Shear bearing capacity of Self-drilling screw group connections of CFS sheets

Abstract

Self-drilling screws are commonly used as connectors in cold-formed steel (CFS) buildings as they can be drilled easily through thin sheet steels, allowing on-site assembly. The screw connections in the project all appear in the form of screw group connections. Studies have shown that the shear bearing capacity of a screw group connection of CFS sheets is not simply the shear bearing capacity of a single screw connection multiplied by the number of screws. But instead, there is a reduction effect of the screw group connection, called the Group Effect. However, there is no design provision for the shear bearing capacity of the screw group connection in the current design specifications, AISI S100-16w/S1-18, AS/NZS-4600:2018, EN1993-1–3, and GB50018-2002. Based on the authors' and other researchers' tests collected by authors, this paper verifies and analyzes the four existing design equations for the connection strength of the screw group connections that consider the Group Effect. The results show that the four current design equations cannot cover the test data that list in the paper because the existing four design equations all have their respective scopes and limitations, such as the screw spacing and the strength of steel sheetings, etc. For that, the paper proposed a new design equation that can calculate the nominal shear capacity of self-drilling screw group connections, including high-strength steel such as G550 CFS sheets and extensive screw spacing connections. The authors' new test of twelve screw group connections and the other 237 tests verified the new equation. The unsafe rate for the new design equation is 4.42% among the 249 connections test, and the new design equation has high reliability and broader application scope.