Analysis On Stability Test And Bearing Capacity Of Glulam Members Under Axial Compression

Glued laminated timber (glulam in short) is made of laminations,whose thicknessis less than45mm, by gluing. The research and application of glulam is still in itsinfancy in China. Glulam can be produced with different strength grade anddifferent size through the lamnations’ combination, extension and blending. So it canbe widely used in various industrial and civil construction. While “Technical code ofguled laminated timber structures” is drawn up in reference to foreign standards. It isnecessary to carry out the relevant research work.In this thesis,150glulam specimens were manufactured for the axial compressiontest. The specimens are members of same lamina grade, whose section dimension is105mm×105mm. The strength grade of specimens were designed for TCT21. The150specimens with the same section dimension but different length are divided into5groups according to the slenderness ratio,named Groop A,Groop B,Groop C,GroopD,Groop E. This paper completed the following work:First, full-scale short specimens (Groop A) of axial compressive test werecompleted in order to get the compression strength parallel to grain. It is found throughthe statistical analysis of test results that the compressive strength parallel tograin value obey normal distribution, and the5%percentile of it is26.6N/mm2. Thestandard value of this grade is24N/mm2in the “Technical code of glued laminatedtimber structures”.Second, the modulus of elastic were measured in bending test with full-scalespecimens, in the conditions of the force both parallel to the glue-line and perpendicularto the glue-line. It is defined that the axis parallel to the glue-line is X axis and the axisperpendicular to the glue-line is Y axis. The apparent modulus of elastic and purebending modulus of elastic were obtained. For the same group of specimens, when thebending direction is different, a difference exists in both apparent modulus of elastic andpure bending modulus of elastic. It appears that both modulus are bigger when thespecimen is bending around the Y axis. For the different group of specimens, when thebending direction is not different, the both modulus is close correspondingly.Third, the axial compression stability test of glulam specimens are completed, with4slenderness ratios (Groop B~Groop E). The ultimate bearing capacity were got whenthe specimens buckled around the weak axis. Fourth,Whole section wood pieces with a thickness of15~20mm were cut near thedamage area to measure the density and moisture content.Fifth, analyzed the test data deeply, obtained the stress-strain curve ofcompression strength parallel to grain. The modulus in bending test and compressingtest were compared.Sixth, take the test data in comparison with Code’s formula. The results showedthat the calculation method of Code’s formula is safe. For the largerslenderness specimens, the fomula in “Technical code of glued laminated timberstructures” is the most conservative.Seventh, analyzed the main parameters of stability factor formula in “Technicalcode of glued laminated timber structures”.