Identifying Critical Connections for the Global Performance of Steel Moment Resisting Frames

The investigations following the unacceptable performance of moment resisting frames (MRFs) in the 1994 Northridge Earthquake led to the development of a variety of alternative ductile connections. Tests have shown that these connections have reliable component-level performance, leading to them being recommended in standards worldwide as pre-qualified for MRFs. Current design practice consists of applying a single type of ductile connection, often the reduced beam section (RBS), uniformly throughout an entire frame. These connections are detailed and inspected to ensure that each connection has a similar minimum deformation capacity throughout the building, regardless of local deformation demands.This paper examines the potential design implications of identifying local areas within a MRF having the greatest joint rotational demands. Once identified, the connections at these locations are deemed critical to the global performance of the frame. First, the collapse analysis of a six-storey MRF with well-detailed RBS connections was conducted to quantify an upper bound system-level performance. Thereafter, a lower bound system-level performance was determined by considering a frame constructed using only connections with a lowered rotational capacity. Subsequent series of analyses were conducted to identify critical locations within the frame where RBS connections must have a high reliable rotational capacity to ensure adequate system-level performance.