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Fire Endurance of High-Strength Columns
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Favorable Fire Tests Spark Code
Revisions for High-Strength Concrete
Data from PCA and CAC sponsored research completed
at the National Research Center of Canada on the fire endurance
of high-strength concrete columns has resulted in proposed revisions
to ACI Standard 216.1 "Standard Method for Determining Fire
Resistance of Concrete and Masonry Construction Assemblies."
Proposed changes in the standard, currently being balloted, address
concrete columns when the specified compressive strength is in excess
of 12,000 psi. Variables in the ten 16-inch-square columns tested
included compressive strength, loading, tie geometry, type of aggregate,
and the addition of silica fume.
Researchers have long questioned the fire rating of high-strength
concrete. Early fire tests on small samples showed a significant
loss of strength compared to that of normal strength concrete. The
proposed revisions for concrete columns having specified compressive
strength in excess of 12,000 psi are:
- The least dimension of reinforced concrete columns of different
types of concrete having a specified compressive strength greater
than 12,000 psi for fire resistance rating of 1 to 4 hr shall
be 24 inches.
- Ties shall be formed with hooks having a six-diameter extension
that engages the longitudinal reinforcement and projects into
the interior of the hoop. Hooks for rectangular hoops shall be
formed with minimum 135 degree bends and hooks for circular hoops
shall be formed with minimum 90 degree bends.
- The minimum thickness of concrete cover to main longitudinal
reinforcement in columns, regardless of type of aggregate used
in the concrete and specified compressive strength of the concrete,
shall not be less than 1 in. times the number of hours of required
fire resistance, or 2 in., whichever is less.
 Complete
test results are available in a PCA R&D report, Fire
Endurance Experiments on High Strength Columns (RD138).
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