.The "GL Grade" of laminated timber relates to the performance rating of the beam. By increasing the GL grade enables the beam to carry a higher load or have smaller beam dimensions ie: a GL 10 grade beam can carry a greater load than a GL 8. The below table was taken from AS/NZS 1328.2:1998

 
Characteristic Strengths (MPa)
Elastic Moduli (MPa)
GL Grade
Bending
Tension Parallel to grain
Shear in Beam
Compression parallel to grain
Short modulus of elasticity parallel to the end grain
Short duration modulus of rigidity for beams
GL 12
25
12.5
3.7
29
11500
770
GL 10
22
11
3.7
26
10000
670

GL 8

19
10
3.7
24
8000
530