Correlation Between the Load-Bearing Capacity, Fire Resistance, and the Price of Glued Laminated Timber

In this study, a continuation of the research on the influence of the bearing capacity proof on the fire resistance of an element’s cross-section is presented; however, in this particular case, we focus on elements made of homogeneous glued laminated timber. This influence is assessed by considering the variations in the cross-section’s area and the strength class, which are at the end of this paper, expressed through the actual material price. In order to obtain numerical results, similarly to the case of softwood, the limit states method and reduced cross-section method were used. The main aim of this research was to determine the actual price of homogeneous glued laminated timber if the limit state of load-bearing capacity is met and a certain fire resistance is required. By reviewing the available literature, a certain lack of practical solutions that might provide an appropriate answer to this question is evident. Namely, it is a common practice in the engineering community that when a certain limit state of load-bearing capacity is met in the case of homogeneous glued laminated timber material, an acceptable assumption of 30 min (R30) fire resistance class is automatically fulfilled when fire acts on three sides of the cross-section. However, it was shown that this is not entirely correct and always applicable. The main results of this study are precisely related to the above notion and clearly indicate the importance of the bearing capacity proofing procedure in the determination of the GLT fire resistance. Following the numerical results makes it possible to make decisions about the optimal selection of the element’s cross-section and its influence on the required fire resistance, even in the early design phase. The correlation of the load limit state capacity proof with the corresponding fire resistance functions makes it possible, for any stress state case, to obtain the optimal price for timber material as their intersection point.