Stability analysis and reliability-based assessment of truss highway sign support structures

Date of Completion

January 2000


Engineering, Civil




The design of truss sign support structures is based on the guidelines provided by American Association of State Highway and Transportation Officials Standard Specifications for Highway Signs, Luminaries and Traffic Signals and the American Institute of Steel Construction Design Specifications. Using these specifications, the column design strength is normally determined using the effective length approach. This approach does not always accurately address all issues associated with frame stability, including the actual end conditions of the individual members, variations of the loads in the members, and the resulting sidesway buckling for truss type sign support structures. This research provides insight into the problems with the simplified design approach for determining the effective lengths, discusses different approaches for overcoming these simplifications and presents an approach that can be used to better predict the design strength of truss sign support structures. ^ Structural condition assessment is often best made with probabilistic based methods. This is done by replacing the structural system with a reliability based model, based on the different possible failure nodes. The system model is then used to determine the failure probability. The study in this report illustrates the procedure needed to conduct a systems reliability analysis for highway truss sign supports. The procedure provides a method to update the resistance strength as the structure deteriorates. In this way, the structural reliability can be computed at different stages in the life span of the structure. This report discusses the minimum acceptable failure risk for the highway sip support structure based on a systems reliability model. The results of the study demonstrate how changes should be made in the structure as it ages to insure structure safety. ^