localForce record

[pkm]

hello,
i want to record element localforces so i use this : ( my model is 2D)

recorder Element -file ele1local.out -time -ele 1 localForce

it records 6 column for each step that i don't know what are ther refer to?!
in the manual there is :
localForce
2D, 3dof: Fx Fy Mz

3D, 6dof: Fx Fy Fz Mx My Mz

means that i should have 3 columns (Fx Fy Mz)!! but there is 6!!

please help me
tnx

[vesna]

With your recorder you should have 7 columns: the first column is time, columns 2-4 are forces at node i and columns 5-7 are forces at node j. If you record local forces in -xml format instead of -file format, in the header of the file you will get information about all recorded data.

e.g.,
recorder Element -xml ele1local.out -time -ele 1 localForce

[pkm]

oh yes 7 colums! tnx
i have checked in a simple beam with concentreted force at the midspan. following :
wipe
#--set up------------
file mkdir SB;
model basic -ndm 2 -ndf 3;

#y
#|
#2----------3----------4----> x
#|slave|
#1
#|master|

# Define nodes
# x y
node 1 0.0 0.0
node 2 100.0 0.0
node 3 50.0 0.0

#Boundary Condition
fix 1 1 1 0;
fix 2 0 1 0;

# Define Elements ------------------------------------
# Define Geomtransf element
geomTransf Corotational 1

#------------------------------------------------------
# Fiber Sections
#
# material
set matID 1;
set Fy 2400;
set E 2.1e6;
set b .02;
uniaxialMaterial Steel01 $matID $Fy $E $b

section Fiber 012 { #IPE12 ---->012

# patch quad $matID $numSubdivIJ $numSubdivJK $yI $zI $yJ $zJ $yK $zK $yL $zL
patch quad 1 31 3 -6 3.2 -6 -3.2 -5.37 -3.2 -5.37 3.2
patch quad 1 2 49 -5.37 0.22 -5.37 -.22 5.37 -.22 5.37 .22
patch quad 1 31 3 5.37 3.2 5.37 -3.2 6 -3.2 6 3.2
}

#element nonlinearBeamColumn $eleTag $iNode $jNode $numIntgrPts $secTag $transfTag
element nonlinearBeamColumn 13 1 3 5 012 1
element nonlinearBeamColumn 32 3 2 5 012 1

######################## STATIC ANALYSIS #################################

# Create Recorders
recorder Element -xml SB/LForce13.out -ele 13 localForce
recorder Element -xml SB/LForce32.out -ele 32 localForce

# Pattern Plain
pattern Plain 1 Linear {
load 3 0.0 -1.0 0.0 0;
}

# Set up analysis parameters
constraints Transformation ;
numberer RCM ;
system BandGeneral ;
test EnergyIncr 1.e-6 25 0 ;
algorithm Newton ;
#integrator LoadControl 1
integrator LoadControl -1;
analysis Static ;
analyze 1

1)why in ele 13 or 32 forces direction changes? forexample shear force in node 1 is -0.5 but in node 3 is 0.5 .
2) in fact i want to have element forces along the element not just at the ends. what i should do?

[vesna]

To satisfy equilibrium of forces at the node they need to have opposite sign. For example, if you apply axial compressive force on en element and divide it into two elements, you know that both elements will be in compression. Let's say that the element is vertical column and force is acting at the top of the element pointing downwards. If you look at the elements forces at the common node, the bottom element will have vertical force at node j in downward direction and the top element will have a vertical force in the upward direction at node i. These forces but put elements in compression but have different sign. Sign of element forces in local coordinate system will comply with orientation of local axis.

With opensees you can record forces only at the element ends. How they are changing along the member you can calculate either by using equilibrium equations or you can divide an element into a smaller pieces and record the forces at their ends.

[pkm]

oh yes i got it!! thanks alot