Vibrations of composite steel-concrete floors induced by human activities

The latest demands in construction design towards slender structures with large spans, large open interiors, unconventional shapes and constructional solutions are leading to the extensive problems related to the serviceability limit state. Slender structures with large spans have lower natural frequencies and lower natural damping, considerably influencing the dynamic response of the structure. Annoying vibrations induced by human activities can significantly affect the structure's functionality, comfort of people and quality of life. Design recommendations for composite steel-concrete floor vibrations can be found in different standards. This paper presents a short overview of design procedures for vibrations of composite steel-concrete beams and design recommendations of floor vibrations induced by human activities, through two design criteria.Najnovije tendencije u građevinarstvu u pogledu projektovanja vitkih konstrukcija s velikim rasponima, velikim otvorenim unutrašnjim prostorima, nekonvencionalnim oblicima i konstrukcijskim rešenjima, često uzrokuju izražene probleme u pogledu graničnih stanja upotrebljivosti. Vitke konstrukcije velikih raspona - s niskim sopstvenim frekvencijama oscilovanja i sopstvenim koeficijentom prigušenja - značajno utiču na dinamički odgovor konstrukcije. Izražene vibracije međuspratnih konstrukcija, izazvane ljudskim aktivnostima, mogu veoma da utiču na funkcionalnost objekta, komfor ljudi i kvalitet života unutar objekta. Preporuke za projektovanje spregnutih konstrukcija, s ciljem zadovoljenja kriterijuma vibracija, mogu se naći u različitim standardima. U ovom radu dat je kratak prikaz proračuna spregnutih nosača na dejstvo vibracija, kao i preporuke za proračun vibracija izazvanih ljudskim aktivnostima, putem prikaza dva proračunska kriterijuma

Experimental investigation of preload losses in high strength bolts under cyclic loading

Slip-resistant shear connections with preloaded bolts have traditionally been used in steel structures exposed to cyclic. Hence, shear load is transferred through friction surfaces rather than through contact between the bolt surface and the hole. The main influencing parameters determining slip resistance of the connection are the friction between contact surfaces and the bolt preload level. This paper presents an experimental study of preloaded bolted connections under cyclic load, the main objective being to investigate the influence of cyclic load on the losses of preload force in high strength bolts and lock bolts