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V. AISC LRFD - Wide Flange Flexural Strength 2

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 (b), page 5-12.

Problem

The beam is braced at the ends and at third points such that Lb = 11.7ft.

Fy = 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
Design flexural strength (ft·kips) 211

209.5

(2,514 in·kips)

<1%
Note: The STAAD.Pro result is based on a Cb of 1.0, while the theoretical solution is based on a Cb of 1.01

STAAD Input

The file C:\Users\Public\Public Documents\STAAD.Pro CONNECT Edition\Samples\ Verification Models\09 Steel Design\US\AISC\LRFD 3rd Edition\AISC LRFD - Wide Flange Flexural Strength 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 5.1, CASE (B), PAGE 5-12, AISC LRFD 3RD ED.
*  CAPACITY (MNZ) SHOULD BE ABOUT 211 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
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 UNI GY -1.3
PERFORM ANALYSIS
PARAMETER 1
CODE LRFD
MAIN 1 ALL
CB 1 ALL
FYLD 7200 ALL
UNT 11.7 ALL
TRACK 2 ALL
CHECK CODE ALL
FINISH

STAAD Output

                       STAAD.PRO CODE CHECKING - (LRFD 3RD EDITION)   v1.0
                       ********************************************
  |--------------------------------------------------------------------------|
  |                                                    Y        PROPERTIES   |
  |*************                                       |        IN INCH UNIT |
  |            *  |=============================|   ===|===     ------------ |
  |MEMBER   1  *  |  AISC SECTIONS              |      |        AX=0.1180E+2 |
  |            *  | ST  W18X40                  |      |   --Z  AY=0.5638E+1 |
  |DESIGN CODE *  |                             |      |        AZ=0.4214E+1 |
  | LRFD 2001  *  ===============================   ===|===     PY=0.1000E+2 |
  |            *                                                PZ=0.7840E+2 |
  |            *  |&lt;---LENGTH (FT)=   35.00 --->|               RY=0.1272E+1 |
  |*************                                                RZ=0.7202E+1 |
  |                                                                          |
  |                199.1 (KIP-FEET)                                          |
  |PARAMETER        |               L1  L1  L1                  CAPACITIES   |
  |IN KIP  INCH     |                                           IN KIP  INCH |
  |---------------  +           L1              L1              -------------|
  | KL/R-Y= 330.12  |                                           PNC=0.2310E+2|
  | KL/R-Z=  58.32  +       L1                      L1          pnc=0.0000E+0|
  | UNL   = 140.40  |                                           PNT=0.5310E+3|
  | CB    =   1.00  +   L1                              L1      pnt=0.0000E+0|
  | PHIC  =   0.85  |                                           MNZ=0.2514E+4|
  | PHIB  =   0.90  +                                           mnz=0.2389E+4|
  | FYLD  =  50.00  |L0                                     L0  MNY=0.4283E+3|
  | NSF   =   1.00  +---+---+---+---+---+---+---+---+---+---|   mny=0.0000E+0|
  | DFF =     0.00 -11.1                                        VN =0.1522E+3|
  | dff =     0.00               ABSOLUTE MZ ENVELOPE           vn =0.0000E+0|
  |                                 (WITH LOAD NO.)                          |
  |                                                                          |
  |                      MAX FORCE/ MOMENT SUMMARY  (KIP-FEET)               |
  |                      -------------------------                           |
  |                                                                          |
  |                AXIAL      SHEAR-Y    SHEAR-Z    MOMENT-Y    MOMENT-Z     |
  |                                                                          |
  |      VALUE       0.0        22.7        0.0         0.0       199.1      |
  |   LOCATION       0.0         0.0        0.0         0.0        17.5      |
  |    LOADING         0           1          0           0           1      |
  |                                                                          |
  |**************************************************************************|
  |*                                                                        *|
  |*                         DESIGN SUMMARY  (KIP-FEET)                     *|
  |*                         --------------                                 *|
  |*                                                                        *|
  |*       RESULT/     CRITICAL COND/     RATIO/         LOADING/           *|
  |         FX              MY             MZ           LOCATION             |
  |        ======================================================            |
  |          PASS        LRFD-H1-1B-C     0.950              1               |
  |          0.00 C          0.00      -199.06            17.50              |
  |*                                                                        *|
  |**************************************************************************|
  |                                                                          |
  |--------------------------------------------------------------------------|