Reduced Southern Pine Design Values and their effect on Glulam

For those who are familiar with designing wood members, you may also be aware that the allowable design values for dimension and sawn Southern Pine timber have been reduced. Tests have indicated that the juvenile wood, used in todays markets, have lower allowable strength values than those that have been published before. 

As a designer, it is important to know that these reductions are not applicable to the design of Glued Laminated Timber members.   Our laminator, ALAMCO Wood Products have provided us with the following from the APA-AITC white paper on Glue Lam lumber grading  (select link below)

 See PDF

Steel truss decking

     For many years, glued laminated decking has been a preferred choice for existing steel truss bridges for both vehicular and pedestrian applications. And for good reasons...Take a look at dead loads. Timber weighs in at 50 PCF while concrete tips the scales at 150 PCF. That's a factor of 3 whereas the thickness required doesn't come near that factor increase. 

     Glued laminated timber also benefits from the quick assembly time it provides thanks to extensive prefabrication of the material at the plant. Panels can be manufactured continuous over multiple floor beams increasing the structural design while saving on installation times. In most cases, a deck for a truss can be set within two days depending upon site characteristics. And of course, treated decking is resistant to road salts, which probably was a main contributor to the need for a bridge repair.

     Feel free to contact us at 607.562.8110 to learn more about decking for trussed bridge structures.

​Glulam decking on pedestrian truss rehab

photos courtesy of Larson Design Group, Williamsport, PA.