Civil Engineering Reference
In-Depth Information
The use of precast segmental construction of the bridge deck was considered, but
rejected due to the perceived impossibility of making a satisfactory shear connection
across a precast node. The full shear force in the deck is transferred across the node
of a truss, Figure 9.35 (c). If a vertical joint plane crosses the node, this plane has to
transfer the shear, either in friction or through shear keys. However, the node may be
put into direct tension by the overall bending of the deck, under normal loading or at
the ULS. It did not appear to be possible to design such a shear connection, particularly
with the very large shear forces associated with this massive deck.
Clearly, the main issue with casting the trusses in-situ was the possible diffi culty of
effectively fi lling the moulds and compacting the concrete through dense reinforcement,
particularly for the diagonal and the bottom longitudinal member. This was put to
the test by building a full-size test panel, complete with reinforcement, Figure 9.36.
It was discovered that the scale of the truss was such that the diagonal could be cast
and the concrete vibrated through trapdoors located at several locations in its top
surface. Similarly, there was no problem of access to the bottom member. However,
for shallower trusses with more slender members, these problems would be likely
to dominate the design. The use of self-compacting concrete would make the use of
smaller trusses far more attractive.
Figure 9.36
Trial panel of truss (Photo: Engineer Leo K.K. Leung, Executive Director of
Hopewell Highway Infrastructure Ltd (Hong Kong Stock Code: 737))
