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Universal high‐performance columns made of high‐strength steels without welding In recent years, steel‐concrete composite columns made of normal‐strength steels are seldom used owing to the economic and technological advantages of precast reinforced concrete columns. Though, the use of high‐strength structural steels bears high potential for the efficient production of composite columns with excellent structural performance that are economically competitive to precast concrete columns, there are currently major obstacles to use of the ultra‐high‐strength steels (UHSS) in Germany. Hollow section composite columns with embedded high strength steel core without welded connections provide an opportunity to regain lost market share. A research project, funded by the AiF (Arbeitsgemeinschaft industrieller Forschungsvereinigungen), is intended to explore the potential of UHSS composite columns by experimental and theoretical investigations. The present paper demonstrates the concept of such composite columns with UHSS and gives first exciting insights into the research results. In addition to column tests under ambient and fire conditions, small scale tests are necessary to investigate various influencing factors and to create the basis for new and easy to use design and construction principles that allow efficient application. [ABSTRACT FROM AUTHOR]

Experimental investigations on novel composite columns with a concrete filled hollow section and high‐strength steel plates as core in ambient and fire conditions High‐performance composite columns are commonly carried out with solid steel sections as core profiles. These profiles imply limitations due to reductions of the yield strength depending on the thickness and high residual stresses. In this publication, the authors present a novel section consisting of a concrete filled circular hollow section with locally connected steel plates as core. To increase the load bearing capacity, steels with yields strengths up to 960 N/mm2 are used. Experimental investigations for ambient conditions and in case of fire are presented. The columns showed a promising load bearing behaviour. These investigations will serve as basis for a systematic development of this innovative, high‐performance composite column with a corresponding design concept. [ABSTRACT FROM AUTHOR]

Bar bundle columns with high‐strength reinforcing steel As part of the AiF project "Bar bundle columns with high‐strength reinforcement steel" the load‐bearing behavior of bar bundle columns in cold and fire conditions was investigated. Bar bundle columns are a new type of composite columns. To this purpose, a bundle of high‐strength reinforcing bars with a yield strength of 670 MPa is placed in a steel tube and then grouted with mortar. The bundle can consist of 1, 3, 7 or 19 bars. To analyze the load‐bearing behavior, relevant material parameters were determined in cold and in fire conditions. Subsequently, large‐scale buckling tests were carried out under room temperature and in fire case. Considering the obtained results, an FE model was created and calibrated. On this basis, a design concept was developed. [ABSTRACT FROM AUTHOR]