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123456789_123456789_1123456789Steel Frame

Aanalysis Model Lusas
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Welcome to automatic models creation of Steel Frame Connection.


ICDAS Steel Frame allows you to create connection at the corner of the steel frame in shell elements.

The FEM model will create in LUSAS including surface load on top that you can run and analyze immediately. 


The inputs are simple and illustrate in Figure and Excel file and below.


Figure: Parameters of steel frame model

Figure: Excel input of steel frame model

Case study




Buckling and stress


This case study outlined buckling of profile IPE100 in dimension 2040mm + 2670mm for a frame of 40 degree



Figure 1 shows support condition and loads on the frame. The spring stiffness UX and UY represent a condition

where the frame connected to the opposite part on the right side (not modelled). It should be mention that these

spring stiffness affect strongly on the results. Chose a small value of 10kN/m will be on the safe side since the

frame will be connected to the neighbour frames by IPE100 in Y-direction, at the corner point.


Figure 2 shows detail at the connection where Thin Shell element has been applied for the buckling and stress

analyse (LUSAS QSL8)


Figure 1: IPE100 frame 


Figure 2: Corner connection


Figure 3 shows buckling of the frame for deadload

and 40kN/m2 on the top beam.


In LUSAS Eigenvalue Analysis Control the following

parameters are used:


§      Buckling Load solution for the Minimum number

      of eigenvalues


§      Type of eigensolver Subspace Jacobi


§      Number of eigenvalues : 1


§      Number of starting iteration vectors : 2


§      Shift to be applied as -10


The eigenvalue is found as 9.43606 as shown to the

right to give buckling in the first mode shape. The

initial buckling load is therefore 9.436 x the applied

deadload and 40kN/m2.


Considering on the live load, it is 9.436 x 40kN/m2
= 377kN/m2.

See animation

123456789_123456789_1123456789123456789_123456789_123456789_123456789_123456789_123456789_123456789_1231234Figure 3: Buckling of the top beam 


Change the live load factor to 2, i.e. a vertical load

of 80kN/m2, the eigenvalue is found as 7.20317 as

shown to the right, still buckling in the first mode

shape. The initial buckling load is now 7.203 x

80kN/m2 = 576kN/m2, i.e. a factor 1.53 on the

previous case.


Note that the buckling mode shape is now also
violent in the bottom beam.

See animation

123456789_123456789_1123456789123456789_123456789_123456789_123456789_123456789_123456789_123456789_1231234Figure 3: Buckling of the top and bottom beam. 


In Figure 4 and 5 below the frame is loaded further with wind load WY in Y-direction.


Figure 4 shows maximum stress SX on the top beam. Compression SX=-118MPa found at the middle of the

top beam which yield an utility ratio of 0.40. Increase the live load factor to 5xPZ, the compression is raised

to -161MPa from -118MPa (UR=0.54). However a concentrated compression stress on -306MPa found at the

connection corner. I.e. the yielding stress 296MPa is achieved on the frame before it buckle at factor 9.436.



Figure 5 shows maximum vertical displacement of 26mm at the top point of the beam when it carries



Figure 4
: Stress SX (kPa)

Figure 5: Vertical displacements (m) 




The reference model has input as shown in the Excel file above, where (hbot, htop)=(300, 200)mm.

The steel frame is single, having 5m width in X-direction and 5m height at top point, where angel v=w=20°.


Assume an UDL 2.5kN/m2 on top of the frame, the max vertical displacement DZ at the cantilever node is 64mm.


By increasing (hbot, htop)=(500, 250)mm, the displacement is reduced 25% to 48mm. 




Figure: Reference (hbot, htop)=(300, 250)mm        

See animation  


Figure(hbot, htop)=(500, 250)mm

See animation
Updated 30-05-2015

123456789_123456789_1123456789ICDAS  •  Hans Erik Nielsens Vej 3  •  DK-3650 Ølstykke  •   E-mail: helena@icdas.dk   •  Tel.: +45 29 90 92 96 •  CVR no.: 34436169