Steeple Loading – Did You Know?
In an earlier post I touched on special loading situations that you may encounter when designing a truss system. One of these was steeple loading. These structures can have significant impact on the design of a roof truss system. When dealing with a steeple, the most important thing to remember is to account for the load that will be generated by the wind overturning moment and not just the dead load.
Wind acting on the steeple will want to push it over and the roof needs to be able to handle this. Load from the wind overturning moment could add thousands more pounds depending on the size.
Multiple load cases will need to be run to look at the reactions based the wind going parallel or perpendicular to the ridge. The EOR should provide this information on the plans, but that is not always the case. Here is an example to demonstrate the impact of wind loads on steeples.
For this example we will look at a steeple that will have an 8’x8’x10’ base with 20’ triangular top. We will use a steeple weight of 1000# and wind load of 20 psf. Steeple will be supported at the corners.
As you can see, the effect of wind load on a steeple adds significant loads to the supporting structure. Keep these loads in mind next time you encounter a steeple or similar structures. Chances are they will not be specified on the plan. If they are attached to the truss system, they MUST be loaded accordingly. NOTE: This also applies to chimneys that are built on top of trusses!
Bill Hoover – Design Professional Gould Design, Inc.