Integration of Analytical Investigations on the Fracture Behavior of Welded Moment Resisting Connections

The objective of this investigation is to utilize finite element analyses to investigate the fracture behavior of welded beam-column connections and, thereby, examine how fracture resistance is influenced by various design and detailing parameters. A related objective is to help integrate fracture-related data from other SAC investigations on materials, welding/joining and connection testing. The ultimate goal is to provide behavioral information to guide the development of guidelines and acceptance criteria for the design of fracture resistant welded beam-column connections.

This study is a follow-up to a preliminary investigation by the authors, conducted under SAC Subtask 5.3.1, to examine “pre-Northridge” style connections tested during Phase I of SAC. The present investigation extends the earlier study to address a broader range of design and detailing parameters and fracture effects. Elastic and inelastic finite element fracture analyses are used to evaluate fracture toughness demands in terms of mode I stress intensity factor (KI) and Crack Tip Opening Displacement (CTOD). In addition, advanced analyses that employ a micromechanical fracture criterion (Stress Modified Critical Strain) are used to examine ductile crack initiation in locations without an initial flaw. Computed fracture demands are evaluated in light of test data from relevant material, weldment and connection tests.

Parameters investigated include the following:

· weld flaw locations
· built-up welds with filleted reinforcement
· variations in beam and column sizes
· relative strength of beam to joint panel zone
· influence of continuity plates
· significance of welding-induced residual stresses
· influence of weld access hole geometry
· connections with Reduced Beam Sections (RBS)
· through-thickness fractures in column flanges

Data from the analyses substantiate observations from connection tests which indicate that improved weld details and higher toughness materials alone are not sufficient to reliably provide the inelastic deformation capacity required for seismic design.