Stability of Lift Slab Structure During Construction Stage

Masih, Rusk; ,

Stability of Lift Slab Structure During Construction Stage

by Rusk Masih, Univ of Connecticut, Groton, United States,

Document Type: Proceeding Paper

Part of: Structures Congress XII

Abstract:

The lift slab structures impose stability problems during the construction phase. The process of constructing this type of structure requires placing the masses of the floor slabs at a very high elevation, supported by columns laterally unbraced. Such structures are weak and unstable during the construction stage. Engineering consultants call them, during construction, 'house of cards' structures. Dynamic instability could play a big role in the collapse of the structure. Placing a big mass on very slender, unstiffened supports, makes the first mode of the natural frequency of the structure very low. Higher modes of vibration could still be low enough to be activated by the dynamic loads, inducing unstable conditions, high internal forces and stresses in the structural elements. This theoretical study shows that even though each individual column was designed to withstand the static stability, yet the whole structure became, more and more, dynamically unstable when the number of stories increased.

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