V. AISC LRFD - Non Compact Wide Flange 2

To determine the design bending strength of a non-compact American wide flange section bent about its strong axis. The deflection at mid-span due to 2 concentrated loads acting at the third points along the beam is also to be calculated.

Reference

AISC Load Factor Resistance Design, 3rd Edition, Example 5.2, case (a), page 5-16.

Problem

W21x48 shape

F_y = 50 ksi

Length = 40 ft

L_b = 5 ft

Comparison

The reported STAAD.Pro value is based on the term MNZ in the STAAD.Pro output.

Table 1. Comparison of results
Result Type	Theory	STAAD.Pro	Difference
Deflection (in)	1.41	1.41	none
Design bending strength, ϕ_bM_n	398	398.4 (4,780.24 in·kips)	none

Note: Fully braced condition can be achieved by setting the UNT parameter equal to 1.0 inch.

STAAD Input

The file C:\Users\Public\Public Documents\STAAD.Pro CONNECT Edition\Samples\ Verification Models\09 Steel Design\US\AISC\AISC LRFD - Non Compact Wide Flange 2.STD is typically installed with the program.

STAAD SPACE BENDING CAPACITY PER AISC LRFD 3RD ED
START JOB INFORMATION
ENGINEER DATE 23-Sep-18
END JOB INFORMATION
*
*  EXAMPLE PROBLEM 5.2, CASE (A), PAGE 5-16, AISC LRFD 3RD ED.
*  CAPACITY (MNZ) SHOULD BE ABOUT 398 KIP-FT
*
UNIT FEET KIP
JOINT COORDINATES
1 0 0 0; 2 40 0 0;
*
MEMBER INCIDENCES
1 1 2;
*
MEMBER PROPERTY AMERICAN
1 TABLE ST W21X48
*
DEFINE MATERIAL START
ISOTROPIC MATERIAL1
E 4.176e+06
POISSON 0.3
END DEFINE MATERIAL
CONSTANTS
MATERIAL MATERIAL1 ALL
*
SUPPORTS
1 PINNED
2 FIXED BUT MZ
*
LOAD 1
MEMBER LOAD
1 CON GY -10 13.333
1 CON GY -10 26.667
*
PERFORM ANALYSIS
*
SECTION 0.5 ALL
PRINT SECTION DISPL
*
PARAMETER 1
CODE LRFD
MAIN 1 ALL
FYLD 7200 ALL
UNT 5 ALL
TRACK 1 ALL
CHECK CODE ALL
FINISH

STAAD Output

     MEMBER SECTION DISPLACEMENTS
     ----------------------------
     UNITS ARE - INCH
     MEMB  LOAD     GLOBAL X,Y,Z DISPL FROM START TO END JOINTS AT 1/12TH PTS
       1     1       0.0000    0.0000    0.0000    0.0000   -0.3644    0.0000
                     0.0000   -0.7057    0.0000    0.0000   -1.0010    0.0000
                     0.0000   -1.2273    0.0000    0.0000   -1.3654    0.0000
                     0.0000   -1.4114    0.0000    0.0000   -1.3654    0.0000
                     0.0000   -1.2273    0.0000    0.0000   -1.0010    0.0000
                     0.0000   -0.7057    0.0000    0.0000   -0.3644    0.0000
                     0.0000    0.0000    0.0000
     MAX LOCAL  DISP =    1.41141   AT     240.00  LOAD    1   L/DISP=    340
         ************ END OF SECT DISPL RESULTS ***********
    40. *
    41. PARAMETER 1
    42. CODE LRFD
    43. MAIN 1 ALL
    44. FYLD 7200 ALL
    45. UNT 5 ALL
    46. TRACK 1 ALL
    47. CHECK CODE ALL
 STEEL DESIGN    
      BENDING CAPACITY PER AISC LRFD 3RD ED                    -- PAGE NO.    4
                         STAAD.Pro CODE CHECKING - (LRFD 3RD EDITION)   v1.0
                         ***********************
 ALL UNITS ARE - KIP  FEET (UNLESS OTHERWISE Noted)
 MEMBER     TABLE       RESULT/   CRITICAL COND/     RATIO/     LOADING/
                          FX            MY             MZ       LOCATION
 =======================================================================
      1  ST   W21X48                   (AISC SECTIONS)
                           PASS     LRFD-H1-1B-C       0.335         1
                        0.00 C          0.00        -133.33       13.33
 +---------------------------------------------------------------------+
 | DESIGN STRENGTHS FOR MEMBER     1       UNITS - KIP IN              |
 | PNC=   35.84  PNT=  634.50  MNZ= 4780.24  MNY=  636.75  VN=  194.67 |
 +---------------------------------------------------------------------+