Load Combinations Represent Plausible Events

Load Combinations Represent Plausible Events LRFD Load Combinations

Load Combinations Represent Plausible Events LRFD Load Combinations Huge Party, and Some Snow (or roof construction or rain)

Load Combinations Represent Plausible Events LRFD Load Combinations

Load Combinations Represent Plausible Events LRFD Load Combinations Huge Snow (or huge roof constr. or rain) And Modest Party (or modest rain)

Load Combinations Represent Plausible Events LRFD Load Combinations ASD Load Combinations

Load Combinations Represent Plausible Events LRFD Load Combinations ASD Load Combinations Huge Party

Load Combinations Represent Plausible Events LRFD Load Combinations ASD Load Combinations

Load Combinations Represent Plausible Events LRFD Load Combinations ASD Load Combinations Huge Snow (or roof constr. or rain)

Live Load Reduction Factor?

This is a Likely Event The probability that 100psf occurs at the bar is high.

This is a Likely Event The probability that 100psf occurs at the bar is high. The probability that 100psf occurs on a few beams is high. BAR

Makes sense cuz $1 Drafts This is a Likely Event The probability that 100psf occurs at the bar is high. The probability that 100psf occurs on a few beams is high. The probability that 100psf occurs locally is high. BAR Makes sense cuz $1 Drafts

This is a Likely Event The probability that 100psf occurs at the bar is high. The probability that 100psf occurs on a few beams is high. The probability that 100psf occurs locally is high. The probability that 100psf occurs over bigger areas is low. $1 Drafts? $1 Drafts? $1 Drafts? $1 Drafts? $1 Drafts? $1 Drafts?

$1 Drafts on every floor? Seems unlikely… This is a Likely Event The probability that 100psf occurs at the bar is high. The probability that 100psf occurs on a few beams is high. The probability that 100psf occurs locally is high. The probability that 100psf occurs over bigger areas is low. $1 Drafts $1 Drafts $1 Drafts $1 Drafts $1 Drafts $1 Drafts $1 Drafts on every floor? Seems unlikely…

This Explains the Live Load Reduction Factor (see Reading)

This Explains the Live Load Reduction Factor (see Reading) Small Tributary Areas (AT) are unlikely to see the full 100 psf loading. So, larger tributary areas are designed for lower pressures:

This Explains the Live Load Reduction Factor (see Reading) Small Tributary Areas (AT) are unlikely to see the full 100 psf loading. So, larger tributary areas are designed for lower pressures: 𝐿= 𝐿 0 0.25+ 15 𝐾 𝐿𝐿 𝐴 𝑇

This Explains the Live Load Reduction Factor (see Reading) Small Tributary Areas (AT) are unlikely to see the full 100 psf loading. So, larger tributary areas are designed for lower pressures: 𝐿= 𝐿 0 0.25+ 15 𝐾 𝐿𝐿 𝐴 𝑇 L = Reduced Live Load Pressure (apply this to the member) L0 – The Code Specified Design Live Load (psf) KLL = 4 for columns = 2 for beams AT = the Live-Loaded AT (which may not be the same as the total tributary area.

This Explains the Live Load Reduction Factor (see Reading) Small Tributary Areas (AT) are unlikely to see the full 100 psf loading. So, larger tributary areas are designed for lower pressures: 𝐿= 𝐿 0 0.25+ 15 𝐾 𝐿𝐿 𝐴 𝑇 L = Reduced Live Load Pressure (apply this to the member) L0 – The Code Specified Design Live Load (psf) KLL = 4 for columns = 2 for beams AT = the Live-Loaded AT (which may not be the same as the total tributary area. SEE READING FOR FURTHER DETAILS.

e.g.,

e.g., ASD Combinations

e.g., LRFD Combinations

The ASD Example was done on the board. Result: R = 139 kips Applied Load Rn/W = 115 kips Allowable Load OK

The ASD Example was done on the board. Here is the LRFD Version: Combo 1: 1.4D = 1.4 (100.8kips) = 141.1 kips Combo 2: 1.2D+1.6L+0.5S = 1.2(100.8)+1.6(33.36)+0.5(18) = 183.3 kips Combo 3: 1.2D+1.6S+0.5L = 1.2(100.8)+1.6(18)+0.5(33.36) = 166.4 kips Others not controlling, by inspection. Ru = 183.3 kips Factored Applied Load fRn = 0.9(192) = 172.8 kips Reduced Resisted Load OK?

The ASD Example was done on the board. Here is the LRFD Version: Combo 1: 1.4D = 1.4 (100.8kips) = 141.1 kips Combo 2: 1.2D+1.6L+0.5S = 1.2(100.8)+1.6(33.36)+0.5(18) = 183.3 kips Combo 3: 1.2D+1.6S+0.5L = 1.2(100.8)+1.6(18)+0.5(33.36) = 166.4 kips Others not controlling, by inspection. Ru = 183.3 kips Factored Applied Load fRn = 0.9(192) = 172.8 kips Reduced Resisted Load Not OK!