Date of this Version
Gee, D. 2020. "Eliminating Rebar Splicing in Transverse Joints of Precast Full Depth Bridge Deck Panels," MS Thesis, University of Nebraska-Lincoln, Lincoln, NE.
This study looks at the removal of longitudinal rebar splicing when sufficient longitudinal post-tensioning is provided for full-depth precast deck panels for simply supported bridges. Full-depth precast prestressed concrete deck panels are high quality plant produced pretensioned panels. They are often post-tensioned at the site to provide an average net compression in the joint of at least 250 psi due to effective prestress. This is to ensure adequate transfer of load as truck wheels pass over the joint. This net compression on the transverse joint is not explicitly clear by the AASHTO LRFD Bridge Design Specifications. Based on this section, it is unclear if the use of post-tensioning that provides a net compression of at least 250 psi at the joint, due to effective prestress, still requires the coupling of rebars over the transverse joint. However, in cast-in-place deck construction, no longitudinal post-tensioning is generally introduced and no transverse joint is required. It is a requirement of the ASSHTO LRFD Bridge Design Specifications that secondary reinforcement be placed continuously along the direction of traffic. Following the empirical deck design in AASHTO, two-thirds of the primary transverse reinforcement should be provided for secondary longitudinal reinforcement. The problem is observed when a number of designers insist on strictly following the code for full-depth precast deck panel designs without considering the impact of longitudinal post-tensioning and naively emulating cast-in-place practice without taking full advantage of precast concrete. Although providing secondary reinforcement for each precast panel is possible, the number of splices and the number of pockets for field splicing due to these extended bars become a significant challenge to this type of construction. By using sufficient net compression at the joint, rebar splicing can be removed. The objective of this research is to investigate the post-tensioning level required to eliminate rebar splices in transverse joints for full-depth precast deck panels. Two full scale full-depth precast deck panels were post-tensioned to multiple levels varying the net compression at the joint between 100 to 350 psi. Static tests with a point load simulating one-wheel load of the 32-kip axle multiplied by the dynamic allowance factor (1.75 for the deck joint) was applied to the panel-to-panel connection joint for various post-tensioning levels. The test results show that when a net compression of at least 300 psi is applied at the transverse joint, rebar splicing is not needed. This is supported by the lack of cracking that occurs when applying the 32-kip loading along the joint.
Testing along the longitudinal joint was also conducted as a separate research topic, and some of the results are presented. The main objective of this testing was to determine the viability of using a staggered rebar joint with a minimal joint width. This was accomplished by using ultra-high-performance concrete (UHPC) and self-consolidating concrete (SCC) with steel fibers to enhance the ductility and strength of the joint. By using a joint that gives sufficient development length of the bars, which is shorter for fiber reinforced concretes, it is shown that the joint detailing is adequate for service loadings.
Advisor: Chungwook Sim