Full-Depth Precast Concrete Bridge Deck Panel Systems (2008)

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106 Conclusions and Recommendations Panel To Panel Connection Details Using Conventional Reinforcement • Full-depth precast concrete panels can be effectively con- nected with conventional reinforcing bars. • Bar splice length can be significantly reduced through use of HSS tubes, which effectively confine the grout sur- rounding the bars. In this research, two panel-to-panel connection details were successfully developed utilizing a 4 in. (102 mm) long cut of an HSS 4 × 12 × 3⁄8 in. (102 × 305 × 10 mm) tube, as follows: – The first connection detail requires threading a No. 6 (19) reinforcing bar, which extends about 71⁄2 in. (190 mm) outside the panel to be installed, into the old panel; this results in a 6 in. (152 mm) bar embedment length. The testing program has shown that this em- bedment distance is sufficient to develop the bar yield strength. However, accomplishing this connection re- quires that the panel to be installed be tilted during installation. – The second connection detail allows vertical installation of the new panels, where a No. 6 (19) bar is embedded 11 in. (280 mm) in the HSS tube, in each of the mating joints. After a new panel is installed, a 24 in. (610 mm) No. 6 (19) long splice bar is dropped through a vertical slot, which results in an 11 in. (280 mm) splice length. The testing program has shown that this splice length is adequate to develop the bar yield strength. • The research provided a mathematical model to estimate the required development length of bars confined with an HSS tube. The model uses the development length formula currently used by the AASHTO LRFD specifications, mod- ified for the type of confinement used in this research. • The research provided a procedure to calculate the shear capacity of the reinforced joint and check it against the LRFD specifications requirements. The procedure is based on the shear friction theory already covered in the LRFD specifications. Panel to Concrete Girder Connection Detail A new connection detail was developed, where clusters of three double-headed 11⁄4 in. (31.8 mm) studs are used. The clusters are spaced at 48 in. (1220 mm). This connection de- tail opens the way for using full-depth precast deck panels for concrete girders. Additional reinforcement was found to be necessary in the web to help reach the capacity of the studs and distribute the concentrated stud stresses into the beam. Article 5.8.4.1 of the AASHTO LRFD specifications can be used to determine the horizontal shear capacity of the new detail. A group of three 11⁄4 in. (31.8 mm) studs clustered at 48 in. (1220 mm) was found sufficient for bridges with spans up to 130 ft (39.6 m), with girder spacing up to 11 ft (3.35 m), and designed in accordance with the LRFD specifications. Panel to Steel Girder Connection Detail A new connection detail was developed, where clusters of eight 11⁄4 in. (31.8 mm) studs at 48 in. (1220 mm) spacing were used. HSS tubes or individual closed ties were shown to be effective in confining the grout surrounding the studs. Experimental and analytical investigation of the new connec- tion detail found the following: • The confinement provided by the HSS tubes or the closed ties was effective in distributing the shear force among the studs in each cluster and in protecting the grout at the base of each stud against crushing. If closed ties are used, the lowest tie should be placed as close to the top surface of the girder as possible. • Equation 6.10.10.2-1 of the LRFD specifications, which is currently used to estimate fatigue capacity, does not require C H A P T E R 4 Conclusions, Recommendations, and Suggested Future Research

modification for design of stud clusters at 4 ft (1220 mm) spacing. • Equation 5.8.4.1-1 of the LRFD specifications may be used to estimate the ultimate capacity of stud clusters at 4 ft (1220 mm) spacing. Equation 6.10.10.4.3-1 should not be used for stud clusters at 2 ft (1220 mm) or greater spacing. This recommendation is expected to result in about a 30% increase in the required number of studs. • The recommendation immediately above is based on the results of push-off testing of stud groups at 4 ft (1220 mm) spacing, which gave about 30% lower capacity than the current LRFD equation for single studs. The conclu- sion may be unnecessarily conservative as the authors do not believe that the push-off testing is as realistic in mod- eling beam behavior as is the actual beam test, which showed no reduction in capacity due to use of stud clus- ters. However, the authors believe that it is a conservative approach and it does not significantly affect the overall economy of bridges. Recommended Guidelines for Full-Depth Precast Concrete Bridge Deck Panel Systems Recommended guidelines for design, detailing, fabrica- tion, and construction of full-depth precast concrete bridge deck panel systems were developed. The guidelines cover nonproprietary full-depth precast concrete bridge deck panel systems. Individual deck construction projects may have their own unique features and constraints, which may affect the design, fabrication, and construction process. The reader should therefore evaluate the relevance of the provisions in accordance with the project requirements. Proposed Revisions to AASHTO LRFD Specifications Proposed revisions to Section 9 of the AASHTO LRFD spec- ifications were developed to help provide minimum design requirements. The revisions reflect the findings from the liter- ature review, the national survey, and the experimental and analytical investigation conducted in this research. Explicitly covering precast full-depth panel systems in the LRFD specifi- cations should help promote more extensive application of these relatively new systems. Suggestions for Future Research The recommendation to use Equation 5.8.4.1-1 of the AASHTO LRFD specifications, instead of Equation 6.10.10. 4.3-1, to estimate the ultimate capacity of stud clusters at 4 ft (1220 mm) spacing is based on push-off specimen testing and may result in using as much as 30% more studs than in con- ventional single-stud applications. This recommendation may, however, be too conservative as full-scale composite beam test- ing revealed no reduction in fatigue or strength capacity as de- termined by current LRFD specifications for single-stud design. The authors believe that the push-off specimens are not as ac- curate as beams in modeling interface shear behavior in beams. The loading arrangement and the limited specimen size provide neither the true shear/flexure interaction nor the redundancy that exists in the more expensive beam testing. Therefore, the authors recommend additional full-scale beam testing if a less conservative approach than that recommended here is desired. The authors recommend a follow-up study of an actual demonstration bridge project be used to implement the re- sults of this research and to observe interaction of the various system components under actual field conditions. 107