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Exposed column base plate connections are crucial components in earthquake-resistant steel structures, but previous research has produced a limited quantitative understanding of its load transfer mechanisms. Recently, a large-scale experimental program was performed at the University of California at Davis to achieve a fundamental understanding of the base connection response under axial compression and strong-axis bending. The study described in this Thesis complements the experimental program and consists of two series of finite element simulations conducted to: (1) develop a validated approach for simulation of exposed column base connections and (2) to perform an analytical parametric study using the validated approach to generalize the findings of the experimental program to untested situations. The parameters scrutinized in the numerical study are anchor rod grade and configuration, base plate size and thickness, column size, magnitude of axial load, and the direction of lateral load. The FEM models were validated by comparing the analytical results against various experimental observations (e.g. the load deformation curve, and measurements of anchor rod strains). The finite element simulations reproduced the experimental results and produced new findings. The simulations were determined to appropriately simulate deformation (and failure) modes (i.e. deformed base plate shape, anchor rod yield, etc.), and the excellent ductility of the base connections (i.e. excess of 6% drift capacity). The "thin" base plates displayed more ductility compared to "thick" base plates. The bearing stress distribution gets concentrated underneath the column flange (e.g. compression region), and it varies depending on the base plate thickness. Contrary to current design considerations, inclined and straight yield line patterns developed on the tension and compression region of the base plate, as well as on the sides of the plate, depending on the base plate footprint and thickness. In addition, two base connections with realistic, first-story column sizes were tested to observe their response. It was discovered that a substantially "thick" base plate develops most of its yield lines on the tension region of the plate, caused by the large prying anchor rod forces.
Column base plate (CBP) connections are one of the most crucial structural components of steel structures that act as a transfer medium for all the forces and moments from the entire building into the foundation. Importance of this type of connection becomes significant when the structure experiences dynamic loading, such as wind or earthquake, which incorporates dynamic effects in the structure that need to be transferred to the foundation. Considerable research efforts have been made over the past few decades on CBP connections, which led to the publication of AISC Design Guide 1 (2006) for CBP design. This design guide is still widely used in the industry. All the previous studies and design guidelines considered only the uniaxial (major axis) bending moment combined with axial load for CBP connection design. However, very often the base plate experiences a bidirectional bending moment from lateral loads during any dynamic loading event. Although, the column is designed and checked under combined axial load and bi-axial bending, when it comes to the base plate connection, only the axial load and major axis bending are considered. Therefore, the objective of this research is to investigate the behavior of CBP connections subjected to combined axial load and biaxial bending through an extensive numerical parametric study, using general purpose finite element software ABAQUS. For this numerical study, an accurate nonlinear finite element (FE) model is developed, considering both geometric and material nonlinearities and validated against experimental results that are available in the literature subjected to monotonic and uniaxial cyclic loading. Validation results show that the developed FE model can effectively simulate force transfer at major contact interfaces in the connection. Concurrently, a database of CBP connection subjected to axial load and uniaxial bending, is constructed from the literature to identify the influential parameters as well as different failure modes of the CBP connection, using Machine Learning (ML) approach. Among nine different ML models, the Decision tree based ML model provides an overall accuracy of 91% for identifying the failure mode whereas base plate thickness, embedment length, and anchor rod diameter are found to be the influential parameters that govern the failure mode of CBP connections. Therefore, a total of 20 different FE models that have different base plate thicknesses and yield strengths, anchor bolt sizes and quantity as well as embedment lengths, grout thicknesses and axial load ratios are developed. Furthermore, a bidirectional symmetric lateral loading protocol is developed and applied with constant axial compressive load in the developed models. The study reveals that the thickness of base plate and anchor rod diameter are the governing parameters for different base connection behavior such as moment rotation response, maximum bolt tensile force, and yield line pattern of the base plate. Moreover, the rigidity of the base plate connection is found to be in the semi-rigid region under biaxial bending condition. Finally, this study found that the available methods for uniaxial bending overpredicts the connection rotational stiffness compared to the stiffness obtained from numerical analysis considering biaxial bending.
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Structural mechanics in Australasia is the focus of the some 100 papers, but among them are also contributions from North America, Japan, Britain, Asia, and southeast Asia.