Alternative Support Systems for Cantilever - National Transportation ...

CHAPTER 2
BACKGROUND
The following sections cover the history of signal/sign anchor bolt foundations and present
the various foundation systems recommended by FDOT Report BD545 RPWO #54 and
alternatives used in other industries. The current anchor bolt foundation system is revisited so
that its particular structural concerns can be identified and explored in alternative foundations.
The recommended foundations are analyzed for potential problems and benefits, particularly on
how they transfer load from the cantilever’s monopole to the substructure. Based on the
information gathered, a recommended alternative is identified.
2.1 Current Anchor Bolt Foundation System
During a recent survey (2) of state DOTs, an assessment of typical signal/sign foundations
was conducted, particularly on the structural application of each foundation type and frequency
of use (See Table 2-1). The information obtained from this survey shows that at present,
reinforced cast-in-place foundations are the most common foundation types for overhead
cantilever signs, with spread footings the next most common foundation.
Table 2-1. Support structure foundation frequency of use (7)
Structure type Reinforced
Cast-In-Place
Drilled Shafts
Unreinforced
Cast-In-Place
Drilled Shafts
3
Steel Screw-
In
Foundation
Spread
Footings
Directly
Embedded
Overhead Cantilever Common None Rare Intermediate None
Over Head Bridge Intermediate None Rare Intermediate None
Road Side Sign Intermediate Rare Rare Rare Rare
Street Light Poles Intermediate Rare Rare Rare Rare
High-Level Lighting
Poles
Common None None Rare None
Traffic Signal Common None None Rare Rare
Supports
Span Wire Supports Intermediate None None Rare Rare
Notation
Common = 67-100% of the states reporting use
Intermediate = 34-66% of the states reporting use
Rare = 1-33% of the states reporting use
None = 0% of the states reporting use