Analysis and capacity assessment of span wire and mast arm traffic signal support structures

Abstract

To address this issue, for span wire structures having multiple spans a simplified method for applying wind load is proposed and evaluated relative to a complex method of applying the wind load in which multiple wind load directions are considered. Although a simplified method of analysis is desirable for programming purposes, too much simplification can result in overly conservative predictions of demand and capacity and thus care must be taken to avoid excessive simplification. With that in mind, reasonable simplifying assumptions were made regarding span wire traffic signal support structures, resulting in a simplified method of wind load application that was shown to be reasonably accurate. Furthermore, for a wide range of structural configurations and geometries, the simplified method was shown to be conservative in terms of estimating the maximum force applied to a pole from the span wire. Regarding mast arm structures, the relative simplicity of the structures allows multiple wind directions to be considered explicitly in the analysis.

This thesis provides a general introduction to traffic signal support structures, describes the proposed methods for application of wind loads to span wire and mast arm structures, and provides an overview of the software that has been developed for performing analysis and capacity assessment of such structures.

The analysis and capacity assessment of traffic signal support structures is investigated in this thesis. Traffic signals are supported either by a hanging cable and vertical poles (span wire structure) or a mast arm and vertical post (mast arm structure). A variety of configurations are used in practice (e.g., single span, box span, single mast arm and dual mast arm) and in all cases must be designed to resist dead, wind, ice and fatigue loading. In this project, an alpha version of a software program has been developed to perform efficient analysis and capacity assessment of such structures in accordance with both federal (AASHTO) and state (NYSDOT) specifications. One challenge with implementing such specifications in software is the application of wind load to the structure. Simplified methods for wind load analysis of span wire structures are defined in the AASHTO specifications but the method does not clearly distinguish between analysis for tethered and non-tethered spans. Furthermore, an accurate wind load analysis for a specific structural configuration and geometry requires that the critical wind load direction be determined. In some cases, the critical direction is readily identifiable but in most cases it is not.