CVEN 4555 Reinforced Concrete Design
George.Hearn@coloado.edu 1
Aug 23 – Loads. Load Combinations.
ACI 318-14
Chapter 2 Notation and Terminology
Chapter 5 Loads
Using ACI318-14, define these terms and notations
Mn
nominal flexural strength at section, in.-lb
Mu
factored moment at section, in.-lb
Pn
nominal axial compressive strength of member, lb
Pu
factored axial force; to be taken as positive for compression and negative for tension,
lb
U
strength of a member or cross section required to resist factored loads or related
internal moments and forces in such combinations as stipulated in this Code
Vn
nominal shear strength, lb
Vu
factored shear force at section, lb
design load
combination
- combination of factored loads and forces.
load
- forces or other actions that result from the weight of all building materials,
occupants, and their possessions, environmental effects, differential movement, and
restrained dimensional changes; permanent loads are those loads in which variations
over time are rare or of small magnitude; all other loads are variable loads.
load, dead
- (a) the weights of the members, supported structure, and permanent attachments or
accessories that are likely to be present on a structure in service; or (b) loads meeting
specific criteria found in the general building code; without load factors.
load, factored
- load, multiplied by appropriate load factors.
strength,
design
- nominal strength multiplied by a strength reduction factor .
strength,
nominal
- strength of a member or cross section calculated in accordance with provisions and
assumptions of the strength design method of this Code before application of any
strength reduction factors.
strength,
- strength of a member or cross section required to resist factored loads or related
CVEN 4555 Reinforced Concrete Design
required
George.Hearn@coloado.edu 2
internal moments and forces in such combinations as stipulated in this Code.
CVEN 4555 Reinforced Concrete Design
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ACI 318-14 Chapter 5 Loads
5.3.1 Required strength U
shall be at least equal to the effects of factored loads in Table 5.3.1, with exceptions and additions in
5.3.3 through 5.3.12.
Table 5.3.1—Load combinations
Load combination
Equation Primary load
U = 1.4D
(5.3.1a)
D
U = 1.2D + 1.6L + 0.5(Lr or S or R)
(5.3.1b)
L
U = 1.2D + 1.6(Lr or S or R) + (1.0L or 0.5W) (5.3.1c)
Lr or S or R
U = 1.2D + 1.0W + 1.0L + 0.5(Lr or S or R)
(5.3.1d)
W
U = 1.2D + 1.0E + 1.0L + 0.2S
(5.3.1e)
E
U = 0.9D + 1.0W
(5.3.1f)
W
U = 0.9D + 1.0E
(5.3.1g)
E
List of load terms
D
= effect of service dead load
E
= effect of horizontal and vertical earthquake-induced forces
L
= effect of service live load
Lr
= effect of service roof live load
R
= cumulative load effect of service rain load
S
= effect of service snow load
U
= strength of a member or cross section required to resist factored loads or related internal
moments and forces in such combinations as stipulated in this Code
W = effect of wind load
CVEN 4555 Reinforced Concrete Design
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Exercise – Loads, Load Combinations
Given loads acting on a reinforced concrete deck
D psf
L psf
Lr psf
S psf
W psf
50
40
20
22
-8
Run load combinations, find greatest U in psf on deck
Solution
D
L
Lr
S
W
50
40
20
22
-8
psf
psf
psf
psf
psf
a
1.4
0
b
1.2
1.6
0.5
0.5
Load factors
D
L
Lr
S
W
c
1.2
0.5
1.6
1.6
0.5
d
1.2
0.5
0.5
0.5
1
e
1.2
0.5
c
60
20
32
35.2
-4
d
60
20
10
11
-8
e
60
20
0
4.4
0
f
0.9
g
0.9
0.2
1
Factored Loads
D psf
L psf
Lr psf
S psf
W psf
a
70
0
0
0
0
b
60
64
10
11
0
Combos, psf 70.0 135 115
f
45
0
0
0
-8
g
45
0
0
0
0
83.0 84.4 37.0 45.0
5.3.2 The effect
of one or more loads not acting simultaneously shall be investigated.
Combos, psf 70.0 135 115 91.0 84.4 45.0 45.0
U = 135psf
CVEN 4555 Reinforced Concrete Design
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Deck is supported by reinforced concrete joists and reinforced concrete
columns
CVEN 4555 Reinforced Concrete Design
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Joist spacing is 3 ft. Get U.
Factored Loads
D plf
L plf
Lr plf
S plf
W plf
a
b
c
d
e
f
g
210 180 180 180 180 135 135
0 192 60 60
60
0
0
0 30 96 30
0
0
0
0 33 106 33 13.2
0
0
0
0 -12 -24
0 -24
0
Combos, plf 210 405 346 249
253 111 135
5.3.2 The effect
of one or more loads not acting simultaneously shall be investigated.
Combos, psf 210 405 346 273 253 135 135
U = 405plf
CVEN 4555 Reinforced Concrete Design
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Column spacing is 14’ x 16’
Trib area is 224 SF.
Get U
Factored Loads
D lb
L lb
Lr lb
S lb
W lb
a
15680
0
0
0
0
b
13440
14336
2240
2464
0
c
13440
4480
7168
7884.8
-896
Combos, lb 15680 30240 25805
15700 30200 25800
d
13440
4480
2240
2464
-1792
e
13440
4480
0
986
0
f
10080
0
0
0
-1792
18592 18906 8288
18600 18900 8290
g
10080
0
0
0
0
10080
10100
5.3.2 The effect
of one or more loads not acting simultaneously shall be investigated.
Combos, lb 15700 30200 25800 20400 18900 10100 10100
U = 30,200 lb