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To overcome the drawbacks of bond-type anchors for carbon fiber–reinforced polymer (CFRP) cables, an innovative bonded anchor with steel wedges at the free end is developed in this study. T...

The technique of prestressing near-surface-mounted (NSM) carbon fiber–reinforced polymer (CFRP) has good potential and future prospects for structural strengthening due to its improvement o...

The precast ballastless track slab has been widely applied in the Chinese high-speed railway system. However, the current slabs, made of normal concrete (NC) materials and designed in a “plane” structural configuration, were found vulnerable to the train loads and temperature effects. This paper proposed an innovative slab type, which was made of an alternative reactive powder concrete (RPC) material and designed in a “frame” structural type. Four frame slabs with different cross section profiles were parametrically investigated, and the best configuration was proposed. The results demonstrated the proposed RPC slabs can well meet the requirements of the stiffness and strength. Compared with the NC plane slabs, the warping deformation of the RPC frame slabs were decreased as much as by 41.7% and 37.0%, respectively, under the −10°C temperature gradients and the combination of train and temperature effects. The simulated tensile stresses were within the corresponding RPC strength capacity. The crac...

The current highway bridge design in the United States follows the AASHTO-LRFD specifications, which prescribe a dynamic load allowance, IM, of 0.33 for the dynamic effect of truck/tandem loading. Studies have shown that the IM value prescribed by the LRFD code may underestimate this dynamic effect under poor road surface conditions (RSCs). One reason for this underestimation is that the IM value employed in the AASHTO specifications was obtained from the statistical properties of the IM relative to average RSC, as defined by the ISO 1995 standards. In addition, the IM, which is a random variable with certain statistical properties, was modeled as a deterministic constant in the code calibration process. In this paper, the reliability indexes of a selected group of prestressed concrete girder bridges, designed following the AASHTO-LRFD code, are calculated by modeling the IM explicitly as a random variable for different RSCs. It is found that although the calculated bridge reliability indexes are usually above the target reliability index value of 3.5 under above-average RSCs, they can be significantly below the target value of 3.5 when the RSCs are below average. Following the load rating procedure proposed by the AASHTO load and resistance factor rating (LRFR) manual, it is also found that the code-employed IM value may overestimate the rating factors when RSCs are below average. Based on these results, appropriate IM values are suggested for different RSCs to achieve a consistent target reliability index and a reliable load rating. The results presented in this paper are particularly valuable for the rating of existing prestressed concrete girder bridges, for which the actual RSCs can be directly evaluated. The RSCs must be properly taken into account to accurately estimate the actual safety of the considered bridge.

This paper describes the initial efforts to explore a new application of metakaolin-based geopolymers to structural health monitoring. A distributed geopolymer-fiber optic sensing G-FOS system is proposed, where geopolymers are used as smart adhesives to affix optical fibers to existing in-service structures to form an integrated G-FOS sensor. Results of feasibility testing in the laboratory indicated that the tensile cracking strain of geopolymers can be controlled by finely tuning the Si/Al ratios or adding appropriate aggregate fillers such as sand, thus rendering the "smart" nature of geopolymers for deformation-based sensing. Geopolymers with SiO2 /Al2O3 ratios 3.8 are viable adhesives that can develop strong bond to concrete, steel, and glass fiber. Laboratory prototype testing on steel specimens under uniaxial tension and on concrete beams under four-point bending validated the concept and feasibility of the proposed G-FOS system for structural health monitoring. It further demonstrated that the G-FOS system cannot only detect overstraining events in steel but also measure the crack size in concrete.

The present study formulated a three-dimensional (3D) vehicle-pavement coupled model to simulate the pavement dynamic loads induced by the vehicle-pavement interaction where both the vehicle vibration and pavement deformation were considered. Based on this model, the effects of road surface conditions, vehicle parameters, and driving speed on pavement dynamic loads were analyzed. The impact factor, dynamic load coefficient, and frequency distribution of pavement loads were mainly concerned in this study. The simulated results indicated that under rough road conditions the dynamic loads of vehicles are significantly higher than the static loads. The developed methodology can be used to further study the vehicle-induced pavement response, and the loading information will be useful in analyzing vehicle-induced pavement damage.

Eleven steel-concrete composite beams, four under pure torsion, and seven under combined bending and torsion were tested to study their torsional behaviors. Torsion-dominated and bending-dominated failure modes were observed, depending on the ratio between the applied bending and torsional moments. Testing results also showed that the reinforced concrete slab contributes mainly to the torsional resistance of composite beams and the contribution of steel joists to torsion is negligible. However, the steel joist plays a vital role in restraining the concrete slab from deforming longitudinally, which enhances the torsional strength of the concrete slab. Based on the experimental observations, a three-dimensional behavioral truss model capable of analyzing composite beam sections subjected to the combined bending and torsion was presented. In this model, the section is subjected to one- and two-dimensional stresses separately. The former resists the longitudinal stresses due to bending and torsion while the latter resists the shear stresses due to torsion. These two systems are related based on the compatibility of strains and the equilibrium of stresses in the longitudinal direction. The results predicted with this method are in good agreement with those obtained from the tests. Additionally, the interaction between bending and torsional strengths was discussed.

The negative effects of weather (e.g., strong winds, snow, and icy rain) on the safety of vehicles have been recognized and reported upon for some time worldwide. As an important category of vehicle accidents, the single-vehicle noncollision accident has not been studied sufficiently under adverse environmental and topographic conditions. In the United States, strong wind, together with other adverse weather and topographic conditions, has been blamed for many single-vehicle accidents every year, especially those involving trucks. Vehicle safety not only threatens people's lives during normal operations, but may even put many people in miserable situations when an emergency evacuation is interrupted by frequent accidents on key routes. As a result, the safety of many people who are delayed in congestion on evacuation routes may be jeopardized. The reasons that cause single-vehicle accidents can be very complicated: from a single primary reason such as strong wind gusts to the combination of several reasons such as weather conditions, vehicle conditions, road surface conditions, driver operational errors, etc. This study seeks to investigate the safety of vehicles during normal operations as well as emergencies through replicating the natural environments. It starts with a brief overview of single-vehicle accidents caused by environmental and topographic conditions around the United States in normal operations, followed by discussions about the current challenges existing in the evacuation practices. An attempt is then made to model the complicated weather, road surface, and driver operational process, such as rain, snow, camber, grade, and acceleration/deceleration as well as steering processes. With the proposed accident assessment framework, the accident-related response is studied and accident risks are assessed for vehicles. The study may also provide a useful basis for traffic designs on highways with complicated topographic and weather conditions and optimization of evacuation routes and strategy with minimized single-vehicle accident risks.

Soil embankment settlement causes concrete approach slabs of bridges to lose their contact and support from the soil. When soil settlement occurs, the slab will bend in a concave manner that causes a sudden change in slope grade near its ends. Meanwhile, loads on the slab will also redistribute to the ends of the slab, which may result in faulting across the roadway at the ends of the approach slab. Eventually, the rideability of the bridge approach slab will deteriorate. The current American Association of State Highway Transportation Officials code specifications do not provide clear guidelines to design approach slabs considering the embankment settlements. State Departments of Transportation are spending millions of dollars each year to deal with problems near the ends of approach slabs. To investigate the effect of embankment settlements on the performance of the approach slab, a three-dimensional finite element analysis was conducted in the present study, considering the interaction between the approach slab and the embankment soil, and consequently the separation of the slab and soil. The predicted internal moments of the approach slab provide design engineers with a scientific basis to properly design the approach slab considering different levels of embankment settlements. A proper design of the approach slab will help mitigate the rideability problems of the slab.

Work is described which focuses on biaxially loaded cases and consisted of three aspects: experimental study of the ultimate load carrying capacity of biaxially loaded beam-columns; numerical study of the ultimate strength of beam-columns; and verification study of the validity of the AISC LRFD (load resistance factor design) interaction equations through comparisons with these experimental and numerical results. The details of the study are described. It was found that the specification interaction equations are conservative for rolled members. However, for the welded members with the type of residual stress distribution considered in the study, the interaction equations may slightly overestimate the load-carrying capacity of some beam-columns. These and other study findings are presented. It is concluded that the AISC LRFD equations are reasonable for design, give a realistic representation of column behavior and strength, and meet the requirement for simplicity in use.