Joints - The Behaviour and Design of Steel Structures to EC3 - page 414

9.7 Design of bolted plates

9.7.1 General

Aconnectionplateusedinajointisrequiredtotransferactionswhichmayactinthe
planeoftheplate,oroutofit.Theseactionsincludeaxialtensionandcompression
forces,shearforces,andbendingmoments,andmayincludecomponentsinduced
by prying actions.The presence of bolt holes often weakens the plate, and failure
may occur very locally by the bearing of a bolt on the surface of the bolt hole
through the plate (punching shear), or in an overall mode along a path whose
positionisdeterminedbythepositionsofseveralholesandtheactionstransferred
by the plate, such as that considered in Section 2.2.3 for staggered connectors in
tension members.
Generally, the proportions of the plates should be such as to ensure that there
are no instability effects, in which case it will be conservative for the strength
limit state to design against general yield, and satisfactory to design against local
fracture.
Theactualfailurestressdistributionsinboltedconnectionplatesarebothuncer-
tainandcomplicated.Whendesignistobebasedongeneralyielding,itislogical
to take advantage of the ductility of the steel and to use a simple plastic analysis.
Acombined yield criterion such as

σ y + σ z − σ y σ z + 3 τ yz ≤ f y (9.15)

(Section1.3.1)maythenbeused,inwhich σ y and σ z arethedesignnormalstresses
and τ yz is the design shear stress.
When design is based on local fracture, an elastic analysis may be made of the
stress distribution. Often approximate bending and shear stresses may be deter-
mined by elastic beam theory (Chapter 5). The failure criterion should then be
tested at all potentially critical locations.

9.7.2 Bearing and tension

Bearingfailureofaplatemayoccurwhereaboltbearsagainstpartofthesurface
of the bolt hole through the plate, as shown in Figure 9.19a.After local yielding,
theplatematerialflowsplastically, increasingthecircumferenceandthicknessof
the bearing area, and redistributing the contact force exerted by the bolt.
EC3-1-8[1]requirestheplate-bearingforce F b , Ed duetothedesignloadstobe
limited by

F b , Ed ≤ F b , Rd = k 1 α d f u dt /γ M 2 (9.16)

in which f u is the ultimate tensile strength of the plate material, d is the bolt
diameter, t istheplatethicknessand γ M 2 = 1.25isthepartialfactorforconnector
resistance (1.50 for Grade 4.6 bolts).