Behavior of Concrete-Filled Tube Through-Beam Connections Subjected to Varying Load Rates

Open Access
Author:
O'Hare, Edward Vincent
Graduate Program:
Civil Engineering
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
June 18, 2015
Committee Members:
  • Tong Qiu, Dissertation Advisor
  • Zoltan Ivan Rado, Committee Member
  • Sean Brennan, Committee Member
  • Daniel Linzell, Special Member
Keywords:
  • Through-beam
  • steel
  • concrete
  • connection
  • lateral loads
  • blast
  • impact
  • quasi-static
  • concrete-filled tube
  • Through-connection
Abstract:
In recent years, hollow structural sections (HSS) have become more widely used in steel construction and design. This increase in popularity is not only due to the favorable aesthetics of this member in architecturally exposed situations, but also due to the efficiency of the section’s reduced weight and area, and its increased stability compared to equivalent open sections. However, HSS connections are a major challenge to designers. In many situations this is due to the local strength limitations of this type of section and the lack of practical connection techniques. One method to overcome local strength limitations is to fill the internal cavity of the closed HSS section with concrete, forming a concrete-filled tube (CFT) member. However, there is a lack of techniques and guidelines for designing and constructing connections that directly and effectively transfer forces and moments to CFT members. This research expanded on the current state of knowledge of CFT connections through evaluation of the behavior and performance of a CFT through-beam-to-CFT column connection. The primary objective of this research was to develop a method to model the behavior of CFT through-beam connections and to expand their use to typical building structures subjected to varying load rates. The second objective included the development of quasi-static CFT through-beam connection design guidelines through the derivation of force transfer mechanisms and behavioral models that validated the effective transfer of forces and moments to both steel and concrete components in the composite CFT sections. This was accomplished using a computational parametric approach utilizing Response Surface Methodology (RSM). Finite element (FE) models of the connection were created in LS-DYNA and successfully validated against published quasi-static and dynamic test results. RSM was then used to identify significant connection parameters and to develop the connection’s behavioral model and design guidelines. General Factorial Design (GFD) was first used to determine connection failure modes, flexural behavior, and significant shear capacity and applied load contributors. Next, a Plackett-Burman Design (PBD) was used for connection parameter screening to identify those that most significantly affect each shear strength contributor. These significant connection parameters were then used in a Central Composite Design (CCD) to determine connection shear strength equations. RSM results were compiled to develop connection quasi-static design guidelines. Overall, CFT through-beam connections were shown to be an effective and reliable method in CFT building construction. Finally, preliminary analyses were performed to determine CFT through-beam dynamic connection behavior with an emphasis on establishing appropriate connection load rates to model its behavior. To accomplish this full-frame FE model containing the connection were created in LS-DYNA and subjected to impact and blast loads. Conservative connection load rates were determined for impact and blast events, which were recommended to be used in RSM models to determine dynamic connection behavior.