Statics: Smaller Internal Forces

Raleigh Arena

Fig. 9-10 The force paths of the Rayleigh Arena [9.4]

The roof structure of the Raleigh Area (Fig. 9-10) consists of carrying (sagging) cables and stabilising (hogging) cables which are supported by a pair of inclined arches. The structure forms, at least in part, a self-balanced system, which effectively reduces the internal forces in the arches. The carrying cables apply large forces to the arches and some of the vertical components of the forces are transmitted to external columns. Significant portions of the bending moments and the horizontal components of the shear and compressive forces in the arches are self-balancing at the points of contact between the two arches. Most of the horizontal components of the remaining shear and compressive forces in the lower parts of the arches are balanced by underground ties, which have a similar function to the wire tie in the ring used in the demonstration. The reduced internal forces not only allow the use of less material but also lead to a stiffer structure.

Fig. 9-11: A stadium in Nanjing, China

Another example is the newly built stadium in Nanjing, China. The roof of the stadium is supported by a pair of arches, which are inclined outwards symmetrically and do not support each other. Fig. 9-11 shows one of the arches. The pair of arches generates large horizontal forces of 13,000 kN at their supports. In order to avoid these horizontal forces at the ends of the arches being applied to the pile foundations, which are on soft soil, eight post-tension cables of a diameter of 25mm and a length of 400 m are placed underground to link the two ends of each arch to balance the large horizontal forces. The cables have the same functions as demonstrated in the tied rubber ring.