Einsatz von hochfesten Stählen und Betonen bei Hohlprofil‐Verbundstützen

Composite columns made of high‐strength steel and high‐strength concrete. The paper deals with the use of composite columns made of high‐strength steel and high‐strength concrete. Based on the design methods in Eurocode 4‐1‐1 and DIN 18800‐5 a simplified design method is presented for composite columns with high strength concrete and high strength steel in combination with massive inner steel core‐profiles. The ultimate strength of these special type of columns is significantly influenced by the residual stresses in the core profiles resulting from the cooling process during fabrication. Based on Finite Element studies new models are presented for the determination of the distribution of residual stress taking into account the steel grade, the dimensions of the core profiles and the cooling conditions during fabrication.     

Zur Geschichte der Biegesteifigkeit bei Verbundstützen

On the history of bending stiffness of composite columns. The simplified design method for composite columns has been modified in the sequence of the historical changes in the design codes. This can be recognized by the bending stiffness of the column. The modifications were necessary due to a change in the safety concept, due to a harmonization in the definition of strengths and due to a change in the consideration of the influence of imperfections. The development steps are described and compared by a design example.     

Bewertung nichtlinearer Nachweiskonzepte für Verbundstützen anhand des Kriteriums der Versagenswahrscheinlichkeit

Evaluation of non‐linear structural analysis for composite columns based on criterion of probability of failure. Four methods to proof the ultimate limit state of composite columns are presented. Non‐linear structural analysis is used and the main focus is laid upon the structural reliability. The criterion for the structural reliability is the probability of failure P_f. The results of all four methods are compared relatively to each other and to the reliability index β=4.7 given in EC 1 and DIN 1055‐100. At the end a discussion of the characteristic features of all four methods including their advantages and disadvantages is given.     

Verbund‐Opferzellen zum Schutz von Stützen bei Nahdetonation

Lasttragende Bauteile wie Erdgeschossstützen von Hochhäusern oder Brückenpfeiler, ausgeführt als Verbundkonstruktion, gewährleisten vermehrten Schutz bei Nahdetonation. Opferzellen, die um den Stützenquerschnitt konstruiert sind, schaffen zusätzliche Sicherheit. Sie bewirken, dass die Anströmfläche der Stütze erst bei relativ hohen reflektierten Drücken einreißt – meist an der Geländeoberkante. Untersucht wird, welcher Opferzellenquerschnitt durch Druckverteilung und Energieabsorption einen effektiven Schutz der abgeschirmten lasttragenden Stütze bietet. Außerdem wird der Frage nachgegangen, inwieweit der schichtweise alternierende Aufbau von verformbarem Material geringerer Dichte und von massigem Material hoher Steifigkeit im Opferzellenquerschnitt durch Impedanzfehlanpassung die lasttragende Stütze schützt. Impedanzfehlanpassung führt zu einer verstärkten Reflexion der Schockwellen und dadurch zu einer Reduzierung ihrer Transmission. Eine Schockwellenreflektion innerhalb des Opferzellenquerschnitts wirkt sich folglich günstig auf die zu schützende Konstruktion aus. Die Ergebnisse veranschaulichen das Schutzpotential und die Wirksamkeit von Opferzellen im Vergleich zu anderen Schutzmaßnahmen wie der Verwendung nachgiebiger Auflagerbedingungen und der Variation des Stützenquerschnitts. Die in Vergleichsberechnungen gewonnenen Erkenntnisse werden in einem Bemessungsdiagramm zusammengefasst. Die Resttragfähigkeit der Stütze wird als Indikator für die Effektivität der untersuchten Schutztechnologien vorgestellt. Multi‐layer composite sacrificial cells to protect columns against close‐standoff blast. Composite cross sections have been shown to be generally well suited for constructing explosion‐resistant load‐bearing structural members, such as columns or bridge piers, with high protection demands. Composite sacrificial cells which are built around the member's cross section enhance the protection of columns and piers exposed to high dynamic loading. Due to energy absorption outside the load‐carrying cross section the reflected pressure and induced shock wave are significantly reduced. It is investigated whether the layer sequence of two distinct materials (a less dense, more deformable material versus one that is denser and stiffer) is measurably different for protection of other material layers including the structural member's inner core. We also study whether shock wave reflection and reduced transmission of shock waves, achieved with specific material layering in sacrificial cells, practically result in significant protection of the underlying structure. We also compare the protection potential of sacrificial cells with the effectiveness of other protective measures such as the variation of boundary condition and the cross section design. The paper finalizes with an elaborate design diagram which summarizes the residual axial capacity of columns after the blast event and the extent of damage when using sacrificial cells.     

Nachweis des konstruktiven Brandschutzes bei Stahlbetonstützen

Design of the Structural Fire Protection of Reinforced Concrete Columns It is necessary to explain the background of the structural fire design of reinforced concrete columns with a modified new firedesign‐table in the German standard DIN 4102. The limit condition of this table with a maximum 6 m length for rectangular columns and 5 m length for circular columns results often in very conservative reinforcements and dimensions of columns with smaller length. For these cases is proposed an extension of the firedesign‐ table. An example completes the paper.