507 WOOD RESEARCH 65 (3): 2020 507-520 ECONOMICAL DESIGN OF TIMBER-CONCRETE COMPOSITE BEAMS Nikola Velimirović 1 , Ivan Stanimirović 2 , Dragoslav Stojić 2 , Nemanja Marković 2,3 Milivoje Milanović 1 1 State University of Novi Pazar Serbia 2 University of Niš Serbia 3 Ruhr-University Bochum Germany (Received July 2019) ABSTRACT The aim of the presented study is to find the best solution for the cross-sectional dimensions of timber-concrete composite (TCC) beam by focusing on serviceability limit state verification and cost of the beam, simultaneously. The population of 10.000 samples of the observed variables according to the predetermined ranges using Monte Carlo sampling method was generated. In order to find a number of Pareto-optimal solutions on the Pareto front, the weighted sum method was employed using original algorithm. The results have shown that minimum relative cost of the TCC beam can be increased even by 26.6% if the rheological effects that are neglected by the Effective modulus method are counted in the calculation of the final deflection. The presented trade-off strategy in design of the TCC beams has shown that with the slight increase of relative cost compared to the minimum, it is possible to get Pareto optimal design solution of the TCC beam that has drastically decreased final deflection and therefore is a more reliable design solution. KEYWORDS: Timber-concrete composite, multi-criteria decision-making, Pareto optimality, weighted sum method. INTRODUCTION The timber-concrete composite (TCC) structure is a structural system in which a timber beam is connected to an upper concrete flange using different types of connectors (Dias et al. 2015). They were able to exploit the best properties of both materials due to bending and tensile doi.org/10.37763/wr.1336-4561/65.3.507520