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Performance of Retrofit Highway Barriers with Mechanical Anchors

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The Texas Department of Transportation (TxDOT), like all other state highway departments, uses vehicular barriers at the edges of highway bridge decks to ensure the safety of the motoring public. A recent TxDOT research study conducted at the University of Texas at Austin was intended to develop designs for retrofit barriers connected to bridge decks using post-installed mechanical anchors, which could be used to replace highway barriers damaged by vehicular collisions. In this research study, two retrofit barrier designs were developed: one an intermittent barrier with through anchors, and the other a continuous barrier with undercut anchors. The undercut-anchor design involved groups of inclined anchors, whose capacity was governed by concrete breakout, and for which current design provisions were not directly applicable. The barriers were tested under impact loading using a specially designed pendulum that was built in the Ferguson Structural Engineering Laboratory of the University of Texas at Austin. Research results show that the current provisions of ACI 318-05, Appendix D, can safely be used to design retrofit mechanical anchors for such barriers. [PUBLICATION ABSTRACT]

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									 ACI STRUCTURAL JOURNAL                                                                                TECHNICAL PAPER
Title no. 107-S37


Performance of Retrofit Highway Barriers
with Mechanical Anchors
by G. Mitchell, M. T. Strahota, V. Gokani, R. Picón, S. Yang, R. E. Klingner, and E. B. Williamson

The Texas Department of Transportation (TxDOT), like all other
state highway departments, uses vehicular barriers at the edges of
highway bridge decks to ensure the safety of the motoring public. A
recent TxDOT research study conducted at the University of Texas
at Austin was intended to develop designs for retrofit barriers
connected to bridge decks using post-installed mechanical
anchors, which could be used to replace highway barriers
damaged by vehicular collisions.
   In this research study, two retrofit barrier designs were developed:
one an intermittent barrier with through anchors, and the other a
continuous barrier with undercut anchors. The undercut-anchor
design involved groups of inclined anchors, whose capacity was
governed by concrete breakout, and for which current design provisions
were not directly applicable. The barriers were tested under
impact loading using a specially designed pendulum that was
built in the Ferguson Structural Engineering Laboratory of the
University of Texas at Austin. Research results show that the current     Fig. 1—Basic approach of study.
provisions of ACI 318-05, Appendix D, can safely be used to
design retrofit mechanical anchors for such barriers.
                                                                          versus the design equations of ACI 318-05, Appendix D (ACI
Keywords: anchors; barriers; crash simulation; finite elements; post-     Committee 318 2005).
installed; retrofit.
                                                                          FHWA requirements for bridge barrier testing
                       INTRODUCTION                                          Under the jurisdiction of the FHWA, the testing procedures
   Bridge rails (also referred to as barriers) are very important         and evaluation criteria developed by the NCHRP govern the
structural components for ensuring highway safety. They                   performance of highway bridge barriers throughout the U.S.
should redirect impacting vehicles back onto the roadway                  Bridge barrier designs to be installed must be crash-tested in
while deforming so as to limit the forces on the occupants of             accordance with NCHRP Report 350 and must pass that
the vehicle, and they should resist impact from a collision.              document’s established performance criteria. NCHRP
To meet these demands, the U.S. Federal Highway                           Report 350 applies to all longitudinal barriers, including the
Administration (FHWA) requires that barriers meet the                     original and retrofit T203 and T501 barriers addressed by the
testing and performance requirements established in the                   project described in this paper. The Texas Department of
National Highway Cooperative Research Program                             Transportation (TxDOT) designation T203 corresponds to a
(NCHRP) Report 350 (1993).                                                commonly used intermittent barrier, and the TxDOT designation
   If an original cast-in-place barrier is slightly damaged by            T501 corresponds to a continuous barrier that is cast in the
vehicular impact, it can be repaired. More severe damage,                 frequently employed “safety” shape (also commonly called
however, may require that the original barrier be replaced                a Jersey barrier).
with a retrofit barrier. Existing barriers that are substandard
by modern requirements may also be replaced by retrofit                   Test criteria of NCHRP Report 350
barriers. Post-installed mechanical anchors are widely used                  A longitudinal barrier has two functions: 1) to prevent
to connect structural components to hardened concrete. The                penetration of the barrier by a vehicle; and 2) to redirect a
use of these anchors can be extended to retrofit barriers. As             vehicle without causing it to flip, vault, or snag on the
shown in Fig. 1, the basic approach of the research described             barrier. For any longitudinal barrier to pass an NCHRP test,
in this paper involved the design, construction, and verification         it must satisfy criteria based on both of these functions.
of a full-scale impact-test pendulum; the comparison of                   NCHRP Report 350 prescribes six test levels for evaluating
results from that pendulum with previously obtained crash                 longitudinal barriers against vehicular impact. According to
test results; and the comparison of experimental results with             that report, “Agencies should develop objective guidelines for
nonlinear finite element (FE) analyses using LS-DYNA
(Livermore Software Technology Corporation 2006).
   The research program on which this paper is based is                     ACI Structural Journal, V. 107, No. 4, July-August 2010.
                                                                            MS No. S-2008-217.R2 received July 27, 2009, and reviewed under Institute
discussed in detail by Mitchell (2006), Tolnai (2005), and                publication policies. Copyright © 2010, American Concrete Institute. All rights reserved,
Golkani (2007). This paper emphasizes the performance of 2                including the making of copies unless permission is obtained from the copyright proprietors.
                                                                          Pertinent discussion including author’s closure, if any, will be published in the May-June
and, in particular, the performance of the retrofit anchors               2011 ACI Structural Journal if the 
								
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