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.