huangyhg

glulam vs parallam beam
i'm looking at both products and would like to determine whether i specify proprietary product or go to a performance spec. and give sizes and grades. my end result will be the same it’s just that i don't want an rfi form the contractor during construction asking me to switch out one for another. does anyone have any thoughts or experiences with this issue?
tia

i have always done performance spec (size, fb, fv, e, and grade). no problems from the contractors standpoint. my terminology on the drawings for the parallams is "scl" for structural composite lumber.
spec parralam for work with short spans and where you need the beams quickly. you can get them at a local builders yard. if you have more time and larger spans, spec glulam as they tend to be less expensive and can accomadate a greater range of loads and spans, however they are ordered from the plant and take longer to get.
have you considered warranty information per manufacturer regarding the "creek" effect?
do you mean "creep"?
i work for a glulam supplier and would reccomend specifying lvl or glulam. parallam is a proprietary product produced by one manufacturer, i believe when you specify it, you increase the project costs.
my design philosophy is to specify the best product for the design application. parallam has high design values which work well for applications that require small highly loaded sections. so i recommend using it where you need it and not specifying it for all beam and column applications on a project.
it appears that a lot of engineers if they have a need for parallam on part of the project they will specify it every where. as a structural engineer i can understand why that approach is appealing. you only have to deal with one set of design values and will be able to minimize the depth and width of your sections.
also it may reduce your time later. if some one submits a substitution request, you just mark it rejected and instruct the contractor to provide what was specified on the drawing.
if you are going to take the above approach however you should know what the limitation of parallam are. i work in minnesota and would question the statement that parrallam is more readly available than glulam. i am not aware of any local lumber yards in this area who stock parallam. like glulam they are order from wholesalers. common glulam sizes are ordered from wholesalers not from the plant.
also one must keep in mind that parallam is not produced in curved shapes or with camber. while treated parallam is available it is a specialty product. treated glulam is available in a wide range of sizes from any stocking glulam wholesaler,
one thing to keep in mind with parallam is that the material swells in wet or humid conditions. without special manufacturing procedures to minimize it, the swelling can be as much as 8%. if your application is highly restrained, you need to watch this.
rarswc,
a parallam, manufacturered by a well known company, is what the nds call parallel strand lumber (psl). right? who else makes psl
stro4 is corect. the generic name for parallam is psl. properties for psl are also listed in aashto.
for "parallam" type applications, i am willing to accept lvl's (laminated veneer lumber such as microllam), lsl's (laminated strand lumber, such as timber strand), or psl's, as long as they meet my performance spec. all three categories fall under the broader generic category of structural composite lumber, which is why on the drawings i typically show "scl" followed by the
scl's almost always have better stress and deflection ratings than glb, so if you spec glb, a equal size scl swap is easy. truss joist makes products called psl, lvl, and lsl. when i spec them on plans, it's in reference to that specific manufacturer, with a not that any substitution requires approval by me, as they are not all created equal.
as far as avoiding rfi's go, your best bet would be to figure out what the contractor wants and spec it. past that, you can make them easier by spec'ing glb's, and then most all scl will have superior values (providing the camber and moisture differences are a non issue as pointed out above), or use minimum values of scl so most anything will work.
you can put the design values used in the plans and leave the product selection up to the contractor, but i wouldn't recommend it, since they may not know/understand all the implications of what they're looking at.

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