STEEL: DESIGN OF CONNECTIONS
Section 10 of IS 800:2007 deals
with the design and detailing requirements for joints between members. The
connections in a structure shall be designed so as to be consistent with the
assumptions made in the analysis of the structure and comply with the requirements
specified in section 10 of the code.
Connections shall be capable of
transmitting the calculated design actions. In most structures connections are
the weakest link. This leads often to failure in spite of the strong members
used. This draws our attention to the design of connections with utmost care.
The behaviour of connections is quite complex due to geometric imperfections
and complexities, lack of fit, residual stresses etc; making it complex to
analyse. This can be simplified by a number of assumptions and approximations
based on past experience, experimental results and ductility of steel. It is
the ductility of steel assists the distribution of forces generated within a
joint. This is outlined in Cl. 10.1.4 of IS 800:2007.
The ultimate aim of connection
design is to have a simple, compatible, feasible, easy to fabricate, safe and
TYPES OF CONNECTIONS.
Connection elements consist of
components such as cleats, gusset plates, brackets, connecting plates and
connectors such as rivets, bolts, pins, and welds. Connections are classified
based on the connecting element and the fixity of the joint
1. Classification based on the connector
Connections are classified based
on the connecting element in to
(c) Pinned and
(d) Welded connection. Of these
riveted, bolted and pinned connections behave in a similar manner.
2. Classification based on the fixity of the joint
Based on the fixity of the joint,
connections are classified in to
(a) Rigid joint,
(b) Semi rigid joint and
(c) Flexible joints.
2. SELECTIONS OF TYPE OF CONNECTION
connections were once very popular and are still used in some cases but will
gradually be replaced by bolted connections. This is due to the low strength of
rivets, higher installation costs and the inherent inefficiency of the
connection. Welded connections have the advantage that no holes need to be
drilled in the member and consequently have higher efficiencies. However,
welding in the field may be difficult, costly, and time consuming. Welded
connections are also susceptible to failure by cracking under repeated cyclic
loads due to fatigue which may be due to working loads such as trains passing
over a bridge (high-cycle fatigue) or earthquakes (low-cycle fatigue). A
special type of bolted connection using High Strength Friction Grip (HSFG)
bolts has been found to perform better under such conditions than the
conventional black bolts used to resist predominantly static loading. Bolted
connections are also easy to inspect and replace. The choice of using a
particular type of connection is entirely that of the designer and he should
take his decision based on a good understanding of the connection behaviour,
economy and speed of construction. Ease of fabrication and erection should be
considered in the design of connections. Attention should be paid to clearances
necessary for field erection, tolerances, tightening of fasteners, welding procedures,
subsequent inspection, surface treatment and maintenance.