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Steel Designers' Manual - 6th Edition (2003)
606 Composite beams
ram
M
M developed by
shear—connectors
in this zone
bending moment
tension in anchorage
reinforcement lenath mesh
-
I
.,.
L
çIL-1I
bolt
7
...., . .. ... ... ..;. -y t• It
compression
stiffener
Fig. 21.5 Representation of conditions at internal column of continuous beam
girder system also utilizes continuity of the secondary members (see Fig. 21.4(c)).
Other methods of continuous design are presented in References 3 and 6.
Continuous composite beams may be more economic than simply-supported
beams where plastic hinge analysis of the continuous member is carried out, provided
the section is plastic according to BS 5950: Part 1. However, where the lower
flange or web of the beam is non-compact or slender in the negative (hogging)
moment region, then elastic design must be used, both in terms of the distribution
of moment along the beam, and also for analysis of the section. Lateral instability
of the lower flange is an important design condition, although torsional restraint is
developed by the web of the section and the concrete slab. 6
In bridges, continuity is often desirable for serviceability reasons, both to reduce
deflections, and to minimize cracking of the concrete slab, finishes and wearing
surface in road bridges. Special features of composite construction appropriate to
bridge design are covered in the publication by Johnson and Buckby 7 based on
BS 5400: Part 5. 5
21.6 Analysis of composite section
21.6.1 Elastic analysis
Elastic analysis is employed in establishing the serviceability performance of composite
beams, or the resistance of beams subject to the effect of instability, for