Timber-concrete composite girders are a modern type of structure. They are formed by composite connection of a timber and concrete girder. They are designed in such a way that the concrete part of the girder is placed in the compression zone and the timber part of the girder in the tension zone. Various types of shear connectors are used for establishing this connection: from mechanical ones (bolts, nails, perforated plates, parts of steel sections, etc.) to chemical ones (various types of glue). The possibility of active strengthening of such girders with prestressed reinforcement is investigated in this paper. One possibility of applying external prestressing force is presented. Some strengthened-girder test results are presented and compared with results for similar girders but without strengthening.

Technological development, thanks to which high-performance materials were produced, allowed engineers to design elegant structures, which in the total load have smaller share of dead weight. All this gave an opportunity to bridge the large spans. Technological development is accompanied by the development of powerful computer software that is able to, in the phase of construction modelling, include many parameters. Thanks to that, designers have a better insight into how elements behave under load, and they are able to choose how to use material and exploit their good characteristics. Composite structures, formed by coupling of steel and concrete, rank among the modern structures. Their advantage lies in the fact that the steel part of the cross-section takes part in tensile stresses transfer, while the concrete part, because of its massiveness, takes part in compressive stress transfer. Redistribution of stresses in one composite cross-section depends on many factors. In this paper, using finite element method, the influence of number coupling points on the deformation of simply supported beam, with a composite cross-section was analyzed. The span of the beam is 5m

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UVODSavremene građevinske konstrukcije najčešće se izvode od čelika, armiranog betona, drveta ili cigli (zidane konstrukcije). Koji materijal će biti korišćen za neku konstrukciju, zavisi od više parametara, a može biti određen i naklonošću projektanta. Čelik, kao građevinski materijal koji se intenzivno koristi u graditeljstvu, raspolaže izuzetnim karakteristikama koje su omogućile premošćavanje velikih raspona, projektovanja konstrukcija koje odgovaraju na kompleksne estetske zahteve, adaptilnost, funkcionalnost, itd. Ono što predstavlja problem, kad su čelične konstrukcije u pitanju, je to što pri visokim temperaturama gube nosivost i što, kada su izloženi istovremenom dejstvu vode i vazduha, koroziraju. Korozija je negativna pojava iz prostog razloga što deo koji je zahvaćen korozivnim procesom umanjuje efektivni deo poprečnog preseka, što za posledicu ima smanjenje nosivosti jednog dela, ili cele konstrukcije. Budući da je korozija jedan proces koji traje, cilj u ovom rada je da se odredi koliko će neki noseći elementi konstrukcije, koji su izloženi tom dejstvu, biti u stanju da nose opterećenje koje im pripada, a da stabilnost konstrukcije ne bude ugrožena.

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