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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
2Level 1: Section 07 – Version 3© 2014 SBCA
7
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
10
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
11
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
3Level 1: Section 07 – Version 3© 2014 SBCA
13
ASCE 7 Table 4-1TTT I Sec 07 Handout_3
14
Roof Live Load
Section 08 – Truss Design, Manufacture, & Installation Overview
15
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
4Level 1: Section 07 – Version 3© 2014 SBCA
19
Wind Load
20
Seismic Load
21
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
5Level 1: Section 07 – Version 3© 2014 SBCA
25
Load Duration Factors
TPI 1-2007 Selection
Section 01
26
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.
27
Structural Specifications
Building Codes
ASCE 7
Minimum Load Requirements
28
Minimum Load Requirements
What is the Building Type?
Hotel?
TTT I Sec 07 Handout_3
29
Minimum Load Requirements
TTT I Sec 07 Handout_3
30
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
6Level 1: Section 07 – Version 3© 2014 SBCA
31
Building Code History
32
Local Variations
City and County (e.g., New York City)
State Codes (e.g., Florida)
33
Special Load Considerations
Concentrated Load Check
Partition Loads
Partial Loads
Unbalanced Loads Floors
Roofs
34
Concentrated Load Check
TTT I Sec 07 Handout_3
35
Partition Loads
36
Partition Loads
7Level 1: Section 07 – Version 3© 2014 SBCA
37
Partial Load
38
Partial Load
39
Unbalanced Loads
40
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
8Level 1: Section 07 – Version 3© 2014 SBCA
43
Snow and Ice Impact Load
44
Water Accumulation
Water Accumulation
45 46
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
9Level 1: Section 07 – Version 3© 2014 SBCA
49
Load over an Area
Load in pounds distributed over area
Pounds per square foot or PSF
Most design loads are in PSF
50
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
51
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
10Level 1: Section 07 – Version 3© 2014 SBCA
55
Uniformly Distributed Load
Most trusses are uniformly loaded because they are evenly spaced & support uniform design loads.
56
Uniform Load Equation
Total Load = w x L
2
Lw2R1R
57
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.
58
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
59
Triangular Load
Tapered Load
60
Triangular Load
Skewed or hip framing often results in triangularly loaded girders
11Level 1: Section 07 – Version 3© 2014 SBCA
61
Triangular Load Equation
62
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.
65
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
12Level 1: Section 07 – Version 3© 2014 SBCA
67
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.
68
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
70
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
13Level 1: Section 07 – Version 3© 2014 SBCA
73
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
14Level 1: Section 07 – Version 3© 2014 SBCA
79
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
15Level 1: Section 07 – Version 3© 2014 SBCA
85
Loads from Framing Layouts
86
Loads from Framing Layouts
87
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?
16Level 1: Section 07 – Version 3© 2014 SBCA
91
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.
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
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
19Level 1: Section 07 – Version 3© 2014 SBCA
109
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
20Level 1: Section 07 – Version 3© 2014 SBCA
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