AbstractA number of portal RC structures made of precast RC members (PPRC frames) have shown poor performance under strong earthquake ground motion. In particular, PPRC framed buildings with simple connections where beams sit on top of columns have experienced total collapse due to loss of seat. This research presents a feasible solution to enhance the seismic response of the above frames. Low cost yield devices of C shape (C-devices) are incorporated in a non-invasive fashion around the beam-to-column joints in order to introduce additional sources or hysteretic energy dissipation that lead to significant reductions of drift and residual displacements with minimum increase of base
A number of analytic models are studied in their original and upgraded conditions to evaluate the efficiency of the proposed retrofitting technique. The behaviour of PPRC frame models with pinned joints at the beam- column connections is covered in the study. The limit of efficient device strength (LEDS) is derived to ensure device activation as a result of the formation of plastic hinges at column bases of the above frames. Nonlinear inelastic models of these frames in their original and upgraded states with device strengths tuned at the LEDS are subject to the action of the 7 natural accelerograms scaled to three levels of seismicity.
The applicability of the C-devices for a wide range of existing PPRC frames (used in industrial facilities) for different combinations of seismic detailing, gravity load levels and seismic actions were studied. In these analyses, the C-devices are modelled using equivalent inelastic springs with strengths calibrated at the optimum device strength (ODS). Special attention is given to the modelling of the connection between the beam
and the columns in order to estimate the frictional slippage between the beam and column surfaces in contact. Other mechanical phenomena such as the pounding between beam and column surfaces in contact when gaps in connections close are also accounted for. Results indicate that the suggested retrofitting
technique offers an effective economic alternative to reduce damage and/or to avoid the seismic collapse of PPRC framed
Complementary work aimed at visualizing the behaviour of the C-device in detail using an elaborate 2D finite element (FE) model accounts for the frictional forces developed between the steel plate and the bolts used to connect the C-device to structural members. The above 2D analyses also allow the visualization of the inelastic regions of the device where energy dissipation is expected to occur across the device. Furthermore, to assess
the inelastic response of the C-device, monotonic and reversed cyclic tests were also conducted for different geometries of the C-device considering the effects of heat treatment and laser cutting.
|Date of Award
|Enrique Martinez-Rueda (Supervisor) & Kevin Stone (Supervisor)