Advanced Materials Research Vols. 163-167

Abstract: An effective crack identification method has been developed based on the dynamic behavior of a cracked beam. The nature frequencies of a generally supported beam with crack are calculated by Rayleigh-Ritz method. The crack is then identified from the changes of the nature frequencies caused by the appearance of crack. A hybrid PSO (Particle Swarm Optimization) algorithm is employed as a global search technique to back-calculate the damage. Numerical experiments are carried out on beams with different crack damage. The results demonstrate that the proposed method is able to effectively and reliably locate and quantify the crack in the beam with elastically restraint against translation and rotation.

Abstract: In order to realize non-destructive testing of concrete strength of pouring stakes at the construction stages, the paper establishes two kinds of mathematics models between the concrete strength and the sound-speed through experiment on concrete test squares, model stakes and engineering piles ─ all of differently designed strength with method of ultrasonic. The concrete average strengths of the pouring piles were reckoned through engineering piles of practical testing and the errors were within the allowable range. So the validity of mathematics models was proved.

Abstract: Heat generation of concrete during hardening causes early age temperature rise, and if the associated tendency of volume change is restrained, thermal stresses would be induced and early thermal cracking would result. This issue should be duly considered in concrete bridge construction as the bridge piers as well as other structural members are typically mass concrete members. In this paper, a real-life bridge pier is selected for study. The pier was instrumented to measure its early age temperature rise on site. Finite element analysis was conducted to evaluate the time variations of temperature distributions and thermal stresses induced in the bridge pier. The measurement and analysis results threw light on the evaluation of risk of thermal cracking and planning of temperature control measures in similar projects.

Abstract: Connected with the practical construction and considering Structural properties of single-tower self-anchored suspension bridge, the multi-level safety evaluation model is established according to the main risk factor and weighting rate of risk factor is analyzed by the analytic hierarchy process. A safety assessment method with qualitative analysis and quantitative analysis is proposed based on the grey theory and fuzzy mathematics theory for the practical problem of multi-index comprehensive evaluation, and risk ranking is given.

Abstract: A system, which is real-time, remote, automatic for monitoring the subsidence of building, is introduced. Hydrostatic leveling, displacement sensing by electromagnetism, GPRS wireless communication and computer technology are integrated into the system. The system has the following functions: real-time, continuous acquisition and management of the monitored data; automatic computation and analysis of the subsidence; remote, wireless release of information and early-warning. Applied successfully to monitor the subsidence of the main building of Tianjin West Railway Station in its integral moving, the system has taken the key directive effect in adjusting the schedule and the methods of construction timely.

Abstract: The vibration features are affected by damage in structure and environmental conditions while the bridges are in the operation. Environment effects should not be ignored in making correct diagnoses of structures. Negative selection algorithm inspired by immune system has the capability for self-nonself discrimination. Temperature effect on natural frequency is analyzed in the paper, and the algorithm based on Euclidean distance is applied to natural frequencies of structures under temperature variations. The results indicate that negative selection algorithm using natural frequency passes the false-positive tests, and effectively detect the anomalous condition of structure under varying temperature.

Abstract: Bridges monitor and control plays a important part in the bridge construction technology. Besides, It is the key factors of ensuring the bridge construction safety in the construction project and meeting design and construction code requirements. The Article takes a high-speed railway bridge as engineering background, and adaptive control system will be applied to the monitoring measurement. The Main Parameter of construction is proposed, which is based on the sensitivity analysis of design parameter in theory. According to take elastic modulus and volume weight of concrete as the main Parameters, identified and adjusted them by least square method, to forecast errors, analyze and adjust parameters. Using the adaptive control system to collect the data of displacement and stress in bridge construction.Calculate through the Computer simulation model, and obtain initialize height during construction, on this basis, guiding the construction and complete the construction of control successfully.

Abstract: This paper investigates the performance of Artificial Neural Network (ANN) learning algorithms for vibration-based damage detection. The capabilities of six different learning algorithms in detecting damage are studied and their performances are compared. The algorithms are Levenberg-Marquardt (LM), Resilient Backpropagation (RP), Scaled Conjugate Gradient (SCG), Conjugate Gradient with Powell-Beale Restarts (CGB), Polak-Ribiere Conjugate Gradient (CGP) and Fletcher-Reeves Conjugate Gradient (CGF) algorithms. The performances of these algorithms are assessed based on their generalisation capability in relating the vibration parameters (frequencies and mode shapes) with damage locations and severities under various numbers of input and output variables. The results show that Levenberg-Marquardt algorithm provides the best generalisation performance.

Abstract: The shear lag effect on box girders has been studied by quite a few researchers for many years. However, most of studies are related to shear lag formulas and analytical methods and very few have investigated the effect of stress concentration and deflection. The present study investigates the stress concentration and deflection under shear lag effect in a continuous box girder and a simply supported beam by using the three-dimensional finite element method. The whole girder is modeled by shell elements, and an extensive parametric study with respect to the geometry of a box girder is carried out. The influence of finite element mesh on the shear lag is carefully treated by the multi-mesh extrapolation method.

Abstract: A combined method for the Benchmark structure damage identification base on the frequency response function(FRF) and genetic algorithm(GA) is presented. The reducing factors of element stiffness are used as the optimization variables, and the cross signature assurance criterion (CSAC) of the test FRF and the analysis FRF is used to constructing the optimization object function and the fitness function of the GA. To avoid the weakness of binary encoding, the floating point number encoding is used in the GA. At last, the Benchmark structure established by IASC-ASCE SHM group is caculated by the proposed method, the results show that even if the serious testing noise is considered, the patterns of damage of the Benchmark structure can be identified well. The effectiveness of the presented method is verified.