Josip Atalić

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

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.

Influence of spatial variability of ground motion on seismic response of bridges

U radu je prikazan pristup seizmickoj analizi mostova pri prostorno promjenjivoj potresnoj pobudi. Objasnjen je fenomen prostorne promjenjivosti potresa, utjecaj na odziv mostova i razlike u odnosu na istodobnu pobudu oslonaca. Detaljno je opisan model takve pobude, s osvrtom na postupke tvorbe prostorno promjenjivih zapisa. Prikazane su i numericke metode proracuna, ucinkovite za rjesenje ovoga problema. Opisana metodologija je primijenjena na seizmicku analizu lucnog mosta. Rezultati analize su pokazali nepovoljan ucinak prostorne promjenjivosti pobude na odziv vecine razmatranih velicina mosta.U radu je prikazan pristup seizmickoj analizi mostova pri prostorno promjenjivoj potresnoj pobudi. Objasnjen je fenomen prostorne promjenjivosti potresa, utjecaj na odziv mostova i razlike u odnosu na istodobnu pobudu oslonaca. Detaljno je opisan model takve pobude, s osvrtom na postupke tvorbe prostorno promjenjivih zapisa. Prikazane su i numericke metode proracuna, ucinkovite za rjesenje ovoga problema. Opisana metodologija je primijenjena na seizmicku analizu lucnog mosta. Rezultati analize su pokazali nepovoljan ucinak prostorne promjenjivosti pobude na odziv vecine razmatranih velicina mosta.

Reconstruction of Rector’ s Palace atrium in Dubrovnik: a key role of column connections

Rector’ s Palace is one of the most valuable heritage buildings in the historic Old town of Dubrovnik and the world famous setting for concerts and exhibitions. The Palace Atrium is surrounded by two stories structure comprising quadripartite masonry vaults supported by masonry walls and stone columns. Historically, this structure has suffered numerous collapses and damages and restorations were frequently made. Despite this, many distinct fractures are concentrated around the traditionally made column connections with capitals and bases. Carefully smoothed stone contact areas are joined with iron dowel, which is centrally placed in a slightly larger hole, with a lead infill. These contacts do not have sufficient rotational stiffness and the ability to transmit eccentric loads. Therefore, high edge stresses and fractures at connections are unavoidable. With time, the small rotational stiffness of joints becomes even smaller and the behaviour is approaching one of the hinge joint. This effect may endanger the global stability of this structure, as only three aligned hinges are sufficient to render the system unstable, i.e. the system is “ almost” statically determinate and has only a small reserve in bearing capacity. Various retrofit strategies for column connections can cause considerably different stress distribution and by ignoring or underrating these effects, the safety factor can be seriously overestimated. This paper confirms the above assertions using a range of computational models: from simple frame and shell models to complex 3D solid models. This work also points out the significance of connections in historical buildings and attempts to investigate possible retrofit concepts. Numerous retrofit solutions were considered and results show a significant influence of this small detail of the bearing system on the global behaviour and stability of structure.

Učinak prostorne promjenjivosti potresne pobude na seizmički odziv mostova

U radu je prikazan pristup seizmickoj analizi mostova pri prostorno promjenjivoj potresnoj pobudi. Objasnjen je fenomen prostorne promjenjivosti potresa, utjecaj na odziv mostova i razlike u odnosu na istodobnu pobudu oslonaca. Detaljno je opisan model takve pobude, s osvrtom na postupke tvorbe prostorno promjenjivih zapisa. Prikazane su i numericke metode proracuna, ucinkovite za rjesenje ovoga problema. Opisana metodologija je primijenjena na seizmicku analizu lucnog mosta. Rezultati analize su pokazali nepovoljan ucinak prostorne promjenjivosti pobude na odziv vecine razmatranih velicina mosta.U radu je prikazan pristup seizmickoj analizi mostova pri prostorno promjenjivoj potresnoj pobudi. Objasnjen je fenomen prostorne promjenjivosti potresa, utjecaj na odziv mostova i razlike u odnosu na istodobnu pobudu oslonaca. Detaljno je opisan model takve pobude, s osvrtom na postupke tvorbe prostorno promjenjivih zapisa. Prikazane su i numericke metode proracuna, ucinkovite za rjesenje ovoga problema. Opisana metodologija je primijenjena na seizmicku analizu lucnog mosta. Rezultati analize su pokazali nepovoljan ucinak prostorne promjenjivosti pobude na odziv vecine razmatranih velicina mosta.