Article from the National Precast Concrete
Association Australia
Connections are defined as the system or assembly used to
tie a precast member to the supporting structure or to an adjacent member while
fixings are the hardware component of connections.
In the design of connections structural redundancy is
generally eliminated to minimise forces. Therefore, it is critically important
that load paths for forces through the structure, from elements through
connections down to the footings and foundation are carefully reviewed. Where
possible it is prudent to design a statically determinate system, which will
accommodate long-term, incremental volume-change movement. Consideration of
connection behaviour during both erection and the life of the structure are
important.
Practical and economical connection design must consider
the manufacture of the elements and construction techniques, as well as the
performance of the connections for both serviceability and ultimate limit
states. Design of the overwhelming majority of connections is a simple everyday
affair but the principles summarised here are the basis of all connection
design.
Connections and fixings must meet the following criteria.
- Structural Adequacy
- Ductility
- Accommodation for Volume Change
- Durability
- Fire Resistance
- Production Simplicity
- Construction Simplicity
A connection must resist the forces to which it will be
subjected during its lifetime. Some of these forces are apparent, for example
those caused by dead and live gravity loads, wind, earthquake, and soil or
water pressure. Others are not so obvious and are frequently overlooked. These
are the forces caused by restraint of volume changes in the elements (see
below) and forces required to maintain stability. Instability can be caused by
eccentric loading, as well as lateral loads from wind and earthquake. Measures
taken to resist instability may aggravate the forces caused by volume changes,
and vice versa.
The connection resistance can be categorised by the types
of force to which it is subjected. These include:
- Compression
- Tension
- Flexure
- Shear
- Torsion.
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