Eigen values -----> Elastic periods & modes of 3 Stor

[HBP]

Hi,

I'm new using OpenSees, and I have a question I hope you can help me solve.

There is this 3 story steel frame that I've been using to implement MPA procedures. First I did the complete process using SAP, and now I'm using OpenSees.

My problem is that I can't obtain the elastic modes from OpenSees. From my Open Sees model I'm obtaining
Eigen values : 924.5 1733.8 2757.4

The periods of the structure should be about this:
T1=1.10 sec
T2=0.37 sec
T3=0.21 sec

I'm attaching the model in OpenSees, if you can help me find the way to get the results, like periods and modes.

Thanks,
Hugo Bobadilla

---------------------------- 0 --------------------------------


# Units: kip, in
#
#
# ______________________________________ _
# | | | |
# | | | | 162"
# | | | |
# |____________|____________|____________| _
# | | | |
# | | | | 162"
# | | | |
# |____________|____________|____________| _
# | | | |
# | | | |
# | | | | 162"
# | | | | _
#=== === === ===
# | 360" | 360" | 360" |


model BasicBuilder -ndm 2 -ndf 3

# tag X Y
node 1 0 0
node 2 0 162
node 3 0 324
node 4 0 486
#
node 11 360 0
node 12 360 162
node 13 360 324
node 14 360 486
#
node 21 720 0
node 22 720 162
node 23 720 324
node 24 720 486
#
node 31 1080 0
node 32 1080 162
node 33 1080 324
node 34 1080 486

# node DX DY RZ
fix 1 1 1 1
fix 11 1 1 1
fix 21 1 1 1
fix 31 1 1 1

#Constraints
equalDOF 2 12 1
equalDOF 12 22 1
equalDOF 22 32 1
equalDOF 3 13 1
equalDOF 13 23 1
equalDOF 23 33 1
equalDOF 4 14 1
equalDOF 14 24 1
equalDOF 24 34 1

# Define beam and column property variables
set E 29000.0
set fy 50.0

# tag E fy Hiso Hkin
uniaxialMaterial Steel01 1 $fy $E 0.02

source Wsection.tcl

# Column 1 - W14x257
set A1 75.6
set I1 3400

# Column 2 - W14x311
set A2 91.4
set I2 4330

# Beam 3 - W33x118
set A3 34.7
set I3 5900

# Beam 4 - W30x116
set A4 34.2
set I4 4930

# Beam 5 - W24x68
set A5 20.1
set I5 1830

# Coordinate transformation
geomTransf Linear 1

# tag ndI ndJ A E I transfTag
#Columns
element elasticBeamColumn 21 1 2 $A1 $E $I1 1
element elasticBeamColumn 22 2 3 $A1 $E $I1 1
element elasticBeamColumn 23 3 4 $A1 $E $I1 1
element elasticBeamColumn 24 11 12 $A2 $E $I2 1
element elasticBeamColumn 25 12 13 $A2 $E $I2 1
element elasticBeamColumn 26 13 14 $A2 $E $I2 1
element elasticBeamColumn 27 21 22 $A2 $E $I2 1
element elasticBeamColumn 28 22 23 $A2 $E $I2 1
element elasticBeamColumn 29 23 24 $A2 $E $I2 1
element elasticBeamColumn 30 31 32 $A1 $E $I1 1
element elasticBeamColumn 31 32 33 $A1 $E $I1 1
element elasticBeamColumn 32 33 34 $A1 $E $I1 1

# tag ndI ndJ secI lenI secJ lenJ E A I transfTag
element elasticBeamColumn 41 2 12 $A3 $E $I3 1
element elasticBeamColumn 42 3 13 $A4 $E $I4 1
element elasticBeamColumn 43 4 14 $A5 $E $I5 1
element elasticBeamColumn 44 12 22 $A3 $E $I3 1
element elasticBeamColumn 45 13 23 $A4 $E $I4 1
element elasticBeamColumn 46 14 24 $A5 $E $I5 1
element elasticBeamColumn 47 22 32 $A3 $E $I3 1
element elasticBeamColumn 48 23 33 $A4 $E $I4 1
element elasticBeamColumn 49 24 34 $A5 $E $I5 1


# ----------------------------------------------------
# Start of additional modeling for dynamic loads
# ----------------------------------------------------
# Define nodal mass in terms of axial load on columns
set g 386.4
set m1 0.7675
set m2 0.7675
set m3 0.6282
# tag MX MY RZ
mass 2 $m1 $m1 .001
mass 12 $m1 $m1 .001
mass 22 $m1 $m1 .001
mass 32 $m1 $m1 .001
mass 3 $m2 $m2 .001
mass 13 $m2 $m2 .001
mass 23 $m2 $m2 .001
mass 33 $m2 $m2 .001
mass 4 $m3 $m3 .001
mass 14 $m3 $m3 .001
mass 24 $m3 $m3 .001
mass 34 $m3 $m3 .001

#Eigenvalue problem
eigen frequency 3
recorder Node -file 3storysteelframe-eigen1.out -node 2 3 4 -dof 1 "eigen 1"
recorder Node -file 3storysteelframe-eigen2.out -node 2 3 4 -dof 1 "eigen 2"
recorder Node -file 3storysteelframe-eigen3.out -node 2 3 4 -dof 1 "eigen 3"
puts "eigen values [eigen 3]"

[silvia]

i don't know what you are asking exactly. but i hope this helps.

this is a script i added at the end of your input file. and it gives the following periods:
Mode=1: Tperiod=0.207 sec
Mode=2: Tperiod=0.151 sec
Mode=3: Tperiod=0.120 sec

i guess there is some model difference between opensees and sap. you should check all your stiffnesses, masses, and boundary conditions.

Code: Select all

	set Neigen 3
	set fmt1 "Mode=%.1i: Tperiod=%.3f %s"
	set PI 	[expr 2*asin(1.0)];		# define constants
	set TunitTXT sec ;	# load global unit variable
	set iTperiod ""
	set lambdaN [eigen $Neigen]
	for {set i 1} {$i <= $Neigen} {incr i 1} {;		# zero to one
		set lambda [lindex $lambdaN [expr $i-1]];
		set omega [expr pow($lambda,0.5)]
		set Tperiod [expr 2*$PI/$omega];	   	# period (sec.) 
		lappend iTperiod $Tperiod
		puts [format $fmt1 $i $Tperiod $TunitTXT]
	}

also, the recorder you are using gives you the eigevectors...

[HBP]

Hi Silvia,

I appreciate your code and your comments. As you well said, I have to check my models in order to match results.

One last questions, with the recorders I used to obtain the eigenvectors I'm getting some files, but these files are empty. How can I make this work?

Thanks,

Hugo

[silvia]

i'd focus on the model first, then the recorders might fix themselves.

[endryus]

I obtained the same empty files for the recorder with eigen option.
This option seems to be not working.
I solved the problem by using the print node command.

andrea

[silvia]

mmmmm,
i know of someone who did get numbers.... just didn't know what to do with them.
i'll look it over