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.
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.
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.
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.
In this article, the tension–tension fatigue behavior of newly developed pultruded E-glass/polyurethane composites is characterized, and an improved model for fatigue life prediction including the effects of stress ratio, frequency, and mean stress as the testing parameters is proposed. The proposed non-dimensional analysis is in good agreement with the predictions of existing available fatigue data and present testing data. The model is consistent with the Goodman line relationship and has a clear physical meaning. The fatigue test data of E-glass/polyurethane composites are analyzed using the proposed model, and they are compared with other common E-glass fiber-reinforced plastic composites. It indicates that the E-glass/polyurethane composites are more fatigue sensitive but comparable to other fiber-reinforced plastic composites in their fatigue behaviors. The effects of stress ratio, frequency, and mean stress on fatigue life of E-glass/polyurethane composites are studied and discussed. The corresponding S–N curve and its bounds based on 95% confidence are provided for the pultruded E-glass/polyurethane composites. The present fatigue model can be used as a useful tool to characterize the effects of various parameters on the fatigue behavior of fiber-reinforced plastic composites, and it provides the fatigue life prediction for newly developed pultruded E-glass/polyurethane composites.
One of the common damages in existing highway bridges is the damage at the bottom corners or edges of the reinforced concrete beams or box girders induced by an impact of trucks exceeding the allowable height clearance of the bridges. In this study, a collision protection and scarifying system is developed, and it utilizes advanced materials/structures to protect highway bridge girders. The proposed collision protection and scarifying system is in a new “I-Lam” (Impact Laminate) configuration and bolted and/or bonded to the bottom portions or edges of concrete girders. The I-Lam panels are made of a composite sandwich construction with multi-layer aluminum honeycomb core and top and bottom thin face sheets, and they are developed/designed specifically for impact damage protection of bridge girders (e.g., concrete girders). Design criteria and guideline for I-Lam are developed, and the analysis, optimal design, and quality control tests of the collision protection system are conducted. Smart piezoelectric sensors are integrated with the I-Lam panels for monitoring the performance of the collision protection system. The collision protection system is implemented in an identified bridge. The developed smart bilayer honeycomb I-Lam sandwich is capable of reducing the transferred contact force dramatically, absorbing/mitigating impact energy, protecting the underneath concrete structures by system scarifying and core crushing, and monitoring the impact incident with smart piezoelectric sensors, and it is applicable to protecting other structures (e.g., steel girders, columns) from accidental vehicle impact in the highways.
Durability has always been a major concern in concrete-based infrastructures. Alkali–silica reaction (ASR) is the result of a chemical reaction between hydroxyl ions in pore water and silica from aggregates and cement of the concrete matrix. Geopolymer is a type of alkaline reactivated binder which can be synthesized by a polycondensation reaction of geopolymeric precursors and alkali polysilicates. Due to the alkaline solution brought in by alkali polysilicates, it is intuitive that a higher alkaline concentration in pore solutions of geopolymer concrete will adversely affect long-term performance. This study researched the preceding hypothesis and reports the finding of an experimental investigation of alkali–silica reaction between reactive aggregates and the geopolymer matrix. Specimens were prepared using Class C fly ash with a high CaO content and three types of aggregates (granite, carbonate, and gravel), each with different alkaline activator ratios and Na2O doses. Each aggregate also had different percentages of silicate and aluminum content. Mechanical testing of potential resistivity of the aggregates was performed via length change. Pore solution of the hardened geopolymer concrete was extracted and the pH value of the pore solution was determined. Results suggest that the extent of ASR reaction based on the presence of all three types of aggregates in fly ash–based geopolymer concrete is substantially smaller than that of ordinary portland cement (OPC)-based concrete. Scanning electron microscopy (SEM) and Fourier-transform infrared spectroscopy (FTIR) tests also revealed that the amount ASR gel formed in geopolymer is less than that formed in ordinary portland cement concrete. Hence, utilizing ASR vulnerable aggregates in the production of geopolymer concrete might be permissible.
In this paper, the effect of carbon curing procedure on low reactive fly ash alkali-activated pastes was investigated. Specimens were cured with pure carbon dioxide (CO2) gas for different curing times under 4 bar pressure. Chemical and physical characteristics of the geopolymer pastes were obtained from mass monitoring, titration test, XRD, FTIR and TGA-DTG analyses. Regarding the test results, after three days of CO2 curing, the highest CO2uptake was obtained at 4.8 wt% of fly ash precursor, with carbon sequestration efficiency at 22.6%. The ratio of carbon dioxide absorbed as efflorescence to the total absorbed CO2 was measured. The results show that at early age, almost 50% of carbonated products appeared as efflorescence; however, by increasing the curing time, and after 3 days of curing, about 80% of carbon dioxide was stored in the matrix. It was found that, in all cases, carbonation curing was detrimental to the geopolymerization process due to a high amount of efflorescence and led to a reduction in the compressive strength. At 24 h and 3 days, the specimens showed a lower reduction in compressive strength in comparison to CO2 samples cured at 3 h, 6 h and 12 h. Regarding the XRD results, calcite was detected in the 24 h and 3 days specimens, which contributes to lower pore sizes due to a higher molar volume and production of silica gel that might participate in the polymerization processes and results in densified microstructures.
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.
Foundation settlement is a common issue for bridges, which not only generates additional static stresses in continuous bridge members but also may affect the dynamic interaction between the bridge and vehicle traveling over it. In this paper, a new bridge-vehicle model with consideration of foundation settlement effect is created through the principle of virtual works to investigate the settled bridge and vehicle interaction responses. The correctness and accuracy of the model are validated with theoretical and numerical results. Based on the proposed model, numerical simulations have been conducted using the Newmark’s β method to investigate the effects of settlement mode, vehicle traveling speed, road surface roughness and boundary condition. It is shown that foundation settlement has a significant effect on impact factors of the bridge at high vehicle speeds, and road surface roughness may act together with the settlement to have a coupling effect, which needs special attentions in bridge design.
This study analyzes a hybrid computational framework that combines peridynamics (PD) and the finite element (FE) method to model wave propagation in a one-dimensional bar, focusing on their integration for enhanced accuracy and efficiency. The analysis investigates PD’s ability to capture non-local interactions in regions near loading points, with computationally efficient coarse discretization in other areas through finite element methods. The dynamic response to symmetric and asymmetric axial loading, including loading and unloading phases, is analyzed through time-dependent external forces, solving displacement, velocity, and acceleration fields at each time step. The effects of PD-specific parameters, such as the horizon size, and the FE–PD node spacing size ratios on the performance of the hybrid model in wave propagation are investigated. Additionally, the study examines the von Neumann stability for PD to ensure stability and reliability, offering a robust framework for integrating PD and FE in dynamic analyses.
Mode shape curvature-based method was originally developed to identify the damage in one-dimensional beam-like structures. In this paper, the method is gen
Prestress force loss in prestressed concrete bridge is inevitable; however it is the amount of the prestress force loss matters, which determines the safety of load-carrying members.More than 60% of all new and replaced bridges built in US are prestressed concrete bridges since the year 2000, which demands a fast and accurate inspection technique to monitor their prestress loss.
In this study, a higher-order impact sandwich beam model is presented to simulate the response of a soft-core sandwich beam subjected to a foreign object impact. The effects of asymmetric lay-up of the sandwich and arbitrary boundary conditions are accounted for in the analysis, and the solution is obtained by employing a finite difference method (FDM). A static and free vibration problem of sandwich beams is first solved, and the results are validated by comparing with the numerical finite element predictions of ABAQUS. The validity of the impact response is then examined using the LS-DYNA model. The contact force and deflection history as well as the propagation of axial, shear, and transverse normal stresses in the sandwich beams during the impact are analyzed. The local effect at the boundary and the loading location is captured by the present model, and the influences of boundary conditions (i.e., the top face sheet free and the bottom pin—pin supported versus both the top and bottom face sheets clamped) and the load spreading process on the impact behavior are discussed. The calculated stresses under the foreign object impact are further incorporated with the failure criteria to assess the failure location, time, and mode in the sandwich beams. The damage induced by the impact process is predicted and comprehensively compared with the experimental results. The higher-order impact model of sandwich beams with the FDM provides accurate predictions of the generated stresses and induced damage, and it can be used effectively in design analysis of anti-impact structures made of sandwiches.
