D8.E.5 Beam Design

Beams are designed for flexure, shear and torsion. If required the effect the axial force may be taken into consideration. For all these forces, all active beam loadings are prescanned to identify the critical load cases at different sections of the beams. The design is performed at 13 evenly spaced points along the length of the beam, including start and end points (i.e., 1/12th points or at ends of 12 equal length segments). All of these sections are scanned to determine the design force envelopes.

The sections used for design along the length of a member

D8.E.5.1 Design for Flexure

Maximum sagging (creating tensile stress at the bottom face of the beam) and hogging (creating tensile stress at the top face) moments are calculated for all active load cases at each of the above mentioned sections. Each of these sections is designed to resist both of these critical sagging and hogging moments. Where ever the rectangular section is inadequate as singly reinforced section, doubly reinforced section is tried. However, presently the flanged section is designed only as singly reinforced section under sagging moment. It may also be noted all flanged sections are automatically designed as rectangular section under hogging moment as the flange of the beam is ineffective under hogging moment. Flexural design of beams is performed in two passes. In the first pass, effective depths of the sections are determined with the assumption of single layer of assumed reinforcement and reinforcement requirements are calculated. After the preliminary design, reinforcing bars are chosen from the internal database in single or multiple layers. The entire flexure design is performed again in a second pass taking into account of the changed effective depths of sections calculated on the basis of reinforcement provide after the preliminary design. Final provisions of flexural reinforcements are made then. Efforts have been made to meet the guideline for the curtailment of reinforcements as per IS:456-2000 (Clause 26.2.3). Although exact curtailment lengths are not mentioned explicitly in the design output (finally which will be more or less guided by the detailer taking into account of other practical consideration), user has the choice of printing reinforcements provided by STAAD.Pro at 11 equally spaced sections from which the final detail drawing can be prepared.

Once you have specified SFACE and EFACE parameters to indicate sections, the MFACE parameter can be used to design for flexure at any point along the length of the beam, in addition to the equally spaced sections normally used.

D8.E.5.2 Design for Shear

Shear reinforcement is calculated to resist both shear forces and torsional moments. Shear design are performed at 11 equally spaced sections (0.0 to 1.0) for the maximum shear forces amongst the active load cases and the associated torsional moments. Shear capacity calculation at different sections without the shear reinforcement is based on the actual tensile reinforcement provided by the program. Two-legged stirrups are provided to take care of the balance shear forces acting on these sections.

As per Clause 40.5 of IS:456-2000 shear strength of sections (< 2d where d is the effective depth) close to support has been enhanced, subjected to a maximum value of τ_cmax.

D8.E.5.3 Beam Design Output

The default design output of the beam contains flexural and shear reinforcement provided at 5 equally spaced (0, .25, .5, .75 and 1.) sections along the length of the beam. User has option to get a more detail output. All beam design outputs are given in IS units. An example of rectangular beam design output with TRACK 2.0 output is presented below:

                  B E A M  N O.       1   D E S I G N  R E S U L T S

         M20                    Fe415 (Main)               Fe250 (Sec.)

       LENGTH:  6400.0 mm      SIZE:   300.0 mm X  400.0 mm   COVER: 25.0 mm


                          DESIGN LOAD SUMMARY (KN MET)
   ----------------------------------------------------------------------------
   SECTION |FLEXURE  (Maxm. Sagging/Hogging moments)|           SHEAR
   (in mm) |     P        MZ        MX   Load Case  |    VY       MX  Load Case
   ----------------------------------------------------------------------------
       0.0 |     0.00      0.00      0.00     1     |   60.61     0.00      1
           |     0.00      0.00      0.00     1     |
     533.3 |     0.00     29.63      0.00     1     |   50.51     0.00      1
           |     0.00      0.00      0.00     1     |
    1066.7 |     0.00     53.88      0.00     1     |   40.41     0.00      1
           |     0.00      0.00      0.00     1     |
    1600.0 |     0.00     72.73      0.00     1     |   30.31     0.00      1
           |     0.00      0.00      0.00     1     |
    2133.3 |     0.00     86.20      0.00     1     |   20.20     0.00      1
           |     0.00      0.00      0.00     1     |
    2666.7 |     0.00     94.28      0.00     1     |   10.10     0.00      1
           |     0.00      0.00      0.00     1     |
    3200.0 |     0.00     96.98      0.00     1     |    0.00     0.00      1
           |     0.00      0.00      0.00     1     |
    3733.3 |     0.00     94.28      0.00     1     |  -10.10     0.00      1
           |     0.00      0.00      0.00     1     |
    4266.7 |     0.00     86.20      0.00     1     |  -20.20     0.00      1
           |     0.00      0.00      0.00     1     |
    4800.0 |     0.00     72.73      0.00     1     |  -30.31     0.00      1
           |     0.00      0.00      0.00     1     |
    5333.3 |     0.00     53.88      0.00     1     |  -40.41     0.00      1
           |     0.00      0.00      0.00     1     |
    5866.7 |     0.00     29.63      0.00     1     |  -50.51     0.00      1
           |     0.00      0.00      0.00     1     |
    6400.0 |     0.00      0.00      0.00     1     |  -60.61     0.00      1
           |     0.00      0.00      0.00     1     |
   ----------------------------------------------------------------------------



                        SUMMARY OF REINF. AREA (Sq.mm)

   ----------------------------------------------------------------------------
   SECTION |          TOP            |         BOTTOM          |    STIRRUPS
   (in mm) | Reqd./Provided reinf.   | Reqd./Provided reinf.   |   (2 legged)
   ----------------------------------------------------------------------------
       0.0 |    0.00/ 402.12( 2-16í )|    0.00/ 981.75( 2-25í )|  8í  @ 180 mm
     533.3 |    0.00/ 402.12( 2-16í )|  237.32/1472.62( 3-25í )|  8í  @ 180 mm
    1066.7 |    0.00/ 402.12( 2-16í )|  450.84/1472.62( 3-25í )|  8í  @ 180 mm
    1600.0 |    0.00/ 402.12( 2-16í )|  632.82/1472.62( 3-25í )|  8í  @ 180 mm
    2133.3 |    0.00/ 402.12( 2-16í )|  773.83/1472.62( 3-25í )|  8í  @ 180 mm
    2666.7 |    0.00/ 402.12( 2-16í )|  863.91/1472.62( 3-25í )|  8í  @ 180 mm
    3200.0 |    0.00/ 402.12( 2-16í )|  894.99/1472.62( 3-25í )|  8í  @ 180 mm
    3733.3 |    0.00/ 402.12( 2-16í )|  863.91/1472.62( 3-25í )|  8í  @ 180 mm
    4266.7 |    0.00/ 402.12( 2-16í )|  773.83/1472.62( 3-25í )|  8í  @ 180 mm
    4800.0 |    0.00/ 402.12( 2-16í )|  632.82/1472.62( 3-25í )|  8í  @ 180 mm
    5333.3 |    0.00/ 402.12( 2-16í )|  450.84/1472.62( 3-25í )|  8í  @ 180 mm
    5866.7 |    0.00/ 402.12( 2-16í )|  237.32/1472.62( 3-25í )|  8í  @ 180 mm
    6400.0 |    0.00/ 402.12( 2-16í )|    0.00/ 981.75( 2-25í )|  8í  @ 180 mm
   ----------------------------------------------------------------------------

Parent topic: D8.E. Indian Codes - Concrete Design per IS 456

Related topics
V. IS456 2000-Doubly Reinforced Rectangular Beam V. IS456 2000-Singly Reinforced Rectangular Beam V. IS456 2000-Singly Reinforced Square Beam