07.21: Experimental setups for the measurement of the rotational restraint provided to cold‐formed Z‐purlins by sandwich panels

Abstract

ABSTRACTSandwich panels supported by purlins are widely used as the main load bearing part of roof systems of steel buildings. Sandwich panels provide lateral and rotational restraint to purlins which positively influences their resistance. Lateral restraint given by sandwich panels is equal for both the downward and uplift loads applied on the panel's surface, though the rotational restraint may have different character. The uplift load reduces contact area between the panels and purlins which can result in smaller restraint value.ECCS Publication N° 135/CIB Publication 379 states, the rotational restraint for uplift shall be determined by tests with the recommended setup, otherwise a zero value has to be considered. The recommended setup, originally developed by Joachim Lindner, was also used for the large EASIE testing program which was the base of the aforementioned recommendation. The test setup from EN 1993‐1‐3, originally developed by Teoman Peköz for tests with cold‐formed purlins and corrugated sheeting, has been considered as inappropriate for sandwich panels because it does not consider effects from transverse load.During the EASIE test program only hot‐rolled purlins were tested and therefore evaluation did not take into account section distortion which is negligible for hot‐rolled sections. The application of the test results for cold‐formed purlins and conclusion related to the rotational restraint under uplift load therefore required re‐confirmation by tests with cold‐formed purlins.The experimental research, to determine the rotational restraint given to cold‐formed Z purlins by sandwich panels, was performed at Brno University of Technology (BUT) in collaboration with Astron Buildings S.A. (Astron). Sandwich panels with direct fastening and hidden fastening, with PUR/PIR and mineral wool core were tested. ECCS/CIB test setup with the application of a torsional moment and a modified setup with the application of a direct force were used. Several tests were additionally done with the setup described in EN 1993‐1‐3. The creep effect was investigated as well. Based on the tests results, available test setups for cold‐formed purlins were weighted and commented. The correction of the current draft of EN 1993‐1‐3 was proposed.