Shervin Shameli

Topic

Seismic Evaluation of High-Capacity Shear Walls Used in Mid-Rise Light Wood Frame Buildings

Department of Civil Engineering

Date & location

• Tuesday, July 16, 2024

• 10:00 A.M.

• Virtual Defence

Reviewers

Supervisory Committee

• Dr. Lina Zhou, Department of Civil Engineering, University of Victoria (Co-Supervisor)

• Dr. Chun Ni, Department of Civil Engineering, Uvic (Co-Supervisor)

• Dr. Min Sun, Department of Civil Engineering, UVic (Member)

• Dr. Minghao Li, Department of Wood Sciences, UBC (Outside Member) 

External Examiner

• Dr. Hossein Daneshvar, Department of Civil and Environmental Engineering, University of Alberta 

Chair of Oral Examination

• Dr. Gregory Rowe, Department of Greek and Roman Studies, UVic

   

Abstract

The primary construction method for single-family homes and low-rise multi-family residences in North America is characterized by the prevalent use of light wood framing. The increasing urban population and the imperative to achieve sustainability goals demand permitting taller structures in regions previously marked by low-rise building practices. Since 2009, the Building Code of British Columbia has raised the storey limit of residential light wood frame buildings to 6 storeys. Adopting the same approach, in 2015, the National Building Code Canada (NBCC) also allowed the design and construction of wood-framed buildings up to 6 storeys. The increase in height leads to more flexible structures, potentially necessitating a more robust shear load resisting system. While light wood frame structures have, by and large, performed well during earthquakes, the evolution in construction practices creates additional demand on the lateral load-resisting system. This calls for innovative designs that boost the lateral resistance of light wood frame shear walls, especially for buildings located in high seismic zones. The seismic force-resisting system of light wood frame buildings consists of studs, sheathing panels and fasteners, which are usually nails. This system is commonly known as light wood frame shear walls. In order to enhance the seismic performance of light wood frame buildings, modifications need to be made to the conventional shear wall system. 

This dissertation explores the implications of a novel light wood frame shear wall named High Capacity Shear Wall (HCSW). The introduced HCSW has two rows of fasteners along sheathing edges. Through comprehensive analyses, this research adopts a testable approach to the investigation of HCSWs under seismic loads. This research program consists of three parts.

The first part of the study addressed the effect of the loading protocol (namely ISO, CUREE, and SPD) and loading rate on the characteristics of timber nail joints. Since nail joints are one of the key components that control the lateral performance of light wood frame shear walls, it is of paramount importance to determine how different loading rates and protocols can influence the mechanical properties of the system. Accordingly, 96 nail joint samples were tested under monotonic and reversed-cyclic loading. The findings of this part of the research laid the foundation for the reversed-cyclic loading testing program of HCSWs, which is the second part of the study. 

The second part of this research study delved into evaluating the seismic performance of HCSWs through conducting full-scale experiments. The experimental program consisted of 10 full-scale shear walls (9 HCSWs and 1 standard shear wall), and the test matrix included specimens with different sheathing thicknesses, nail diameters, and nail spacing. Test results showed that HCSW had 1.8–2.0 times the lateral load resistance of a standard shear wall (also known as the regular shear wall) with the same sheathing thickness, nail diameter, and nail spacing. The initial stiffness and ultimate displacement of the HCSWs were also greater than those of the comparable standard shear wall. Based on seismic equivalency criteria, shear walls with two rows of nails (i.e. HCSWs) could be assigned a design value of the comparable standard shear wall multiplied by a factor of 1.7.

In the last part of the study, the seismic performance of light wood frame buildings with HCSWs was investigated. The full-scale reversed-cyclic loading test results revealed that the ductility ratio of some HCSWs could be lower than that of the regular wall based on the ASTM D7989 method. This method is in fact a simplified and straightforward method for assessing the behaviour of light wood frame shear walls. Thus, a more comprehensive seismic evaluation can employ the time-history analysis of buildings following available guidelines. Consequently, the seismic performance of 1-storey and 6-storey light wood frame buildings under 12 archetypes undergoing 22 ground motions suggested by FEMA P695 was evaluated. Incremental Dynamic Analysis (IDA) was performed to evaluate the collapse capacity of archetypes. Also, the effect of initial stiffness on collapse margin ratios (CMRs) and maximum inter-storey drifts (MISD) at the design level was studied. The results showed that utilizing HCSWs improved the collapse capacity of both low-rise and mid-rise buildings. Models with HCSWs demonstrated larger CMRs (with a maximum of 2.47). Additionally, it was observed that the increase in initial stiffness could reduce the MISD at the design level as low as 0.42%. The findings of this study prove that the use of HCSWs enhances the seismic capacity of light wood frame buildings (using the same 𝑅𝑑 and 𝑅𝑜 factors of regular shear walls) in regions of high seismicity.