Centrifuge modelling of the response of buildings to tunnelling

The response of surface structures to tunnelling induced ground movements is an area of great importance for any urban tunnelling project. Testing described in this paper aims to investigate soil structure interaction effects by observing the response of aluminium beams of varying stiffness to tunnelling, using the 8 m diameter beam centrifuge at Cambridge University. Soil and structure displacements are extensively monitored through a photo imaging technique which enables a detailed analysis of the interaction behaviour. Results to date indicate that the relative structure-soil stiffness is the governing factor in determining how a structure will respond to tunnelling. This parameter is highly dependent on both the structure and soil stiffness. It is also shown that contrary to common assumptions in the literature, negligible axial strains are transferred into the structure. This paper outlines the results of the research to date. © 2010 Taylor & Francis Group, London.

Modelling and Fragility Analysis of Non-Ductile Reinforced Concrete Buildings in Low-to-Moderate Seismic Zones

Reinforced concrete buildings in low-to-moderate seismic zones are often designed only for gravity loads in accordance with the non-seismic detailing provisions. Deficient detailing of columns and beam-column joints can lead to unpredictable brittle failures even under moderate earthquakes. Therefore, a reliable estimate of structural response is required for the seismic evaluation of these structures. For this purpose, analytical models for both interior and exterior slab-beam-column subassemblages and for a 1/3 scale model frame were implemented into the nonlinear finite element platform OpenSees. Comparison between the analytical results and experimental data available in the literature is carried out using nonlinear pushover analyses and nonlinear time history analysis for the subassemblages and the model frame, respectively. Furthermore, the seismic fragility assessment of reinforced concrete buildings is performed on a set of non-ductile frames using nonlinear time history analyses. The fragility curves, which are developed for various damage states for the maximum interstory drift ratio are characterized in terms of peak ground acceleration and spectral acceleration using a suite of ground motions representative of the seismic hazard in the region.

Important aspects when modelling the interaction between surface structures and tunnelling in sand

Tunnelling in urban areas continues to increase and has highlighted the need for a better understanding of the impact of tunnel excavations on existing buildings. This paper considers the influence of surface structures on ground displacements caused by tunnelling in sand through finite element modelling and centrifuge testing. First, the importance of modelling assumptions is evaluated by comparing centrifuge modelling results to finite element modelling results for various soil constitutive models: both a Young's modulus that linearly increases with depth and a power law relation between the soil stiffness and stresses are considered. Second, the most effective soil constitutive model was used to perform a sensitivity study on the effect of different factors governing the structural response. In particular, the effect of the building stiffness and weight on the modification of soil displacements is investigated by introducing a simple surface structure. The use of a no-tension interface between the building and the soil was found to be essential to investigate the effect of weight on gap formation between the soil and the structure, as observed during the experimental tests. Results show the importance of considering the relation between the building weight and the relative stiffness between the building and the soil when assessing the structural response. © 2014 Korean Geotechnical Society.