Design of earthquake-resistant steel frames with knee bracing

Abstract

A new structural system, called the knee-brace-frame (KBF), is investigated here for its suitability for seismic resistant steel structures. In this framing system, one end of the diagonal brace is connected to a knee anchor instead of the beam-column joint. The diagonal brace provides the required stiffness during moderate earthquakes, while the knee anchor yields in flexure to dissipate energy during a severe earthquake, whereby buckling of the brace or yielding of beam or column is prevented. Large scale dynamic tests were carried out to assess the ductility capacity of the KBF, which is shown to be suitable for seismic design. A set of design charts are thus produced, using the program DRAIN-2D, for proportioning the member sizes to meet the seismic design requirements. © 1991.