Civil Engineering Reference
In-Depth Information
9 Design of Connections
for Steel Members
9.1 INTRODUCTION
The design of connections is of equal importance to the safety and reliability of
steel railway bridges as the design of the axial and flexural members that are con-
nected to form the superstructure (see Chapters 6 and 7, respectively). Connections
in modern steel railway superstructures are made with welds, bolts, and/or pins.
Typically, these connections transmit axial shear (e.g., truss member connections and
beam flange splices), combined axial tension and shear (e.g., semirigid and rigid
beam framing connections that transmit shear and moment), or eccentric shear (e.g.,
welded flexible beam framing connections and beam web plate splices). Connection
behavior is often complex but may be represented for routine design with relatively
simple mathematical models. AREMA (2008) recommends design forces for axial
and flexural member connection design.
Truss member end connections at the top chord of deck trusses or the bottom
chord of through trusses should be designed for the allowable strength of the member.
Vertical post end connections in deck trusses without diagonals in adjacent panels at
the top chord and hangers in through trusses should be designed for 125% of the
calculated maximum force in the member. The connections must also be designed
considering the allowable fatigue stress ranges and the calculated live load stress
range magnitude (with reduced impact) for members subjected to tensile cyclical
stress ranges from live load (see Chapter 4).
Beamframingconnectionsgenerallybehaveasrigid(fixedorwithsubstantialrota-
tional restraint), semirigid (intermediate level of rotational restraint), or flexible (little
ornorotationalrestraint)atserviceloads.Theconnectionstransferonlyshearforcesif
consideredasflexible(i.e.,assimplysupportedbeams).AREMA(2008)recommends
Rivets may be used in the design of some historical structures. However, riveting is not a modern or
often used fastening method and the engineer should confirm that expertise in riveting is available for
both design and installation.
Pins are generally only used in special circumstances in modern steel railway superstructures such as at
suspended spans of cantilever structures (Chapter 5) or as components of support bearings in long spans.
Forexample,forslip-resistantboltedconnectionswithoutpresenceofstressesfromout-of-planebending,
the allowable fatigue stress range is 18 ksi for less than 2 million stress range cycles and 16 ksi for greater
than 2 million stress range cycles (Fatigue Detail Category B).
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