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Horizontal Shear Composite Action

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					Horizontal Shear/Composite Action
Testing Program Proposal
Outline 2/16/04

Objectives
The objective of this research centers around several important questions introduced
during the design of a recent arch bridge. The main issue addressed is the composite
action between the girders and the deck slab.

The first main questions involves cross beams that connect between two main
longitudinal girders: “How much does the horizontal shear reinforcement in the cross
beams contribute to the composite action between the main girders and the deck slab?”
The answer to this question has very important implications for the design of bridges with
a limited number of girder lines and cross beams. An arch bridge system is a good
example of this type of bridge.

The second main question involves the spacing of the horizontal shear reinforcement:
“What is the maximum spacing of horizontal shear reinforcement?” Currently, both the
AASHTO and the ACI codes specify a maximum shear connector spacing of 2 feet. This
is generally thought to be very small and not necessary. Maximum spacing requirements
between horizontal shear connectors needs to be investigated and, if warranted, updated.
A larger spacing will result in the development of new bridge construction systems
utilizing full depth precast deck panels placed between the shear connectors.
Consequently, construction time and risk will be reduced, and the life of the bridge will
be increased.

Problem Statements
1. On a typical multi-girder stringer bridge, shear connectors running the length of each
girder resist horizontal interface shear and create composite action between the girders
and the deck slab. Naturally, in the case of having fewer girders such as arch bridges or
cable stayed bridges, there are significantly fewer connectors to resist the shear force.
Therefore, creating sufficient composite action between the girders and the deck becomes
a much more critical design issue. This is a typical of an arch bridge or any other bridge
relying heavily on two exterior girders (see Figure 1).




                Figure 1 – Typical multi-girder stringer bridge with and
                without the interior girders removed.
How much of the deck is acting compositely with each girder (see Figure 2)? Often,
cross beams connect these two exterior girders. Will adding shear connectors to these
cross beams help resist the horizontal interface shear? If so, how much?




         Figure 2 – How much of the deck is acting compositely with the girders?


2. Currently, the maximum shear connector spacing per AASHTO LRFD is 2 ft. This
maximum allowable spacing is a significant limiting factor for the use of precast deck
panels.

What is the maximum connector spacing that would still achieve full composite action.
An increased connector spacing (8 ft if possible) would make the use of precast deck
panels much more feasible (see Figure 3).




             Figure 3 – An increased connector spacing would make the use of
             precast deck panels much more feasible.
Testing Program
In order to answer the questions in problem statement one, the following testing program
is proposed:

Two large steel TSS sections will be connected with smaller TSS sections acting as cross
beams. The small TSS sections will be welded to the sides of the larger longitudinal
girders. The specimen will be simply supported at each end of the longitudinal girders.
This is to simulate the bridge situation described in problem statement one. Studs will
then be placed only on the cross beams. A deck will be cast over the entire specimen (see
Figure 4). A point load will be applied at the center of the deck. Strategically placed
strain gauges will provide information on how much of the deck is acting compositely
with the longitudinal beams.




           Figure 4 – Test setup to answer questions in problem statement 1.


In order to answer the questions in problem statement 2, the following testing program is
proposed:

A deck will be cast over a simply supported TSS section. Four different specimens will
be created with:
        1) studs at 2’,
        2) studs at 4’,
        3) studs at 6’, and
        4) studs at 8’ (see Figure 5).

Strategically located strain gauges will tell us for each spacing how much of the deck is
acting compositely with the TSS section.




           Figure 5 – Test setup to answer questions in problem statement 2.

				
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