16-01-2014, 04:59 PM
COMPARISON BETWEEN PORTAL & CANTILEVER METHOD OF ANALYSIS of frame
COMPARISON BETWEEN PORTAL.pdf (Size: 710.02 KB / Downloads: 14)
INTRODUCTION
Multi-storey building frames subjected to lateral loads due to wind pressure
and seismic effects are statically indeterminate and exact analysis by hand
calculation takes much time and effort. Such forces introduce direct loads on
columns and bending moments in all members of the frame. Since these effects
are small, an elaborate and rigorous method of analysis is not required. Using
simplifying assumptions, approximate analysis of these frames yield good
estimate of member forces in the frame, which can be used for checking the
member sizes. The following methods can be employed for lateral load analysis
of rigidly jointed frames.
The Portal method.
The portal method and the cantilever method yield good results only when the
heightdimension. Either classical techniques such as slope deflection or moment
distribution methods or computer methods using stiffness or flexibility matrices
can be used if a more exact result is desired. of a building is approximately more than five times its least lateral
PORTAL METHOD OF ANALYSIS :
This method is satisfactory for buildings up to 25 stories, hence is the most
commonly used approximate method for analysing tall buildings. The following
are the simplifying assumptions made in the portal method:
1. A point of contraflexure occurs at the centre of each beam.
2. A point of contraflexure occurs at the centre of each column.
3. The total horizontal shear at each storey is distributed between the columns
of that storey in such a way that each interior column carries twice the shear
carried by each exterior column.