Ancient Materials and Singular Constructions: Numerical, Experimental, and Heritage Strategies to Preserve Masonry Structures in Seismic Areas

1. Heritage Strategies: The Wisdom Of Ancient Architects Using Materials Under Dynamic Loading

According to Kirikov (1992), an earthquake-resistive building must be protected against two main features: (i) unequal settlements of the foundation that overstress the structure and (ii) the resonant phenomena. The present day builders take into account the aforementioned features and recognize the vital task of ductility, reinforcements and new composite materials, as main issues under dynamic loading. But unfortunately, it is common to forget the importance of “simple” material properties as effective way of improving the structural response under major or minor earthquakes. However, the most highly qualified ancient builders knew the crucial role of the building materials and their associated properties, as seismic-resistive elements, joining structural techniques together with other multipurpose measures. For instance, the relationship between hydraulic properties and seismic resistance and the use of non-rigid, light or reinforced materials as collapse controllers were well known by ancient builders.

Sumerian builders systematized the erection of earthquake resistive walls by combining two external rigid layers (burnt bricks) with a soft core (adobe bricks bonded by clay mortar and bitumen). High elasticity and ductility was provided due to that material combination. Some earthquake-resistance improvements were also reached by the Aegean culture in Crete (e.g. by means of reinforcing masonry with wooden beams). Roman builders also combined rigid and elastic materials, for instance embedding rings of clay vessels into the cast concrete (Adam, 1994), in order to increase ductility and decrease the weight. They also built facing walls of brick with internal core of concrete and stones, improving the structural response under seismic loading (Fig.1). In Byzantium, courses of chiselled stone were combined with bricks resulting in seismic-resistant belts. In addition, high plasticity lead plates were placed between the units providing seismic isolation.

Figure 1.

Three layered walls which improve the seismic behaviour, (a) Sumerian wall; (b) Roman wall

As it is well known, if the structural weight is reduced the seismic stability is improved. A clear example of this is the masterpiece of Apollodorus of Damascus, the Pantheon dome: hard travertine was used as aggregate of the concrete where the stresses are higher, that is, at the lower part; however tuff and pumice, both light filling materials, were used at the top.