Abstract:In order to obtain actuator placement optimization for the spatial truss stucture，this paper constructs the active vibration control system of spatial truss structure based on linear quadratic regulator （LQR） optimal controller theory， and maximizing the modal damping of the target control mode is proposed as the actuator placement optimization criterion. The effectiveness of the proposed method is verified by using the square pyramid space grid structure and the Levy-type cable dome structure， and the control effect and energy input are compared with those of the existing method. The comparison results show that with the increase of the number of actuators， the control effect and control energy input of the proposed method tend to stabilize faster than that of the existing method； when the number of actuators is the same or the energy input is the same， the control effect of the proposed method is better than that of the existing method.

Abstract:A novel hybrid damping scheme was proposed to control the longitudinal motion response at the girder ends during train passage on a railway suspension bridge，utilized multiple types of dampers to control girder-end displacements to meet diverse vibration reduction requirements. With a long-span railway suspension bridge under construction as the engineering background， a detailed spatial truss model and an equivalent single beam simplified model were established. The study systematically investigates the influence of different damper parameters in the hybrid damping scheme on motion control effectiveness. The proposed solution involves installing low-exponent fluid viscous dampers longitudinally between the bridge tower and the stiffening girder. Simultaneously， eddy current dampers are installed longitudinally between the bridge abutment and the stiffening girder. Considering the unique characteristics of the bridge abutment structure， the eddy current dampers are designed as devices capable of withstanding only compressive loads and validated through prototype testing. To further enhance damping performance， the eddy current dampers are equipped with a friction energy dissipation component. This hybrid damping solution effectively controls the longitudinal motion response at the girder ends during train passage， significantly improving the safety and durability of bridge structures. The findings have significant reference value and practical implications for similar engineering projects.

Abstract:Currently， the majority of structure damage identification methods based on deep learning rely on deep neural networks to automatically extract damage-sensitive features of structures and achieve pattern classification recognition through the differences in features between damage states. However， these methods face challenges in the accurate quantification of damage and require a large amount of data for model training. This article proposes a damage detection method based on a model-embedding recurrent neural network （MERNN）. Firstly， a data-driven convolutional neural network was used to establish the mapping relationship between load and response. Then， the traditional recurrent neural network was improved using the Runge-Kutta method to create a numerical computing unit based on the recurrent neural network architecture. Finally， based on the loss function composed of the residual errors between measured responses and computed responses， the structural stiffness parameters were updated with the automatic differentiation mechanism of the neural network to achieve structural damage identification. Damage identification results of a numerical three-layer frame and a laboratory-scale shear-type frame indicate that the proposed method can accurately quantify structural damage based on the limited amount of response datas.

Abstract:Large-scale chemical pipelines， influenced by factors such as fluid flow， boundary constraints， and source excitations， often experience vibrations during service. Unlike civil structures， these vibrations exhibit higher frequencies and may involve multiple dominant frequency components. Traditional single-frequency tuned mass dampers （TMD） struggle to achieve optimal control in this context. Meanwhile， the application of multiple tuned mass dampers （MTMD） is hindered by the challenges in determining optimal installation locations due to on-site constraints. This paper explores the mitigation of pipeline harmonic responses using MTMD. Firstly， an on-site measurement study was conducted on a propane dehydrogenation unit in a chemical plant， revealing evident frequency multiples or harmonic phenomena. Subsequently， a finite element model for local pipeline segments was established to analyze dynamic characteristics. A parameter design method for MTMD based on numerical search algorithms was proposed. Lastly， considering the limit of practical installation conditions for chemical pipelines， the impact of MTMD installation positions on vibration reduction effectiveness was investigated. Numerical results show that the vibration of pipelines can be significantly reduced by using MTMD.

Abstract:In this study， a refined in-plane dynamic model of cable-stayed bridges was constructed， and the corresponding free vibration characteristics were analyzed. Firstly， the in-plane motion equations of the cable-stayed bridge were derived using the Hamilton variational principle， and the characteristic frequency equation of the linearized model was determined based on boundary conditions. A three-span cable-stayed bridge with double towers was chosen for the numerical calculation， and the correctness of the corresponding solution was verified through the finite element method. Then， the modal characteristics of the cable-stayed bridge were quantitatively reflected by introducing localization factors. Finally， the effects of structural parameters， cable-deck interaction， and structural systems on the natural frequencies and modes were discussed. The results show that the natural modes of the system exhibit the local characteristics when the natural frequencies of the cable-stayed bridge are close to the ones of pure cable. Moreover， the cable-deck interaction may significantly affect the low-order non-local modes. However， the effects on the higher-order frequencies can be ignored.

Abstract:Based on the concrete damage plasticity model， the dynamic characteristics of bending damaged RC/PC bridges are investigated through numerical simulations in this paper. Firstly， a FE model generation framework was proposed to conduct the nonlinear vibration analysis of RC/PC bridges. Then， the constructed FE model was validated by comparison with experimental results from bending failure tests on simply supported RC beams. Finally， a 3D FE model of a 3-span PC continuous girder bridge from the Xiamen Bus Rapid Transit was established to study the changes in frequencies and mode shapes under different bending damage levels. It can be observed from the results that the dynamic characteristics of RC/PC bridges with bending damage change to varying degrees as the damage increases. The small vibration of the damaged bridge with concrete cracks is still linear， but the frequency decreases with the increasing vibration amplitude， indicating the nonlinear vibration. When cracks are closed， the changes in the first three frequencies and mode shapes are not significant， making it hard to identify bending damage in practice. However， when cracks are open， noticeable changes occur in the first three frequencies and mode shapes， which can serve as damage detection indicators for identification purposes.

Abstract:The accuracy of modal test results is affected by uncertain influencing factors such as data acquisition， data processing， and parameter estimation. To study the uncertainty levels of modal parameters and their behaviors under different influencing factors in modal testing， a fast uncertainty quantification analysis method based on the state space model and Fisher information matrix （FIM） is adopted. The influence of multiple factors including data duration， sampling frequency， signal-to-noise ratio， and damping ratio of vibration signal on the uncertainty levels of modal parameters is discussed， and a practical way for optimizing the sensor layout scheme through uncertainty analysis is proposed. Results show that the uncertainty level of modal parameters decreases with the increase of data duration， sampling frequency， signal-to-noise ratio， and the number of sensors， and increases with the increase of damping ratio； for uniformly distributed structures， the majority of the sensors at the upper and middle region of the structure and only a few at the lower region is a preferred sensor layout scheme with small overall uncertainty of modal parameters.

Abstract:To investigate the statistical errors inherent in this classical process and its influence on PSDT measurements， based on the perturbation technique， the mean and variance of the quotient of the random variables are approximately expressed with the application of the statistical moment method. Then， the statistical moments of two response spectral estimates are substituted to derive the formulae for the mean and variance of the PSDT’s amplitude regarding the coherence function of the response and the number of averaging segments in spectrum analysis. Based on this， the error law in the amplitude of the PSDT estimate at the resonance frequency is revealed to quantify the estimation error of the mode shape. It is found that the error in the PSDT’s amplitude estimate at the resonances tends to a local minimum value， and the coefficient of variation is smaller than the counterparts of two associated response power spectrum densities. Finally， the accuracy of the derived error formulation in the paper is verified by vibration data from one numerical frame. Moreover， a parameter study regarding the influence of the selection of reference response， the time duration of measurements， and the type of window function on the PSDT and mode shape estimates is performed. The results show that using two basic responses of PSDT as the reference responses is beneficial to reduce the error in PSDT estimates and outcomes of modal analysis， and the standard variance of the estimate also decreases with the increasing time duration of measurements and finally to a specific limit.

Abstract:The self-centering buckling-restrained brace combined both disc springs and steel tendons （DT-SCB） was proposed to solve the shortage problem of the deformation ability of the traditional self-centering buckling-restrained brace （SCBRB）. The steel tendons in series with combination disc springs are used to provide the self-centering force， and two parallel flat steel cores are responsible for dissipating seismic energy. The detailed configuration， working mechanism at different stages， and restoring force model of DT-SCB were introduced in this study. The finite element model was established， through which the effect of self-centering ratio αsc， the ratio of steel tendons and combination disc springs K1 and the ratio of self-centering unit and energy dissipation system K2 on the hysteretic behavior， self-centering level and energy dissipation capacity of DT-SCB were conducted， respectively. The results indicated that the proposed DT-SCB restoring force model agreed well with that from numerical simulation. No obvious failure characteristics were observed even if the maximum loading displacement （corresponding to the axial strain of 2.5%） was achieved. The hysteretic curve of DT-SCB was flag-shaped， with stable energy dissipation. The deformation ability of proposed DT-SCB was significantly greater than that of the conventional SCBRB with steel tendons. The maximum residual displacement sharply decreased with the increasing self-centering ratio， while the greater K1 weakened the control effect of αsc on residual deformation. The disc springs were prematurely flattened with an excessive ratio of self-centering system and energy dissipation system （K1≥2.0）， which would reduce the deformation capacity of DT-SCB. The stiffness ratio K2 had a significant influence on the energy dissipation capacity of DT-SCB， and the equivalent viscous damper ratio of DT-SCB decreased with the increase of the stiffness ratio K2. The nonlinear dynamic analysis results of the braced frame subjected to severe earthquakes showed that DT-SCB can effectively reduce the maximum and residual inter-story drifts and improve the seismic performance of the frame.

Abstract:Hence， further investigation is needed. Taking the stay cables with ribs installed as the object， a series of wind tunnel tests were conducted to systematically study the effects of the installation methods （through-length installation and intermittent staggered installation）， sizes and numbers of ribs on the VIV， and aerodynamic force. Additionally， the suppression mechanism of vortex-induced vibration （VIV） was analyzed. Results show that stay cables with ribs can effectively suppress VIV compared with standard stay cables. The intermittent staggered installation exhibits a better vibration suppression effect than the through-length installation. The control effect was better for 8 ribs than for 6 and 12 ribs. Increasing rib width and thickness can reduce the amplitude of VIV. The fluctuating lift coefficients of the stay cables with ribs are remarkably smaller than those of the standard stay cables. Moreover， the amplitudes of the power spectrum peaks are significantly reduced， or the peaks are even vanished. This suggests that intermittent staggered rib can weaken the strength of Karman vortex shedding or even control it completely. For aerodynamic forces， the Reynolds number effect on the mean aerodynamic coefficient is significantly weakened by the ribs. Compared to standard stay cables， the installation of ribs throughout the entire length increases the mean drag coefficient of the stay cables. When the installation is intermitte staggered， the increase and decrease in the drag varies with the number and size of ribs and the wind attack angle. When the ribs with the size of 20mm×15mm and the number of 8 are intermittently staggered， good vibration suppression effects can be obtained at all wind attack angles. The maximum reduction of VIV amplitude can reach 96.79%， the mean drag coefficient is near 1.13， and the mean lift coefficient is near 0.

Abstract:In order to be able to detect the abnormal condition of sensors in time， a sensor abnormality detection model for bridge health monitoring system based on gray correlation analysis is designed. First， the datas collected from multiple strain sensors in normal operation and single sensor abnormality are analyzed by gray correlation analysis， respectively， and the least correlated count columns that characterize the degree of geometric similarity between each column of sensor data and the rest of the columns of data are obtained. The comparison revealed that the distribution of the least correlated counts when there was no abnormality and when there was an abnormality showed marked differences， thus verifying the feasibility of this method； then， a weight calculation strategy was designed to transform the least correlated count columns into a normalized value and use it as an evaluation index， which quantified the degree of correlation between each column of sensor datas and the rest of the columns of datas； finally， through the analysis of the evaluation indexes of multiple sets of strain datas， the multi-threshold warning mechanism was set up to realize the corresponding determination of different degrees of sensor anomalies. On another set of acceleration monitoring datas to simulate a variety of degrees of anomalies and detection， the results show an overall anomaly recognition rate of over 90%.

Abstract:A fast iterative algorithm for solving the eigenvalue perturbation problem is proposed in this paper for solving the problem of slow convergence of traditional methods for eigenvalue perturbation calculation. Firstly， the eigenvalue perturbation problem of the initial matrix is transformed into the eigenvalue perturbation problem of the diagonal matrix by matrix transformation. Then， a fast iterative algorithm is proposed to solve the perturbation parameter. The convergence of the algorithm is analyzed and compared with the method derived based on the perturbation series expansion method， and the strategy of solving the eigenvalues one by one and reducing the order of the matrix is adopted to effectively reduce the computation cost. Finally， two examples are used to show the calculation process of the algorithm and its application in the tracking of modal parameters of vibration structures.

Abstract:To reduce the cost of the monitoring system and improve the accuracy of bridge damage identification， this paper used limited sensors to obtain high-resolution modal shapes. Considering the road roughness， the damage identification method is proposed based on the flexibility change rate. In different road roughness levels， the proper orthogonal decomposition is used to analyze the displacement response measured on the bridge under moving vehicle loads to obtain the principal component matrix. High-resolution modal shapes can be obtained by filtering the high-frequency dynamic component information in the principal component matrix. The flexibility change rate is calculated using high-resolution modal shapes by limited sensors as an indicator for bridge damage localization. To verify the effectiveness of this method， simulation and experiments were conducted on a simply supported beam. The results show that this method can accurately detect damage by obtaining the flexibility change rate of high-resolution modal shapes based on limited sensors considering different road roughness levels.

Abstract:The Benchmark model of the floor response spectrum established by our study group was used to study the effect of different friction coefficients of the elastic slide bearing on the floor response spectrum. ETABS software was used to establish the finite element model of the seismic isolation structure， and the elastic slide bearing was arranged between the bottom of the ground floor column and the foundation. To make the floor response spectrum practical and representative， the 22 far-field vibrations recommended in ATC-63 were inputted to carry out the nonlinear time-distance analysis for the four friction coefficients of the base seismic isolation structure， respectively， and to study the effect of the friction coefficients of the elastic slide bearing on the floor response spectrum， which was compared with that of the friction coefficient of lead core rubber bearing seismic isolation. The results show that the friction coefficient affects the spectral value of the floor response spectrum but does not change the period of the peak value of the floor response spectrum and does not affect the spectral characteristics of the floor response spectrum； in the period of 0~6 s， the spectral value of the floor response spectrum of the four friction coefficients of elastic slide bearing structure in the paper is less than that of the lead core rubber bearing， which indicates that the seismic isolation performance of this structure of elastic slide bearing is better than that of the lead core rubber bearing.

Abstract:A strengthening system for RC columns with adhesive-bonded vertical carbon fiber reinforced polymer （CFRP） plates was proposed. The strengthening system consisted of prefabricated vertical CFRP plates adhesively bonded to the column surface and a concrete jacket preventing the CFRP plates from debonding. To investigate the effect of adhesive-bonded CFRP plates on flexural behavior， five full-scale rectangular RC columns were tested under lateral cyclic loading. Experimental results showed that the cracking load of CFRP-strengthened columns was significantly improved compared to that of the reference column. The ultimate load-carrying capacities of the CFRP-strengthened columns were improved by 15.1% and 17.4%， respectively. The flexural capacity， and stiffness were improved by adhesively bonded vertical CFRP plates. However， no significant improvement in load-carrying capacity and stiffness of columns was observed for different amounts of CFRP plates. The ductility factor of the strengthened columns decreased by 16.2% and 35.1%， respectively. Since the limitation of column-foundation joint capacity， the strength of CFRP plates was not fully developed， and the CFRP strain at column failure was 24% of the ultimate strain. In addition， the proposed strengthening system was applied in a hospital strengthening project. A follow-up study showed that the flexural capacity of strengthened columns was significantly improved. The proposed strengthening system has been recognized by the civil engineering industry.

Abstract:To improve the economy of structural health monitoring and expand its application scope， a temperature field prediction method of long-span bridges based on big-data information from weather stations was proposed to realize lightweight and sustainable bridge temperature field and temperature deformation calculation. Taking a large-span steel arch truss bridge as the research object， the big-data information （including weather， temperature， and wind speed information） from the weather station was obtained through the meteorological data platform， the radiation intensity of each surface for the main components of the bridge was calculated by Elbadry’s improved Kelbek radiation model， the boundary conditions of structural thermal analysis were calculated based on the heat exchange transfer theory， and the structural transient thermal analysis was carried out in combination with the finite element analysis method， to obtain the time-varying temperature field of the main components of the target bridge. The calculation results of the temperature field are in good agreement with the measured temperature on the bridge in terms of time history and vertical distribution of the structure， and absolute value of the average error is within 3%. The calculated structural temperature was applied to the overall finite element model of the bridge structure， and the temperature deformation of the bridge structure was obtained. Moreover， the calculated value of the longitudinal displacement of the bridge support is in good agreement with the measured value， and the average error is within 13mm. The analysis verifies that the proposed bridge temperature field prediction method based on big data from weather stations is feasible， and the temperature deformation of the bridge structure can be further obtained by using this method as well.

Abstract:To solve the technical problems of large lifting weight and difficulty to realize prefabrication and assembling of cantilevered bent caps， using the excellent mechanical properties of UHPC， a new type of semi-precast prestressed UHPC-S-NC non-demolition molded bent caps， with the use of groove-type combination structure made of UHPC， steel plate and steel section （S） as the permanent formwork， and the pouring of normal concrete （NC） after erection， were put into position. In order to study its crack resistance and stiffness and evaluate its safety， a 1∶2.5 large-scale scaled model was designed and loaded in the whole process in conjunction with the actual project， and key experimental datas such as the deformation characteristics of the test beams， the magnitude of the cracking and ultimate loads， and the pattern of crack development and distribution were obtained. The crack distribution and strain development law of the test beams were analyzed； considering the plastic stress-strain relationship of the NC material， the cracking moment calculation mode and calculation method of the structural UHPC layer and NC layer were proposed； and the bending capacity calculation mode of the combined structure was proposed based on the cross-section equilibrium condition， while the calculation mode of the structural shear capacity was explored based on the code. The results show that： the new type of bent cap structure has the characteristics of fast construction and a high degree of assembly； the calculation results of cracking bending moment are in good agreement with the test values； the new type of bent cap structure has sufficient load carrying capacity， and so it is suggested to use the equilibrium conditions and superposition method to evaluate the load carrying capacity of the structure， and the results are biased towards safety； some specific suggestions for the design and construction of the structure are put forward for the actual project. The research results can provide a reference for the application of semi-precast bent caps.

Abstract:The nonlinear finite element （FE） models of stainless steel I-section and rectangular hollow section （RHS） stub columns were established to analyze the local stability of the novel high-strength QN1803 stainless steel axial compression members after elevated temperature. Parametric analysis was carried out to analyze the effects of residual stress， initial local imperfections， and elevated temperature conditions on the local stability and bearing capacity of the members. The results show that for RHS and “non-slender” plate of I-section members with non-dimensional plate slenderness ratio less than 1.0， residual stress has little effect on bearing capacity； for “slender” I-section members， residual stress reduces the section bearing capacity， and the reduction decreases with the increasing temperature. In addition， with the increase of temperature， the limit value of non-dimensional plate slenderness ratio at which the initial local imperfections have a significant impact on the bearing capacity of stainless steel I-shaped members becomes larger， and the influence on the bearing capacity of stainless steel RHS members gradually becomes smaller. Finally， an assessment of the applicability of the design provisions for stainless steel structures at room temperature， as given in the European code EN 1993-1-4 and ASCE/SEI 8-02， together with the Chinese specification CECS 410： 2015， to the design of stainless steel stub columns after elevated temperature is subsequently performed through comparisons against the obtained numerical data. It is found that the existing design codes at room temperature are not fully applicable to the design and prediction of stainless steel stub columns after elevated temperature. And there were still unreasonable aspects in the post-fire design in the existing research. It is suggested to further optimize the evaluation method of local stability of stainless steel members after elevated temperature.

Abstract:To study the static bending mechanical properties of UHPC （Ultra-High Performance Concrete， UHPC） bridge deck of a super-kilometer hybrid composite beam cable-stayed bridge， UHPC materials with compressive strength greater than 160 MPa and elastic modulus greater than 45 GPa were designed and prepared in this paper， and two full-size UHPC bridge decks with length， width and height of 3.8 m×1.0 m×0.17 m were tested under static load. By analyzing the bending stress state and failure mechanism of UHPC bridge decks， the stress calculation diagram of UHPC bridge deck was proposed， and the cracking moment of UHPC bridge decks and the bearing capacity calculation formula considering the stress reduction of UHPC in the tensile softening section were established. The results show that the UHPC bridge decks have excellent flexural mechanical properties. The average cracking moment reaches 77.4 kN?m， and the average bending moment corresponding to the yield of the tensile longitudinal reinforcement is 237.1 kN?m. The failure mode of the plate is mainly characterized by the yield of the tensile longitudinal reinforcement at the bottom. The calculated values of the theoretical formula are in good agreement with the experimental values. This research work provides a theoretical and experimental basis for the application of UHPC bridge decks in the main girder of kilometer-level cable-stayed bridges.

Abstract:To study the bond-slip behavior of the interface between the section steel and the high-strength self-compacting concrete， nine self-compacting concrete specimens with the section steel were launched for tests， with the thickness of the high-strength concrete protective layer and the length of the molding serving as the variable parameters. The specimens’ failure process， failure morphology， and crack formation pattern were observed. Specifically， the whole process load-slip curve of the loading end of the specimen was obtained， along with the study of the effect of various parameters on the specimen’s bond behavior. According to the findings， the ultimate bond strength of steel reinforced high-strength self-compacting concrete composite structure increases with the increase of thickness of the high-strength concrete protective layer， and the maximum increase was 94.9%； but it decreases with the increase of the embedded length of the section steel， and the maximum reduction is 38.1%. The shear stiffness of interfacial bonding first strengthens and then weakens by an increase in the protective layer thickness of high-strength self-compacting concrete， and the maximum increase was 85.1%. Meanwhile， it is marginally strengthened with the increase of the insertion length， and the maximum increase was 30%. Besides， the interface’s capacity for consuming energy has a tenuous relationship with its factors. With the increase of the thickness of the high-strength steel protective layer， the interface damage develops later. With the increase in the embedded depth of the section steel， the interface damage speed slows down. Finally， the calculation formula for the bond strength of steel reinforced high strength self-compacting concrete is proposed， which can predict the bond strength of section steel reinforced high strength self-compacting concrete well.