Section 07: Load Development - wtcatko.com · Uniformly Distributed Load (UDL) Triangular or...

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1 Level 1: Section 07 – Version 3 © 2014 SBCA Section 07: Load Development 2 Section Downloads Download & Print TTT I Sec 07 Slides TTT I Sec 07 Handout_1 Load Distribution & Reaction Equations TTT I Sec 07 Handout_2 Truss Dead Load Weights TTT I Sec 07 Handout_3 ASCE 7-10 Tables (4-1 & C3-1) TTT I Sec 07 Handout_4 & TTT I Sec 07 Handout_5 Quiz Questions (5-26) TPI 1-2007 Selection (Section 01) Version 2.1 3 Load Development Outline Types of Loads Load Duration Minimum Load Requirements Load Distribution 4 Background Section 06 - Design Principles The structural design process can be broken into two functions: LOAD vs. RESISTANCE 5 ANSI/ASCE 7 TTT I Sec 07 Handout_3 ASCE 7-2010 referenced by IBC & IRC 2012 ASCE 7-2005 referenced by IBC & IRC 2006/2009 ASCE 7-2002 referenced by IBC & IRC 2003 6 Types of Loads Dead Loads Live Loads Environmental Loads

Transcript of Section 07: Load Development - wtcatko.com · Uniformly Distributed Load (UDL) Triangular or...

Page 1: Section 07: Load Development - wtcatko.com · Uniformly Distributed Load (UDL) Triangular or Tapered Load Point or Concentrated Load convert to 53 Load Distribution & Reaction Equations

1Level 1: Section 07 – Version 3© 2014 SBCA

Section 07: Load Development

2

Section Downloads Download & Print TTT I Sec 07 Slides

TTT I Sec 07 Handout_1 Load Distribution & Reaction Equations

TTT I Sec 07 Handout_2 Truss Dead Load Weights

TTT I Sec 07 Handout_3 ASCE 7-10 Tables (4-1 & C3-1)

TTT I Sec 07 Handout_4 & TTT I Sec 07 Handout_5 Quiz Questions (5-26)

TPI 1-2007 Selection (Section 01)

Version 2.1

3

Load Development Outline

Types of Loads

Load Duration

Minimum Load Requirements

Load Distribution

4

Background

Section 06 - Design Principles The structural design process can be broken into

two functions:

LOAD vs. RESISTANCE

5

ANSI/ASCE 7

TTT I Sec 07 Handout_3

ASCE 7-2010 referenced by IBC & IRC 2012ASCE 7-2005 referenced by IBC & IRC 2006/2009ASCE 7-2002 referenced by IBC & IRC 2003

6

Types of Loads

Dead Loads

Live Loads

Environmental Loads

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Dead Loads

Gravity load due to all permanent components of the structure Specified by the Building Designer

or Determined from actual weights of specified

materials Must be approved by the Building Official or Building

Designer

8

A downward vertical force created from the pull of gravity on a mass.

Gravity Load

9

ASCE 7 Table C3-1TTT I Sec 07 Handout_3

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Live Loads

Load Superimposed by the Use & Occupancy of the Building Includes impact loads

Does not include environmental loads wind, snow, or seismic

Section 05 – Truss Materials

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Floor & Roof Live Loads

Determined by the Building Designer In absence of a governing building code use

ASCE 7

12Image Courtesy of Trus Joist, A Weyerhaeuser Business

Floor Live Load

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ASCE 7 Table 4-1TTT I Sec 07 Handout_3

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Roof Live Load

Section 08 – Truss Design, Manufacture, & Installation Overview

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Environmental Loads

Snow, Wind, Seismic & Rain Determined by the Building Designer In absence of a governing building code use ASCE 7

16

Snow Load

17

Snow Load

18

Wind Load

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Wind Load

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Seismic Load

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Load Duration

Wood can support more load for a shorter time than for a longer one.

The longer the load is in place the weaker the wood becomes.

Load duration factors account for this behavior.

22

Load Duration

23

Normal Load Duration

24

Normal Load Duration

CD = 1.0

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Load Duration Factors

TPI 1-2007 Selection

Section 01

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Load Duration Factors

Permanent 0.90

Normal - 10 Years duration 1.00

Snow – 2 Months duration 1.15

Construction – 7 Days duration 1.25

Wind & Earthquake – 5-10 minutes 1.60

Impact* 2.00

* For FRT and pressure-preservative lumber and all connections subject to an impact load, the duration of load factor shall not exceed 1.6.

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Structural Specifications

Building Codes

ASCE 7

Minimum Load Requirements

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Minimum Load Requirements

What is the Building Type?

Hotel?

TTT I Sec 07 Handout_3

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Minimum Load Requirements

TTT I Sec 07 Handout_3

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Building Code History

Up until the year 2000, there were three major model building codes and one residential code National Building CodeTM (NBC-BOCA)

Standard Building CodeTM (SBC-SBCCI)

Uniform Building CodeTM (UBC-ICBO)

CABO One and Two Family Dwelling Code

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Building Code History

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Local Variations

City and County (e.g., New York City)

State Codes (e.g., Florida)

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Special Load Considerations

Concentrated Load Check

Partition Loads

Partial Loads

Unbalanced Loads Floors

Roofs

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Concentrated Load Check

TTT I Sec 07 Handout_3

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Partition Loads

36

Partition Loads

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Partial Load

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Partial Load

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Unbalanced Loads

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Special Considerations

Snow Drift Loads High/Low

Adjacent Roof

Sliding

Roof Projections

Intersecting Drifts

Rain On Snow Load

Snow and Ice Impact Loads

Water Accumulation

41Image Courtesy of Alpine Engineered Products, Inc.

Snow Drift Loads

42

Rain On Snow Load

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Snow and Ice Impact Load

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Water Accumulation

Water Accumulation

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Bottom Chord Live Loads

ASCE 7 lists the minimum design loads for attic spaces: Table 4-1

Truss Design software

•Uninhabitable attics without storage•Uninhabitable attics with storage•Habitable attics and sleeping areas

Always check first with your local building department to see how these provisions are interpreted.

Quiz 1

48

Load Development

How loads are represented?

How loads are distributed?

Reactions?

Load over an Area, PSF

Load along a Line, PLF

Load at a Point, LB

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Load over an Area

Load in pounds distributed over area

Pounds per square foot or PSF

Most design loads are in PSF

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Load along a Line

Load in PSF transformed along a line

Pounds per lineal foot of length or PLF

Span charts for beams often in PLF

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Load at a Point

Point or concentrated load in pounds

When calculating reactions, PSF or PLF loads can be simplified to point loads, but not when designing the structural member

52

Load Distribution

Design Load in PSF → → → PLF & Calculate Reactions

Only for Bulk Reactions

Uniformly Distributed Load (UDL)

Triangular or Tapered Load

Point or Concentrated Load

convert to

53

Load Distribution & Reaction Equations

TTT I Sec 07 Handout_1

54

Uniformly Distributed Load

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Uniformly Distributed Load

Most trusses are uniformly loaded because they are evenly spaced & support uniform design loads.

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Uniform Load Equation

Total Load = w x L

2

Lw2R1R

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Uniformly Distributed Load Example Problem 1

Given:

Find: R1 & R2

37 ft.

290 PLF

2

Lw2R1R

=

(290 lbs./ft.) x (37 ft.)

2= 5365 lbs.

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Uniformly Distributed Load Example Problem 2

Given:

Find: R1 & R2

16 ft.

440 PLF

2

Lw2R1R

=

(440 lbs./ft.) x (16 ft.)

2= 3520 lbs.

TTT I Sec 07 Handout_4

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Triangular Load

Tapered Load

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Triangular Load

Skewed or hip framing often results in triangularly loaded girders

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11Level 1: Section 07 – Version 3© 2014 SBCA

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Triangular Load Equation

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Triangular Load Equation

R1 - the light side is 1/3 total load:

R1 =

3

1

2

Lw

R2 - the heavy side is 2/3 total load:

R2 =

3

2

2

Lw

6

Lw =

3

Lw =

63

Triangular Load Equation

64

Triangular LoadExample Problem 1

Given:

Find: R1 & R2

18 ft.

175 PLF

=(175 lbs./ft.) x (18 ft.)

6= 525 lbs.

6

Lw =R1

3

Lw =R2 =

(175 lbs./ft.) x (18 ft.)

3= 1050 lbs.

x 2 = 1050 lbs.

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Triangular LoadExample Problem 2

=(390 lbs./ft.) x (40 ft.)

6= 2600 lbs.

6

Lw =R2

3

Lw =R1 =

(390 lbs./ft.) x (40 ft.)

3= 5200 lbs.

Given:

Find: R1 & R2

40 ft.

390 PLF

x 2 = 5200 lbs.

66

Point Load

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Point Load There are few situations where point loads

are the only load on a structural member. In most cases, point loads will occur along with

uniform loads.

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Point Load Equation

R1 + R2 = P

R1 + R2 = P

A + B = L

69

Point LoadExample Problem

Given:

Find: R1 & R2

21 ft.

800 #

=

4 ft.

L

AP R2 =

L

BPR1 = =

(800 lbs) x (4 ft.)

21 ft.= 152.38 lbs.

(800 lbs x 17 ft.)

21 ft.= 647.62 lbs.

B = L - A = 21 - 4

17 ft.

647.62 + 152.38 = 800

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Solving Quiz Problems

TTT I Sec 07 Handout_1

TTT I Sec 07 Handout_4

TTT I Sec 07 Handout_5

Quiz 2

72

R1TOTAL R2TOTAL

R1PT LD R2PT LD R1UDL R2UDL

R1TOTAL R1PT LD R1UDL

R2TOTAL R2PT LD R2UDL

Combination Load Distributions

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R1TOTAL R2TOTAL

R1PT LD R2PT LD R1TRI R2TRI

R1TOTAL R1PT LD R1TRI

R2TOTAL R2PT LD R2TRI

Combination Load Distributions

74

R1TOTAL R2TOTAL

R1UDL R2UDL R1TRI R2TRI

R1TOTAL R1UDL R1TRI

R2TOTAL R2UDL R2TRI

Combination Load Distributions

75

Combination Load DistributionsExample Problem

Given:

Find: R1 & R2

L

BPR1400 = =

(400 lbs x 20 ft.)

28 ft.= 285.7 lbs.

L

APR2400 = =(400 lbs x 8 ft.)

28 ft.= 114.3 lbs.

285.7 + 114.3 = 40076

Combination Load DistributionsExample Problem (continued)

Given:

Find: R1 & R2

L

AP R2250 =

L

BPR1250 = =

(250 lbs x 5 ft.)

28 ft.= 44.6 lbs.

=(250 lbs x 23 ft.)

28 ft.= 205.4 lbs.

44.6 + 205.4 = 250

77

Combination Load DistributionsExample Problem (continued)

Given:

Find: R1 & R2

R2250 = 205.4 lbs.

R1250 = 44.6 lbs. R1400 = 285.7 lbs.

R2400 = 114.3 lbs.

R1TOTAL = 285.7 + 44.6 = 330.3 lbs.

R2TOTAL = 114.3 + 205.4 = 319.7 lbs.

330.3 lbs + 319.7 lbs. = 400 lbs. + 250 lbs. = 650 lbs.

Quiz 3

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R1 = R2 =w L

2R1 =

w L2

13 =

w L6

R2 =w L2

23 =

w L3

Do Not Apply t o Part ial Loads!

Do Not Applyt o Part ial Loads!

Partial Load Distributions

Centroid

80

Centroids

Do not apply to Loads

Every shape has a centroid

TTT I Sec 04 Handouts

81

Partial Load Distribution Partial Load DistributionsExample Problem

Given:

Find: R1 & R2

R1 R2

300 PLF

30 ft.

10 ft.

12 ft.

½ x 12 ft. x 300 PLF = 1800 lbs.

L

AP R2 =

L

BPR1 =

R1 R2

300 PLF

30 ft.

1800 LB

8 ft.

10 ft.

12 ft.

4 ft.

=(1800 lbs x 12 ft.)

30 ft.= 720 lbs.

=(1800 lbs x 18 ft.)

30 ft.= 1080 lbs.

720 lbs + 1080 lbs. = 1800 lbs.82

Quiz 4

84

Simple Span vs. Multiple Span

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Loads from Framing Layouts

86

Loads from Framing Layouts

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Loads from Framing Layouts

88

Truss Total Load = 40 SF x 45 PSFTruss Total Load = 1800 lbs.

Loads from Framing Layouts

R1 R2

R1 = R2 = 1800 lbs. / 2 = 900 lbs.

89

Loads from Framing Layouts

What is the PLF?90

R1 = R2 =

R1 = R2 =

R1 = R2 = 900 lbs.

2

2090

2

1800

Loads from Framing Layouts

What if the trusses were not spaced at

2 ft. on center?

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PLF = TW x PSF

Loads from Framing Layouts

92

R1 = R2 =2

Lw

Loads from Framing Layouts

2

2060=

2

1200= = 600 lbs.

93

R1 = R2 = 2Lw

R1 = R2 = 22072x = 2

1440

R1 = R2 = 720 LB

Loads from Framing Layouts

94

Loads from Framing Layouts

95

Loads from Framing Layouts

96

Loads from Framing Layouts

R1 = R2 = 2Lw

R1 = R2 = 2

14450 x = 26300

R1 = R2 = 3150 lbs.

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17Level 1: Section 07 – Version 3© 2014 SBCA

Quiz 5

98

Load Paths

Quiz Question 20

Quiz 6

100

Dead Load Calculations

TTT I Sec 07 Handout_3

ASCE 7 Table C3-1 TTT I Sec 07 Handout_3

101

ASCE 7 Table C3-1 continuedTTT I Sec 07 Handout_3

102

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18Level 1: Section 07 – Version 3© 2014 SBCA

103

Slope Correction Factor

Slope Correction

Factor =12

12PSCF

22

Slope Correction Factor = cos

1

12

12PSCF

22 = 1.414 7 PSF (1.414) ≈ 10 PSF

Slope Correction Factor

104

105

Roofing Felt

PLF = TW x PSF PSF = OCPLF

= 2.75 PSFPSF = 25.5

Ex. What is the weight of a roof truss with 2x6 chords and 2x4 webs at 2 ft o.c.?

Truss Weight

TTT I Sec 07 Handout_2

106

107

26' roof truss, 24" o.c., 2x4 bottom chord, 2x6 top chord, 2x4 webs, 6/12 pitch

5/8" OSB roof sheathing

15 pound felt

280 pound shingles

6" fibrous glass insulation

5/8" Gypsum board ceiling

Dead Load Calculations Example Problem

Given:

Calculate horizontal loads & adjust top chord load for slope.

108

8.42x82x102x8

7.22x62x82x8

6.62x42x82x8

7.22x62x102x6

6.62x42x102x6

5.92x42x82x6

6.22x62x62x6

5.52x42x62x6

4.82x42x42x6

5.62x42x82x4

4.32x42x42x4

Weight per Lineal Foot

WebsBottomChord

TopChord

Dead Load Weight of Roof Trusses

PSF 2.42

8.4

OC

PLFPSF

2.4 PSF divided evenly between TC & BC = 1.2 PSF

Truss Dead Load

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5/8" OSB: Plywood = 0.4 PSF per 1/8" of thickness

5 x 0.4 = 2.0 PSF

Shingles: Specified at 280 lbs. per square (100 square feet)

280 lbs. /100 SF = 2.8 PSF

Felt: 15 lbs. per square (100 square feet)

15 lbs. /100 SF = 0.15 PSF

Roofing Material

110

Item TC PSF1/2 Truss 1.25/8" OSB 2.0

15 lb Felt 0.15

280 lb Shingles 2.8

Total 6.15

Total Top Chord

111

Fibrous Glass Insulation 1.1 PSF per inch of thickness

6 x 1.1 = 6.6 PSF

Gypsum Board (not Sheathing) 0.55 per 1/8" of thickness

5 x 0.55 = 2.75 PSF

1/2 Truss 1.2 PSF

BC Dead Loads = 6.6 + 2.75 + 1.2 Total BC Dead Load = 10.55 PSF

Bottom Chord

112

Item TC PSF BC PSF

Truss 1.2 1.2

5/8" OSB 2.0 -

15 lb Felt 0.15 -

280 lb Shingles 2.8 -

6" Fibrous Insul. - 6.6

5/8" Gypsum - 2.75

Total 6.15 10.55

Slope Correction

6.88 -

12

12PSCF

22

12

126SCF

22

PSF 6.8815.61180.1SCF

Dead Load Summary

113

Dead Load Diagram

Quiz 7

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