Straight and curved steel I-girder bridges - Computational Analysis and Design of Bridge Structures - page 219

Figure 7.24 MD140 haunched 15-steel girder system.
• Assumed constant deck width, parallel beams with about the same stiffness
• Use of design trucks
• Designed within the bound for that structural type
• Limited ranges of applicability, such as applicable for straight bridge
and for constant girder spacing only (When exceeded, the AASHTO
LRFD specifications mandate refined analysis.)
This bridge fits all the conditions, and 2D line girder method was
adopted for the analysis, and the girder sections were designed accord-
ingly. Figure 7.24 shows the parabolic-haunched 15-steel girder system
with one interior girder isolated for the analysis. The prospective view
of this line girder is shown in Figure 7.7. The calculation of the section
properties in three stages, noncomposite ( N = infinity), LT composite
( N = 3 n ), and ST composite ( N = n ) sections, are shown in Figure 7.25.
This table lists the 2D beam section properties at the interior pier loca-
tion used in the analysis where S top , S bot , and S topc refer to section moduli
at the top and bottom of the steel girder and the top of concrete slab,
respectively. Also, Q slab is the first moment of inertia of the slab, and I x
is the moment of inertia of the composite section wherein AASHTO Q slab / I x
is used for the calculation of the shear connector fatigue requirement.
Herein, n is the modulus ratio of the steel girder to concrete deck and
N is the actual modulus ratio used in that stage where N is the infinity
mean steel section only. For 4000 psi (27.6 MPa) normal concrete, n = 8
is used.
As this bridge was the first few applications of HPS in the state of
Maryland, full bridge testing, including 3D FEA, in all phases and stages
was conducted. As described in Table 7.1, this 15-girder system was recon-
structed in three phases: (1) the first phase—girders 6-11, (2) the sec-
ond phase—girders 1-5, and (3) the third phase—girders 12-15. Each
phase has three pouring sequences. 3D FEAs by ANSYS were conducted
(Figure 7.26).