Structural Concrete - Hassoun

926 Chapter 22 Prestressed Concrete Bridge Design
b. For two or more design lanes loaded:
DV ext2 = e.DV int2 = 0.85(0.884) =0.751
Distribution factors for shear at the exterior girder:
DV ext = max(DV ext1 , DV ext2 )=1.2
6. Skew correction factor for shear (AASHTO 4.6.2.2.3c)
lane Therefore, use DF_VE = 1.2 lane
θ = 0 Exterior and first interior beams on the obtuse side
[ ] 0.3
12Lt
3 [ ]
SC = 1.0 + 0.2 s
12 × 100 × 8
3
tanθ = 1.0 + 0.2
tan(0) =1
K g 926,689
Typically, maximum moments and shears are governed by live (truck) loads. In this case, interior
girders will likely govern the design and a sample calculation will be performed for an
interior girder design only.
MOMENT DEMANDS
The maximum moments due to dead loads and live loads occur at the midspan. Calculate the maximum
moment due to dead loads.
Unfactored Moment
1. Dead Load
x = 0.5L = 50 ft
W DC1_NC = w g_int = 0.743 klf
M DC1_NC = w DC1_NCx(L − x)
2
(0.743)(50)(100 − 50)
=
2
= 928.4kip⋅ ft
w DC1_C = w slab_int + w haunch_int
= 0.85 + 0.044 = 0.894 klf
M DC1_C = w DC1_Cx(l − x)
2
(0.894)(50)(100 − 50)
=
2
= 1117.2 kip⋅ ft
Distance at midspan from the left of the bridge
Dead-load unit weight due to noncomposite
section (DC1): girder only
Maximum moment due to noncomposite
section
Dead-load unit weight due to composite
section (DC1): deck slab and haunch
Maximum moment acting on hardened girder:
composite section
The maximum moment due to DC1: girder, deck, and haunch
M DC1 = M DC1_NC + M DC1_C = 928.4 + 1117.2 = 2045.6 kip⋅ ft
The maximum moment due to DC2: railing and future utilities
M DC2 = w DC2_intx(L − x) (0.205)(50)(100 − 50)
= = 255.6 kip⋅ ft
2
2