Code of Massachusetts Regulations › 780 CMR - STATE BOARD OF BUILDING REGULATIONS AND STANDARDS › Chapter 7 - Fire and Smoke Protection Features › Section 721 - CALCULATED FIRE RESISTANCE › Subsection 721.2 - Concrete assemblies

Current through Register 1525, July 5, 2024
The provisions of this section contain procedures by which
				  the
fire-resistance ratings
of concrete assemblies are
				  established by calculations.
721.2.1
Concrete walls.
Cast-in-place and precast concrete walls shall
				comply with Section 721.2.1.1. Multiwythe concrete walls shall comply with
				Section 721.2.1.2. Joints between precast panels shall comply with Section
				721.2.1.3. Concrete walls with gypsum wallboard or plaster finish shall comply
				with Section 721.2.1.4.
721.2.1.1
Cast-in-place or precast walls.
The minimum equivalent thicknesses
				of cast-in-place or precast concrete walls for
fire-resistance
				ratings
of 1 hour to 4 hours are shown in Table 721.2.1.1. For solid
				walls with flat vertical surfaces, the equivalent thickness is the same as the
				actual thickness. The values in Table 721.2.1.1 apply to plain, reinforced or
				prestressed concrete walls.
TABLE 721.2.1.1 MINIMUM EQUIVALENT THICKNESS OF
				  CAST-IN-PLACE OR PRECAST CONCRETE WALLS, LOAD-BEARING OR
				  NONLOAD-BEARING
CONCRETE
TYPE
MINIMUM SLAB THICKNESS
							 (inches)
FOR FIRE-RESISTANCE RATING OF
1-hour
11/2-hour
2-hour
3-hour
4-hour
Siliceous
3.5
4.3
5.0
6.2
7.0
Carbonate
3.2
4.0
4.6
5.7
6.6
Sand-lightweight
2.7
3.3
3.8
4.6
5.4
Lightweight
2.5
3.1
3.6
4.4
5.1
For SI: 1 inch = 25.4 mm.
721.2.1.1.1
Hollow-core precast wall panels.
For hollow-core precast concrete
				wall panels in which the cores are of constant cross section throughout the
				length, calculation of the equivalent thickness by dividing the net
				cross-sectional area (the gross cross section minus the area of the cores) of
				the panel by its width shall be permitted.
721.2.1.1.2
Core spaces filled.
Where all of the core spaces of hollow-core wall panels are filled with
				loose-fill material, such as expanded shale, clay, or slag, or vermiculite or
				perlite, the
fire-resistance rating
of the wall is the same as
				that of a solid wall of the same concrete type and of the same overall
				thickness.
721.2.1.1.3
Tapered cross sections.
The thickness of panels with tapered cross
				sections shall be that determined at a distance 2
t
or 6 inches
				(152 mm), whichever is less, from the point of minimum thickness, where
t
is the minimum thickness.
721.2.1.1.4
Ribbed or undulating
				surfaces.
The equivalent thickness of panels with ribbed or undulating
				surfaces shall be determined by one of the following expressions:
For
s
>= 4
t
, the
				  thickness to be used shall be
t
For
s
<= 2
t
, the
				  thickness to be used shall be
t
e
For 4
t
>
s
>
				  2
t
, the thickness to be used shall be
Click to view
							 image
(Equation 7-3)
where:
s
= Spacing of ribs or undulations.
t
= Minimum thickness.
t
e = Equivalent
				  thickness of the panel calculated as the net cross-sectional area of the panel
				  divided by the width, in which the maximum thickness used in the calculation
				  shall not exceed 2
t
.