Uses and Limitations of SB-2 - Ontario Association of ... - Liz Hilfrich - Uses and... · Uses and...

Uses and Limitations of

SB-2

Liz Hilfrich, P. Eng. CBCO

Uses and Limitations of SB-2

SB-2 is one of two sources of fire

resistance ratings recognized by Part 3 of

the OBC, and one of three sources in Part

9 of the OBC

It is based on Appendix D to the NBC


Because it is extremely generic, the

assigned times are more conservative

than either listed assemblies or SB-3

assemblies

It is also limited in the component

materials included


There are sections for

Masonry and Concrete Walls

Reinforced and Prestressed Concrete Floor

and Roof Slabs

Wood and Steel Framed Walls, Floors and

Roofs

Solid Wood Walls, Floors and Roofs

Solid Plaster Partitions


There are sections for

Protected Steel Columns

Individually Protected Steel Beams

Reinforced Concrete Columns

Reinforced Concrete Beams

Pre-stressed Concrete Beams

Glued-Laminated Timber Beams and

Columns


It also contains information with respect to:

The flame spread rating and smoke

developed classification of various common

construction materials

Non-combustibility testing

Protection of Openings


Let’s start by looking at the provisions for

masonry and concrete walls, both unreinforced

and reinforced


For masonry and concrete, SB-2 uses an

“equivalent thickness” measure

The required equivalent thickness will depend

on the type of concrete used and the desired

fire rating


Section 1.6 provides the methods of

determining the equivalent thickness of

brick, block, hollow core pre-cast concrete,

ribbed or undulating concrete panels and

tapered concrete panels


A plaster finish and gypsum wall board will

also contribute, with limitations, to the

equivalent thickness

The time contribution of these materials is

different for the fire exposed and non-fire

exposed sides of the assembly


The contribution of finishes on the fire exposed

side of the assembly is determined from Tables

2.3.4.A. or 2.3.4.B.

On the non-fire exposed side, Table 1.7.1.

provides a multiplying factor varying from 0.5 to

1.75 times depending on the type of plaster and

the type of masonry or concrete


Table 2.1.1. lists the minimum required

equivalent thickness for the various

masonry and concrete types for fire

resistance ratings from 30 minutes to 4

hours


Ratings for reinforced & prestressed

concrete floor and roof slabs are also

determined using thickness

measurements for both the concrete slab

and the concrete cover over the

reinforcement


Specific provisions are included for

composite slabs composed of two layers

of different types of concrete, or of

concrete topped with gypsum wallboard,

portland cement or terrazzo


Plaster finishes on the underside of

reinforced concrete floors provide a time

contribution on the same basis as for

concrete or masonry walls.


Under SB-2 the maximum attainable fire

resistance rating for wood and steel framing is

90 minutes.

All of the times given in Article 2.3.4. are

contributions to a total rating and are not

intended to be treated as a rating of the

individual materials by themselves.


Interior walls need a membrane on both

sides

Exterior walls need exterior sheathing and

cladding

Floor assemblies need subflooring and

finished flooring


Wallboard membranes are permitted to be

installed in multiple layers only as listed in

Table 2.3.4.A. (Double 12.7 mm Type X

gypsum wallboard).


When calculating the fire resistance rating, a

time assignment is included:

For the membrane or finish only on the fire

side, not on the unexposed side

For the framing members

For any additional protection


There are specific provisions included for

how to measure a plaster thickness,

framing members, fastening of

membranes and permitted openings in

ceiling membranes of assemblies


SB-2 Article 2.3.12. contains provisions for

determining a rating of up to 60 minutes

based only on a ceiling membrane, not on

the entire assembly

This option prohibits any openings in the

ceiling membrane.


Section 2.3.14. lists the requirements for

untested wired glass assemblies used as

a closure in a fire separation as permitted

by Sentence 3.1.8.14.(2) of the OBC


Section 2.4 provides minimum thickness

information for solid wood walls, floors and

roofs for fire resistance rating for up to 90

minutes

Section 2.5 deals with solid plaster

partitions with fire resistance ratings of up

to 4 hours


Protection of steel columns is addressed

in many forms, including the use of

concrete, block, brick, clay tile, plaster,

sheet steel and insulation, and gypsum

wallboard on the exterior of the column

Concrete filled hollow steel columns are

also included


Let’s have a closer look at Table 2.6.1.F.

for drywall protection of a column

This requires that you know the M/D ratio for the

column. This information is available in AISC

and/or CISC design manuals


Where a steel beam is exposed on three

side, methods of protecting the beam are

provided in Section 2.7. of SB-2

The methods listed are unfortunately

limited to concrete and plaster, and do not

include any gypsum board options


The fire resistance rating determination for

reinforced concrete columns is dependant

of the type of concrete, the effective length

of the column and the cross sectional area

of reinforcing

A plaster finish can contribute to the cover

over the reinforcing, but not to the required

size of the column itself


For reinforced and pre-stressed concrete

beams, the main factors are the type of

concrete and the amount of concrete

cover protecting the reinforcing

For reinforced concrete beams, there are

limitations to the maximum rating based

on the width of the beam


Lastly, Section 2.11. provides the formulas

to be used establish the fire resistant

ratings for glue-laminated timber beams

and columns

It is most likely intended to be used for fire

resistance ratings greater than those

provided by the heavy timber construction

provisions


There are separate equations for beams

and columns exposed to fire on three or

four sides

Some structural information is required to

complete the calculations


Questions?

Uses and Limitations of SB-2 - Ontario Association of ... - Liz Hilfrich - Uses and... · Uses and...

Documents

Transcript of Uses and Limitations of SB-2 - Ontario Association of ... - Liz Hilfrich - Uses and... · Uses and...