Finite Element Study of Mast Arm Socket Welded Connections

There has been a rise in the number of failures of traffic cantilever signal mast arms in recent years due to increasing spans of mast arms and the inherent flexibility of the structures. This increased flexibility makes mast arm socket welded connections more critical.

Extensive finite element analysis using Abaqus was carried out in this study to determine the effect of different geometric variables like end plate thickness, mast arm diameter, mast arm thickness and weld geometry on stress at the weld toe by estimating the Stress Concentration Factor (SCF) at weld toe. Two different approaches, Dong’s Structural Stress and Det Norske Veritas (DNV), were used to calculate the SCF at weld toe. To study the effect of end plate thickness, six models with different end plate thicknesses were analyzed. Effect of geometric variables like mast arm thickness, mast arm diameter, and weld geometry were studied for all the six different end plate thicknesses. It was found that of all of the geometric variables analyzed, end plate thickness had a greater effect on stresses at weld toe.

Experimental results of fatigue behavior of mast arms socket welded connections from other research projects were used to investigate the hypothesis which states that, fatigue life (N) is some constant (A) times the stress range (SCF x SR) raised to the third power, where the constant (A) is the fatigue life coefficient. Investigation of the above stated hypothesis was done using both approaches for calculating SCF, namely Dong’s Structural Stress and DNV. From hypothesis investigation, it was found that scatter in the experimental data is reduced when maximum stress range at weld toe (SCF x nominal stress range) is plotted against fatigue life as compared to plotting nominal stress range against fatigue life.