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
| 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 318-02 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 2.63 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**************************