Journal of Bridge Engineering

To evaluate the contribution of the concrete slab to the shear resistance of composite concrete-steel plate girders, two tests were carried out on one full-scale composite plate girder. The tested specimen was loaded to failure under shear load and positive moment. Vertical deflection of the girder and out-of-plane deflection of the web panels were monitored during each test. Principal strains and their inclination were obtained by instrumentation on the web, flanges, stiffeners, and concrete slab. The observed failure mechanism of the tested specimen is presented using the test results. Nonlinear finite-element analysis of the tested specimen was carried out and calibrated using the tests results. To study a wider range of composite girders, further finite-element models were built with different concrete slab and steel web thicknesses. The experimental and analytical results indicate that the ultimate capacity of the tested composite specimen is higher than what is predicted by the current AASHTO design specifications for a bare steel plate girder.

This study investigated the shear performance of an RC beam strengthened in shear with externally bonded carbon fiber-reinforced polymer (CFRP) strips, subjected to a cyclic loading for 2 million cycles at 1 Hz. The stress level in the stirrups caused by the cyclic loading used in this study was higher than those typically used in fatigue studies, which could have caused the yielding of some stirrups from the beginning of cyclic loading. This was done to reflect the fact that many RC beams in need of shear strengthening do not meet the minimum stirrup requirement for the new and increased shear demand. The experimental results obtained in this study and a comprehensive review of 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, the 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 suggested that limiting the interfacial stress in CFRP strips to less than 1.5 MPa or 25% of its ultimate interfacial strength would increase fatigue life by avoiding debonding of CFRP strips.

Corrosion-induced deterioration of steel RC highway bridges is one of the major distress types that can render a structurally deficient bridge before reaching the design life. One feasible solution to the problem is to replace the conventional steel reinforcement with noncorrosive carbon fiber–reinforced polymer (CFRP) reinforcements. However, the CFRP reinforcement as an internal reinforcement has not been explored in AASHTO-type prestressed concrete beam bridges. AASHTO-type beams have an I-type cross section with a bottom flange, and on integration of the deck slab, the final shape is a bulb-T section. This paper discusses the experimental investigation of a precast prestressed AASHTO control beam and a bridge model. A 12.5-m-long one-third scale AASHTO-type control beam was experimentally investigated for its flexural behavior when reinforced and prestressed with CFRP. Subsequently, a one-third scale bridge model made of five such beams was constructed, instrumented, and tested under both service and ultimate load conditions. As anticipated, the control beam and the bridge model failures were initiated by rupturing of the prestressing CFRP tendons at the bottom layer. The observed flexural response of the bridge model was in close agreement with that of the control beam. As expected, the 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. It is therefore highly recommended to provide the CFRP tendons in different layers along the depth of the beams to effectively address the issues related to brittle failure exhibited by CFRP reinforcements.

In this paper, the factors and variables that affect the amplitude of the lateral vibration of the footbridge induced by pedestrians in Nakamura’s model are investigated in the aspect of nonlinear dynamics. Nakamura’s model is based on the motion of equations including coefficients of the rate of a pedestrian’s lateral force, the pedestrian density, the rate of synchronized pedestrians, the function $G\left(f_B\right)$ describing how pedestrians synchronize with the bridge natural frequency, and the pedestrians’ attitude to large vibration amplitude. The important coefficient $G\left(f_B\right)$ cannot be decided in this model because of the lack of data available on the lateral load behaviors of walking people. Nakamura assumed that $G\left(f_B\right)=1.0$ in his model by considering that pedestrians are most likely to synchronize at the bridge frequency around 1.0 Hz. The analysis results presented in this paper demonstrate that the amplitude of the lateral vibration increases when the function $G\left(f_B\right)$ increases. This suggests $G\left(f_B\right)=1.0$ may not be the worst case scenario for the lateral vibration of footbridges. Assuming $G\left(f_B\right)=1.0$ may be one reason why most of the predicted results of Nakamura are on the large side. Through modifying Nakamura’s model, an equation of motion including the time delay of the interaction between the pedestrians and the footbridge is proposed to preferably agree with the measure data. The analysis shows that the amplitude of the lateral vibration of the footbridge decreases as the time delay increases. The ignored time delay of the interaction between pedestrians and the footbridge in Nakamura’s model is another reason why the numerical results of Nakamura are larger than the measured data. From the analysis, appropriately increasing the time delay of the interaction between pedestrians and the footbridge is a possible way to reduce the lateral vibration induced by pedestrians.

The dynamic response of railway bridges to moving trains is complicated because of the involvement of the moving loads and the moving masses. Among various response characteristics, bridge resonance is of particular interest in terms of the structural effect and safety of the bridge. As far as the global bridge response is concerned, it is generally understood that when one of the apparent trainload excitation frequencies coincides with the fundamental natural frequency of the bridge, resonance could occur. However, such a general criterion is of little practical use because a typical trainload would involve numerous apparent frequencies (at equal intervals); consequently, for a given bridge (natural frequency), there could be many train speeds that satisfy the preceding resonance condition. Therefore, it is necessary to establish the relative severity of the resonance associated with each resonance scenario. This paper presents 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.

The welded truss composed of circular hollow section (CHS) braces and concrete-filled circular hollow-section (CFCHS) chords is a new kind of structural system that has been increasingly applied in large span arch bridges in China. It is necessary to have a good knowledge of fatigue strength of the welded CHS-to-CFCHS joints for the design of this kind of composite bridge. This paper reports on 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 circular hollow sections and different concrete strength grades. The quality of welds connecting brace and chord members were examined using the magnetic particle and radiographic inspection methods. The conditions of hot spot stress at both the crown and saddle positions in 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, the crack initiation positions, crack propagation patterns, and the final failure modes were recorded. Fatigue strength of the CHS-to-CFCHS T-joints was compared with that of CHS-to-CHS T-joints. It is concluded that the CHS-to-CFCHS T-joints have a much lower stress concentration factor and consequently have better fatigue strength than the CHS-to-CHS T-joints, when both kinds of joints have the same nondimensional geometrical parameters and same nominal stresses on the brace. The $S_{\mathit{rhs}}\text{-}{N}_f$ curves in the Comité International pour le Développement et l’Étude de la Construction Tubulaire 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.

This paper presents a detailed comparative environmental life cycle assessment (LCA) case study of three built bridges in Norway. To encompass a wide scale of bridge designs, the analysis dealt with a steel box girder bridge, a concrete box girder bridge, and a wooden arch bridge. This study presents the first LCA of road bridges using a standardized bridge classification. The LCA includes a wide range of pollutants and a high level of detail in life cycle material and energy consumption. Findings here and from earlier LCAs on bridges are together used as bases for general recommendations on conducting 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, as these parts require large quantities of materials, with a limited number of materials being the important ones. The construction phase accounts for relatively fewer impacts. The use phase contributes more significantly, mainly because of resurfacing with asphalt. Use of building equipment and transport of personnel in all the life cycle phases are of minor importance, as are the use of formwork, mastic, blasting, and the end-of-life incineration of wood. The environmental issues of global warming, abiotic depletion, and acidification are found to be the most important given the assumptions made in this study. A comparison of the three bridges shows that the concrete bridge alternative performs best environmentally on the whole, but when it comes to global warming, the wooden bridge is better than the other two. The results support the idea that it is possible to decide upon environmentally effective design alternatives, at a fair level of accuracy, at different stages of the bridge design process, a target that is now becoming more and more emphasized in the bridge-engineering sector.

The safety of an in-service brick arch railway bridge is assessed through field testing and finite-element analysis. Different loading test train configurations have been used in the field testing. The response of the bridge in terms of displacements, strains, and accelerations is 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 is carried out. The margin of safety with respect to cracking and stability failure is computed. Conclusions are drawn with some remarks on the state of the bridge within the framework of the information available and inferred information.

This paper presents a maintenance strategy optimization method for RC girder bridges by considering the performance indicators, service life and life cycle maintenance cost, as criteria. The condition and reliability indices 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. The condition index, reliability index, service life, and life cycle maintenance cost of the 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.

This paper presents the findings of 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.

A robotic total station (RTS) [or robotic theodolite or theodolite positioning system (TPS)] was used for the first time to measure the deflections of a short-span bridge in response to passing trains. The RTS measurements aimed to a reflector which was set on one of the midspans of the historical Gorgopotamos Bridge in Greece permitted to identify 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 confirm previous experiments and indicate that, under certain conditions (mostly favorable atmospheric conditions), an RTS can be used for monitoring dynamic displacements of relatively stiff bridges, and as a useful tool for structural health monitoring.