Ron Pierce, David Evans & As - WSU Conference Management

Gusset Plate Inspection &
Load Rating Strategy
April 21, 2011
Gary Bowling, PE; Bridge Operations Managing Engineer
Jon Rooper, PE; Senior Load Rating Engineer
Oregon Department of Transportation
1

Our Legal Responsibility
• Each bridge owner is charged with
the responsibility to inspect and
report on the condition of each
structure, as thoroughly as necessary
to clearly establish its condition and
to insure its continued safe
operation, and to rate or restrict the
loads on the bridge, when the
maximum unrestricted legal load
exceeds the safe load carrying
capacity of the bridge.
2

Gusset Plates are very Unique
• The portion that connects truss
members that are in tension are
considered to be Fracture Critical.
• Since gusset plates are constructed
of thin steel plates, the portion that
connects truss members that are in
compression can be very susceptible
to localized buckling, out-of-plane
bending or distortion.
3

Areas of Concern / Reporting Tools
• Corrosion – Elements # 162 & 515
• Section Loss – SF # 363
• Pack Rust – SF # 357
• Steel Fatigue – SF # 356
4

Areas of Concern / Reporting Tools
• Loss of Connectors – Element # 162
• Out-of-Plane Distortion – SF # 364
– Fit-up
– Load Induced
– Loss of Section
• Existing Gusset Plate Geometry as
compared to the Bridge Plans
5

ODOT Strategy
• Visual Triage of all gusset plates
during the next inspection cycle
(Inspection).
• Use visual triage information to
assure the most critical structures
are assessed first (Load Rate).
7

As-Built As Built
Steel Gusset Plate
Data
9

Steel Truss Bridges in Oregon
• Out of approximately 6500 NBI bridges
in Oregon, steel trusses make up 2.6%
• 79 on the State Highway System
– 49 have been load rated
• 93 belonging to local or other agencies
– 41 have been load rated
• No gusset plates have been load rated
10

“As As-Constructed
Constructed” bridge plans usually only show the
general shape and plate thickness for the gusset plates.
11

Information needed for each unique joint
• A photo to verify
the number and
layout of the
bolts/rivets
• If not stated on the
plans, a
measurement or
estimate of the size
of the bolts/rivets
• A measurement
verifying the
thickness of the
gusset plate
• Measurements and
sketch of the
gusset plate
geometry and
bolt/rivet layout
12

Weather
also had a
negative
impact!
13

Lessons Learned
• This work is very time consuming
• Attempting to add this work to
Fracture Critical Inspections is not
the best idea due to the level of
detail and time involved
• Need to set up special inspections
just to obtain this information when
we plan to load rate each truss
14

New Idea: Attempt to obtain
measurements from digital photos
15

Second attempt at obtaining
measurements from digital photos
No constant scale could be determine due to the angle of
the camera lens versus the plane of the plate in the image
16

Oregon State University Research
ODOT funded research in 2008 to develop a
procedure to minimize hand-on field
measurements of gusset plates
Usable for Load Rating
Yield quality consistent data between inspectors
Capture all photos necessary to characterize each
joint
Correct perspective distortion of photos so scaling
will be accurate in any direction
Use a calibrated scale to measure all required
dimensions
17

Original Image with OSU Target
18

Rectified Image can now provide accurate
dimensions of the gusset details
19

Current Strategy…
Strategy
• Prioritize which bridges need their gusset plates
load rated first
– Inspector recommendations
– Data from Gusset Plate Condition Assessment Forms
– Performed during Fracture Critical Inspections
• Obtain gusset dimension and perform load ratings
based on priority list
– When OSU completes the research and development of the
tools and procedures
• Bridges that raise immediate concerns from
inspection
– Schedule special inspections to obtain gusset dimensions
– Perform Load Rating when gusset dimensions are available
20

Questions?
21