Compressive strength and stiffness of end grain contact joints in glulam and CLT

In all of the tested specimens, in CLT and glulam andwithout as well as with wetted surfaces, compressivefailure and large deformation were observed close tothe contact joint. In a few cases, also locally limitedfailure was observed at defects apart from the contactjoints, e.g. knots or finger joints, but no significantimpact on the overall deformation could be observed.CLT and glulam | (values for glulam in brackets)For CLT and glulam reductions of the compressivestrength resulting from the end grain contact jointsof 8.2 % (6.0 %) for the mean values and 9.1 % (11.5%) for the characteristic values were found. Although,the strength reduction is significant, the reducedvalues of characteristic strength of 32.0 N/mm² (28.5N/mm²) is still by far higher than the nominal valuesof the tested strength classes.For CLT and glulam the additional deformationresulting from the end grain contact joints is about1 mm (0.5 mm) under ultimate load and about 0.5mm (0.2 mm) under the design compressive stress atultimate limit state which equals approximately 40 %of the ultimate load measured in the tests.CLT with wetted surfaces | (values for steel platejoints in brackets)For CLT tested with wetted surfaces reductions ofthe compressive strength resulting from the endgrain contact joints of 29.1 % (20.3 %) for the meanvalues and 29.3 % (20.5 %) for the characteristicvalues were found. Although the strength reduction isvery significant, the reduced values of characteristicstrength of 24.9 N/mm² (28.0 N/mm²) are still higherthan the nominal value of the tested strength classes.However, for CLT with wetted surfaces (simulationof a possible rainfall or other precipitation duringtransport and erection) the additional deformationresulting from the end grain contact joints is morethan 10 mm under ultimate load for both, contactjoints without and with steel plate in the contact