Page 250 - Bridge and Highway Structure Rehabilitation and Repair

CHAPTER 5 LOAD AND RESISTANCE FACTOR RATING AND REDESIGN 225

5.7.2 Symmetric and Non-Symmetric Patterns of Deck Pour
1. Alternate non-symmetric deck pour: Nonsymmetric pattern of deck pour is assumed.
Pattern to be provided by contractor
(DC1 4 DC2) 4 1.5 (CE1 4 CE2) 4 1.4 (WS)
p nonsym pour
For strength V condition, use construction wind load on construction equipment (WCEL),
the load combination is
(DC1 4 DC2) 4 1.5 (CE1 4 CE2) 4 1.35 (CLL) 4 0.4 (WS) 4 1.0 (WCEL);
p
3 0.9 to 1.25
p
• Stage 1 symmetric pattern of deck pour is assumed.
(DC1 4 DC2) 4 1.5 (CE1 4 CE2) 4 1.35 (CLL) 4 0.4 (WS) 4 1.0 (WCEL)
p pour-1
• Stage 2 symmetric pattern of deck pour is assumed.
(DC1 4 DC2) 4 1.5 (CE1 4 CE2) 4 1.35 (CLL) 4 0.4 (WS) 4 1.0 (WCEL)
p pour-2
• Stage 3 symmetric pattern of deck pour is assumed.
(DC1 4 DC2) 4 1.5 (CE1 4 CE2) 4 1.35 (CLL) 4 0.4 (WS) 4 1.0 (WCEL)
p pour-3
2. Alternate nonsymmetric deck pour:
Nonsymmetric pattern of deck pour is assumed. Pattern to be provided by contractor.
(DC1 nonsym pour 4 DC2) 4 1.5 (CE1 4 CE2) 4 1.35 (CLL) 4 0.4 (WS) 4 1.0 (WCEL)
p
Specification developments and special provisions will ensure quality assurance.

5.7.3 Summary of AASHTO LRFD Load Combinations
Older bridges were originally designed as per ASD or LFD. For new bridges, almost all
structural designs in the U.S. follow AASHTO LRFD code.
There are 14 load combinations based on probability for evaluating strength, serviceability,
and fatigue in AASHTO code. External actions need to be clearly defined in short-term and

long-term behavior. Excessive deformation such as deflection, rotation, curvature, vibration,
side sway, and settlement needs to be kept to a minimum.
Principal stresses due to combined bending and shear resulting from settlement of supports
may exceed what is allowable and lead to cracking, formation of plastic hinges, and disintegra-
tion of elements. When designing for maximum shear stress, principal stress along diagonal
planes also needs to be checked.
5.7.4 AASHTO LRFD Shear Capacity Evaluation of Steel Girders

All section numbers are based on AASHTO 2007 specifi cations.
1. Compact and non-compact sections:
• Strength limit states I to V
• Construction limit state and uncured slab
• For stiffened webs refer to Section 6.10.7.3
• For unstiffened webs refer to Section 6.10.7.2.
2. Interior panels of compact sections:
• Strength limit states I to V
• Uncured slab
• Refer to Section 6.10.7.3.3a.
3. Interior panels of non-compact sections:
• Strength limit states I to V
• Construction limit state and uncured slab
• Refer to Section 6.10.7.3.3b.