Journal of Bridge Engineering

The writers summarize all fatigue test data for cover plates on steel beams that were reported since 1969. The earlier studies established the fatigue strength of thin cover plates of Category E fatigue strength as well as thick cover plates of Category ${\mathrm{E}}^{\prime }$ fatigue strength. The later studies focused on improving the fatigue strength. The various techniques increased the mean fatigue life over that of Category E by factors of 1.5, 2.1, and 4.4 for ground, shot-peened, and remelted toes of the end welds, respectively; 6.5 for end-welding and grinding the cover plate ends to a 1:3 taper; 19 and more for bolting the ends that were left nonwelded; 18 and 13 for bridging the welded ends of noncracked and precracked cover plates, respectively, with bolted splices; and over 20 for adhesive-bonding the entire cover plate and bolting the ends. The last three methods cited above would fatigue proof rolled beams with cover plates typical of multigirder highway bridges.

Circular reinforced concrete highway bridge piers, designed in accordance with the requirements of the California Department of Transportation (Caltrans) in the U.S., New Zealand, and Japanese specifications, are experimentally investigated to assess their seismic performance. Pseudodynamic test procedures are developed to perform experiments on 30% scaled models of the three prototype bridge piers. Each specimen is subjected to a sequence of three different earthquake ground motions scaled appropriately to represent: (1) the design basis earthquake (DBE) with a 90% nonexceedance probability; (2) the maximum considered earthquake (MCE) with a 50% nonexceedance probability; and (3) the MCE with a 90% nonexceedance probability. Damage states after the earthquakes are assessed and mapped for seismic risk assessment. The damage outcomes and the corresponding seismic risks validate the objectives of the performance-based design codes of the three countries. The results show that when bridge piers are designed to the specifications of each of the three countries, satisfactory performance with only slight to moderate damage can be expected for DBE. For the MCE, severe damage without collapse is likely for the Caltrans and Japanese piers. However, the NZ pier may not be able to survive MCE motions with sufficient reliability to ensure the preservation of life-safety.

This paper presents the field performance evaluation of an integral abutment bridge constructed in Massachusetts that was monitored for a period of three years. Emphasis is primarily made on observed seasonal and yearly behavior. Although the bridge abutments were constructed without any skew, differences have been observed in performance between the north and south abutments and are attributed to differences in construction conditions. Longitudinal displacement and rotation fully characterize the abutment deformation response. Fundamental parameters that control the response of the bridge (longitudinal restraint, pile moments) are evaluated through the use of simple mechanical models. The use of simple models allows estimation of bridge parameters for use in more involved finite element models. Data collected during the monitoring period indicate that current design procedures used for integral abutment bridges in Massachusetts are conservative.

This paper summarizes field-testing of eight decked bulb-tee girder bridges as well as development of three-dimensional finite-element (FE) models. Using the calibrated 3D FE models, parametric studies have been performed to study the effect of shear connectors and intermediate diaphragms on live-load distribution and connector forces. It was found that: (1) in all cases studied, the live- load distribution factor (DF) for a single-lane loaded bridge was smaller than one for a double-lane loaded bridge; (2) connector forces caused by wheel loads were not uniform along the longitudinal joint—adding intermediate diaphragms tended to reduce the difference among horizontal shear forces in connectors; (3) the maximum horizontal shear force increased with the increase of the connector spacing—intermediate diaphragms reduced the maximum horizontal shear force in connectors; (4) the maximum vertical shear force and in-plane normal tensile force in connectors do not necessarily increase with the increase of the connector spacing; and (5) the summation of connector forces in each direction along the longitudinal joint remained constant irrespective of the number of connectors in the joint.

A group of five full-depth male–female shear key specimens were match cast and tested to examine the shear capacity of epoxy-jointed single keys. Another group of four specimens were match cast using full-scale dimensions of a segmental construction bridge deck system for testing the fatigue and water tightness at a segment joint. Both cold-weather and hot-weather epoxy types were used to join the specimens. In addition to the experimental testing, finite-element analysis was also used to model the static response of the joint specimens. The observed failure mode of all shear-key specimens was fracture of concrete along the joint with shearing of the key. Good agreement was observed between the experimental test results and the finite-element analysis in terms of the failure mode of unreinforced specimen and the load of crack initiation of the specimens. Fatigue loading had a minor effect on the behavior of the posttensioning bars. The contribution of either the cold-weather or hot-weather epoxies to the joint shear strength was significant knowing that for similar concrete properties, the hot-weather epoxy specimens showed an increase of about 28% in the shear capacity, in comparison to the cold-weather epoxy specimens. The excellent performance of the epoxy-jointed shear keys was verified by field application on a prototype model simulating a portion of the Wacker Drive Bridge system. It was concluded that implementing AASHTO procedures result in conservative estimates of the shear strength of the single keyed joint since it neglects the contribution of the epoxy and underestimates the strength of the key itself.

In a composite section, in-plane shear strain in the slab (acting as a flange in the composite girder) under the applied bending causes the longitudinal displacements in the parts of the slab remote from the webs to lag behind those near the webs. This phenomenon, termed shear-lag, can result in an incorrect calculation of the displacement and extreme fiber stresses when using only the elementary theory of beam bending. The effective width concept has been introduced, widely recognized, and implemented into different codes of practice around the world as a simplified practical method for design and evaluation of structural strength and stiffness while accounting for shear-lag effects indirectly. Each code implements different ideas and approaches for specifying effective width. This paper proposes simpler and more versatile design criteria for computing the effective width $\left(b_{\mathrm{eff}}\right)$ in steel-concrete composite bridges. A parametric study was conducted based on finite-element analysis of bridges selected by a statistical method—namely, design of experiment concepts. Both simple-span and multiple-span continuous bridges were considered in the parametric study. The finite-element methodology was validated with companion experiments on 1/4- and 1/2-scale specimens. Effective width values at the critical sections were computed from stresses extracted from FEM models and used in developing candidate design equations. The final design criteria were selected based on assessment of impact of candidate equations. Use of full width—the most versatile, simplest, and sufficiently accurate effective width design criteria, is proposed for both positive and negative moment regions.

Currently, the AASHTO-LRFD design code specifies the same effective slab width design criteria for both positive moment sections and negative moment sections. The only difference in computing effective slab width between the positive and negative moment regions is the value of effective span length $\left(L_e\right)$ , the definition of which is problematic. The effective slab width concept for the positive moment regions has been investigated by many researchers. However, the classical effective slab width definition does not take into account both the strain variation through the slab thickness and the mechanism that redistributes load from concrete to steel reinforcement after cracking. In this paper, a more robust effective slab width definition for the negative moment section is introduced to account for these factors. The proposed definition is developed for negative moment regions and explored by using the finite-element method (FEM). The finite-element modeling scheme is briefly discussed, and the model is successfully verified with experimental results. Numerical results show the simplicity, accuracy, and robustness of the proposed definition in extracting effective slab width values from FEM results. Numerical results also indicate that the effective slab width criteria in the current AASHTO-LRFD Specifications is typically conservative for larger girder spacings. Detailed calculations of effective slab width for the negative moment regions using the proposed definition are summarized at the end of this paper.

Over the past years, with increasing traffic volumes and higher wheel loads, fatigue damage in steel parts of typical orthotropic steel bridge decks has been experienced on heavily trafficked routes. A demand exists to find a durable system to increase the fatigue safety of orthotropic steel bridge decks. A solution might be to enhance the stiffness of the traditional orthotropic bridge deck by using a cement-based overlay. In this paper, an orthotropic steel bridge deck stiffened with a cement-based overlay is analyzed. The analysis is based on nonlinear fracture mechanics, and utilizes the finite-element method. The stiffness of the steel deck reinforced with an overlay depends highly on the composite action. The composite action is closely related to cracking of the overlay and interfacial cracking between the overlay and underlying steel plate (debonding). As an example, a real size structure, the Farø bridges located in Denmark, are analyzed. The steel box girders of the Farø bridges spans $80\mathrm{m}$ , and have a depth of $3.5\mathrm{m}$ , and a width of $19.5\mathrm{m}$ . The focus of the present study is the top part of the steel box girders, which is constructed as an orthotropic deck plate. Numerous factors can influence the cracking behavior of the cement-based overlay system. Both mechanical and environmental loading have to be considered, and effects such as shrinkage, temperature gradients, and traffic loading are taken into account. The performance of four overlay materials are investigated in terms of crack widths. Furthermore, the analysis shows that debonding is initiated for a certain crack width in the overlay. The load level where cracking and debonding is initiated depends on the stress-crack opening relationship of the material.

The implications of earthquake loading during balanced cantilever construction of a cable-stayed bridge are examined. Finite-element models of a cable-stayed bridge were developed and multiple ground motion time history records were used to study the seismic response at the base of the towers for six stages of balanced cantilever construction. Probabilistic seismic hazard relationships were used to relate ground motions to bridge responses. The results show that there can be a high probability of having seismic responses (forces/moments) in a partially completed bridge that exceed, often by a substantial margin, the $10\%∕50\text{-}\text{year}$ design level (0.21% per annum) for the full bridge. The maximum probability of exceedance per annum was found to be 20%. This occurs because during balanced-cantilever construction the structure is in a particularly precarious and vulnerable state. The efficacy of a seismic mitigation strategy based on the use of tie-down cables intended for aerodynamic stability during construction was investigated. This strategy was successful in reducing some of the seismic vulnerabilities so that probabilities of exceedance during construction dropped to below 1% per annum. Although applied to only one cable-stayed bridge, the same approach can be used for construction-stage vulnerability analysis of other long-span bridges.

Nonlinear time history analyses were performed to investigate the seismic response of the new San Francisco–Oakland Bay Bridge East Span self-anchored suspension (SAS) bridge and cable-stayed (CS) bridge alternative with the signature towers protected by friction dampers and viscous dampers in lieu of the as-designed steel shear links. Response of the damper and shear link equipped towers were compared to determine if equipping bridge signature towers with passive dampers, that would not experience residual deformations, is a viable option for cable supported bridges, particularly in retrofit applications. Viscous dampers were the most beneficial to the SAS and CS tower response in the transverse direction of the bridges. Dampers placed in toggle-braced configurations further improved the tower response for the SAS bridge transverse direction by magnifying the damper displacement demands. With the addition of stiffness to the signature tower being more critical in the longitudinal direction than in the transverse direction, the diagonal friction dampers were the most beneficial in the longitudinal direction of the SAS bridge tower.

This paper details research conducted to determine the applicability of the 2nd and 3rd editions of the AASHTO LRFD Specifications to hybrid I-girders fabricated from high-performance steel (HPS) $690\mathrm{W}$ $\left(100\mathrm{ksi}\right)$ flanges and HPS $480\mathrm{W}$ $\left(70\mathrm{ksi}\right)$ webs. Specifically, the scope of this paper is to evaluate the applicability of the negative moment capacity prediction equations for noncomposite I-girders subjected to moment gradient. This evaluation is carried out using three-dimensional nonlinear finite-element analysis to determine the ultimate bending capacity of a comprehensive suite of representative hybrid girders. In addition, a design study was conducted to assess the economical feasibility of incorporating HPS $690\mathrm{W}$ $\left(100\mathrm{ksi}\right)$ in traditional bridge applications. This was accomplished by designing a series of I-girders with varying ratios of span length to girder depth ( $L∕D$ ratios) for a representative three-span continuous bridge. Results of this study indicate that both the 2nd and 3rd editions of the specifications may be used to conservatively predict the negative bending capacity of hybrid HPS $690\mathrm{W}$ $\left(100\mathrm{ksi}\right)$ girders, however increased accuracy results from use of the 3rd edition of the AASHTO LRFD Specifications. Thus, it is concluded that the restriction placed on girders fabricated from steel with a nominal yield strength greater than $480\mathrm{MPa}$ $\left(70\mathrm{ksi}\right)$ can be safely removed. Additionally, results of the design study demonstrate that significant weight saving can result from the use of hybrid HPS $100\mathrm{W}$ girders in negative bending regions, and that hybrid HPS $690\mathrm{W}$ /HPS $480\mathrm{W}$ girders may be ideally suited to sites with superstructure depth restrictions.

The purpose of this work is to provide a simple, rational basis for combining bridge loads in the extreme event limit state. Classic methods are used to evaluate the probabilities of traffic, seismic, and storm-related bridge loads occurring simultaneously and in various intensities. The loads are modeled using a Poisson distribution, which circumvents problems encountered when using normal- or log-normal distributions. The hazard level is evaluated directly using a negative exponential function in the time domain. An acceptable hazard level for combined events is subjectively based on that deemed acceptable for the strength limit state and extreme events occurring individually, as well as fiscal prudence. It is shown that (1) application of seismic loads to a structure already subjected to the combined effects of degradation, local pier scour, and contraction of the waterway is not justifiable; (2) live loads reduced from the anticipated 75-year maximum to a 2-week maximum are appropriate when designing a bridge in its 100-year “scoured-out” storm configuration; and (3) vehicular live loads are likely to be on a bridge during a seismic event, but other issues need to be considered.

Glass fiber-reinforced polymer (GFRP) composite bridge decks behave differently than comparable reinforced concrete (RC) decks. GFRP decks exhibit reduced composite behavior (when designed to behave in a composite manner) and transverse distribution of forces. Both of these effects are shown to counteract the beneficial effects of a lighter deck structure and result in increased internal stresses in the supporting girders. The objective of this paper is to demonstrate through an illustrative example the implications of RC-to-GFRP deck replacement on superstructure stresses. It is also shown that, regardless of superstructure stresses, substructure forces will be uniformly reduced due to the lighter resulting superstructure.