MIDWEST STATES POOLED FUND PROGRAM
Attachment of Combination Rails to Concrete Parapets Utilizing Epoxy Adhesive Anchors
Sponsoring Agency Code
TPF-5(193) Supplement 73
Combination bridge rails are commonly used by many state departments of transportation and often consist of a concrete parapet with an upper steel railing system. In the past, these types of bridge rails have typically been designed with the steel posts attached to the concrete parapet using a cast-in-place anchorage system. While cast-in-place anchors have performed well, they have several disadvantages, including added complexity and construction costs as well as issues with dimensional tolerances regarding their placement in the parapet.
The Iowa Department of Transportation (IaDOT) is currently interested in investigating the use of epoxy adhesive anchorages for the attachment of posts used in combination rails. IaDOT currently has selected the BR27C combination railing system where an alternative anchorage method is desired for the attachment of the steel beam and post system to a concrete parapet. An alternative epoxy adhesive connection detail was proposed, as shown in Figure 1. The Midwest Roadside Safety Facility (MwRSF) performed initial calculations to evaluate the capacity of the epoxy anchorage based on a previous MwRSF research study involving the dynamic component testing of anchors and applying the ACI code. From this preliminary analysis, it was found that the capacity of the proposed anchorage was potentially insufficient. However, the methodology provides conservative results and may underestimate anchorage capacity. As such, it was noted that the best evaluation of this proposed alternative anchorage system may be to perform dynamic component testing of the epoxy adhesive system.
IaDOT indicated that they desired an epoxy adhesive anchorage system for the BR27C combination bridge railing as well as continued development of epoxy adhesive anchorages for use in other combination railing systems.
Limited prior research has been conducted related to the use of epoxy adhesive anchors for attachment of beam and post railing system to the top of concrete parapets. In 2010, Texas A&M Transportation Institute (TTI) conducted a research study to develop two new retrofit combination steel and concrete bridge rail designs. This effort included the design of a retrofit epoxy anchorage design and pendulum testing of the anchorage system on a short section of concrete parapet in order to verify the capacity of the connection. Thus, the methodology of evaluating the alternative epoxy anchorage systems through dynamic component testing has been previously accepted.
MwRSF also conducted a research study involving epoxy adhesive anchors for attachment of concrete barriers to bridge decks. The objective of this project was to determine if epoxy adhesive anchors could be utilized to attach concrete barriers to bridge decks and to develop design procedures for implementing epoxy adhesive anchorages into concrete bridge railings. A series of 16 dynamic bogie tests and one static test were conducted to investigate the behavior of epoxy adhesive anchors under dynamic load. Additional dynamic tests were conducted on 1 1/8-in. diameter ASTM A307 threaded rods.
Comparisons were made between the results from the component tests and analytical models for epoxy adhesive anchors. The cone and full uniform bond model and ACI 318-11 procedures were both compared with the component tests in order to verify their effectiveness. Review of the comparisons between the analytical models and the tensile component tests found that both the cone and full uniform bond model and ACI 318-11 provided reasonable predictions for the failure mode of the epoxy adhesive anchors, but both methods were conservative for the prediction of capacities (i.e., under-estimated strength). The shear testing results and predicted capacities were compared, but findings were limited due to the observed failure modes in the component tests. However, it was found that ACI 318-11 provided reasonable yet conservative estimates for shear capacity of the epoxy adhesive anchors. It was also found that the proposed dynamic increase factors for concrete breakout, steel fracture, and bond strength improved the prediction of the anchor failure modes and capacities. It was recommended that the ACI 318-11 procedures be combined with the proposed dynamic increase factors for designing epoxy adhesive anchors. Recommendations for future research were made to fill gaps in the existing research effort and to evaluate the conservative nature of the proposed design methodology.
The research objective is to design and evaluate alternative epoxy adhesive anchorages for use in IaDOT combination bridge rail systems. The alternative epoxy adhesive anchorages would be developed to have equal or greater capacity than the current cast-in-place anchorages so that they could be used in new construction or as a retrofit to modify existing bridge railings. All of the proposed attachment designs would be evaluated through dynamic component testing.
The research is anticipated to be completed in two phases. The Phase I research effort will consist solely of the redesign, testing, and evaluation of an alternative epoxy anchorage system for attaching the beam and post system to a concrete parapet according to the details provided for the BR27C combination bridge railing. The Phase II research effort would consist of the design, selection, testing, and evaluation of additional alternative epoxy adhesive anchorage configurations for potential use in future IaDOT combination bridge railings.
The research effort for this project will be divided into two phases. The first phase would consist of redesign, testing, and evaluation of an alternative epoxy adhesive anchorage system for attaching the beam and post system to the concrete parapet according to the details for the BR27C combination bridge railing. IaDOT would like the connection design to be developed and tested in a shorter time frame. Thus, it would be conducted as the first phase of the research effort. This first task in this effort would be for MwRSF to review the current cast-in-place anchorage design and develop alternative epoxy adhesive anchorage configurations. This effort could include an inline anchor system or a four anchor system similar to the cast in place configuration but with spacing more compatible with the clearances required for a drill in system. The alternative epoxy adhesive anchorage systems would be submitted to IaDOT for review and selection of the preferred system to be tested and evaluated.
Dynamic component testing would be used to evaluate the proposed epoxy adhesive anchorage and to demonstrate that the capacity of the proposed epoxy anchorage was equal to or greater than the existing cast-in-place anchorage system. The capacity of the current cast-in-place anchorage has not been fully quantified with testing. Thus, one dynamic component test would be performed on the post using the current cast-in-place anchorage configuration. A second dynamic component test would also be performed on the proposed alternative epoxy adhesive anchorage system. The target impact conditions for both tests would be identical. The tests would be configured so that the applied impact load would occur at a height on the post/rail in order to produce a bending moment in the post and combined loading on the anchorage system similar to that provided during vehicle crash events. The force versus deflection, energy dissipated versus deflection, and failure modes would be documented for each test and compared to one another. These comparisons would be used to verify that the proposed anchorage provided equal or greater capacity than the current anchorage, and that the alternative anchorage did not display undesirable failure modes. This testing would require construction of a short section of simulated bridge rail for attachment of the post, base plate, and anchor hardware.
The second phase of the research effort would consist of the design, selection, testing, and evaluation of additional alternative epoxy adhesive anchorage systems for IaDOT combination bridge railings. At the present, there are multiple combination bridge railings for which the IaDOT desires to convert existing, cast-in-place, beam and post anchorages to those using epoxy adhesive anchorages. The research plan would be to review IaDOTâ€™s existing combination bridge railings with cast-in-place anchorages and select a two anchorage designs that would represent the critical installation types for conversion to epoxy adhesive anchorages. The selection of the critical designs would be based on the concrete parapet design, the structural capacity of the attachment, and the design existing cast-in-place anchorage. After selecting critical systems, MwRSF would develop proposed epoxy adhesive anchorages for those designs and submit them to the IaDOT for review, comment, and selection of preferred configurations for testing and evaluation. Once a set of proposed epoxy adhesive anchorages were selected, dynamic bogie testing would be conducted to evaluate the proposed anchorages similar to that used in Phase I. For each of the two selected anchorage designs, two dynamic component tests would be required. These tests would consist of one test on the cast-in-place anchorage and one test on the proposed alternative anchorage. The test results from the original and proposed anchorages would be compared to demonstrate equal or greater capacity and desirable failure modes. This testing would require additional construction of a short section of simulated bridge rail for attachment of the post and post plates as well as the anchorages.
If the testing epoxy adhesive anchor configurations demonstrate that they provide acceptable structural capacity, MwRSF will provide design recommendations for alternative epoxy adhesive anchorages for the remaining IaDOT combination rail attachments based on the selected critical designs.
Following completion of Phase II effort, a summary report will be completed detailing the design, analysis, and testing efforts for both phases of the research as well as future recommendations for implementation.
Planning for this project could be initiated 6 to 8 weeks after a research agreement is completed between the sponsor and UNL. It may be possible for the CAD preparation, material ordering, and Phase I construction effort to begin in March 2014. Phase I dynamic bogie testing would be planned to occur after the concrete parapet has properly cured and gained satisfactory strength, and this effort has been integrated into our existing testing queue. The Phase I testing effort would likely occur between late March and early May with documentation and reporting being completed following the Phase II effort.
The development of alternative epoxy adhesive anchorage systems for use in IaDOT combination bridge rails would provide for simpler and more cost-effective construction of combination bridge rails. The new designs would also provide more effective options for new and retrofit construction.
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