structural mean (median) responses by both methods can be controlled within an engineering acceptable range (±20%), but the LSM method may cause larger structural responses than the ASM method. The LSM method has a better capacity for reducing the variability of structural responses than the ASM method, and this advantage is more significant for longer-period structures (e.g., 20-story structure) with more severe nonlinear responses.

In this paper, a new rotation-magnified viscoelastic damper (RMVD) was developed. The damper applying the lever principle amplified the relatively small angular deformation manyfold at the beam-column joints, increased the shear deformation and hysteretic energy dissipation of viscoelastic materials to achieve an ideal energy dissipation effect. Firstly, the basic structure and working principle of the RMVD were introduced, and the quality index of high damping butyl rubber was discussed through the uniaxial tensile test and shear test. Secondly, the physical model of a new rotation-magnified viscoelastic damper was built, and its hysteresis curve was obtained through experiments. Additionally, the mechanical properties were compared with those of the traditional non-amplification function angle damper. Then, according to the structural characteristics and experimental results of the RMVD, the mechanical models were proposed to conduct a numerical simulation. Finally, the dynamic time-history analysis of the steel frame structure with the new damper installed at the beam-column joints was performed, and the results showed that the RMVD has a better damping control effect.

Many previous investigations of reinforced concrete (RC) frame structures have demonstrated that beam-column joints may experience significant nonlinearities under earthquake excitations. However, most available analysis methods assume that the joint region remains rigid. Because joint failure may result in strength and stiffness losses and even induce structural collapse, it is difficult for an analytical model with a rigid joint assumption to obtain an accurate prediction of the structural nonlinear response. The behavior of a joint is mainly affected by the shear deformation of the joint core and bond-slip of beam longitudinal reinforcements in the joint. Although many different types of modeling approaches have been presented to effectively represent the behavior mechanism of beam-column joints, the introduction of joint models inevitably increases the complexity of the analytical model of the global structure and the effort of the solution process. Therefore, achieving highly efficient analysis on the premise of accurately predicting the seismic response of RC frame structures is still a topic that deserves investigation. This study presents an efficient analysis method for the accurate evaluation of the nonlinear response of RC frames considering the effect of beam-column joint deformation based on the concept of local inelasticity separation. The proposed method captures the bond-slip behavior at beam ends by adding inelastic rotation hinge mechanisms to the ends of the existing inelasticity-separated fiber beam-column model and uses a sliding hinge mechanism to simulate the inelastic shear response of the joint core. A small number of additional inelastic degrees of freedom that are separated from the global displacement degrees of freedom of the structure is introduced to describe both the inelastic rotation behavior and the inelastic deformation of the proposed bond-slip hinge mechanism and the sliding hinge mechanism. Consequently, the Woodbury formula can be utilized for nonlinear iterative solutions to avoid updating the global stiffness matrix, thus significantly improving the computational efficiency. The exactness of the proposed method is verified against experimental data, and its application is illustrated through a seismic response analysis example.

The roof of Dalian gymnasium was designed in the form of suspen-dome structure. A structural health–monitoring system has been developed for the roof structure to guarantee the safety condition during construction process as well as in future service. In this article, a monitoring scheme was proposed in detail according to the mechanical characteristics of the roof structure. Fiber Bragg grating sensors, inclinometers, and accelerometers were applied to measure necessary structural information. In order to interrogate different types of sensors, a novel data acquisition device of the structural health–monitoring system was also introduced and has achieved multitudinous physical variable synchronization acquisition. By analyzing the data obtained during the construction and normal operation of the gymnasium, the structural health condition was evaluated and the structural damage could subsequently be located.

In practical engineering, power spectral density is always used to identify structural dynamic properties by picking peak points. However, the peaks in the spectral curve are not easy to be determined sometimes. A lot of peaks in the curve would cause some peaks close, which induces the closely spaced modes. The damping ratio is another reason to generate closely spaced modes, because the damping can make some peaks merge together. This paper proposes an innovative method to identify the closely spaced modes. First, the formulation is derived to reveal the components of the closely spaced modes in the power spectral density based on frequency domain decomposition. Then singular vector comparison is presented to determine whether there are closely spaced modes or not, where an angle criterion between two vectors is proposed. Finally, a numerical example is used to validate the effectiveness of the proposed method. The results show that the angle criterion can find the independent and dependent modes. For the close peak points in the spectral curve, the angle can determine that the points are single or closely spaced modes. Therefore, the proposed method to identify the closely spaced modes is efficient.

Wireless sensor networks are becoming attractive data communication patterns in structural health monitoring systems. Designing and applying effective wireless sensor network–based structural health monitoring systems for large-scale civil infrastructure require a great number of wireless sensors and the optimal wireless sensor networks configuration becomes critical for such spatially separated large structures. In this article, optimal wireless sensor network configuration for structural health monitoring is treated as a discrete optimization problem, where parameter identification and network performance are simultaneously addressed. To solve this rather complicated optimization problem, a novel swarm intelligence algorithm called the automatic-learning firefly algorithm is proposed by integrating the original firefly algorithm with the Lévy flight and the automatic-learning mechanism. In the proposed algorithm, the Lévy flight is adopted to maximize the searching capability in unknown solution space and avoid premature convergence and the automatic-learning mechanism is designed to drive fireflies to move toward better locations at high speed. Numerical experiments are performed on a long-span bridge to demonstrate the effectiveness of the proposed automatic-learning firefly algorithm. Results indicate that automatic-learning firefly algorithm can find satisfactory wireless sensor network configurations, which facilitate easy discrimination of identified mode vectors and long wireless sensor network lifetime, and the innovations in automatic-learning firefly algorithm make it superior to the simple discrete firefly algorithm as to solution quality and convergence speed.

Pipelines function as blood vessels serving to bring life-necessities, their safe usage is one of the foremost concerns. In our previous work, fiber Bragg grating (FBG) hoop strain sensor with enhanced sensitivity was developed to measure the hoop strain variation on a pressurized pipeline. In this paper, combined with multi-class support vector machine (SVM) learning method, the hoop strain information is used to classify pipeline abnormal working conditions, including cases of external impact, normal leakage and small rate leakage. The parameters of different kernel functions are optimized through 5-fold cross validation to obtain the highest prediction accuracy. The result shows that when taking radial basis kernel function (RBF) with optimized C and γ values, the classification accuracy for abnormal condition reaches up to 95%. The error appears only in separating the small leakage cases from normal working conditions. This pipeline abnormal classification approach using FBG hoop strain sensor combined with multi-class SVM shows potential prospective in pipeline accident monitoring and safety evaluation.

Strain gauges and accelerometers are widely used in bridge structural health monitoring systems. Generally, the strain gauges are placed on the key locations to obtain local structural deformation information; the accelerometers are used to obtain the structural modal information. However, the modal information contained in the measured strains is not taken into account. In this article, to fully utilize the modal information contained in strains, a mode shape estimation method is proposed that the strain mode shapes of the strain locations are used to obtain the displacement mode shapes of some positions without accelerometers. At first, to simulate the practical situation, some positions with large structural deformations are selected as the strain gauge locations. Using the proposed mode shape estimation method, the displacement mode shapes of some locations without accelerometers are estimated by the strain mode shapes using the least squares method, and the locations with the smallest estimation error are finally determined as the estimated locations. Then, accelerometers are added to the existing sensor placement. Here, the modal assurance criterion is used to evaluate the distinguishability of the displacement mode shapes obtained from the strain gauges and accelerometers. The accelerometer locations that bring the smallest modal assurance criterion values are selected. In addition, a redundancy can be set to avoid the adjacent sensors containing similar modal information. Through the proposed sensor placement method, the deformation and modal information contained in the strain gauges is fully utilized; the modal information contained in the strain gauges and accelerometers is comprehensively utilized. Numerical experiments are carried out using a bridge benchmark structure to demonstrate the sensor placement method.

The post-tensioning method, which involves the post-tensioning tendon duct (PTTD), is often used to reinforce concrete beams. An important procedure of the post-tensioning method is to fill the tendon duct with grout to protect the prestressed reinforcement from moisture and air. The grouting quality has a great impact on the corrosion prevention for the prestressed reinforcement and the bearing capacity of the concrete structures. In this paper, a method using Lead Zirconate Titanate (PZT) enabled time-reversal method to monitor the grouting quality is proposed. PZT is a commonly used piezoceramic material with strong piezoelectric effect. In the proposed method, one PZT ring installed on the prestressed reinforcement is used as an actuator to generate stress waves and the other distributive PZT patches bonded on the outer surface of the tendon duct are applied as sensors to detect the propagated stress waves. The grout in tendon duct forms conduits between PZT ring actuator and PZT patch sensors. To quantitatively represent the grout’s presence, the time-reversal method is used. The received signals from the sensors are reversed by the time-reversal operation and re-emitted. The grouting quality is evaluated by analyzing the peak value changes of the time-reversal focused signal. Experiments with 0%, 50%, 75%, and 100% grouting levels are conducted by the proposed method. The experimental results show that the grouting quality in the tendon duct can be estimated by monitoring the peak value changes of the time-reversal focused signal.

Pipeline is an important structure to transport oil and gas through long distances. However, pipeline also suffers from many threats especially corrosion and leakage. Therefore, it is necessary to conduct pipeline safety monitoring. With the advantage of high precision in distributed strain measurement, the optical frequency domain reflectometry (OFDR) technique is more suitable for pipeline monitoring. In this paper, a new application of the OFDR technique is introduced to monitor both corrosion and leakage. In order to verify this method, simulation tests of corrosion and leakage were conducted. In the corrosion test, several optical fiber sensors were bonded to the pipe surface with the same interval, forming a sensor array. Based on the sensor array, a hoop strain nephogram was created to show the corrosion level and corrosion location. In the leakage test, the results indicated that pipeline leakage can be detected by the distributed optical fiber sensor (DOFS). All the test results demonstrate that it is possible to monitor pipeline corrosion and leakage based on the hoop strain theory and the DOFS.

This paper presents a novel approach to model and simulate the multi-support depth-varying seismic motions (MDSMs) within heterogeneous offshore and onshore sites. Based on 1D wave propagation theory, the three-dimensional ground motion transfer functions on the surface or within an offshore or onshore site are derived by considering the effects of seawater and porous soils on the propagation of seismic P waves. Moreover, the depth-varying and spatial variation properties of seismic ground motions are considered in the ground motion simulation. Using the obtained transfer functions at any locations within a site, the offshore or onshore depth-varying seismic motions are stochastically simulated based on the spectral representation method (SRM). The traditional approaches for simulating spatially varying ground motions are improved and extended to generate MDSMs within multiple offshore and onshore sites. The simulation results show that the PSD functions and coherency losses of the generated MDSMs are compatible with respective target values, which fully validates the effectiveness of the proposed simulation method. The synthesized MDSMs can provide strong support for the precise seismic response prediction and performance-based design of both offshore and onshore large-span engineering structures.

As key components in the transportation networks at coastal areas, sea-crossing cable-stayed bridges play a very important role in the development of regional economy. These bridges may be subjected to severe earthquakes during their life-cycles. Owing to the lack of actual seafloor earthquake recordings and approaches in synthesizing offshore seismic motions, the onshore seismic motions are commonly utilized as inputs in the seismic design of sea-crossing cable-stayed bridges. However, this approach may lead to erroneous structural response predictions since the characteristics of onshore and offshore seismic motions are different. In this paper, the seismic performance of a sea-crossing cable-stayed bridge is comprehensively evaluated based on the fragility function methodology. A novel approach is presented to theoretically calculate the ground motion transfer function at any location within an offshore site and stochastically synthesize the offshore multi-support ground motions at different depths (MGMDDs). The OpenSees analysis platform is employed to develop the three-dimensional finite element model of the example bridge, in which the p-y, t-z and q-z elements are installed at the pile nodes to simulate the interaction between the bridge piles and surrounding soils. Moreover, the effect of seawater on the bridge seismic responses is modeled using the hydrodynamic added mass method. The seismic fragility curves of the example bridge are generated by using the synthesized MGMDDs as inputs. The influences of spatial and depth varying offshore seismic motions, soil-structure interaction (SSI) and seawater added mass on the bridge component and system fragilities are investigated and discussed. Numerical results show that the seismic fragility of the example sea-crossing cable-stayed bridge is affected by the above mentioned influencing factors with different extents. The proposed approach can rationally and effectively assess the seismic fragilities of sea-crossing cable-stayed bridges.

The strain rate effect can inevitably impact the seismic responses of reinforced concrete (RC) structures because the dynamic properties of RC materials under earthquakes change significantly with the time-varying loading rates. This paper carries out systematic experimental tests and numerical simulations to investigate the effects of strain rates on the seismic responses of RC structures. The dynamic properties of micro-concrete and iron wire used in the shaking table specimen are firstly tested under seismic loading rates and the corresponding dynamic increase factors (DIFs) are estimated based on the test data. The shaking table test of a 1/5 scaled RC structure is performed to realistically reproduce the dynamic responses of RC structures with strain rate effect. Moreover, a three-dimensional rate-dependent fiber beam-column element is developed in the ABAQUS platform to establish the finite element (FE) model of the shaking table specimen, in which the estimated DIFs for the key parameters of micro-concrete and iron wire are employed to consider the strain rate effect. Besides, the rate-independent structural FE model is also developed using the traditional beam-column element with the static RC material constitutive models. The numerical results demonstrate that the seismic responses of RC structures are overestimated when the strain rate effect is neglected. As validated by the experimental data of the shaking table test, the FE model developed using the proposed rate-dependent fiber beam-column element can yield better structural seismic response predictions in comparison with the rate-independent model.

Considering future seismic risk and life-cycle cost, the life-cycle seismic design of bridge is formulated as a preference-based multi-objective optimization and decision-making problem, in which the conflicting design criteria that minimize life-cycle cost and maximize seismic capacity are treated simultaneously. Specifically, the preference information based on theoretical analysis and engineering judgment is embedded in the optimization procedure. Based on reasonable displacement ductility, the cost preference and safety preference information are used to progressively construct value function, directing the evolutionary multi-objective optimization algorithm’s search to more preferred solutions. The seismic design of a reinforced concrete pier is presented as an application example using the proposed procedure for the global Pareto front corresponding with engineering designers’ preference. The results indicate that the proposed model is available to find the global Pareto front satisfying the corresponding preference and overcoming the difficulties of the traditional multi-objective optimization algorithm in obtaining a full approximation of the entire Pareto optimal front for large-dimensional problems as well as cognitive difficulty in selecting one preferred solution from all these solutions.

Many tower structures have collapsed during strong wind events; therefore, the objective of the present study is to estimate the strength capacity of transmission towers accurately and to identify all potential failure modes. An uncertainty analysis method for tower structures subjected to a wind load is presented. Subsequently, random samples of material properties and section dimensions are generated based on the Latin Hypercube Sampling technique and then used to establish uncertain finite element models for transmission towers. A static non-linear buckling analysis for structures subjected to a wind load is conducted using ANSYS software. Based on tower models incorporating uncertainty, our analysis reveals that there are six possible initial failure tower members but only one for the deterministic model, indicating that the uncertainties regarding material properties and section dimensions should be taken into account. Furthermore, a sensitivity analysis is conducted, and the results reveal that the uncertainty of material properties has a stronger influence than the uncertainty of section dimensions. Finally, the influence of wind attack angle is discussed, and the initial failure positions and corresponding probabilities for various wind attack angles are obtained. The results show that the most unfavorable wind attack angle is 0° and that the most probable failure position of the tower of interest is the middle of the tower body.

Thermal actions greatly influence the mechanical behavior of cable-stayed bridges. The objective of this research is to investigate the characteristics of the thermal field and the variability of the quasi-static responses of the bridge towers. Based on the monitoring temperature and displacement data, the distribution of the thermal field for the bridge was studied and the time variability of the tower displacement was investigated. The correlation was analyzed to study the relationship between the temperature and the tower displacements and the tower-girder distances. The temperature-induced cable force increments were calculated and a linear regression between the cable force increments and the structural temperatures was performed. A strong linear relationship between the temperature and quasi-static responses of the tower was observed. It is concluded that thermal actions have substantial effects on the quasi-static displacement. Moreover, the temperature-induced cable forces should be fully considered in the safety design of the bridge cables.

In this paper, a damage imaging method for 2-D concrete structures is proposed by employing embedded tubular piezoceramic transducers. The proposed method can image the damages when few numbers of transducers are used or less experimental data is collected. First, the time difference of arrival-based delay and sum (DAS) imaging method is adopted to improve the damage localization accuracy for concrete structural health monitoring. Compared with the conventional DAS imaging algorithm, the proposed method increases the potential number of combinations between the response signals induced by the damage in each transmitter and sensor pair, improving the signal to noise ratio of the imaging map and enhancing the performance of the defect detection and location. Second, to enable the proposed method applicable to a 2-D concrete structure (such as cement concrete pavement and shear walls), embeddable tubular lead zirconate titanate (PZT) transducers rather than conventional PZT patches are used. The new tubular PZT transducers are able to generate radially uniform stress waves in a planar concrete structure. Due to the special construction of the tubular PZT transducers, the detection aperture is significantly improved. Therefore, a few transducers are needed in contrast with the conventional PZT patches. The experimental results conducted on a concrete slab with eight embedded tubular PZT transducers demonstrate that the proposed method can predict the defect accurately and efficiently even with few transducers and less experimental data.

Reinforcement steel corrosion is one of the major causes of premature deterioration of concrete structures in marine environments or subjected deicing salts. Steel corrosion causes economic loss and even results in structural collapse and consequently loss of human life. Various optical fiber sensors have been proposed to monitor steel rebar corrosion in concrete structures over the past two decades due to light weight, compactness, small size, immunity to electromagnetic interference, and capacity of being multiplexed into a sensor network. This study presents a state-of-the-art review of optical fiber sensors for corrosion monitoring of reinforcement steel in concrete structures with emphasis on sensing principle and performance parameters including measurand, sensitivity, monitoring range and service life. The optical fiber corrosion sensors reviewed in this study mainly include fiber Bragg grating (FBG) based corrosion sensors, long-period fiber grating (LPFG) corrosion sensors, extrinsic Fabry-Perot interferometer (EFPI) corrosion sensors, Brillouin backscattering-based distributed fiber optic corrosion sensors, optical frequency domain reflectometry (OFDR) corrosion sensors, and other fiber optic corrosion sensors. This review aims to clarify performance and limitations of fiber optic sensors for reinforcement steel corrosion monitoring in concrete for the purpose of providing a foundation for future research and engineering applications.

Currently, the construction process of large offshore platforms worldwide involves building the topside and hull separately and then having them integrated. The jacking closure scheme by overlapped support tower bearing the topside is a new integration method, which has a great advantage over other traditional methods in vertical bearing capacity. But its weak bearing capacity to lateral forces like wind load limits the jacking height. Moreover, few engineering examples and academic researches also cause insufficient understanding of it. Therefore, this paper, based on the first deep-water semi-submersible platform with the10,000-ton oil storage worldwide, i.e. “Deep Sea No. 1” energy station, aims to evaluate the wind-resistant performance during the jacking closure process. Firstly, the background and the jacking closure scheme of this project are introduced in detail. Secondly, the finite element models (FEMs) of the jacking system are established according to the overlapped characteristics of jacking towers and the corresponding failure criteria. Then, the wind-induced vibration response is simulated, and the static pushover is conducted to evaluate the ultimate bearing capacity and its influencing factors. The failure criteria are checked using ANSYS parameter design language. It is found that “the occurrence of tensile stress on the contact surface” is the first and main failure mode of the structure. Additionally, the results also reveal that the strand cables can not only improve the ultimate bearing capacity of the structure but also change its weak direction. However, the improvement is gradually weakened with the increase of jacking height. In contrast, the contribution of the bracing pipes to the structural bearing capacity is always significant. These findings can be used to develop a more reasonable closure plan.

Engineering structures may inevitably be subjected to earthquakes and winds during their life cycles, furthermore, with the probability of simultaneous occurrence, the hit of combined earthquake and wind shall pose a stiffer threat to the structural functionality and safety. Passive control technique is a practical and effective method to mitigate earthquake and wind hazards for new or existing engineering structures. This paper develops a multi-hazard protective system with the hybrid energy-dissipated devices of buckling-restrained braces (BRBs) and viscous dampers (VDs), and investigates the effectiveness and optimum design parameters of different supplemental devices using the fragility function method. The OpenSees platform is employed to establish the finite element (FE) models of bare steel–concrete moment resisting frame (MRF), buckling-restrained braced frame (BRBF), viscous damped frame (VDF) and hybrid damped frame (HDF) with both BRBs and VDs. In total 120 groups of combined “earthquake-wind” events with a wide range of hazard intensities are developed using the Monte Carlo simulation, which are applied to the dynamic time history analyses of the aforementioned four frame structures. The multi-hazard fragility surfaces, which depict the exceeding probability of structures under simultaneous earthquake and wind loads, can be generated for different damage states. The numerical results indicate that the HDF is an effective structural system against the multiple hazards attacks, and the energy dissipation contributions of BRB and FVD vary with the hazard intensities of earthquake and wind. To further identify the optimum design scheme for the HDF system, the parameters of hybrid passive control devices are extensively investigated by evaluating the hazard intensities required when achieving specified damage states in the fragility surfaces. The findings can provide a practical guide for the design of structure with energy-dissipated devices against the multi-hazard scenarios of earthquake and wind.

Due to the shortage of offshore seismic records and inhere difficulty in simulating artificial offshore ground motions, numerous existing works have been performed to investigate the seismic responses of free-spanning submarine pipelines, not only using onshore seismic records as inputs but also adopting uniform seismic excitations. These analytical schemes may result in severe misestimates of the seismic responses. In this content, this paper numerically investigates the seismic behaviors of a free-spanning submarine pipeline by using multi-support earthquake motions within offshore sites (MEMOSs) as inputs. The soil-pipe and water-pipe interactions are modeled using the nonlinear soil spring and added mass methods, respectively. The effects of spatially varying and overlying seawater are explicitly taken into account in the simulation of MEMOSs. The seismic behavior law of the free-spanning submarine pipeline under the synthesized MEMOSs is analyzed and summarized. Moreover, the impacts of the seismic excitation type, offshore seismic motion, coherence loss, local site condition and free span length on the Mises stress, vertical displacement and failure PGA of the submarine pipeline are examined and discussed comprehensively. Numerical results show that the middle and ends of free span are the dangerous regions; and the MEMOSs, coherence loss, local site condition and free span length have significant influences on the seismic responses and operational capacity of the pipeline. Based on the obtained results, some meaningful advices are recommended to the pipeline designers that (1) more attentions should be paid to the middle and ends of free span in the pipeline design; (2) the MEMOSs should be adopted as seismic inputs to accurately predict the seismic behaviors of pipelines; (3) the construction of submarine pipelines in soft clay and formation of large-dimensional free span are adverse for the safe operation of pipelines under earthquake actions, which should be avoided in engineering practice.

Earthquakes are the most harmful natural hazard to engineering structures. During a rain event, the increased moisture content in the adobe walls of masonry-adobe composite structures may lead to short-term degradation in wall capacity. Neglecting this degradation will result in large errors in the risk assessment of structures subjected to an earthquake that occurs after a heavy rain. In this paper, marginal probability distribution models of the earthquake intensity and rain intensity were separately established based on a large amount of measured data for areas with frequent high-intensity rainfall events. A copula-based joint probabilistic model of earthquake intensity and rain intensity was proposed and subjected to a goodness-of-fit test to obtain the multihazard joint return period and annual exceedance probability. Additionally, a failure risk assessment method for masonry-adobe composite structures was proposed based on the multihazard joint probabilistic model and structural vulnerability analysis. The proposed method was used for the risk assessment of a single-story masonry-adobe composite structure. The results showed that the seismic failure probability of the structure was 142% higher when the rain-based degradation of the adobe wall was considered than when this degradation was neglected. Therefore, the accuracy of failure probability calculations for masonry-adobe composite structures can be improved by using the multihazard joint distribution.

Current design specifications often deal with seismic and wind events in isolation, which may underestimate the failure probability. In this paper, a reliability-based approach is presented to compute the load modification factor for designing high-rise buildings in regions prone to earthquake and strong wind events. The paper illustrates the proposed procedure from the construction of hazard models to load modification calculations, which is implemented in a 42-story steel frame-reinforced concrete (RC) core tube building located in the Dali region, southwest of China. The uncertainties associated with hazard models, material properties, input loads, demand models and structural capacity are considered to improve the accuracy of failure probability estimations. The effects of individual and concurrent earthquakes and strong winds are accounted for in the reliability-based design method. Then, the load modification factor is determined by comparing the calculated failure probability with the rational target value. Finally, a suggested combined factor will be used to modify the value of the design wind load in the limit state function. More work is needed before load modification can be applied in practice. However, this study offers a practical and extensible approach to improve the future calibration of load combination criteria for designing high-performance structures against various hazards.

The effect of geometric imperfections on the decrease of the ultimate capacity of transmission towers has not been sufficiently studied. Despite bucking mode-shaped imperfections are commonly used in deterministic imperfection simulation methods, the current efforts still exist many limitations such as unknown worst buckling mode shape or indeterminate modal combination rules, participation coefficients and truncation order of buckling modes. Herein, a new method named eigenmode assembly method (EAM) is proposed based on linear buckling analysis (LBA). In this method, the first three order local buckling modes of each weak position predicted by LBA are assembled in their sequential order. Two full-scale test towers are employed to implement and validate the proposed approach in this study. The effect of discretized element numbers on the buckling mode shape is firstly discussed, then material and geometric nonlinear analysis is conducted for each case of the EAM-based imperfection assembly process. The results indicate that the EAM can obtain a stable reduction factor for the ultimate capacity of the ideal tower structure which benefited from the advantage of horizontal segment of the capacity curve and can accurately predict the failure positions of transmission towers. Finally, the minimum discretized element number, the minimum introduced buckling mode number and the simplified imperfection assembly formula are recommended by parametric analysis.

In past earthquakes, low-ductility steel concentrically braced frame (CBF) buildings have been observed to retain reserve capacity after brace fracture. The failure mechanisms and earthquake ground motion-sensitive characteristics of the reserve system of low-ductility CBFs are not understood due to limited dynamic experimental data. In this study, a series of shaking table tests is presented to examine the reserve capacity of a scaled two-bay, three-story, low-ductility CBF model in which a pair of square hollow section braces are arranged in a chevron pattern. The model structure was repeatedly subjected to two unidirectional ground motions with successively increasing magnitudes in a stiff soil site and a soft soil site. The experimental phenomena of elastic response, brace buckling behavior, brace reengagement behavior, reserve system response and collapse state were observed. The braces of the low-ductility CBFs were vulnerable to local buckling under dynamic loads and resulted in a soft story where braces failed, while braces and frames in the other stories had no further damage. The reserve stiffness, rather than energy dissipation or reserve strength, was the most important factor in the collapse-prevention capacity for the reserve system of the tested low-ductility CBF, and the lateral stiffness of the columns was the main source of reserve stiffness. Flexible reserve systems with small lateral stiffness were never significantly excited at their natural periods by hard soil site-specific ground motions, while with such systems, a greater risk of potential collapse appears to be posed due to earthquakes at soft soil sites than at hard soil sites for the test model.

Wind action is one of the environmental actions which has substantial static and dynamic effects on the long-span bridges. The main objective of the paper is to reveal the static and dynamic characteristics of the regular wind and typhoon condition. A monitoring-based investigation has been carried out to analyze the characteristics of the wind actions. The static characteristics of regular wind and typhoon condition are investigated by analyzing the average wind speed. Moreover, the dynamic characteristics of the two conditions of wind actions are studied by analyzing the parameters of turbulence intensity and gust factors. The correlation analysis is performed between the lateral wind speed and the lateral girder displacement to reveal the static effects of the wind actions on the bridge structures. It is concluded that static and dynamic characteristics of regular wind and typhoon conditions are quite different, and the dynamic effects of wind actions obtained based on monitoring data need to be further studied.

Sensor faults, which occur when sensor outputs display unacceptable deviations from the true values of measured variable, will cause false alarms and missed detections in structural health monitoring (SHM) systems. The study about sensor validation is a relatively new research direction in the SHM field and it is meaningful to guarantee the accuracy and reliability of health-condition evaluations for monitored structures. This paper provides a comprehensive review of current research and development activities in sensor validation methodology for SHM. At first, seven typical sensor fault types are described and a detailed methodology categorization is provided. Following that, the progresses on sensor validation, which mainly focusses on the detection, isolation and reconstruction of sensor faults, are reviewed based on the categorization. Finally, concluding remarks and promising research efforts about sensor validation are summarized in detail.

Output-only modal identification methods are practical for large-scale engineering. Recently, independent component analysis (ICA) which is one of the most popular techniques of blind source separation (BSS) has been used for output-only modal identification to directly separate the modal responses and mode shapes from vibration responses. However, this method is only accurate for undamped or lightly damped structures. To improve the performance of ICA for high damping structures, this article presents an extended ICA-based method called ICA-F, which establishes a BSS model in frequency domain. First, the basic idea of BSS and ICA applied in modal identification is introduced in detail. The free vibration responses and the correlation functions of ambient responses can be cast into the frequency-domain BSS framework just by mapping the time history responses to frequency domain through fast Fourier transform (FFT). Then, an ICA-based method in frequency domain called ICA-F is proposed to accurately extract mode shapes and modal responses for both light and high damping structures. A simulated 3 degree of freedom mass-spring system and a 4-story simulated benchmark model developed by the IASC-ASCE Task Group in Health Monitoring are employed to verify the effectiveness of the proposed method. The results show that the proposed method can perform accurate modal identification for both light and high damping structures. Finally, the IASC-ASCE experimental benchmark structure is also utilized to illustrate the proposed method applied to practical structure.

According to the inverse magnetostrictive effect, magnetic permeability variations in ferromagnetic materials under elastic stress offer the potential to measure tension. In this study, a prototype sensor was designed, fabricated, and tested. An eddy current sensor (ECS) with a single coil structure was used to detect tension due to its lower cost, simpler structure and less mutual interference than that of conventional elastomagnetic (EM) sensors. In addition, the influence of a sleeve structure on the ECS was investigated through experimental studies. The experimental results indicated that the use of sleeve structure could enhance the relative sensitivity and reduce the repeatability error of the sensor. Furthermore, a bypass structure was designed to adjust the bias magnetic field by changing air gap in the lower magnetic circuit or by rotating yoke in the upper magnetic circuit. The results demonstrated a linear relationship between voltage across the sensor and tension. Finally, the bias magnetic field and working frequency were optimized by monitoring the sensor sensitivity.

Pounding phenomenon between base-isolated structures under near-fault earthquakes has been widely investigated with various impact models around the world. Firstly, the existing impact analysis models are summarized and discussed in this paper. For the Hertz-damp impact model, the damping constant does not coincide with its physical fact. Then, the damping constant in the Hertz-damp impact analysis model was modified based on the Hertz theory. Next, the approximate formula of the damping constant is theoretically derived, and the effectiveness is verified by a simulation analysis. The numerical results show that the pounding can significantly increase the floor acceleration, especially at the isolation layer. In addition, the impact stiffness has a significant effect on the acceleration response, and the inter-story drifts are also sensitive to the variety of impact stiffness. The simulation results indicate that excessive flexibility at the base-isolated system may lead to a susceptible pounding with a limited seismic gap.

The review summarizes recent studies on D-shaped optical fibers and their recent applications in optical sensors. The configurations and working principles of D-shaped optical fibers are introduced. For each optical fiber sensor, the structure principles and measuring methods are all discussed in detail, with their optimal characteristics and performances being compared. Results from various studies show that it is possible to realize a high-sensitivity optical fiber sensor with a simple structure, good mechanical properties, and strong anti-interference ability. This may be due to the excellent structural design of the D-shaped optical fiber. Finally, key issues and new challenges on the D-shaped optical fiber are discussed.

In this study, three rapid repair techniques are proposed to retrofit circular bridge piers that are severely damaged by the flexural failure mode in major earthquakes. The quasi-static tests on three 1:2.5 scaled circular pier specimens are conducted to evaluate the efficiency of the proposed repair techniques. For the purpose of rapid repair, the repair procedure for all the specimens is conducted within four days, and the behavior of the repaired specimens is evaluated and compared with the original ones. A finite element model is developed to predict the cyclic behavior of the repaired specimens and the numerical results are compared with the test data. It is found that all the repaired specimens exhibit similar or larger lateral strength and deformation capacity than the original ones. The initial lateral stiffness of all the repaired specimens is lower than that of the original ones, while they show a higher lateral stiffness at the later stage of the test. No noticeable difference is observed for the energy dissipation capacity between the original and repaired pier specimens. It is suggested that the repair technique using the early-strength concrete jacket confined by carbon fiber reinforced polymer (CFRP) sheets can be an optimal method for the rapid repair of severely earthquake-damaged circular bridge piers with flexural failure mode.

Purpose Magnetic permeability variations of ferromagnetic materials under elastic stress offer the potential to monitor tension based on the inverse magnetostrictive effect. The purpose of this paper is to propose an innovative self-inductance tension eddy current sensor to detect tension. Design/methodology/approach The effectiveness of conventional elasto-magnetic (EM) sensor is limited during signal detection, due to its complex sensor structure, which includes excitation and induction coils. In this paper, a novel self-inductance tension eddy current sensor using a single coil is presented. Findings The output signal was analyzed through oscilloscope in the frequency domain and via self-developed data logger in the time domain. Experimental results show the existence of a linear relationship between voltage across the sensor and tension. The sensor sensitivity is dependent on operating conditions, such as current and frequency of the input signal. Practical implications The self-inductance sensor has great potential for replacing conventional EM sensor due to its low cost, simple structure, high precision and good repeatability in tension detection. Originality/value A spilt sleeve structure provides a higher permeability path to magnetic field lines than a non-sleeve structure, thus reducing the loss of magnetic field. The self-developed data logger improves sensitivity and signal-to-noise ratio of sensor. The novel sensor, as a replacement of the EM sensor, can easily and accurately monitor the tension force.

In order to study the differences in vertical component between onshore and offshore motions, the vertical-to-horizontal peak ground acceleration ratio (V/H PGA ratio) and vertical-to-horizontal response spectral ratio (V/H) were investigated using the ground motion recordings from the K-NET network and the seafloor earthquake measuring system (SEMS). The results indicate that the vertical component of offshore motions is lower than that of onshore motions. The V/H PGA ratio of acceleration time histories at offshore stations is about 50% of the ratio at onshore stations. The V/H for offshore ground motions is lower than that for onshore motions, especially for periods less than 0.8 s. Furthermore, based on the results in statistical analysis for offshore recordings in the K-NET, the simplified V/H design equations for offshore motions in minor and moderate earthquakes are proposed for seismic analysis of offshore structures.