Behavior and Kinematic-Based Modeling of Short RC Walls under Seismic Loading
Motivated by the prevalence of seismic damage and failures in short walls, this work is a study on predicting their behavior.
Nom: Nikola Tatar
Promoteur: Prof. Boyan Mihaylov
PhD summary
Motivated by the prevalence of seismic damage and failures in short walls, this work is a study on predicting their behavior. This was achieved by an experimental study and development/evaluation of several methods of analyses with varying complexity. The main goal was to develop simple and reliable procedures based on macro-kinematic modeling techniques for the predicting seismic response envelopes of short walls.
The emphasis was put on the aspect of practical application of the studied procedures from the viewpoint of modern performance-based design and assessment procedures. The behavior of short walls was evaluated experimentally by loading to failure three cantilever wall specimens featuring a span-to-depth ratio of 1.7. The applied compression load was varied between the walls. The specimens had light shear reinforcement which is commonly observed in existing structures where modern seismic design concepts were not considered.
The experimental data indicated that flexural deformation patterns and failures dominated the behavior of the walls. The lateral resistance of the walls increased with larger compressive load while accompanied with the reduced displacement capacity at failure. Detailed measurements of the entire deformed shapes of the walls were conducted in the tests for developing and validating of macro-kinematic modeling procedures. A new single-degree-of-freedom (SDOF) kinematic approach was developed to predict cyclic response envelopes of flexure-dominated walls. The approach combines an SDOF kinematic representation of the deformations in the wall and a sectional analysis of the base section. In nonlinear constitutive modeling, the approach considers various physical aspects of the behavior of walls, including the development of deformations due to cracking, simplified effects of shear, and modeling of concrete behavior in compression.
The validation of the approach against the test data and a literature database showed a good agreement between predicted and observed behavior at both global and local level. The procedure combines simplicity and accuracy, and is suitable for application in performance-based design and assessment procedures. Shear-dominated short walls were modeled using a three-parameter-kinematic theory (3PKT). The 3PKT uses three degrees of freedom kinematic model to describe the deformation patterns in diagonally cracked walls. In addition to kinematics, the 3PKT also includes equations for equilibrium and constitutive relationships for the load-bearing mechanisms in walls. This modeling approach is herein extended to account for the effects of barbells, strain penetration in the foundation, cracking above the critical shear cracks, and stirrup ruptures.
The validation of the approach with the test data from the literature of squat walls and walls with barbells showed promising results in predicting their global and local response. However, the analysis of the underlying assumptions of the 3PKT kinematics against the data from the experimental study highlighted the approach limitations in predicting the response of flexure-dominated walls. In comparison to simple modeling, a more complex nonlinear finite element analysis approach in software VecTor2 was applied to short walls. This method is based on two widely-used theories for nonlinear behavior of reinforced concrete, the Modified Compression Field Theory and the Disturbed Stress Field Method. VecTor2 response envelopes were compared against experimental data to evaluate the suitability of this method for practical application. VecTor2 was found to accurately predict the force resistance. The limitations of this method were identifed to adequately predict the displacement capacity of short walls.
In conclusion, the main contributions of this work to the body of knowledge include: 1. the experimental findings from the tests on large-scale walls; 2. the SDOF kinematic model for flexure-dominated walls that can accurately predict both global and local behavior; and 3. the defined limitations for practical application of the 3PKT and SDOF kinematic approaches, and the finite element method in VecTor2.
Publications :
Journal articles
Tatar, N. and Mihaylov, B. I. (2019). “Kinematic-Based Modelling of Shear-Dominated Concrete Walls with Rectangular and Barbell Sections”, Journal of Earthquake Engineering, DOI: 10.1080/13632469.2019.1577764
Sinha, A., Tatar N., and Tatar, J. (2020). “Rapid heat-activated post-tensionng of damaged reinforced concrete girders with unbonded near-surface mounted (NSM) NiTiNb shape-memory alloy wires”, Materials and Structures (2020) 53:88, DOI:10.1617/s11527-020-01522-8
Conference papers and presentations
