Evaluation of a High-Performance Steel Bridge
Using Field Test Data
NSF Research Experiences for
Undergraduates in Bridge Engineering
University of Delaware
Location / History of Churchman’s Bridge
Strain Gage Data
Results / Discussion
Location - Map
University of Delaware Churchman’s Road Bridge
Location - Pictures
New bridge looking from the east.
Aerial view of old bridge (notice skew).
History of Churchman’s Bridge
Work began in 2004
to replace existing
773’ long steel bridge
with five spans
Sharply skewed at an
angle of 27º
Cross frames (to
connect the girders)
are parallel to the
abutments (with the
skew and not normal
to the girders)
Eight girders and two cross frames have been
instrumented with Geokon vibrating wire strain
Gauges have been continuously recording data
since before construction began.
Data has been removed from the data loggers
approximately every two weeks, and then
stored as text files.
Previous Research – Strain Gauges
Cross Frame Detail frames have
gauges on all
All eight girders
gauges on the
and two also
have them on
End View top.
Research Objectives and Importance
Very few skewed steel bridges have been
instrumented before construction.
Currently they require significant design
experience due to cross-frame and girder
This project aims to increase the understanding
of dead load stresses in these bridges.
Modeling Program: STAAD 2003
Easy to learn, available and
Girder Details - Side View
Using STAAD, a line model was
G2 to G7 PL16'x13 4" PL20'x118"
Top Flange G1 & G8
PL16'x15 8" PL20'x118"
Members are treated 2-d lines,
as compared to a 3-d model in Web
PL72"x 8" (TYP.)
which they are solids.
Girder cross-sections produced in Field Splice 1
Section Wizard and imported into G2 to G7 PL16'x13 4" PL20'x118"
STAAD. G1 & G8
PL16'x15 8" PL20'x118"
AutoCad used to organize the 26
different sizes of girders on this
Modeling - Simplifications
Cross-frames modeled as single members.
Models were created in STAAD and their
effective areas determined.
W-sections with the same area were then
chosen to represent these cross-frames.
Modeling - Cross-Frames, Utility Supports
By modeling the cross-frames as single members,
their true weight was not being represented.
The utility supports were not modeled, and
instead loads were added to represent them.
Modeling - Supports and Errata
Middle pier modeled as fixed support, with all other piers being
modeled as rollers.
Modeled this way since k-values for springs would be difficult to
Also, STAAD has a node limitation of 500 nodes, so only the west
half of the bridge was analyzed, although entire model was
Model of Entire Bridge
Model of West Half of Bridge
Modeling - Construction Process
Each step in the construction process was
modeled, with one shown below.
Done so that the evolution of stresses in the
girders could be analyzed.
Strain Gage Data
Strain data was plotted versus time for months
before construction to weeks after construction
In High Steel’s In transit /
fabrication yard At construction site
Strain Gage Data – Three Types
Three types of strains were determined.
1. Overall Strain on Bottom Of Girder 1 During Construction
2. Construction 250
3. Maximum 50
-150 Strain Overall Strains
Stresses from gages compared to the results from the
models. West End of Bridge Stresses
Agreed on stress
development, such as
both having largest
stresses after girder
six was placed.
Did not agree on magnitude of stresses with gages
reading 12-14 KSI and model predicting 5 KSI
Discrepancy in stresses is most likely due to
loads not being taken in account.
From plan drawings and bridge visits it is not
clear what these loads would be.
Possibly welds, safety devices, stiffener plates
Results could also be improved by better
modeling of supports and of cross-frames.
Determine k-values for all the supports
Take into account other properties besides effective
area for the frames.
3-D modeling of the bridge.
Would allow accurate modeling of the cross-
frames, since could attach members to the
tops and bottoms of girders
Relationship between temperature and
strain in the girders, since temperature
causes significant strain variation.
National Science Foundation
This material is based on work supported by the National
Science Foundation under Grant No. EEC 0139017 “ Research
Experiences for Undergraduates in Bridge Engineering” at the
University of Delaware.