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Experimental investigation of CFS to steel connection using self-drilling screws

Abstract
Screws are one of the most used methods for joining structural steel to Cold Formed Steel (CFS). An improved substitute for conventional nail and bolt connections is self-drilling screws. The wings in the screws make it easier to drive the screw into the steel without the use of a pre-drilled hole. Given that joints are the primary means of transferring energy to a structure, it is especially crucial to comprehend the seismic behaviour of their connection. New Zealand, for example, is a country that primarily experiences seismic activity and builds its buildings using a combination of structural steel and CFS. Numerous research that looks into how structural joints behave under cyclic and monotonic loading conditions are available in the literature. However, the majority of these studies did not address the use of self-drilling screws in cyclic stress to link CFS to structural steel. Thus, by experimental testing, this research examines the load deformation and failure mechanisms of CFS and steel connections utilising screws under cyclic and monotonic loads. Tensile testing was done to evaluate the material's properties of steel. A total of 54 experimental investigations were conducted to determine the cyclic nature of the junction. The structural steel thickness (8mm, 12mm, 16mm, and 20mm), the CFS thickness (1.8mm), and the screw diameter (6.3mm hexagonal screw), and varying the number of screws (1 and 2) were considered in test program. The same samples were subjected to monotonic tests in order to determine the maximum and minimum displacement for the cyclic loading. A total of 24 tests were performed in order to acquire the values. The experiment's findings, including load deformation and the failure process, are identified. Based on the contrasting data, the cyclic nature of all the connections can be analysed to ascertain which is the most correct. The New Zealand standard AS/NZS 4600:2018, which particularly addresses the screw spacing with each other and the distance from the screw to the edge of the specimen, will serve as the basis for both the assembly and the spacing of the structural joints. The loading procedures and the number of cycles employed for cyclic loading are detailed in the Federal Emergency Management Agency 461 (FEMA). Appropriate displacement amplitudes for cyclic tests were determined using the initial results from the monotonic tests. During the cyclic testing it could be found that most of the specimens failed due to bearing and tear out failure. There is an average increase of 56.77 % in capacity as the number of screws were increased from single screw to double screw connection. As the steel thickness was increased as 8mm, 12mm, 16mm, and 20mm, the average capacity was reduced to 10.13%, 18.11%, 7.98% accordingly for a single screw connection. For double screw connection as the steel thickness was increased as 8mm,12mm, 16mm, and 20mm, the average capacity was increased to 0.79%, 4.91%, 2.15% accordingly.
Type
Thesis
Type of thesis
Series
Citation
Date
2025-02-22
Publisher
The University of Waikato
Supervisors
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