Journal of Bridge Engineering

Horizontally curved I-girders are subjected to combined vertical bending and torsion under gravity loading alone. The torsional behavior of open I-shaped girders is commonly and conveniently equated to self-equilibrating lateral bending moments in the flanges. The interaction of vertical bending and this lateral flange bending effectively reduces the vertical moment carrying capacity of the section. Yield interaction equations for predicting the nominal bending strength of horizontally curved steel I-girders subjected to vertical moment and torsion are derived. Singly symmetric composite and noncomposite I-shaped cross sections in both the positive and negative moment zones are considered. Strength criteria considered are: (1) complete plastification of the cross section for compact sections; (2) partial yield penetration for compact-flange sections; and (3) initial yielding at the extreme flange tip for noncompact sections. A total of 17 interaction cases are ultimately considered. These strength criteria are based purely on the static equilibrium of the cross section with no secondary amplification considered. The limitations and applicability of the derived equations toward design use are demonstrated and analyzed.

To achieve consistent levels of safety over the bridge inventory, consideration should be given to the ultimate capacity of the system. Although multispan, longitudinally redundant bridges show significant reserve capacity beyond first-hinge limits, it is important to examine the level of safety related to this reserve capacity. If inelastic limits are to be used to evaluate existing bridges, the reliability at the inelastic limit must meet or exceed target levels associated with single-hinge limit state methods. This paper examines load capacity ratings and reliability indices of a simple-span and a three-span bridge for the first-hinge limit, the single-girder shakedown limit, and the system shakedown limit. First-order second-moment reliability models are presented that consider lognormally distributed variates and correlation between variables to determine the safety index β for the load capacity limit states. Results show that the three-span bridge possesses significant available reserve capacity beyond the first-hinge limit. Incorporating the reserve capacity in the load rating evaluation also results in levels of safety above target levels and those associated with the first-hinge limit.

A newly developed method for the fatigue evaluation of riveted railway bridges is presented in the paper. The data that were collected during a large-scale bridge instrumentation program along with the fatigue resistance test database compiled at the University of Illinois at Urbana-Champaign, were used extensively during the formulation of the method, or fatigue model. The fatigue model is based on reliability theory due to the high degree of scatter in all fatigue strength tests and the uncertainty associated with estimating fatigue loadings. Fatigue strengths and loadings are both described by probability distributions. The probability of failure is calculated using these two sets of distributions and a performance function that is a modified form of Miner's damage law. Several parametric studies were conducted using the new fatigue evaluation method. The studies give a broad view of the potential remaining lives of shorter-span railway bridges subjected to unit train loadings.

In this paper, the effect of number of cables and the length of central panel on the behavior of radiating-type cable-stayed bridges has been investigated. The study was carried out for double-plane bridges with 12, 20, 28, and 36 cables per plane, with side to main span ratios of 0.35, 0.40, 0.45, and 0.50, respectively. The bridges were analyzed by the stiffness matrix method, treating the bridges as two-dimensional structures. A uniformly distributed load of 10 kN/m (1 t/m) was considered over the entire length of the bridge. The computational work was carried out on an IBM 360 main frame computer. The investigation shows that maximum cable tension decreases rapidly with the increase in the number of cables. In general, the effect of length of the central panel on the sagging moment is significant; on the hogging moment, the effect of length is not appreciable. Both the hogging and sagging moments increase with the increase in the number of cables from 12 to 36. The parametric charts useful for the design of cable-stayed bridges, incorporating the foregoing parameters, have also been prepared. A comparison of the weight of steel in cables and girders, as well as the total weight of steel (cables and longitudinal girders only) in the harp and radiating arrangements was also carried out. In both harp and radiating bridges, the weight of steel decreases with the increase in the number of cables.