Draft

14.3ApproximateAnalysisof Buildings 241

ColumnShear Points of in
ectionareat mid-height, withpossibleexceptionwhenthecolumns

onthe rst
oor arehingedat thebase,Fig.14.11

V=

M

top

h

2

(14.34)

Girderaxialforcesareassumedto be negligibleeventhoughtheunbalancedcolumnshears

above andbelow a
oor willbe resistedby girdersat the
oor.

14.3.2 HorizontalLoads

34 We mustdierentiatebetweenlow andhighrisebuildings.

Low risebuidlings, wheretheheight is at leastsamllerthanthehrizontaldimension,the

de
ectedshape is characterizedby sheardeformations.

Highrisebuildings, wheretheheight is severaltimesgreaterthanitsleasthorizontaldi-

mension,thede
ectedshape is dominatedby overall
exuraldeformation.

14.3.2.1 PortalMethod

35 Low risebuildingsunderlateralloads,have predominantlysheardeformations. Thus,the

approximateanalysisof thistype of structureis basedon

1. 
   

   Distributionof horizontalshearforces.

   
   


2. 
   

   Locationof in
   ectionpoints.

   
   

36 Theportalmethodis basedonthefollowingassumptions

1. In
   ectionpoints arelocatedat

(a)Mid-height of allcolumnsabove thesecond
oor.

(b)Mid-height of
oor columnsif rigidsupport,or at thebaseif hinged.

(c) At thecenterof each girder.

2. Totalhorizontalshearatthemid-height of allcolumnsatany
   oorlevel willbe dis-

tributedamong thesecolumnssothateach of thetwo exteriorcolumnscarryhalfas

much horizontalshearas each interiorcolumnsof theframe.

37 Forcesareobtainedfrom

ColumnShear is obtainedby passinga horizontalsectionthroughthemid-height of the

columnsat each
oor andsummingthelateralforcesabove it, thenFig.14.12

V

ext

=

P

F

lateral

2 No.of bays

V

int

= 2V

ext

(14.35)