Cross (CLT) and diagonal (DLT) laminated timber as innovative material for beam elements: Fid-Bau Portal

Cross (CLT) and diagonal (DLT) laminated timber as innovative material for beam elements

Bejtka, I.

Within this research work, beams were manufactured using self-made CLT and DLT elements. To enforce shear failure, short CLT and DLT beams were made. Long CLT and DLT were made to enforce bending failure. For beams made using DLT elements, two cases were studied: Beams were made either with DLT elements with separated diagonal layers or with DLT elements with side by side orientated diagonal layers. Altogether 60 short and long, CLT and DLT beams with four and five plies were produced. All beams were tested in bending. 30 tests were done on unchanged beams while 30 tests were done on beams with notched beam supports or with holes. The results for beams with notched beam supports and with holes are nearly similar to those for beams without any singularities. Using CLT and DLT instead of solid wood, brittle timber failure could be prevented. The beams with notched beam supports and with holes were designed to enforce timber splitting at lower loads. Due to the perpendicular or diagonal reinforcing layers, timber splitting was prevented very well. Unfortunately, the test results couldn't be used to qualify, whether CLT or DLT elements are better for beams loaded in bending. To quantify CLT and DLT beams, a finite element analysis was performed. First, different numerical models were studied. A beam, a plane and a solid model were discussed. Governing parameters were investigated and those, which don't affect the load-displacement behaviour, were neglected. Finally, the solid model was used for a parameter study. The solid model fits the load-displacement behaviour of CLT and DLT beams the best. Numerical calculations were done on totally 270 beams. Thereby, it was clearly demonstrated, that DLT elements provides a higher performance than CLT elements for beams loaded in bending. However, this result is more valid for DLT beams with side by side and in the opposite direction and diagonal to the beam axis orientated layers. Against it, diagonal orientated layers, which are separated by at least one parallel layer, are less good.