Temporary Strengthening Technique of Marble Columns with Steel Wires and Wood Spars

Granite, marble and heavy stone columns have been used in the architects from all the ages to answer to both aesthetical and structural requirements in ancient churches and historical buildings. Such materials offer great visual impact and have mechanical properties that allow their use in construction and to obtain bright and slender structures. Marble is a very high strength but brittle material. It often occur that marble or granite columns of historical building are cracked along their height due to external actions and the risk of buckling occurs. Because this kind of failure is sudden and very brittle in stone and rocks, an immediate strengthening of the columns is needed. Among e temporary strengthening technique consisting in steel collaring with wood spars and steel wires is of interest. This technique was widely utilised by Firemen and Civil protection during the earthquakes occurred in Italy in the last years, but very few experimental and theoretical researches are available on this topic. In this paper the interest was on this technique and an experimental program based on compressive tests on monolithic and cracked marble columns with circular cross-section reinforced externally with wood spars and steel wires was carried out. A simple model based on the determination of the critical load of an elastic beam on elastic springs is able to take into account the steel collaring. The results obtained highlight that from a theoretical point of view, the presence of steel collaring in cracked column increases the critical load, ensuring monolithic behaviour, while from the practical point of the view the technique is very cheap and easy to apply in temporary strengthening of cracked columns.