Enhancing Masonry Wall Seismic Design: A Finite Element Approach

Title:

Design for Out-of-Plane Direction of Nonstructural Masonry Walls Using Finite Element Analysis

Authors and Publication Details:

Authors: Myeong Gyu Choi, Eunjong Yu, and Min Jae Kim Published in: Journal of Earthquake Engineering, Volume 26, Issue 1 Date: January 2022

Objective and Background

The study aims to develop a simplified finite element analysis (FEA) method for designing nonstructural masonry walls subjected to out-of-plane forces. This is particularly important following seismic events, such as the 2016 Gyeongju Earthquake and the 2017 Pohang Earthquake, which exposed the vulnerability of nonstructural elements in buildings. Since out-of-plane failures of masonry walls pose direct risks to human safety, the study proposes a bilinear elastic analysis approach to estimate failure loads and compare the results with the yield line method (YLM) in Eurocode 6 (EC6).

Introduction

Nonstructural masonry walls are commonly used as partition walls in buildings. While they do not contribute to the primary load-bearing system, earthquake-induced loads can significantly impact their out-of-plane stability, leading to failure. The Korean seismic design codes (KDS 41 34 03–06) and similar international standards lack specific procedures for designing masonry walls under out-of-plane seismic loads.

Eurocode 6 provides moment coefficients for designing masonry walls against overturning. However, these coefficients are based on rectangular walls without openings and are derived using the yield line method (YLM), which assumes a plastic behavior of the masonry. The study aims to validate a finite element analysis (FEA) approach as an alternative to YLM and provide an accurate yet practical seismic design method.

Methodology

The study proposes a two-step elastic analysis procedure to approximate the nonlinear behavior of masonry walls under out-of-plane forces. The method consists of:

1. Step 1: Initial elastic analysis using the stiffness before yielding, estimating behavior up to the effective yield point.
2. Step 2: Post-yield elastic analysis using reduced stiffness values to approximate failure behavior.
3. Integration of Orthotropic Material Properties: Since masonry walls have different material strengths along different directions, the finite element model accounts for this anisotropic behavior.
4. Calculation of Maximum Load: The total failure load is determined by summing the results from both analysis steps. The obtained moment coefficients are then compared with the YLM values in EC6.

The study evaluates walls with varying height-to-length ratios and different boundary conditions. The ThinkHazard! tool is used to assess seismic risks, and the results are mapped using georeferenced hazard data.

Key Findings

1. FEA results closely matched the YLM method in Eurocode 6, with differences under 6%, confirming its accuracy.
2. Seismic hazard assessment revealed that out-of-plane overturning is the primary failure mode for masonry walls.
3. Orthotropic material modeling significantly improved the accuracy of the finite element simulations.
4. The study provided moment coefficients for different height-to-length ratios, which could be used in practical design applications.
5. YLM results were more conservative compared to FEA results, but the proposed bilinear elastic method offered a balance between accuracy and practicality.
6. The study identified seismic performance gaps in existing masonry wall design codes, particularly for walls with openings.

Conclusion

The research successfully developed a simplified yet accurate FEA-based approach to assess out-of-plane stability of nonstructural masonry walls. The proposed method provides a more detailed representation of the wall’s behavior than YLM while maintaining computational efficiency.

Since existing design standards lack clear guidance for walls with openings, further refinements are necessary. The study confirms that bilinear elastic analysis can be a practical alternative to plastic yield line methods, enabling safer and more efficient masonry wall designs in seismic regions.

Future Work and Applications

1. Extending the methodology to walls with openings (e.g., doors and windows) for more comprehensive design recommendations.
2. Incorporating more advanced nonlinear modeling techniques to enhance accuracy while maintaining computational efficiency.
3. Validating the proposed method with experimental tests on full-scale masonry wall specimens under seismic loads.
4. Developing an automated design tool that integrates FEA-based moment coefficients into structural engineering software.
5. Expanding hazard assessment tools to include additional factors such as soil-structure interaction and dynamic loading effects.

The findings have direct applications in seismic design standards and building codes to improve the resilience of masonry structures worldwide.

?