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Dynamic instability of frames having thin‐walled columns
Author(s) -
Sridharan Srinivasan,
Ashraf Ali M.
Publication year - 1988
Publication title -
earthquake engineering and structural dynamics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.218
H-Index - 127
eISSN - 1096-9845
pISSN - 0098-8847
DOI - 10.1002/eqe.4290160506
Subject(s) - instability , buckling , structural engineering , critical load , moment (physics) , dynamic load testing , structural load , column (typography) , seismic loading , mechanics , materials science , engineering , physics , classical mechanics , connection (principal bundle)
Dynamic instability of single storey frames having thin‐walled columns has been investigated. The lateral loads sustained by the frame are dynamic in character, while the axial loads are deemed to be quasi‐statically applied. The analytical model employed by the authors has the capability of modelling the combined action of the two ‘companion’ local modes whose amplitudes are variable along the length of the column and any type of end conditions of the members. For given levels of axial loads sustained by the columns, the magnitudes of lateral loads causing instability can be significantly smaller than those corresponding to static buckling, provided the dynamic load is of sufficient duration. There exists, however, a threshold value of axial force carried by the columns, below which there is no elastic instability—static or dynamic. For columns with overall critical loads several times greater than the local critical load, there is no danger of elastic instability, but the deflections under dynamic lateral loads of less than 1 per cent of the axial load may reach such huge values that there is a serious danger of localized plastic collapse. It is also shown that moment frames having thin‐walled columns such as those fabricated out of cold formed steel are extremely vulnerable to moderate seismic excitations.