Papers in This Issue

This March 2013 issue of the Journal features eight technical papers covering different areas of bridge engineering. The first two papers are related to the seismic response of bridges. In the paper “Markovian Bridge Maintenance Planning Incorporating Corrosion Initiation and Nonlinear Deterioration,” O'Connor et al. developed a maintenance management model by incorporating a two-step deterioration process (i.e., initiation and propagation of corrosion) into account. This allows owners/managers of bridges to compare the efficiency of different maintenance strategies in terms of both the initiation phase and the propagation phase of deterioration to determine the optimum maintenance strategy for the structure or group of structures being considered. The capabilities of the developed methodology were demonstrated using a practical example. In the paper “Experimental Study on Fatigue Strength of Corroded Bridge Wires,” Nakamura and Suzumura showed through fatigue tests of corroded galvanized steel wires with three corrosion levels that the fatigue strength of corroded wires decreases with a progress in corrosion. Corrosion pits were measured on the corroded specimens, showing that more severe corrosion produced deeper pits in more condensed areas. Fatigue tests were then conducted for wire specimens with artificial pits whose sizes were decided by the measured corrosion pit data. Three different pit shapes were assumed: round, triangle, and triangle with a notch. The wire specimens with round pits did not break until 1 million cycles in the stress range of 400 MPa. The fatigue strength of wires with the triangle pit was lower than that with a round shape. Triangle pit specimens broke at fewer cycles for a shorter pit length. The fatigue strength of wires with a notched triangle further decreased, and critical cycles did not depend on pit length. As the S-N relation of the wire specimens with triangle pits and notched triangle pits corresponded to those of the actual corroded wires, the pit shape seems to be a dominant factor in lowering fatigue strength. The stress concentration factor at the sharp edge of pits was obtained by strain gauge measurement and finite-element model analysis. Both methods show that stress concentration is larger for sharper pit shapes, indicating that this is the major cause for the decrease of fatigue strength.

The next four papers are related to loads and load capacities of bridges. The paper “Live-Load and Shear Connection Testing of Full-Scale Precast Bridge Panels” by Brackus et al. presented an investigation to quantify the behavior of a precast deck system. As part of this investigation, a live-load test was performed on a steel I-girder bridge made with accelerated bridge construction precast deck panels. It was found that the bridge was behaving compositely in some locations and noncompositely in others. When the bridge was decommissioned, a two-girder specimen was salvaged and transported to Utah State University for shear capacity testing. The primary shear failure mechanism was found to be buckling of the girder web. A nonlinear finite-element analysis was conducted using ANSYS that was found to replicate the experimental behavior and reproduce the failure mechanism and magnitude. It was concluded that the effect of the noncomposite behavior on the ultimate shear capacity was a reduction of approximately 8.0%. The measured ultimate capacities were compared with estimates calculated according to procedures in the AASHTO LRFD specifications. When using the specified steel strength, the code-predicted shear resistance ranged from 8.0% higher to 0.7% lower. In the paper “Nonlinear Seismic Response and Parametric Examination of Horizontally Curved Steel Bridges Using 3D Computational Models,” Seo and Linzell investigated a computational modeling approach for the seismic behavior of horizontally curved steel bridges. The computational, three-dimensional (3D) bridge models consisting of the concrete deck, steel girders, cross frames, pier columns and caps, and the abutments and footings were created in OpenSees and examined for accuracy via application to a representative, three-span continuous, curved, steel, plate girder bridge in Pennsylvania. Sensitivity studies in the form of tornado analyses were also carried out to investigate the influence of critical curved bridge parameters on seismic response using a group of representative bridges. Each representative bridge was subjected to an ensemble of synthetic ground motions, and the seismic response was examined. Results from the sensitivity study indicated a 17–22% variation in maximum bearing and abutment deformations, column curvature ductility, and cross-frame axial forces parameters for the range of bridge radii and span numbers that were investigated. In the paper “Using Weigh-in-Motion Data to Determine Aggressiveness of Traffic for Bridge Loading,” OBrien and Enright presented results based on the analysis of an extensive database of WIM data collected at five European highway sites in recent years. The data were used as the basis for a Monte Carlo simulation of bridge loading by two-lane traffic: both bidirectional and unidirectional. Long runs of the simulation model were used to calculate characteristic bridge load effects (bending moments and shear forces), and these characteristic values were compared with design values for bridges of different length as specified by the Eurocode for bridge traffic loading. Various indicators were tested as possible bases for a bridge aggressiveness index to characterize the traffic measured by the WIM data in terms of its influence on characteristic bridge load effects. WIM measurements can thus be used to determine the aggressiveness of traffic for bridges. The mean maximum weekly gross vehicle weight was proposed as the most effective of the indicators considered and was shown to be well correlated with a wide range of calculated characteristic load effects at each site. In the paper “Multiple Presence Factor for Truck Load on Highway Bridges,” Fu et al. investigated the derivation of the multiple presence factor (MPF) based on weigh-in-motion (WIM) truck data for both the strength and fatigue limit states. The WIM truck data consisted of 68 million trucks gathered for 436 months from 43 sites in California, Oregon, Michigan, and New York. The resulting MPFs are proposed as functions of bridge span length, truck traffic volume, and number of lanes available. The authors showed that the code-specified MPF values are conservative and sometimes overconservative by 400% or more, which may have caused too high requirements for load rating of existing bridges, especially for shorter spans and/or low truck traffic. The recommended MPF may be considered to be adopted in specifications for highway bridge design and evaluation. The authors also presented a new truck-by-truck analysis approach for understanding the load effect of trucks in motion, taking advantage of increasingly available WIM data of large quantities to avoid unsupported assumptions in live-load modeling. The remaining two papers are in the areas of corrosion in bridge components. In the paper “Response of Seismic-Isolated Bridges in Relation to Intensity Measures of Ordinary and Pulselike Ground Motions,” Özgür Avşar and Özdemir investigated the efficiency of numerous ground motion intensity measures (IMs) in estimating the response of seismic-isolated bridges (SIBs). Efficiency of commonly used IMs was investigated through their correlation with maximum isolator displacement (MID) obtained from nonlinear dynamic analyses. Two sets of ground motions, classified as ordinary and pulselike,were used in nonlinear dynamic analyses of SIBs. In the analyses, varying isolation parameters such as isolation period, $T$, and the characteristic strength of isolator, $Q_d/W$, were studied. Sensitivity to varying $T$ and $Q_d/W$, as well as the effect of ground motion type, on the correlation of IMs with MID of SIBs were examined. To improve the correlation of existing IMs, modified IMs were proposed. The results revealed that isolation period has a pronounced effect on the correlation of IMs with MID of SIBs, especially for pulselike GMs. Among the investigated IMs, modified velocity spectrum intensity appears to have the strongest correlation with MID of SIBs for a wide range of isolation parameters and ground motion type. In the paper “Structural Analysis and Load Test of a Nineteenth-Century Iron Bowstring Arch-Truss Bridge,” Moen et al. investigated the oldest remaining metal bridge in Virginia, a wrought-iron bowstring arch-truss bridge, through structural analysis. FEA was used to evaluate the interaction between the arch and truss, and the results were compared with field measurements from a live-load test. The study revealed that diagonal truss elements decrease arch bending by distributing concentrated vertical loads along the arch toward the abutments in a way consistent with that of modern network arch bridges. With truss diagonals absent, vertical bridge deck deflection doubles. Underslung portal frames provide lateral stiffness to the arch, an innovation that accommodated a shallow arch profile conducive to transportation and erection.