Applied Mechanics and Materials Vols. 351-352

Abstract: In this research, the correlations between the magnetic signals and the mechanical behavior of a ferromagnetic steel structure under tensile loads were investigated. The failure mode of the tested steel joint was the buckling of the annular plate. It was observed that during the loading process the piezomagnetic response demonstrated a different behavior compared to the mechanical response. The greater variation of the load-B field curve shows that piezomagnetic signal is a more sensitive indicator of structural failure than the mechanical response. The piezomagnetic effect may be used as a promising method to monitor the failure process of civil infrastructures.

Abstract: This paper presents a two-stage method for damage identification in cantilever beam structures using the incomplete measured static and dynamic paramenters. The first stage locates damages preliminary by using the static displacement changes, which is obtained by the static test of structure. It has been shown that the point from which the static displacement difference starts increasing linearly is the location of damage. After the suspected damaged elements are determined in the first stage, the first order sensitivity of the structural natural frequency is used to identify damages more precise in the second stage. The significant advantage of the proposed method is that it is economical in computation and is simple to implement. A cantilever beam structure is analyzed as a numerical example to verify the present method. Results show that the proposed method performs well even if the measurement errors inevitably make the damage assessment more difficult. It has been shown that the presented two-stage methodology may be a promising tool to be used by research groups working on experimental damage detection.

Abstract: The process of implementing a damage identification strategy for aerospace, civil and mechanical engineering infrastructure is referred to as structural health monitoring. Many different types and degrees accidents take place, especially some important collapse accidents, the significance of steel structural health monitoring has been recognized. The introduction begins with a brief research status of steel structural health monitoring in china and the world. The paper analyzes the projects and contents of steel structures monitoring from nine aspects and summarizes the diagnosis methods of steel structural damages which include power fingerprint analysis, the methods of model correction and system identification, neural network methods, genetic algorithm and wavelet analysis, it provides us theoretical guidence. In conclusion, structural health monitoring for steel structures could reduce the impact of such disasters immediately after natural hazards and man-made disasters both economically and socially, thus it is becoming increasingly important.

Abstract: In order to study Particle Swarm Optimization (PSO) algorithm and structural damage diagnosis, a method based on PSO algorithm and Evidence theory is presented in this paper. First, structural frequency and modal strain energy are considered as two kinds of information sources, and frequency change method and modal strain energy method are utilized to extract damage information. Then, evidence theory is utilized to integrate the two information sources and preliminarily detect structural damage locations. Finally, the PSO algorithm is used to identify structural damage extent. An improved PSO algorithm is also presented. Simulation results show that the evidence theory can identify the suspected damage locations, and the PSO algorithm can precisely detect the damage extent. It can also be observed that the improved PSO algorithm is obviously better than the simple PSO algorithm.

Abstract: For the beam with certain degree, it was difficult to reflect by displacement modal and natural frequency. The present paper first derived nodal strain modal through its corresponding displacement modal, and then evaluates the strain modal, both prior and post damage, the difference between the strain mode was used as a criterion to assess the damage experienced, based on a simple beam element damage localization method. The formulated method had been demonstrated through ANSYS numerical modeling to be capable of effectively identifying the damage.

Abstract: Huatugou in Qaidam Basin is a saline soil area with special geological condition, and there has special climatic conditions. The buildings appear serious cracks and inclined in this area. This article uses the investigation and inspection which we collect to analyze the present situation for the buildings. Explain why this situation happened and put forward some treatments.

Abstract: Due to the shrinkage, creep, friction and other factors, the pre-stress applied to the beam is not a constant. It is important to obtain the information of the pre-stress in order to ensure security of the bridge in service. To solve the problem mentioned above, the paper puts forward a new way to analyze the effective pre-stress using the displacement inversion method based on the inversion theory according to the measured vertical deflection of the bridge in service at different time. The method is a feasible way to predict the effective pre-stress of the bridge in service. Lastly, taking the pre-stressed concrete continuous rigid frame bridge for example, the effective pre-stress and stiffness are analyzed by establishing the finite element model.

Abstract: Outrigger damping system is used in JZ20-2 north high wellhead platform, making simulation analysis to the whole structure subjected to pushing ice load by finite element software ANSYS, calculating displacement and acceleration response under different length of horizontal pole and different height of damper. The height of the damper has great influence on displacement and acceleration. The damping effect of horizontal bar length has an impact on the damping system, and the main influencing factor is the damper height, and when the height is H2 the damping effect is the most ideal.

Abstract: Based on the dynamic, selecting the vibration shape functions for obtaining the structural frequency, without using the differential operation of the conventional Rayleigh law which improved the calculation accuracy, the three-parameter model was built which include the frequency of the exposed segment, the segment length of the exposed steel reinforcements and anchorage segment increased stiffness coefficient. Meanwhile the validity of the three-parameter model was verified using finite element numerical simulation. The vertical pretensioning force of the box girder webs model was designed at laboratory. The natural frequency of vertical prestressing tendons exposed section was obtained through the high-frequency acceleration sensor which was set up at the top of the exposed section. Relying on experimental test data, the model which had the nonlinear relationship between the effective tensile force and anchorage segment increased stiffness coefficient was established.

Abstract: Optimal sensor placement technique plays a key role in structural health monitoring and structural vibration control. Based on the advantages and disadvantages of effective independence (EI) and modal kinetic energy (MKE) methods, two improved optimal sensor placement methods which are Effective Independence - Average Acceleration Amplitude (EI-AAA) method and Effective Independence - Modal Kinetic Energy (EI-MKE) method are proposed in this paper. Firstly the formulas are deduced from modal expansion of multiple-input-multiple-output (MIMO) displacement frequency response function matrix. Then a computational simulation of steel cross beam structure has been implemented to demonstrate the feasibility of the two improved methods above. The obtained optimal sensor locations using the two improved methods are compared with those gained by EI method and MKE method. Finally six classical comparison criteria are employed to demonstrate the advantage and disadvantage of these four methods. The results showed that some innovations proposed in this paper are effective and reliable. The two improved optimal sensor placement methods (EI-AAA method and EI-MKE method) can not only make the truncated mode shapes as linearly independent as possible but also enable the measured modal kinetic energy to maintain the maximum value.