Post And Beam Home: Load and Line of Thrust

Any post and beam home structure has to support itself and anything that is added to it, such as furniture, people, earth, snow, even wind.

All of these things fall under the general category of load, but the term should be broken down even further.

The dead load or structural load is the weight of the structure.

First, a building must be able to support itself.

The live load is the total of the forces acting on the frame as a result of its use, such as furniture, people, items in storage, and the like.

The snow load on a post and beam home is a specific live load, which varies from place to place.

It is the weight of the maximum accumulation of snow that can be expected in your area. C

heck with the local building department.

Plattsburgh, New York, for example, uses a snow load of 70 pounds per square foot (PSF).

Wind load is different in that it is not predicated upon weight.

Those living in earthquake zones will need to consider yet another load, a lateral live load that occurs as a building oscillates during the quake, this lateral load can be more severe than wind load) with your local building department if you live in a seismic zone.

The resultant or combined load is the total effect and resulting direction of all of the various loads that act on a structure.

We'll see an example of this when we discuss the several different loads on an earth roof.

Sam Clark, author and professional builder, explains the business of a structure in a very clear way: To withstand the loads on it, a house structure must meet three criteria. One, the individual members of the structure, such as beams, joists, and studs, must be strong enough.

Two, the members must be attached to one another properly.

The joints must be strong.

Three, the lumber must be assembled so that the structure as a whole is rigid. (Clark, 1996.)

A term frequently used in discussions of stress in post and beam home structure is the line of thrust or thrust line, which can be thought of as the transfer of a load.

Structural design deals with thrust lines so that the building is kept in a state of static equilibrium, which, with timber framing, often consists of balancing compression and tension forces.

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