Structural Plan Review

Walls and Bracing

Lesson 6

Updated: March 2017

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Headers

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Header Size Determination

Based on floor design

Use Table R502.5(1) for headers in exterior walls

Use Table R502.5(2) for interior walls

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Headers

• Table R502.5(1) exterior bearing walls

• Table R502.5(2) interior bearing walls

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Headers

5

Exterior

walls

Interior

walls

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Headers • What size Doug Fir header and number of

jacks:

• Interior wall on first floor of a two story house

9’

24’

7

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Headers - answer

Supports one floor

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Skill Check

• What size header do I need:

• One-story, 28’ wide house in Salem

• Header supports a roof and ceiling only

• Window is 36” wide x 62 tall”

• Doug-fir

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Skill Check - answer

• One-story, 28’ wide house in Salem

• Header supports a roof and ceiling only

• Window is 36” wide x 62 tall”

• Hem-fir

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Skill Check

• What is the minimum size header over

the window?

• House is 36’ wide

• The 2nd floor joists

bear on center wall

and rear wall.

• 25 psf snow load

• Window is 8’wide

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Skill Check -answer

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Beams Constructions

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Beam Design Assumptions Know structural theory

Knowledge of arithmetic and

basic algebra

Simple loading criteria

Uniform loads

Beam simple span

Shear will not to govern

Allowable stress design

Wood and LVL only

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Beam Load Calculations

In the field of construction, beam load

calculations can become truly critical

A simple yet effective way of calculating beam

loads is discussed here through derived formulas

and expressions

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Point load: A load or weight subjected over a point

area is called a point load. However, mathematically a

point load doesn’t look feasible, simply because any

load will need to have a certain area of impact and

cannot possibly balance over a point, but if the impact

area is to small compared to the length of the beam,

may be taken as defined.

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Equally Distributed load: As the name implies a

load that’s equally aligned across the whole beam is

termed an equally distributed load.

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Uniformly Varying Load: Loads distributed over

a beam which produces a uniformly increasing

load gradient across the entire beam end to end.

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Beam Reaction

Referring to the diagram

alongside, let’s consider

a beam being supported

at its ends (left and

right), denoted by the

letters A and B

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Now, there are primarily a couple of forces ( turning effect ) that’s

acting over the beam ends A and B, clockwise and counter-

clockwise moment of force

Let there be point loads acting on the beam over

positions marked W1, W2 and W3.

Also let: Ra = Reaction at the end A of the beam

Rb = Reaction at the end B of the beam

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Since the moment of force over a supported beam is

equal to the point load (weight here) and its distance from

the support or the pivot, total clockwise moment acting at

point A may be given as:

(W1 x a) + (W2 x b) + (W3 x c)

Also, the counter-clockwise moment of force acting over

point B must be: Rb x I

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Now, because the beam is in equilibrium, implies that the two moments

of force must be equal in magnitudes, therefore equating the two

expressions gives:

(W1 x a) + (W2 x b) + (W3 x c) = Rb x L

Rb = (W1 x a) + (W2 x b) + (W3 x c)/I

The equilibrium with the beam also implies that:

Ra + Rb = 2 [ (W1 x a) + (W2 x b) + (W3 x c)] / L

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Now as per the conditions of equilibrium, the algebraic

sum of all horizontal components in the above expression

becomes immaterial and can be nullified.

Therefore, the final equation becomes

Ra = (W1 + W2 + W3) - Rb

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Skill Check

• How many 2x4 jack studs

would I need under this beam?

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Skill Check - answer

• How many 2x4 jack studs would I need

under this beam?

9’

2k 4k 6k 8k 10k

2 x 4

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Columns and Supports

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Columns

9’

3.3k 6.6k 10k

2 x 6

9’

2k 4k 6k 8k 10k

2 x 4

Rule of thumb

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Skill Check

• What size

posts

would I

expect? PB02 (12)

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Columns

> 10k use manufactured lumber

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Skill Check - answer

• What size

posts

would I

expect?

• 9’ column PB02 (12)

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Skill Check

• What is the maximum wall height allowed?

• 2x4 walls with continuous OSB sheathing

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Skill Check - answer

• What is the maximum wall height

allowed?

• 2x4 walls with continuous OSB

sheathing and a CS-PF header

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Stud Walls

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Wall Systems

• Topics

• Stud walls

• Wall height

• Tall walls

• Wall bracing

• Headers

• Lintels

• Columns

• Wall coverings

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Tall Walls

Section R602.3.1

Size, height and spacing

Maximum Height:

Table R602.3.1

Tall Wall Conditions:

Wind speeds 110 mph

Grade #2 or better

Snow load ≤ 25 PSF

Joist, rafter and truss

span ≤ 12’

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Tall Walls

• What if the tall walls are carrying more

than 6’ of tributary area?

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Wall Stud Design Check

Studs must be continuous from sole to top plate

Standard grade and higher, use Table R602.3(5)

Utility grade restricted to:

16” maximum spacing

Supports roof/ceiling only

Maximum height:

8’ load bearing walls

8’ exterior walls

10’ non-load bearing walls

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Wall Stud Design Seismic Design Categories A, B, C, D and D(2)

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Story Height

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Stud Wall Species and Grades

R602.2

SELECT STRUCTURAL

#1

#2

#3

STUD

CONSTRUCTION

STANDARD

UTILITY

NO

T A

S G

OO

D

BE

TT

ER

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Stud - Size, Height, Spacing

Table R602.3(5)

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Stud - Size, Height, Spacing

12-0” MAX STUD HT

11’-7” MAX FLOOR - FLOOR HT

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R301.3 Story Height Maximum story height = 11'-7"

I-joists floor joists

11'-7"

max.

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Stud - Size, Height, Spacing

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The Habitable Attic

Using Table R602.3(5), determine the stud size of

the walls highlighted below.

1st floor

Walkout basement

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The Habitable Attic Walkout basement:

Supporting, two floors & habitable attic

Required studs = 2x6@16"o.c.

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The Habitable Attic

1st floor:

Supporting, one floors & habitable

attic

Required studs = 2x6@24"o.c. min.

Table

R602.3(5)

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Skill Check What size of studs are required for each floor?

Habitable attic trusses span 34’

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Skill Check - answer What size of studs are required for each floor?

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Wall Coverings

• Scenario:

• Customer calls and

says contractor did

not put Tyvek

under the vinyl

siding.

• Is it required?

• Cite the code

reference.

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Wall Coverings - answer

R 703.2 and R 703.1.1

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Wall Construction and bracing

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Objectives

Determine stud size and spacing for vertical load.

Determine compliance alternatives for resistance of

horizontal load.

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KING STUDS

Fig. R602.3(2)

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Understanding Basics of Bracing

Basic provisions of Lesson 4:

The basic provisions of lesson 4 will cover the bracing provisions

in Chapter 6 for the basic dwelling unit. The module will move

through the code provisions in R602.10 and other related

provisions in non-sequential order as they apply to structural

bracing.

What is bracing?

Bracing is the structural component of a building that resists the

lateral forces imposed on the structure by wind or seismic events.

Bracing is typically part of the vertical wall framing system and

can be sections of wall that are sheathed with plywood, gypsum

board, fiberboard, cement plaster and carious other materials.

The walls resist lateral forces through their attachment to the

roof, floor, and foundation structures.

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The Lateral Load Path As we learned in Lesson 3 all buildings

must be braced to resist the lateral loads

due to wind and seismic. Wall

construction must include bracing to

resist imposed lateral loads

resulting from wind or seismic

loading and to provide stability

to the structure. When subjected

to wind loads, the upper portion of the

structure moves horizontally while the

lower portion is restrained at ground level.

During an earthquake, the

ground motion displaces the

foundation while the top portion

of the structure tries to remain

stationary. In both of these cases

the bracing resists the differential

movement and thus prevents or

limits damage to the building.

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The Lateral Load Path cont.

A typical residential structure experiences lateral loading starting at the roof

sheathing that transfers the load to the rafters/trusses then through the double top

plate to the wall studs to the sole plate to the floor sheathing to the rim joists/floor

joists to the mud sill to the foundation stem wall to the supporting soil. In either

the wind or seismic loading condition the walls will distribute one-half of the wall

height load into the double top plate and the lower half of the wall will transfer

loading directly into the foundation

system. The lower half wall loading

will not affect the forces being

transferred into the brace/shear

walls. In the seismic loading

condition the weight of the endwalls

will be added to the forces going

into the brace/shear walls. With

this understanding it is time to

adventure into the world of wall

bracing in Section R602.10 of the

Residential Code.

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Table R602.3(5) – Bearing Wall

Known values:

Stud size

Stud height

Story level

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Table R602.3(5) – Non-bearing Wall

Known value:

Stud size

Stud height

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Wall Bracing

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Wall Bracing

Section R602.10,

“Prescriptive” Wall Bracing

Section R602.12, “Any

additional” Wall Bracing

Other wall bracing:

Engineered solutions

Proprietary products

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“Classic” Wall Bracing

Section R602.10.

Prescriptive solution.

Based on:

Braced wall panels

Braced wall lines.

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Braced Wall Panels

Full height of wall.

Minimum length.

(Based on sheathing and

material type.)

Length

Heig

ht

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Braced Wall Panels

Full height of wall.

Minimum length.

(Based on sheathing and

material type.)

Vertical, horizontal joints

permitted.

Multiple

pieces of

sheathing

allowed

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Braced Wall Lines

Straight lines

In each plan

direction

Permitted to “float”

At each floor

B C

2

1

A

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Prescriptive Bracing Types

Intermittent bracing

Sheath at BWP locations

only

Continuous sheathing

Sheath all exposed areas

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Continuous Sheathing Methods

CS-WSP: wood

structural panels.

CS-SFB: structural

fiberboard

CS-G: wood structural

panels at garage.

CS-PF: wood structural

panel portal frame.

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Engineered Shear Walls

Stud size, spacing

Sheathing type, thickness

Fastening schedule

Hold-down requirement,

capacity

Anchor bolt location,

capacity

length

he

igh

t

stud

size

sheathing

thickness

anchor

bolts

hold-down

capacity

edge,

field

nailing

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Wall Bracing

• Two methods of analysis

3

2 1

4

R602.10.2

Intermittent

Method

R602.10.4

Continuously

Sheathed Method

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Review Lesson 4: Wall Systems

Topics:

1. Stud walls

a) Wall height

b) Tall walls

2. Wall bracing

3. Headers

4. Lintels

5. Columns

6. Wall coverings

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