This is utterly untrue. Starting a sentence with the word Fact does not make it factual.

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1 Fact: the number one cause of structural collapses in the contiguous United States is $1 Bud Light Night 1 LESSON 7: LOAD PATH & TRIBUTARY AREA III ASD VS LRFD September 10, 2018 LESSON OBJECTIVES 1. Describe the differences between the ASD and LRFD methods (e.g., applied loads versus factored loads, allowable strengths versus design strengths). 2. Compute ASD applied forces and moments in a simple-braced building, using tributary areas and widths. 3. Compute LRFD factored forces and moments in a simple-braced building, using tributary areas and widths. 4. Assess the adequacy of members using the ASD or LRFD methods, given the member s nominal resistance. READING: Several pages on the website version of this handout Optional textbook (Segui) Chapter 2 LAB THIS WEEK: Downstairs in the Structures Lab. Proper lab clothing is essential (long pants, shoes that fully cover all skin on the feet, short-sleeve shirt, hair tied back, if applicable). Be prepared to get filthy, as you will learn to MIG weld. Wear clothing that you don t mind ruining. Bring headphones or earbuds, as you will be following video instructions as you conduct computer models, when not welding. LOAD COMBINATION: A load combination is a combination of loads that represents a plausible event. For example, the blizzard of the century is an event that is likely to control the roof beams of a building. Implausible means that it is unlikely that the biggest live load that can ever occur (probably a huge party) will occur on the same day as the biggest blizzard. Consequently, you must understand why the live load is not 100% when the snow is 100%, etc. Every member in the structure may be controlled by a different event. For example, braces are usually controlled by wind or earthquake events, floor beams are usually controlled by live load events, and roof beams are usually controlled by snow events. ASD Load Combinations: LRFD Load Combinations: IN-CLASS EXAMPLE BUILDING: 1 This is utterly untrue. Starting a sentence with the word Fact does not make it factual.

2 A B C D Given: 6 thick slab ( =150 lb/ft 3 ) 1 Fill beams: W14x30 Girders: W16x50 Columns: W12x40 (20 -long) 2 Design Live Load: 100psf Live Load Reduction Factor is applicable Roof Live Load L r = 20 psf Roof Snow Load S = 30 psf 3 W12x40 column buckling strength: P n = 192 kips for a 20 -long column 30, typ. 20, typ. 4 LRFD: = 0.9 for column buckling (ductile) ASD = 1.67 for column buckling (ductile) Example Building Homework Assignment (Due Wednesday. Standard Homework Assignment Presentation counts) 0. Study Segui example 2.1. Do not hand in. THE FOLLOWING PROBLEMS REFER TO THE BUILDING ON THE NEXT PAGE. 1. Compute the controlling ASD applied load P on the column at grid location B2 at the ground level, then determine if the column is safe, per ASD. 2. Compute the controlling LRFD factored load P u on the column at grid location B2 at the ground level, then determine if the column is safe, per LRFD. 3. Compute the ASD controlling applied moment M on a typical interior 2 ND FLOOR Long Girder. If the nominal moment strength of a W21x93 is M n = 920 kip-ft, determine if this 2 nd Floor Girder is adequate, per ASD. 4. Compute the ASD controlling applied moment M on a typical interior ROOF Long Girder. If the nominal moment strength of a W21x93 is M n = 920 kip-ft, determine if this ROOF Girder is adequate, per ASD. 5. Compute the LRFD controlling Factored moment M u on a typical interior ROOF Long Girder. If the nominal moment strength of a W21x93 is M n = 920 kip-ft, determine if this ROOF Girder is adequate, per LRFD. NOTE THE FACT THAT THE ROOF AND 2 ND FLOOR BEAMS ARE CONTROLLED BY DIFFERENT LOAD EVENTS (LOAD COMBINATIONS). ALSO NOTE THAT LRFD AND ASD GIVE DIFFERENT CONCLUSIONS BECAUSE LRFD FEARS LIVE AND SNOW LOADS BUT ASD DOES NOT

3 A B C Given: 4 2 nd thick Floor slab 4 thick ( =150 slab lb/ft ( =150 3 ) lb/ft 3 ) Roof Fill beams: does not W14x30 have a slab. Instead, it has roofing material Short Girders: on corrugated W16x35 metal deck, which have a dead Long load Girders: pressure W21x57 of 20 psf. This 20 psf must be added All Columns: to the dead W12x40 loads of beams and girders, as necessary. Each story height is 12 All Fill beams: W14x30 All Short Girders: W16x36 All Long Girders: W21x93 All Columns: W10x54 Each story height is 20 30, typ Design Live Load for 2 nd flr: 100 psf Live Load Reduction Factor is applicable Roof Snow Load: 60 psf Roof Live Load L r = 20 psf W10x54 column buckling strength: R n = 249 kips for a 20 -long column Roof LRFD: = 0.9 for column buckling (ductile) ASD: = 1.67 for column buckling (ductile) 2 nd flr. Ground

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