A lattice modelling framework with applications on reinforced concrete and autoclaved aerated concrete masonry infill walls

Aydın, Beyazıt Bestami
The heterogeneous nature and the mixture rules of concrete result in complex behavior at different domain levels as micro, meso and macro scales. Cracks evolve randomly from the micro to the macro level and result in nonlinear response of structures. Predicting the nonlinear response of concrete is directly related to the performance assessment of reinforced concrete (RC) structures, which is becoming more important, given the observed of aging infrastructure and the need for sustainability. Strength and deformation capacity estimations along with crack width predictions appear to play a key role for structural engineers in the design and assessment of structures. Another quasi-static material mostly used in structures after the concrete is the masonry elements. Masonry walls consist of different materials and exhibit complex responses similar to concrete. A combination of walls and reinforced concrete (RC) frames create infill walls. Significant infill wall damage in RC frame buildings was observed in past earthquakes. Collapse of these walls may cause loss of life. Still, understanding RC frame-infilled wall interaction is challenging, while the nonlinear behavior has been investigated in different scales by many researchers. Despite significant developments, the computational modeling of concrete and masonry fracture initiation and propagation is still under development. Many different numerical approaches have been used in the past. Recent studies in the last decade in this field have focused on using particle-based simulation methods (such as the discrete element method, lattice-based methods, smoothed particle hydrodynamics, etc.) to capture the local character of the fracture phenomenon. The advantages of these tools are the relative ease of modeling and the simulation of crack propagation using a few key parameters with the ability to bridge various scales from micro to macro levels. In this work, a practical two-dimensional lattice approach at the mesoscale level is proposed, where the continuum is discretized using truss elements extending over a predefined horizon, similar to the concept used in peridynamics with static and dynamic solution techniques for nonlinear problems. The compression response of concrete is critically reviewed and explained as an indirect tension failure by using the proposed lattice approach with a novel calibration technique that employs the magnitude of grid perturbation. Promising numerical results show that compression failure can be estimated with lattice models with tension-only failure envelopes. Simulation results of RC beams, columns, walls, and frame tests with different failure types focusing on the influence of the mesh size, horizon, and softening functions on the sensitivity of results are in good agreement with the experimental results based on estimating crack patterns, spacings, and overall monotonic load-deflection response. An explicit time integration technique with a novel proportional-integral-derivative control is used to efficiently simulate the response under monotonic loading in quasi-static manner. The proposed approach is then applied to simulate the response of unreinforced aerated autoclaved concrete (AAC) masonry-infilled RC frames. Two AAC-infilled walls were tested to have a benchmark for comparison purposes. The wall components used in these tests were used for characterization tests of AAC masonries in order to determine the mechanical properties of such behavior. The results were used to calibrate the model. In addition to the tests conducted, two other tests from the literature were used for further validation. The proposed lattice model was capable of estimating crack propagation in the infill walls with reasonable accuracy. The frame-infill wall interaction was successfully simulated by providing a realistic representation of strut formation. Finally, a parametric study was conducted to examine contact length and strut width as a function of lateral deformation. The results show that the infill wall-frame contact length is significantly dependent on the lateral deformation demand levels and properties of the interaction region. It can be stated that all simulation results demonstrate the ability of accurately predicting the direction of crack propagation and the flowing force over the structure with the proposed modeling approach, with a rather simple and intuitive method.


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Citation Formats
B. B. Aydın, “A lattice modelling framework with applications on reinforced concrete and autoclaved aerated concrete masonry infill walls,” Ph.D. - Doctoral Program, Middle East Technical University, 2022.