FEMA P55 Coastal Construction Manual, Fourth Edition - Mad Cad

10 DESIGNING THE FOUNDATION Volume II
publication, Technical Fact Sheet 1.8, Non-Traditional Building Materials and Systems, in FEMA P-499
provides guidance on using new materials and new systems in coastal environments.
Table 10-3 is a summary of the advantages and special considerations for three of the more common pile
materials.
Table 10‑3. Advantages and Special Considerations of Three Types of Pile Materials
Material Advantages Special Considerations
Wood
Concrete
Steel
• Comparatively low initial cost
• Readily available in most areas
• Easy to cut, saw and drill
• Permanently submerged piles resistant to decay
• Relatively easy to drive in soft soil
• Suitable for friction and end bearing pile
• Available in longer lengths than wood piles
• Corrosion resistant
• Can be driven through some types of hard
material
• Suitable for friction and end-bearing piles
• Reinforced piles have high bending strength
• High bending strength allows taller or more
heavily loaded pile foundations to be constructed
without grade beams
• High resistance to bending
• Easy to splice
• Available in many lengths, sections, and sizes
• Can be driven through hard subsurface material
• Suitable for friction and end-bearing piles
• High bending strength, which allows taller or
more heavily loaded pile foundations to be
constructed without grade beams
• Difficult to splice
• Subject to eventual decay when in soil
or intermittently submerged in water
• Vulnerable to damage from driving
(splitting)
• Comparatively low compressive load
• Relatively low allowable bending stress
• High initial cost
• Not available in all areas
• Difficult to make field adjustments for
connections
• Because of higher weight, require
special consideration in high seismic
areas
• Vulnerable to corrosion
• May be permanently deformed if struck
by heavy object
• High initial cost
• Some difficulty with attaching wood
framing
The critical aspects of pile foundations include the pile material and size and pile embedment depth. Pile
foundations with inadequate embedment do not have the structural capacity to resist sliding and overturning
(see Figure 10-2). Inadequate embedment and improperly sized piles greatly increase the probability for
structural collapse. However, when properly sized, installed, and braced with adequate embedment into the
soil (with consideration for erosion and scour effects), a building’s pile foundation performance allows the
building to remain standing and intact following a design flood event (see Figure 10-3).
10.5.1 Compression Capacity of Piles – Resistance to Gravity Loads
The compression capacity of piles determines their ability to resist gravity loads from the elevated structure
they support. One source that provides an equation for the compression capacity of piles is the Foundation
and Earth Structures, Design Manual 7.2 (USDN 1986). The manual contains Equation 10.2 for determining
10-12 COASTAL CONSTRUCTION MANUAL