Wavelet transform (WT) is theoretically studied to recover the bridge mode shapes from a passing two-axle test vehicle by using the correlation between the front and rear contact points. In this paper, closed-form solution is derived for the dynamic response of the bridge. To avoid the masking effect brought by vehicle’s natural frequencies on bridge’s natural frequencies, the wheel-bridge contact responses are used instead, which are derived from the vehicle responses considering the suspension effect. Next, the WT is employed to obtain the ridges of the bridge component response, based on which the bridge mode shapes are retrieved by using the correlation between the front and rear contact points. Conclusions made for this study include: (1) the contact responses for the two-axle test vehicle can be better used for frequency extraction than the vehicle responses; (2) the WT can be successfully used for constructing bridge mode shapes; (3) the procedures proposed for calculating the contact responses and for recovering the bridge mode shapes are robust with regard to the vehicle damping and speed for beam-type bridges; and (4) the mode shapes recovered by the proposed procedure are good even in the presence of pavement roughness with the aid of ongoing traffic.
Aim To observe the effect of Vitamin B 6 on reduction of the main side effects of Praziquantel for schistosomiasis.Methods Villagers aged 6-60 in 328 endemic villages were selected and divided into experimental and control groups.The experimental group were given single oral dose of both praziquantel and Vitamin B 6,while the control group were given single oral dose of praziquantel and placebo.The dosages of praziquantel were,body weight limit being below 60 kg.45mg /kg for those of 6-14 years old and 40mg/kg for those aged 15-60.Dosages of Vitamin B 6 were 20mg per capita for those of 6-14 years old and 30mg/kg per capita for those aged 15-60.Results Occurrence rate of praziquantel side effects in the experimental group and in the control group were 73 78% and 81 10% respectively,showing significant difference (P0.05).The Occurrence rates of main side effects on the nervous and digestive systems were 72.86% in the experimental group and 79.57% in the control group respectively,also indicating significant difference (P0.05).By contrast of disappearance time of dizziness within 2,4,6,8,and 10 hours,the accumulated disappearance rate of side effects of the experimental group was obviously higher than that of the control group.Conclusion Vitamin B 6 is effective in reducing occurrence rate of the main side effects of Praziquantel for schistosomiasis and speeding up the disappearance time of dizziness.
Based on a strict and novel decomposition of deformation patterns of a sandwich beam under transverse loading, the flexural and indentation responses of sandwich beams are analyzed with consideration of elastic-plastic behavior of the crushable core material. The analytical model is capable of predicting the flexural response, indentation failure load, and indentation deformation. Some interesting phenomena, such as the global elastic-plastic hardening behavior and three distinct failure stages, are revealed using the present approach. Different from the existing plastic foundation model, a generic model for analyzing the flexural and indentation responses of the elastic-plastic sandwich beams is proposed, and it sheds new light on the effects of skin membrane and elastic-plastic core during indentation process.
No abstract is provided for this article.
Impact event identification is a primary concern in many structural health monitoring applications. Model-based inverse analysis is a common approach for system identification as long as the physical model can accurately capture the behavior of structure. A layered analysis including estimation of impact location (IL) in the first layer and reconstruction of impact load time history (ILTH) in the second layer was proposed. An implementation of the theory on a simply supported plate structure is conducted in this study. The results indicate that the proposed inverse scheme is capable of detecting impact location and reconstructing impact load time history with a satisfactory precision. Due to presence of system error, a suitable cost function has to be chosen to guide the fitting process toward the desired parameters.
In this paper, three translations and three rotations of the unmanned aerial vehicle (UAV) were derived through the suggested Normalized Cross Correlation (NCC) based template matching computer vision method and their effect on the monitored structural displacement is analyzed. The NCC-based template matching is used to obtain the vibration of UAVs by tracing far-field background points at the recorded images. The images captured at any general orientations are rotated back to their original positions which could detect errors in the monitored displacement induced by the rotation angles. A fast NCC-based template matching method was also proposed in this paper, which could accelerate the original NCC-based template matching method significantly and reaches the same level accuracy as that of the original NCC-based template matching method. In order to verify the concept, a series of experiments were performed on a Multipurpose Testing System (MTS) machine with amplitudes of 10 mm, 5 mm, and 2.5 mm and frequencies of 2 Hz, 1 Hz and 0.5 Hz, respectively, at the same time a UAV and a fixed camera were used to record the motions of the MTS piston. The derived displacements through the UAV and the fixed camera are compared with the true motions of the MTS machine. Excellent precision and consistence were obtained for the UAV monitored displacement, the MTS piston motion, and the fixed camera derived displacement. Comparing to the case of the fixed camera, scales and rotation angles of the UAV are critical and largely affect the accuracy of monitored displacements. A field experiment was conducted to test the proposed method in a windy environment. Excellent agreement was found between the monitored displacement obtained by the UAV and that derived from the fixed camera.
The application of guided wave techniques to nondestructively determine the structural integrity of various engineering materials, like alumina, laminated composites, and composite sandwiches, is presented. In particular, a combined theoretical, numerical, and experimental investigation of the fundamental aspects of the pulse-echo method using piezoelectric sensors and actuators is conducted. The dispersion effect of wave guides on these materials is first analyzed, and the transient propagation process of wave guides and its interaction with internal damage are then numerically simulated. The implementations of the pulse-echo method are illustrated in experimental testing and damage detection of aluminum beams, carbon/epoxy laminated composite plates, and composite sandwich beams. The effects of frequencies, wave forms, and types of piezoelectric material on the damage detection process are discussed, in consideration of locating damage in structures. As illustrated in this study, the pulse-echo method combined with piezoelectric material can be used effectively to locate damage in various engineering materials and structures.
Alkali-Silica reaction (ASR) is a deleterious chemical reaction in concrete and manifests itself through pore structure changes. Alkali activated fly ash geopolymer concrete is a new type of green concrete that forms binder through alkali activated materials without using Portland cement. However, due to the alkali solution used, alkali activated fly ash geopolymer concrete is naturally susceptible to ASR. In this paper, ASR effect is traced through pore distribution and its change with time through micro-computed tomography (Micro-CT). Through Micro-CT images, it is found that ASR in fly ash geopolymer concrete is less severe than its ordinary Portland cement concrete counterpart, since the pore distribution in fly ash geopolymer concrete is more uniform and does not change with time, while increasing sizes of pores are found in the ordinary Portland cement concrete.
Existence of prestress in bridges affects the dynamic responses of both bridges and vehicles traveling over them. In this paper, the bridge is modeled as a continuous beam with eccentric prestress, and a half-vehicle model with 4 degrees of freedom is used to represent the vehicle passing the bridge. A new bridge–vehicle model with consideration of prestress effect is created through the principle of virtual works to investigate the continuous prestressed bridges and vehicle interaction responses. The correctness and accuracy of the model are validated with literature results and Abaqus model. Based on the created model, numerical simulations have been conducted using the Newmark integration method to perform a parametric study on effects of number of bridge span, span length, eccentricity and amplitude of prestress. It is shown that prestress has a significant effect on the maximum vertical acceleration of vehicles, which may provide a good index for detecting the change of prestress.
Structural snow fences have been increasingly used in northern regions of the United States. They are known as a cost-effective and efficient technology to prevent snow accumulation on highways and, therefore, improve road safety. Structural snow fences, however, are used only during winter, and to add more value to the structure, an idea to install solar photovoltaics (PV) panels on structure snow fences was first proposed by the Minnesota Department of Transportation (MnDOT), who was interested in looking at the feasibility of integrating structural snow fences with PV panels, called PV snow fences (PVSF). The PVSF would be constructed by replacing the rails between the poles of the structural fences with customized PV panels that have the same dimension as the rail. This arrangement is to ensure that the original function of the snow fences, that is, eliminating blowing and drifting snow on highways, would not be affected. Considering different factors or parameters, such as project size, panel size, installation angle or orientation of the panels, discount rate, energy selling price to a utility company, availability of incentives, ownership of the PV system, etc., a comprehensive cost–benefit model has been established to analyze the pros and cons of different implementation plans. The analysis results show that the longer the length of the PVSF is, the more cost-effective the project is, due to a lower capital cost and increased power generation. A Power Purchase Agreement (PPA) would significantly shorten the payback period in consideration of the key benefits brought through a PPA, including minimal up-front capital costs, lower energy costs, no risk, no upkeep, leveraging available tax credits, and enhancing the value of the property, which is, therefore, more realistic and would be a higher priority for an agency like MnDOT or other state DOTs.
Due to intense use of sandwich structures in civil and aerospace engineering, there is a pressing need to analyze impact effects, which may cause the damage in materials and reduce the structural effectiveness. In this study, an elastic model for static and nonlinear impact responses of a composite sandwich plate on an elastic half-space including the antiplane core effect is developed. The effects of the elastic half-space and the anti-plane core are studied, and the contact force history and maximal deflection are predicted. The predicted non-uniform distribution of transferred force under static load sheds new light on understanding of force action mechanism between the sandwich system and the solid halfspace. The two important impact factors (i.e., the maximal deflection and the peak contact force) provided by this study can be used to determine the damage size and position. Further, the analytical model developed can be served as a basis for optimal design of fullybacked sandwich collision protection systems.
