On selected directions of improvement in method of design of timber structures

Abstract

Durability of timber structures depends on quality of design, conditions of manufacturing, transportation, assembling and exploitation. Any depart from the standard principle and requirements at any stage of structure preparation, as well as any abandon of specifi cations leads to commencement and progress of defects in the structure in process of exploitation and finally it causes the decrease of durability and sustainability and in effect decrease of life-service time. Load bearing capacity of timber structures decreases in time. Influence of load lasting time on strength parameters of timber derivative materials, and conditions of exploitation and common load action are included in application of partial modification factor kmod, which was obtained in empirical way basing on experience of timber structure exploitation and wood parameters. This coefficient does not take into account state of stressing in structural element (bending, compression, tension parallel to the grain or perpendicular to the grain or shear). Wood considered as a solid body, undergoes failure in result of accumulation of sub-micro-defects. Factor kmod in case of wood under static constant load tension perpendicular to grain within 50 years for service class 1 will give value of 0,15 what is four time lower than given in EN 1995. Work also consider some glulam defects and cracking under varying load action in the structures. Connections in glulam structures shall be designed to transfer the design load to and from structural element without causing local stress concentrations. These local stresses may initiate failure in the connection and then failure of whole structure. It is also important to design the connections isolating all timber elements from potential sources of potential moisture. The next part of the work refers to the cross laminated timber CLT as a new wood technology. This technology may soon open up the construction sector to wood building. There presented characteristic parameters of CLT and principles of design of modern timber structure using this new material.