To be held on Monday, January 4th, 2021, 12:10-13:00
via zoom meeting - link
Multiscale, numerical and experimental study on concrete structure
Dr. Gili Lifshitz Sherzer
Post-doctorate, Department of Civil and Mineral Engineering, Faculty of Applied Science and Engineering, University of Toronto
This study deals with development, calibration, validation and comparison of two distinct finite element models that explicitly account for crack propagation in concrete: Lattice Discrete Particle Model (LDPM) and Finite Discrete Element Method (FDEM). Calibration was achieved by evaluating a combination of input parameters for 3D modeling performed at a laboratory-scale. Mechanical properties including compressive and splitting tensile strengths and a microscopic assessment of crack development were utilized to calibrate and validate the models. Calibration, validation and crack pattern analyses were all performed on the same mix design. It was observed that the uniaxial compressive strength (UCS), Brazilian disc (BD) strength and macroscopic fracture patterns showed a good fit to the results from laboratory experiments. The capabilities and limitations of LDPM versus FDEM are also discussed. This study includes details on parametric study, and validation of the models by three-point bending of a beam with/without a notch as compared to the size effect law. The yielding load obtained from the numerical simulations of the models for the beams with height (d) of 75 and 100mm both exhibit similar results, and there was also agreement between modeled yielding loads and experimental UCS and BD results. The application to the scale effect resulted in a good correlation between LDPM and FDEM simulations for d=100mm (3.2 vs. 8.7% error), whereas for d=50mm errors of 14.6% and 20.7% were obtained for the methods.
The second aim of this study is to develop a lattice model for modeling the response of high strength concrete under loading. Our solution is based on utilizing the Lattice Discrete Particle Model (LDPM). While for an ordinary concrete the static failure can satisfactorily be modeled by analysis of damages in the mortar alone, this is not the case for concretes with high strength, high strain-rate, and or with large number of voids, where critical damages can happen through the aggregates as well. The heterogeneous structure of concrete affects significantly the crack propagation phenomenon. Fracturing through aggregates may lead to a brittle failure which is of greater risk for fatal damages e.g., in concrete based constructions. Beside such a change in failure mechanism, the shear transfer is also affected by new pathways introduced due to fracturing through aggregates. The original LDPM does not account for fracturing through aggregates. We aimed to solve this problem as we believe that its role in development and modification of fracturing, i.e., introducing different fracture patterns (failure pathways) is of great importance in civil engineering applications. Furthermore, this study would help to better understand relationships between dynamic fracture toughness and the strain rate.
The third object of this study was to predict the behavior of a T cross section steel fiber reinforced concrete beam with conventional longitudinal (R/SFRC) and without conventional shear reinforcement in the shear span where the beam is predicted to fail in shear.
About the speaker:
Dr. Gili Lifshitz Sherzer received her PhD from Ben-Gurion University of the Negev (BGU) in 2019. Her research was to develop a computational technology for numerical simulation of concrete structures. Toward achieving this goal, her specific scientific objective was to formulate, calibrate, validate multi-scale models and up-scaling methodology. In addition, during her PhD she served as an external lecturer and teacher assistant.
Currently she is a Postdoctoral research fellow at the University of Toronto under supervision of Profs. Giovanni Grasselli and Karl Peterson. Her research interest is on development models, calibration, validation, experimental and predicting reinforced concrete material behavior under different loading conditions. Her research so far has yielded three Q1 peer reviewed papers, fourteen papers published in peer-reviewed conference proceedings, two submitted Q1 peer reviewed papers, seven research project reports and eleven research grants.