USFOS Analysis
(Ultimate Strength for Framed
Offshore Structures)
- A nonlinear numerical tool mainly for the
analysis of space frames
- Pushover analysis
1
Outline
Features of USFOS
USFOS input file preparation
Running analysis & post-processing
Examples: simply supported beam
Examples: 2D frame and jacket
2
Basic features
Ultimate Strength for Framed
Offshore Structures
Beam, Shell, Solid Elements
one finite element is sufficient for one physical
member based on element formulation
Nonlinearities: geometry,
material and boundary
conditions
Consistent Unit System
N (force), m (length) E in Pa
N (force), mm (length) E in MPa
3
Add-on features
Joint Capacity Checks
Spud Can
Soil-Structure Interaction
Hydrodynamic Loading
4
File Types I nvolved in And Analysis
USFOS
R e a l i t y E n g i n e e r i n g
5
Usfos
(engine)
Structural
input file-
model.fem
USFOS analysis
control file
(named f ex head.fem)
Result
Database
for XACT.
Name:
res.raf
Xact
(Graphical Interface)
Text output file (res.out).
Contains general print and
error messages
INPUT OUTPUT
Installing software
Download from http://www.usfos.com/
6
Installing software
Replace the key file at C:\Program
Files\USFOS\bin
7
Open software
Open from start all programs USFOS
USFOS GUI
8
Run software (1)
Open analysis control
9
Run software (2)
Input example file by
clicking
Example files are
available in C:\Program
Files\USFOS\examples
You can edit the example
file by clicking
Save the file before
running.
10
Head_orig.fem
model.fem
Left empty
Name the result
file in the same
folder
Attention: In PC cluster, drive C is protected, users cant write
any files on it. But you can write files on desktop. So before running the
software, you have to copy the example files to desktop and name your
result file in the same folder on the desktop.
If you forget this for the first time, restart USFOS.
Analysis results
11
Change load
step
Try this by
yourself
Drag with the left button or
the right button to translate
or rotate
View the node numbers
and element numbers
View the animation
12
P
Step1: model structure
Step2: add loading condition
A
P
B
l
x
y
z
1
2
3
USFOS input file - Structural file
13
Node
Global Coordinate
Boundary Condition
Element
Material
Cross Section data
Structure
Coordinate
system
' Node ID X Y Z Boundary code
NODE 1 .000 .000 .000 1 1 1 1 0 1
NODE 2 10.000 .000 .000 0 1 1 1 0 1
NODE 3 5.000 .000 .000 ' ..
' Elem ID np1 np2 material geom lcoor
BEAM 1 1 3 1 1 1
BEAM 2 3 2 1 1 1
' ..
' VecID dx dy dz
UNITVEC 1 .000 .000 1.000
' ..
' Geom ID Do Thick
PIPE 1 .24070 .0050
' Geom ID H T-web W-top T-top W-bot T-bot
IHPROFIL 5 0.4250 0.0400 0.4250 0.0400 0.8405 0.0250
' ..
' matno. E v yield density therm
MISOIEP 1 210E9 0.3 358E6 7.85E3 1.4E-5
Define nodes and boundary
conditions
Define elements
Define cross section data
Define material properties
Boundary Condition: x,y,z,rx,ry,rz;
0:free; 1:fixed;
Define local z-axis coord. of
beam elements
l
1
2
3
COORDINATE SYSTEM
14
Local Coordinate
x
y
z
1
2
Global Coordinate
COORDINATE SYSTEM
The global coordinate system is defined as a right-handCartesian
system.
Local coordinate system for the beam element is also defined in right-
handCartesian system : the local x-axis is from the first node (i)
towards the second node (j); the local y- and z-axis are perpendicular
to the local x-axis.
UNITVEC in the model file defines the local z-axis in terms of global
coordinates. This vector should not coincide with the local x-axis.
If not defined, the default local z-axis is parallel to the global (X,Z)
plane.
15
USFOS input file - Control file
-Static load
16
Load case: pressure, CF, etcUsually in structural file
Load Magnitude
Load control parameters: Lfact Minstp nstep etc
Control node displacement
Other information: Joint check Saved information
A
P
B
l
1
2
3
x
y
z
USFOS input file - Control file
-Static load
17
' load case node ID load intensity
NODELOAD 1 3 0.0000E+00 0.0000E+00 -1.0000E+04
' nloads npostp mxpstp mxpdis
CUSFOS 10 10 1 1.00
' lcomb lfact mxld nstep minstp
1 0.1 1 10 0.1
' ncnods
CNODES 1
' nodex idof dfact
3 3 -1
Specify the control displacement of the structure
Load control for static analysis
Different lines refer to the
sequence of load applications
Define a concentrated load
A
P
B
l
1
2
3
x
y
z
Running USFOS analysis
If the results are not satisfactory, go
back to analysis control to adjust the
parameters
18
19
Output file
Binary output file:
*.raf file : opened in Xact
Text output file:
*.out file : records the structural input and every
incremental steps.
*_status.text file: records the occurrence of yielding,
plastic hinges, and member buckling in the analysis.
20
.out file
OUT file summarizes the structural data both in terms of user definition as well as the
USFOS internal treatment of some of the input (e.g. spring properties). The .OUT also
summarizes the numerical results in each step, as exemplified in the following. The
symbols at the end of element indicates
0: a yield hinge is inserted +: position checked for plasticity
*: plastic hinge removed at element mid-span. Internally, the element is divided into
two sub elements.
0-0-0: plastic tension failure. The axial tension has reached the plastic capacity and a
membrane element is inserted.
ELEM ES Node1 Midspan Node2
1 2 -1.00(-1.00) -0.49(-0.36) 0.00( 0.00) +---+---O
2 1 0.00( 0.00) -0.49(-0.36) -1.00(-1.00) O---+---+
-------- G L O B A L R E A C T I O N F O R C E S --------
NODE X-for Y-for Z-for X-mom Y-mom Z-mom
1 -3.806E-10 0.000E+00 1.948E+04 0.000E+00 0.000E+00 0.000E+00
2 0.000E+00 0.000E+00 1.948E+04 0.000E+00 0.000E+00 0.000E+00
TOTAL: -3.806E-10 0.000E+00 3.897E+04 , Vector_Sum XY : 3.806E-10
21
_status.text file
The _status.text file lists the nonlinear events during the analysis: first
yielding, plastic hinges and buckling.
The time step at which the nonlinear event occurs provides a hint to
view the fringe plots.
-- Yielding Status (hinge introduced) --
Elem ID Position Cross sect. Comb Step Load
utilization No No level
1 node 2 0.79 1 50 2.90
2 node 1 0.79 1 50 2.90
-- Plastic hinge Status (fully developed) --
Elem ID Position Cross sect. Comb Step Load
utilization No No level
1 node 2 1.00 1 101 3.77
2 node 1 1.00 1 101 3.77
22
2D frame analysis(1)
1. Input the existing
control file and
structure file.
2. Check the structure
file .
3. Press F1 to add
comments to an
existing command.
4. Press F2 to select
and insert another
command.
5. For more
information, go to
help\USFOS input
commands and
search. 23
View the model
without running
For command
description
2D frame analysis(2)
1. Check the control file .
2. Check the control
parameters
3. Press F1 to add
comments.
4. Press F2 to select and
insert another
command.
5. For more information,
go to help\USFOS
input commands and
search.
24
2D frame analysis(3)
25
To choose a nodal/element result, click
here and use CTRL + Left click the
member you want to see
2D frame analysis(4)
1. The default joint is
rigid joint.
2. CHJOINT: the capacity
of the tubular joint will
be checked!
26
Left empty
2D frame analysis(5)-MSL
27
Due to deformation limitation of MSL
just click OK
Load factor times the basic load
Right click
HELP
28
Help is also available
online at
http://www.usfos.com/,
where you can find:
-Online manuals
-Related publications
-USFOS setup
download
Jacket(1)
Wave loading can be interpreted as static loading
or dynamic loading .
For static loading USFOS will step through the
actual wave and identify the worst wave
position(the position causing the highest base
shear or overturning moment)
For dynamic loading, some may be implemented:
Marine growth; buoyancy; current
29
Jacket(2)
30
Identify the worst
wave phase to be
used in the static
pushover analysis.
Jacket(3)
31
1. Find the load level
2. Find the baseshear and
overturning moment
