DIRECT METHOD ANALYSIS - GENERAL

The only minor thing I found is you used a young's modulus a little higher than 29000 ksi. Probably because you've got STAAD set up to use metric and they don't use the exact same value for E between Imperial and metric. When I changed this I got 0.148 inches of first order deflection vs. 0.149" in the example. I stil didn't get AISC's values for bending, even in the first-order case. Very odd. There must be a difference in stiffness between the two models but AISC doesn't give us enough info to check what they actually used for the moment of inertia.

Does anybody have acces to another program this can be checked with?

One other minor thing, if you change this to a PLANE model instead of SPACE you will get rid of your warnings.

Anyway, where AISC is getting 149 k-ft moment, I'm getting 127 k-ft. About 17% less. We definately need to get to the bottom of this because that's a significant difference.

Thank you very much RKillian for your post.

I was in doubt since it was the first time I was using Staad Direct Method, so I needed some confirmation.

Considering what you wrote, it seems that the procedure was correct, so I agree with you wedefinately need to get to the bottom of this because that's a significant difference.

I will wait for any other user that could help, in the meantime i will try to get in deep with this issue.

What I did I follow directly according to the original example of AISC example C1.A  

I got Mz=135.358 ft-kips.  A very significant difference from AISC example.

STAAD PLANE

START JOB INFORMATION

ENGINEER DATE 22-Jul-13

END JOB INFORMATION

INPUT WIDTH 79

UNIT FEET KIP

JOINT COORDINATES

1 0 0 0; 2 0 20 0; 3 30 0 0; 4 30 20 0; 5 60 0 0; 6 60 20 0; 7 90 0 0;

8 90 20 0; 9 120 0 0; 10 120 20 0;

MEMBER INCIDENCES

1 1 2; 2 2 4; 3 3 4; 4 4 6; 5 5 6; 6 6 8; 7 7 8; 8 8 10; 9 9 10;

MEMBER RELEASE

2 6 8 START MY MZ

2 6 8 END MY MZ

DEFINE MATERIAL START

ISOTROPIC STEEL

E 4.176e+006

POISSON 0.3

DENSITY 0.489024

ALPHA 6e-006

DAMP 0.03

TYPE STEEL

STRENGTH FY 5184 FU 8352 RY 1.5 RT 1.2

END DEFINE MATERIAL

MEMBER PROPERTY AMERICAN

1 3 5 7 9 TABLE ST W12X65

2 4 6 8 TABLE ST W18X40

CONSTANTS

MATERIAL STEEL ALL

SUPPORTS

1 3 5 7 9 PINNED

*

*

*

*

*

DEFINE REFERENCE LOADS

LOAD R1 LOADTYPE None  TITLE REF LOAD CASE 1

*SELFWEIGHT Y -1

MEMBER LOAD

2 4 6 8 UNI GY -2.4

END DEFINE REFERENCE LOADS

*

*

*

*

*

*

DEFINE DIRECT ANALYSIS

FLEX 1 LIST 4

AXIAL LIST 3 5

NOTIONAL LOAD FACTOR 0.002

END

*

*

*

*

*

*

LOAD 1 LOADTYPE None  TITLE LOAD CASE 1

REFERENCE LOAD

R1 1.0

NOTIONAL LOAD

R1 X 0.002

*

*

*

LOAD 2 LOADTYPE None  TITLE LOAD CASE 2

REFERENCE LOAD

R1 1.0

NOTIONAL LOAD

R1 X -0.002

*

*

*

*

*

*

PERFORM DIRECT ANALYSIS LRFD ITERATION 10 TAUTOL 0.01 DISPTOL 0.001 -

PRINT LOAD DATA

*

*

*

FINISH

Is there any more recent resolution to this issue? I would also like to see the solution. Thank you.

Please note the calculations in V14.0 Design Examples had errors and the AISC have published updates. The current version of the publication is 14.2 (avaialble from the AISC site) and you will see that there have been corrections in the forces reported.