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- 2014 (11) (entfernen)
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- Beitrag zu einem Tagungsband (4)
- Vortrag (4)
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Schlagworte
- Earthen materials (3)
- Anchor pins (2)
- Compression test (2)
- Diagonal compression test (2)
- Earth block masonry (2)
- Pull-out tests (2)
- Diagonal-compression (1)
- FEM modelling (1)
- Initial shear strength (1)
- Lime based hydraulic gout (1)
Eingeladener Vortrag
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Earth represents one of the oldest construction materials, which is still utilised both in developed and in developing countries. In this paper a comparison of the mechanical performance of structural elements built in three basic techniques, earth block (adobe) masonry, rammed earth and cob, is presented. In order to gain better knowledge on the structural behaviour under static loads an extensive compression and diagonal compression (shear) test campaign was performed. First compression results showed brittle mechanical behaviour in the case of earth block masonry and rammed earth elements, whereas cob exhibited a very different stress–strain pattern: cob can deform beyond the elastic range with a gradual drop in capacity. Despite its low compressive strength, cob thus presents a relatively good performance within the earthen material range as far as shear behaviour is concerned.
The data here reported represents a base for a further investigation on the dynamic behaviour of the three materials considered. The study was carried out within the framework of the project NIKER funded by the European Commission dealing with improving immovable Cultural Heritage assets against the risk of earthquakes.
Connections improvement plays a key role in seismic upgrade of historical buildings. Their global response is related to the behavior of the single structural elements as well as to their mutual connections. Up to now only few data are available about the performance of grouted anchor pins in earthen materials where the critical point is the bond between the grout and the earthen substrate. In this paper, results of the experimental testing performed on earth block masonry, rammed earth and cob are presented. Pull-out tests were carried out to investigate the bond strength and failure modes of stainless steel rods with a lime based hydraulic grout and their compatibility with earthen materials. Rods with nuts were investigated to improve the pull-out capacity of the anchors. They showed higher pull-out capacity than rods without nuts. The performances of rods with nuts in cob were influenced by the rough surface at/of the earthen substrate. It is assumed that the non homogeneous surface caused an interlocking mechanism, which allowed to reach a pull-out capacity of about 54% higher than in earth block masonry.
The intensive use of earth as a building material since ancient times resulted in an important and significant earthen built heritage currently existing worldwide spread. The rammed earth technique has a significant presence in this heritage, where it served to build from simple dwell-ings to fortresses. However, the high vulnerability of rammed earth constructions to decay agents and to seismic events puts in risk their further existence and the lives of millions of peo-ple. With respect to the seismic behaviour of rammed earth walls, the understanding and mod-elling of their shear behaviour are topics underdeveloped in the bibliography. Nevertheless, these topics are of extreme importance in the preservation and strengthening of rammed earth constructions. Therefore, this paper presents a numerical work aiming at modelling the non-linear behaviour of unstabilised rammed earth under shear loading, resorting to the finite ele-ments method (FEM). The models were used to simulate the behaviour of a set of rammed earth wallets tested under diagonal compression. Both macro- and micro-modelling approach-es were considered, where the objective of this last approach was to evaluate the influence of apparent weakness of the interfaces between layers on the shear behaviour. The total strain ro-tating crack model (TSCRM) was used to simulate the behaviour of the rammed earth material, while the Mohr-Coulomb failure criterion was used to simulate the behaviour of interfaces be-tween layers. Furthermore, uncertainties related to the definition of the input parameters re-quired performing a sensitivity analysis. The numerical models achieved good agreement with the experimental results and the compressive strength, the Poisson’s ratio, the tensile strength and the tensile fracture energy revealed to be the most important parameters in the analyses.
Connections improvement plays a key role in seismic upgrade of historical buildings. Their global response is related to the behaviour of the single structural elements as well as by their mutual connections. Up to now limited data is available on the performance of grouted anchor pins in earthen materials where the critical point is the bond between the grout and the earthen substrate.
In this paper results of the experimental testing performed on earth block masonry are presented. Pull-out tests were carried out to investigate the bond strength and failure modes of stainless steel as well as glass fiber reinforced polymer (GFRP) rods with a lime based hydraulic grout and their compatibility with earth block masonry. GFRP rods were investigated as an alternative bonded-in anchorage material to the commonly used steel. In comparison with steel, they have a reduced weight and a reduced coefficient of thermal expansion. Their lower modulus of elasticity seems to be more compatible with the modulus of elasticity of earthen materials, although they exhibit a brittle fracture with lack of plastic phase.