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Seismic analyses of structures typically require the spectrum of the scaled seed accelerogram to be consistent with a specified target spectrum. Peak ground acceleration (PGA) and Arias intensity levels of scaled and matched ground motions are difficult to maintain after spectral matching with existing time-domain methods. An improved method is thus proposed to address these issues by introducing Arias Intensity Fitting (AIF) and PGA correction algorithms. In addition, adaptive relaxation parameters obtained from particle swarm optimization (PSO) are used to improve convergence efficiency. The effectiveness of the proposed method is validated by a comparison of the spectrally matched records with the scaled time series characteristics. Moreover, the proposed method is compared with two existing time-domain spectral matching methods. Results show that the proposed method performs better in generating the acceleration time series compatible with the target spectrum while preserving the nonstationary characteristics of the scaled seed accelerogram. Considerable improvements in the aspects of PGA and Arias intensity consistency between scaled and matched accelerograms are achieved without reducing the spectral matching accuracy. The convergence efficiency of the proposed method is improved with the implementation of adaptive relaxation parameters. • An improved time domain spectral matching method is proposed. • PGA correction and AIF methods are proposed to appropriate intensity measures. • The intensity measures contain Arias intensity and peak ground acceleration. • Adaptive relaxation parameter is applied to improve convergence efficiency. [ABSTRACT FROM AUTHOR]

In this study, multiple analytical mode decompositions (M-AMD) are proposed to identify the parameters of nonlinear structures from forced vibration. For the time-varying damping (or stiffness) coefficient of a weakly-to-moderately nonlinear system, the slow-varying part is first estimated from the system responses and their Hilbert transforms, which is corrected with an adaptive low-pass filter referred to as analytical mode decomposition (AMD). The fast-varying part can then be identified from the responses together with the estimated slow-varying part, which is again corrected with the AMD. The computational efficiency and accuracy of the proposed M-AMD are demonstrated with a Duffing oscillator subjected to harmonic loading. The errors in estimation of all model parameters are less than 3% from uncontaminated displacement responses, which is more accurate compared with the results from Hilbert spectral analysis. Changes of the fast-varying stiffness part have been taken into account with high accuracy. The M-AMD algorithm is then validated with a ¼-scale, 3-story building with one piezoelectric friction damper under earthquake excitations. The parameters of such a semi-active damper are identified with less than 1% error on average. [ABSTRACT FROM AUTHOR]

In this study, six 1/3-scale short bridge column specimens are investigated for shear strength under the same quasi-static cyclic loading protocol. The specimens consist of one cast-in-place (CIP) reference column and five precast columns, and the precast columns are designed with different connection approaches. The test includes the comparison between the specimens with or without shear keys, bonded or unbonded prestressing tendons, and column or footing embedment. Test results show that the shear strengths of precast columns using only mild reinforcement are emulative of the CIP column. Shear keys employed in the connection do not retain significant improvement in terms of hysteretic behavior, while specimens with prestressing tendons possess higher shear strength but lower ductility. The unbonded prestressing tendon provides unique self-centering capability with good energy dissipation. Finite element models of the columns were created with ANSYS by considering the bond-slip effect between reinforcement and concrete, contact behavior of connection surface, and material nonlinearity, depending on different structural details. The models can effectively simulate damage development under monotonic loading, and the load-displacement curves are in good agreement with the backbone curves of the test results. [ABSTRACT FROM AUTHOR]

In this study, seven 1/3-scale bridge column specimens are investigated under the same quasi-static cyclic loading protocol both experimentally and numerically. The specimens consist of one cast-in-place (CIP) reference column and six precast columns. The precast columns are designed with different connection details, and they are tested for the feasibility study of the urban viaducts of highway S6 in Shanghai, China. The seismic performance of the precast columns needs to be investigated and verified prior to the practical application of these connection designs. Based on the experimental results, the precast specimens solely using mild reinforcement exhibit similar hysteretic behavior to the CIP reference column, though various grouted connection approaches are employed. The differences between these precast specimens and the CIP reference column are less than 15% for all indices. The precast specimens with bonded tendons (prestressing strands or prestressing bars) retain higher strength, but no less than 30% decrease of energy dissipation capacity is found. The bonded prestressing strands give at least 10% increase in strength compared with the CIP reference column, while the bonded prestressing bars provide approximately 50% improvement. The precast specimen utilizing unbonded tendon (prestressing strands) shows unique self-centering capability with equivalent energy dissipation capacity of the CIP reference column, but it has 33% lower ductility. Finite element modeling is performed and calibrated with the test data. Bond-slip behavior near column-to-footing interface is modeled by using a ZeroLength element at the interface. Buckling, fatigue and strength reduction of reinforcement are also considered in the model. Hysteretic behaviors of the specimens can be effectively simulated, and differences of ultimate strengths between the experimental and numerical results are less than 9%. [ABSTRACT FROM AUTHOR]

In this study, quasi-static cyclic test was conducted for three 1/3-scale specimens of different precast concrete frame pier structure systems of an urban viaduct in Shanghai, China. Various connection deployment strategies were utilized for the specimens, in order to verify these precast concrete frame piers used in the real structure. Two of the specimens were of the same cap beam design, while the third one was with tie beam. The two frame piers with cap beam had the same column-footing connection (grouted splice sleeve coupler), but the column-cap connections were grouted splice sleeve coupler and grouted corrugated duct connection, respectively. The frame pier with cast-in-place tie beam, however, only kept the grouted splice sleeve coupler for column-footing connection. The cyclic test results showed similar seismic behavior of the two specimens with cap beam, whereas the specimen with tie beam exhibited less energy dissipation capacity. This indicated that the seismic performance differences among the specimens are mainly caused by different structure systems, and the two types of the connections behave similarly with little damage. Finite element models that were optimized by considering joint region behavior and bond-slip phenomena showed good agreement with the test results. [ABSTRACT FROM AUTHOR]

• Five short precast columns with different connection are tested under direct shear. • Shear failure mechanism is investigated and compared for all column specimens. • A new theoretic method is proposed to estimate shear strength for precast columns. • The proposed theoretic model can effectively predict shear strength at various stages. Precast bridge structures have been increasingly applied in recent civil engineering applications, which shortens construction time, lowers cost, improves structure quality, decreases traffic interruption, and reduces environment pollution. However, studies regarding to the shear behavior of short precast columns are limited. In this study, five short precast bridge columns, with span-to-depth ratio of 0.43, are tested under direct shear load. This is to understand shear failure mechanism of precast bridge columns with different design details. Two types of shear failure are found due to different embedment location of grouted splice sleeve (GSS) connectors. Different design details (e.g. steel grade of rebar, bonding material of joint interface, and existence of shear keys) also have certain impact on the shear strength of precast columns. Based on the test results, a new theoretic method is proposed to estimate shear strength of tested precast column specimens. The proposed method incorporates possible influencing factors of shear strength along with different failure stages and types. The parameters and formulas are calibrated and adjusted accordingly. It is found that, for short precast columns with GSS connectors, the theoretic solutions are within 5% in difference compared with test results, which shows better accuracy than other methods. This indicates that the proposed method is effective for the estimation of shear strength in this case. [ABSTRACT FROM AUTHOR]

• Seismic performance of self-consolidating concrete bridge column is evaluated. • Specimens are based on practical engineering application in high seismic region. • Comprehensive experiment is performed including quasi-static and shake table tests. • Results of unidirectional, bidirectional cyclic and shake table tests are compared. • Nonlinear numerical models with improved bond-slip modeling approach are developed. In this study, three different types of experimental approaches are carried out for the seismic evaluation of high strength self-consolidating concrete bridge columns in high seismic zone, including unidirectional quasi-static, bidirectional quasi-static and shake table tests. The 1/4-scale bridge column specimens are based on the practical engineering application of urban viaduct in high seismic region of northern China. The use of high strength self-consolidating concrete is to fulfill the demand of short construction time, high seismic resistance and harsh weather durability in the area. Based on the experimental results, it is found that similar damage progression is observed from all the tested specimens with concrete crush and longitudinal rebar buckling. Quasi-static cyclic tests tend to be more conservative but to overestimate the energy dissipation capacity and ductility, and the coupling effect from bidirectional loading cannot be ignored. In addition, nonlinear numerical models with improved bond-slip modeling approach are developed and calibrated by OpenSEES with the experimental data, where good agreement is achieved especially at early loading stage. [ABSTRACT FROM AUTHOR]

• Acoustic signal types are obtained through cable tension test from time difference. • Multiband wavelet transform is proposed for analyzing acoustic emission signals. • Multiband wavelet transform can effectively differentiate various signal features. • Unique time-frequency characteristics of each acoustic signal type are extracted. • Prediction and detection of wire fracture are achieved with the new technique. In this study, acoustic emission (AE) features to predict and detect wire fracture in seven-wire strands were characterized with multiband wavelet analysis. Two steel strands were tested up to 89 kN with each instrumented with a pair of AE sensors at two ends. The cross section of one wire was locally reduced up to 90% in 10% increment at center and support of the two strands, respectively. For both strands, the AE parameters (hits, energy, and counts) changed little up to 80% reduction in cross section of the partially cut wire, and suddenly jumped at the fracture (under 73 kN) of the notched wire with 90% reduction in cross section. The acoustic signals of inter-wire slippage and fracture initiation are significantly shorter in time duration than the signal of fracture. Their dominant frequencies and frequency bandwidths are increasingly higher and wider. The frequency band of the fracture signal is significantly broader than that of either the fracture-induced echo or artificial tapping noises. The time duration of artificial tapping noises is substantially longer than that of either fracture or fracture-induced echo. These distinct time-frequency characteristics allow an early detection and localization of wire fracture following the proposed procedure. [ABSTRACT FROM AUTHOR]

Seismic isolation of long-span cable-stayed bridges in the transverse direction requires both large restoring force and large deformation capacity for the girder–tower connections, especially in critical seismic conditions, which challenges a lot for the design of earthquake resisting system (ERS). A capable and resilient lateral isolation system (CRLIS) is proposed that comprises FRP cables and a parallel FVD for the girder–tower connections and can provide the desired large restoring force and large deformation capacity. Based on a practical long-span cable-stayed bridge, detailed design parameters of the CRLIS were presented through a parameter analysis, and then a 1/35-scale physical model of the long-span cable-stayed bridge was made and tested on a four-shake-table testing system in the Multi-functional Shaking Table Lab at Tongji University. Details of the physical model including the scale factor, configuration of the structural members, additional mass blocks, boundary conditions, and the essential pretest numerical validation were briefly introduced. The experimental results show that the CRLIS could significantly reduce the acceleration response of the girder and the shear force to the girder–tower connections, as well as a considerable reduction of the forces to the towers. Numerical simulation is also conducted and validated by the experimental data; specifically, the sensitivity of the numerical simulation result to the Rayleigh damping matrix is investigated and a definition of the Rayleigh damping matrix is suggested. Furthermore, the isolation effectiveness of the CRLIS is concisely analyzed. • A capable and resilient lateral isolation system (CRLIS) is proposed for cable-stayed bridges. • Shaking table test on a 1/35-scale long-span cable-stayed bridge was conducted. • Numerical model is developed and validated with the experimental data. • A definition of the Rayleigh damping matrix for cable-stayed bridges is advised. • The isolation effectiveness of the proposed NLIS is analyzed. [ABSTRACT FROM AUTHOR]

Accurate simulations of typhoon-induced wind speeds on wind farms are crucial for the refined assessment of typhoon risks in wind turbines. Southeastern coastal area in China is rich in wind resources but is also severely threatened by typhoons. As an extremely destructive weather system with complex structures, the refined near-surface wind fields of typhoons are difficult to simulate by meso-scale models for risk assessment. Therefore, a coupled meso- and micro-scale model under typhoon conditions is proposed to simulate typhoon-induced winds on a wind farm. The Coriolis force is considered in the coupled model to reflect the rotating effect of typhoons caused by the vortex structure. A coupling algorithm based on objective analysis is proposed to construct boundary conditions at the coupling interface, to consider the variation of inflow variables in the vertical and cross-wind directions. Model constants of the two-equation turbulence model are calibrated based on typhoon field observations, to more reasonably simulate typhoons. A validation study is conducted, and the results show that the maximum wind speed on the wind farm simulated by the coupled model exhibits an increased accuracy compared with that of the meso-scale model, where the absolute error decreases by 34%. • Multiple variables from meso-scale output are applied at the coupling interface. • Variation of inflow variables in vertical and cross-wind directions is considered. • Momentum equation is modified to consider Coriolis force and typhoon rotation. • Model constants in the turbulence model are calibrated for typhoon conditions. [ABSTRACT FROM AUTHOR]

With the increasing utilization of fiber-reinforced polymer (FRP) bars in concrete structures, the issue of retrofitting damaged FRP-reinforced concrete (FRP-RC) structures will emerge. However, limited research is available on the seismic performance of damaged FRP-RC structures after retrofitting. In this study, cyclic tests were conducted to evaluate the efficiency of precast ultra-high performance concrete (UHPC) plates in retrofitting the seismic performance of GFRP-RC columns with continuous or lap-spliced GFRP bars. Three GFRP-RC columns, among which one column with lap-spliced details was strengthened with precast UHPC plates, and the other two columns were retrofitted with precast UHPC plates combined with NSM after simulated seismic damage testing. To compare the retrofitting efficiency of this method for GFRP-RC and steel-RC columns, a previous study on steel-RC columns retrofitted with UHPC was incorporated. For the pre-damaged GFRP-RC columns after retrofitting with precast UHPC plates combined with NSM, the peak load experienced an increase of 76 %–79 %, and the ductility was complete restored. The failure modes of strengthened or retrofitted GFRP-RC columns differ from those of strengthened or retrofitted steel-RC columns. Further, the flexural strength of GFRP-RC columns and beams after being strengthened or retrofitted by UHPC can be predicted well based on the cross-section analysis model. • Cyclic behavior of pre-damaged GFRP-RC columns retrofitted with UHPC was investigated. • The seismic performance of GFRP-RC columns was significantly improved after retrofitting with precast UHPC plates. • The design method accurately predicts the flexural strength of GFRP-RC columns and beams strengthened with UHPC. [ABSTRACT FROM AUTHOR]

Pile-slab bridges with prestressed high-strength concrete (PHC) piles or prestressed and reinforced high-strength concrete (PRC) piles are widely used in low-seismic zones. To further understand the seismic performance of pile-slab bridges and to promote their applications in high-seismic regions, specimens of PHC bent (PHCB) or PRC bent (PRCB) from pile-slab bridges with a new bent-cap-pile pocket connection are studied through quasi-static cyclic tests. Seismic performance of the PHCB and PRCB is evaluated and compared in terms of damage development, failure mode, lateral stiffness, residual displacement, peak strength, displacement and energy-dissipation capacity. The experimental results show that both PHCB and PRCB fail due to non-ductile fracture of prestressing rebars in the piles, and the proposed bent-cap-pile pocket connection remains functional throughout the tests. Additional mild rebars of PRCB significantly increase displacement capacity of PRCB against PHCB. Finite element (FE) models are then developed and validated by the experimental results, after which the influence of initial prestressing force level and longitudinal prestressing reinforcement ratio of piles is investigated through parametric study based on the validated models. The proposed FE models can accurately predict the overall hysteretic behavior. Based on the parametric study, the seismic performance of both PHCB and PRCB can be improved by decreasing initial prestressing force level or increasing longitudinal prestressing reinforcement ratio. • Seismic performance of pile-slab bridge bents with a new bent-cap-pile pocket connection design is investigated. • Damage development and test data of pile-slab bridge bents with different pile types are compared and discussed. • Nonlinear finite element models for the proposed pile-slab bridge bents are developed and verified. • Influence of prestressing reinforcement on the seismic performance of pile-slab bridge bents is parametrically studied. [ABSTRACT FROM AUTHOR]

Doppler wind lidar (DWL) is being increasingly employed in various areas, such as wind energy, meteorology, aviation, and so on. Extensive studies have been conducted to validate its accuracy and reliability compared with anemometers mounted on meteorological towers. However, previous examinations mainly focused on a range up to 100 m because of the limited heights of meteorological towers. To further validate the DWL performance, especially above a height of 100 m, experimental tests were carried out at two national meteorological observatories in China (Shenzhen and Xilinhaote). The meteorological tower at Shenzhen Observatory is 356 m high, which enables validation of DWLs above 100 m. Different environmental variables, including humidity, precipitation, wind characteristics, and surface roughness length, were investigated to quantify their effects on the measurement errors of DWLs. Moreover, a correction methodology based on multiple linear regression model was proposed to eliminate the measurement error induced by environmental conditions. The corrected DWL data can be improved by up to 9.6% regarding the slope of the linear regression between the DWL and tower data, and the associated root mean square errors can be reduced by up to 37%. [ABSTRACT FROM AUTHOR]

In this study, shear damage development of four precast bridge columns with different connection design details are first examined via quasi-static test. The short columns are of identical dimension and reinforcement arrangement for both pier and footing segments, and the span-to-depth ratio is 0.85 for shear study. The connection utilizes grouted splice sleeve (GSS) couplers for all four specimens. Different bonding materials are compared, effectiveness of shear keys is investigated, and variation of steel rebar grades is carried out. It is found that epoxy retain lower bond strength than high strength mortar, lower grade of longitudinal rebar significantly reduces shear strength of bridge column, and shear keys are of limited effectiveness on the overall shear damage development. An analytical method for shear strength calculation is then proposed and calibrated based on different test results, which incorporates possible influencing factors for shear strength estimation. Maximum difference between the test results and estimated strength values are less than 10%, and it indicates that the proposed method can be used as a reference for shear strength estimation of short precast bridge columns for seismic strength estimation. • Quasi-static test of four short precast columns with different design is performed. • Seismic performance of the specimens towards shear strength is investigated. • An analytical method is proposed to estimate column shear strength for seismic study. • The proposed analytical model effectively estimates shear strength of precast columns. [ABSTRACT FROM AUTHOR]

• Shaking table test of a long-span cable-stayed bridge model was conducted. • Two schemes for the modeling strategy of the inverted-Y towers were compared. • Errors due to simplifications in the test model were specifically evaluated. • Design of the bridge model were described in detail. • The design was validated by the test from structural properties and failure mode. Existing studies on the seismic responses of long-span cable-stayed bridges under strong earthquake excitations have mostly been performed through numerical methods. In this work, a shaking-table experiment was conducted based on a long-span cable-stayed bridge with a main span of 1088 m and typical inverted-Y-shaped towers. The test model had a total length of 59.65 m and a height of 9.1 m. Micro-concrete was used for the model to meet the payload limit of the shaking tables. Pretest numerical analyses were carried out and the results showed that both the flexural and compressive/tensile properties of the column elements had effects on the seismic responses of the inverted-Y-shaped towers. Thus, the frequently used scaling strategy for conventional columns, with only strictly scaled sectional flexural stiffness and bending moment capacity, is not suitable for structures with stable triangle frames. The steel girder was designed to have properly scaled flexural stiffness, and the decreased strain responses in turn allowed the simplification of the cable system. A total of 28 pairs of cables were used for the bridge model compared to 136 pairs of cables for the prototype bridge, and 42 and 50 additional mass blocks were utilized for the girder and for each of the model towers, respectively. The errors induced by the simplification of the cable system and the additional lumped mass were no greater than 8% when compared with the theoretical mass distribution. Based on the white-noise tests, the identified natural modes of the scaled bridge model are consistent with those extracted from the numerical simulation. The observed failure mode matched well with the numerical prediction, and comparative responses between the numerical simulation and experimental test were shown. These results validated the design of the scaled bridge model. [ABSTRACT FROM AUTHOR]