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.
Approaches to improve the early strength of geopolymer mortar were studied in order to apply it to a fast-tack concrete pavement repair. The effects of modifying the molar ratio of silicon dioxide/sodium oxide (SiO 2 /Na 2 O) of the alkaline solution in a conventional geopolymer mixture and the addition of calcium aluminate cement and slag were studied. The early strength measured in the experiments was at curing times of 8 and 24 h, which are typically construction controlling times for pavement repair. It was found that a molar ratio of silicon dioxide/sodium oxide of 1·0 gave the shortest curing time and the highest early strength after 24 h. Adding calcium aluminate cement was found to reduce the curing time, but decrease the early strength. Slag substitution helped workability, but reduced the early strength at 8 and 24 h. Durability was also tested for the purpose of finding an economical pavement repair solution. A freeze–thaw durability experiment of the suggested metakaolin-based geopolymer concrete was conducted. It was found that a mix with a silicon dioxide/sodium oxide molar ratio of 1·0 produced higher durability than a mix with a silicon dioxide/sodium oxide molar ratio of 1·4. The geopolymer concrete mix with slag showed less weight loss than the other mixes.
Based on virtual simulations of vehicle–bridge interactions, the possibility of detecting stiffness reduction damages in bridges through vehicle responses was tested in two dimensional (2D) and three dimensional (3D) settings. Short-Time Fourier Transformation (STFT) was used to process vehicles’ acceleration data obtained through the 2D and 3D virtual simulations. The energy band variation of the vehicle acceleration time history was found strongly related to damage parameters. More importantly, the vehicle’s initial entering conditions are critical in obtaining correct vehicle responses through the vehicle bridge interaction models. The offset distance needed before executing the vehicle–bridge interaction (VBI) modeling was obtained through different road profile roughness levels. Through the above breakthroughs in VBI modeling, the presented study provides a new and integrated method for drive-by bridge inspection.
Many bridges inevitably experience foundation settlement during their lifetime. Structural engineers need to limit the foundation settlement so that the bridge structure does not develop intolerable stresses. One factor in the effect of foundation settlement on bridge structures that has not been considered so far is the dynamic interaction between bridge and moving vehicle. In this study, Hamilton principle is adopted to derive the governing equations for the vibration of line supported orthotropic thin plates due to moving vehicles. The effect of foundation settlement on the bridge–vehicle interaction (BVI) is investigated by modifying the interaction forces due to the deformed shape of deck. The effect of fully or partially developed membrane stresses on the BVI will be also discussed. The results show that dynamic load allowance (IM) increases depending on the support location where settlement occurs, mode of settlement, span length, and magnitude of the foundation settlement. However the effect of membrane stresses on IM is insignificant. The analysis results indicate importance of considering the effect of bridge support settlement on the dynamic BVI.
High blast absorbing materials have been consistently sought by the US Departments of Defense and Homeland Security, especially after 9.11. These materials can be used to effectively absorb blast wave energies and impact impulses and protect human lives and properties under extreme blasting events. The chapter reviews the current research status, outlines design philosophy for blast resistant design, and points to several case studies for using advanced materials and technology for blast mitigation, such as metal and foam sandwich panels, magneto-rheological fluids, and porous shape memory alloy.
This report presents a research examining the feasibility of creating an integrated structural health monitoring and impact/collision detection system for bridges in remote cold regions, where in-person inspection becomes formidable. The research report includes a theoretical analysis of the impact event identification in Chapter II, laboratory experiment verification in Chapter III, and a field testing and an integrated Structural health monitoring system in Chapter IV. Based on the systematical research outcomes, the impact/collision event and the real-time bridge structural health status have been successfully identified and recorded, which could be used for bridge management and resources allocation in future.
Expansive soil is considered one of the most common causes of pavement distresses in FM roadways. Depending upon the moisture level, expansive soils will experience changes in volume due to moisture fluctuations from seasonal variations. The objective of this research was to evaluate existing repair projects on selected FM roadways. Those roadways experienced failures in the form of fatigue and rutting in the wheel path, and longitudinal (faulted) cracking including edge cracking. The causes of those failures were mainly linked to high PI expansive soil and narrow pavement.
The quasi-static crushing behavior of aluminum honeycomb materials is thoroughly evaluated using a combined experimental, analytical, and numerical approach. Based on experimental characterization, the constitutive properties of the honeycomb cores under flat-wise compression are approximated by an elastic perfectly plastic material with inclusion of hardening after densification. Two different cell size materials are tested and compared, and the effect of strain rate on the crushing stress is studied. The experimental results show that the crushing platen stress is directly related to the relative density of core materials, and it can be associated with the strain rate, even though the effect of strain rates is not so dominant based on the conducted quasi-static tests. A simple physical model for predicting the crushing wave length and stress is proposed and compared with the experimental data and available formulas in the literature. It is observed that the crushing wave length is close to the cell size and related to the geometric dimension and strain rate. The folding mechanism is also measured by the ARAMIS system (a photogrammetry technique), and the measured von Mises strains are compared with the numerical results from LS-DYNA, demonstrating that the folding mechanism is initiated by two plastic hinge lines formed at the cell corners. Multilayer effect is also investigated, and it indicates that including the second layer slightly decreases the maximal crushing stress, but the simple superposition is still applicable for crushing multilayer honeycomb cores with different density. Partial crushing due to small size cylindrical indenter is further studied, and the experiment shows that the partial crushing process can be described by an elastic—plastic hardening material. Side impact process of honeycomb materials is also investigated, and the collapse band and its propagation process are captured. The thorough characterization of core crushing behavior conducted in this study provides better understanding of the failure process of honeycomb materials and can be further employed to study energy absorption and impact response of sandwich structures.
In this paper, a systematic methodology for identifying damages in bridges is presented, which includes the baseline calibration through field testing data
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
With the development of tourism, the number of multistorey buildings in mountain areas is increasing gradually, and the requirements of the form and bearing capacity of foundation in landslide areas are getting more demanding than ever. In‐situ testing of rock and soil mass in slope area has important practical significance for improving the stability of building foundation. Taking a project in Baishi Mountain located in southwest of China as an example, firstly, the geological structure and mechanical properties of soil are analyzed. Then, two types of pile foundations, i.e., empty‐bottom pile foundations and solid‐bottom pile foundations, are designed based on the characteristics of the geological structure for carrying out the static load test on pile foundation. The test results are as follows: (a) the load settlement curve (Q‐S) of the empty‐bottom test pile shows a steep drop, while the Q‐S curve of the solid‐bottom test pile shows a gradual change, showing that the end‐bearing friction pile’s property and the ultimate bearing capacity of the solid‐bottom pile are higher than those of the empty‐bottom pile. (b) The maximum lateral friction of the four test piles is 139.158 kPa, 148.015 kPa, 150.828 kPa, and 154.956 kPa, respectively. (c) The shaft skin resistance under ultimate load is coming close to the maximum value, and the maximum values are 9.792 mm, 7.939 mm, 9.881 mm, and 14.97 mm, respectively. Research results can serve as design bases for the pile foundation of multistorey buildings located in landslide areas of Baishi Mountain in the southwest of China and also as references for the engineering application of pile foundation in similar geological fracture areas.
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.
