Papers in This Issue

This February 2013 issue of the Journal features 11 articles: eight technical papers and three technical notes covering different areas of bridge engineering. In the paper “Effect of Concrete Slab on Shear Capacity of Composite Plate Girders under Positive Moment,” Sherafati et al. carry out tests on a full-scale composite plate girder to evaluate the contribution of the concrete slab on the shear resistance of the composite concrete-steel plate girders. The tested specimen was loaded to failure under the shear load and positive moment. Vertical deflection of the girder at three points and out-of-plane deflection of the web panels at 25 locations were monitored during each test. Racking of each panel was measured by using a mounted potentiometer on the web plate. Principal strains and their inclination were obtained by instrumentation of the web, flanges, stiffeners, and the concrete slab. The experimental results indicated that the ultimate capacity of the tested composite specimen is higher than that predicted by the current AASHTO design specifications for a bare steel plate girder. In the paper “Behavior of RC T-Beams Strengthened in Shear with CFRP under Cyclic Loading,” Bae et al. investigate the shear performance of RC beams, strengthened in shear with externally bonded carbon fiber–reinforced polymer (CFRP) strips, subjected to a cyclic loading for 2 million cycles at 2 Hz. The stress level in the stirrups caused by the cyclic loading was found to be higher than those typically used in fatigue studies, resulting in yielding of some stirrups. Experimental results obtained in this study and the comprehensive review on the existing literature showed that RC beams strengthened in shear with externally bonded CFRP could survive 2 million cycles of cyclic loading without failure. Furthermore, residual shear strength of the FRP-strengthened beam appeared to be greater, albeit slightly, than the static shear strength of the unstrengthened control beam. This study's results also suggest that the fatigue life of CFRP strips can be increased by limiting the interfacial stress in the CFRP strip to less than 1.5 MPa or 25% of its ultimate interfacial strength, which will avoid debonding of CFRP strips. In the paper “Performance of an AASHTO Beam Bridge Prestressed with CFRP Tendons,” Grace et al. present an experimental investigation of the flexural behavior of CFRP reinforcement in AASHTO-type prestressed concrete beam bridges. The AASHTO-type beams have an I-type cross section with a bottom flange and have the final shape of a bulb-T section on integration with the deck slab. A 12.5-m-long one-third scale AASHTO-type control bridge with five beams reinforced and prestressed with the CFRP was constructed, instrumented, and tested under both service and ultimate load conditions. Failures of both the control beam and the bridge model were initiated because of rupture of prestressing CFRP tendons in the bottom layer. Observed flexural response of the bridge model was found to be in agreement with that of the control beam. Failure mode was progressive, with extensive cracking of the bridge model, which gives significant warning prior to the ultimate collapse, overcoming issues related to the otherwise brittle behavior of the CFRP-reinforced structures. Hence, CFRP tendons are recommended to be applied in different layers along the depth of the beams to effectively address the issues related to brittle failure exhibited by CFRP reinforcements. In the paper “Nonlinear Analysis for the Lateral Vibration of Footbridges Induced by Pedestrians,” Bin et al. investigate factors and variables affecting the amplitude of the lateral vibration of the footbridge induced by pedestrians in Nakamura's model through nonlinear dynamics. The Nakamura model is based on the equation of motion, including coefficients of the rate of a pedestrian's lateral force, pedestrian density, rate of synchronized pedestrians, function $G\left(f\text{\_}B\right)$ describing how pedestrians synchronize with the bridge natural frequency, and the pedestrians' attitude to large vibration amplitude. The important coefficient $G\left(f\text{\_}B\right)$ cannot be concluded in this model because of the lack of data available on the lateral load behaviors of walking people. Nakamura assumed that $G\left(f\text{\_}B\right)=1.0$ in his model by considering that pedestrians are most likely to synchronize at the bridge frequency of around 1.0 Hz. The analysis results presented in this paper demonstrated that the amplitude of the lateral vibration increases with the function $G\left(f\text{\_}B\right)$. This suggests that $G\left(f\text{\_}B\right)=1.0$ may not be the worst case scenario for the lateral vibration of footbridges. Assuming $G\left(f\text{\_}B\right)=1.0$ may be one reason why most of the predicted results of Nakamura are on the large side. By modifying Nakamura's model, an equation of motion, including the time delay in the interaction between the pedestrians and the footbridge, is proposed. The analysis showed that the amplitude of the lateral vibration of the footbridge decreases with an increase in the time delay. The ignored time delay in the interaction between pedestrians and the footbridge in Nakamura's model may be responsible for larger values of numerical results by the Nakamura model than those of measured data. On the basis of analysis results, increasing the time delay in the interaction between pedestrians and the footbridge may be a possible approach for reducing pedestrian-induced lateral vibration. In the paper “Critical Speed and Resonance Criteria of Railway Bridge Response to Moving Trains,” Mao and Lu investigate resonance severity in railway bridges caused by moving trains. Among various response characteristics, the bridge resonance is of particular interest in terms of the structural effect and safety of the bridge. A typical trainload would involve numerous apparent frequencies (at equal intervals). Consequently, for a given bridge (natural frequency), many train speeds could satisfy the preceding resonance condition. In this paper, the authors presented the development of a new resonance severity indicator, called $Z$-factor, for the assessment of the resonance effect. It is found that the resonance severity is essentially governed by the ratio between the bridge and carriage lengths. When the carriage mass is significant, the same $Z$-factor will apply; however, the underlying resonance speeds will change because of the altered natural frequency of the bridge-train system. Numerical results demonstrate that the proposed methods are effective for the determination of the resonance effects associated with the potential resonance speeds. In the paper “Fatigue Behavior of Welded T-Joints with a CHS Brace and CFCHS Chord under Axial Loading in the Brace,” Wang et al. investigate the fatigue behavior of a welded truss composed of circular hollow section (CHS) braces and concrete-filled circular hollow section (CFCHS) chords. They presented a series of tests on welded CHS-to-CFCHS T-joints subjected to axial cyclic fatigue loading in the brace. Eleven joints were designed to investigate various influence factors such as different nondimensional geometric parameters of CHSs and different concrete strengths. The quality of welds connecting brace and chord members was examined using the magnetic particle and radiographic inspection methods, respectively. Hot spot stress distributions at both the crown and saddle positions in the brace and chord members were determined by means of linear and nonlinear extrapolation methods. During the fatigue testing process, the number of cycles relating to several stages of failure, crack initiation positions, crack propagation patterns, and final failure modes were recorded. Fatigue strength of the CHS-to-CFCHS T-joints was compared with that of the CHS-to-CHS T-joints. It was observed that the CHS-to-CFCHS T-joints have a much lower stress concentration factor and consequently better fatigue strength than the CHS-to-CHS T-joints. The curves in CIDECT guidelines used for CHS-to-CHS joints are not appropriate for the reliable fatigue assessment of CHS-to-CFCHS T-joints based on the current test data. In the paper “Environmental Life Cycle Assessment of Bridges,” Hammervold et al. carry out a detailed environmental life-cycle assessment (LCA) case study comparison of three bridges built in Norway. To cover a wide scale of bridge designs, the analysis compared a steel box girder bridge, a concrete box girder bridge, and a wooden arch bridge. The LCA includes a wide range of pollutants and a high level of detail in material and energy consumption throughout the lifetime. Findings here and from previous LCAs on bridges are used as the basis for general recommendations on performance of LCAs on bridges. The study shows that it is the production of materials for the main load-carrying systems (i.e., the bridge superstructure) and the abutments that accounts for the main share of the environmental impacts because these parts require large amounts of materials, with a limited number of materials being the important ones. The construction phase contributes small impacts. The use phase contributes more significantly, mainly as a result of resurfacing with asphalt. Use of building equipment and transport of personnel in all life-cycle phases are of minor importance, as also are use of formwork, mastic, blasting and finally incineration of wood at end of life. A comparison of the three bridges showed that the concrete alternative performs best environmentally, except for global warming, where the wooden bridge performs the best. In the paper “Safety Assessment of a Masonry Arch Bridge: Field Testing and Simulations,” Chandra Kishen et al. investigate the safety of an in-service brick arch railway bridge through field testing and finite-element analysis. Different loading test train configurations were used in the field testing. The response of the bridge in terms of displacements, strains, and accelerations was measured under the ambient and design train traffic-loading conditions. Nonlinear fracture mechanics–based finite-element analyses are performed to assess the margin of safety. A parametric study is done to study the effects of tensile strength on the progress of cracking in the arch. Furthermore, a stability analysis to assess collapse of the arch caused by lateral movement at the springing of one of the abutments that is elastically supported was carried out. The margin of safety with respect to cracking and stability failure was computed.

In the technical note “Performance Life Cost-Based Maintenance Strategy Optimization for Reinforced Concrete Girder Bridges,” Zhu and Liu present a maintenance strategy optimization method for a RC girder bridge by considering the performance indicators service life and life-cycle maintenance cost as criteria. The condition and reliability indeces are defined as performance indicators. The deteriorated processes of performance indicators with and without maintenance actions are described as multilinear models. The life-cycle maintenance planning optimization of deteriorating bridges is formulated as a multiobjective problem to be solved by an improved nondominated sorting genetic algorithm with controlled elitism (NSGA-II). Condition index, reliability index, service life, and life-cycle maintenance cost of bridge are considered as four separate objective functions. A simply supported RC girder bridge is analyzed as an application example to demonstrate the usefulness of the proposed procedure. In the technical note “Integral Bridge Abutment to Approach Slab Connection,” Phares et al. carry out a performance investigation of two approach slabs (a cast-in-place slab and a precast panel slab) integrally connected to two parallel bridges. The goal of using the integral connection is to eliminate the “bump at the end of the bridge.” To measure the performance, a long-term structural monitoring system consisting of various vibrating wire transducers was installed. From the year-long monitoring, the following general conclusions were made: (1) the integral connection functions well with no observed distress or relative movement between the approach slab and bridge; (2) most of the force at the integral connection is induced by forces at the pavement/approach slab expansion joint; and (3) the observed responses generally followed an annual cycle with short-term ratcheting patterns also apparent. In the technical note “Measuring Deflections of a Short-Span Railway Bridge Using a Robotic Total Station,” Psimoulis and Stiros investigate the use of a robotic total station (or robotic theodolite, RTS, or TPS) to measure the deflections of a short-span bridge caused by passing trains. Measurements to a reflector set on one of the midspans of the historical Gorgopotamos Bridge in Greece permitted identification of the measurement noise (apparent displacements), up to ±1.3 mm, when no trains were passing and deflections with peaks of 2.5−6 mm during intervals when small or larger trains were passing. These results confirmed previous experiments and indicated that, under certain conditions (mostly favorable atmospheric conditions), RTS can be used for monitoring of dynamic displacements of relatively stiff bridges and can serve as a useful tool for structural health monitoring.