Numerical simulation of soil-structure interaction experiments on shallow founded structures for different mass configurations

Soil-Structure Interaction (SSI) phenomena and foundation rocking can modify the structural response signifi- cantly with respect to the response predicted adopting the fixed-base assumption. The importance of SSI and rocking depends, among other factors, on the structural mass and the distribution of static stresses at the soil-foundation interface. Within this context, an experimental campaign was carried out aiming to investigate the SSI effects on the response of a 3m x 3m x 5m steel- framed structure. The prototype structure, called EUROPROTEAS, was founded on a shallow footing at the well-characterised Euroseistest site, while its mass was either 18Mgr or 9Mgr. The present study simulates free vibration experiments, placing particular emphasis on soil nonlinearity and soil-foundation interface. A novel approach to simulate gaps at the soil-foundation interface, foundation rocking and to manipulate interface stresses under static conditions is presented. The three aspects are shown to significantly affect the response, while they are found to be more important for the lighter structure

Optimisation of impact pile driving using optical fibre Bragg grating measurements

This paper reports the use of optical Fibre Bragg Grating (FBG) sensors to monitor the stress waves generated below ground during pile driving, combined with measurements using conventional pile driving analyzer (PDA) sensors mounted at the pile head. Fourteen tubular steel piles with a diameter of 508 mm and embedded length to diameter ratios of 6 to 20 were impact driven at an established chalk test site in Kent, UK. The pile shafts were instrumented with multiple FBG strain gauges and pile head PDA sensors, which monitored the piles’ responses under each hammer blow. A high frequency (5kHz) fibre optic interrogator allowed a previously unseen resolution of the stress wave propagation along the pile. Estimates of the base soil resistances to driving and distributions of shaft shear resistances were found through signal matching that compared time series of pile head PDA measurements and FBG strains measured below ground surface. Numerical solutions of the onedimensional wave equation were optimised by taking account of the data from multiple FBG gauges, leading to significant advantages that have potential for widespread application in cases where high resolution strain measurements are made

Keynote Lecture – The Interplay of Multiple Hazards and Urban Development: The context of Istanbul

Tomorrow’s Cities is the UK Research and Innovation (UKRI) Global Challenges Research Fund (GCRF) Urban Disaster Risk Hub – an interdisciplinary research hub with the aim to catalyse a transition from crisis management to multi-hazard risk-informed and inclusive planning in four cities in low-and-middle income countries. Istanbul in Turkey is one of the four cities investigated. It is one of the largest urban agglomerations in Europe where more than 15 million people reside in more than 1 million buildings. Considering that the population was 4.75 million in 1980, Istanbul’s urban sprawl was inevitable. Due to an imbalance between the population growth and housing supply, Istanbul’s urbanization was shaped by illegal construction processes producing the gecekondus in almost every part of the city (Gencer and Mentese, 2016). Unplanned urban expansion was so rapid that the urban master plan of 1980, which set the limits and strategies for urban development, became completely invalid by 1989 (Tapan, 1998). This situation led to the development of a new urban master plan in 1994 that included geoscientific analysis, and which highlighted the possibility of losses due to an earthquake on the segments of the North Anatolian Fault in the Marmara Sea. Uncontrolled and unplanned development continued in Istanbul until 1999 when two major earthquakes hit the region causing at least 18.000 deaths and $16 billion economic loss. These events changed the authorities’ perspective to earthquake risk and its mitigation. As a result, the 1998 earthquake resistant design code (published one year before the 1999 earthquakes) was widely embraced and implemented. Furthermore, several urban transformation projects have taken place in the last 20 years for reducing disaster risk. These have had varied success, with research to date showing that areas selected for urban transformation were often chosen on the basis of land value rather than hazard risk, and that a pro-poor approach is missing. Despite these efforts, Istanbul’s earthquake risk remains high. Furthermore, recent urban development plans are seeing the city expand into undeveloped lands to the west, increasing exposure to new hazards, namely flash flooding and landslides. The combined impact of these hazards is not evenly distributed, and the associated risks are heightened by poor infrastructural resilience and social vulnerabilities. Therefore, it is crucial to integrate different types of hazards and risks into the urban development context for future scenarios, so that a physically and socio-economically safer development that prioritizes the wellbeing of local communities can be facilitated. This presentation summarises the research conducted in Istanbul over the first 18 months of the Tomorrow’s Cities Project by a consortium of Turkish and UK researchers. This research spans the better characterisation of earthquake and landslide hazards, development of analysis methods for predicting the response of case study buildings to multiple hazards and a Bayesian network based approach for assessing road infrastructure resilience under multiple hazard scenarios. Furthermore, plans for building a Resilient Urban Development Decision Support Environment (RUD-DSE) for communicating the relevance of this research on future urban planning is described

The ALPACA research project to improve design of piles driven in chalk

Chalk is present under large areas of NW Europe as a low - density, porous , weak carbonate rock. Large numbers of offshore wind turbines, bridge s and port facilities rely on piles driven in chalk. C urrent European practice assume s ultimate shaft resistances that appear low in comparison with the Chalk’s unconf ined compression strength and CPT cone resistance ranges and can impact very significantly on project economics. L ittle guidance is available on pile driveability, set - up or lateral resistance in chalk, or on how piles driven in chalk can sustain axial or lateral cyclic loading. This paper describes the ALPACA (Axial - Lateral Pile Analysis for Chalk Applying multi - scale field and laboratory testing) p roject funded by EPSRC and Industry that is develop ing new design guidance through comprehensive field testin g at a well - characterised low - to - medium density test site , supported by analysis of other te sts. Field experiments on 36 driven piles, sixteen of which employ high resolution fibre - optic strain gauges, is supported by advanced laboratory and in - situ testing, as well as theoretical analysis. The field work commenced in October 2017 and was largely complete in May 2019

Numerical simulation of SSI free and forced vibration experiments on real scale structures of different stiffness

Time domain finite element (FE) analysis is a powerful tool for the study of Soil-Structure-Interaction (SSI) phenomena, but it requires a rigorous calibration of all aspects of the numerical model. This study presents three-dimensional (3D) FE analyses that are calibrated and validated against real scale free and forced vibration experiments on the prototype structure of EUROPROTEAS which is founded on soft alluvial sediments. The proposed calibration procedure exploits data recorded during experiments on structures with different structural stiffness, that mobilised SSI effects at different intensities. Particular focus is placed on the modelling of the soil-foundation interface, where zero thickness elastoplastic interface elements are used to allow foundation separation from the soil. A novel approach to simulate contact imperfections (gaps) between the foundation and the adjacent soil is proposed. The results demonstrate the significant impact of the interface gaps and soil nonlinearity on the response of the examined SSI systems, highlighting the importance of a rigorous model calibration