Assessment of structural concrete approach slab cracking at integral abutment bridges

Integral Abutment Bridge, Approach Slab, Cracks, Field Monitoring

Chee, Marian Min Wei ; Fahnestock ; Larry A. ; LaFave ; James M.

关键词: Integral Abutment Bridge, Approach Slab, Cracks, Field Monitoring;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/101450/CHEE-THESIS-2018.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

The elimination of expansion joints between the bridge deck and approach slabs in an integral abutment bridge (IAB) decreases the potential for water and salt damage to the bridge superstructure and bearings. However, the lack of expansion joints in an IAB can lead to complex interactions between the superstructure and substructure, which may have unintended consequences. In particular, cracking and settlement of structural concrete approach slabs have been observed at IABs. Field observations indicate that approach slabs with skews larger than 30° tend to have diagonal cracks that concentrate in the acute corner and travel in the direction of the obtuse corner. Longitudinal cracks are more common in approach slabs that have little to no skew. The Illinois State Toll Highway Authority (ISTHA) initiated a research project to investigate approach slabs at IABs. This thesis documents the first portion of the ISTHA project, including a synthesis of existing approach slab cracking and a survey related to design, construction and performance of approach slabs, as well as field monitoring and structural analysis of approach slabs. A precast (Prospect Avenue) and cast-in-place (Arlington Heights Road) approach slab were instrumented with embedded strain gages and crackmeters to monitor their structural behavior. Models of approach slabs were created in SAP2000 to study the effect of wing walls and skew on the maximum compressive and tensile stresses in the slab. Analysis results indicate that:(1) as the length of the wing wall supporting the edge of the approach slab increase, the displacement, maximum and minimum principal stresses, and the maximum moment decrease; (2) as the skew of the slab increases, the displacement, maximum and minimum principal stresses, and maximum moment decrease; (3) there was no significant difference between a slab with half wing wall support and a slab with full wing wall support. Strain readings collected to date from the field instrumentation program were extrapolated to estimate the strains at the top and bottom of the slab, for comparison with strains from the numerical model. Maximum tensile strains from the model are approximately equal to the maximum tensile strain observed in the approach slab at Prospect Avenue. In conjunction with research that is still in progress, the work documented in this thesis will contribute to determining the causes of approach slab cracking at IABs and to developing design criteria for approach slabs to prevent cracking.