Master of Science / Department of Architectural Engineering and Construction Science / Sutton F. Stephens / Log construction is becoming increasingly popular throughout the U.S. Currently, seismic coefficients are not provided in model building codes for the design of the log shear walls as a lateral force resisting system for seismic forces. Current design practice is to use a response modification coefficient, R, of around 4.5. Several tests by other researchers on log shear walls showed strong energy dissipation and good lateral strength with stability after high displacements. This behavior of the log shear wall system is evidence that a higher R could possibly be used in design. The purpose of this study was to establish a response modification factor for single story log shear walls based on available shear wall tests using the definition of R provided in ATC-19. This research did not conduct testing according to the protocol and methodology of ATC-63. This work contains a history of the development of seismic design provisions in the U.S. and the evolution of the response modification coefficient. Common log construction practices are reviewed, with reference to ICC 400- Standard on Design and Construction of Log Structures. Using data provided by other researchers from physical testing and computer modeling of various types of log shear walls, an R of 6.0 is proposed based on the provisions of ATC-19. Finally, recommendations for further research to fully understand the behavior of the log shear wall system, including possible archetypes required by the methodology set forth in ATC-63, are provided.

The mechanisms that control the lateral response of stiff column-supported shallow foundations, resulting from the application of horizontal load on shallow foundations supported by stiff columns, are uncertain. Stiff columns constructed in soft clayey soil have been used to support retaining walls and in such cases, the lateral thrust applied behind these geotechnical structures is a source of horizontal loading. For seismic events, stiff columns constructed in soft clayey soil have been used to support shallow foundations subjected to horizontal load coming from the upper structure of buildings. Due to its practical applications, it has become important to understand the consequences of subjecting a shallow foundation supported by stiff columns to horizontal load by identifying the factors that control the lateral response of such systems. A series of centrifuge tests were carried out to examine the lateral response of stiff column-supported shallow foundations. The experimental trends suggested that the thickness of the coarse-granular mattress placed above the soil-column composite, called the Load Transfer Platform (LTP), controlled the lateral capacity and the overall lateral response of these systems. A numerical study using the finite element method confirmed the experimental trends. A parametric analysis was conducted with the purpose of investigating the influence of different geometry-based and material-based variables in the lateral response of these systems. The results of the parametric analysis further confirmed the importance of the thickness of the LTP in controlling the lateral response. The parametric results also emphasized the contribution of other variables to this lateral response, and these variables included the undrained shear strength of the soft clayey soil around the stiff columns, the stiff column diameter, and the spacing of the stiff columns after they are constructed in the soft clayey soil. / Doctor of Philosophy / Ground improvement is the process of improving the properties of weak soils. In practice, there are several ways to accomplish the ground improvement of weak soils. One way is to use stiff columns. Stiff columns are solid cylinders that are constructed in the weak soil in order to produce a stiff and strong soil-column composite capable of better supporting the square-shaped foundations of structures. Under horizontal load, there is uncertainty on the factors that control the lateral behavior of the stiff columns when used for the support of the square-shaped foundations of structures. An experimental and numerical approach was used to determine these factors and to understand their influence in the lateral behavior of such systems. The findings showed that the controlling factors of this lateral behavior included the thickness of a sand layer placed above the stiff columns, the diameter of the stiff columns, the spacing of the stiff columns after they are constructed in the weak soil, and the strength of the soil around the stiff columns. These findings will aid in improving the design of stiff columns used for the support of square-shaped foundations of structures subjected to horizontal load.