Abstract
Approximate methods of structural analysis are utilized for preliminary design and analysis of multi-story framed buildings subjected to externally applied forces. The behavior of a structure subjected to lateral forces are dependent on its height to width ratio. Deformation in low-rise structures, where the height is smaller than its width, is governed by shear deformations. In buildings where the height is several times greater than its width, it is governed by the bending moment.
For preliminary design and analysis of these multi-story framed buildings, two approximate methods, Portal Method and Cantilever Method, are commonly used. The Portal Method is most commonly used for short frames likely to deform in shear mode, based on the distribution of base shears proportional to influence areas. Whereas the Cantilever Method is recommended for tall frames likely to deform in flexure mode. This is based on the distribution of the base bending moment as axial forces on columns proportional to their distance from the centroidal axis of the building. However, there are currently no guidelines available to determine which approximate method is more appropriate to use over the other method.
The objective of this project is to (1) analyze several buildings with lateral loads of varying height using the approximate methods of structural analysis (Portal Method and Cantilever Method) and a matrix-based structural analysis program (MASTAN2), (2) evaluate the accuracy and reliability of the Portal Method and Cantilever Method compared with the MASTAN2 structural analysis program, and (3) establish a preliminary basis to decide which approximate method is more appropriate to use given a particular structure.
Based on the results of this project, the following formulas can be used as a preliminary guideline to help the analyst decide which approximate method to use:
H/L < 2.0 Portal Method
H/L ≥ 2.0 Cantilever Method
Where H = the building height and
L = the building length