EUROCODE COMPRESSION RESISTANCE OF STEEL HOLLOW SECTION (CHS & BOX)

The code requires you to perform two checks, the first is the cross-section resistance which depends on the cross-section classification which is the equations you note (6.10 & 6.11), the second is the buckling resistance which is the result you may be seeing. Can you confirm what section you are evaluating or provide me with your Staad.Pro file and I will check the results?

Hi rtully14,

Thanks. I did some hand calculations for the second checking you have mentioned and that is in accordance with Section 6.3.1 Buckling Resistance of members (uniform members in compression) but still failed to get the same output as STAAD did.

My section is a welded box (see image attached on my first post), fy = 275N/mm^2. I evaluated this using EQ 6.47 and manually calculated the elastic critical force (Ncr), then obtain the reduction factor (X) considering imperfection factor (alpha) under Table 6.1. I have tried all the values of alpha but still were lost in track and not able to arrive at the same value as STAAD has calculated. Below is the STAAD output for your reference and i hope you can turn the lights on for better understanding on this.

Thanks,

Mac

      1 ST   BOX_GIRDER  (UPT: DESIGNED AS I-SECTION)

                          PASS     EC:6 - A.1         0.908         3

                       0.00          196.20       -3101.47       20.00

=======================================================================

  MATERIAL DATA

     Grade of steel                  =   S 275

     Modulus of elasticity    =  205 kN/mm2

     Design Strength  (py)    =  275  N/mm2

  SECTION PROPERTIES (units - cm)

     Member Length =                    4000.00

     Gross Area =  422.40          Net Area =  422.40

                                     z-axis          y-axis

     Moment of inertia        :   965653.000      135901.000

     Plastic modulus          :    18316.998              7108.800

     Elastic modulus          :    15600.200               5662.500

     Shear Area               :           187.805                     182.400

     Radius of gyration       :       47.813                      17.937

     Effective Length         :        4000.000              4000.000

  DESIGN DATA (units - kN,m)   EUROCODE NO.3 /2005

     Section Class            :   CLASS 3

     Squash Load              :  11616.00

     Axial force/Squash load  :     0.000

     GM0 :  1.00          GM1 :  1.00          GM2 :  1.25

                                                                       z-axis          y-axis

     Slenderness ratio (KL/r) :                  83.7          223.0

     Compression Capacity     :             8024.3         1542.8    

     Tension Capacity         :                 11616.0        11616.0

     Moment Capacity          :                 4290.1         1557.2

     Reduced Moment Capacity  :      4290.1         1557.2

     Shear Capacity           :                      2981.8         2896.0

Please attach that STAAD.Pro model if possible.

Hi Modestas,

I'm having problem attaching the Staad file but i have the Staad Input File below. Actually my model is just a simple beam (L=40m) with concentrated load P=100kN at the center and section as User Table 1 (box section, see image above).This is just to analyze what is the capacity/resistance of the customized section based on Eurocode. Thanks

INPUT WIDTH 79
UNIT METER KN
JOINT COORDINATES
1 0 0 0; 2 40 0 0;
MEMBER INCIDENCES
1 1 2;
START USER TABLE
TABLE 1
UNIT METER KN
GENERAL
BOX_GIRDER
0.04224 1.238 0.01 0.48 0.019 0.00965653 0.00135901 0.0034819 0.0156002 -
0.00566253 0.024 0.01824 0.0187805 0.0071088 0 1.238
END
DEFINE MATERIAL START
ISOTROPIC STEEL
E 2.05e+008
POISSON 0.3
DENSITY 76.8195
ALPHA 1.2e-005
DAMP 0.03
TYPE STEEL
STRENGTH FY 253200 FU 407800 RY 1.5 RT 1.2
END DEFINE MATERIAL
MEMBER PROPERTY
1 UPTABLE 1 BOX_GIRDER
CONSTANTS
MATERIAL STEEL ALL
SUPPORTS
1 2 PINNED
LOAD 1 LOADTYPE Live TITLE P
MEMBER LOAD
1 CON GY -100
PERFORM ANALYSIS
LOAD LIST 1
PARAMETER
CODE EN 1993-1-1:2005
TRACK 2 MEM 1
SGR 1 MEM 1
RATIO 1 MEM 1
TORSION 0 MEM 1
CHECK CODE MEM 1
FINISH

Thank you. Could you also attach your hand calculations?