Geographically distributed hybrid testing & collaboration between geotechnical centrifuge and structures laboratories

© 2018, Institute of Engineering Mechanics (IEM). All rights reserved. Distributed Hybrid Testing (DHT) is an experimental technique designed to capitalise on advances in modern networking infrastructure to overcome traditional laboratory capacity limitations. By coupling the heterogeneous test apparatus and computational resources of geographically distributed laboratories, DHT provides the means to take on complex, multi-disciplinary challenges with new forms of communication and collaboration. To introduce the opportunity and practicability afforded by DHT, here an exemplar multi-site test is addressed in which a dedicated fibre network and suite of custom software is used to connect the geotechnical centrifuge at the University of Cambridge with a variety of structural dynamics loading apparatus at the University of Oxford and the University of Bristol. While centrifuge time-scaling prevents real-time rates of loading in this test, such experiments may be used to gain valuable insights into physical phenomena, test procedure and accuracy. These and other related experiments have led to the development of the real-time DHT technique and the creation of a flexible framework that aims to facilitate future distributed tests within the UK and beyond. As a further example, a real-time DHT experiment between structural labs using this framework for testing across the Internet is also presented

MRCP compared to diagnostic ERCP for diagnosis when biliary obstruction is suspected: a systematic review

BACKGROUND: Magnetic resonance cholangiopancreatography (MRCP) is an alternative to diagnostic endoscopic retrograde cholangiopancreatography (ERCP) for investigating biliary obstruction. The use of MRCP, a non-invasive procedure, may prevent the use of unnecessary invasive procedures. The aim of the study was to compare the findings of MRCP with those of ERCP by the computation of accuracy statistics. METHODS: Thirteen electronic bibliographic databases, covering biomedical, science, health economics and grey literature were searched. A systematic review of studies comparing MRCP to diagnostic ERCP in patients with suspected biliary obstruction was conducted. Sensitivity, specificity, likelihood ratios, acceptability and adverse events were reported. RESULTS: 25 studies were identified reporting several conditions including choledocholithiasis (18 studies), malignancy (four studies), obstruction (three studies), stricture (two studies) and dilatation (five studies). Three of the 18 studies reporting choledocholithiasis were excluded from the analysis due to lack of data, or differences in study design. The sensitivity for the 15 studies of choledocholithiasis ranged from 0.50 to 1.00 while specificity ranged from 0.83 to 1.00. The positive likelihood ratio ranged: from 5.44–47.72 and the negative likelihood ratio for the 15 studies ranged from 0.00–0.51. Significant heterogeneity was found across the 15 studies so the sensitivities and specificities were summarised by a Receiver Operating Characteristic (ROC) curve. For malignancy, sensitivity ranged from 0.81 to 0.94 and specificity from 0.92 to 1.00. Positive likelihood ratios ranged from 10.12 to 43 and negative likelihood ratios ranged from 0.15 to 0.21, although these estimates were less reliable. CONCLUSION: MRCP is a comparable diagnostic investigation in comparison to ERCP for diagnosing biliary obstruction

Numerical modelling of real-time sub-structure testing

Current dynamic testing methods can prove unrealistic due to the scale at which test components are modelled, the rate at which they are loaded or the boundary conditions to which they are subjected. A new test method, termed "Real-Time Sub-Structure Testing" seeks to provide a more realistic testing environment for energy dissipative components. The method tests structural components at full or large scale and in real-time. The physical test interacts with a computer model of the structure surrounding the test component. In this way, the in-situ behaviour of the test component is evaluated in relation to the overall structural response. The testing method requires fast and realistic modelling of the surrounding structure and a rapid interaction with the physical test specimen. For these reasons, a new non-linear finite element method has been proposed in order to model the surrounding structure behaviour efficiently. The method uses the Central Difference Method time stepping integration scheme together with a newly devised basis. The proposed basis consists of the structure’s elastic modes and additional Ritz vectors, which are calculated from the inelastic static displacement shapes of the structure. The displacement shapes correspond to the same static spatial distribution of loading as the intended dynamic excitation, and are intended to characterise the inelastic behaviour of the structure. The method has been validated against a Newmark event to event algorithm as well as Drain2DX. The non-linear dynamic response of a propped cantilever beam and portal frame structure was investigated. The response evaluated by the algorithm agrees closely with both validation analyses. The new algorithm was also shown to be faster than the Newmark procedure in simple benchmark tests. In addition, a numerical model of the testing apparatus has been developed in order to simulate complete tests for the purposes of testing procedure development and validation. The model is developed using Matlab Simulink. Parameters for the model are deduced from published data, experimental component tests and open loop step response calibrations. The model behaviour was found to be very sensitive to the parameters used. However, after calibration against open loop tests the model reproduces the observed laboratory behaviour to a good degree of accuracy. In an attempt to predict the behaviour of an actual test, the laboratory model has been coupled with the new structural solution algorithm to simulate a virtual test. The simulated results compare well with experimentally observed data demonstrating the usefulness of the overall simulation as a test modelling tool

Upheaval buckling of offshore pipelines buried in loose and liquefiable soils

Pipelines used for the transportation of oil and gas products offshore are often buried beneath the seabed for protection from mechanical damage and for thermal insulation. During high temperature and high pressure operations, these pipelines are susceptible to resurfacing behaviour known as upheaval buckling, a structural response that is strongly influenced by the resistance of the surrounding soil. Despite much previous research on pipe uplift, the influence of the initial soil state – particularly in loose and liquefiable soil conditions – on the uplift resistance and corresponding buckling behaviour of the pipe is not well understood. This thesis presents research that examines the implications of these backfill conditions in the context of the global behaviour of the pipeline. The work consists of plane-strain monotonic uplift experiments focusing on density, rate, and stress level effects on the initial pipe-soil response. This is followed by numerical modelling of the global buckling behaviour using the experimental data as inputs. Finally, plane-strain cyclic experiments examine the possibility of progressive upward displacements over a number of cycles causing eventual upheaval buckling. A key finding from the uplift tests is that very loose backfill conditions may result in a localised flow-around failure mechanism, associated with lower peak resistance and a softer force-displacement response than with the sliding block mechanism that is typically assumed. This leads to lower peak buckling loads/temperatures than those predicted by current design guidelines. High quality data from both the monotonic and cyclic experiments was used to assess and suggest improvements to design guidance for these conditions.This thesis is not currently available in ORA

Seismic Performance Assessment of a Conventional Multi-storey Building

Abstract Recent earthquakes have revealed that conventional seismic design philosophy allows for large levels of nonstructural damage. Nonstructural earthquake damage results in extensive repair costs and lengthy functional disruptions, as nonstructural systems comprise the majority of building investment and are essential to building operations. A better understanding of the expected overall seismic performance of code-compliant buildings is needed. This study investigates the seismic performance of a conventional building. A 16-storey steel office building was designed using a modern seismic structural code (Eurocode 8). This study is the first to assess in detail the substantial earthquake repair costs expected in a modern Eurocode concentric braced frame structure, considering nonstructural systems with the FEMA P-58 procedure. The breakdown of total repair costs by engineering demand parameter and by fragility group is novel. The seismic performance assessment indicated that substantial earthquake repair costs are expected. Limitations of the Eurocode nonstructural damage methodology were revealed in a novel manner using FEMA P-58, as the prescribed drift limits did not minimize nonstructural repair costs. These findings demonstrate the need for design procedures that improve nonstructural seismic performance. The study results provide a benchmark on which to evaluate retrofit alternatives for existing buildings and design options for new structures

A comparison of viscous damper placement methods for improving seismic building design

This article compares the effectiveness of five viscous damper placement techniques, two standard and three advanced, for reducing seismic performance objectives, including peak interstory drifts, absolute accelerations, and residual drifts. The techniques are evaluated statistically for two steel moment-resisting frames under varying seismic hazard levels, employing linear viscous dampers and nonlinear time history analyses. Usability of the methods is also assessed. All the placement methods meet the desired drift limit but advanced techniques achieve additional improvement in drift reduction and distribution. Performance differences between the advanced techniques are minor, making usability a significant selection factor amongst the methods