基于瞬态热桥法的固体材料导热系数测量及其不确定度的评定

在Hammerschmidt建立瞬态热桥(THB)法理论的基础上,改进了恒定输入电流模式下导热系数解析模型和修正模型,对THB测量传感器进行了结构设计和仿真验证。搭建了测量范围为0.01~150 W/(m·K)的实验装置,并对修正模型进行了测量验证。对聚苯乙烯、有机玻璃和45号钢等7种固体材料进行了实验测量,对测量结果进行了不确定度的评定,并与不同仪器的测量结果进行了比较。结果表明,实验装置的测量重复性优于1.7%,与参考值的相对偏差在±5%以内,经评定测量结果的相对扩展不确定度为U_(rel)=2.94%(k=2)。

PSR_n模型下M序列的构造及其AVR单片机优化实现

M序列是一类具有最长周期的非线性移位寄存器序列。基于全新的M序列生成模型———PSRn,并结合AVR高速嵌入式单片机Atmega128的特点,构造了一种M序列的快速生成方法。该方法可以在资源十分有限的条件下快速的生成任意阶数n的M序列。

Application of uncertain type of AHP to condition assessment of cable-stayed bridges

In order to guarantee the safety service and life-span of long-span cable-stayed bridges, the uncertain type of analytic hierarchy process （AHP） method is adopted to access the bridge condition. The correlative theory and applied objects of uncertain type of AHP are introduced, and then the optimal transitive matrix method is chosen to calculate the interval number judgment matrix, which makes the weights of indices more reliable and accurate. Finally, with Harbin Songhua River Cable-Stayed Bridge as an example, an index system and an assessment model are proposed for the condition assessment of this bridge, and by using uncertain type of AHP, the weights of assessment indices are fixed and the final assessment results of the bridge are calculated, which proves the feasibility and practicability of this method. The application of this assessment method can provide the scientific basis for maintenance and management of long-span cable-stayed bridges.

Operational modal identification of suspension bridge based on structural health monitoring system

An output-only modal identification method by a combination use of the peak-picking method and the cross spectrum methods are presented. Meanwhile, a novel mode shape optimum method of the deck is proposed. The methods are applied to the operational modal identification system of the Runyang Suspension Bridge, which can be used to obtain the modal parameters of the bridge from out-only data sets collected by its structural health monitoring system （SHMS）. As an example, the vibration response data of the deck, cable and tower recorded during typhoon Matsa excitation are used to illustrate the program application. Some of the modal frequencies observed from deck vibration responses are also found in the vibration responses of the cable and the tower. The results show that some modal shapes of the deck are strongly coupled with the cable and the tower. By comparing the identification results from the operational modal system with those from field measurements, a good agreement between them is achieved, but some modal frequencies identified from the operational modal identification system （OMIS）, such as L1 and L2, obviously decrease compared with those from the field measurements.

On the Ecological Landscape Design of Urban Bridges in Chongqing City

This paper elaborated the special geological conditions of Chongqing City and the characteristics of urban bridges formed by natural environment, and put forth the ecological landscape design ideas of urban bridges. 3 principles of ecological landscape design were presented including paying attention to the creation of great environment, focusing on the comparison and harmony between natural and artificial factors and seeking for simple lines and unified colors, and the application of ecological landscape design principles in constructing ecological landscape of bridges in Chongqing City was analyzed. By discussing the existing problems of ecological landscape design of bridges in Chongqing City, some suggestions were summarized, which were expected to produce positive effects for the researches of ecological landscape design of bridges.

Synthetical condition assessment of long span suspension bridge based on closeness degree and FAHP

Based on the theory of pattern recognition, the concept of closeness degree between fuzzy sets is brought into the condition assessment of long span bridges. Using the fuzzy analytic hierarchy process （FAHP）, a mathematical model of a multi-objective assessment of a long span suspension bridge is set up. An example is given to show the procedure in the synthetical condition assessment of the Runyang Suspension Bridge, which includes the hierarchical division, the definition of factor weights and fuzzy membership functions, and the calculation of closeness degrees, etc. The assessment combines both the data from the health monitoring system and the manual tests. The classification of evaluation items as well as the calculation of deterministic and nondeterministic items is presented. Compared with the traditional method of point rating, this method can better describe the discreteness of monitoring data and the fuzziness in the condition assessment.

Determination of reasonable finished state of self-anchored suspension bridges

A systematic and generic procedure for the determination of the reasonable finished state of self-anchored suspension bridges is proposed, the realization of which is mainly through adjustment of the hanger tensions. The initial hanger tensions are first obtained through an iterative analysis by combining the girder-tower-only finite element(FE) model with the analytical program for shape finding of the spatial cable system. These initial hanger tensions, together with the corresponding cable coordinates and internal forces, are then included into the FE model of the total bridge system, the nonlinear analysis of which involves the optimization technique. Calculations are repeated until the optimization algorithm converges to the most optimal hanger tensions(i.e. the desired reasonable finished bridge state). The "temperature rigid arm" is introduced to offset the unavoidable initial deformations of the girder and tower, which are due to the huge axial forces originated from the main cable. Moreover, by changing the stiffness coefficient K in the girder-tower-only FE model, the stiffness proportion of the main girder, the tower or the cable subsystem in the whole structural system could be adjusted according to the design intentions. The effectiveness of the proposed method is examined and demonstrated by one simple tutorial example and one self-anchored suspension bridge.

Rigid-Plastic Dynamic Response of Reinforced Concrete Bridge Pier Impacted by Automobile

Bridge piers are impacted by autos sometimes. The pier usually has not been destroyed after once impact by auto. But there are few research on damage which will affect pier's capability, and most relative studies have focused the problems on piers impacted by vessels. The methods involve mainly sutra experience theory, numerical analysis, and experimental method. Owing to the complicacy of the bridge pier impacted by a vessel, there are few research derived with the sutra mechanics model and the piers impacted by autos. The dynamic response is studied here under the assumption of the rigid-plastic small-deformation for the pier impacted by auto. According to the Parkes beam model, the rigid-plastic theoretical solution is deduced. The final deformation is calculated by a practical example for the pier impacted by auto.

Effect of Downward Seepage on Turbulent Flow Characteristics and Bed Morphology around Bridge Piers

In this work, experimental investigations have been pursued to analyse the influence of downward seepage on the turbulent characteristics of flow and corresponding changes in vortex structure around circular bridge pier in alluvial channel. Experiments were conducted in sand bed channel with circular piers of different sizes for no seepage, 10% seepage and 20% seepage cases. The measurement of turbulent flow statistics such as velocity and Reynolds stresses is found to be negative within the scour hole at upstream of the pier whereas application of downward seepage retards the reversal of the flow causing a decrement in the velocity and Reynolds stresses. Higher Reynolds shear stress prevails at the downstream side because of the production of wake vortices. Contribution of all bursting events to the total Reynolds shear stress production has been observed to increase with downward seepage. The analysis of integral scale suggest that size of eddies increases with seepage, which is responsible for increase in particle mobility. Initially rate of scouring is more which abatements gradually with expanding time as well as with the increased of downward seepage. Presence of downward seepage reduces the depth and length of vortex and shifts towards downstream side of the pier.

Transient response of piles-bridge under horizontal excitation

Moving ships and other objects drifting on water often impact a bridge' s pile foundations. The mechanical model of the piles-bridge structure under horizontal forcing was established, and a time-domain approach based on Finite-difference Method was developed for analyzing the dynamic response of the piles-bridge structure. For a single pile, good agreement between two computed results validated the present approach.The slenderness ratio of the pile, the pile-soil stiffness ratio and the type of the structure influence the dynamic response of the piles-bridge structure. The computed results showed that the stiffness of the structure determines the dynamic response of the piles-bridge structure under horizontal forcing.

Study on effects of environmental temperature on dynamic characteristics of Taizhou Yangtze River Bridge

The dynamic characteristics of three-tower and two-span suspension bridge are analyzed at different global temperatures. An equivalent cable inner force method is proposed to consider temperature effects and to study the effects of environmental temperature on dynamic characteristics of Taizhou Yangtze River Bridge. The result demonstrates that the effects of temperature can not be neglected in static or dynamic analysis of Taizhou Yangtze River Bridge. The relationship between temperature and frequency is negative. The effects of temperature should be taken into account in experimental modal analysis of long-span bridges and damage identification.

Monitoring the Modal Frequency and Velocity Variations of Bridges under Ambient Excitation

We conducted a long-term monitoring experiment on the Lutuanxilu Bridge located in Changping District of Beijing, employing our recently developed real-time bridge monitoring system based on the Guralp CMG-6TD broadband seismometer. We identified the modal parameters with the stochastic subspace identification( SSI) algorithm,and continuously monitored the temporal velocity variation with coda wave interferometry.The results show that:( 1) the highly sensitive Guralp CMG-6TD broadband seismometer,which records the three-component vibration signal within broad frequency range,is well suited for long-term bridge health monitoring.( 2) With the continuous vibration signal from ambient excitation,the stochastic subspace algorithm can robustly identify the low-order modal parameters and the coda wave interferometry can accurately monitor the tiny velocity variation.( 3) The elastic modulus of bridge materials changes significantly associated with varying temperature,leading to diurnal velocity variation with amplitude of approximately 1%. The velocity variation shows strong negative correlation with temperature fluctuation. Meanwhile,the modal frequencies remain quite stable,suggesting that the velocity variation may be a more sensitive quantitative damage index.( 4) While the modal frequencies reflect the integrated health status of the bridge,the velocity variation can be utilized to monitor the local elastic modulus. Therefore,it is crucial for bridge health monitoring to continuously monitor the two key damage indexes under ambient excitation.

Simulink Based Simulation of the Behavior of a Ribbon Pontoon Bridge

A mathematical model of a ribbon pontoon bridge subjected to moving loads was formulated using the theory of simply supported beams.Two types of moving load models were used, the first a moving-constant-force model and the second a moving-mass model.Using both types of loads, the dynamic behavior of a ribbon pontoon bridge was simulated while subjected to a single moving load and then multiple moving loads.Modeling was done with the Simulink package in MATLAB software.Results indicated that the model is correct.The two types of moving load models made little difference to the response ranges when loads moved on the bridge, but made some difference to the response phases.When loads left, the amplitude of the dynamic responses induced by the moving-constant-force model load were larger than those induced by the moving-mass model.There was a great deal more difference when there were more loads.

FSM-Monitoring of Fatigue Crack in Lattice-Stiffened Steel Plate Deck for Bridge Structures

For elucidating applicability of FSM （field signature method） on detection of fatigue crack initiation and monitoring of its propagation, a series of fatigue tests on steel plate decks （4,625 × 2,250 mm^2） stiffened in lattice-shape by longitudinal and lateral ribs was carried out by using a wheel load traveling test machine. The fatigue crack was observed by visual inspection at the weld toe between the deck plate and the longitudinal rib when the number of wheel load traveling repetition was around 210 thousands. The response of FSM-monitoring, which was the potential difference change between the sensing pins （pair）, became clear when the number of the repetition was around 190 thousands. The fatigue crack initiation could be detected by FSM considerably earlier than visual inspection. The fatigue crack propagation such as the direction could also be monitored even though the distance of the sensing pins was extended to 230 mm. On the other hand, the electric field analysis for the virgin situation without any cracks was carried out. The results of analysis indicated that 60 mm length of crack which could not be confirmed by visual inspection could be detected by FSM.

Novel dynamic test system for simulating high-speed train moving on bridge under earthquake excitation

China’s high-speed railways are always facing the potential damage risk induced by strong earthquakes.And the route design concept of“using bridge instead of embankment”has also greatly increased the probability of high speed trains moving on bridges when a strong earthquake happens.In the past decades,a bunch of theoretical and numerical studies have been conducted in the seismic dynamic field of high-speed railway.However,the effective dynamic test system for verifying the given method and theoretical results is still lacking.Therefore,a novel dynamic test system(DTS)consisting of a shaking table array and a train-pass-bridge reduced-scale model is proposed in this paper.Through some crucial technical problems discussion,the effectiveness of similar design scheme and the feasibility of reduced-scale DTS are elaborated,and then the detailed DTS structures are given and displayed as part-by-part.On this basis,the demonstration tests are conducted and compared with the numerical simulation.The results show that the proposed DTS is accurate and effective.Therefore,the DTS can provide a new physical simulation approach to study the high-speed train’s running safety on bridges under earthquakes and can also provide a reference for the construction of related systems.

Influence of Random Track Irregularities on Dynamic Response of Bridge/Track Structure/High-Speed Train Systems

Random vertical track irregularities are one of essential vibration sources in bridge, track structure and high-speed train systems. The common model of such irregularities is a stationary and ergodic Gaussian process. The study presents the results of numerical dynamic analysis of advanced virtual models of composite BTT （bridge/ballasted track structure/high-speed train） systems. The analysis has been conducted for a series of types of single-span simply-supported railway composite （steel-concrete） bridges, with a symmetric platform, located on lines with ballasted track structure adapted for high-speed trains. The bridges are designed according to Polish bridge standards. A new methodology of numerical modeling and simulation of dynamic processes in BTT systems has been applied. The methodology takes into consideration viscoelastic suspensions of rail-vehicles, nonlinear Hertz wheel-rail contact stiffness and one-side wheel-rail contact, physically nonlinear elastic-damping properties of the track structure, random vertical track irregularities, approach slabs and other features. Computer algorithms of FE （finite element） modeling and simulation were programmed in Delphi. Both static and dynamic numerical investigations of the bridges forming the series of types have been carried out. It has been proved that in the case of common structural solutions of bridges and ballasted track structures, it is necessary to put certain limitations on operating speeds, macadam ballast and vertical track roughness.

Seismic Performance of Bridges with Different Pier Heights： Longitudinal Analysis of an Existing Bridge

This paper is dedicated to the study of the seismic performance of an existing RC （reinforced concrete） bridge localized in a region of moderate seismicity. The bridge has six spans and piers with very different heights, three of which are monolithically connected to the deck. To understand the roles of the different pier sizes in the overall behavior, several analyses were carried out in the longitudinal direction： （1） linear dynamic approach; （2） non-linear static approach; （3） non-linear dynamic approach. Linear dynamic analysis was made in order to design the bridge for the ultimate limit state considering the largest value of the ductility factor. No safety verification was made for the other loads. Using non-linear static analyses, sensitivity was performed to check the influence of reinforcement quantities of each pier on the overall behavior of the bridge under Lisbon seismic action. For the non-linear dynamic approach, a series of strong motion records compatible with the EC-8 spectrum for Lisbon area were generated. The very same combinations of reinforcement quantities were studied. Comparisons between static and dynamic non-linear analysis were made to confirm the validity of the first one in the case under analysis, where the period of vibration is quite high.

Crack detection using integrated signals from dynamic responses of girder bridges

An innovative approach for the identification of cracks from the dynamic responses of girder bridges was proposed.One of the key steps of the approach was to transform the dynamical responses into the equivalent static quantities by integrating the excitation and response signals over time.A sliding-window least-squares curve fitting technique was then utilized to fit a cubic curve for a short segment of the girder.The moment coefficient of the cubic curve can be used to detect the locations of multiple cracks along a girder bridge.To validate the proposed method,prismatic girder bridges with multiple cracks of various depths were analyzed.Sensitivity analysis was conducted on various effects of crack depth,moving window width,noise level,bridge discretization,and load condition.Numerical results demonstrate that the proposed method can accurately detect cracks in a simply-supported or continuous girder bridges,the five-point equally weighted algorithm is recommended for practical applications,the spacing of two discernable cracks is equal to the window length,and the identified results are insensitive to noise due to integration of the initial data.

Modeling Bridge Condition Levels in the United States

The objectives of this paper are to （I） quantify the effects of age and other key factors on bridge deterioration rates, and （2） provide bridge managers with strategic forecasting tools. A model for forecasting substructure conditionisestimated from the National Bridge Inventory that includes the effects of bridge material, design load, structural type, operating rating, average daily traffic, water, and the state where the bridge is located. Bridge age is the quantitative independent variable. The relationship between age and substructure condition is a fourth-order polynomial. Some of the key findings are： （I） a bridge substructure is expected to lose from 0.52 to 0.11 rating points per decade as it ages from 10 to 70 years; （2） levels of deterioration increase significantly as the material changes from concrete, to steel, to timber; （3） slab bridges have lower levels of deterioration than other structures; （4） bridges that span water have lower condition ratings; （5） bridges with higher operating ratingshave higher condition ratings; and （6） substructure condition ratings vary significantly among states.

Dynamic Detection of Reinforced Concrete Bridge Damage by Finite Element Model Updating

The present work consists of dynamic detection of damages in reinforced concrete bridges by using a MMUM （mathematical model updating method） from incomplete test data. A well suited finite element model of a repaired bridge is carried out. The diagnosis enables us to locate and detect the damage in a reinforced concrete bridge. Thus, developments of analytical predictions have been checked by modal testing techniques. Besides, the FTCS （finite time centered space） scheme is developed to solve the set of equations which can easily handle finite element matrices of a bridge model. It is shown in this study that the method is applied to detect damages as well as existing cracks in real time of a repaired bridge. To check the efficiency of the method, the repaired bridge of OuedOumazer in Algeria has been selected. It is proven that identification methods have been able to detect the exact location of damage areas to be corrected avoiding the inaccuracy from the finite element model for the mass, stiffness and loading.