Structural Analysis of Existing RC Bridge Deck Slabs Structural Analysis of Existing RC Bridge Deck Slabs

Licentiate thesis, 2015

Due to ageing of the bridge stock, continuously increasing load requirements, the need for assessing existing bridges is becoming increasingly important. Reinforced concrete (RC) bridge deck slabs are among the most critical parts to the load carrying capacity of bridges. Previous research indicated that the assessment method used in current practice largely underestimate the load-carrying capacity. The objective of the study reported in this licentiate thesis is to develop and calibrate improved methods for assessment of load-carrying capacity and response of existing bridge deck slabs. This study proposes an enhanced assessment through improved structural analysis and resistance evaluation in order to achieve higher detectable load-carrying capacity. To achieve this objective, the scientific approaches including literature study, laboratory tests, analytical analyses and finite element analyses were adopted. Two major studies and a series with supporting tests were conducted as following: A large test series, in which three specimens containing traditional steel bar reinforcement in ordinary concrete, were carried out to study the load carrying capacity and structural behavior of two-way slab. A proposed multi-level assessment method was validated through two case studies: a two-way slab and a cantilever slab. The multi-level assessment method includes simplified analysis, 3D linear FE analysis, 3D nonlinear analysis with shell elements, 3D nonlinear FE analysis with continuum elements include fully bonded reinforcement as well as 3D nonlinear FE analysis with continuum elements including bond-slip for the reinforcement. To develop the modeling strategies for two-way RC slabs with continuum elements, parameter studies has been carried out to investigate the influence of different modeling choices. Parameters including finite element properties, modeling of concrete, modeling of reinforcement and stiffness of supports were varied in different comparative models to investigate the influence. The study shows that existing methods currently used in assessment are not able to accurately reflect the response of RC bridge deck slabs, and underestimate their capacity. With enhanced assessment methods, such as the nonlinear finite element method, it is possible to better reflect the structural behavior, and more accurately determine the load carrying capacity. Two case studies have proven that the multi-level assessment method is able to reflect the structural behavior at different levels of approximation, which is beneficial in evaluating existing RC slabs. The parameter studies indicate that modeling choices such as geometric nonlinearity, crack bandwidth and Poisson’s ratio have significant impact on determination of the load-carrying capacity. Finite element properties, reinforcement model and stiffness of supports influence crack pattern and load distribution respectively.