P_1.1.3 clt_long_time

When proving the limit state of suitability of application CLT elements used as plates – e.g. in the form of ceiling constructions – additionally to the vibration proof the deflection proof is of significant importance. The deflection shares are – roughly speaking – composed of a share of permanently or practically permanently working short-term loads. As far as the permanently working loads are concerned, it is necessary to determine the creep share and take this into account concerning proof. In order to be able to determine this share, knowing proportional creep coefficient k_def is indispensable. Because of this importance, a project has been carried out and is about to be completed. In the course of the project, a comparable look at GLT and CLE-CLT was taken, and the creep behaviour of both products was compared. The results obtained have revealed that – depending on the climate and load level – a k_def–value for CLT that is approximately 30% to 40% higher. The presented creep figures were determined using 5s-CLT elements by way of experimental testing.

In order to be able to establish a valid model for considering the creep influences, the envisaged follow-up project which is presented here deals with the determination of the creep figure for the shear share k_c,9090. In this way, it shall be possible to evaluate and, if necessary, improve the current calculation model for smeared creep figures for CLT k_c,BSP. Particularly, by means of a generally valid model, the various build-ups shall be able to be considered.

In a project of the same name in an interim financing period, the principles in terms of an experimental planning und set up shall be carried out. Only after the interim financing period will this project carry out a final evaluation and determination of the creep figures, this being due to the long duration of the experiment for determining the creep value for a shear strain and, based on it, the smeared creep figures for cross laminated timber.