forceBeamColumn + Section Aggregator Error

[mpnewcombe]

Hello,

Can section aggregator be used to combine the flexural, shear and axial stiffness of an elastic member and be used as a force Beam Column element? Please see the following extracts from my code:

# SECTION AND SPRING PROPERTIES
# Columns
set hc [expr 700*$mm]; # Column depth
set bc [expr 300*$mm]; # Column width
set Ec [expr 11000*$N/$mm]; # Elastic modulus of column
set Gc [expr 600*$N/$mm]; # Shear modulus of column
set Ac [expr $bc*$hc*pow($mm,2)]; # Cross-sectional area of column
set Ic [expr $bc*pow($hc,3)/12*pow($mm,4)]; # Second moment of area of column
set Asc [expr 0.8*$bc*$hc*pow($mm,2)]; # Shear area of column
# Flexural stiffness
# Property Mat. Tag Stiffness
uniaxialMaterial Elastic 1 [expr $Ic*$Ec];
# Shear stiffness
# Property Mat. Tag Stiffness
uniaxialMaterial Elastic 2 [expr $Asc*$Gc];
# Axial stiffness
# Property Mat. Tag Stiffness
uniaxialMaterial Elastic 3 [expr $Ac*$Ec];
# Aggregate flexural and shear stiffness
# Sec Tag matTag1 string1 matTag2 string2 matTag3 string3
section Aggregator 1 1 Mz 2 Vy 3 P

Then....

element forceBeamColumn 1 7 13 5 1 $IDColTransf # COLUMN FRAME ELEMENT

The error message I get when I try this is:

SectionAggregator: :getSectionFlexibility -- singular section stiffness

Can you see what I am doing wrong.

Many thanks,

Mike Newcombe

[mpnewcombe]

Got it... In the code I was running I had 2/3 in the expression for Asc (not 0.8 as shown above). This gave a result of Asc = 0, which was causing the problem. Tcl syntax must take some getting use to...

[paperairplane]

good question，better answer！

[wuhaoshrek]

mpnewcombe wrote:
> Got it... In the code I was running I had 2/3 in the expression for Asc
> (not 0.8 as shown above). This gave a result of Asc = 0, which was causing
> the problem. Tcl syntax must take some getting use to...

I got a exact same problem, thanks for your share.

[mhscott]

Tcl performs integer division, much like many other programming languages. Always make sure at least one value floating point in your expressions. 2.0/3 or 2/3.0 for example