Journal of Bridge Engineering

Construction of bridges’ decks involves different types of resources that interact in a cyclic manner. Further, the construction operation inherits uncertainties and a variety of demands. Contractors have to select the construction method that suits project constraints including: project conditions, technical, financial, and time constraints. There are several construction methods that can be used to construct bridges’ decks. This paper presents a special-purpose simulation model that aids government agencies and/or their representative in planning the construction of bridges’ decks using cast-in-place and precast balanced cantilever techniques. The pouring of concrete in cast-in-place balanced cantilever techniques can be executed either by using pump station and pump line, or truck mixers, whereas, the precast balanced cantilever technique is carried out using two methods: (1) placement by an independent lifting apparatus; and (2) placement with the help of a beam and winch carried by the bridge deck itself. The developments made to model these methods are detailed in the paper. The proposed special purpose simulation model utilizes STROBOSCOPE as a simulation engine and is coded utilizing Visual Basic 6.0. All actual project data are fed to the developed model in order to carry out the what-if analysis.

Research has been carried out to evaluate the structural behavior and influence of aging on a century-old steel railroad truss bridge. The structure is located in Connecticut and services a large number of trains traveling into and out of New York City. The trusses are made of built-up members, with either multiple eyebars or laced channel sections. All panel point connections are joined with true pins and the interior panels are indeterminate. The bridge had experienced problems relating to the lateral shifting of some of the middepth pins. This study was carried out to evaluate the structural behavior and live load distribution throughout the bridge. A major component of the research involved extensive field monitoring. The results show that the actual live load distribution is significantly different than expected from conventional analytical approaches that were most likely used in the original design. The load distribution in multiple eyebar elements is far from uniform, and the distribution of shear through indeterminate panels is significantly different than expected from a normal truss analysis. Significant out-of-plane bending was found in the truss due to floorbeam end rotations, which is thought to be the major factor that is causing the pins to move. The study shows the necessity of using field monitoring to better understand the behavior of older bridges prior to the design of renovation approaches.

An investigation was conducted of unexpected damage to a pair of three-span continuous-spread prestressed box beam bridges after 12 years of service. Routine inspection had revealed cracks in the box beams near the piers and abutments. An investigation was conducted to assess the condition of the beams in the bridges as well as their as-built properties and remaining strength. The investigation showed that the beams were built in accordance with the design drawings and specifications. One beam was tested under a combination of flexure and shear. These tests showed that the effective prestress was lower than standard design estimates. Measurable slip of the strands initiated as shear or flexure-shear cracks developed; however, the bond strength was sufficient for the strands to fail by fracture. The measured ultimate strength exceeded the analytical estimates by 7 to 9%. The conclusion of the investigation is that the cracks in the beams developed from a combination of conditions created by the design, detailing, and production of the beams.

Cross frames and diaphragms are critical elements for the stability of I-shaped steel bridge girders during construction. The AASHTO specifications are relatively vague with regards to the stability design requirements of the braces. Spacing limits that have been used in past AASHTO specifications have been removed from the Load and Resistance Factor Design Specification, which instead requires the bracing to be designed by a rational analysis. Whereas the AASHTO specification does not define what constitutes a rational analysis, stability bracing systems must possess adequate stiffness and strength. The commercially available software packages that are typically used in bridge design generally do not have the capabilities to determine the adequacy of the bracing from a stability perspective. This paper outlines the stability bracing requirements for bridges with normal and skewed supports. The effects of support skew on the stiffness and strength requirements for stability bracing are addressed. Solutions that are available for systems with normal supports were modified to account for the effects of the support skew angle. Two orientations of the intermediate bracing were considered: parallel to the skew angles and perpendicular to the longitudinal girder axis. The solutions are presented and compared with finite-element results. The design solutions have good agreement with the finite-element solutions.

Based on observed damage patterns from previous earthquakes and a rich history of analytical studies, asynchronous input motion has been identified as a major source of unfavorable response for long-span structures, such as bridges. This study is aimed at quantifying the effect of geometric incoherence and wave arrival delay on complex straight and curved bridges using state-of-the-art methodologies and tools. Using fully parametrized computer codes combining expert geotechnical and earthquake structural engineering knowledge, suites of asynchronous accelerograms are produced for use in inelastic dynamic analysis of the bridge model. Two multi-degree-of-freedom analytical models are analyzed using 2,000 unique synthetic accelerograms with results showing significant response amplification due to asynchronous input motion, demonstrating the importance of considering asynchronous seismic input in complex, irregular bridge design. The paper, Part 1 of a two-paper investigation, presents the development of the input motion sets and the modeling and analysis approach employed, concluding with sample results. Detailed results and implications on seismic assessment are presented in the companion paper: Effect of Asynchronous Motion on Complex Bridges. Part II: Results and Implications on Assessment.

Nonuniform seismic excitation has been shown through previous analytical studies to adversely affect the response of long-span bridge structures. To further understand this phenomenon, this study investigates the response of complex straight and curved long-span bridges under the effect of parametrically varying asynchronous motion. The generation process and modeling procedures are presented in a companion paper. A wide-ranging parametric study is performed aimed at isolating the effect of both bridge curvature and the two main sources of asynchronous strong motion: geometric incoherence and the wave-passage effect. Results from this study indicate that response for the $344\mathrm{m}$ study structure is amplified significantly by nonsynchronous excitation, with displacement amplification factors between 1.6 and 3.4 for all levels of incoherence. This amplification was not constant or easily predicable, demonstrating the importance of inelastic dynamic analysis using asynchronous motion for assessment and design of this class of structure. Additionally, deck stiffness is shown to significantly affect response amplification, through response comparison between the curved and an equivalent straight bridge. Study results are used to suggest an appropriate domain for consideration of asynchronous excitation, as well as an efficient methodology for analysis.

A quarter-scale, two-span reinforced concrete bridge was tested using the shake-table system at the University of Nevada, Reno. The shake-table tests were part of a multiuniversity, multidisciplinary project utilizing the network for earthquake engineering simulation, with the objective of investigating the effects of soil-foundation-structure interaction on bridges. This paper discusses the development and testing of the bridge model, and selected experimental results, including those that demonstrate the effects of incoherent motions and stiffness irregularities on the distribution of forces and deformations within the bridge system. Motion incoherency affected the asymmetric bridge response (planar torsion of the superstructure), but had little effect on the symmetric bridge response (center-of-mass displacement of the superstructure). These experimental findings are consistent with conclusions from numerical analyses conducted by other researchers. During a $2.0\mathrm{g}$ PGA earthquake excitation, numerous longitudinal bars buckled and fractured at a drift ratio between 5.5 and 7.9%. Despite the level of damage, detailing of the column transverse reinforcement according to NCHRP 12-49 guidelines provided sufficient column ductility to prevent collapse during a subsequent $1.4\mathrm{g}$ PGA earthquake excitation.

While composite-reinforced glulam beams have been used in several bridge demonstration projects, knowledge of their fatigue behavior is quite limited. In this study, the response of full- and partial-length fiberglass composite-reinforced glulam beams under fatigue cycling followed by quasi-static bending to failure is examined. To mimic anticipated in-service conditions, a hygrothermal cycling regime was developed that replicates the effective stress history of a 50-year service life with a 55-day period in a moisture-controlled kiln. In addition, some of the beams had initial delaminations introduced between the reinforcing and the wood similar to those observed in field investigations of reinforced glulam bridge girders. For the partial-length reinforced beams, reinforcing with both confined and unconfined ends was considered. The results of the postfatigue tests to failure were compared with the expected strength. In addition, the stiffness of the beams was monitored during the fatigue cycling. It was found that, with the exception of the unconfined, partial-length reinforced beams, all specimens had a residual strength that compared favorably with the expected strength. Further, neither the preconditioning nor the fatigue cycling had an appreciable impact on the stiffness of the reinforced beams. The unconfined, partial-length reinforced beams did not perform well under fatigue loading and do not seem to be a viable alternative for use as reinforced glulam bridge girders.

Acceptance of carbon fiber-reinforced polymer (CFRP) materials for strengthening concrete structures, together with the recent availability of higher modulus CFRP strips, has resulted in the possibility to also strengthen steel structures. Steel bridge girders and building frames may require strengthening due to corrosion induced cross-section losses or changes in use. An experimental study investigating the feasibility of different strengthening approaches was conducted. Large-scale steel-concrete composite beams, typical of bridge structures, were used to consider the effect of CFRP modulus, prestressing of the CFRP strips, and splicing finite lengths of CFRP strips. All of the techniques examined were effective in utilizing the full capacity of the CFRP material, and increasing the elastic stiffness and ultimate strength of the beams. Results of the experimental program were compared to an analytical model that requires only the beam geometry and the constitutive properties of the CFRP, steel, and concrete. This model was used to investigate the importance of several key parameters. Finally, an approach for design is proposed that considers the bilinear behavior of a typical strengthened beam to the elastic-plastic behavior of the same beam before strengthening.

This paper describes detailed flexural behavior, including live load distributions, of a four-span prestressed concrete girder bridge supported by $14\mathrm{m}$ long C-shape girders (4 @ $14.05=56.2\mathrm{m}$ ). The bridge has been damaged by frequent impact from heavy trucks, and repaired using prestressed carbon fiber-reinforced polymer sheets. A calibrated finite element analysis is conducted to investigate the flexural behavior (i.e., stress redistribution, deflection, live load distribution, and applied load effects) of the bridge in three different phases (i.e., undamaged, damaged, and repaired states) under various loading configurations. Strain localizations are noted at the damaged and repaired locations. Assessment of existing bridge codes such as the Association of State Highway and Transportation Officials Load Resistance Factor Design and Canadian Highway Bridge Design Code is conducted. The bridge codes predict well the nominal live load effect on the exterior girder, but underestimate the effect on the interior girders. A refined analysis may be recommended for this type of bridge.