Safety risk to the timber roof structure of swimming pool halls after two decades of constant use

This work presents a case study exploring the structural safety risk to the timber roof structures of the swimming pool halls in one of the oldest Polish water parks, which was built in 2001. The superstructures of the roofs of these two swimming pool halls were made of glued laminated timber girders, in the form of two independent but similar structures with single-slope roofs. The superstructure consisted of main curved girders and straight intermediate girders with a span at the support axes of 25.0 m and a height at the ridge of approximately 11.3 m above floor level. The substructure of this roof structure consisted of continuous, multi-span (min. two-span) purlins, made from glued laminated timber, and single-span bracing purlins. The roof cover was laid on the purlins, and was made of 1.0 m wide sandwich panels consisting of an 80 mm thick polyurethane core and two sheet metal cladding layers. On the inside, the roof panels had an almost flat surface (with slight profiling), while on the outside, they had a trapezoidal shape. They were related to the use of insulated longitudinal joints. Two transverse joints of the roof sandwich panels were provided. After two decades of constant service, numerous leaks and moisture stains were observed in both structural elements of the timber roof, due to roof leakage and incorrect hygrothermal behaviour of the roofing panels. Buckling of the sandwich roof panels caused this problem. The structure showed a lack of proper fastening of the purlins to the main and intermediate girders made of glued laminated timber, which could have led to the roof being lifted in the event of strong wind exposure (due to wind suction on the roof surface). This situation resulted in the need for a comprehensive assessment of the timber roof safety, rechecking of the load-bearing capacity of their structures, and the formulation of repair recommendations.