Design upgrade for the hybrid glulam-steel roof structure of the sports hall for the new High School in Graçanica

This paper presents the design upgrade of the roof structure for a sports hall which consists of coupled glulam beams with steel substructure. The initial design has foreseen main glulam beams which are coupled with steel trusses and strengthened with rigid steel bars over the entire length. Due to some construction issues and design misinterpretation, the as-built structure did not follow completely the design and reinforcement rebars have been used instead of steel bars intended to be acting as steel ties. A design upgrade was required to preserve the main structure of the roof established with glulam beams, purlins and all the necessary layers to create a flat roof deck for students’ access. The main challenge of the new design was to preserve the glulam beams and the initial architecture for the roof structure while ensuring safety for both the ultimate and serviceability loading cases. Initially, four proposals are provided with different solutions and among them only two are chosen for the further assessment based on safety, cost estimation, feasibility and ease of implementation in order to avoid problems on site. One of the proposals consists of steel cables anchored at both ends and deviated on each steel truss and the other proposal consists of stainless-steel rods connected at each intersection with the steel trusses. After careful and detailed assessment of the two proposals, the second proposal consisting of steel rods was chosen as the most appropriate one in terms of safety, cost, feasibility and ease for construction. Additional assessment, detailing, specifications and test procedure, are given to ensure an effective structural solution for a practical problem on an existing structure.