Structural Concrete - Hassoun

920 Chapter 22 Prestressed Concrete Bridge Design
3’–6”
9’–0”
5’–3”
3.5”
2”
2”
4.5”
6”
3’–9”
1’–4”
2”
cg
10”
y bg = 30.88 y tg = 32.12
6’–0”
8”
32.12
1”
30.88
cg of girder
3’–6”
y bc y tc
cg of composite section
2’–2”
(a)
Figure 22.13
Typical sections of (a) BT-63and(b) composite section.
(b)
SECTION PROPERTIES (AASHTO PCI BT-63) (FIG. 22.13)
1. BT-63 Section Properties
A g = 713 in. 2
I g = 392638 in. 4
H g = 5.25 ft
y bg = 32.12 in.
y tg = H − y bg = 30.88 in.
S bg = I g
y bg
= 12224 in. 3
S tg = I g
y tg
= 12715 in. 3
Area of BT-63 girder
Moment inertial of BT-63 girder
Height of BT-63 girder
Center of gravity of BT-63 girder from the bottom
Center of gravity of BT-63 girder from the top
Bottom section modulus of BT-63 girder
Top section modulus of BT-63 girder
2. Composite Section Properties
t haunch = 1 in.
D s = 6 ft
Thickness of haunch may be neglected conservatively in section properties
Depth of composite section
To transform the cast-in-place deck slab into equivalent girder concrete, the following modular
ratio will be applied:
n = E c_deck
E c_girder
= 0.707
Section properties for the composite section are calculated below.
A deck = nb eff_int t s =(0.707)(8.5ft)(8in.) =577 in. 2
(Area of transformed deck)