IS800SECTION6

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					                      SECTION 6 DESIGN OF TENSION MEMBERS


6.1 Tension Members
    Tension members are linear members in which axial forces act causing elongation
(stretch). Such members can sustain loads upto ultimate load, at which stage they may fail by
rupture at a critical section. However, if the gross area of the member yields over a major
portion of its length before the rupture load is reached, the member may become
nonfunctional due to the excessive elongation. Plates and other rolled sections in tension may
also fail by block shear of end bolted regions, under combined shear along longitudinal
sections along bolt lines and normal tensile stresses on a transverse section across a bolt line.
     The factored design tension T, in the members shall satisfy the following requirement
                                             T < Td
where
        Td = design strength of member as given below
     The design strength of a member under axial tension, Td, is the lowest of the design
strength due to yielding of gross section, Tdg, rupture of critical section, Tdn and block shear
Tdb.
6.2 Design Strength due to Yielding of Gross Section
    The design strength of members under axial tension Tdg, as governed by yielding of gross
section, is given by
                                               Tdg = fy Ag /m0
where
        fy = yield strength of the material in MPa
      Ag = gross area of cross section in mm2
     m0 = partial safety factor for failure in tension by yielding
6.3 Design Strength due to Rupture of Critical Section
    6.3.1 Plates  The design strength in tension of a plate, Tdn, as governed by rupture of net
cross sectional area, An, at the holes is given by
                                            Tdn =0.9 fu An / m1
where
        m1 = partial safety factor
          fu = ultimate stress of the material in MPa
                                                                        pi2 
         An = net effective area of the member,        = b  nd h          t
                                         ps             
                                                                   i    4gi 
                                                                             

                                      g
                                               dh
                                      g
                                                         b
                                      g
                                      g


                      FIG 6.1 PLATES WITH BOLTS HOLES IN TENSION
                                                  52
where
       b, t = width and thickness of the plate respectively
        dh = diameter of the bolt hole (additional 2 mm to the diameter in case the directly
               punched holes)
          g = gauge length between the bolt holes as shown in Fig 6.1
         ps = staggered pitch length between line of bolt holes as shown in Fig 6.1
          n = number of bolt holes in the critical section
    6.3.2 Threaded Rods  The design strength of threaded rods in tension, Tdn, as governed
by rupture is given by
                                             Tdn =0.9 fu An / m1
where
        An = net root area at the threaded section
    6.3.3 Single Angles  The tearing strength of an angle connected through one leg is
affected by shear lag. The design strength, Tdn, as governed by tearing at net section is given
by
                                    Tdn = 0.9 fu Anc / m1 + Ago fy /m0
where
         = 1.38 – 0.076 (w/t) (fy/fu) (bs/L ) ≈ 1.4-0.54(bs/L)
where w and bs are as shown in Fig 6.2
        L = Length of the end connection, i.e., distance between the outermost bolts in the
               joint along the length direction or length of the weld along the length direction
Alternatively, the tearing strength of net section may be taken as
                                                  Tdn =  An fu /m1
where
         = 0.6 for one or two bolts, 0.7 for three bolts and 0.8 for four or more bolts in the
               end connection or equivalent weld length
        An = net area of the total cross section
        Anc= net area of the connected leg
        Ago= gross area of the outstanding leg
           t = thickness of the leg

        Error!                                          w
                            w



                                        w1 bs=w+w1                  bs=w
                                  FIG 6.2 ANGLES WITH END CONNECTION
    6.3.4 Other Sections – The tearing strength, Tdn, of the double angles, channels, I sections
and other rolled steel sections, connected by one or more elements to an end gusset is also
governed by shear lag effects. The design tensile strength of such sections as governed by
tearing of net section may also be calculated using equation in 6.3.3, where  is calculated
based on the shear lag distance, bs taken, from the farthest edge of the outstanding leg to the
nearest bolt/weld line in the connected leg of the cross section.



                                              53
6.4 Design Strength due to Block Shear ─ The block shear strength at an end connection is
calculated as given below:
   6.4.1 Plates –The block shear strength, Tdb, of connection shall be taken as the smaller of
                                 Tdb = ( Avg fy /( 3 m0) + fu Atn /m1 )
                                                    or
                                  Tdb = ( fu Avn /( 3 m1) + fy Atg /m0 )
where
       Avg, Avn = minimum gross and net area in shear along a line of transmitted force,
                    respectively (1-2 and 4 –3 as shown in Fig 6.3 and 1-2 as shown in Fig
                    6.4)
       Atg, Atn = minimum gross and net area in tension from the hole to the toe of the angle
                  or next last row of bolt in plates, perpendicular to the line of force,
                  respectively (2-3) as shown in Fig 6.3 and Fig 6.4
         fu, fy = ultimate and yield stress of the material respectively
                                            1
                                                       2
                                            4
                                                       3




                               FIG 6.3 BLOCK SHEAR FAILURE OF PLATES

   6.4.2 Angles – Strength as governed by block shear failure in angle end connection shall
be calculated as given in Section 6.4.1 by using appropriate areas in shear and tension as
shown in Fig 6.4.




                                    1             2
                                    4            3




                                 FIG 6.4 BLOCK SHEAR FAILURE OF ANGLES




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