Replies

1. 
   DoRight | Jan 14, 2011 04:20pm | #1

   Anyone know anything about beams and deflection

   Bump

1. 
   calvin | Jan 14, 2011 05:38pm | #2

   See your similar post in that other thread.

   thanks.

1. 
   DaveRicheson | Jan 18, 2011 06:24am | #6

   Apple or oranges?

   Been trying to figure out if you guys are on the same page.

   He was talking about gluelams and you gave him information on paralams. Diffrent beast, but I understand you questioning the l/180. I havent seen that used in any load  calculations for many, many years. Most company's use L/360 to over engineer any beams today.

2. 
   calvin | Jan 14, 2011 05:53pm | #3

   I looked at the calcs on a porch structural ridge from I did....

   I saw a number that was a whole lot bigger than what you list.  Where did you get that "believe most" number?

   thanks.

1. 
   DoRight | Jan 17, 2011 08:31pm | #4

   L/180 vs L/360

   Agreed, I saw teh 180 in reference to some off teh shelf beam.  Don't recall where.  Since that time I have seen 240 and 360.  I am not sure what is standard and what is custom order.

1. 
   calvin | Jan 17, 2011 09:41pm | #5

   lvl on the porch ridge............

   here's some of the calcs on the paperwork for ridge beam-rafter span, wall to wall 14'-2x8 rafters-16oc.

   13'-8" Long. 

   1-ply-1-3/4 x 11-1/4

   Standard Load  dead >105 PLF

   Standard Load  snow>210PLF 

   Deflection criteria-L/360 live, L/240 total

   in the Allowable Stress Design:

   TL Deflection-0.5312" Actual       0.6615" Allowable     L/298 Capacity      6.61' Location    Total Load  D+S

   LL Deflection-0.4410" Actual       0.4410" Allowable     L/455 Capacity      6.61' Location    Total Load  S

   Hope there's something in there that you can use, but this was local specific 2 yrs ago.  Engineered by the LVL company, accepted by City inspection.

3. 
   McMark | Jan 18, 2011 11:06am | #7

   Your basic mathematical premise of deflection is wrong

   A ridge beam of 20' long, supported on both ends will not have a L/180 deflection approaching 1.32 inches because the deflection will be based on one half of 20'.  In this case the L/180 deflection of a 20' ridge beam is 0.66 inches

1. 
   DoRight | Jan 26, 2011 12:49pm | #8

   Deflection

   Thanks McMark for clarifying the deflection issue.  I was thinking deflection was like looking at a giant circle and the beam was like a small section of the circumfrance (spelling?) so that you would divide the lenght of your portion of the circumfrance (ie your beam lenght) by the 180 or 240 or 360.  I am sure nobody can understand what I am saying.

   Anyway, you are sure deflection is calculated on half the beam length?  I can see that can make sense. 

   Thanks.