2012 irc simplified wall bracing 4-30 -...

2012 IRC Simplified Wall Bracing Provisions 4/28/2015

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This webinar provides an explanation of the 2012 International Residential Code® (IRC®) simplified wall bracing requirements. The seminar will focus on basic requirements and step through the process of applying the Simplified Wall Bracing procedure.

2012 IRC Simplified Wall Bracing


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Sandra Hyde, P.E.

ICC Senior Staff Engineer

ICC Product Development


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Polling questions



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GoalParticipants will successfully apply the provisions of Section R602.12 of the 2012 IRC to problems involving bracing requirements for wood-framed residential structures in their region.


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Objectives Upon Completion of this webinar, you will be able to:

› Identify methods of resistance of a dwelling to lateral forces such as high winds or earthquakes.

› Identify bracing requirements of Section R602.12.

› Use the simplified wall bracing provisions of Section R602.12.


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Wind

Force =Pressure x Area

Force =Mass x Acceleration

Seismic



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Wind Speed


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Wind Design

Required


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SDC – United States (2012 IRC)



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Resisted by Bracing

Racking

Resisted by Anchors

Base Shear

Resisted by hold-downs & Dead Load

OverturningEffects of Forces


Resisted by Bracing

RackingEffects of Forces


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Lateral ForcesRacking


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Lateral Forces2003 Missouri Tornado

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Wall FramingHinge

Hinge


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Wall Framing

Panelresistanceimparted towall framing(Prevents hinging)



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Resisted by Anchors

Base ShearEffects of Forces


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Base Shear

Anchors

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Resisted by hold-downs & Dead Load

OverturningEffects of Forces


February 2008

Macon Co.

‘Super Tuesday’ Tornado

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Overturning


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hold-downs



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Upper Story Hold-downs


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The goal of simplified wall bracing is to cut the number of options down to speed up the process of determining bracing length.


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Prescriptive Limits The structure must meet the following requirements: Seismic Design Category (SDC) A, B, or C (SDC A or B for townhouses) Basic Wind Speed of 90 mph or less with Wind Exposure Category A or B One or two story structure Wood structural panel (WSP) or structural fiberboard sheathing (SFB) is

used to brace exterior walls with ½ in gypsum board fastened to the interior side of walls

60 ft. maximum length and width of the building Max eave-to-ridge height of 15 ft. Wall max height of 10 ft. Max ratio between long and short side of building: 3 to 1 Max cantilever of 24 inches beyond foundation No cripple walls in two story buildings



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Wind Exposure

Prescriptive LimitsWind Speed =

90 mph or less

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Prescriptive Limits

WSP

1 or 2 story

SFBBraced Wall Panel

Material

Building Length


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Eave to Ridge Height

Prescriptive Limits

Wall Height

< 15 ft.

< 10 ft.



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Maximum Cantilever

Prescriptive Limits

Max. Length to Width Ratio < 3 to 1

≤ 24 in.


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SDC A or B

1 or 2-family SDC C

Prescriptive Limits

Cripple walls on single story only

Upper Story

Cripple Wall

Bottom Story

Single Story

Cripple Walls


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Advantages to the Simplified Method:› No seismic requirements› Bracing only occurs on the perimeter (exterior walls)

(No braced wall line length or spacing)› No additional adjustment factors to check› No interpolation

2012 IRC Simplified Wall Bracing 33


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Procedure:

1. Draw a rectangle around the perimeter of the building and stagger the required number of bracing units along the four wall lines. Rectangle sides 60 feet long or less Ratio of side length a maximum of 3:1

R602.12.1


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Rectangle Circumscribing an Enclosed Building

Figure R602.12.1


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Procedure cont.:

2. Identify the number of bracing units required on each side of the rectangle and their minimum length.

R602.12.4


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Minimum Number of Bracing Units on Each Side of the Circumscribed Rectangle

Simplified Wall Bracing

Story Level

Eave-to Ridge Height(Feet)

Minimum Number of Bracing Units on Each Long Side a,b

Minimum Number of Bracing Units on Each Short Side a,b

Length of short side (ft.) c Length of long side (ft.) c

10 20 30 40 50 60 10 20 30 40 50 60

101 2 2 2 3 3 1 2 2 2 3 3

2 3 3 4 5 6 2 3 3 4 5 6

151 2 3 3 4 4 1 2 3 3 4 4

2 3 4 5 6 7 2 3 4 5 6 7

Table R602.12.4

a. Interpolation shall not be permitted.b. Cripple walls or wood-framed basement walls in a walk-out condition of a

one-story structure shall be designed as the first floor of a two-story house.c. Actual lengths of the sides of the circumscribed rectangle shall be

rounded to the next highest unit of 10 when using this table.


MaterialStud Spacing

& Fastener Criteria

Fastener Spacing Criteria

Bracing Unit Method

Minimum Bracing Unit Length (feet)

Wood Structural Panel Table R602.3(3) 6'' edge

12'' field

Continuous 3

Intermittent 4

Structural Fiberboard Sheathing

Max 16''spacing

Table R602.3(1)

3" edge 6'' field

Continuous 3

Intermittent 4

Bracing Methods for Simplified Wall Bracing

a. Mixing of wood structural panel and structural fiberboard sheathing in one building is not permitted.

b. Continuous and intermittent bracing units may be mixed from one story to another. c. Continuous and intermittent bracing unit methods may not be mixed within one

story.

R602.12.2, R602.12.3

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Procedure cont.:3. Bracing Requirements

Wall lines 8 feet or longer must have at least one bracing unit placed along the wall line.

Each wall line shall have a bracing unit within 12 feet of the end of the wall line (wall corner).

Bracing units shall be within 20 feet of one another.

R602.12.5


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Procedure cont.:4. Narrow bracing units

Add narrow bracing units when full length units do not fit if additional bracing is required.

R602.12.6


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Narrow Bracing Method

Equivalent Bracing

UnitsCS-G 0.5

CS-PF 0.5

PFH 1

PFG 0.75

Narrow Bracing Methods for Simplified Wall Bracing

R602.12.6


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Narrow Bracing Methods

Method CS-G

H8’ to 10’

H/6 Method CS-PF


8’ to 10’


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Narrow Bracing MethodsH

8ꞌ to 10ꞌ

16"

Method PFH

H/4

H8ꞌ to 10ꞌ

Method PFG2012 IRC Simplified Wall Bracing

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Lateral Support and Stem Walls› Use Section R602.10.8.2 to add bracing to rafter or

truss areas to complete the load path from roof sheathing to the bracing unit.

› Stem walls … Less than 4 feet long and

More than 1 foot tall

… need to meet the requirements of Section R602.10.9 when the concrete wall is less than 6 inches thick or when a masonry wall is used.

R602.12.6



Rafters connected to the top plates of braced wall panels with blocking:

Figure R602.10.8.2(1) Table R602.3(1)


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Narrow Wall Requirements Only required for walls less than 48" long.

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Example 1› SDC A› Wind 90 mph, Wind Exposure B› Method WSP › 2 Story› Walls – Top Story - 9 ft. › Walls – Bottom Story - 10 ft. › Eave to ridge height - 10 ft.

Example Highlights:› Strategic placement of bracing units

Two Story

90mph

SDCA

NA


24'-

11"

36'-10"

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Round to 30 ft

Round to 40 ft

Upper Story

1.Draw rectangle around the entire building

Check the length of the N-S and E-W sides the of rectangle

Less than 60 ft.?

OK



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Table R602.12.4 Minimum Number of Bracing Units

Walls – top story - 9 ft Eave to ridge height - 10 ft

24'-

11"

36'-10"

50

Upper Story

WSP WSP

WSPWSP WSP

WSP 1. 2 bracing units required along each wall line

2. With WSP, the minimum bracing unit length is 4 ft.

3. Panels must be within 12 ft. of the end of wall line and within 20 ft. of one another.

Sufficient space?Yes, there are more than two panels on each wall within 12 feet of the end of the wall and 20 feet of each other

24'-

11"

36'-10"

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Upper Story

WSP WSP

WSP

WSP

1. 2 bracing units required along each wall line



Sufficient space?Yes, there are two panels on each wall within 12 feet of the end of the wall and 20 feet of each other


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24'-

11"

36'-10"

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Upper Story

WSP WSP

WSPWSP WSP

WSP

WSP WSP

WSP

WSP

Total required bracing

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Example 1 – Bottom Story› SDC A› Wind 90 mph, Wind Exposure B› Method WSP › Walls – Bottom Story - 10 ft. › Eave to ridge height - 10 ft.


36'-10"Bottom Story

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Assume 40 ft

Assume 30 ft

24'-11"

1.Draw rectangle around the entire building

Check the length of the N-S and E-W sides the of rectangle

Less than 60 ft.?

OK


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Walls – bottom story - 10 ft Eave to ridge height - 10 ft

36'-10"Bottom Story

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24'-11"

WSP WSP

WSPWSP WSP

WSP




Sufficient space?Yes, there are three panels on each wall within 12 feet of the end of the wall and 20 feet of each other.

36'-10"Bottom Story

24'-11"

WSP WSP

WSP

WSPWSP

WSP




Sufficient space?No, there is only space for three panels on each wall. All panels are not a minimum of 4 ft in length.

4′-6ʺ

5′-6ʺ

3' 3′-6ʺ

4′-6ʺ

4′-6ʺ

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36'-10"Bottom Story

24'-11"

WSP

WSP

WSP

WSP


2. With CS-WSP, the minimum bracing unit length is 3 ft.


Sufficient space?Yes, all panels are at

least 3 feet in length. Adding the panel lengths together gives more than 12 feet of bracing.

4′-6ʺ

5′-6ʺ

3' 3′-6ʺ

4′-6ʺ

4′-6ʺCS-WSP

CS-WSP

CS-WSP

CS-WSP

CS-WSP

CS-WSP

13 f

t

12

.5 f

t

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Bottom Story

WSPWSP

WSP

WSP

WSP

CS-WSP

CS-WSP

CS-WSP

CS-WSP

CS-WSP

CS-WSP

CS-WSP

CS-WSP CS-WSPCS-WSP

CS-WSP

CS-WSP

Total required bracing – all must be CS-WSP on the

bottom story

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Example 2› SDC B› Wind 90 mph, Wind Exposure B› Method CS-WSP › 1 Story› Walls - 9 ft. › Eave to ridge height - 12 ft.

Example Highlights:› Strategic placement of bracing units

One Story

90mph

SDCB

NA



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49'-4"

59'-8"

1. Draw rectangle around the entire building

2. Check the length of the N-S and E-W sides the of rectangle

Less than 60 ft.?

OK61

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Bracing: Simplified Wall Bracing


Walls - 9 ftEave to ridge height - 12 ft

49

'-4

"

59'-8"


2. With CS-WSP, the minimum bracing unit length is 3 ft.


Sufficient space?Yes, CS-PF units are only worth 0.5 units each so 5 B.U.s min will be needed on the south wall.

Furthermore, 3 CS-PF are needed to space units less than 20 ft. apart.

10'-2"18' 19'-6" 12'

CS-WSP

CS-WSP

CS‐PF

CS‐PF

CS‐PF

CS-WSP

CS-WSP

CS-WSP

CS-WSP

CS-WSP

CS-WSP


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59'-8"

Sufficient space?

Yes, 4 CS‐WSP bracing units fit along the east and west wall lines.

CS-WSP

CS-WSP

CS-WSP

CS-WSP

CS-WSP

CS-WSP

CS-WSP

CS-WSP

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7'-0"

9'-7"

14'-1"

6'-2"

8'-3"

5'-6"

3'-2"

16'-8"

22'-2"

4 bracing units required along each wall line

Panels must be within 12 ft. of the end of wall line and within 20 ft. of one another.

59'-8"

What about the exterior wall lines in the courtyard

area?

CS-WSP

CS-WSP

CS-WSP

CS-WSP

CS-WSP

CS-WSP

CS-WSP

CS-WSP

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49'-4"

59'-8"

Each exterior wall needs at least one

bracing unit.66

CS-WSP

CS-WSP

49'-4"


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59'-8"

CS-WSP

CS-WSP

CS-WSP

CS-WSP

CS-WSP

CS-WSP

CS-WSP

CS-WSP

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49'-4"

CS-WSP

CS-WSP

CS-WSP

CS-WSP

CS‐PF

CS‐PF

CS‐PF

CS-WSP

CS-WSP

CS-WSP

CS-WSP

CS-WSP

CS-WSP

Total bracing units

required

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Sandra [email protected]

888-422-7233 x7755


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