LRFD Strength Combination

U = 1.2 D + 1.6 L + 0.5 (L_{r} or S or R)

ASCE 7 / Handbook LRFD combinations apply load factors to service loads to produce required strength U. The classic gravity combination is 1.2D + 1.6L. Wind and seismic have their own factors and allowable-stress counterparts (ASD).

$D$: Dead load
$L$: Live load
$U$: Required strength

Step-by-step solved example

A girder has D = 40 k, L = 60 k (no roof live). Governing gravity U?

Factored uniform load on the tributary strip: 1.2D+1.6L.

1. Combination
U = 1.2(40) + 1.6(60) = 48 + 96 = 144 k.
$U = 144 k$

Answer: 144 k

10 practice questions

0/10 correct

1.Load factor on live load in 1.2D+1.6L is

2.Dead load is factored 1.2 rather than 1.6 mainly because

3.φ is the

4.ASD safety is applied by

5.D = 20 psf, L = 40 psf. 1.2D+1.6L =

6.A combination 1.4D governs when

7.Nominal moment strength of a compact steel beam (yielding) is

8.Concrete Whitney block depth a is

9.Slenderness of a pinned steel column uses

10.Serviceability checks (deflection, drift) generally use