IABSE SYMPOSIUM LISBON 2005 Seismic Performance of Moment-Resisting Timber Frames with Fibre Reinforced and Densified Connections Andreas HEIDUSCHKE Civil Engineer Technical University Dresden, Germany Andreas.Heiduschke@mailbox.tu- dresden.de Andreas Heiduschke, born 1974, is PhD candidate and received his civil engineering degree from the Univ. of Dresden Peer HALLER Professor, Dept. of Steel- and Timber Structures TU Dresden, Germany peer.haller@mailbox.tu- dresden.de Peer Haller, born 1958, received his engineering and PhD degree from the Institut Polytechnique de la Lorraine, France Bo KASAL Professor, Dept. of Wood and Paper Science, NCSU Raleigh, NC, USA bo_kasal@ncsu.edu Bo Kasal, born 1956, received his MS civil engineering degree and PhD in wood engineering from the Oregon State University, Corvallis, OR Summary This paper describes results of the shake-table tests of glue-laminated timber frames with glass-fibre reinforced connections. Typical design (control frame) was compared with an alternative design (reinforced frame) that contained densified wood in the connection zones that were further reinforced with glass-fibre epoxy composite. The densified wood increased the moment and normal force capacities and stiffness. Glass-fibre fabric was used in laminated wood to mitigate potentially brittle failures resulting from tensile stresses across wood fibres. The tests showed superior performance of reinforced frames that behaved as self-correcting system with plastic deformations in beam-to-column connections and the elastic energy stored in beams and columns. Keywords: moment-resisting frame, glue laminated timber, glass-fibre reinforced connection, densified wood, shake table experiments. 1. Introduction Wood buildings traditionally perform well under dynamic loads due to the low mass density of the material, high strength-to-mass ratio and high dissipative properties of mechanical connectors. Moment-resisting (MR) frames with non-linear beam-to-column (B-C) connections are efficient lateral load resistance systems in buildings where large open spaces are required. The design of such structures in high-risk earthquake zones is a complex issue, involving a number of different interaction factors that need to be analysed. Main criteria for the application of MR frames in seismic zones are lateral stiffness and energy dissipation capacity of the system. In comparison to other more commonly used structures such as braced frames or shear wall systems, the MR frames often suffer from relatively low stiffness. This is one of the primary problems of this construction type. To avoid significant damage of non-structural elements, it is necessary to limit horizontal drifts. On the other hand, higher deformations in the connections results in more energy dissipation. This will lower the forces induced by the earthquake ground motion and redistribute the loads within structure. Typically, beam-to-column connections use steel mechanical fasteners, such as dowels or bolts. Capacity of connections is controlled by dowel bearing strength of wood, arrangement of fasteners and parameters of the steel dowels (diameter and yield strength). The need for reinforcement of MR connections in glue laminated frames results from difficulties in balancing the moment capacities of members and connections whereby connections usually limit the frame design. Achieving full moment connections in timber frames is impossible due to the material anisotropy and significant differences in stress-strain behaviour and strength along and across the fibres of wood. Close-to- zero tensile strength across fibres makes the connections prone to brittle failures when loaded by moments and shear forces. Considering that frames must rely on a finite number of highly stressed connections, it is clear that such failures can lead to a catastrophic failure of the entire system. 1