Beam Types and Spans

hello and welcome to a trip down the load path session 5 this video is about beams girders headers whatever the term index they are doing the same thing we're going to discuss the different beam types there's solid sawn lumber beams and these are called by many names multiply built up laminated they're also often built as spaced beams where the plies are separated by a small gap sometimes these are referred to as flitch beams heavy timber is another kind of solid sawn beam but usually it's only a single member due to its size and we will discuss engineered lumber used usually to achieve longer spans PSLs and glue lambs are common in deck construction like many things for decks there is nothing in the IRC for beams but there will be in the 2015 edition so for now we have to look to other sources first we'll talk about beam design though it's dependent on the pounds per linear foot that the beam must support and that's dependent on the joist span and any joist cantilever beyond the beam let's take a look at an example deck with joy spanning 10 feet half of the joists are bearing on the beam 5 feet now this beam must support a uniformly distributed 40 pound per square foot live load and a 10 pound per square foot dead load this gives us a total load of 50 pounds per per square foot to find how many pounds per linear foot the beam supports add the length of any cantilever beyond the beam none in this case to half of the joist span and multiply the PI of the pounds per square foot the design calls for for this example the beam is supporting 250 pounds total per linear foot now this does not account for large concentrated loads that the beam may carry like this post carrying a roof load and bearing a mid span of the beam below the dca six from the American wood Council includes a span table for various deck beam sizes that already accounts for the beam load per linear foot this table is based on joist span so all you do is select the total joy span from across the top will pick 12 feet for this example which calculates to 300 pounds per linear foot if we select a 4 by 10 beam from any one of these species then the maximum beam span is 7 feet however in looking at the details for this table joists are also allowed to cantilever up to 1/4 of their span beyond the beam looking at the figure provided in the guide you see that the area of cantilever assumed to be carried by the beam so a beam sized for joy spanning 12 feet with no cantilever equal to 300 pounds per linear feet on the beam is actually sized for a three foot cantilever anyway this would add another 150 linear pounds per linear foot on the beam design but that's not actually there so the American would counsel beam span table is very helpful but keep in mind that it is also conservative when joists do not have cantilevers organizations that represent specific species also provide assistance such as the southern forest Products Association they provide a similar beam span table to the American wood Council one also designed for decks the IRC provides a schedule for fastening the plies together in a multi ply beam but it's not really intended for the exterior environment where wetting and drying cycles tend to warp lumber this schedule would require 1/16 d nail every 16 inches staggered high and low down the beam for a three ply beam it would need to be nailed from both sides now code aside I really recommend using a couple of nails every 16 inches high low and in-between as opposed to only one engineered lumber is also available for exterior deck construction and it would allow that 10-foot deck we were talking about before to have one beam spanning over 24 feet one type of engineered beam is parallel strand lumber or PSL this one is from trust joist and is treated for decay resistance and designed specifically for decks they provide span tables marketed specifically for decks and they provide simple instructions for using the tables as well as general general notes I'll do an example analysis but always use the information that comes from the specific engineered wood manufacturer or distributor we've got to determine three items first the total load per linear foot which is the live and dead load combined this is what we did before as well as the live load per linear foot by itself and we need to know that the total beam span that we're looking for our example deck is a ten-foot deck with a beam spanning 24 feet as before we take half the joist span 5 feet using the standard pounds per square foot design load 4 decks we need to determine the pounds per linear foot the beam supports for both conditions the total load is 50 pound 50 pounds per square foot times 5 feet for 250 pounds per linear foot and the live load alone is 40 pounds per square foot times 5 feet for 200 pounds per square per linear foot now with this information we can go to the manufacturers span table the first step is looking down the left column in this table and selecting the total beam span needed for this example we're looking for a 24 foot span now we scan across the row looking for a pair of live load and total load values that are equal or greater to ours zooming in we can check out the total load and live load and we are also given the minimum end bearing desists distance at the posts both the outer and the inner posts looking up that at the table at the top we can see the different beam choices and this beam must be a five and a quarter wide by 16 inch deep beam another type of engineered beam is a glued laminated beam called a glulam there are outfits across the country that provide these kinds of beams specifically for decks we'll go through another sizing example for our 10 by 24 foot deck using a ross perot treated glulam using their floor load chart and our previous load values we find the span we need across the top on this table and we look down for a combination of loads that meet or exceed ours just as we did before for this example we can use a three and a half inch wide by 16 inch deep glue Liam the final notes are simple beam span is dependent on joist pan and joist cantilever and that calculates out to a pounds per linear foot on the beam the American wood Council's DC a6 provides an easy to use span table but it's very conservative when Joyce don't cantilever and there are various engineered lumber and other products available and manufacturers often provide easy to use span tables for these products I'm Glenn Mathewson and I thank you for learning with me today you

Channel: Glenn Mathewson

Views: 119,494

Rating: 4.7321014 out of 5

Keywords: IRC, International Code Council, International Residential Code, ICC, Decks, Decking, building codes, training, Glenn Mathewson

Id: 51qk6xi75VU

Length: 7min 39sec (459 seconds)

Published: Mon Mar 10 2014