Stress Concentration Factor in Tubular to a Girder Flange Joint: A Numerical and Experimental Study

Abstract

Tubular to a girder-flange joints are widely used in various applications. For fatigue design of such joints, stress concentration factors (SCFs) are required. The stress concentration, especially in the welded joints of these structures, is a complex phenomenon. Usually, at the locations of high stress, cracks initiate and grow leading to a fatigue failure. For evaluation of SCF, in current practice, the ‘hot spot stress’ method is used. In this study, at first, a finite element (FE) analysis has been performed to predict the location of hot spot stresses in a fillet welded tubular to girder-flange joints under in-plane bending. The FE results show that the stresses are very high on the brace near the weld-toe and gradually decrease in the direction away from the weld. The SCFs and strain concentration factors (SNCFs) are then determined at the weld toe using linear extrapolation method. Further, a full scale tubular to a girder-flange joint was fabricated and tested in Structural Engineering Laboratory at IIT Kanpur. A monotonic loading scheme was used for applying in-plane bending through a displacement control scheme. Apart from the measurement of actuator load and displacement data, strains were measured at several locations through micro strain gauges. Based on the strain data, SNCF was calculated at various stages of loading. Although the trend of SNCF calculated from the experiments is found to be in reasonable agreement with the numerically obtained trend, the experimental results are, in general, found to be higher than those obtained from the FE analysis. This anomaly may be due to the placement of strain gauges. Further research is needed to confirm the findings.