2017 Annual Stability Conference Presentation

Session S10 – Stability of Plates
Friday, March 24, 2017
8:00 am

A New Design Method for Longitudinally Stiffened Plates

Longitudinally stiffened steel plates are becoming increasingly important in bridge design as the size and span of new bridges increase.  An example is the Straits of Messina bridge, proposed to link Italy and Sicily, which will have a steel deck and steel towers. Now that most large bridges are part of design-build-finance contracts, in which the bid design phase determines the price of the project, it is especially important that the design process be as simple as possible to understand and implement rapidly.  This paper proposes a unified design method for plates, with or without  transverse stiffeners, that avoids some of the limitations, shortcomings or anomalies that engineers find in either AASHTO LRFD or the Eurocode.

Charles M. King, COWI North America, North Vancouver, BC, Canada

2017 Annual Stability Conference Presentation

Session S1 – Stability of Steel Bridges
Wednesday, March 22, 2017
8:30 am

Nonlinear Behavior of Global Lateral Buckling of I-Girder Systems

I-girder systems with relatively long spans and narrow widths are susceptible to a system buckling failure mode that is relatively insensitive to the spacing between cross frame or diaphragm braces. This global buckling mode is of particular concern during deck placement and can compromise the safety and/or constructability of steel bridge systems. This paper presents computational studies on the nonlinear behavior of a variety of steel I-girder systems. A number of geometric factors affecting the nonlinear buckling behavior of I-girder systems such as the shape and distribution of the imperfection along the length as well as the girder curvature were investigated. The process of cross frame installation was simulated to investigate the impact of the installation process of the braces on the resulting behavior. The results demonstrate that the susceptibility of the system mode of buckling to 2nd order amplification is significantly reduced compared to the “critical-shape imperfection”. The initial girder imperfection was significantly altered by fit-up of cross frames and the likely imperfection pattern afterwards. The FEA results demonstrate that the “critical shape” imperfection that has been used for stability bracing of cross frame systems may not be likely to occur in practice. The results of this study provide insight into adequate limits on second-order displacement amplification of I-girder systems under transverse non-composite loading.

Liwei Han and Todd A. Helwig, University of Texas at Austin, Austin, TX

2017 Annual Stability Conference Presentation

Session S12 – Advances in Stability Analysis
Friday, March 24, 2017
1:00 pm

CUFSM Elastic Buckling Analysis Software Module for Quantifying Hole Effects in Thin-Walled Structural Members

A new hole effects calculator for finite strip eigen-buckling analysis in CUFSM is introduced.  The calculator allows users to input varying hole sizes and locations along the length of a structural member, and to obtain the influence of this hole configuration on critical elastic local, distortional, and global buckling loads and moments.    The use of the hole effects calculator is demonstrated with examples for a cold-formed steel joist and stud, and the elastic buckling results are verified with thin shell finite element eigen-buckling analyses.

Junle Cai, Virginia Polytechnic Institute and State University, Blacksburg, VA; Benjamin W. Schafer, Johns Hopkins University, Baltimore, MD, Cristopher D. Moen, NBM Technologies, Inc., Baltimore, MD

2017 Annual Stability Conference Presentation

Session S3 – Advances in Stability Bracing
Wednesday, March 22, 2017
3:15 pm

Experimental Study of Steel Tub Girders with Partial Top Lateral Bracing

Steel box girder systems, which consist of steel tub girders with a cast in-place concrete deck on top, are a popular alternative for straight and horizontally curved bridges due to their high torsional stiffness and aesthetic appearance. However, steel tub girders possess a relatively low torsional stiffness during transport, erection and construction because of the thin-walled open section. Additionally, during the casting of concrete, the top flanges of the tub girder are in compression in the positive moment region and they are susceptible to lateral torsional buckling (LTB). Usually, top flange lateral bracing, in the form of a horizontal truss, is fully installed along the steel tub girder to prevent flanges from buckling and to increase the torsional stiffness of the girder. However, the horizontal truss is mainly effective near the ends of the girders where the shear deformations are the largest.  The contribution of the top lateral bracing to control lateral torsional buckling is notably reduced at the mid-span region. This paper provides an overview of on an ongoing research study focused on improving the efficiency of steel tub girders by investigating the impact of the girder geometry and bracing details on the behavior of the girders.  The study includes large-scale experimental tests and parametric finite element analytical (FEA) studies.   This paper highlights the experimental tests.  The efficiency of the horizontal truss is assessed by conducting multiple elastic-buckling tests on a steel tub girder with different amounts of top lateral bracing along the girder. A tub girder is subjected to combined bending and torsion using eccentric loads applied by gravity load simulators.  The goal of the study is to improve the efficiency of steel tub girders by defining adequate amounts of bracing without undermining their structural performance.

Stalin Armijos Moya, Yang Wang, Todd A. Helwig, Michael D. Engelhardt, Patricia Clayton and Eric Williamson, University of Texas at Austin, Austin, TX