Civil Engineering Reference
In-Depth Information
Figure 8.2
Distribution of longitudinal stiffness to provide support for top slab
areas of high shear, and will minimise redundant concrete near mid-span. Clearly this
concept will place more demands on the transverse spanning action of the top slab.
Traditional bridges had their longitudinal bending strength distributed evenly
across the width of the deck, with closely spaced beams. This arrangement lead to
much redundant concrete in the webs and bottom fl anges and virtually eliminated the
transverse bending role of the top slab. Many pseudo-slabs made of adjacent precast,
prestressed beams are still conceived in this way. Rationally designed decks minimise
the number of webs and the bottom fl ange area, and use the transverse strength of the
slab to distribute concentrated live loads. A comparison between the two approaches
can be seen in the example of Figure 8.3 which shows the alternative design proposed
by the author, and eventually built, for a bridge crossing the Sungai Kelantan in
Malaysia.
8.3 Transverse distribution of live loads
It is essential for the bridge designer to understand how bridge decks cope with the
transverse distribution of concentrated live loads. Where the specifi ed highway loading
includes a single indivisible load, for instance the HB load in the UK, this distribution
has a major effect on the sizing and the economy of decks. Under such concentrated
