Experimental and Numerical Analysis of Traditional Column Connections with the Possible Retrofit Concept

Abstract

Several historical constructions in Croatia have permanent column problems, particularly at connections with capitals and bases, characterized by specific fractures. Experimental and numerical analysis of traditional column connections were conducted. Distinct fractures concentrated around the connections, as well as the traces of previous restorations noted by the chronicles, intrigued us to conduct research of the possible fundamental deficiency of the structural system. Traditional connections can be described as carefully smoothed stone contact areas, joined with centrally placed iron dowel fixed with a lead infill in a slightly larger hole. The comprehensive numerical and experimental efforts have shown that even a small imperfection in the construction process or a disturbance of bearing system have consequence, the contact leans to one side. As the joint has a very limited ability to compensate rotations, the relative rotation between column elements causes high local stresses at the edge of a column, which eventually results in numerous fractures. Ignoring or not fully appreciating the real nature of connections leads to significantly different stress distributions and orientations of thrust lines which may grossly overestimate the safety factor. This usually leads to inadequate rehabilitation, but also if no action is taken continuous fracture propagation can endanger local or global stability of the structure. Laboratory tests were performed on stone samples provided from traditional quarries and we tried to restore a rather similar level of stress and stress distribution caused by eccentric forces. Although some results will be presented, final objective will be to obtain the value of rotational stiffness and stress – strain diagram for connections, which is crucial for understanding of the load carrying mechanism, numerical treatment of connections and adequate retrofit strategies. In order to ensure serviceability and durability, we have started to test the possible retrofit concept with a layer of lead placed between two connected areas. The material such as lead enables small rotations and protects connected areas from large stress concentrations. Lead has already been used to fill the dowel holes and the additional horizontal thin layer appears to be an appropriate and almost invisible intervention.