Hybrid connection of cold formed steel plates utilizing adhesive and self-drilling screws

Abstract

The application of cold-formed steel (CFS) on roof structures has become popular in construction practices in Malaysia. Generally, CFS structure joints use self-drilling screws (SdS) for easy and fast installation purpose. However, a premature collapse of a CFS structure may occur due to connection failure. Therefore, in order to avoid and better prepare for such an eventuality, a study to overcome the failure of the connection on CFS structures is needed. Research suggests that a combined joint (connection) between SdS and adhesive (Hybrid connection) on CFS structures could prevent premature collapse. Informed by past and current research developments, this study therefore investigated the behaviour and failure modes of CFS connections with three different types of connection methods; adhesive, SdS and hybrid connection. Shear test was conducted to determine the ultimate failure load, where the connection failed as a result of direct shear acting on it. The effect of adhesive thickness, number of screws, bonded area, plate thickness and screw arrangement on connection strength was also studied and reviewed through experiment and statistical analyses using Pearson Correlation. The results demonstrated the existence of statistically significant correlation between the bonded area and bonding strength for C-section of CFS. Specifically, an increase in the bonded area provides an increase in bonding strength. In this study it is also found that with an increase of screw quantities and plate thickness, the connection strength increased. Comparisons on the connection strength between adhesive, SdS and hybrid connections was carried out and statistical analysis using ANOVA test prove that the strength of hybrid connections is statistically significantly higher compared to adhesive connection and SdS connection. It was found that hybrid connection specimen utilising 0.5mm adhesive thickness, 4 screws connection, with a web depth of 100mm, plate thickness of 1.20mm and lapping length of 80mm, has the highest connection strength, specifically at 66% higher than adhesive connection, and 46% higher than SdS connection. Based on the regression analysis, this research proposed an empirical formula to calculate the hybrid connection strength. A comparison of hybrid connection strength between the experimental result and predicted connection strength (proposed empirical formula) was conducted and generally the predicted connection strength is in accordance with the experimental result. Therefore, the proposed empirical formula is considered ideal for calculating the connection strength of the hybrid connection limited to plate thickness range 0.75mm – 1.20mm.