Abstract

Earthen architecture is one of the most relevant building technologies among heritage structures. However, mechanical properties are commonly obtained from destructive tests. To contribute at changing this trend, two non-destructive mechanical techniques (ultrasound and modal analysis) are studied to determine their ability at characterizing earthen materials and their possible correlation. To achieve these purposes, twenty cubic-shaped earthen specimens were produced for testing the capability of ultrasound transmission method to control moisture content and its evolution during drying process at different environments. Additionally, a real-scale rammed earth wall was built to assess the feasibility of using ultrasound technique to determine elastic dynamic Young modulus. This analysis was validated by indirect comparison with experimental modal analysis test results. The most important findings are that the relationship between moisture content and ultrasound transmission speed is linear. This information is useful to control the drying process of earthen materials and to control the moisture content distribution on larger in-service structures. Finally, numerical simulation using ultrasound transmission data as input information allow to predict the vibrational response of the tested wall with an error around 3%.

Abstract

The effects of the 2015 Gorkha earthquake in Nepal revealed deficiencies in the most recent vernacular architecture, which no longer uses wooden reinforcements due to national anti-deforestation laws. It also highlighted the shortcomings found in reinforced concrete architecture, which is generally scanty and poorly reinforced due to the high import cost of construction steel. The geography of Nepal has led to the development of a wide variety of vernacular architecture using local materials such as stone, brick or earth in the form of rammed earth and adobe walls [1]. Moreover, although its tradition in the construction of vaults is not as prominent as in neighbouring regions of India, Nepal has developed its own tradition in the construction of vaults and domes, which are generally self-supporting and made of brick or adobe with lime mortar. The design of a prototype of seismic house in Nepal aims to use a modular housing unit with rammed earth walls and/or walls made of materials recycled from previous earthquakes, as well as tile vaults with bamboo sleepers, and possibly vegetable fibre grids. These avoid the use of imported materials, favouring km0 and sustainable materials while following local tradition. Several potential housing units have undergone linear seismic analysis on finite element models, with variations in planimetric layout and the types of tile vault, from the simpler barrel vault to the sail vault. Both are analysed searching for the best shape in terms of seismic efficiency, evaluating stress and strain state. The results obtained from this preliminary study clearly show that, under seismic actions, the response from the construction system using depressed sail vaults and rammed earth walls with bamboo reinforcements is more efficient and homogeneous in terms of tension and deformation. This is due to the geometric symmetry which determines the same response in several directions, unlike vaults with a characteristically strong directionality (barrel vault). The seismic response of the prototype described is examined by assessing the influence in terms of thrust and deformation of bamboo reinforcements inside the walls. For this, laboratory tests are used to identify the mechanical characteristics of bamboo to be employed in the finite element modelling and calculation, as the values found in the literature vary depending on the physical and chemical characteristics of the material. This study therefore proposes a more sustainable architectural model with greater antiseismic resistance, always in keeping with local constructive tradition.