SUMMARY OF TESTS AND RESULTS
LEHIGH UNIVERSITY
At Lehigh University in 1984, Professors
Daniels and Slutter tested two
Exodermic™ panels, one with 2" of concrete and one with
3" of concrete.
Substantial static testing was done before and during extended
fatigue tests.
The 3" panel was subjected to 3.3 million cycles of simulated
HS 20 loading.
Although a small amount of surface cracking eventually developed
in the slab,
this was considered typical of concrete decks in general. Daniels
and Slutter
concluded that "...an infinite in-service fatigue life
can be expected..."
WEST VIRGINIA
UNIVERSITY
Professor Hota V.S. GangaRao,
with Penmatsu Raju and K. Ramesh, conducted extensive tests
of various grid decks at West Virginia
University
beginning in the late 1980's at West Virginia University's
Constructed Facilities
Center. Four Exodermic™ panels were tested: two newly constructed
panels of
fairly light design, and the two original panels from the
Lehigh tests.
An attempt
to test the 'ultimate strength' of
the older panels was
inconclusive; the strength of the Exodermic™ panels exceeded
the capacity of the
university's testing equipment -- 90,000 lbs loading. The
test successfully
demonstrated the strength and safety factors inherent in Exodermic™
design.
Static and
fatigue tests were conducted on the new panels, with excellent
results. Once again, Exodermic™ design was shown to offer excellent
internal
composite behavior. In the final report for the Federal Highway
Administration,
the researchers concluded that:
CLARKSON UNIVERSITY
The "revised" design
of Exodermic™ decks is simpler and less expensive to
fabricate, and with the elimination of the tertiary bars, contractors
have more
working room for installation of shear studs.
Historically, the Exodermic™ deck
evolved from traditional concrete-filled grids. The idea was
to move the concrete from within the grid
to the top of the
grid in order to make more efficient use of the two components.
Putting the
concrete on top also allowed the use of reinforcing steel in
the slab to
significantly increase the negative moment capacity of the design,
and to movethe fabrication welds of the grid closer to the neutral
axis of the section. A shear
connecting mechanism was required between the grid and the slab,
and this was
provided by the addition of “tertiary bars” to which
were welded short, 1⁄2" diameter studs.
The tertiary bars are welded to the grid during fabrication of
the
Exodermic™ grid panels, and extend up 1" into the structural
slab.
In the "revised" design,
the standard for all Exodermic™ decks since 1997,
the tertiary bars are eliminated, and their function is taken
over by the extension
of the main bars of the grid 1" into the slab. 3/4" diameter
holes are punched in
the top 1" of the main bars, to aid in the engagement of
the bars with the
concrete.
Testing of the
revised design was conducted by Dr. Christopher Higgins,
then an Assistant Professor at Clarkson University (now at Oregon
State
University). Professor Higgins and graduate student Heath Mitchell
completed
both static and fatigue tests of the revised design, and went on
to do push out
and pullout tests, looking specifically at the shear connecting
mechanism
between the concrete slab and the structural grid.
Results of the static and fatigue
tests were published in the January/February 2001 issue of the
Journal of Bridge Engineering.
Results of
additional testing have been submitted for publication.
The first
test, in the autumn of 1997, involved testing a panel spanning
8'
between supports to failure. Load was delivered through a load
patch sized to
simulate an HS-25 (20,000 pounds plus 30% impact factor) double
truck tire
footprint at 100 psi. The deflection and main bar strain were linear
to 80,000
pounds loading, indicating full composite behavior to at least
that point. The
load/deflection curve gradually "softened" to 123.5
kips, when there was a
punching shear failure of the concrete. Far from dramatic, a rectangular
area
around the load patch dropped approximately 1⁄2", and
the panel was still carrying
66,000 pounds of load. Concrete used was a standard 3500 psi mix,
using 3/8" maximum coarse aggregate.
The second test was a fatigue test, consisting of two million
load cycles
delivered to a two span continuous panel through two 9.1" x
22.8" steel loading
shoes simulating a full simulated HS-20 truck axle. The tested
spans were 7'2".
Static tests were conducted at intervals of 250,000 cycles. No
significant
difference in behavior of the panel was observed from start to
finish of the test.
For example, strains measured at the bottom of the grid main bars
at maximum
load didn’t change meaningfully over the course of the test.
After completion
of the fatigue test, the panel was cut in half, and a static
test conducted in which it was sought to fail one half of the
deck, with the test
set-up being as close as possible to the first such test.
Despite
the two million fatigue cycles, the panel performed well,
demonstrating a linear load-deflection response similar to
that of the earlier
panel. Due, in part, to the high performance conc rete (NYSDOT
Class DP, a
5000 psi mix) used in this test, the limits of the test setup
were reached before
the panel failed.
The applied load was increased gradually to 143,000 pounds, the
limit of
the load cylinder, and the panel did not reach punching shear as
did the first one
at 123,500 pounds. Surface cracking did not appear until approximately
118,000
pounds, versus 80,000 pounds in the first test. The crack pattern,
when it did
appear, was similar.
The testing was in accordance with the ASTM specification D6275-98,
Standard Practice for Laboratory Testing of Bridge Decks. In
addition to the
report published in the Journal of Bridge Engineering, a comprehensive
test
report was prepared by Professor Higgins. For further information,
please
contact EBDI.
RUSSELL
ROAD BRIDGE — FIELD
TEST
One of the earliest Exodermic™ decks, the Russell
Road Bridge over the
New York State Thruway in Albany, NY, was field tested by Professor
Darlow
and other researchers from Rennselaer Polytechnic Institute (RPI)
with
assistance from Neal Bettigole, the inventor of the Exodermic™ design.
Static live
load testing was conducted before and after redecking. "Good
agreement"
between AASHTO design and measured strains, was found. A major
goal of the
testing was to evaluate the properties of the composite girders.
The researchers
concluded that “Composite behavior was verified for an effective
deck width...” equal to center-to-center stringer
spacing, and "...with "t" equal
to the full depth of
the deck.” This result makes intuitive sense in that the
steel grid, which is
transverse to the girders, does an excellent job of mobilizing
a large portion of
the concrete slab, allowing it to work compositely with the girders.
The results of
this research were published in the American Society of Civil Engineering's
Journal of Structural Engineering in October of 1989.
HIGH STREET
BRIDGE — FIELD TEST
In 1992, an Exodermic™
deck on the High Street Bridge over the Metro
North railroad in Dobbs Ferry, N.Y. underwent field testing.
On this structure, the
Exodermic™ deck spans 11' between floorbeams without stringers
or other
supports. The tests were conducted by M.G. McLaren, P.C., the consultants
to
Westchester County on the project, with assistance from EBDI. Static
live load
testing involved placing strain gauges on one of the trusses, a
floor beam, and on
the bottom of several deck main bars. According to McLaren's
detailed report, "...testing and analyses show that the steel
floor beams act compositely with the
Exodermic™ system. "Testing confirmed that the width of deck
acting compositely
with the floorbeams was at least 12t (with t = the full thickness
of the Exodermic™
deck). The consultant’s report concluded that “this
structure does not need to be posted." NYSDOT agreed, and
the 10 ton limit sign, posted when the bridge
carried a timber deck, was removed.
GALVANIZED COATING TESTING
Hot dip galvanizing has been specified for Exodermic™
decks for many
years, and provides excellent protection from corrosion. Due
to the 5.5 to 6.0
mils of zinc typically deposited on steel grids during hot dip
galvanizing, coating
life is expected to be at least 55 to 60 years.
In 1994, Chuck Wofton of Young Galvanizing conducted tests of
coating
thickness on the Exodermic™ deck on the New York State Thruway’s
Russell Road
Bridge. The grid portion of the Exodermic™ deck was fabricated
and galvanized in
1986, and the deck erected in 1987.
Despite seven years of exposure to salt spray from the Thruway
below it,
the galvanized steel was visually in excellent condition, exhibiting
the mottled
appearance of newly galvanized steel. A few quotes from Mr. Wofton’s
report to
the New York State Thruway Authority follow:
