Character of Overhung Concrete Deck with Barrier under Lateral Load

1
Character of Overhung Concrete Deck with Barrier
under Lateral Load

• Huali Geng
• JR Engineering, LLC.
• 6020 Greenwood Plaza Blvd
• Greenwood Village, CO. 80111

2
Overview

• This paper presents a research model showing
  stress distributions of a overhung concrete deck
  w/barrier, under imitated lateral load.
• Concrete deck and barrier is considered an
  assembled element in the research model.
• The research results show the reactions on
  supports, the stress distributions on top of the
  deck along the major axis, and potential yield
  zones on the concrete deck.
• It will assist practical engineers to
  re-recognize this type of structure.

3
Conventional Design Methods

• Unit length method is one of the common design
  methods often used by practical engineers to
  analyze a concrete barrier w/ an overhang
  structure. It is considered a conservative design
  method.
• AASHTOs barrier design method is another common
  design method. Previous research shows that there
  are some limitations for using the AASHTO method
  and it may only be used for concrete barriers
  which are fixed to the ground. When the barrier
  sits on a support not the ground, the AASHTO
  method will be inaccurate due to the lack
  sufficient rigidity of the support.

4
Research Model

• The research model was established by SAP2000 and
  analyzed by the Finite Element Method (FEM).
• Dimensions of the barrier were adopted from Type
  7 concrete barrier of Colorado Department of
  Transportation (CDOT) .
• The Lateral load was adopted from TL-6 of AASHO.

5
Research Model Details

• Concrete one span deck w/overhang and barrier at
  the end of overhang
• Span of the deck8 ft
• Thickness of concrete deck8 in
• Length of overhang4.5 ft
• Length of the model200 ft

6
Assumptions

• Concrete cracking control stress less than 0.1
  fc.
• Rolled joint is used at first support.
  Rotation-free joint is used at second support. It
  will exaggerate moments on top of the deck at the
  first support.
• Continuity at each of structural elements.
• Lateral impact load is simplified as a
  concentrated, static load at the top of barrier.
• Stresses discussed and observed are tensile
  stresses.

7
Reactions on Deck First Support

• Major reactions on the first support are in the
  Z-axis direction.
• The results show that at five feet from the
  action point of the load, the reactions are
  downward forces. Contrarily reactions more than
  twenty feet from the action point are under
  upward forces.
• The reactions on the research model are different
  than the assumed reaction distribution based on
  the laws of classic structural analysis.

8
Reactions on Deck Second Support

• The tensile forces (in X-axis direction) on the
  second support are present from the center to
  fifteen feet on each side of the center due to
  the effect of lateral load.
• These tensile forces dominate in the center and
  decrease from that point to the far end of the
  model due to the integrity of structure.
• The conventional design methods will not reflect
  it.

9
Stresses Distribution on Top of Concrete Deck

• The tensile stress distribution (on Y-axis
  direction) widely spreads from the inner corner
  of the barrier and deck to the first support, and
  then declines dramatically before it approaches
  the second support.
• Tensile stresses on the top of deck spread in a
  angle (from the center of the model) that is
  greater than 45 degrees, an example of classic
  structural analysis.

10
Stresses Distribution on Top of Concrete Deck
(continues)

• The tensile stress distribution (on X-axis
  direction) shows that the top of the deck will be
  convex (lighter gray areas). These convex areas
  may result in yield zones. This phenomenon
  presents the yield line theory of cantilever
  slab.
• However, the tensile stresses on Y-axis direction
  are dominated stresses.

11
Conclusions

• The research model reacts like a monolithic
  element under external lateral force.
• Reactions on the supports vary along supports.
• The spread angle (from the center of load) of
  tensile stress distribution on the deck is
  greater than 45 degrees, commonly explained by
  the law of classic structural analysis.