Seismic ratcheting of steel low-damage buildings
Author: Dr Ali Abdolahi Rad, University of Canterbury (supervised by Associate Professor Greg MacRae)
Paper number: 404
Journal papers and a thesis presented for the degree of Doctor of Philosophy in Structural Engineering was accepted as a final report and is available on request - please contact research@eqc.govt.nz for access.
Abstract
During earthquake shaking some structures tend to deform more in one direction than in the other. This phenomenon is sometimes termed “ratcheting” and the displacement demands may become significantly larger than for structures without a ratcheting tendency. This thesis explores the numerical and experimental studies on performance of steel low damage buildings with ratcheting tendency under seismic demands.
Numerical studies are used to develop simple methods to estimate the displacement demands of such structures. Shake table studies of two storeys half-scale steel moment frame with low damage connections were carried out. A tested structure was retrofitted using several methods to minimize the possibility of increase in displacements due to aftershocks.
Technical Abstract
During earthquake shaking some structures tend to deform and yield more in one direction than in the other. This phenomenon is sometimes termed “ratcheting” and the displacement demands may become significantly larger than for structures without a ratcheting tendency. This thesis explores the numerical and experimental studies on performance of steel low damage buildings with ratcheting tendency under seismic demands.
Numerical studies are used to develop simple methods to estimate the displacement demands of such structures with different periods (T) and force design reduction factors (R). Shake table studies of two storeys half-scale steel moment frame with asymmetric friction connections (AFCs) at the column bases and at the beam ends were carried out. A tested structure with residual displacements due to earthquakes was strengthened/stiffened using several methods to minimize the possibility of increase in peak/residual displacements in the residual displacement direction due to aftershocks. Experimental tests were conducted with i) no brace, ii) a buckling brace with slackness, (iii) a ratcheting brace, and (iv) gapping braces, which had a ratcheting brace in conjunction with a buckling brace with a displacement gap.
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