|TTI Research Supervisor:
William F. Williams, P.E.
Texas Transportation Institute
Texas A&M University System
College Station, Texas 77843-3135
|Pooled Fund Technical Representative:
Design Policy, Standards and Research Manager
Washington Department of Transportation
P.O. Box 47329
Olympia, WA 98504-7329
Many steel sign supports and light standards require a concrete foundation. This foundation is usually a 2 ft to 3 ft diameter shaft. When these foundations are located on a slope, the down slope edge of the foundations typically extends more than 4 inches above ground, creating a potential snagging point. These foundations are generally used to support a triangular slip base. One option is to install the foundation below grade such that the pipe support with slip base connection does not extend more than 4 inches above grade.
For this project, a foundation was designed for a single sign support that utilizes a multi-directional breakaway sign support. This foundation was designed for a sign area of approximately 30 ft2 or less with 7 ft from grade to the bottom of the sign. A new foundation was designed and detailed for omni-directional large sign supports that incorporate a larger sign area of approximately 110 ft2. This design incorporates the use of a proprietary omni-directional slip base system. For both designs, the structural supports with slip base attachments will extend approximately 4 inches maximum from the down slope grading edge. A typical foundation on a slope is shown as follows.
The objective of this study was to design a concrete foundation for small sign supports using multi-directional slip base supports that can be constructed completely below grade on a 2H:1V slope or flatter similar to that shown in Figure 2. This new foundation design will incorporate a new steel stub post that is bolted to the foundation with a multi-directional slip base connection at the ground line for the break-away features for the sign. Foundation details as well as slip base anchoring details to the top of the foundation were developed for this project. In addition, engineering calculations were performed for a foundation and sign support attachment to be used for larger signs incorporating multiple supports and using a proprietary omni-directional slip base system. Details of the design developed for this project are shown as follows.
The above design is recommended for signs 300 square feet or less using an embedded anchor tube. For anchor bolts cast within a concrete foundation, the following design is recommended.