Earthquake
Loads and the Florida Building Codes
James
R. Schock P.E., C.B.O., C.F.M.
Floodplain
Manager, Plans Examiner
St.
Augustine, Florida
T.
Eric Stafford, PE
T.
Eric Stafford & Associates
July
13, 2017
Research
Summary
This
research project is intended to investigate the basis for the earthquake design
requirements in the 2015 International Building Code (IBC) as they apply to the
State of Florida and to develop simplified code requirements if the need is
determined to be warranted. This research
will address the following questions:
1.
Is
there an historic need for earthquake design in the State of Florida?
2.
What
is the basis for the current mapped ground motion response accelerations and
other earthquake design requirements in the 2015 IBC that are applicable to
Florida?
3.
How
have the recent reductions in required design wind loads affected the
relationship between wind and earthquake loads in regard to the controlling
design method?
4.
Are
there simplified solutions or certain classes/categories of buildings that
should be required to consider earthquake loads in Florida?
Background and History
Since
the first edition of the Florida Building Code the earthquake design provisions
in the base code have not applied to the design of buildings. For the 2001 Edition through the 2010
Edition, the code requirements for earthquake design were deleted (shown as
“Reserved”) from the Florida Building Codes.
In the 5th Edition (2014) code, the earthquake design
requirements were left in the code but language was added to the preface
stating the following:
“However,
code requirements that address snow loads and earthquake protection are
pervasive; they are left in place but should not be utilized or enforced
because Florida has no snow load or earthquake threat.”
The 6th Edition (2017) Florida
Building Code, Building (FBCB) is a bit more specific stating the following in
Exception 2 to the general scoping section in Chapter 1:
“Code
requirements that address snow loads and earthquake protection are pervasive; they
are left in place but shall not be utilized or enforced because Florida has no
snow load or earthquake threat.”
During the development of the 6th Edition (2017) FBCB, several
proposals sought to require earthquake design in the FBCB consistent with the
requirements in the 2015 IBC. Other
modifications proposed to exempt earthquake design for buildings where the
mapped acceleration values were below a certain number. A few design examples were submitted
asserting that earthquake loads controlled over wind loads for the location and
building types chosen for the example. However,
the examples were provided late in process and didn’t permit a thorough peer
review. Determining whether wind or
earthquake loads control can be complex particularly for an area such as
Florida where wind loading has historically been the most critical threat.
While the proposals were not approved, they did raise several questions
about the need for earthquake design in Florida. The adoption of ASCE 7-10 in the 2010 FBC
resulted in significant wind loading reductions for many areas of the state
(30% or more in some areas of Northeast Florida). As a result, it is possible that earthquake
loading exceeds wind loading for certain building types and sizes in some areas
of the state. However, a more thorough
analysis is required to make this determination.
While earthquake design requirements have been exempted in every edition
of the FBCB, to our knowledge no specific analysis was performed to
specifically support this modification to the base code. It appears that it is based primarily on the
perceived notion that wind loading controls the design of buildings for lateral
loads due to the historic threat of hurricanes in Florida.
Proposed Research
The
following tasks will be performed:
1. Review the history of
earthquakes in Florida and any documented damage. A preliminary review of the earthquake
history in Florida does suggest some significant ground shaking has occurred in
the past.
2. Review the basis and
supporting criteria that establishes the mapped ground motion response
accelerations in the 2015 IBC for Florida.
3. Perform trial
designs/comparisons of wind vs. earthquake loads.
4. Develop code language
to address earthquake loads for Florida.
Anticipated
Outcomes
This
outcome of this project will be a report assessing the need for earthquake
design for Florida. The report will
summarize the findings and basis for the determination. If earthquake design is determined to be
needed, the report will recommend code language for the FBCB to address
earthquake loads.
Budget
The
estimated budget for this research is $18,000.