Section Downloads. Background. Load Development Outline. Types of Loads ANSI/ASCE 7. Section 07: Load Development. Download & Print. Version 2.

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1 Section 07: Load Development Section Downloads Download & Print TTT I Sec 07 Slides TTT I Sec 07 Handout_1 Load Distribution & Reaction Equations TTT I Sec 07 Handout_ 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 (5-6) TPI Selection (Section 01) Version.1 Load Development Outline Types of Loads Load Duration Minimum Load Requirements Load Distribution Background Section 06 - Design Principles The structural design process can be broken into two functions: LOAD vs. RESISTANCE 3 4 ANSI/ASCE 7 Types of Loads TTT I Sec 07 Handout_3 Dead Loads Live Loads Environmental Loads ASCE referenced by IBC & IRC 01 ASCE referenced by IBC & IRC 006/009 ASCE 7-00 referenced by IBC & IRC

2 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 Gravity Load A downward vertical force created from the pull of gravity on a mass. 7 8 TTT I Sec 07 Handout_3 ASCE 7 Table C3-1 Live Loads Load Superimposed by the Use & Occupancy of the Building Includes impact loads Does not include environmental loads wind, snow, or seismic 9 Section 05 Truss Materials 10 Floor & Roof Live Loads Determined by the Building Designer In absence of a governing building code use ASCE 7 Floor Live Load 11 Image Courtesy of Trus Joist, A Weyerhaeuser Business 1

3 TTT I Sec 07 Handout_3 ASCE 7 Table 4-1 Roof Live Load 13 Section 08 Truss Design, Manufacture, & Installation Overview 14 Environmental Loads Snow, Wind, Seismic & Rain Determined by the Building Designer In absence of a governing building code use ASCE 7 Snow Load Snow Load Wind Load

4 Wind Load Seismic Load 19 0 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. Load Duration 1 Normal Load Duration Normal Load Duration C D =

5 Load Duration Factors TPI Selection Section 01 Load Duration Factors Permanent 0.90 Normal - 10 Years duration 1.00 Snow Months duration 1.15 Construction 7 Days duration 1.5 Wind & Earthquake 5-10 minutes 1.60 Impact*.00 * For FRT and pressure-preservative lumber and all connections subject to an impact load, the duration of load factor shall not exceed Minimum Load Requirements Structural Specifications Building Codes ASCE 7 Minimum Load Requirements Hotel? TTT I Sec 07 Handout_3 What is the Building Type? 7 8 Minimum Load Requirements TTT I Sec 07 Handout_3 Building Code History Up until the year 000, there were three major model building codes and one residential code National Building Code TM (NBC-BOCA) Standard Building Code TM (SBC-SBCCI) Uniform Building Code TM (UBC-ICBO) CABO One and Two Family Dwelling Code

6 Building Code History City and County (e.g., New York City) Local Variations State Codes (e.g., Florida) 31 3 Special Load Considerations Concentrated Load Check Partition Loads Partial Loads Unbalanced Loads Floors Roofs Concentrated Load Check TTT I Sec 07 Handout_ Partition Loads Partition Loads

7 Partial Load Partial Load Unbalanced Loads 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 Snow Drift Loads Rain On Snow Load Image Courtesy of Alpine Engineered Products, Inc

8 Snow and Ice Impact Load Water Accumulation Water Accumulation Bottom Chord Live Loads ASCE 7 lists the minimum design loads for attic spaces: Table 4-1 Uninhabitable attics without storage Uninhabitable attics with storage Habitable attics and sleeping areas Truss Design software Always check first with your local building department to see how these provisions are interpreted Load Development Quiz 1 How loads are represented? How loads are distributed? Reactions? Load over an Area, PSF Load along a Line, PLF Load at a Point, LB 48 8

9 Load over an Area Load in pounds distributed over area Pounds per square foot or PSF Most design loads are in PSF 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 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 Load Distribution convert to Design Load in PSF PLF & Calculate Reactions Only for Bulk Reactions Uniformly Distributed Load (UDL) Triangular or Tapered Load Point or Concentrated Load 51 5 Load Distribution & Reaction Equations Uniformly Distributed Load TTT I Sec 07 Handout_

10 Uniformly Distributed Load Uniform Load Equation Most trusses are uniformly loaded because they are evenly spaced & support uniform design loads. w L R1 R Total Load = w x L Uniformly Distributed Load Example Problem 1 Uniformly Distributed Load Example Problem Given: 90 PLF Given: 440 PLF TTT I Sec 07 Handout_4 37 ft. 16 ft. Find: R1 & R Find: R1 & R w L R1 R (90 lbs./ft.) x (37 ft.) = = 5365 lbs. w L R1 R (440 lbs./ft.) x (16 ft.) = = 350 lbs Triangular Load Triangular Load Skewed or hip framing often results in triangularly loaded girders Tapered Load

11 Triangular Load Equation Triangular Load Equation 61 R1 - the light side is 1/3 total load: w L 1 w L R1 = = 3 6 R - the heavy side is /3 total load: w L w L R = = Triangular Load Equation Triangular Load Example Problem 1 Given: 175 PLF 63 Find: R1 & R 18 ft. w L (175 lbs./ft.) x (18 ft.) R1 = = = 55 lbs. x = 1050 lbs. 6 6 w L R = = 3 (175 lbs./ft.) x (18 ft.) = 1050 lbs Triangular Load Example Problem Point Load Given: 390 PLF 40 ft. Find: R1 & R w L (390 lbs./ft.) x (40 ft.) R1 = = = 500 lbs. 3 3 w L R = 6 (390 lbs./ft.) x (40 ft.) = = 600 lbs. x = 500 lbs

12 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. Point Load Equation R1 + R = P R1 + R = P A + B = L Point Load Example Problem Solving Quiz Problems Given: 4 ft. 800 # B = L - A = ft. TTT I Sec 07 Handout_1 1 ft. Find: R1 & R P B R1 = = L (800 lbs x 17 ft.) 1 ft = 800 = lbs. TTT I Sec 07 Handout_4 TTT I Sec 07 Handout_5 R = P A L = (800 lbs) x (4 ft.) 1 ft. = lbs Combination Load Distributions Quiz R1 TOTAL R TOTAL R1 PT LD R PT LD R1 UDL R UDL R1 TOTAL R1 PT LD R1 UDL R TOTAL R PT LD R UDL 7 1

13 Combination Load Distributions Combination Load Distributions R1 TOTAL R TOTAL R1 TOTAL R TOTAL R1 PT LD R PT LD R1 TRI R TRI R1 UDL R UDL R1 TRI R TRI R1 TOTAL R1 PT LD R1 TRI R TOTAL R PT LD R TRI R1 TOTAL R1 UDL R1 TRI R TOTAL R UDL R TRI Combination Load Distributions Example Problem Given: Combination Load Distributions Example Problem (continued) Given: Find: R1 & R P B R1 400 = = L (400 lbs x 0 ft.) = 85.7 lbs. 8 ft. Find: R1 & R P B R1 50 = = L (50 lbs x 5 ft.) 8 ft. = 44.6 lbs. P A (400 lbs x 8 ft.) R 400 = = = lbs. L 8 ft. P A (50 lbs x 3 ft.) R 50 = = = 05.4 lbs. L 8 ft = = Combination Load Distributions Example Problem (continued) Given: Quiz 3 Find: R1 & R R1 400 = 85.7 lbs. R 400 = lbs. R1 50 = 44.6 lbs. R 50 = 05.4 lbs. R1 TOTAL = = lbs. R TOTAL = = lbs lbs lbs. = 400 lbs lbs. = 650 lbs

14 Partial Load Distributions Centroids Do not apply to Loads Every shape has a centroid R1 = R = wl Do Not Apply t o Part ial Loads! Centroid R1 = wl 1 = wl 3 6 R = wl = wl 3 3 Do Not Apply t o Part ial Loads! TTT I Sec 04 Handouts Partial Load Distribution Partial Load Distributions Given: 10 ft. Example Problem 300 PLF ½ x 1 ft. x 300 PLF = 1800 lbs. 81 R1 Find: R1 & R P A R = L 1 ft. 30 ft. P B (1800 lbs x 1 ft.) R1 = = L 30 ft. = 70 lbs. (1800 lbs x 18 ft.) = = 1080 lbs. 30 ft. 70 lbs lbs. = 1800 lbs. R R1 10 ft. 8 ft. 4 ft LB 300 PLF 1 ft. R 30 ft. 8 Simple Span vs. Multiple Span Quiz

15 Loads from Framing Layouts Loads from Framing Layouts Loads from Framing Layouts Loads from Framing Layouts R1 R Truss Total Load = 40 SF x 45 PSF Truss Total Load = 1800 lbs. 87 R1 = R = 1800 lbs. / = 900 lbs. 88 Loads from Framing Layouts Loads from Framing Layouts R1 = R = R1 = R = What if the trusses were not spaced at ft. on center? What is the PLF? 89 R1 = R = 900 lbs

16 Loads from Framing Layouts Loads from Framing Layouts PLF = TW x PSF w L R1 = R = = = = 600 lbs Loads from Framing Layouts Loads from Framing Layouts R1 = R = w L 7x0 R1 = R = = 1440 R1 = R = 70 LB Loads from Framing Layouts Loads from Framing Layouts R1 = R = w L R1 = R = 450 x 14 = 6300 R1 = R = 3150 lbs

17 Load Paths Quiz 5 Quiz Question 0 98 Dead Load Calculations Quiz 6 TTT I Sec 07 Handout_3 100 ASCE 7 Table C3-1 TTT I Sec 07 Handout_3 ASCE 7 Table C3-1 continued TTT I Sec 07 Handout_

18 Slope Correction Factor Slope Correction Factor Slope Correction Factor = SCF P 1 1 Slope Correction Factor = 1 cos 103 P 1 SCF = PSF (1.414) 10 PSF Roofing Felt Truss Weight PLF = TW x PSF PLF PSF = OC Ex. What is the weight of a roof truss with x6 chords and x4 webs at ft o.c.? PSF = 5.5 =.75 PSF TTT I Sec 07 Handout_ Dead Load Calculations Example Problem Given: 6' roof truss, 4" o.c., x4 bottom chord, x6 top chord, x4 webs, 6 / 1 pitch 5 / 8 " OSB roof sheathing 15 pound felt 80 pound shingles 6" fibrous glass insulation 5 / 8 " Gypsum board ceiling Dead Load Weight of Roof Trusses Top Chord x4 x4 x6 x6 x6 x6 x6 x6 Truss Dead Load Bottom Chord x4 x8 x4 x6 x6 x8 x10 x10 Webs x4 x4 x4 x4 x6 x4 x4 x6 Weight per Lineal Foot PLF 4.8 PSF.4 PSF OC.4 PSF divided evenly between TC & BC = 1. PSF Calculate horizontal loads & adjust top chord load for slope. x8 x8 x8 x8 x4 x x8 x10 x

19 Roofing Material 5 / 8 " OSB: Plywood = 0.4 PSF per 1 / 8 " of thickness 5 x 0.4 =.0 PSF Shingles: Specified at 80 lbs. per square (100 square feet) 80 lbs. /100 SF =.8 PSF Felt: 15 lbs. per square (100 square feet) 15 lbs. /100 SF = 0.15 PSF Total Top Chord Item TC PSF 1 / Truss 1. 5 / 8 " OSB.0 15 lb Felt lb Shingles.8 Total Bottom Chord Dead Load Summary 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 =.75 PSF 1/ Truss 1. PSF BC Dead Loads = Total BC Dead Load = PSF Item TC PSF BC PSF Truss /8" OSB.0-15 lb Felt lb Shingles.8-6" Fibrous Insul /8" Gypsum -.75 Total Slope Correction SCF SCF P SCF PSF 11 Dead Load Diagram Quiz

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