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Structural performances of earthen building materials. A comparison between different typologies
(2011)
Traditional construction techniques utilizing earthen materials are often seen as inferior compared to modern ways of building. Structural earthen elements are perceived as vulnerable towards environmental influences (moisture, frost) and in particular towards the load scenarios during earthquakes. In comparison to the recent advances in research on stone and brick masonry, knowledge on the structural performance of earthen building construction is limited and scattered. Consequently the confidence in the performance of these earthen buildings constructed in the traditional techniques during earthquakes is fairly low. The research presented here aims to make a comparison of mechanical behavior between different earth masonry material typologies, consisting of earth block masonry, rammed earth and cob. The paper has been developed in the framework of a larger research program called NIKER. BAM and other seventeen research partners from the Mediterrean area are jointly involved to develop and validate innovative materials and technologies for the systemic improvement of the seismic behavior of Cultural Heritage assets
The paper has been developed in the framework of a larger EC‐research program called NIKER, in which BAM and other seventeen research partners from the Mediterrean area are jointly involved. It aims to develop and validate innovative materials and technologies for the systemic improvement of the seismic behavior of Cultural Heritage assets. The death tolls brought about by recent catastrophes in
developing countries where many inhabitants lived in earthen dwellings (Gujarat, India 2001, Bam, Iran 2003 and Concepción, Chile 2010 Earthquakes, Tamil Nadu 2004 Tsunami) have brought about research studies aimed at improving earth construction in terms of strength, seismic resistance and speed of construction.
In comparison to the recent advances in research on stone and brick masonry, knowledge on the material properties and failure mechanisms of earthen Building construction is limited and scattered.
The research presented here by aims making a comparison of mechanical behaviour between different earth masonry material typologies, consisting of earth block masonry, rammed earth and cob.
Both in developed and developing countries, modern building materials tend to be preferred to traditional earthen construction. Reasons include low durability, inadequate performance under seismic loading and, in developing countries, a wish to replace what is perceived as 'poor' with what is perceived as 'rich'. In an age when building permissions and construction standards are a must, particularly in seismic areas, even when an owner is willing to build in earth, construction approval needs to be granted: we rely on values and standards to build, but the necessary data on material properties and structural performance of earthen building techniques is scarce if compared to the abundance of data for other materials (clay brick masonry, concrete, steel) available to the engineer. At the same time, traditional builders' skills, knowledge and confidence in earthen building techniques are decreasing if not disappearing. A wallette testing campaign was thus carried out with the aim of filling this knowledge gap. Prior to the wallette campaign, material properties, including composition and physical-mechanical parameters, were determined. Compression and diagonal compression (shear) tests were then performed, and a basic analysis of the mechanical behaviour of structural elements built in cob is provided in relation to earth block (adobe) masonry and rammed earth elements. Cob, shown to have low compressive resistance, has a relatively ductile post-peak behaviour if compared to earth block masonry specimens which, as expected, show a marked brittle behaviour. In terms of shear strength, cob performs relatively well in view of its low compressive strength. The study is part of our work within the framework of the ongoing project NIKER funded by the European Commission dealing with improving the structural performance of Cultural Heritage assets in order to limit earthquake hazards.
DIN 50100 definiert die Bedingungen für den Schwingfestigkeitsversuch, der zur Ermittlung von Kennwerten dient, die das Verhalten metallischer Werkstoffe und Bauteile bei zyklischer Beanspruchung mit einer konstanten Lastamplitude beschreiben (Wöhlerversuch). Die Norm umfasst die Versuchsdurchführung, die Versuchsauswertung sowie die Dokumentation von lastgeregelten Wöhlerversuchen im Zeit- und Langzeitfestigkeitsbereich. Mit DIN 50100 soll erreicht werden, dass die Wöhlerlinien verschiedener Prüfstellen miteinander vergleichbar und die wesentlichen Randbedingungen der Versuchsdurchführung dokumentiert werden. Da die Ergebnisse von Schwingfestigkeitsversuchen streuen, ist die Treffsicherheit für die Schätzung der Kennwerte von der Anzahl der Versuche einer Versuchsreihe abhängig. In Abhängigkeit von einer geforderten Treffsicherheit wird durch die DIN 50100 der erforderliche Stichprobenumfang vorgegeben.
Bioresorbable carriers for subchondral anchoring of tissue-engineered cartilage in articular defects
(2000)
When pushed to the limits of their detection capability, NDE systems do not produce consistent hit/miss
indications. Their capability of detecting small defects is therefore expressed in terms of POD. An adequate
NDE system is required to ensure the structural integrity. In conventional signal response analysis, the POD is
expressed as a function of the defect size, and its adequacy for the inspection task is tested against the maximum
allowable defect size which will not undermine the structural integrity. Analyses of modern structures show that
other parameters, beside the defect size, can both significantly influence the POD and determine the severity of
the defect for the structure. Within the multi-parameter reliability analysis, the POD is expressed as a function of
those influencing parameters. When determining the adequacy of the NDE system, the capability of detecting a
defect has to be expressed and tested against the critical value of exactly that parameter that determines defects
severity for the structure. Failing to do so can lead to a rejection of the healthy, or acceptance of the bad part.
The principle is demonstrated on the example of the Transmit-Receive Longitudinal (TRL) ultrasonic inspection
of the iron cast component for semi-elliptical surface defects.