Explanation Plate Staad

Fistly I would like to tell u STAAD is not a powerful package for finite element analysis..ANSYS software is a much better software for  FEA..But this software is not user friendly because of its poor  GUI(graphical user interface) and suited for academic purpose … Inspite of so much limi tation of FEA in STAAD industry adopts it because it is user friendly and speedy…other good FEA packages are L S DYNA and ABAC ABACUS US .

Modelling.

1)Always connect plate in anticlockwise direction and this should be common to all plates.To see this go to “label” where u have plate orientation command.. 2)Always check that the connection between members and plates should be node to node…which is the basic principal of Finite element. To ensure this after modeling go to pull down menu in STAAD and check a)Improper connected plate b)overlapping plate c)Check beam to plate connectivity 3)Dicretization of plate..please mesh element of smaller size ..dont use 1m x1m or 2 mx2m element size

Output

Refer Figure 1.18 of STAAD technical manual..I have attached the document.This are the output which we get after plate analysis.Figure 1.19, 1.2, 1.21 ,1.22 ,1.23 ,1.24 & 1.25 explains these output graphically.

SQX

=Shear stress on the local X face in the Z direction

SQY

=Shear stress on the local Y face in the Z direction

MX

=Moment per unit width about the local X face

MY

=Moment per unit width about the local Y face

MXY

=Torsional Moment per unit width in the local X-Y plane

SX

=Axial stress in the local X direction

SY

=Axial stress in the local Y direction

SXY

=Shear stress in the local XY plane

VONT

=Von Mises stress on the top surface of the element

VONB

=Von Mises stress on the bottom surface of the element

SMAX

=Maximum in-plane Principal stress

SMIN

=Minimum in-plane Principal stress

TMAX

=Maximum in-plane Shear stress

Generally after the analysis u will find that SQX,SQY,MX ,MY and MXY are governing.In case of plate result interpretation note that MX is along X direction and MY is along Z direction..this is opposite to what we have for beam members…where MX is about X and MY is about Y… If you feel that ur structure is going to experience good amount of torsion…then the MXY becomes very important…

Calculation

1)Area of steel from bending moment criteria Design the section for MX and MY using SP16. 2)Area of steel from shear criteria.

Please note here STAAD directly gives the shear stress..U can refer SP16 (page 178) and provide shear reinforcement..Please note this are only way shear so u can take this value at a distance d from face of column/wall.STAAD does not do any calculation for two way shear..that u have to do manually. Now if torsion guides….area of steel will be calculated based on combination of  moment MX ,MY and MXY..This combination is called wood and armer  combination.

Wood and armer combination.. TOP REINFORCEMENT CALCULATION

Mx1 = Mx + abs(Mxy) My1 = My + abs(Mxy) Mx2 = Mx + abs(Mxy2/My) My2 = My + abs(Mxy2/Mx) CONDITION: 1 If both Mx1 and My1 are positive, then design moment Mxd=Mx1 & Myd=My1 2 If both Mx1 and My1 are negative, then design moment Mxd=0 & Myd=0 3 If Mx1 is negative My1 is positive, then design moment Mxd=0 & Myd=My2 4 If My1 is negative Mx1 is positive, then design moment Mxd=Mx2 & Myd=0 BOTTOM REINFORCEMENT CALCULATION Mx1 = Mx - abs(Mxy) My1 = My - abs(Mxy) Mx2 = Mx - abs(Mxy 2/My) My2 = My - abs(Mxy 2/Mx) CONDITION: 1 If both Mx1 and My1 are positive, then design moment Mxd=0 & Myd=0 2 If both Mx1 and My1 are negative, then design moment Mxd=Mx1 & Myd=My1 3 If Mx1 is negative My1 is positive, then design moment Mxd=Mx2 & Myd=0 4 If My1 is negative Mx1 is positive, then design moment Mxd=0 & Myd=My2