Statement of the Problem
- The recent earthquakes in Chile and New Zealand led to a significant number of wall failures (Kam et al., 2011). Some of these failure modes involved out-of-plane displacements, which could potentially be affected by directional excitation
Figure 1. New observations in the 22 Feb 2011 Canterbury eaarthquake (Karn et al. 2011)
- There is a global concern on the contribution of bi-directional loading on these failure modes.
- So far The effect of bi-directional loading on the design/assessment of rectangular shear walls is ignored.
Purpose of Research
- Identify the key parameters influencing the seismic performance of rectangular RC shear walls under bi-directional loading.
- Assess if bi-directional loading can change the damage/failure mode expected in uni-directionally loaded walls, and if yes, what are the likely changes.
- Improve the understanding of the traditional distinction between columns vs. wall.
- Investigating different bi-directional loading patterns on rectangular shear walls.
- Simulating the possible failure mode(s) that can be activated in shear walls due to bi-directional loading in the lab.
- Develop a simplified analytical/mathematical method to predict the drift capacity of rectangular RC shear walls taking into account the effect of bi-directional loading.
- Verify the reliability of current (national and international) code-based design requirements for walls subject to more realistic cyclic loading regimes.
- Suggest recommendations/guidelines (based on experimental and analytical/numerical evidences) to improve current practice (taking into account bidirectional loading/response) for both the design of new walls and the assessment of existing ones to assist engineers in their daily practice.
1. Literature Review
- There is a limited number of study on rectangular RC shear walls under bi-directional loading.
Figure 2. Experimental study on shear walls under uni- and bi-directional loading (Kabeyasawa et al. 2014)
- Reduction in flexural stiffness
- Reduction in Plastic deformation capacity
- Reduction in ductility • Reduction in hysteretic energy dissipation capacity
- High axial strains in the boundary elements
- The effect of bi-directional loading on the boundary elements
2. Analytical Study
Analytical study is including two parts:
1. Predicting the seismic performance of rectangular RC walls under in-plane loading Including a flexural response of a wall resulting from a section analysis while controlling the shear capacity and bar buckling
Figure 3. Analytical method to predict the seismic performance of an RC Shear wall (Krolicki et al. 2011) + bar buckling
2. Predicting the seismic performance of rectangular RC walls considering the effect of bi-directional loading using simplified analytical expressions resulting from numerical study
3. Numerical Study
Numerical study is conducting using Finite Element (FE) Analysis by DIANA and has three steps:
1. Verifying the FE model with the experimental results (both under uni and bi- directional loading).
2. A parametric study with the purpose of identifying the key parameters influencing the seismic performance of rectangular RC shear walls under bi-directional loading. These parameters are introduced in the following:
3. Blind prediction of rectangular shear walls that possibly have failure mode that can be activated due to bi-directional loading before conducting the experimental tests in the lab.
4. Experimental Study
The main purpose of the experimental study is to observe the possible type of failure than can be activated by bi-directional loading.
Figure 4. bi-directional loading pattern
Figure 5. Test set up for the bi-axially loaded shear walls (Almeida et al. 2015)