Joints - The Behaviour and Design of Steel Structures to EC3 - page 413

this,bearingfailureusuallytakesplaceintheplatematerialratherthaninthebolt.
The design of plates against bearing failure is discussed in Section 9.7.2.
Forthesituationinwhichbearingfailureoccursintheboltratherthantheplate,
EC3-1-8[1]requiresthedesignbearingforce F b , Ed onaboltwhoseultimatetensile
strength f ub is less than that of the plate material f u to be limited to
F b , Ed ≤ F b , Rd = f ub dt
γ M 2

(9.11)

inwhich γ M 2 = 1.25(1.50forGrade4.6bolts), t isthethicknessoftheconnected
element,and d isthediameterofthebolt.Equation9.11ignorestheenhancement
of the bearing strength caused by the triaxial stress state that exists in the bearing
area of the bolt, but it seldom governs except for very high-strength plates.

9.6.5Preloaded friction-grip bolts

9.6.5.1 Design against bearing

High-strengthboltsmaybeusedasbearingbolts,oraspreloadedboltsinfriction-
grip joints (Figure 9.1b) which are designed against joint slip under service or
factoredloads.Whenhigh-strengthboltsareusedasbearingbolts,theyshouldbe
designed as discussed in Sections 9.6.1-9.6.4.

9.6.5.2 Design against slip

Fordesignagainstslipinafriction-gripjointforeitherserviceabilityoratultimate
loading,theshearforceonapreloadedbolt F v , Ed , ser or F v , Ed determinedfromthe
appropriate loads must satisfy

F v , Ed ≤ F s , Rd = nk s µ F p , C /γ M 3 (9.12)

in which γ M 3 = 1.25 for ultimate loading (for serviceability γ M 3, ser = 1.1), n is
the number of friction surfaces, k s is a coefficient given in Table 3.6 of EC3-1-8
[1] which allows for the shape and size of the hole, µ is a slip factor given in
Table 3.7 of EC3-1-8, and the preload F p , C is taken as

F p , C = 0.7 f ub A s .

(9.13)

When the joint loading induces bolt tensions, these tend to reduce the friction
clampingforces.EC3-1-8requirestheshearserviceabilityorultimatedesignload
F v , Ed , ser or F v , Ed to satisfy
F v , Ed ≤ F s , Rd = nk s µ F p , C − 0.8 F t , Ed /γ M 3 (9.14)

inwhich F t , Ed , ser or F t , Ed isthetotalappliedtensionatserviceloadingorultimate
loading, including any prying forces, and the slip resistance partial safety factor
is γ M 3 = 1.1 for service loading and 1.25 for ultimate loading.