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3 1.1 General Public inconvenience and loss of income during bridge construction and rehabilitation have prompted exploration of rapid construction methods. In 2001, FHWA launched the ABC initiative (FHWA 2011). ABC is bridge construction that uses innovative planning, design, materials, and construction methods in a safe and cost-effective manner to reduce the con- struction time associated with maintenance of traffic when building new bridges or replacing and rehabilitating existing bridges. CIP bridge deck slabs represent a significant part of construction of stringer-type bridge super- structures. Much of the construction time is consumed in deck forming, placement of steel bars, and placement and curing of CIP deck concrete. Also, studies conducted by bridge owners, such as the Oregon Department of Transportation (DOT), have shown that CIP decks are considered one of the major elements of highway bridges that require continuous maintenance (i.e., patch- ing, sealing, and overlays) (Johnson 2012). CIP decks pose low durability performance because of shrinkage cracking, high permeability, and exposure to deicing chemicals and moisture. As a result, full-depth precast concrete deck panel systems have been increasingly used to replace CIP decks. In addition to high construction speed, full-depth precast concrete deck panel systems have many advantages, such as high-quality plant production under tight toler- ances, low permeability, and much-reduced volume-change cracking caused by shrinkage and temperature effects during initial curing. High-quality precast concrete decks are often two-way prestressed. They have relatively low life-cycle costs, even though they may have higher initial costs in some U.S. markets. 1.2 Literature Review Development of the full-depth precast concrete deck panel systems has occurred during three distinct periods. The first period was from the early 1960s to the early 1980s, where no stan- dard geometry, connection details, or specifications were used. The second stage was from the early 1980s to the end of the 1990s, where more experimental efforts were set towards studying the structural behavior of full-depth precast concrete deck panel systems made composite with the supporting girders (Issa et al. 1995, Issa et al. 1998). Towards the end of the second stage, innovative ideas of connecting the precast panels with the supporting girders were devised. These included the development of large 1.25-in.-diameter steel studs (Badie et al. 2002), the dovetail steel connection (Tadros and Baishya 1998), and the debonded shear key detail for concrete I-girders (Tadros et al. 2002). During this era, new rapid-construction full-depth precast concrete deck panel systems were also developed and tested (Yamane et al. 1998, Badie et al. 1998, Badie et al. 1999). C H A P T E R 1 Background
4 Simplified Full-Depth Precast Concrete Deck Panel Systems The third period started in 2000 and has continued. Most of the research activities in this period have been focused on developing standard geometry and connection details that ensure high construction speed and reduced future maintenance. Among these efforts were studies conducted at the University of WisconsinâMadison (Carter III et al. 2007). In addition, research was conducted jointly by George Washington University in Washington, D.C., and the University of NebraskaâLincoln (Badie and Tadros 2008). Other notable research was conducted at Purdue University in West Lafayette, Indiana (Frosch et al. 2010); Virginia Polytechnic Institute and State University in Blacksburg (Scholz et al. 2007, Sullivan et al. 2011); and Utah State University in Logan (Wells et al. 2013). In-progress research is being conducted at the University of NebraskaâLincoln. The goals of these research projects can be summarized as follows: (1) examine the possibility of extending the spacing of the shear pockets to 48 in., (2) simplify panel-to-panel and panel-to-girder connection details, and (3) develop recom- mended guidelines for design, detailing, fabrication, installation, and construction for the AASHTO LRFD Bridge Design Specifications. A summary of notable connection details for full-depth precast concrete deck panel systems developed in the past 25 years is given in Appendix A. More information can be found in the following references: Issa et al. 1995, Tadros and Baishya 1998, Markowski et al. 2005, Carter III et al. 2007, Scholz et al. 2007, Badie and Tadros 2008, Sullivan et al. 2011, Frosch et al. 2010, and Wells et al. 2013. Additional information can be found in the state-of-the-art report on full-depth precast concrete deck panels (Precast/Prestressed Concrete Institute 2011A) and in NCHRP 10-71 (French et al. 2011). Although the research conducted in NCHRP 10-71 was for precast/pretensioned members connected longitudinally, some of the developed connection details can be used for full-depth precast concrete deck panels supported by concreteâsteel girders. The following sections provide a summary of some of the major issues relevant to the goals of this project. 1.2.1 Variable-Depth Precast Deck Panel Systems A variable-depth precast deck panel system was developed at the University of Nebraskaâ Lincoln (Yamane et al. 1998, Tadros and Baishya 1998), as shown in Figure 1.1. This system had the following unique features: 1. A two-way ribbed panel was used to reduce the weight of the deck. Longitudinal ribs were provided only at the girder lines. Transverse ribs were provided at about 26-in. spacing. 2. The panels were transversely pretensioned and longitudinally post-tensioned. Longitudinal post-tensioning was provided using high-strength threaded bars installed in the longitudinal ribs at girder lines. 3. Shear key detail dimensions were optimized to reduce the amount of grout. 4. Shear pockets were hidden to minimize potential joints and color variation of the com- pleted deck. 1.2.2 SlabâGirder Systems Made with Discrete Joints In the early 1990s, a full-depth precast concrete deck system was used on the Suehiro Viaduct at the Kansai International Airport Line in Japan (Matsui et al. 1994, Manabe and Matsui 2004). This system had the following features: â¢ A variable-depth precast concrete panel system, as shown in Figure 1.2. The thickened ends of the panel provide enough space to support the panel and to accommodate the leveling bolt system used to adjust panel elevation. This helped the designer to reduce the self-weight of the deck and to splice the supporting steel girders without the need to use a thick haunch.
Background 5 â¢ Shear connectors provided only at the transverse panel-to-panel joints and at a relatively wide spacing of 4 ft, 11 in. This simplified the production of the precast panels, as no shear pockets were created in the panel. â¢ Discrete joints. Only the space between the steel girder and the thickened ends of the panels was filled with grout, as shown in Figure 1.3. Using the discrete joints reduced the amount of labor and materials required to fill the haunch. â¢ The precast panels were transversely pretensioned, and the completed deck was longitudinally post-tensioned. The longitudinal post-tensioning was applied after the panel-to-panel joints were grouted and cured but before the panel-to-girder joints were grouted. Therefore, the full post-tensioned force was applied only on the deck. â¢ The superstructure was designed as a noncomposite girder, conforming to the Japanese bridge design specifications. Therefore, a small number of studs were used only to anchor Figure 1.1. Details of the variable-depth precast deck panel developed in NCHRP Report 407: Rapid Replacement of Bridge Decks (Tadros and Baishya 1998) (25.4 mm = 1.0 in.). Figure 1.2. Cross section of the precast panel system used on the Suehiro Viaduct at the Kansai International Airport Line in Japan.
6 Simplified Full-Depth Precast Concrete Deck Panel Systems the precast slab with the supporting girders. However, the field instrumentation and analysis conducted on the bridge found that the superstructure behaved as a partially composite system (Manabe and Matsui 2004). It is a common practice in the United States to design slabâI-girder assemblies as composite structures for superimposed dead and live loads. Article 126.96.36.199 of AASHTO LRFD Bridge Design Specifications states that noncomposite sections are not recommended but are permitted. 1.2.3 Shear Connector Spacing and Capacity Traditionally, the AASHTO LRFD Bridge Design Specifications up to the 6th edition in 2012 specified that the spacing between shear connectors for steel- and concrete-girder bridges should not exceed 24 in. The source of this limit is unclear. An investigation described in NCHRP Report 584 (Badie and Tadros 2008) on full-depth precast concrete deck panels attributes that limit to a rule of thumb in design suggested in 1943 (Newmark and Siess 1943). The 24-in. limit first appeared in 1944 in AASHTO Standard Specifications for Highway Bridges, 4th edition, and was kept without change in the following editions until the 17th edition in 2002. When the 1st edition of the AASHTO LRFD Bridge Design Specifications appeared in 1994, the 24-in. limit was kept without change in the subsequent editions until the 6th edition. It should be noted that the 24 in. recommended by Newmark and Siess (1943) was developed for shear connectors placed at relatively small spacing along the length of the supporting girders, which is common with cast-in-place decks. The research team believes that the 24-in. limit was not intended for widely spaced clusters of studs, which are now used with full-depth precast concrete deck panels. Minimizing the number of connectors and blockouts was preferred for precast panel systems to simplify production and reduce potential conflicts at the construction site (Oliva and Okumus 2013). 188.8.131.52 Composite Deck on Concrete Girders In a study conducted at Virginia Polytechnic Institute and State University, hooked reinforc- ing bars anchored in the girder web and embedded in the concrete deck were used to examine the possibility of extending the spacing between the shear pockets beyond the 24-inch limit (Scholz et al. 2007, Sullivan et al. 2011). A full-scale mock-up was built and tested in the labora- tory, where the spacing between the shear connector clusters was set at 24 in. and 48 in. The test results showed that full composite action was achievable in both 2-ft and 4-ft pocket spacing. Figure 1.3. Precast deck during construction showing the wide spacing of the shear connectors and the grout barrier for the panel-to-girder connection.
Background 7 Based on the experimental investigation conducted at the University of NebraskaâLincoln, the Nebraska Department of Roadsânow the Nebraska DOTâused a full-depth precast deck panel system on the Kearney East Bypass Bridge in Kearney, Nebraska (Morcous et al. 2013). The precast deck was supported by concrete girders. The shear connectors were made of clusters of two 1.25-in.-diameter, 120-ksi threaded rods spaced at 48 in. The threaded rods were anchored in the girder web and in the precast panels using heavy nuts. Steel tubes provided special confinement of the grout around the threaded rods. 184.108.40.206 Composite Deck on Steel Girders Steel studs are typically used for composite decks supported on steel girders. Many studies were conducted between 2002 and 2015 to investigate the possibility of extending the spacing beyond the traditional 24 in. Among these studies was the work conducted by Issa et al. (2003) to investigate the effect of providing the steel studs in clusters on the capacity value for studs, which is known as the group effect. The test data obtained using push-off specimens showed up to 25% capacity reduction because of the clustering effects. AASHTO LRFD Bridge Design Specifications do not recommend any change in capacity with the number of studs in a cluster. Issa et al. (2003) recommended calculating the capacity as 85% or less of AASHTOâs value when more than two studs clustered in a pocket were recommended. Testing of panels connected to 84-ft-long steel girders with both 24-in. and 48-in. connector spacing was conducted at the University of WisconsinâMadison (Markowski et al. 2005). That study found no reduction in composite action stiffness or strength caused by the wider spacing, even after 2 million cycles of repeated service loading. Upon testing to the theoretical ultimate capacity, no deck uplift was detected; and the 48-in. connector spacing provided an experi- mental ultimate load capacity higher than predicted using AASHTO procedures, even though no capacity reduction was taken for multiple studs per cluster. In NCHRP 12-65, Badie and Tadros (2008) tested two composite beams where spacing between the shear connector clusters was set at 24 in. and 48 in. The beams consisted of full- depth precast deck panels supported on steel girders. The composite beams were exposed to 2 million cycles of fatigue load and then tested to failure. The test results showed that extending the stud spacing from 24 in. to 48 in. had no detrimental effect either on the composite beam stiffness or on the ultimate flexural capacity. However, the study recommended providing special confinement of the stud clusters to guarantee full development of the studs. A study conducted at Virginia Polytechnic Institute and State University examined the possibility of extending the spacing between the shear pockets beyond the 24-in. limit (Scholz et al. 2007, Sullivan et al. 2011). A full-scale mock-up was built and tested in the laboratory, where the spacing between the shear connector clusters was set at 24 in. and 48 in. The test results showed that full composite action was achievable using shear studs as shear connectors at both 2-ft and 4-ft spacing. Researchers at the TurnerâFairbank Highway Research Center in McLean, Virginia, evaluated whether the AASHTO Strength and Fatigue Limit States were applicable to clustered shear studs used for precast deck panel systems (Provines and Ocel 2014A, Provines and Ocel 2014B). Based on a review of the current domestic and international shear stud specifications, the researchers found that the fatigue provisions might be overly conservative, while the strength provisions might be unconservative. The experimental program included 16 large-scale tests using four configurations of shear stud spacing that ranged from a typical cast-in-place deck detail with studs every 12 in. or 24 in. to configurations more conducive to precast panels with clustered shear studs spaced at 36 in. and 48 in. Of the 16 large-scale tests, four were static and 12 were fatigue tests. Upon completion of the large-scale tests, small-scale (push-off) fatigue and static tests were also conducted. The static
8 Simplified Full-Depth Precast Concrete Deck Panel Systems tests focused on evaluating the AASHTO minimum longitudinal and transverse stud spacing, while the fatigue tests focused on evaluating the AASHTO shear stud constant amplitude fatigue limit. The test results showed that, regardless of the spacing between the clusters, the specimens were unable to reach the nominal design strength. The measured flexural strength was about 80% of the nominal design capacity. The static test results suggested a shear factor close to the 0.8 factor found in some international codes. The extended stud cluster spacing up to 48 in. did not appear to have a negative effect on either the relative slip or uplift between the concrete deck and steel beam. This is consistent with the conclusions reported in NCHRP 12-65 (Badie and Tadros 2008). No special confinement was provided to the stud clusters in the specimens tested at FHWA. The only source of confinement was provided by the slab reinforcement that was designed using the LRFD Empirical Design Method. 220.127.116.11 Current Provisions of AASHTO LRFD Bridge Design Specifications, 8th Edition Composite deck on concrete girders. Article 18.104.22.168 of the AASHTO LRFD Bridge Design Specifications permits a longitudinal spacing up to 48 in. but not greater than the beam depth. Equation 22.214.171.124-3 of Article 5.7.4 provides the formula for the nominal shear resistance that is a modified version of the basic shear friction model. In this formula, the shear resistance is proportional to the normal clamping force provided by the shear connectors through a friction coefficient. Additional shear resistance is provided by the cohesion and/or aggregate interlock, depending on the nature of the interface. Two upper bound limits of the nominal shear resistance are provided in Equation 126.96.36.199-4 and Equation 188.8.131.52-5. The AASHTO LRFD Bridge Design Specifications do not provide any provisions when the shear connectors are set in clusters nor any recommendations regarding any additional special confinement. Composite deck on steel girders. Article 184.108.40.206.2 of the AASHTO LRFD Bridge Design Specifications permits a longitudinal spacing up to 48 in. for members having a web depth greater than or equal to 24.0 in. For members with a web depth less than 24.0 in., the center-to-center pitch of shear connectors shall not exceed 24.0 in. Article 220.127.116.11.2 states that the spacing between the shear connectors is determined to satisfy the Fatigue Limit State given in Article 18.104.22.168 and the Strength Limit State given in Article 22.214.171.124. Equation 126.96.36.199.3-1 of Article 188.8.131.52.3 provides the formula for the nominal shear resistance. The formula shows that the shear connector strength is a function of both the concrete modulus of elasticity and concrete strength. The formula has an upper bound that is the product of the cross-sectional area of the connector times its ultimate tensile strength. AASHTO LRFD Bridge Design Specifications do not provide any provisions when the shear connectors are set in clusters nor any recommendations regarding additional special confinement. Article I8 of the Steel Construction Manual, 15th edition, published by the American Institute of Steel Construction (2017), uses the same formula as the AASHTO LRFD Bridge Design Speci- fications to determine the nominal shear capacity of the shear connectors. However, the formula applies a 75% reduction factor on the upper bound. This is consistent with the recommendation given by the study conducted at the TurnerâFairbank Highway Research Center (Provines and Ocel 2014A, Provines and Ocel 2014B).