Martin Empelmann

Design Compressive Strength Values of Concrete Under Sustained Loads

Experimental investigations on the material behaviour of concrete show, that the concrete compressive strength under sustained loads is lower than the short-term compressive strength. The effects of sustained loads are considered in EN 1992-1-1 (EC2) by the factor α cc for the design values of concrete compressive strength.

Concrete Columns with High Reinforcement Ratios

According to Model Code 2010 (2011) and EN 1992-1-1 (2011) the longitudinal reinforcement ratio of reinforced concrete columns should not exceed a value of 8%. Several national annexes to EN 1992-1-1 (2011) allow the use of higher longitudinal reinforcement ratios up to 12%. Concrete columns with reinforcement ratios larger than 8% offer new opportunities. On the one hand they permit higher load-bearing capacities with constant cross-sectional areas, on the other hand they allow smaller cross-sectional areas with constant load-bearing capacities. Examples from practice and research prove that detailing and casting of such highly reinforced concrete columns can be contrived. In order to review present limitations and to enhance the existing construction methods, experiments on highly reinforced concrete columns with bundled bars and large diameter bars are currently carried out at the iBMB, Division of Concrete Construction of the TU Braunschweig. This paper reflects the current state of research and covers the results of six column tests with longitudinal reinforcement ratios up to 25.6%. Test specimens and test setup are going to be presented, as well as the backgrounds that led to their determination. Furthermore the most important test results, such as load-deformation and post-fracture behaviour, are going to be illustrated and discussed.

Brücken im Bestand - Herausforderungen und Lösungsansätze

Nachrechnungen bestehender Bruckenbauwerke auf Basis des aktuellen Normenstands zeigen in vielen Fallen, dass die rechnerischen Querkrafttragwiderstande entscheidend fur die Belastbarkeit des Tragwerks sind. Zur Ermittlung der wahren Tragreserven sind die normativ vorgegebenen Ansatze zur Bestimmung der Querkrafttragfahigkeit jedoch nur bedingt geeignet, da verschiedene bruckenbauspezifische Randbedingungen, insbesondere bei vorgespannten Brucken, nicht erfasst werden. In objektspezifischen Untersuchungen ist die Bestimmung der Querkrafttragwiderstande mit erweiterten Ansatzen moglich. Im vorliegenden Beitrag werden hierzu verschiedene rechnerische Ansatze vorgestellt und Unterschiede anhand eines typischen Beispiels aufgezeigt.