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Introductory steel design courses focus on the analysis and design of primary members, which typically include tension members and connections, compression members, flexural members, and beam-columns. Introducing structural steel design concepts to students presents its fair share of challenges. First, it is difficult for students to visualize and accurately predict the potential failure modes of a tension member: yielding of the gross section, rupture of the net section, and block shear. Second, it is also difficult for students to visualize the buckling modes of steel columns, which vary with shape and type of bracing. Students particularly struggle with the determination of buckling modes between strong and weak axes based on effective lengths. Third, flexural failure modes of steel beams are very difficult for students to visualize and understand when each mode controls. The failure modes are complex and fall into three categories for compact shapes: yielding of the cross section, inelastic lateral torsional buckling, and elastic lateral torsional buckling, which is dependent on the unbraced length of the compression flange. Non-compact sections also include local buckling of the flange or web, but identifying the relationship between the unbraced length and beam span and how the unbraced length affects the flexural capacity tends to be the most difficult concept for students to grasp. This paper provides a detailed overview of the design, fabrication, and implementation of three large-scale experiential learning modules for an undergraduate steel design course. The first module focuses on the tension connections by providing physical models of various failure types including yielding of the gross section, rupture of the net section, and block shear; the second module focuses on the capacity of columns with different amounts of lateral bracing about the weak axis; and the third module focuses on the flexural strength of a beam with different unbraced lengths to illustrate the difference between lateral torsional buckling and flange local buckling/yielding of the gross section. The three modules were used throughout the steel design course at Saint Louis University and Rose-Hulman Institute of Technology to illustrate the failure mechanisms associated with the design of steel structures.
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A Novel Fiber Element to Simulate Interactive Local and Lateral Torsional Buckling in Steel Moment Frames
attributed to loss of load carrying capacity of the individual members. Dominant failure modes in structural steel members include interactions between inelastic lateral torsional buckling, global buckling, and local buckling (referred to as Interactive Buckling). Accurate performance assessment of steel moment frames highly relies on the accuracy of the model-based simulations of such limit states. Commonly used concentrated hinge and fiber-based models fail to address the physics of this response leading to inaccurate performance assessment of structures. A nonlinear displacement-based fiber element [named Torsional Fiber Element (TFE)] to simulate monotonic and cyclic interactive buckling in steel members is proposed and implemented on OpenSees (an open-source finite element software). The element includes St. Venant as well as warping torsion response that are essential for lateral torsional buckling response in a wide-flange I-section, through enriched displacement fields and strain interpolation. Response of local buckling is represented in a quantitative manner using a novel multi-axial constitutive relationship with calibration of an effective softening behavior in the post-buckling response. Mesh dependency issue related to the softening material model is also discussed and addressed through a proposed non-local strain measure. The efficacy of the model is assessed through several continuum finite element simulations and experimental data.
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- Award ID(s):
- 1926202
- PAR ID:
- 10568550
- Publisher / Repository:
- Structural Stability Research Council
- Date Published:
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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