Code-check of preloaded bolts according to Indian standards

Slip resistance

Slip resistance of preloaded bolt is checked according to IS 800, Cl. 10.4.3:

\[ V_{sf} \le V_{dsf} \]

where:

• \(V_{dsf} = V_{nsf} / \gamma_{mf}\) – design shear capacity of a bolt as governed by slip for friction type connection
• \(V_{nsf} = \mu_f n_e K_h F_0\) – nominal shear capacity of a bolt as governed by slip for friction type connection
• \(\mu_f\) – coefficient of friction (slip factor) as specified in IS 800, Table 20; editable in Code setup
• \(n_e = 1\) – number of effective interfaces offering frictional resistance to slip; each shear plane is checked separately
• \(K_h\) – factor for bolt holes; \(K_h = 1.0\) for fasteners in standard holes, \(K_h = 0.85\) for fasteners in oversized and short slotted holes, \(K_h = 0.7\) for fasteners in long slotted holes
• \(\gamma_{mf}\) – partial safety factor for bolts – friction type – IS 800, Table 5, \(\gamma_{mf}=1.10\) if slip resistance is designed at service load, \(\gamma_{mf}= 1.25\) if slip resistance is designed at ultimate load; editable in Code setup
• \(F_0 = A_n f_0\) – minimum bolt tension (proof load) at installation
• \(A_n\) – net tensile stress area of the bolt
• \(f_0 = 0.7 f_{ub}\) – proof stress

Capacity after slipping (IS 800, Cl. 10.4.4) should be checked by switching bolt type from friction to bearing – tension/shear interaction for design capacity at ultimate load.

Tension capacity of bolts

A bolt subjected to a factored tensile force is checked according to IS 800, Cl. 10.3.5:

\[ T_f \le T_{df} \]

where:

• \(T_{df} = T_{nf} / \gamma_{mf}\) – design tensile capacity of the friction bolt
• \(T_{nf} = \min \{ 0.9 f_{ub} A_n, \, f_{yb} A_s (\gamma_{mf} / \gamma_{m0}) \}\) – nominal tensile capacity of the friction bolt
• \(f_{ub}\) – ultimate tensile strength of the bolt
• \(f_{yb}\) – yield strength of the bolt
• \(A_n\) – net tensile stress area of the bolt
• \(A_s\) – cross-section area at the shank
• \(\gamma_{mf}\) – partial safety factor for bolts – friction type – IS 800, Table 5, \(\gamma_{mf}=1.10\) if slip resistance is designed at service load, \(\gamma_{mf}= 1.25\) if slip resistance is designed at ultimate load; editable in Code setup
• \(\gamma_{m0} = 1.1\) – partial safety factor for resistance governed by yielding – IS 800, Table 5; editable in Code setup

Prying forces are determined by finite element analysis and are included in the tensile force.

Friction bolt subjected to combined shear and tension

A bolt required to resist both design shear force and design tensile force at the same time shall according to IS 800, Cl. 10.3.6 satisfy:

\[ \left( \frac{V_{sf}}{V_{df}} \right)^2 + \left( \frac{T_{f}}{T_{df}} \right)^2 \le 1.0 \]

where:

• \(V_{sf}\) – applied factored shear at design load
• \(V_{df}\) – design shear strength
• \(T_f\) – externally applied factored tension at design load
• \(T_{df}\) – design tension strength