Page 288 - Bridge and Highway Structure Rehabilitation and Repair

CHAPTER 6 APPLICATIONS OF BRIDGE DESIGN AND RATING METHODS 263

6.7.3 Sheikh Ibrahim’s Method for Checking Gusset Plate Connections in Steel Truss

Following the collapse of I-35W Bridge, FHWA developed a simplified method for gusset
plate design. (Refer to—Sheikh Ibrahim, F. I., Load Rating Evaluation of Gusset Plates in Truss
Bridges, FHWA Bridge Design Guidance No. 1, February, 2008)
Due to the need for checking the failed gusset connections, it is important to apply Ibrahim’s
method to similar connection details.

Gusset Plate Resistance in accordance with the
Load and Resistance Factor Rating Method (LRFR)

Summary Procedures: The evaluation of gusset connections shall include:
1. The evaluation of the connecting plates and
2. Evaluation of fasteners.
a. The resistance of a gusset connection is determined at the strength limit state only and
is the smaller resistance of the fasteners or gusset plates.
b. For safety, owners may require that connections be checked at other limit states such as
the service limit state to minimize serviceability problems.

The Resistance of Fasteners
For concentrically loaded bolted and riveted gusset connections, the axial load in each con-
nected member may be assumed to be distributed equally to all fasteners, at the strength limit
state.
1. The bolts in bolted gusset connections shall be evaluated to prevent:
• Bolt shear
• Plate bearing failures at the strength limit state.
• At the strength limit state, the provisions of AASHTO LRFD Article 6.13.2.7 and 6.13.2.9
shall apply for determining the bolts’ resistance to prevent bolt shear and plate bearing
failures.
2. Riveted gusset connections
The rivets shall be evaluated for:
• Rivet shear
• Plate bearing failures at the strength limit state.
• The plate bearing resistance for riveted connections shall be in accordance with AASHTO
LRFD Article 6.13.2.9 for bearing at bolt holes.

The Resistance of Gusset Plates
The resistance of a gusset plate shall be determined as the plate’s least resistance in:
• Shear,
• Tension including block shear,
• Compression, and

• Combined flexural and axial loads.
Gusset Plates in Tension
Gusset plates subjected to axial tension shall be investigated for three conditions:
• Yield on the gross section,
• Fracture on the net section,
• Block shear rupture