Design study of two variants of a pedestrian and cyclist bridge in timber-composite design as a construction replacement option for the city of Koblenz

A comparison of both variants shows, that if theservice life is taken into account there are economicand ecological advantages in favour of the timber-granite composite construction. The renewal of theroad surface of the timber-concrete variant leads tohigher maintenance costs and worsens the ecologicalbalance with regard to the CO2 storage potential. Inaddition it leads to an increase in energy consumptionover the lifetime of the timber-concrete compositebridge.The statical analysis of the two bridges shows thatboth variants are technically feasible. Furthermore,the timber-granite composite bridge achievedsignificantly higher stiffness in the final state and thushas a positive effect on the serviceability in the finalstate. That is due to the lack of creep deformationof the granite at hand. The increase in deformationcompared to the initial condition of the timber-granite construction is only 14%. In comparison, thedeformation of the timber-concrete constructionincreases by 80% in the final state. Future projectsin the field of timber-granite composites needto investigate the actual behaviour when facingtemperature fluctuations. Due to the internalstatic indeterminacy, the forced stresses from thetemperature load might have a decisive influence onthe utilisation of the cross sections. Furthermore, theconcrete arrangement of the fasteners as well as theexact calculation and illustration of discontinuouscomposite structures need to be further investigated.22 However, the achieved high load-bearing capacityand rigidity, low maintenance costs, and the positiveecological effects over the entire service lifeshows the superiority of the timber- granite bridgeconstruction over a timber-concrete compositeconstruction. This promises to make further researchinto the substitution of concrete by granite to be arewarding endeavour.