NEGLECTING COMPATIBILITY TORSIONS IN THE DESIGN OF CONCRETE STRUCTURES

摘要

The traditional approach in the design of reinforced and prestressed concrete building structures has been to design each of the two orthogonal directions independently. In calculating the distribution of moments in a structure, this two-dimensional approach neglects the effects of the intersecting members. That is, in the case of compatibility torsions, the torsional stiffness is neglected. This paper provides a summary of the progression of the ACI code and commentary pertaining to the zero torsional stiffness assumption and its origins. The paper then introduces a recently developed nonlinear finite element analysis tool, VAST Ⅱ, capable of predicting the response of reinforced and prestressed concrete structures in three-dimensions. The tool, based on the Modified Compression Field Theory, is capable of modelling entire structures or large portions of structures in order to assess their performance in a manner that accounts for three-dimensional effects, such as compatibility torsions. VAST Ⅱ is then used to model a case study transit center. The transit center is a post-tensioned concrete structure that was designed using the traditional approach of neglecting the effects of compatibility torsions. The results indicate that the traditional approach recommended by the ACI code and commentary, to neglect compatibility torsions, is appropriate and gives robust designs. The paper concludes by providing recommendations for future studies that could be conducted using three-dimensional nonlinear tools such as VAST Ⅱ.