Beam Bearing in Post and Beam Construction
Common wood frame buildings are generally built with 2x dimensional lumber. As well, we often use 4x and 6x and even larger elements, in most cases. These decks follow the typical principles of Western platform framing. Most framed buildings across the United States are also built in a similar fashion. Western platform framing became popular here decades ago, There were other common methods for framing buildings before that though. One of those methods was balloon framing.
Balloon framing is similar to Western platform framing. One of the main differences is that balloon framing was built vertically through multi-story walls in one continuous run. There wasn’t a distinct separation between each floor level. This caused a fire risk because a fire could go right up straight from one point in the building through to the floors above without a distinct separation. The stud bays, for example, created a pathway in which flames could rise upwards, uninterrupted. Western platform framing basically fixed this problem. Before Western framing became popular though and even before balloon framing became popular, there was another type of framing that was more common. That type of framing was called post and beam.
Post and beam framing built the structure of the building with large posts and large beams, as the name indicates. Then, the open walls could be filled in with smaller framing between those posts and beams. Framing used for the infill walls essentially had no role in the actual load path. Instead, the load path ran around those elements across the beams and down the posts.
We don’t see many examples of this type of post and beam framing anymore. Today though, we’re looking at an interesting example of an exposed portion of a building framing where the load path is built with a post and beam type assembly. In the picture below you can see the top of a large vertical post which supports a large horizontal beam.
The individual floor joists are then supported on top of this beam. In a large span floor system, often the joists themselves are not large enough or space tightly enough to run continuously from side to side. An intermediary support, like the post and beam shown here, will essentially break the span into two. Therein, the individual joists have a much higher strength capacity. It’s not the joists though, themselves, are stronger. It’s just that they are able to be isolated into two parts, each with a different rating for strength and capacity. Essentially, if all other configuration type factors are the same yet a joist Spanish shorter, the joist will have a higher resistance capacity.
Another interesting facet of this particular construction is that they have metal connector plates and ties. Today we build with a significant amount of metal connectors. These metal connectors help in a few different ways. They’re able to position fasteners in alternating and opposing angles that allows for better connectivity and resist separation. Some of the most common types of modern metal connectors are hurricane clips, joist hangers, and base plates. These elements help tie the load path together.
As you can see below, these particular plates are built with a steel or cast iron that fits around the three-dimensional context of the post and the beam. There are holes or perforations built into the plates which allow fasteners to be set through the plates into the structural wood elements.
A view of the same post and beam connection, but from the opposite side, follows below. The upper metal tie connects the spanning plinth to the continuous beam or girder above. The lower metal tie wraps around the top of the post like a collar. Because it is a single element instead of two or more separate individual elements, it has a higher rating of strength. Essentially, the fasteners are set in a connected element that resists separation, on both sides of the same post.
The edges of the plinth block between the post and the beam are cut on a chamfer type angle. This particular detail has no specific functional purpose. Instead, it just makes the exposed timber or lumber elements look a bit more purposeful and finished.
Although this type of installation here happens to be on the interior of a building, the elements and principles are similar to the principles of framing a deck. Even where it’s in the exterior or in a backyard, there are similarities. The underlying principles of connectivity, bearing capacity, spanning, and support remain related.
Use a contractor who understands and cares about doing things right. Always, feel free to reach out to us here at Dupont Decks and Patios. We are happy to help with almost all steps of the deck building and design process. A backyard and outdoor space should make a significant, positive impact on both quality of life and home value. We can help with more than just decks, we also build patios, pergolas, ramadas, awnings, gazebos, arbors, and privacy fences.
Let us know about your ideas and talk to us if you have questions about possibilities. We are happy to participate in improving your outdoor space and quality of life! You can call us at (202) 774-9128. You can find us online at https://dupontdeckspatiosdc.com and you can email us there as well at https://dupontdeckspatiosdc.com/contact-us
