Rehabilitation and protection of the bearing structure of the Baptistery of St. John (Jupiter's temple) in Split
The stone bearing system of the Baptistery of St. John (Jupiter's Temple) in Split consists of four walls that, without elements of stone plastics, reach the vault foot height. From that level to the end of all walls, with the exception of the wall on the east side, stone blocks are richly decorated with elements of architectural plastics. The vault of the Baptistery was built of forty stone blocks, positioned in eight longitudinal rows, each with five blocks positioned transversally to the longitudinal axis, with rounded edges and considerable convexities on the external side, but richly moulded on the inner side.
When talking about the support system, we have to mention the cornices of longitudinal walls, those on the exterior side and those supporting the vault on the inside. The external, upper cornices are constructed with stone blocks of ground- plan transversal dimension of approximately 150 cm. The connection with metal couplings in two places vertically to the common expansion joint and the distance between the transverse walls of the Baptistery of 7.20 m gives the cornice a respectable possibility of taking over and transferring horizontal vault thrust. The cornice below the vault heels has the same possibility. Since the Baptistery has been exposed to weathering without any protection for the last thousand years, various damages have been discovered.
The damage on the upper external side of the stone blocks showed an opening of typical hinge/crack, somewhat above the joint with stone blocks of the cornice, at the connection of two stone blocks of the vault. The damage of stone blocks of the external, horizontal cornice occurred due to yield of iron couplings and cracking of stone around them. This damage was significant, not so much because of the damage of the stone, but because of interrupted continuity, formed by connecting stone blocks into one entirety capable to take over the horizontal thrust force of the vault.
Stone blocks were also damaged, due to concentration of stress on their edges, especially on the edge of the west facade. Due to the aforesaid and to potential danger of shifting of stone blocks of the western gable, along the slope and from the wall plane, rehabilitation of the existing state began.
Renovation of the bearing structure of the Baptistery of St. John included overall rehabilitation of stone blocks of western gable and renovation of their joints, grouting of stone walls, part of restoration works and protection from weathering of the entire Baptistery.
For the purpose of rehabilitation of western gable, the existing stone blocks had to be removed to the level of horizontal cornice of the south and north longitudinal wall, which had been rehabilitated previously.
The removed stone blocks were rehabilitated and prepared for new building in. The growing damages of stone plastics on end blocks were remedied by ''patching''.
Particular difficulty in rehabilitation and reconstruction works on the bearing structure of the Baptistery was the fact that the structure's location is in the centre of Diocletian's Palace. Huge and heavy stone blocks and their handling on site in limited space required extraordinary skills in site organization. For performing such exceptionally difficult and responsible work, special portal crane, of capacity 15 t, was constructed and erected for that occasion, without which execution of these works would be impossible.