Earthquake Engineering Research - HKU Libraries - The University ...

Proceedings of the International Conference on
Advances and New Challenges in Earthquake
Engineering Research, Hong Kong Volume
HYBRID FRC-ENCASED STEEL TRUSS BEAMS FOR SEISMIC
UPGRADING OF REINFORCED CONCRETE STRUCTURES
Gustavo Parra-Montesinos 1 , Subhash C. Goel 1 , and Steve Savage 2
Department of Civil and Environmental Engineering,
University of Michigan, Ann Arbor, Michigan, USA
2 Coughlin, Porter and Lundeen, Inc., Seattle, Washington, USA
ABSTRACT
This paper presents an innovative scheme using hybrid beams consisting of steel trusses encased in
fiber reinforced concrete (FRC) for seismic upgrading of RC frames with inadequate beams or slabcolumn
frames. The behavior of various connection details between the hybrid beams and RC columns
was evaluated through testing of four beam-column subassemblies under simulated earthquake
loading. In this paper, experimental results are described in terms of load vs. displacement response,
cracking pattern, beam rotations and energy dissipation capacity of the subassemblies. Test results
indicate that moment connections consisting of either a combination of longitudinal beam bars passing
through the RC column plus external steel plates, or the use of only external steel rods behave
satisfactory under large displacement reversals.
INTRODUCTION
During the last few decades, several seismic retrofit schemes have been used in old non-ductile
reinforced concrete (RC) buildings that include the addition of structural walls, dampers, steel braces,
wrapping or jacketing of RC members with steel or composite materials, and base isolation. With the
development of innovative hybrid structural systems that combine the use of steel and RC elements,
new possibilities for seismic upgrading of RC structures are also becoming available. Hybrid beams
that consist of steel trusses embedded in fiber reinforced concrete (FRC) for use in buildings with slabcolumn
frames or inadequate RC beams is one scheme. These hybrid beams have been shown to
exhibit excellent behavior under large displacement reversals (Khuntia and Goel 1998). In addition,
hybrid FRC-encased steel truss beams are attractive from a construction viewpoint because they could
be prefabricated or constructed on site with little or no shoring required. This can be done by first
connecting the steel truss to the RC columns and then suspending metal or wood forms from the truss
during the FRC casting process.
The addition of hybrid FRC-encased steel truss beams for seismic retrofit was recently considered for
the historic King County Courthouse in Seattle, Washington. The King County Courthouse is an Pishaped
11-story RC building with a plan of approximately 240 by 240 feet and height of 180 feet.