Learning Module – T-stub in tension (EN)

Connection design can be difficult to teach, given the detailed nature of the topic and the fundamentally three-dimensional behavior of most connections. However, connections are critically important, and lessons learned in the study of connection design, including load path and identification and evaluation of failure modes, are general and applicable to structural design broadly. IDEA StatiCa uses a rigorous nonlinear analysis model and has an easy-to-use interface with a three-dimensional display of results (e.g., deformed shape, stress, plastic strain) and thus is well suited for the exploration of the behavior of structural steel connections. Building on these strengths, a suite of guided exercises that use IDEA StatiCa as a virtual laboratory to help students learn about concepts in structural steel connection behavior and design was developed. These learning modules were primarily targeted to advanced undergraduate and graduate students but were made suitable for practicing engineers as well. The learning modules were developed at Laboratory for Numerical Structural Design by Assistent Professor Martin Vild from the Brno University of Technology.

Learning Objective

After performing this exercise, the learner should be able to describe the basic component of bolted connections, T-stub and associated phenomena, like prying action.

Background

Component method in EN 1993-1-8 divides the connection into components. The basic component of bolted connections, widely used for assembly joints, is T-stub. The shape of the T-stub varies depending on its location in the connection, but the calculation remains very similar. Even such a complicated haunched end-plate connection is divided between eight rows of T-stubs. Each such a T-stub is calculated individually or as a part of a bolt group, and the ultimate moment resistance is the sum of T-stub tensile resistance times the lever arm to the center of compression.

A typical feature of T-stubs is prying action. The sum of tension in bolts is higher than the applied tension to T-stub. This is caused by prying – a bearing action of plates to the support, typically another T-stub, in this case consisting of the column flange and web. Notice that the sum of bolt tensile forces in the following figure is \(2 \cdot 187.2 = 374.4\) kN, which is significantly more than 193 kN of applied force.