دانلود رایگان مقاله ارزیابی و ترمیم اولین نیروگاه یونانی

Abstract

The first electric power station in Greece is a registered monument of the international industrial heritage. The building consists of three longitudinal parts with a total area of 4800 m2 approximately in plan and has two levels of a height of 3 m and 12 m respectively. The structural system consists mainly of stone masonry walls and a steel roof. Nowadays the building is scheduled to be reused as a Museum of Electric Power and the need for structural upgrade arose mainly from current seismic requirements. According to the structural assessment study, the prevailing problem of the building is the combination of the presence of very high walls, interrupted by transverse walls at a distance of approximately 80 m, and the complete lack of horizontal diaphragms. The building’s architectural, historic and technological value is significant and its preservation, by minimization of interventions, posed several problems to the retrofit design. New steel frames connected to and cooperating with the masonry walls were designed to bear the vertical roof loads and restore the horizontal diaphragm at the roof level, while also reducing the seismic actions at the walls. The total required strength was achieved by additionally implementing vertical post-tensioning bars and FRP strips.

Conclusions

Most historic monuments of industrial heritage constructed during the first decade of 1900 in Europe have the same structural system, that of stone masonry walls in longitudinal layout in plan and approximately 6–10 m high which support steel truss girders on the roof. The main characteristic of unreinforced masonry walls is that their bearing resistance to vertical loading is very high while their tensile resistance is negligible. Current seismic requirements in Greece drive the need for structural upgrade of these structures, but due to the building architectural, historic and technological value the need for minimum and reversible interventions is crucial. In the present Design, new steel rigid frames and truss girders with stiff horizontal X-shaped bracing are proposed in order to ensure a diaphragm in the roof level, reduce out of plane bending moments in the walls and bear the vertical loads of the roof. Post-tensioning with high tensile threaded bars is applied in order to allow the utilization of masonry in compression which results in out of plane minimization of overturning and in plane shear strengthening. Due to architectural restrictions the prestress bars are placed into the core of circular cavities and in the first step the bottom part of the cavity is grouted so as to ensure anchorage during post-tensioning with the proper bond length. The whole mass of masonry is homogenized with grouting before the application of post-tensioning. Supplementary GFRPs for strengthening in shear of the equivalent beams and some walls are used and Sika TRM system is applied on the wall surface to account for small random tensile stresses. With the implementation of the proposed structural scheme the building is capable of bearing of the loads specified by the current regulations and its architectural form is optimally preserved.