Page 26 - Modern Steel Construction (April 2019)

¾” PARTIAL HEIGHT
11” STIFFENER (TYP.)
DIAPHRAGM

7 ∕16
TYP.
7
∕16 6½”
TYP.
9 ∕16
1ӯ WELDED STUDS CAP PLATE
(TYP.) COUNTER BORE
OR OVERSIZE HOLES PIER COLUMN
TO CLEAR STUD WELD (TYP.)

left: A casting for the Y support above: Welded studs for
connections, made by Cast Connex. alignment at the piers.

The most extreme forming condition
involved a reversing R=2-ft curve
with a 15° off-plumb profile at a
grade change.
Courtesy of Cast Connex Corp. Courtesy of Newport Industrial Fabrication
the desired appearance while not incurring the cost of plug welds and assumptions, and it was determined that the group loading assump-
the associated grinding. tions in SETRA were most appropriate given the size and anticipated
Engineer of record STV’s designers recognized early on that a use of the bridge. The allowable accelerations from the other guides
slender main span and flexible pier system could provide the potential were also compared to the allowable limits provided by SETRA to
for pedestrian-induced vibrations. Multiple publications that address confirm that the appropriate limits were being used.
vibration, including AISC’s Design Guide 11: Floor Vibrations Due to Modifications to the structure were made to improve the
Human Activity (Second Edition, available at www.aisc.org/dg), the dynamic performance of the bridge. However, providing strength
AASHTO LRFD Guide Specifications for the Design of Pedestrian Bridges and stiffness needed to be balanced with the fact that a continuous
and the SETRA guide Assessment of Vibrational Behavior of Footbridges curvilinear structure would require a certain amount of flexibility
under Pedestrian Loading were used to evaluate the bridge at different to accommodate thermal movements. Some elements, such as the
stages in the design process and to evaluate the as-built structure. The spandrel columns, were used to improve dynamic performance with
various guides provide different analysis methods and varying loading only minor impact on the influence of thermal forces. The span-

26 | APRIL 2019