Repairing Concrete Bridge Girders and Guardrails with Carbon Fiber Reinforced Polymers (CFRP) after a Second Impact Event
Repairing impact-damaged concrete structures, including bridge railings, deck edges at
bridge railings, and girders, is a persistent challenge facing Departments of
Transportation (DOTs) which is expected only to get worse as vehicles get large
to accommodate large payloads. Several different repair techniques have been
developed to repair impact damage which includes removing and replacing damaged
concrete, splicing ruptured prestressing strands, re-establishing internal
reinforcement, external post-tensioning, and installation of externally bonded
(EB) or near surface mounted (NSM) carbon fiber reinforcements. The type of
repair system, or the ability to repair an impact damaged structure at all,
depends on many factors including the location, extent, and severity of the
damage, the site conditions, the importance and age of the structure and the
cost effectiveness of the repair compared to replacement. While these
interventions must be considered on a case-by-case basis, there is a growing
body of research (and field implementation) that can be used to guide the
design and installation of these repairs.
Structures that have been impacted once are often located in places
where it is likely that they may be re-impacted, especially in congested urban
areas. In the event of a second impact
event after an initial repair, there is very little information available to
provide guidance to bridge engineers on how to assess, design, and install a
second repair system. Relevant questions include:
How can the extent of the damage (some of which
may be concealed by previous repairs) be identified?
Should material from previous repairs be removed
prior to a subsequent repair? If so, how should it be removed without further
damaging the substrate and to what extent (how far from the second impact
location) should it be removed?
If a carbon fiber reinforced polymer (CFRP)-based solution is selected for a subsequent
repair, how well will it bond to the existing composite material?
How much capacity can be regained from a second
repair after a second impact event?
The objectives of the
proposed research are to:
i) Identify when it is appropriate to adopt a
CFRP-based system to repair concrete girders and guardrails that have been
subjected to a second (or subsequent) impact event,
ii) Develop techniques to assess the extent and of
damage in repaired structures after a subsequent impact event,
iii) Develop guidelines for how to implement CFRP-based
repairs after a second impact event,
iv) Develop tools to predict the capacity of deck
edges/curbs/parapets under post and beam railings, parapet railings, and both reinforced
and prestressed concrete girders after a second (or subsequent) impact and
repair with CFRP materials, and
v) Compare performance (resistance, concrete
containment, etc.) of CFRP-based repairs to subsequent impact loading with
traditional repair methods.
NCHRP has sponsored a
synthesis study to assess the state of the art in repairing impact-damaged
prestressed concrete bridge girders through NCHRP Project 20-07, Task 307
(Harries et al., 2012). In that study different repair systems were identified
and assessed, and guidelines were provided on when to repair impact damaged
elements and when to replace them. The North Carolina Department of
Transportation (NCDOT) sponsored research to investigate the use of un-stressed
externally bonded CFRP for flexural and shear repair of impact damaged AASHTO
girders (Miller, 2006). The use of prestress externally bonded CFRP to repair
impact damaged prestressed girders was demonstrated through a field application
in Canada (Kim et al., 2008a). In a
subsequent study a numerical model was developed to determine the live load
distribution factors of the repair bridge (Kim et al., 2008b). While
representing only a small subset of the existing literature, these studies
demonstrate that the use of CFRP to repair impact-damaged girders can
effectively restore the capacity of the elements to their original state. While
the NCHRP study identified some structures which have been repaired multiple
times using FRP composites, no comprehensive study or guidelines have been
identified to facilitate the regular use of this repair approach.
Formal adoption of
guidelines through AASHTO is anticipated as the primary outcome of the proposed
research. To that end, it is expected that approval through AASHTO would be
pursued and that that AASHTO Sub-Committee on Bridges and Structures, T-6
(Fiber Reinforced Polymer Composites), T-7 (Guardrail and Bridge Rail) and T-10
(Concrete Design) would play key roles in the development and approval of such
a document. The availability of such an AASHTO guideline would facilitate
implementation by state DOTs. Given the unpredictable nature of impacts and
collisions, it is not possible to predict how soon after completion of the
research implementation of these guidelines could be expected. The report on
NCHRP Project 20-07, Task 307 (Harries et al., 2012) indicates that repairs of
second impacts have been implemented by some DOTs. Implementation on a
demonstration basis is anticipated as the first step towards broader
implementation until confidence in the approach is gained.
Impact damage is an ongoing challenge facing state DOTs. The instances of repaired girders, bridge railings and their supporting elements being re-impacted are common. The lack of a comprehensive set of guidelines for repair after second impacts limits the ability of DOTs to implement effective solutions and will typically require extensive research in the event a second repair is needed. The availability of comprehensive guidelines for these repairs will help extend the life of the existing infrastructure system and reduce the need for costly emergency replacements, hazardous work zones, and prolonged closures.
|Sponsoring Committee:||AFF80, Structural Fiber Reinforced Polymers
|Research Period:||Longer than 36 months|
|RNS Developer:||Dr. Mina Dawood (firstname.lastname@example.org); Dr. Wael Zatar (email@example.com); John Holt, P.E. (firstname.lastname@example.org)|
|Source Info:||Harries, K.A., Kasan, J., Miller, R., and Brinkman, R. (2012). Updated Research for Collision Damage and Repair of Prestressed Concrete Beams: Final Report.|
Kim, Y.J., Green, M.F., and Fallis, G.J. (2008a). Repair of bridge girder damaged by impact loads with prestressed CFRP sheets. ASCE Journal of Bridge Engineering 13(1), 15-23.
Kim, Y.J., Green, M.F., and Wight, R.G. (2008b). Live load distributions on an impact-damaged prestressed concrete girder bridge repaired using prestressed CFRP sheets. ASCE Journal of Bridge Engineering 13(2), 202-210.
Miller, A.D. (2006). Repair of Impact-Damaged Prestressed Concrete Bridge Girders Using Carbon Fiber Reinforced Polymer (CFRP) Materials. Master’s Thesis, North Carolina State University, Raleigh, NC.
|Index Terms:||Reinforced concrete bridges, Girders, Guardrails, Repairing, Carbon fibers, Fiber reinforced polymers, Impact, Loss and damage, |
Maintenance and Preservation
Bridges and other structures