Portal frames, used in several Civil Engineering structures like buildings, factories, bridges have the primary purpose of transferring horizontal loads applied at their tops to their foundations. Structural requirements usually necessitate the use of statically indeterminate layout for portal frames, and approximate solutions are often used in their analyses.
Assumptions for the Approximate Solution
In order to analyze a structure using the equations of statics only, the number of independent force components must be equal to the number of independent equations of statics.
If there are n more independent force components in the structure than there are independent equations of statics, the structure is statically indeterminate to the nth degree. Therefore to obtain an approximate solution of the structure based on statics only, it will be necessary to make n additional independent assumptions. A solution based on statics will not be possible by making fewer than n assumptions, while more than n assumptions will not in general be consistent.
Thus, the first step in the approximate analysis of structures is to find its degree of statical indeterminacy (dosi) and then to make appropriate number of assumptions.
below you can download the program shown above for the portal method analysis of approximate building frame analysis: