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From page 19... ... NCHRP Project 12-102 19 C H A P T E R 4 Technology Synthesis and Knowledge Gaps The project team compiled a significant amount of past research regarding ABC technologies, which made the proposed ABC Guide Specifications technically sound and useful. The results of the findings have been synthesized into major categories and reported in this chapter. Read the entire page →
From page 20... ... NCHRP Project 12-102 20 • Gaps covered indirectly by current AASHTO specification provisions: In many cases, ABC designs can be executed using existing AASHTO provisions; however, the appropriate provisions are not readily apparent. For example, the development of design connections between adjacent precast concrete full-depth deck panels is subjective. Read the entire page →
From page 21... ... NCHRP Project 12-102 21 concrete deck in most cases. The key difference between these systems and cast-in-place construction is the connection between the deck and the girders and the connections between the panels. Read the entire page →
From page 22... ... NCHRP Project 12-102 22 Panels Connected with Post-Tensioning: Post-tensioning has been used extensively for the connection of FDDPs in the distribution direction. Post-tensioning is not typically used for the span direction due to the relatively high bending moments that are generated in the design. Read the entire page →
From page 23... ... NCHRP Project 12-102 23 requirements around the anchorage will need to be met. This may require that the slab thickness be increased above what is typically required for cast-in-place concrete. Read the entire page →
From page 24... ... NCHRP Project 12-102 24 grades. The detailing of forming of the haunches (gap between the girder and bottom of deck) Read the entire page →
From page 25... ... NCHRP Project 12-102 25 4.2.1.4 Knowledge Gaps 1. Design of FDDP: The process for designing FDDPs is not clearly indicated in the AASHTO LRFD Bridge Design Specifications. Read the entire page →
From page 26... ... NCHRP Project 12-102 26 prestress parallel to the joint. To the knowledge of the team, no skewed panels have slipped to date; however this has never been studied in detail. Read the entire page →
From page 27... ... NCHRP Project 12-102 27 4.2.2.2 Grouted Post-Tensioning Connections Grouted post-tensioning duct connections are similar to grouted couplers; however, there are several distinct differences. The ducts are cast into the end of receiving element. Read the entire page →
From page 28... ... NCHRP Project 12-102 28 The use of CMP pockets was further studied for seismic applications, and the performance was found to be very good. Additional confinement reinforcement is recommended in order to develop adequate seismic performance of the connection. Read the entire page →
From page 29... ... NCHRP Project 12-102 29 4.2.3 Decked Beam Elements The typical decked beam element system consists of beam elements that are fabricated with an integral deck. The decked beams are joined together in the field to create the finished superstructure. Read the entire page →
From page 30... ... NCHRP Project 12-102 30 and hooked bars for decked beam connections. Very short lap lengths were used for hooked bars, which did not perform well. Read the entire page →
From page 31... ... NCHRP Project 12-102 31 Texas DOT to investigate better connections for precast double tee bridges, which have had a history of cracked joints and leakage. The study tested several details. Read the entire page →
From page 32... ... NCHRP Project 12-102 32 At that time, a connection is made, and the resulting superstructure is able to carry live load via continuous beam action. This concept is easily applied to prefabricated decked beam elements, since the deck is cast prior to erection. Read the entire page →
From page 33... ... NCHRP Project 12-102 33 4.2.3.3 Knowledge Gaps 1. Non-Shrink Grouts for Closure Joints: There is a need to have better materials specifications for nonshrink grout. Read the entire page →
From page 34... ... NCHRP Project 12-102 34 3 NCHRP Project 12-98 is being completed in parallel with Project 12-102. Fortunately, the Principal Investigator for Project 12-98 is Michael P Read the entire page →
From page 35... ... NCHRP Project 12-102 35 Most couplers use one of the following technologies to transmit tension forces from one bar to the other. They are: • Grouted sleeves • Screw Threads • Headed bars with threaded couplers • External clamping screws. Read the entire page →
From page 36... ... NCHRP Project 12-102 36 4.3.1.1 Types of Bar Couplers A grouted sleeve coupler is composed of a steel sleeve enclosing two bars placed end to end and filled with high strength grout. Tension is transferred from bar to sleeve to bar via the bond of the bars to the grout. Read the entire page →
From page 37... ... NCHRP Project 12-102 37 Threaded Sleeves: Threaded sleeves can provide essentially the full tension strength of bars up to grade 75. The deformation capacity, i.e. Read the entire page →
From page 38... ... NCHRP Project 12-102 38 Construction tolerances are tight, though less stringent than for other bar coupler types, e.g threaded sleeves. A grouted sleeve connection between two precast elements can be completed without the need for a final concrete pour around the connection. Read the entire page →
From page 39... ... NCHRP Project 12-102 39 • Influence of local debonding of reinforcing near coupler 4.3.2 Grouted Duct Connections Grouted duct connections are accomplished by grouting a single bar that projects from one member into a duct in another member. Force transfer occurs from the bar into the grout, from the grout into the duct, and then from the duct into the surrounding concrete. Read the entire page →
From page 40... ... NCHRP Project 12-102 40 Ultimate duct bond strength is decreased when the duct size is increased, though a minor effect is seen in initial bond behavior (Tazarv., et al., 2014) Read the entire page →
From page 41... ... NCHRP Project 12-102 41 Layout and Geometry: During construction, the bars in one member and the ducts in the other must be properly aligned. Use of the same template or two matching templates on connecting members during fabrication helps achieve this. Read the entire page →
From page 42... ... NCHRP Project 12-102 42 difficulties arise in the grouting of the pocket when a column-footing connection is used, as access to the pocket is limited. Figure 4.3.3-1 Pocket Connection 4.3.3.1 Design Considerations Connection Reinforcing: One design condition is that the use of a steel duct removes the need for much of the vertical shear steel in the joint region. Read the entire page →
From page 43... ... NCHRP Project 12-102 43 addition, self-consolidating concrete may be pumped into heavily congested pocket regions (Karapiperis, et al., 2010) Read the entire page →
From page 44... ... NCHRP Project 12-102 44 4.3.4.1 Types of Socket Connections Socket Connection with CIP Receiving Element: This type of socket connection is accomplished by casting in place the receiving element around a prefabricated embedded element. An opening is made in the reinforcing cage of the receiving element to accommodate the embedded element. Read the entire page →
From page 45... ... NCHRP Project 12-102 45 The bottom mat of receiving member steel does not have to pass under/over the column. The bars that would normally be directly beneath/above the column may be moved aside and placed adjacent to it (Haraldsson, et al., 2013) Read the entire page →
From page 46... ... NCHRP Project 12-102 46 erection. This configuration had the advantage of eliminating temporary support from shoring or column clamps. Read the entire page →
From page 47... ... NCHRP Project 12-102 47 Figure 4.3.5-2 Integral Precast Lower-Stage Cap with Precast Girders (NCHRP 12-74) While integral connections are not themselves an ABC connection style, this section will serve as a discussion of utilizing ABC techniques to achieve integral connections. Read the entire page →
From page 48... ... NCHRP Project 12-102 48 connection. This also means that the top of columns require confinement, as a plastic hinge will develop in this region (Khaleghi 2013) Read the entire page →
From page 49... ... NCHRP Project 12-102 49 identifying this work for the report(s) of this NCHRP project is essential, as this is the next generation for bridge seismic engineering. Read the entire page →
From page 50... ... NCHRP Project 12-102 50 loading path. Such an arrangement provides no damping, so bonded reinforcing bars may be added to it. Read the entire page →
From page 51... ... NCHRP Project 12-102 51 • The transverse reinforcement required in the footing by AASHTO is unnecessary if headed bars are used at the end of the column within the socket (Stanton, et al., 2014) Read the entire page →
From page 52... ... NCHRP Project 12-102 52 • An FRP tube adds confinement, which reduces concrete damage and increases strength. However, if the tube slips relative to the concrete a load drop will occur. Read the entire page →
From page 53... ... NCHRP Project 12-102 53 • More precautions must be taken around prestressed strands than mild reinforcement. • A U-shaped tendon with two top anchorages provides better inspectability for anchorages than other PT anchorages. Read the entire page →
From page 54... ... NCHRP Project 12-102 54 • SMA bars are restrictively expensive in their current state. Knowledge Gaps: 1. Read the entire page →
From page 55... ... NCHRP Project 12-102 55 Seating losses, deformation capacity prior to initial wire fracture, additional deformation capacity after initial fracture, and overall load-deformation behavior of unbonded PT strands were explored through monotonic and cyclic testing. Two types of strands, two types of anchorages, and varying levels of prestressing were applied. Read the entire page →
From page 56... ... NCHRP Project 12-102 56 Four large-scale specimens were designed and tested with lateral cyclic loading. Post-tensioning was run in the hollow core of the columns and energy dissipating bars were used in the plastic hinge length with an unbonded region. Read the entire page →
From page 57... ... NCHRP Project 12-102 57 mild steel. One served as a CIP reference, two served as similar base PT cases, one featured a steel jacket, one featured unbonded mild reinforcing bars, and one had a larger pre-stressing force. Read the entire page →

From page 19...

... NCHRP Project 12-102 19 C H A P T E R 4 Technology Synthesis and Knowledge Gaps The project team compiled a significant amount of past research regarding ABC technologies, which made the proposed ABC Guide Specifications technically sound and useful. The results of the findings have been synthesized into major categories and reported in this chapter.