Journal of Bridge Engineering

This paper, summarizing the beginnings, analysis, and future of self-anchored suspension bridges, examines the development of this unique bridge form, its uses over the past century, and its advantages and disadvantages. The Konohana Bridge in Osaka, Japan, illustrates this type and provides a case study to compare conventional suspension bridge theory with the results of a finite-element model. The final portion of the paper evaluates the potential for self-anchored suspension bridge design, and provides recommendations for design engineers. The goal here is to describe the structural behavior of self-anchored bridges in general, and of the Konohana Bridge in particular.

This report demonstrates how short-term field monitoring can be used to evaluate bridges when problems occur. A portable strain monitoring system with software has been used to study four different bridges. Studies to determine load-carrying capacities, causes of cracking, and load distributions are included. The work demonstrates that analytical predictions of stress/strain levels, load distributions, and fatigue estimations are conservative. Analytical models based on conservative assumptions are suitable for the design of new bridges, but when problems occur in existing bridges, field testing combined with careful analysis can provide much more accurate answers to assist engineers on proper courses of action for repair. The field monitoring reported in this study has resulted in substantial savings in the cost and time needed in renovation and/or repairs.

The objective of this paper is to determine the locations of the neutral axis and the effective flange widths for steel girder bridges that may be used in bridge design or, at least, in the bridge rating process. A study using weigh-in-motion field test results was conducted to determine the various section properties for slab-and-beam bridge structures. From the field testing of four existing bridge structures under real truck loading, the girder neutral axis is determined using several alternatives developed by the study team. The results are studied, compared, and evaluated to find the most reliable alternative for the bridge testing. The research is also extended to the determination of the effective flange width from neutral axis results and other parameters. Comparisons are made against some of the previously developed methods and design codes. Results are given in tabulated form and conclusions are drawn from the tables.

A finite-element formulation is developed for analyzing flutter instability and buffeting response of long-span bridges and their interaction. The flutter derivatives, instead of the indicial functions used by previous researchers, are applied in the random parametric excitation (RPE) analysis. This application makes finite-element formulation possible and results in much less computational effort in RPE analysis than those of previous analyses. With the finite-element program developed in the present study, as many modes as desired can be easily included in the flutter and buffeting analyses. Users have the choice of RPE or eigenvalue method for flutter analysis and RPE or spectral method for buffeting analysis.

The practical applications of the finite-element software developed in Part I of this paper are demonstrated by analyzing the aerodynamic response of two prototype bridges, the Luling Bridge with a streamlined section, and the Deer Isle Bridge with a bluff section. In the Luling Bridge analysis, the self-excited forces are treated as random quantities and the wind turbulence effect is simulated with random parametric excitation analysis. In the Deer Isle Bridge flutter analysis, the self-excited forces are treated as deterministic quantities and the wind turbulence effect is included in the flutter derivatives measured in turbulent wind.

The load-carrying capacity of existing slab bridges is commonly calculated based on the equivalent width recommended by the American Association of State Highway and Transportation Officials (AASHTO). Interest in the field load testing of highway bridges has increased significantly in recent years. Load capacity of a bridge based on field testing is generally greater than that determined from standard rating calculations. The main parameters affecting the equivalent width were identified using the grillage analogy method. The results suggest that edge beam size should be considered in the equivalent width calculation. A simplified equation for the equivalent width is proposed for solid slab bridges with or without edge beams. The equivalent widths based on the AASHTO and LRFD cores was compared with those based on the field tests and analyses. The equivalent widths based on the grillage analogy and field tests are higher than those based on the AASHTO and LRFD codes, which indicates that the codes give a conservative estimate of the equivalent width. In the absence of field tests, the grillage analogy provides an accurate estimate for the equivalent width and bridge rating.

This paper investigates the elastic-plastic seismic behavior of long span cable-stayed steel bridges through the plane finite-element model. Both geometric and material nonlinearities are involved in the analysis. The geometric nonlinearities come from the stay cable sag effect, axial force-bending moment interaction, and large displacements. Material nonlinearity arises when the stiffening steel girder yields. The example bridge is a cable-stayed bridge with a central span length of 605 m. The seismic response analyses have been conducted from the deformed equilibrium configuration due to dead loads. Three strong earthquake records of the Great Hanshin earthquake of 1995 in Japan are used in the analysis. These earthquake records are input in the bridge longitudinal direction, vertical direction, and combined longitudinal and vertical directions. To evaluate the residual elastic-plastic seismic response, a new kind of seismic damage index called the maximum equivalent plastic strain ratio is proposed. The results show that the elastic-plastic effect tends to reduce the seismic response of long span cable-stayed steel bridges. The elastic and elastic-plastic seismic response behavior depends highly on the characteristics of input earthquake records. The earthquake record with the largest peak ground acceleration value does not necessarily induce the greatest elastic-plastic seismic damage.

Curvature greatly complicates the behavior of curved plate girders used in bridges. The out-of-plane “bulging” displacement of the curved web results in an increase in stress, which must be considered in the design of plate girders with significant curvature. The currently used Guide Specifications for Horizontally Curved Bridges provides web slenderness reduction equations that account for curvature effects, but these equations were based on a regression of limited data from experimental and unit-strip analyses conducted in the early 1970s. This paper presents a theoretically pure analytical model that can be used to predict the transverse displacement and induced plate bending stresses of curved I-shaped plate girder web panels subjected to bending. Several boundary conditions are demonstrated and compared, and the finite-element method is used to verify the closed-form solutions. The effects of curvature on the elastic buckling behavior of curved web panels is also presented. Furthermore, a comprehensive literature review is presented, including numerous Japanese publications not readily available to American researchers.

Curvature greatly complicates the behavior of curved plate girders used in bridges. The out-of-plane “bulging” displacement of the curved web results in an increase in stress, which must be considered in the design of plate girders with significant curvature. This paper presents results from geometric nonlinear finite-element analyses used to evaluate the finite displacement behavior of such panels and to formulate deflection amplification factors that can be applied to analytical models to get conservative values for predicting the maximum displacements and stresses of the curved panel. Equations are developed that represent the reduction in nominal strength of the curved web due to the effects of curvature. The applicability of the method is demonstrated and a comprehensive comparison is made between the equations developed in this investigation and design equations used in Japanese and American design guides.

Any vehicle whose gross weight exceeds 356 kN (80,000 lb) and/or does not conform to the restriction imposed by the Tennessee Department of Transportation (TDOT) requires a permit issued by TDOT in order to use the Tennessee roads. The current practice in the TDOT Permit Section is that a detailed structural analysis is required for all vehicles with a gross weight over 667.5 kN (150,000 lb). Due to the volume of overload permit applications received, this policy resulted in a large demand in man-hours to perform the structural analysis. Furthermore, the policy does not give consistently safe or conservative assessment. A method has been developed empirically to efficiently extract any suspicious overweight vehicle requesting a permit, regardless of gross weight, for further detailed analysis. The technique utilizes the combination of gross weight, axle loads, and axle spacings. The algorithm can be easily implemented to a computer program for users with limited technical training, since the only input information is the axle load and spacing configurations. The method is intended to be conservative. A study, based on actual permit applications and detailed bridge analyses, has shown that this approach would reduce the number of structural analyses required by approximately 50% when compared to the current policy.