Rationally Designed Staged Posttensioning to Abate Reflective Cracking on Side-by-Side Box-Beam Bridge Decks

Abstract

Side-by-side box-beam bridges are often used at sites with tight under-clearance requirements and specified for accelerated construction. However, longitudinal reflective deck cracking is a recurring problem for these bridges and it raises concern for their durability and long-term safety. North American practices of the transverse connection design of this particular bridge are discussed in NCHRP Synthesis 393, and the Michigan design is presented as the preferred procedure. The most recent design in Michigan is an empirical procedure that incorporates the majority of the Synthesis 393 recommended best practices. Yet reflective deck cracking persists. A rational design procedure for which an analysis model was developed is presented here. In the rational design procedure, the analysis model is utilized to calculate the moment demand along the transverse joints. A two-stage transverse posttensioning procedure is recommended following AASHTO load and resistance factor design stipulations based on the moment demand calculated from the analysis model. The second stage of posttensioning precompresses the cast-in-place concrete deck, ensuring crack control. The objective of this study is to demonstrate the effectiveness of the two-stage posttensioning design and implementation procedure to mitigate reflective deck cracking. The effectiveness of the recommended design is demonstrated by utilizing a multistep finite element simulation of the construction process under construction and service loads. The cracking potential of the deck is evaluated under both current Michigan Department of Transportation and the proposed two-stage transverse posttensioning schemes. It is demonstrated that the two-stage posttensioning process can eliminate tensile stresses developed under gravity loading and reduce the temperature load effects to abate reflective deck cracking.

Experimental Investigation of Shear Keys for Adjacent Precast Concrete Box Beam Bridges

“…Since RDSK has been used as a direct indicator for shear key cracking [4,[7][8][9][12][13][14], it is crucial to accurately simulate the interface of the beam and shear key in finite element models (FEMs) using solid elements. Three commonly used methods are the full bond [15][16][17], friction [13,[18][19][20][21], and traction-separation model [13,[21][22][23]. Full bond is suitable for the interface of concrete and grout materials with strong bonding ability, such as epoxy, MgNH4PO4, and UHPC, but not for commonly used nonshrink grout and concrete.…”

Full-Scale Evaluation of an Innovative Joint Design between Adjacent Box Beams

“…Dong et al ( 4 ) pointed out that radical changes in shear key geometry (i.e., very sharp corners) may result in higher stress levels. Ulku et al ( 5 ) found that the temperature gradient caused by weather changes is the main factor that causes cracks to develop near the top of shear key interfaces. Another cause of cracks was reported to be post-tensioning forces that are not uniformly distributed at the keyway because of shear lag.…”

Longitudinal Joint Performance of a Concrete Hollow Core Slab Bridge

“…The bridge can be analyzed in its entirety: a plate with opposite edges simply supported and the other two edges free under uniformly distributed load; this is a macromechanical model of a precast orthotropic bridge (1,4). The formation process of the longitudinal cracks can be studied with the bonding relationships between cast-in-place and precast concrete (6,7,8,9,10).…”

“…When the box beams are placed adjacent to each other, there is no continuity enabling them to function as a single structure. The small longitudinal joint between hollow core slabs, typically called a hinge joint, is normally filled with grout or an appropriate non-structural sealant to prevent water leakage and moisture penetration between beams, as well as to support load transfer ( 4 ). The deck is built with reinforced cast-in-place concrete.…”

“…The cure of this layer may take some days; however, very little deck forming is needed. Concrete compressive strength and minimum thickness may be required ( 3 , 4 , 5 ).…”