Strength, durability, and application of grouted couplers for integral abutments in accelerated bridge construction projects
In areas of high traffic, long term bridge construction can have significant impacts on the traveling public and surrounding communities. To minimize this impact, engineers and contractors prefabricate bridge elements and utilize technologies that facilitate rapid bridge assembly. This strategy is known as Accelerated Bridge Construction (ABC) and has gained the attention of the bridge community as information and the benefits of ABC projects has been shared. There is untapped potential in this movement as some advantages of certain bridge types, like the integral abutment bridge, have seen limited use. Integral abutment bridges were developed as a means of eliminating the expansion joint from the bridge superstructure which present long term maintenance concerns. To eliminate the joint, integral abutments rigidly connect the superstructure and foundation so that the entire structure experiences thermal expansion and contraction as one. For this reason, the integral abutment is often large and heavily reinforced which present challenges for use in ABC projects. The size of the abutment presents weight issues and mechanical splicing of the abutment to the deep foundation presents tight construction tolerances.
This research investigated integral abutment details for use in ABC projects through mechanical splicing of the integral diaphragm and the pile cap. To complete this task, two ABC details were evaluated in the laboratory based on constructability, strength and durability. The construction process used to fabricate and erect the specimen was documented and is presented in this report, as this criteria often governs the design of ABC details. The specimen were tested for strength and durability by simulating thermal loads and live loads. Strain gages placed on the concrete and reinforcing steel captured the strain developed in the testing to evaluate strength. Displacement transducers placed across the precast joint measured the crack width that developed under loading in order to assess durability. The ABC details investigated are the grouted rebar coupler detail and the pile coupler detail. In order to establish baseline performances for an integral abutment, a typical cast-in-place detail was also constructed and tested.
In the grouted rebar coupler detail, a plywood template was used to “match cast” the pile cap and the integral diaphragm. The template marked the locations of the spliced reinforcing steel and served as the base for the formwork in the integral diaphragm, holding the grouted couplers in position. The template proved to be simple to construct and resulted in the successful alignment of seventeen spliced steel bars and grouted couplers over the length of an eight foot specimen. A grout bed was pumped into the precast joint on the specimen, unfortunately grout leaked past two of the grouted coupler seals and obstructed the grouting of two couplers. Even with the two un-grouted rebar couplers, there was more than adequate strength created by the connection and the crack width that developed at the precast joint was comparable to that of the cast-in-place specimen.
The pile coupler detail was developed to facilitate the use of a slide in bridge with integral abutments. The pile coupler reduced the number of spliced connections between the pile cap and integral diaphragm significantly in order to facilitate adequate construction tolerances. The splicing system worked well during construction; however the detail’s performance in terms of strength and durability was less than ideal. If there is a demand for the benefits of the pile coupler detail in terms of constructability, the detail should be further investigated as several lessons were learned from the testing which could improve the structural performance of the detail.