Research Activities: 1999

Signal Mast Arm Failure Investigation




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Sequential Number


Identification Number


Matching Research Agency

Missouri Department of Transportation (MoDOT)

Principal Investigator

L.R. Dharani, Professor
University of Missouri- Rolla
Mechanical & Aerospace & Engineering Mechanics
101 ERL
Rolla, MO 65409
p(573) 341-4149
f(573) 341-4979

Student Involvement

One (1) graduate student

Project Objective

The Missouri Department of Transportation (MoDOT) has discovered and documented failures in several cantilever signal mast arms on the Missouri highway system. The objective of this project is to identify the exact cause of failure and to recommend remedial actions for preventing future failures in the existing masts and future designs. In particular the following three distinct tasks are involved: Failure analysis of cracked and uncracked mast assemblies, (2) determination of truck and wind induced loads on the mast arm, and (3) Stress analysis and life prediction.

Project Abstract

Using a commercial finite element code called ABAQUS stress and the stress intensity factors will be computed assuming a preexisting flaw the size of which would be extrapolated from the failure analysis task. For the existing structures we will establish a range of crack propagation life knowing the minimum size of the flaw that fabricator can detect. This information will be used in determining if retrofit on the existing assemblies is going to be cost effective. A computer code will be written for predicting the initiation life using the strain-life approach. A separate program will be developed for integrating the crack growth rate model.

Task Description

  1. Failure analysis of failed mast arms.
  2. Dynamic load analysis.
  3. Fatigue analysis.

Anticipated Benefits

Safety of highway structures

Modal Orientation



Project Start Date:06/30/2000
Project End Date:06/30/2002

Relationship to other Research/Projects

NDT of infrastructure materials

Technology Transfer Activities

MoDOT will explore fatigue resistant safe life design for signal mast arms.

Transportation Research Board Keywords

Welded structures, fatigue, wind loads and signal mast arms