Design of CFST Components and Connections for Transportation Structures: Course Module

Background:

Over the past decade, significant research has been conducted on concrete-filled steel tubes (CFSTs) and their connections for use in regions of low to high seismicity. CFSTs have application to the superstructure (piers) and substructure (deep foundations). Both CFST components and connections have been thoroughly evaluated using experimental and numerical (high-resolution, finite element modeling) research approaches. In addition, system-level evaluations have been conducted. The results from the work include new design expressions that have been implemented in AASHTO as well as state department of transportation design manuals. Advantages of the system included: (i) larger strength and stiffness for a given diameter in comparison with conventional RC construction, (ii) facilitation of accelerated bridge construction, (iii) improved constructability, (iv) use of environmentally-friendly (low cement) concrete for the concrete fill, and (v) improved seismic performance through damage mitigation. The course module will provide an overview of the research conducted, design expressions for the CFST components and connections, nonlinear modeling techniques, system-level response to vertical and lateral demands including earthquake and tsunami loading, and design examples.

Objective:

The objective is to develop a multi-part course module appropriate for practicing bridge engineers and graduate students. In addition, it is expected that parts of the course will be relevant to other transportation systems including ports and high-speed rail.

Scope:

  • Task 1 –   Develop outline for course materials.
  • Task 2 – Develop Module 1: Overview and System Configuration. This module will address the fundamentals of composite construction, configurations to facilitate accelerated bridge construction, advantages of CFST relative to RC and precast construction, and examples of CFST components and connections implemented in recent bridge construction. In addition, material savings will be provided.
  • Task 3 – Develop Module 2: Component Design. This module will address material selection and response, geometric limits, strength expressions, and stiffness expressions. This module will include discussion of materials including testing on CFSTs with low-cement concrete for improved sustainability and tube types (spiral and straight seam). Both carbon steel and high-strength, micro-alloyed tubes (40 to 70 ksi steel) will be discussed. Research results from approximately 60 large-scale component tests and large parameter studies will be presented. Design guidelines and expressions will include: (i) D/t ratio limits depending on loading (i.e. seismic vs. non-seismic) and component demands (i.e. axial vs. combined loading). (ii) composite action, (iii) flexural strength, (iv) flexural stiffness, (v) shear strength, and (vi) creep and shrinkage. The participants will be provided with electronic versions of design examples for the salient connections as well as copies of specification language.
  • Task 4 – Develop Module 3: Connection Design. This module will address connection design for ABC. The module will include discussion of: (1) four different connections including application to pier to cap beam, pier to foundation (footing or pile cap) and pile to pile cap connection, (2) experimental research results of large-scale testing of all connections, (3) parametric studies used to extend the research results, (4) design expressions for each connection type, and (5) examples of application of connections in current bridge construction. The participants will be provided with electronic versions of design examples for the salient connections as well as copies of specification language.
  • Task 5 – Develop Module 4: Nonlinear Models for CFST. This module will address nonlinear modeling approaches for CFST components and connections. CFST component modeling will include constitutive models for the steel tube and concrete infill including confinement effects. CFST connection models will use concentrated springs or zero-length fiber sections to simulate yielding of the tube or dowel bars (depending on the connection) into the adjacent component (i.e., cap beam or foundation element). Results from a case study for an RC bridge redesigned using CFST components will be presented, where the nonlinear analysis has been conducted using these nonlinear models.

Research Team:

Principal Investigator:  Dr. Dawn Lehman

Co-Principal Investigator: Dr. Charles Roeder

Research Assistant:  none