How to define Lx,Ly & Lz as per IS 800 LSD steel design?

I just started using Steel design parameters...

Pls. help me out to give proper Lx, Ly & Lz values for the beams in model attached.

Some more queries :

1)  Whether all Lx,Ly & Lz are required to define in model ?

2)  Whether for columns Lx,Ly & Lz  to be defined.

3)  My live load a live load of  7KN/m2 on fifth floor . How to apply it on the beams?

Model details

STAAD SPACE
START JOB INFORMATION
ENGINEER DATE 12-Aug-14
END JOB INFORMATION
INPUT WIDTH 79
UNIT METER KN
JOINT COORDINATES
1 0 0 0; 2 0 0 3.5; 3 3.5 0 0; 4 3.5 0 3.5; 5 0 4 0; 6 0 4 3.5; 7 3.5 4 0;
8 3.5 4 3.5; 9 0 8 0; 10 0 8 3.5; 11 3.5 8 0; 12 3.5 8 3.5; 13 0 12 0;
14 0 12 3.5; 15 3.5 12 0; 16 3.5 12 3.5; 17 0 16 0; 18 0 16 3.5; 19 3.5 16 0;
20 3.5 16 3.5; 21 1.75 16 3.5; 22 0 16 1.75; 23 1.75 16 0; 24 3.5 16 1.75;
MEMBER INCIDENCES
1 1 5; 2 5 6; 3 6 2; 4 5 7; 5 7 8; 6 8 6; 7 8 4; 8 7 3; 9 9 10; 10 9 11;
11 11 12; 12 12 10; 13 13 14; 14 13 15; 15 15 16; 16 16 14; 17 9 5; 18 10 6;
19 12 8; 20 11 7; 21 13 9; 22 14 10; 23 15 11; 24 16 12; 25 17 22; 26 17 23;
27 19 24; 28 20 21; 29 17 13; 30 18 14; 31 20 16; 32 19 15; 33 21 18; 34 22 18;
35 23 19; 36 24 20;
START USER TABLE
TABLE 1 FINALCOL.UPT
TABLE 2 ISMB300FIN.UPT
TABLE 3 BEAM600.UPT
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 INDIAN
2 4 TO 6 9 TO 16 25 TO 28 33 TO 36 TABLE ST ISMB300
1 3 7 8 17 TO 24 29 TO 32 TABLE ST ISMB600
CONSTANTS
MATERIAL STEEL ALL
SUPPORTS
1 TO 4 FIXED
LOAD 1 DEAD + LIVE
JOINT LOAD
21 TO 24 FY -10
SELFWEIGHT Y -1
PERFORM ANALYSIS
PERFORM ANALYSIS PRINT STATICS CHECK
PARAMETER 1
CODE IS800 LSD
CMX 0.9 MEMB 1 3 7 8 17 TO 24 29 TO 32
CMZ 0.9 MEMB 1 3 7 8 17 TO 24 29 TO 32
CMY 0.9 MEMB 1 3 7 8 17 TO 24 29 TO 32
FU 420000 ALL
FYLD 250000 ALL
KX 1 MEMB 1 3 7 8 17 TO 24 29 TO 32
KY 1 MEMB 1 3 7 8 17 TO 24 29 TO 32
KZ 1 MEMB 1 3 7 8 17 TO 24 29 TO 32
FINISH

Pls. help me out to understand the concept on design parameters(Lx,Ly,Lz) 

Parents
  • LX = Effective Length for Lateral Torsional Buckling (as per Table-15, Section 8.3.1)
    LY = Length to calculate Slenderness Ratio for buckling about local Y axis.
    LZ = Length to calculate Slenderness Ratio for buckling about local Z axis.

    LY is the length to calculate slenderness ratio for buckling about local Y axis and LZ is the length to calculate slenderness ratio for buckling about local Z axis.
    The default values that the program considers for LY and LZ are the respective member lengths.
  • Sir,
    buckling is the mode of failure for compression member but in my case top floor beams carry loads at the center which may fail by bending mode. So whether here LX,LY & LZ is applicable???

  • The LY and LZ are required to define the effective length in the Flexural buckling condition when the member experiences compressive force. Similarly, if a beam is failing in bending mode then the failure condition is determined by the critical of the limit states of Lateral torsional buckling, compression flange yielding, Tension flange yielding and the compression flange buckling. So to define the unsupported length for controlling the LTB you need to define the UNT, UNB or UNL parameter depending on the design code you are using.



  • Thank you ..as specified in tech. reference
    LX = Effective Length for Lateral Torsional Buckling , then in the model only Lx is sufficient for beams ???

    whether LTB takes cares of compression flange yielding, Tension flange yielding  failure also ....
    Can you pls provide the parameters for the above model i have discussed for my understanding.

  • Effective length, Lx is only required for defining the length between the points that are either braced against the LTB. For controlling the other limit states, the Lx is not required. For example, the local buckling effect of the compression flange, the web and flange geometrical information are required.



  • If the laterally unrestrained length of the compression flange of the beam is relatively long, then a phenomenon, known as lateral buckling or lateral torsional buckling of the beam may take place. The beam would fail well before it could attain its full moment capacity. This phenomenon has a close similarity to the Euler buckling of columns, triggering collapse before attaining its squash load (full compressive yield load). The bending moment at which a beam fails by lateral buckling when subjected to a uniform end moment is called its elastic critical moment (Mcr). In the case of lateral buckling of beams, the elastic buckling load provides a close upper limit to the load carrying capacity of the beam.

    In STAAD, effective Length for Lateral Torsional Buckling has to be provided as per clause- 8.3 using LX parameter and it will be sufficient for lateral torsional buckling calculation.



Reply
  • If the laterally unrestrained length of the compression flange of the beam is relatively long, then a phenomenon, known as lateral buckling or lateral torsional buckling of the beam may take place. The beam would fail well before it could attain its full moment capacity. This phenomenon has a close similarity to the Euler buckling of columns, triggering collapse before attaining its squash load (full compressive yield load). The bending moment at which a beam fails by lateral buckling when subjected to a uniform end moment is called its elastic critical moment (Mcr). In the case of lateral buckling of beams, the elastic buckling load provides a close upper limit to the load carrying capacity of the beam.

    In STAAD, effective Length for Lateral Torsional Buckling has to be provided as per clause- 8.3 using LX parameter and it will be sufficient for lateral torsional buckling calculation.



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