V. AISC LRFD - Wide Flange Flexural Strength 1

To determine the design flexural strength of an ASTM A992 W18X40 bent about its strong axis on a 35-ft span with a uniformly distributed load.

Reference

Hand calculation using the following reference:

AISC Load Factor Resistance Design, 3rd Edition, Example 5.1, Case (a), page 5-12.

Problem

The beam is braced such that L_b = 2 ft. The deflection at mid-span due to a uniformly distributed service load of 1 kip/ft is also to be calculated.

F_y = 50 ksi

Length = 35 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)	1.90	1.8918	none
Design flexural strength (ft·kips)	294	294 (3,528 in·kips)	none

STAAD Input

The file C:\Users\Public\Public Documents\STAAD.Pro CONNECT Edition\Samples\ Verification Models\09 Steel Design\US\AISC\AISC LRFD - Wide Flange Flexural Strength 1.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 5.1, CASE (A), PAGE 5-12, AISC LRFD 3RD ED.
*  CAPACITY (MNZ) SHOULD BE ABOUT 294 KIP-FT
*
UNIT FEET KIP
JOINT COORDINATES
1 0 0 0; 2 35 0 0;
MEMBER INCIDENCES
1 1 2;
MEMBER PROPERTY AMERICAN
1 TABLE ST W18X40
UNIT FEET KIP
DEFINE MATERIAL START
ISOTROPIC MATERIAL1
E 4.176e+06
POISSON 0.3
END DEFINE MATERIAL
UNIT FEET KIP
CONSTANTS
MATERIAL MATERIAL1 ALL
SUPPORTS
1 PINNED
2 FIXED BUT MZ
LOAD 1
MEMBER LOAD
1 UNI GY -1
LOAD COMBINATION 2
1 1.8 
PERFORM ANALYSIS
LOAD LIST 1
SECTION 0.5 ALL
PRINT SECTION DISPL
LOAD LIST 2
UNIT FEET KIP
PARAMETER 1
CODE LRFD
MAIN 1 ALL
FYLD 7200 ALL
UNT 2 ALL
TRACK 1 ALL
CHECK CODE ALL
FINISH

STAAD Output

  SECTION  DISPL                      
      BENDING CAPACITY PER AISC LRFD 3RD ED                    -- PAGE NO.    3
     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   -0.4973    0.0000
                     0.0000   -0.9571    0.0000    0.0000   -1.3475    0.0000
                     0.0000   -1.6441    0.0000    0.0000   -1.8290    0.0000
                     0.0000   -1.8918    0.0000    0.0000   -1.8290    0.0000
                     0.0000   -1.6441    0.0000    0.0000   -1.3475    0.0000
                     0.0000   -0.9571    0.0000    0.0000   -0.4973    0.0000
                     0.0000    0.0000    0.0000
     MAX LOCAL  DISP =    1.89185   AT     210.00  LOAD    1   L/DISP=    222
         ************ END OF SECT DISPL RESULTS ***********
    37. LOAD LIST 2
    38. UNIT FEET KIP
    39. PARAMETER 1
    40. CODE LRFD
    41. MAIN 1 ALL
    42. FYLD 7200 ALL
    43. UNT 2 ALL
    44. TRACK 1 ALL
    45. 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   W18X40                   (AISC SECTIONS)
                           PASS     LRFD-H1-1B-C       0.938         2
                        0.00 C          0.00        -275.62       17.50
 +---------------------------------------------------------------------+
 | DESIGN STRENGTHS FOR MEMBER     1       UNITS - KIP IN              |
 | PNC=   23.10  PNT=  531.00  MNZ= 3528.00  MNY=  428.32  VN=  152.24 |
 +---------------------------------------------------------------------+