Strength method for exposed base plates with extended anchor bolts

Abstract

Column Base Connections are one of the most critical components of Special Steel Moment Frames (SMFs). These building components transfer the demands from the super-structure to the concrete foundation and constitute an interface between them. Because of their importance, these connections have been extensively studied during the last years. Experimental and analytical studies have been conducted to determine their primary modes of response, limit states, strength and stiffness methods, ending up in design guidelines (e.g. Steel Design Guide 1). Traditionally, exposed base plates are preferred for low to mid-rise buildings while embedded base connections are the norm for taller buildings. This research presents a methodology to design and estimate the strength of a ductile type of exposed base plates with extended anchor bolts. This type of connection is common in seismic areas such as Chile, especially for industrial facility buildings. This method aims at concentrating all plasticity in the extended region of the anchor bolts. The rest of the components (i.e. base plate, steel chair and stiffeners) are detailed by Capacity Design Criteria to sustain the anchor bolts strength. The extended length of the rods relies on an assumed target rotation capacity of the connection (e.g. 0.02, 0.04 rad). The method is validated against sophisticated nonlinear finite element simulations. These simulations serve for two purposes: i) provide general insights into the connection behavior that permit develop the strength method; ii) constitutes a test-bed to validate the proposed strength method. General recommendations for design are suggested, and limitations of the method and recommendations for future research are provided.