Structural Engineer
- Thread starter tri4sale
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Steve is an Architect
I'm not a structural engineer. My degree is mechanical engineering and that was a long time ago. If you are looking at beam deflection you will find steel is much stronger, this is governed by a property called the modulus of elasticity. But the cross section is also important. Enough wood can have the same deflection as steel but it will need to be bigger. The key dimintion is the height. I don't think engineers calculate most of this stuff these days, we look it up online.
As a general rule of thumb, any structural wood component is going to be less expensive, and easier to handle than steel. I assume that you are talking about a residential construction.
Short answer, a wide flange beam vs an LVL , the steel is roughly 10x stronger (same cross section WxH) . LVLs are not typically used in place of WF beams. LVLs are most commonly used in place of built up sandwiched beams like 2x12s. etc. for headers etc.
yes, residential construction, comparing the use of a steel beam vs LVL to span a 20ft distance. talked to a few framing crews and none really want to deal with a steel beam on this project.
I have used structural shapes in some residential constructions, where conditions demanded the properties of a steel beam and the additional cost associated with the steel shape, fabrication, erection, etc. Steel columns of various profiles were used more frequently than wide-flange beams in residential construction.
LVL's can be built-up on site, in situ, often being handled without cranes or special lifting gear. Other engineered structural wood products are available, depending on specific needs. In my many years of constructing some very large, custom designed homes, I was confronted by only a few homes where an engineered wood solution would not have been structurally sufficient within the available space allocated for the beam or girder.
Unless you need a beam that will be carrying additional live loads, such as supporting a hoist, you should have no problem spanning 20', under most load conditions, with an LVL or other engineered wood product. Make sure that the members supporting the end of the beam, and the footing below them, are up to the task.
+1. In a long span like that and not even knowing the spans of the load members resting on it, I would expect to see no less than 3 jack studs and 2 king studs at each end with appropriate reinforcing of the foundation below. Some engineers will also require a laminated column post at each end for jacks instead of a built up jack stud assembly. Also, uplift prevention should be considered unless the dead loads negate the need.
The entire structure needs to be analyzed as a system, not individual components (replacing steel with an LVL.) without that, no one can advise you properly.
As an ex mechanical engineer, I used steel beams in a house I designed and had built. The biggest negative I got from the builders was how to attach joists to the beam (it was in a cathedral roof/ceiling). That was solved by sistering dimensional lumber inside the webs to attach hangers for the joists. I like steel because that’s what I was most familiar with and it’s compact relatively speaking. In any case, the loads have to be chased down all the way to the foundation and accounted for throughout the path.
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This is not well researched and should not be relied upon. But to get some idea of the relative size of steel and a glu lam I googled "beam for a 20 foot span". I don't know what they assumed for loading which can make a big difference. One item said 40 lbs/square foot. But with that caveat I got results indicating a W10x26 steel beam which is 5.75 in x 10 3/8 in or a W8x28 which is 6.5x8 inches would work. Or a glue laminated beam 3 1/8x19 or a beam 5 1/8x15 inches. Obviously the wood beam is much taller because wood does not resist deflection as well. Home floors are designed to keep deflection to the desired maximum under maximum loading, they are not designed to stay a certain percentage away from failure. 40 pounds per square foot is the normal assumption for the main living area in a house. If there are major loads (like a piano) that should probably be addressed. A hot tub would certainly need to be addressed. The 40 lbs per square foot is for just normal furniture and people.
To get reliable information you would want to look for information from a glu lam or steel beam provider. I have looked up glu lams before and found tables without a lot of digging. If you could hide the steel beam in a wall and let the joists rest on top of it the task for the carpenters would be a lot less than if they have to attach the ends of the joists to the beam.
To get reliable information you would want to look for information from a glu lam or steel beam provider. I have looked up glu lams before and found tables without a lot of digging. If you could hide the steel beam in a wall and let the joists rest on top of it the task for the carpenters would be a lot less than if they have to attach the ends of the joists to the beam.
No one in this forum has recommended a specific specification for either a steel or engineered wood beam. We were discussing the advantages and disadvantages of engineered wood, vs, steel beams. I have the software that can make that comparison, I would never make that recommendation in an online forum.
The last beam I had to put together in that length range was two LVLs sandwiched over a steel plate, with a prescribed fastening pattern. This was laid out by an engineer and the inspection department for the county I was working in. So without doing any math on limited information, I recommend biting the bullet and higher a local structural engineer to assess your needs. That will be your least expensive in the long run.
The engineering design data available for engineered wood products is extensive. In most cases, in residential design, you can use tables to determine the spans of simple beams. You are dealing with dead loads, which are the loads that a beam will support, depending on a given dead load, and the live load that you design to. The values include deflection too, which are often determined by building code requirements. Of course, you can design a beam to exceed code requirements. However, tables are often inadequate when accounting for point loads on a beam.
The use of engineering software to design beams and other structural components allow not only the ability to apply loads to a beam that are not uniformly distributed - point loads - but the software provides an analysis of the loads applied to a structural member, that is presented in a graphic with the associated load values. The software can make recommendation of what structural members will work for the given design load specifications, giving you a choice of structural options.
When used correctly, you can graphically watch the impact of loads as they are carried down from the highest point in the structure, across various beams and girders, to vertical structural members, all the way to the footing. But you have to know how to use the software correctly, or there can be problems - big problems.
Over twenty-years-ago, I was building a three-story home and a local supplier was calculating the engineered wood components in the home. When I received the bid, I knew that something was very wrong. Using very sophisticated software, they had calculated the structural components for each level of the home in isolation. They had not added the loads of the previous levels to the lower levels. At multiple point loads, my software returned loads that could have easily resulted in a failure of the component. At the very least, the deflections would have been visibly noticeable, under dead load values alone.
Their software was as capable as mine, but someone at the building supply had unknowingly configured the software to isolate loads to each level, instead of transferring the loads of the upper levels downward. Merely checking the wrong box in the configuration menu put every home that they worked on at risk of structural problems, or worse.
Over the years, I often hired a structural engineer for complex structures, especially before the software market got up to speed. Hiring a structural engineer is never a bad idea. However, for simple load situations, you can usually select your beam from a chart or table. Most building supplies that sell engineered wood products have the engineering software to design and document the products that they sell. As with truss manufacturers, they include the design work at no extra charge.
I've hired an engineer for that, but wanted to discuss w/ an engineer my options to double check what I've already got. Always good to get multiple opinions.
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