CEMP-E
TI 809-02
1 September 1999
g. Requirements for Wear Protection. The total thickness of design sections subject to
wear will be increased beyond that required to meet stress requirements. The amount of such
increase will be based on the material involved, the frequency of use, and the designed
service life. Estimates of the wear requirement will be based on previous experience or
accepted practice for the application. Use of replaceable wear plates should be considered
where extremely severe conditions exist.
7-5. LOAD PATH INTEGRITY.
a. General. Connections between framing elements are critical. They must perform at
limit state and service load levels as intended to assure load path integrity is maintained during
extreme loading events. Under service loading conditions, connection displacements and
rotations should not lead to serviceability problems. Connections can be welded or bolted, or a
combination of both welds and bolts. Design of welded and bolted connections will be in
accordance with the either AISC Load and Resistance Factor Design (AISC-LRFD) or AISC
Specification for Structural Steel Buildings-Allowable Stress Design (AISC-ASD). Bolted
connections can be shear-bearing type connections, slip critical connections, or direct tension
connections. Field welding of connections should be minimized to the maximum extent
possible.
b. Design of Connections for Wind and Seismic Loads. Connection design philosophy is
different for earthquake than it is for wind. Connections used to resist wind load are designed
to perform in the elastic range. Connections used to resist earthquake loads, although
designed in a fashion similar to that for wind load, are expected to experience forces greater
than the code level design forces. This requires that earthquake resistant connections perform
in a ductile manner. Under certain circumstances, such as moment frame connections,
bearing connections may be desirable for wind load, but slip-critical connections may be
recommended to resist earthquake loads. Slip critical connections are recommended for
earthquake resistant beam-column connections where web connections are bolted and flange
connections are welded. Slippage of the bolts in these type connections can increase loads
on the flange welds resulting in connection failure (Reference UCB/EERC-83/02 Report,
"Seismic Moment Resisting Connections for Moment-Resisting Steel Frames": Keep in mind
that the ultimate load capacity of a slip-critical connection is the capacity of the bolts loaded in
shear/bearing. If slip-critical bolts in the web connection of a moment resistant joint are too
near the yielding flanges, the bolts may experience sufficient force to slip into a shear/bearing
type of response, which may have a lower capacity than the slip-critical type of response.).
There are significant differences between the strengths allowed for shear-bearing, and slip
critical bolts. Therefore, the designer must check both wind and seismic loading conditions to
make sure the connection satisfies both shear-bearing and slip-critical requirements.
c. Shear-bearing Type Connections. In a shear-bearing type connection, shear forces
are transferred through the connection by bolts that act in shear. The connected material is in
bearing adjacent to the bolts and must be evaluated for its load bearing capacity. Bolt shear
strength is about 62 percent of the bolt-ultimate tensile strength. It should be recognized that
all shear and moment connections at ultimate load conditions act in shear-bearing whether
they are designed as shear-bearing connections or as slip-critical connections. The bolts in
7-4
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