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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.
This dissertation investigates the design and behavior of column base plate connections, a common structural component used to transfer forces from the steel superstructure to the supporting concrete foundation. Laboratory testing and damage reported in recent earthquakes has demonstrated the susceptibility of these connections to various failure modes. However, compared to other structural connections, column bases have received relatively limited research attention. In order to characterize the connection behavior, results from two series of large-scale testing are presented. The first phase of testing investigates common base connection shear transfer mechanisms, including plate friction, anchor rod bearing and shear key bearing. The second phase of testing investigates the response of exposed bases subjected to axial compression and flexural loading. The test observations are complimented by detailed test analyses and FEM simulations. A detailed review of existing design provisions, design guides and published research reveals that current approaches to characterize the behavior of exposed column base connections loaded in shear or a combination of axial compression and flexure are not well developed nor supported by adequate experimental validation. Thus, the test data is used to evaluate existing approaches and propose refinements. For example, the tests investigating shear key bearing indicate that current strength design provisions may be significantly unconservative for large foundations due to the size effect in concrete. Furthermore, an evaluation of experimental data indicates that the current design methods for flexural loading may be highly conservative with respect to the ultimate strength of the connection. A design approach is proposed in which the ultimate strength of the connection is governed by the formation of a plastic mechanism. All test specimens show outstanding ductility, suggesting that reliable inelastic action is possible for base plate connections. Additional methods, which are based on the concept of the center-of-rotation of the base plate, are proposed to characterize the anchor rod forces and the initial moment-rotation behavior. The proposed behavior predictions are highly accurate with respect to the test data. The dissertation concludes with a detailed overview of current design provisions along with analysis and recommendations for design.
This book comprises the proceedings of the Annual Conference of the Canadian Society of Civil Engineering 2022. The contents of this volume focus on specialty conferences in construction, environmental, hydrotechnical, materials, structures, transportation engineering, etc. This volume will prove a valuable resource for those in academia and industry.
This dissertation investigates the seismic response of Embedded Column Base (ECB) connections and anchor groups, and the rotational stiffness characteristics of exposed column base connections. The research presented is intended to address various unresolved issues on the seismic performance of column base connections. ECB connections are common components in mid- to high- rise steel moment frames, used to transfer base moments and forces into the footing. Despite their prevalence, published research on ECB connections is sparse, and a strength characterization method is yet to be established. Additionally, column base connections are often designed for uplift, requiring use of an anchoring system. Provisions in ACI 318-Appendix D generally govern such systems. However, an alternative detail has become increasingly common, wherein anchors are embedded in the footing with a plate at their lower end, also embedded in the footing. This configuration is subject to less cumbersome design requirements, though no experimental data or validated design guidelines are available to support the design of this detail.Three studies are presented, investigating (1) seismic response of EBC connections, (2) tensile capacity of anchor groups, and (3) rotational stiffness of exposed base connections. The first study includes five full-scale tests on ECB connections subjected to cyclic lateral deformations in the presence of an axial (tensile or compressive) load. Test variables for ECB connections tests include embedment depth, axial load, and column size. The connections demonstrated excellent deformation capacity, and based on test observations, it is determined that ECB connections resist applied moment, axial force, and shear through a combination of the following mechanisms: (1) horizontal bearing stresses acting on the column flanges (2) vertical bearing stresses acting on the embedded base plate at the bottom of the column, and (3) panel shear. In addition, it was determined that although designed as rotationally fixed, the specimens have some flexibility which must be considered in simulation and design. Based on observations, a method is developed to predict the strength of and ECB connection, for the purposes of developing a design model. The method shows good agreement with test data (1.01 test-to-predicted ratio), however, careful application of the method is recommended due to its reliance on empirical factors calibrated to a limited data sample. The second study involves two full-scale tests on anchors grouped to an embedded plate, and analyzes the effect of plate embedment depth (12 and 18 inches) on concrete breakout strength. The results are compared to three strength models, including ACI 318-Appendix D method, the ACI 318 punching shear equation, and the Concrete Capacity Design (CCD) method. It is determined that The CCD method shows the most promise, with an average test-predicted ratio of 0.99, while the ACI 318-Appendix D method and ACI 318 punching shear method appeared conservative and unconservative, respectively. Limitations of the study include the small size of the test set, and the absence of reinforcement in the specimens. The third study was conducted to address observations of significant rotational flexibility in exposed base connections. A method is presented to predict the rotational stiffness of an exposed base connection, validated by experimental data. The method is particularly accurate for conditions where the moment to axial load ratio is large, whereas it overestimates the stiffness of connections where this ratio is low. A detailed analysis and discussion of limitations of each study is provided.
This book highlights the latest advances, innovations, and applications in the field of structural and geotechnical engineering, as presented by leading international researchers and engineers at the 2nd Eurasian Conference on OpenSees—Open System for Earthquake Engineering Simulation (EOS), held in Turin, Italy, on July 7–8, 2022. The conference was meant to give an overview on the latest developments made with the OpenSees framework as well as to present research and practical outcomes in which OpenSees plays an important role. Conference topics cover cutting-edge applications of OpenSees in the field of structural and geotechnical engineering, the development of new elements and materials, and also the development of new pre- and post-processors. The contributions, which were selected by means of a rigorous international peer-review process, present a wealth of exciting ideas that will open novel research directions and foster multidisciplinary collaboration among different specialists.
Next to rectangular, circular and L shapes, Channel section may be the most frequently encountered reinforced concrete columns since they can be used as box wall for elevators. Nevertheless, information about the load deformation behavior is not generally available to structural engineers. Most of the investigations have been emphasized on the ultimate strength of column sections under combined biaxial bending and axial compression and the resulting interaction surface. No attention is paid to load deformation behavior. Current code provisions do not provide adequate guidelines for assessing the strength and ductility of biaxially-loaded reinforced concrete columns. Therefore, this investigation is aimed at an experimental and analytical study of the behavior of biaxially-loaded channel- shaped short columns as the applied load is increased monotonically from zero to failure. For the test purpose four reinforced concrete Channel shaped columns of nearly half the size of the true specimens were casted and tested till failure. Moment-Curvature and Load Deflection curves obtained from testing channel section were compared with the results from a computer program developed by Hsu1 and were found to be in excellent agreement. In addition a computer program was developed to calculate the ultimate flexural capacity of cracked arbitrary concrete sections under axial load and biaxial bending based on the Brondum-Nielsen s paper.
Steel and composite steel–concrete structures are widely used in modern bridges, buildings, sport stadia, towers, and offshore structures. Analysis and Design of Steel and Composite Structures offers a comprehensive introduction to the analysis and design of both steel and composite structures. It describes the fundamental behavior of steel and composite members and structures, as well as the current design criteria and procedures given in Australian standards AS/NZS 1170, AS 4100, AS 2327.1, Eurocode 4, and AISC-LRFD specifications. Featuring numerous step-by-step examples that clearly illustrate the detailed analysis and design of steel and composite members and connections, this practical and easy-to-understand text: Covers plates, members, connections, beams, frames, slabs, columns, and beam-columns Considers bending, axial load, compression, tension, and design for strength and serviceability Incorporates the author’s latest research on composite members Analysis and Design of Steel and Composite Structures is an essential course textbook on steel and composite structures for undergraduate and graduate students of structural and civil engineering, and an indispensable resource for practising structural and civil engineers and academic researchers. It provides a sound understanding of the behavior of structural members and systems.