12/28/2022 0 Comments Risa 3d wall area loadsOur sample homes are in an area where the snow load is 50 pounds per square foot of roof area (treat snow as live load). These examples illustrate how distributed loads are assigned to structural elements. Assume that all are located in the same climate, but have different loading paths because of the way they are built. Let’s trace distributed loads for several different houses. This will enable us to size beams for most common applications. Analysis of point loading is best left to engineers. The load is not shared equally by the supporting structure. Point loads occur when a weight is imposed on one spot in a structure, like a column. Live and dead loads listed in the building code for roofs and floors are approximations of distributed loads. Each square foot of the surface feels the same load. A layer of sand spread evenly over a surface is an example of a pure distributed load. Loads are considered to be either distributed or point loads. For sawn-lumber you must perform mathematical calculations. Engineered wood components are sized using span tables that match various spans to pounds per foot of beam. Armed with this information you can determine the minimum size, span or strength of the beam (credit julio). ![]() This translation is the key to any structural sizing problem. In beam-speak you say: this header must carry X-pounds per lineal foot. ![]() The first step is the same for sawn- and engineered wood materials: add up all the loads acting on a header or beam and then translate this load into terms of how much load each lineal foot of header or beam will feel. Here is a simplified approach that will help you specify the appropriate material for many applications. However, the process for sizing these structural elements can be complicated if you are not an engineer. The beam must be strong enough so it doesn’t break (Fb value) and stiff enough so that it doesn’t deflect excessively under the load (E value). The idea behind sizing headers and beams is straight-forward: Add together all live loads and dead loads that act on the member and then choose a material that will resist the load. They transfer loads from above to the foundation below through a network of structural elements. The job of headers and beams is a simple one. Part II will review sizing procedures, performance and cost of these materials for several applications (see “ Sizing Engineered Beams and Headers” for part 2). Part I will show you how to trace structural loads to headers and beams. In this 2-part series we will review how sawn lumber and these engineered materials measure up as headers and beams. Parallam, Timberstrand, Laminated Veneer Lumber and Anthony Power Beam are examples of alternative materials that provide builders with some exciting choices. Sawn lumber limits design potential and in some cases just doesn’t work. ![]() You can’t beat sawn lumber for most small window headers, but as spans and loads increase, stronger materials are a better choice. Too often builders gang together 2-inch dimension lumber to support roof and floor loads without considering other options. A neat solution, but is this an efficient and cost effective use of material? The same is true for beams like structural ridge beams and center girders. ![]() These headers work to support most residential loads and coincidentally keep the window tops to a uniform height. Most builders automatically choose double -2 x 8 or -2 x 10 headers to frame windows and doors in every house they build. Understanding how loads are transferred through a structure and act on structural members is the first step to sizing headers and beams Some information contained in it may be outdated. Please note: This older article by our former faculty member remains available on our site for archival purposes.
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