Spalling of Concrete - Implications for Structural Performance in Fire

This preliminary paper is a progress report on an analytical investigation into the implications of explosive spalling on the fire performance of reinforced concrete structural elements and whole structures. This study does not attempt to predict whether spalling will occur. For accurate prediction of the occurrence of spalling a complete and fully coupled hygro-thermal-mechanical (HTM) analysis is required, as described by a comprehensive review of current research into the parameters and mechanisms that influence spalling, including a review of physical spalling criteria. This paper describes the structural performance of spalled concrete elements, using finite element analysis where spalling is modelled by removing layers of concrete when a set of spalling criteria are met. The method is presented using a case study of a simply supported reinforced concrete beam, where the analytical results indicate that spalling invariably triggers an early failure (well short of the required FRR rating) of a beam exposed to the standard fire

Influence of EBR on the structural resistance of RC slabs under quasi-static and blast loading: Experimental testing and numerical analysis

Flexural strengthening of reinforced concrete (RC) structures with externally bonded reinforcement (EBR) using carbon fibre-reinforced polymers (CFRP) has in recent years received increased interest from specialists, particularly when dealing with protective structures against terrorist or accidental blast loading. Although a significant number of studies have been conducted on the failure modes of the bonded interface for quasi -static conditions, there is still limited published research on the effects of blast loading. In this paper, RC slabs externally strengthened with CFRP are tested in three-point bending as well as subjected to blast loading. The behaviour of the tested specimens under both loading regimes is evaluated with special focus on the mechanisms that lead to the disruption of the CFRP. It was found that the debonding of the CFRP was caused, in both cases, by the fracture and separation of a thin layer of concrete in the near vicinity of the bonded interface. However, the mechanisms that lead to this failure differ. A numerical model was developed and simulations performed using the finite element (FE) code LS-DYNA to investigate the validity of commonly used simplifications on the modelling of the interface in both cases. It was found that although the modelling technique used to represent the disruption of CFRP under quasi-static conditions provide accurate results, it does not return accurate predictions of the debonding of CFRP under blast loading

Glutathione determination by the Tietze enzymatic recycling assay and its relationship to cellular radiation response.

Large fluctuations in glutathione content were observed on a daily basis using the Tietze enzyme recycling assay in a panel of six human cell lines of varying radiosensitivity. Glutathione content tended to increase to a maximum during exponential cell proliferation, and then decreased at different rates as the cells approached plateau phase. By reference to high-performance liquid chromatography and flow cytometry of the fluorescent bimane derivative we were able to verify that these changes were real. However, the Tietze assay was occasionally unable to detect glutathione in two of our cell lines (MGH-U1 and AT5BIVA), although the other methods indicated its presence. The existence of an inhibitory activity responsible for these anomalies was confirmed through spiking our samples with known amounts of glutathione. We were unable to detect a direct relationship between cellular glutathione concentration and aerobic radiosensitivity in our panel of cell lines

Dynamic Assessment of a FRP Suspension Footbridge

In the past decade, the vibration serviceability of slender footbridges has become the subject of serious investigation. Despite the advantages that FRP materials offer in bridge engineering such as higher strength-to-weight ratio and ease of installation, their use in the construction of slender footbridges has raised concerns with regard to their dynamic response, due to the reduced mass and stiffness of these materials compared with their conventional counterparts. In this paper, the dynamic assessment of a FRP suspension footbridge (the Wilcott footbridge) is described. This is performed using dynamic field testing supported by finite element (FE) modelling: the field testing on the bridge produced values for frequencies, mode shapes and damping which were consequently used to calibrate the FE model. Using the calibrated FE model it was shown that the influence of semistructural or non-structural elements, such as parapets, on the dynamic properties of the structure can be significant. The dynamic response of the structure due to human excitation was also measured during the test. The results confirmed that suspension footbridges built from FRP materials are susceptible to vibrations induced by pedestrians. The response levels of the investigated bridge are lower than the threshold levels specified in the relevant code of practice. © 2009, NetComposites Limited

Model test of the DTI-Floating wind concept

This study aims to de-risk the development of the Deep Turbine Installation-Floating (DTI-F) concept, a hybrid spar buoy-based floating offshore wind turbine with the novelty of being able to raise up and lower down the tower plus nacelle set. The paper presents the design and construction of a Froude-scaled model based on the DTI-F concept, the experimental testing configurations and conditions, and the instrumentation used to measure motions and loads. The test campaign included free decay and stiffness decay tests, along with regular and irregular wave testing. In addition to the hydrodynamic characterisation, the resonance properties of the system with different mooring configurations, i.e. three and four lines, and three lines with a delta connection, were investigated. We present the Response Amplitude Operators (RAOs) in all 6 degrees of freedom for two different mooring configurations. This work is the first step towards the calibration and performance improvement for existing numerical models of the DTI-F concept

Pretreatment apoptosis in carcinoma of the cervix correlates with changes in tumour oxygenation during radiotherapy

A relationship between hypoxia and apoptosis has been identified in vitro and in experimental tumours. The aim of this study was to investigate the relationship between apoptosis, hypoxia and the change in oxygenation during radiotherapy in human squamous cell carcinoma of the cervix. Forty-two patients with locally advanced disease underwent pretreatment evaluation of tumour oxygenation using an Eppendorf computerized microneedle electrode. Twenty-two of these patients also had a second evaluation of tumour oxygenation after receiving 40–45 Gy external beam radiotherapy. Paraffin-embedded histological sections were obtained from random pretreatment biopsies for all 42 patients. Apoptotic index (AI) was quantified by morphology on TUNEL stained sections. No correlation was found between pretreatment measures of AI and either the median pO2(r = 0.12, P = 0.44) or percentage of values < 5 mmHg (r = –0.02, P = 0.89). A significant positive correlation was found between AI and the change in tumour oxygenation (ratio of pre:post-treatment % values < 5 mmHg) following radiotherapy (r = 0.61, P = 0.002). The lack of correlation between apoptosis and hypoxia may occur because the Eppendorf measures both acute and chronic hypoxia, and the relative ability of acute hypoxia to induce apoptosis is unknown. These results indicate that cell death via apoptosis may be a mechanism of tumour reoxygenation during radiotherapy. © 2000 Cancer Research Campaig