V. AISC LRFD - Load Capacity of 3 Wide Flange Beams

To find the design flexural strength capacity of 3 beams of different spans using the data in Table 5-4 of AISC LRFD 3rd edition.

Reference

AISC Load Factor Resistance Design, 3rd Edition, Example 5.5, page 5-21.

Problem

W21x62 section.

F_y = 50 ksi

40 ft, 30 ft, and 8 ft spans are investigated. All beams are fully braced.

Comparison

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

Table 1. Comparison of results
Result Type	Theory	STAAD.Pro	Difference
Utilization ratio, 30 ft span	1.0	1.0	none
Utilization ratio, 20 ft span	1.0	1.0	none
Utilization ratio, 8 ft span	1.0	1.001	none

STAAD Input

The file C:\Users\Public\Public Documents\STAAD.Pro CONNECT Edition\Samples\ Verification Models\09 Steel Design\US\AISC\AISC LRFD - Load Capacity of 3 Wide Flange Beams.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
*
*  OBJECTIVE : TO DETERMINE THE MAXIMUM UNIFORMLY
*  DISTRIBUTED LOAD CARRYING CAPACITY OF 3 BEAMS.
*
*  EXAMPLE PROBLEM 5.5 PAGE 5-21, AISC LRFD 3RD ED.
*
UNIT FEET KIP
JOINT COORDINATES
1 0 0 0; 2 40 0 0; 3 0 10 0; 4 30 10 0; 5 0 20 0; 6 8 20 0;
MEMBER INCIDENCES
1 1 2; 2 3 4; 3 5 6;
MEMBER PROPERTY AMERICAN
1 TO 3 TABLE ST W21X62
DEFINE MATERIAL START
ISOTROPIC MATERIAL1
E 4.176e+06
POISSON 0.3
END DEFINE MATERIAL
CONSTANTS
MATERIAL MATERIAL1 ALL
SUPPORTS
1 3 5 PINNED
2 4 6 FIXED BUT MZ
*
LOAD 1
MEMBER LOAD
* ON MEMBER 1, W=108/40=2.7
1 UNI GY -2.7
* ON MEMBER 2, W=144/30
2 UNI GY -4.8
* ON MEMBER 3, W=454/8
3 UNI GY -56.75
*
PERFORM ANALYSIS
PARAMETER 1
CODE LRFD
MAIN 1 ALL
FYLD 7200 ALL
* FULLY BRACED CONDITION CAN BE ACHIEVED BY SETTING UNT TO 1.0 INCH
UNT 0.1 ALL
TRACK 1 ALL
CHECK CODE ALL
FINISH

STAAD Output

                         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   W21X62                   (AISC SECTIONS)
                           FAIL     LRFD-H1-1B-C       1.000         1
                        0.00 C          0.00        -540.00       20.00
 +---------------------------------------------------------------------+
 | DESIGN STRENGTHS FOR MEMBER     1       UNITS - KIP IN              |
 | PNC=   53.25  PNT=  823.50  MNZ= 6480.00  MNY=  942.05  VN=  226.80 |
 +---------------------------------------------------------------------+
      2  ST   W21X62                   (AISC SECTIONS)
                           PASS     LRFD-H1-1B-C       1.000         1
                        0.00 C          0.00        -540.00       15.00
 +---------------------------------------------------------------------+
 | DESIGN STRENGTHS FOR MEMBER     2       UNITS - KIP IN              |
 | PNC=   94.66  PNT=  823.50  MNZ= 6480.00  MNY=  942.05  VN=  226.80 |
 +---------------------------------------------------------------------+
 *    3  ST   W21X62                   (AISC SECTIONS)
                           FAIL     SHEAR-Y            1.001         1
                        0.00 C          0.00           0.00        0.00
 +---------------------------------------------------------------------+
 | DESIGN STRENGTHS FOR MEMBER     3       UNITS - KIP IN              |
 | PNC=  608.18  PNT=  823.50  MNZ= 6161.00  MNY=  942.05  VN=  226.80 |
 +---------------------------------------------------------------------+
   ************** END OF TABULATED RESULT OF DESIGN **************