Page 21 - Reinforced concrete voided slabs subjected to gravity and seismic actions

21 Structural typology description§cap 1Giovanni Battista Piranesi in one of his famous etchings of Roman antiquities, next to the Helena mausoleum structure, shows the lightenings of pignatte and writes in the no- tes in the table below: «One of the Cretian terracotta clay stacks four palms high which are interned in the wall».Another widespread device for the lightening of domes was the use of so-called “clay pipes” i.e. hollow cylindrical elements in terracotta in the form of a bottomless bottle. They were generally inserted one inside the other to create the downpipe but could be arranged in such a way as to create a row of pipes able to form the profile of a circle whi- le the conical shape of the neck allowed the freedom of movement necessary between the pipes so that they could be arranged according to the curve of an arch or of a vault. The technique for lightening of vaults or domes was then resumed for insertion into the concrete conglomerate of actual formworks: i.e. clay tubes inserted one inside the other. A famous example is the dome of the Basilica of San Vitale in Ravenna (figure 1.9b). Francesco Di Giorgio Martini in his Treaty of civil and military architecture wrote that the “ancients”, in order to decrease the roof loads resting on the retaining walls built vaults using empty terracotta containers. He also provided a sketch of how to build a barrel vault using brickwork hollow elements in the shape of a conical trunk which were referred to as tomboli or cannoli.This device to lighten vaults was widespread. Depending on the different geographical areas, lightening elements assumed different names but it can be said that their use con- tinued with a technique that was essentially unchanged until modern times.For example, in Great Britain Sir John Soane used containers with one end that was squa- re shaped and the other circular called hollow-core terracotta pots for the construction of the roofs of certain areas of the Bank of England in London (South and South-East Transfer Offices, 1817-23).It is clear that the lightening of a vaulted system where the forces converge on the ground, through the vertical support structures, essentially by means of an “arch” mechanism, is conceptually easier that the lightening of a flat orientation.And it is for this reason that with regard to the structural unit defined as horizontal termi- nation, whether it be covering, intermediate, or base, i.e. respectively the casing, internal space partition or element of separation from the foundation site, the techniques and types of lightening are part of a more recent history.1.2.3. Towards the voided slab paradigmIt is clear that in the history of building techniques, the introduction of the slab, with the consequent possibility of exploiting the bidirectional behavior static resource, re- presents a true turning point. This major innovation in structural systems takes place in parallel to the other great revolution represented by the spread of reinforced concrete. Once the full potential of modern concrete had been revealed, it was not long before the concept of lightening was resumed. Just as happened to the Roman vaults and domes, the possibility of introducing stationary formworks within the thickness of the slabsup © Dalifoform Group © Daliform Grouup © Daliform Group © Daliform Group © Dalifoform Group © Daliform Group © Daliform Group © Daliform Grouup © Daliform Group © Daliform Group © Daliform Group © Daliform Group © Dalifoform Group © Daliform Group © Daliform Group © Daliform Group © Daliform Group © Daliform Grouup © Daliform Group © Daliform Group © Daliform Group © Daliform Group © Daliform Group © Daliform Group © Dalifoform Group © Daliform Group © Daliform Group © Daliform Group © Daliform Group © Daliform Group © Daliform Group © Daliform Grouup © Daliform Group © Daliform Group © Daliform Group © Daliform Group © Daliform Group © Daliform Group © Daliform Group © Dalifo form Group © Daliform Group © Daliform Group © Daliform Group © Daliform Group © Daliform Group © Daliform Group © Daliform Grou© Daliform Group © Daliform Group © Daliform Group © Daliform Group © Daliform Group © Daliform Group © Daliform Group © Dalifo iform Group © Daliform Group © Daliform Group © Daliform Group © Daliform Group © Daliform Group © Daliform Grouup © Daliform Group © Daliform Group © Daliform Group © Daliform Group © Daliform Group © Dalifo form Group © Daliform Group © Daliform Group © Daliform Group © Daliform Grouup © Daliform Group © Daliform Group © Daliform Group © Dalifoform Group © Daliform Group © Daliform Grouup © Daliform Group © Dalif form Grou