STAAD.Pro Help

V. ACI 318-02 Rectangular Beam

Determine the reinforced steel quantity for a rectangular beam per the ACI 318 code.

Reference

Notes on ACI 318-02 Building Code Requirements for Structural Concrete, Example 7.1, p7-24, Design of Rectangular Beam with Tension Reinforcement Only

Notes on ACI 318-99 Building Code Requirements for Structural Concrete, Example 10.1, p10-10, Design of Rectangular Beam with Tension Reinforcement Only

Problem

Dead Load moment (service) = 56 fit-kips

Live Load moment (service) = 35 ft·kips

f'c = 4,000 psi

fy = 60,000 psi

Comparison

Table 1. Comparison of results
Result Type ACI Notes STAAD.Pro Difference
Required steel area (in2) per ACI 318-99 2.78 2.793 none
per ACI 318-02 2.40 2.44 1.7%
Provided steel area (in2) per ACI 318-02 2.40 (2 - #8 & 1- #9) (2- #10) 2.45 1.7%

STAAD.Pro reports that it is unable to find a suitable bar arrangement to satisfy the reinforcement requirement per ACI 318-99. However, this does not mean that it is impossible to come up with a bar arrangement. When STAAD looks for a bar arrangement, it uses only bars of the same size. It begins with the bar size corresponding to the parameter MINMAIN. If an arrangement is not possible with that bar, it tries with the next larger bar size. If all the permissible bar sizes are exhausted, the program reports that it could not come up with a bar arrangement. However, the user may be able to satisfy the requirement by mixing bars of various diameters. For example, 3 # 11 bars and 2 # 10 bars may satisfy the requirement. The program is not equipped with facilities to come up with such combinations of bar sizes.

In fact, in the reference mentioned for the 1999 edition of ACI 318, the bar arrangement chosen is 2 # 9 and 1 # 8. It proves the point that finding bars of the same diameter is not possible for the 1999 edition based solution.

STAAD Input

The file C:\Users\Public\Public Documents\STAAD.Pro CONNECT Edition\Samples\ Verification Models\10 Concrete Design\US\ACI\318-2002\ACI 318-02 Rectangular Beam.STD is typically installed with the program.

STAAD PLANE RECTANGULAR CONCRETE BEAM DESIGN PER ACI 318
START JOB INFORMATION
ENGINEER DATE 21-Sep-18
END JOB INFORMATION
*
* REFERENCE : NOTES ON ACI 318-02 BUILDING CODE REQUIREMENTS
*             FOR STRUCUTURAL CONCRETE EXAMPLE 7.1 (PAGE # 7-24)
*                             AND
*             NOTES ON ACI 318-99 BUILDING CODE REQUIREMENTS
*             FOR STRUCUTURAL CONCRETE EXAMPLE 10.1 (PAGE # 10-10)
*
*  OBJECTIVE : TO DETERMINE THE REINFORCED STEEL QUANTITY FOR A
*              RECTANGULAR BEAM PER THE ACI 318 CODE
*
*
INPUT WIDTH 79
UNIT FEET KIP
JOINT COORDINATES
1 0 0 0; 2 10 0 0;
MEMBER INCIDENCES
1 1 2;
UNIT INCHES KIP
MEMBER PROPERTY AMERICAN
1 PRIS YD 16 ZD 10
DEFINE MATERIAL START
ISOTROPIC MATERIAL1
E 3150
POISSON 0.17
END DEFINE MATERIAL
CONSTANTS
MATERIAL MATERIAL1 ALL
SUPPORTS
1 2 PINNED
UNIT FEET KIP
LOAD 1 DEAD LOAD
MEMBER LOAD
1 UNI GY -4.48
LOAD 2 LIVE LOAD
MEMBER LOAD
1 UNI GY -2.8
LOAD COMB 3 ACI 318R-99
1 1.4 2 1.7 
LOAD COMB 4 ACI 318R-02
1 1.2 2 1.6 
PERFORM ANALYSIS
*
** CONCRETE DESIGN AS PER ACI 318R-99
*
UNIT INCHES KIP
LOAD LIST 3
START CONCRETE DESIGN
CODE ACI 1999
FC 4 ALL
FYMAIN 60 ALL
TRACK 1 ALL
DESIGN BEAM ALL
END CONCRETE DESIGN
*
** CONCRETE DESIGN AS PER ACI 318R-02
*
LOAD LIST 4
START CONCRETE DESIGN
CODE ACI 2002
FC 4 ALL
FYMAIN 60 ALL
TRACK 1 ALL
DESIGN BEAM ALL
END CONCRETE DESIGN
FINISH

STAAD Output

      RECTANGULAR CONCRETE BEAM DESIGN PER ACI 318             -- PAGE NO.    3
   =====================================================================
          BEAM  NO.     1 DESIGN RESULTS - FLEXURE PER CODE ACI 318-99
   LEN -  10.00FT.  FY - 60000.  FC - 4000.  SIZE - 10.00 X 16.00 INCHES
   LEVEL    HEIGHT     BAR INFO       FROM            TO         ANCHOR 
          FT.    IN.              FT.     IN.     FT.     IN.   STA  END
   _____________________________________________________________________
   *** A SUITABLE BAR ARRANGEMENT COULD NOT BE DETERMINED.
   REQD. STEEL =  2.793 IN2,  MAX. STEEL PERMISSIBLE =  2.873 IN2
   MAX POS MOMENT =    137.90 KIP-FT,  LOADING    3
  ___   1J____________________  120.X  10.X  16_____________________   2J____ 
 |                                                                           |
 |                                                                           |
 |                                                                           |
 |                                                                           |
 |                                                                           |
 |                                                                           |
 |                                                                           |
 |___________________________________________________________________________|
  _________    _________    _________    _________    _________     _________ 
 |         |  |         |  |         |  |         |  |         |   |         |
 |         |  |         |  |         |  |         |  |         |   |         |
 |         |  |         |  |         |  |         |  |         |   |         |
 |         |  |         |  |         |  |         |  |         |   |         |
 |         |  |         |  |         |  |         |  |         |   |         |
 |         |  |         |  |         |  |         |  |         |   |         |
 |         |  |         |  |         |  |         |  |         |   |         |
 |_________|  |_________|  |_________|  |_________|  |_________|   |_________|
   ********************END OF BEAM DESIGN**************************
    57. END CONCRETE DESIGN
    58. *
    59. ** CONCRETE DESIGN AS PER ACI 318R-02
    60. *
    61. LOAD LIST 4
    62. START CONCRETE DESIGN
 CONCRETE DESIGN 
    63. CODE ACI 2002
    64. FC 4 ALL
    65. FYMAIN 60 ALL
    66. TRACK 1 ALL
    67. DESIGN BEAM ALL
      RECTANGULAR CONCRETE BEAM DESIGN PER ACI 318             -- PAGE NO.    4
   =====================================================================
          BEAM  NO.     1 DESIGN RESULTS - FLEXURE PER CODE  ACI 318-02
   LEN -  10.00FT.  FY - 60000.  FC - 4000.  SIZE - 10.00 X 16.00 INCHES
   LEVEL    HEIGHT     BAR INFO       FROM            TO         ANCHOR 
          FT.    IN.              FT.     IN.     FT.     IN.   STA  END
   _____________________________________________________________________
     1    0 + 2-3/4    2-NUM.10     0 + 0-0/0     10 + 0-0/0    YES  YES
   |----------------------------------------------------------------|
   |   CRITICAL POS MOMENT=    123.20 KIP-FT  AT  5.00 FT, LOAD    4|
   |   REQD STEEL=  2.44 IN2, RHO=0.0183, RHOMX=0.0214 RHOMN=0.0033 |
   |   MAX/MIN/ACTUAL BAR SPACING= 10.00/ 2.54/ 4.73 INCH           |
   |   REQD. DEVELOPMENT LENGTH = 48.52 INCH                        |
   |----------------------------------------------------------------|
     Cracked Moment of Inertia Iz at above location =    1817.34 inch^4
          B E A M  N O.     1 D E S I G N  R E S U L T S - SHEAR
    AT START SUPPORT - Vu=   38.19 KIP  Vc=   21.42 KIP  Vs=   29.50 KIP
    Tu=    0.00 KIP-FT  Tc=   1.95 KIP-FT  Ts=   0.00 KIP-FT  LOAD     4
    NO STIRRUPS ARE REQUIRED FOR TORSION.
    REINFORCEMENT IS REQUIRED FOR SHEAR.
    PROVIDE NUM. 4 2-LEGGED STIRRUPS AT  6.7 IN. C/C FOR   46. IN.
    AT END   SUPPORT - Vu=   38.19 KIP  Vc=   21.42 KIP  Vs=   29.50 KIP
    Tu=    0.00 KIP-FT  Tc=   1.95 KIP-FT  Ts=   0.00 KIP-FT  LOAD     4
    NO STIRRUPS ARE REQUIRED FOR TORSION.
    REINFORCEMENT IS REQUIRED FOR SHEAR.
    PROVIDE NUM. 4 2-LEGGED STIRRUPS AT  6.7 IN. C/C FOR   46. IN.
      RECTANGULAR CONCRETE BEAM DESIGN PER ACI 318             -- PAGE NO.    5
  ___   1J____________________  120.X  10.X  16_____________________   2J____ 
 |                                                                           |
 |                                                                           |
 |                                                                           |
 |  8#4 C/C  7                                                 8#4 C/C  7    |
 | 2#10H   3.   0.TO  120.                                                   |
 ||=========================================================================||
 |                                                                           |
 |___________________________________________________________________________|
  _________    _________    _________    _________    _________     _________ 
 |         |  |         |  |         |  |         |  |         |   |         |
 |         |  |         |  |         |  |         |  |         |   |         |
 |         |  |         |  |         |  |         |  |         |   |         |
 |         |  |         |  |         |  |         |  |         |   |         |
 | 2#10    |  | 2#10    |  | 2#10    |  | 2#10    |  | 2#10    |   | 2#10    |
 |   OO    |  |   OO    |  |   OO    |  |   OO    |  |   OO    |   |   OO    |
 |         |  |         |  |         |  |         |  |         |   |         |
 |_________|  |_________|  |_________|  |_________|  |_________|   |_________|
   ********************END OF BEAM DESIGN**************************