Anthony Battistini

Stiffness Behavior of Cross Frames in Steel Bridge Systems

AbstractCross frames are critical structural elements in both straight and horizontally curved steel bridges. In order to properly size the brace for the strength and stiffness demands of the superstructure, an accurate model of the elements comprising the cross frame is required. Conventional details most commonly used for cross frames consist of single-angle members connected to form a truss system linking adjacent girders together. Most analyses of the bridges treat the cross frames as truss elements that primarily resist applied forces through the axial stiffness of the members. This paper documents the results of a research study that included full-scale laboratory tests to measure the stiffness and strength of cross frames utilizing both conventional and new details. The tests showed that analytical solutions, as well as computer models, that are routinely used to model the cross frames in analysis software can overestimate the in-plane stiffness of the brace by more than 100%. The primary reason fo...

Improved Cross-Frame Connection Details for Steel Bridges with Skewed Supports

Cross frames and diaphragms play an important role in stabilizing straight steel girders. Commonly used connections between these braces and the steel girders can introduce flexibility, which can have detrimental effects on the bracing behavior, particularly on bridges with skewed supports. This paper documents a research investigation sponsored by the Texas Department of Transportation on connection details for stability bracing in steel bridges with skewed supports. One goal of the study is to propose an improved connection method. One detail being investigated is a round half-pipe stiffener connected to the top and bottom flanges. The round stiffener allows perpendicular connections to the cross-frame connection tab, regardless of the skew angle. Additionally, there are substantial structural improvements when the tubular stiffener is used. Fastening the tubular stiffener to the flanges provides a significant increase in the warping stiffness of the cross section at the support. Finite element modeling has predicted increases in buckling capacity as high as 80% because of this warping restraint. As a result, in the vicinity of the half-pipe stiffener, the brace spacing can likely be increased. The increased spacing in these regions will simplify fabrication and reduce the number of fatigue-sensitive details in the congested support region. This paper describes a method to calculate the increase in girder buckling capacity due to the warping restraint provided by the pipe stiffener as well as the size of pipe for a required buckling capacity or unbraced length with design tools already widely used by structural engineers.

Increasing Girder Elastic Buckling Strength Using Split Pipe Bearing Stiffeners

AbstractWarping restraining devices can result in substantial improvements in the girder elastic buckling capacity; however, calculating this increase can be complex. This paper presents a simplified method to evaluate the increase in elastic buckling strength and corresponding unbraced length due to improved warping restraint provided by split pipe stiffeners located at the ends of doubly symmetric W-shapes. The solution is based on analytical studies and results from a finite-element parametric study validated using large-scale laboratory tests. The laboratory tests include specimens exposed to concentrated loads with split pipe warp-restraining devices and others with standard plate stiffeners. The proposed analytic method is based on uniform moment and shows that warping restraint can increase the elastic buckling capacity of a girder by 30–100%. The improved warping stiffness can result in increases in the unbraced length in the range of 20–35% compared with systems with plate stiffeners.