Civil Engineering Reference
In-Depth Information
Continuous beams
The Eurocode design methods for continuous beams (Chapter 4) make
use of both simple plastic theory (as for steel beams) and redistribution of
moments (as for concrete beams).
Columns
The only British code that gives a design method for composite columns
is BS 5400:Part 5,
Composite bridges
. EN 1994 gives a newer and simpler
method, which is described in Section 5.6.
Framed structures for buildings
Composite members normally form part of a frame that is essentially
steel, rather than concrete, so the design methods of EN 1994 are based
on those of EN 1993 for steel structures. Beam-to-column joints are class-
ified in the same way; the same assumptions are made about geometrical
imperfections, such as out-of-plumb columns; and similar allowance is
made for second-order effects (increases in bending moments and reduc-
tion in stability, caused by interaction between vertical loads and lateral
deflections). Frame analysis is outlined in Section 5.4.5. It may be more
complex than in current practice, but includes methods for unbraced frames.
Eurocodes EN 1993 and 1994 contain much new material on the design
of joints.
Structural fire design
The high thermal conductivity and slenderness of structural steel members
and profiled sheeting cause them to lose strength in fire more quickly than
concrete members do. Structures for buildings are required to have fire
resistance of minimum duration (typically, 30 minutes to 2 hours) to
enable occupants to escape and to protect fire fighters. This has led to the
provision of minimum thicknesses of concrete and areas of reinforcement
and of thermal insulation of steelwork.
Extensive research and the recent subject of fire engineering [2] have
enabled the Eurocode rules for resistance to fire to be less onerous than
older rules. Advantage is taken in design of membrane effects associated
with large deformations, and of the provisions for accidental design sit-
uations. These allow for over-strength of members and the use of 'frequent'
rather than 'characteristic' load levels. Explanations and worked examples
are given in Sections 3.3.7, 3.4.6, 3.10, 3.11.4 and 5.6.2.
