Modular Joints for the Accelerated Fabrication and Erection of Steel Structures

A major challenge in the design, fabrication, and erection of steel bridges and buildings is the nodal connection between members. Designers typically develop a structural form, and then design connections to meet geometric and structural demands. However, this leads to complicated connections which are difficult and expensive to fabricate. Each connection is often unique, further complicating the fabrication and erection. To address these challenges, this dissertation introduces a new approach to the design of steel structures that modularizes the nodal connection between members and utilizes standard, rolled wide flange sections as structural members. In this approach, a connector - the modular joint - is designed for ease of fabrication and erection. Specifically, a two-dimensional (2D) modular joint for planar structures (e.g., bridges) and a three-dimensional (3D) modular joint for spatial structures (i.e., grid shells) are investigated. The modular joints are prefabricated, steel nodal connectors composed of a weldment/built up section of webs and flanges, including a starter segment to connect wide flange members through bolted splice connections in double shear. Members are oriented in strong axis bending and flanges and webs are connected independently through these splice connections, forming a moment-resisting connection. This provides flexural stiffness for truss-like, membrane-like or beam-like behavior and enables the structure to tolerate member loss. Variability in form is achieved by bending the flange splice plates to a desired angle and changing the length of the members.

This research develops this new approach through the following objectives: (1) conceptually designing the 2D and 3D modular joints, (2) developing and integrating form-finding methodologies for achieving rational structural forms within the framework of the modular joints, (3) performing sizing optimization to minimize the self-weight of structures composed of the 2D modular joints, while meeting structural performance demands and transportability criteria, and (4) evaluating the redundancy of steel bridges composed of the 2D modular joints in the event of sudden member loss. Ultimately, this research introduces a new paradigm in design - the prefabricated joint becomes a module, while the structural members are readily available standard sections - and demonstrates its feasibility through rigorous geometric and numerical studies.