**Natalia Korcz-Konkol \* and Piotr Iwicki**

Department of Metal Structures, Faculty of Civil and Environmental Engineering, Gda ´nsk University of Technology, ul. G. Narutowicza 11/12, 80-233 Gda ´nsk, Poland; piotr.iwicki@pg.edu.pl

**\*** Correspondence: natalia.korcz@pg.edu.pl

Received: 30 June 2020; Accepted: 8 September 2020; Published: 11 September 2020

**Abstract:** In stressed-skin design, the cladding stiffening effect on structures is taken into account. However, the "traditional" design is more usual, wherein this effect is neglected. Even if the diaphragm actions are not regarded, in particular cases such as big sheds (and others), the parasitic (unwanted) stressed-skin action may occur with the result of leakage or even failure. The structures of this kind have already been built. Thus, an important question arises: How can one assess them if there is a need to correct or redesign them? What kind of non-destructive approach can be used to achieve that? Experimental tests of small-scale shear panels made of trapezoidal sheeting were designed in order to observe the behaviour of the diaphragm under increasing and repeated load. The tests were oriented toward force–displacement relations and strains in selected areas of the sheeting. The results revealed nonlinear, hysteretic force–displacement behaviour of the panel and the occurrence of the persistent deflections and stresses which remain even after the unloading. The relation among the stresses, force–displacement paths and modes of failure can be potentially used in monitoring systems of existing buildings in terms of parasitic stressed-skin action.

**Keywords:** steel structures; stressed-skin effect; diaphragm design; trapezoidal sheeting; condition assessment of steel structure; structural health monitoring
