Limitation of cracking in AAC masonry under the window zone

The article describes the results of tests on the impact of reinforcement on the appearance of cracks and on the manner of damage to masonry under the window zone. Masonry made of Autoclaved Aerated Concrete units with thin layer mortar was tested. Eight unreinforced test specimens (two series) and four series of test specimens (12 specimens) with reinforcement in the bed joints were subject to testing. Two types of reinforcement were used in the tests. It is demonstrated that the reinforcement has a significant impact on the level of cracking stress and propagation of cracks. It was found that when a pillar is correctly designed, cracks should not occur in the masonry under the window zone.     

Untersuchungen zu Herstellungs‐ und Instandhaltungs kosten von unterschiedlichen Konzepten zur Sicherstellung der Dauerhaftigkeit von Parkbauten

Research of production and maintenance costs for alternative concepts to ensure the durability of parking buildings There is currently an intense discussion about how to ensure the durability of parking buildings. Without having carried out a comprehensive cost analysis for the alternatives for durability concepts costs are nevertheless used as an argument for or against a certain execution. In this publication the costs of various execution concepts are compared on the basis of a virtual two‐storey underground garage with standard dimensions for the two major components of ”suspended ceiling“ and ”baseplate“. For instance the cost analysis includes the production costs for the minimum reinforcement in dependence of the examined surface protection or of the waterproofing system respectively. Furthermore the costs for maintenance, inspection and repair among other aspects are compared in dependence of the surface protecting system for a service life of 50 years. This cost approach takes into account consists of market fluctuations as well as scheduled maintenance cycles by considering medium, minimum and maximum costs. For the suspended ceiling the following coating or waterproofing systems respectively are examined: surface protection system ”OS 11“; ”mastic asphalt (single/double layer) with asphalt sheeting ”; ”mastic asphalt (single/double layer) with surface protection systems OS 10“ and ”PMMA“ protecting surface system. For the base plate two load cases are investigated: ”water exchange zone“ (WW) and ”water pressure“ (WD) in combination with the following surface protection systems: ”OS 11“, ”mastic asphalt (single/double layer) with asphalt sheeting“ and ”OS 8 with accompanying crack treatment“. For the ongoing maintenance costs, engineering values are chosen in accordance to the current state of knowledge. It is expected that current research projects are going to provide scientific results in the near future allowing an update of this cost analysis.     

Begrenzung der Rissbreite nach Eurocode 2

Crack width control according to Eurocode 2 – Explanatory notes on factor k _c Reinforced concrete members are designed now according to EC2 [1]. A significant aspect is the determining of the minimum reinforcement area specified in section 7.3.2. Due to the shortened illustrations of the equations (7.1) and (7.2), the mechanical background is difficult to be highlighted. This often results in inaccurate use of the model parameters, which might lead to an unsafe design, particularly for members predominantly reinforced only by the minimum reinforcement. Therefore the mechanical background of the equations (7.1) and (7.2) is focused on in this contribution. Proper discussions and explanations might help the structural engineer in the practical design.     

Erweiterungen des Fließstreifenmodells hinsichtlich verschiedener Einflussfaktoren auf das Ermüdungsrisswachstum

Das Fließstreifenmodell ist ein verbreitetes Hilfsmittel zur Berechnung der zyklischen Rissspitzenöffnungsverschiebung und des Ermüdungsrisswachstums von Strukturen unter isothermer zyklischer Belastung. Im Zuge einer Modellerweiterung kommt das rheologische Masing‐Modell zum Einsatz, das aus parallel geschalteten Reihenschaltungen von Feder und Reibelement besteht. Indem den Reibelementen unterschiedliche Fließspannungen zugeordnet werden, kann mit dem Masing‐Modell die zyklische Spannungs‐Dehnungs‐Kurve des Werkstoffs beschrieben werden. Anstelle einer konstanten Fließspannung werden diese verschiedenen Fließspannungen zufällig den einzelnen Elementen, in die die Riss‐Ligament‐Linie im Fließstreifenmodell unterteilt ist, zugewiesen. Neben einer besseren Modellierung des mechanischen Materialverhaltens ist auf diese Weise die Berücksichtigung mikrostruktureller Aspekte des Ermüdungsrisswachstums möglich, wenn auf die Werte der Fließspannungen im Bereich des frühen mikrostrukturellen Risswachstums Einfluss genommen wird. Zur Untersuchung thermomechanischer Ermüdung werden die Fließspannungen in Abhängigkeit von der Temperatur formuliert.