Cast-in-Place Concrete Connections for Precast Deck Systems (2011)

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453 Chapter 14 Full-Depth Deck Panel and Decked Bulb-T: Summary 14.1. Summary Speed of construction, particularly for bridge replacement and repair projects, has become a critical issue to minimize disruption of traffic and commerce. Promising systems for rapid construction include precast bridge systems fabricated using decked bulb-T (DBT) concrete girders or full-depth precast deck panels on girders. One of the hurdles that must be overcome to enable a wider use of this technology is the development of design guidelines and standard details for the joints used in these systems, which must produce full strength joints, but still allow for accelerated construction. The focus of NCHRP 10-71 was to develop specifications, guidelines, and examples for the design and construction of durable cast- in-place (CIP) reinforced concrete connections for precast deck systems that emulate monolithic construction, considering issues including speed of construction, durability, and fatigue. Chapters 8 through 14 summarize the research effort conducted by the University of Tennessee at Knoxville (UTK) research team, associated with the development of longitudinal and transverse connection concepts between full-depth deck panels and decked bulb-T flanges including the development of durable closure pour materials for accelerated bridge construction. The following provides a summary and conclusions of that study. 1) The analytical parametric study, considering parameters such as different loading locations, effect of bridge width, design truck and lane loading versus design tandem and lane loading, girder geometry (depth, spacing and span), bridge skew, single-lane loading versus multi-lane loading, and impact of cracking of the joints, was conducted to provide the database of maximum forces in the joint. These forces were subsequently used to determine the fatigue loading demand for the large-scale longitudinal joint specimen (flexure and shear-flexure) tests and the large-scale transverse joint specimen (tension) tests. 2) Initial tests were conducted using monolithic specimens that contained details to simulate longitudinal and transverse joint connection concepts (i.e., flexural and tension test specimens, respectively). The connection concepts consisted of two types of U-bar details (i.e., deformed wire reinforcement (DWR) and stainless steel (SS)) and a headed bar detail. Based on the performance of the initial tests, the most promising connection concept in terms of behavior, constructability and cost, was investigated in additional tests where parameters were varied to refine the proposed connection concepts. The results of these tests indicated that a U-bar detail with #5 equivalent deformed wire reinforcement at 4.5 in. spacing with 6 in. overlap length provided a viable detail. 3) Two categories of closure pour (CP) materials, overnight cure and 7-day cure, were proposed and studied. Based on extensive literature reviews and the experimental investigation, performance criteria for selecting durable CP materials were developed as listed in Tables 14.1.1 and 14.1.2.

454 Table 14.1.1: Proposed performance criteria of CP materials Performance Characteristic Test Method Performance Criteria Compressive Strength (CS), ksi ASTM C39 modified 6.0≤CS @ 8 hours (overnight cure) @ 7 days (7-day cure) Shrinkagea(S), (Crack age, days) AASHTO PP34 modified 20<S Bond Strength (BS), psi ASTM C882 modified 300<BS Chloride Penetrationb(ChP), (Depth for Percent Chloride of 0.2% by mass of cement after 90-day ponding, in) ASTM C1543 modified ChP<1.5 Freezing-and-thawing Durability (F/T), (relative modulus after 300 cycles) ASTM C666 Procedure A modified Gradec 1 Grade 2 Grade 3 70%≤F/T 80%≤F/T 90%≤F/T a: No S criterion need be specified if the CP material is not exposed to moisture, chloride salts or soluble sulfate environments. b: No ChP criterion need be specified if the CP material is not exposed to chloride salts or soluble sulfate environments. c: Grades are defined in Table 14.1.2. Table 14.1.2: Application of CP material grades for freezing-and-thawing durability Freezing- and- thawing Durability (F/T) Is the concrete exposed to freezing- and-thawing environments? Yes Is the member exposed to deicing salts? Yes Will the member be saturated during freezing? Yes. Specify F/T- Grade 3 No. Specify F/T- Grade 2 No. Specify F/T- Grade 1 No. F/T grade should not be specified. 4) The final test series included large-scale tests of jointed specimens including static and fatigue flexure and flexure-shear loading of the longitudinal joint details shown in Figures 14.1.1 and 14.1.2. These studies indicated that the proposed longitudinal joint detail has sufficient strength, fatigue characteristics, and crack control for the maximum service loads determined from the analytical

455 studies and was deemed to be a viable connection system to provide continuity in jointed deck systems over piers. Figure 14.1.1: Dimension of Slab Specimen 5) Static and fatigue tests under tension loading were also conducted to simulate transverse joints intended to provide continuity through the deck at bridge piers. It was assumed that at the pier in negative bending, the deck would transmit tension equilibrated by compression in the girder. Test results were evaluated based on tensile capacity, cracking, displacement and steel strain. Based on these test results, the U-bar detail was deemed a viable connection system for the transverse joint. The joint with the 7-day cure material was able to achieve higher strengths which might be attributed to the section with the lower strength overnight cure material being unable to fully develop the reinforcement. To reduce the crack sizes in the joints, it is proposed to reduce the service stresses in the joints. This could be accommodated economically by using more lower-grade reinforcement (i.e., Grade 60 rather than Grade 75 bars). Effects of variables including overlap lengths, rebar spacings, and concrete strengths were investigated. Based on capacity, service level crack widths, constructability, and cost, the U-bar detail, with an overlap length of 6 in., a rebar spacing of 4.5 in. and two transverse lacer bars, constructed of deformed wire reinforcement was recommended as an alternate detail for longitudinal and transverse joints. The tests were based on uncoated reinforcement. If epoxy-coated reinforcement were used, larger joint widths 4'' 5.5'' 0.625'' 2.5'' 4'' 5.5'' 0.625'' 2.5'' Shear Key Detail 64'' 64''6 .2 5 '' 72 '' Panel 1 Panel 2 See "Shear Key Detail" Centerline of Joint

456 may be required to develop the reinforcement across the joint. An alternative is to use stainless steel reinforcement which performed well in the initial study, but was an expensive alternative. See "Joint Reinforcement Detail" Centerline of Joint 4. 5' ' ( T yp .) #5 U bar spacing 4.5'' (Typ.) #4 bar spacing 12'' (Typ.) #5 bar spacing 6'' (Typ.) #4 lacer bar (Typ.) 2'' 1'' 6'' 3 1 8'' (5d) Figure 14.1.2: Reinforcement Layout in Slab 14.2. Full Depth Deck Panel and Decked Bulb T Design Recommendations: The research completed during the NCHRP 10-71 study resulted in the development of a comprehensive design guide for the design and construction of longitudinal and transverse joints for full depth deck panels and decked bulb T’s (DBTs). The design guide covers the detailing requirements for both loop bar and headed bar details. Adequate performance of these systems requires the use of lacer bars which improve the mechanical anchorage of these systems. Tests were conducted to investigate the behavior of these systems in shallow decks to emulate the flanges of DBTs. These shallow deck thicknesses required the use of tighter bends than presently allowed by AASHTO (2010) and thus the recommendations are restricted to wire reinforcement and stainless steel reinforcement which may accommodate tighter bends due to their higher levels of ductility. Another important feature of these joints is the performance of the closure pour materials, which was also investigated through a series of laboratory tests that included an evaluation of the shrinkage and freeze-thaw durability characteristics of candidate overnight-cure and 7-day cure materials which might be considered in rapid construction applications. The proposed modifications to the AASHTO LRFD 2010 Bridge Design Specification, as well as the AASHTO LRFD Bridge Construction Specifications are included in Appendix A, and corresponding design examples showing recommended details for the longitudinal and transverse joints are included in Appendix B.