Joško Krolo

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.

The Analyses of Pure Shear Behaviour of E-Glass Woven Fabrics by Picture Frame Test

This paper describes an experimental study on the pure shear properties of E-Glass woven fabric by picture frame test. During shear deformation, the fabric yarns experience large angular change between warp and weft yarns. The picture frame test is one of the fundamental methods to characterize the in-plane shear behaviour of woven fabrics and can produce a quite uniform shear deformation state in the fabric sheet. Tests are conducted on two different size of EGlass specimens 40x40 mm and 80x80 mm. For a double increase the specimen size, the values of shear force and axial load are also almost double increase at the maximum displacement and shear angle.

LOAD BEARING CAPACITY OF THE GLASS RAILING ELEMENT

In this paper some basic physical and mechanical properties of glass as structural material are presented. This research is about specifically manufactured glass railing element that will be a part of a pedestrian bridge construction in Zagreb, Croatia. Load bearing capacity test of the glass railing element is conducted within the Faculty of Civil Engineering in Zagreb and obtained experimental results are discussed and compared to the ones provided by the numerical model. Taking into account the behaviour of laminated glass and results of experimental and numerical testing, glass railing element can be regarded as safe.

GUBITAK STABILNOSTI I ODREĐIVANJE NOSIVOSTI ČELIČNOG HIDRAULIČNOG PODUPIRAČA

Sažetak: Hidraulicni podupirac prvenstveno je namijenjen uporabi u građevinarstvu, ali svoju primjenu može naci i u drugim podrucjima poput rudarstva ili brodogradnje. Konstrukcija ovog hidraulicnog podupiraca razlikuje se od klasicnog po tome sto umjesto dvije cijevi ima tri, a u najdonjoj, baznoj cijevi, ima ugrađenu hidraulicnu dizalicu. U ovome radu utvrđena je nosivost takvog hidraulicnog podupiraca analitickim rjesenjem diferencijalne jednadžbe, proracunom prema euronormi 3 i metodom konacnih elemenata (SOFiSTiK). Ta rjesenja su uspoređena s nosivoscu dobivenom eksperimentalnim putem.

Modeling Fracture of Fiber Reinforced Polymer

In the present paper 3D rate sensitive constitutive model for modeling of laminate composites is presented. The model is formulated within the framework of continuum mechanics based on the principles of irreversible thermodynamics. The matrix (polymer) is modeled using 3D rate sensitive microplane model. For modeling of fibers (glass) a uni-axial constitutive law is employed. The fibers are assumed to be uniformly smeared-out over the matrix. The formulation is based on the assumption of strain compatibility between matrix and fibers. To account for the de-lamination of fibers, the matrix is represented by the periodically distributed bands with non-uniform strength properties over the band width. The input parameters of the model are defined by the mechanical properties of matrix and fibers (elastic properties, strength and fracture energy), the volume content of fibers and by their orientation in 3D space. The model is implemented into a 3D finite element code. To assure mesh objective results, the localization limiter is based on the assumption of constant energy dissipation within each finite element, i.e. the crack band method is used. The performance of the model is shown on one numerical example for specimens loaded in uni-axial tension. It is demonstrated that the proposed model is able to realistically predict the resistance and failure mode of complex fiber-reinforced composite for different orientation of fibers.