Analytical Investigation of The Behavior of Seismic Collectors in Steel Building Structures

Abstract

This dissertation describes an analytical examination on the fundamental behavior of seismic collectors in steel building structures. Seismic collectors are key elements that collect the inertial forces that are generated in the floor mass in an earthquake and transfers them to the vertical elements of the seismic force resisting system (e.g. braced frames, shear walls, etc.). Collectors, while playing a vital role in seismic load path, have not been given proper attention in research. The fundamental behavior of seismic collectors is not clearly understood. Seismic collectors in a steel building are part of a composite floor with steel deck and concrete slab connected typically using shear studs. In an earthquake, the primary collector forces acting on a collector are axial forces. A key design of collectors includes: (1) designing the collector connections for tension; and, (2) collector members for compression, which involves stability of the collector member. In addition to the axial collector forces, the seismic collector also carries shear due to gravity load and forces due to frame drift. The fundamental behavior of collector connections under combination of load (tension, gravity and frame action) and collector members under compression is addressed in this dissertation. The analytical research covered in this dissertation includes three major parts: (1) The collector load path in a composite floor system is evaluated (horizontal plane) using 3D models of a floor. The examination includes elastic behavior to ultimate. The analytical results are compared with the current design practices. The models are based on an evaluation structure designed for the project. (2) The fundamental behavior of collector connection is examined primarily under axial load using 2D plane stress models. Collector connections are also evaluated for loads due to frame action in combination with axial load. Load path in the vertical plane of the collector is evaluated. Parametric study of key design parameters on the behavior of collector connection is also evaluated. Analytical work performed for large scale testing for collector connections is included. (3) The stability limit states of collector members is examined with 3D models of the collector and the gravity system. The analytical work to support large scale testing of collector members is also included. This dissertation describes the concept and scope of analytical research, analytical results, conclusions, and suggests future work. The conclusions include analytical results for the behavior of collector connections, collector load path in a composite steel deck diaphragm and stability modes of collector. The effect of various parameters on the behavior of collector connection is included in the results. Design recommendations are provided for collector connections.