Calibrated CFD simulation to evaluate thermal comfort in a highly-glazed naturally ventilated room

Natural ventilation is a sustainable solution to maintaining healthy and comfortable environmental conditions in buildings. However, the effective design, construction and operation of naturally ventilated buildings require a good understanding of complex airflow patterns caused by the buoyancy and wind effects.The work presented in this article employed a 3D computational fluid dynamics (CFD) analysis in order to investigate environmental conditions and thermal comfort of the occupants of a highly-glazed naturally ventilated meeting room. This analysis was facilitated by the real-time field measurements performed in an operating building, and previously developed formal calibration methodology for reliable CFD models of indoor environments. Since, creating an accurate CFD model of an occupied space in a real-life scenario requires a high level of CFD expertise, trusted experimental data and an ability to interpret model input parameters; the calibration methodology guided towards a robust and reliable CFD model of the indoor environment. This calibrated CFD model was then used to investigate indoor environmental conditions and to evaluate thermal comfort indices for the occupants of the room. Thermal comfort expresses occupants' satisfaction with thermal environment in buildings by defining the range of indoor thermal environmental conditions acceptable to a majority of occupants. In this study, the thermal comfort analysis, supported by both field measurements and CFD simulation results, confirmed a satisfactory and optimal room operation in terms of thermal environment for the investigated real-life scenario. © 2013 Elsevier Ltd.

Chloride ingress through alkali activated slag concretes

Alkali activated slag (AAS) is a credible alternative to Portland cement (PC) based binder systems. The superior strength gain and low embodied carbon make it a potential binder for next generation concretes. However there is little known about the long term durability of AAS systems, especially the chloride transport and subsequent corrosion of reinforcing steel.
In this study, chloride transport through 12 AAS concretes with different alkali concentrations (Na2O% of mass of slag) and different modulus (Ms) of sodium silicate solution activator was investigated. A non-steady state chloride diffusion test was used for this study due to its similarity to the real exposure environment in terms of chloride transport through concrete. The results showed that the chloride concentration at the surface (Cs) of AAS concretes was higher than that for PC concrete.
However, lower non-steady state chloride diffusion coefficient (Dnssd) was obtained for the AAS concretes. The Dnssd of the AAS concretes decreased with the increase of Na2O% and Ms of 1.50 gave the lowest Dnssd. The results are encouraging and it can be concluded that AAS concrete offers a superior performance in terms of chloride transport.

Influence of compressive loading on chloride ingress through concrete

Chloride-induced corrosion of steel in concrete is one of most important durability and safety concern for reinforced concrete structures. To study chloride ingress into concrete is thus very important. However, most of the researchers focus on the studying chloride ingress through concrete samples without any loading. In reality concrete structures are subjected to different kinds of loads and therefore studying the effect of such loads on chloride transport is critical. In this work, 28 different concrete mixes were subjected to three levels of compressive load (0%, 50% and 75% of compressive failure load – f) for 24 hours. Further to unloading, these samples were subjected to non-steady state chloride diffusion test as per NT Build 443. The results were compared against the diffusion coefficient obtained for concrete samples that had no previous loading. D value for concretes subjected to 75% f showed a significant increase compared to 0% loading condition, but the increase was insignificant for 50% f. The results indicate that the influence of concrete mixes variables on D is more significant than that of loading level. Surface chloride concentration also increased with the loading level, which might be due to the increased concrete surface area caused by micro cracking.

A research-based approach to exploring the adoption of novel UK-based concrete test methods in Chinese construction sector

As part of a UK-China science bridge project - a UK government funded initiative linking leading universities and businesses in selective partnering countries in 2009 a collaborative research programme was initiated between Queen's University and the Research Institute of High Performance Concrete (part of the Central Research Institute of Building and Construction) in Beijing.

For further details email b.magee@ulster.ac.uk

A durability performance-index for concrete: developments in a novel test method

Implementation of both design for durability and performance-based standards and specifications are limited by the lack of rapid, simple, science based test methods for characterising the transport properties and deterioration resistance of concrete. This paper presents developments in the application of electrical property measurements as a testing methodology to evaluate the relative performance of a range of concrete mixes. The technique lends itself to in-situ monitoring thereby allowing measurements to be obtained on the as-placed concrete. Conductivity measurements are presented for concretes with and without supplementary cementitious materials (SCM’s) from demoulding up to 350 days. It is shown that electrical conductivity measurements display a continual decrease over the entire test period and attributed to pore structure refinement due to hydration and pozzolanic reaction. The term formation factor is introduced to rank concrete performance in terms of is resistance to chloride penetration.

Control of biofilm growth through photodynamic treatments combined with chemical inhibitors: in vitro evaluation methods

The rock/atmosphere interface is inhabited by a complex microbial community including bacteria, algae and fungi. These communities are prominent biodeterioration agents and remarkably influence the status of stone monuments and buildings. Deeper comprehension of natural biodeterioration processes on stone surfaces has brought about a concept of complex microbial communities referred to as "subaerial biofilms". The practical implications of biofilm formation are that control strategies must be devised both for testing the susceptibility of the organisms within the biofilm and treating the established biofilm. Model multi-species biofilms associated with mineral surfaces that are frequently refractory to conventional treatment have been used as test targets. A combination of scanning microscopy with image analysis was applied along with traditional cultivation methods and fluorescent activity stains. Such a polyphasic approach allowed a comprehensive quantitative evaluation of the biofilm status and development. Effective treatment strategies incorporating chemical and physical agents have been demonstrated to prevent biofilm growth in vitro. Model biofilm growth on inorganic support was significantly reduced by a combination of PDT and biocides

Optimal design of cold-formed steel portal frames for stressed-skin action using genetic algorithm

This paper describes a stressed-skin diaphragm approach to the optimal design of the internal frame of a cold-formed steel portal framing system, in conjunction with the effect of semi-rigid joints. Both ultimate and serviceability limit states are considered. Wind load combinations are included. The designs are optimized using a real-coded niching genetic algorithm, in which both discrete and continuous decision variables are processed. For a building with two internal frames, it is shown that the material cost of the internal frame can be reduced by as much as 53%, compared with a design that ignores stressed-skin action.

Influence of rheology on the quality of surface finish of cement-based mortars

Aesthetics of concrete structures is directly related to the quality of their surface finish. The objective of this investigation was to examine the effect of rheological properties of cement-based mortars on the quality of their surface finish. The study was divided into two phases. Firstly, the influence of the mix composition of mortars, viz. the water to cement (w/c) ratio, the sand content and the superplasticiser (SP) dosage on their rheology was evaluated. Secondly, the surface finish quality was characterised and related to the rheology of the studied systems. Rheology of these materials, i.e. the yield value, was measured using a vane viscometer. The quality of the surface finish was assessed by quantification of the surface air voids by analysing digital photographs of the mould finished sample surfaces. It was found that an increase in the w/c ratio and the SP content decreased the yield value, whilst the increase in the sand content had an opposite effect. When the surface quality is concerned, an increase in the yield value was found to increase the total content of the surface air voids and especially those with size smaller than 1 mm in diameter. Moreover, the analysis of the location of the surface air voids along the height of the sample revealed that with the increase in the yield value their concentration was higher in the bottom section of the analysed samples.

Crush responses of composite cylinder under quasi-static and dynamic loading

Despite the abundance of studies investigating the performance of composite structures under crush loading, disagreement remains in the literature regarding the effect of increased strain rate on the crush response. This study reports an experimental investigation of the behaviour of a carbon-epoxy composite energy absorber under static and dynamic loading with a strain rate of up to 100s^-1. Consistent damage modes and measured force responses were obtained in samples tested under the same strain rate. The energy absorption was found to be independent of strain rate as the total energy absorption appeared to be largely associated with fibre-dominated fracture, which is independent of strain rate within the studied range. The results from this study are beneficial for the design of energy absorbing structures.

Finite element modelling of composite structures under crushing load

This paper details the theory and implementation of a composite damage model, addressing damage within a ply (intralaminar) and delamination (interlaminar), for the simulation of crushing of laminated composite structures. It includes a more accurate determination of the characteristic length to achieve mesh objectivity in capturing intralaminar damage consisting of matrix cracking and fibre failure, a load-history dependent material response, an isotropic hardening nonlinear matrix response, as well as a more physically-based interactive matrix-dominated damage mechanism. The developed damage model requires a set of material parameters obtained from a combination of standard and non-standard material characterisation tests. The fidelity of the model mitigates the need to manipulate, or "calibrate", the input data to achieve good agreement with experimental results. The intralaminar damage model was implemented as a VUMAT subroutine, and used in conjunction with an existing interlaminar damage model, in Abaqus/Explicit. This approach was validated through the simulation of the crushing of a cross-ply composite tube with a tulip-shaped trigger, loaded in uniaxial compression. Despite the complexity of the chosen geometry, excellent correlation was achieved with experimental results.

Assessment of Atomic Data: Problems and Solutions

For the reliable analysis and modeling of astrophysical, laser-produced, and fusion plasmas, atomic data are required for a number of parameters, including energy levels, radiative rates, and electron impact excitation rates. Such data are desired for a range of elements (H to W) and their many ions. However, measurements of atomic data, mainly for radiative and excitation rates, are not feasible for many species, and therefore, calculations are needed. For some ions (such as of C, Fe, and Kr), there is a variety of calculations available in the literature, but often, they differ significantly from one another. Therefore, there is a great demand from the user community to have data "assessed" for accuracy so that they can be confidently applied to the modeling of plasmas. In this paper we highlight the difficulties in assessing atomic data and offer some solutions for improving the accuracy of calculated results.

Overview of Seismic Hybrid Testing

Even though computational power used for structural analysis is ever increasing, there is still a fundamental need for testing in structural engineering, either for validation of complex numerical models or material behaviour. Many structural engineers/researchers are aware of cyclic and shake table test methods, but less so hybrid testing. Over the past 40 years, hybrid testing of engineering structures has developed from concept through to maturity to become a reliable and accurate dynamic testing technique. In particular, the application of hybrid testing as a seismic testing technique in recent years has increased notably. The hybrid test method provides users with some additional benefits that standard dynamic testing methods do not, and the method is much more cost effective in comparison to shake table testing. This paper aims to provide the reader with a basic understanding of the hybrid test method and its potential as a dynamic testing technique.

Finding a way: Long term care homes to support dementia

An ageing demographic has increased the number of people with dementia. Although dementia is commonly associated with memory loss, other early symptoms include difficulty with wayfinding. Dementia alters visuo-spatial perception and the processes used to interpret the physical environment. The role of the design of the physical environment for people with dementia has gained increased recognition. Despite this, design for dementia is often overlooked, focusing on issues relating to physical impairment. This paper presents the results of a PhD study and aims to examine the role of the design of the physical environment in supporting wayfinding for people with dementia living in long-term care settings in Northern Ireland. Mixed methods combined the observation of wayfinding walks and conversational style interviews to elicit perspectives and experiences of residents with dementia. The findings aim to promote well-being for those with dementia living in long-term care settings.

FRP reinforcement of timber structures

Timber engineering has advanced over recent decades to offer an alternative to traditional materials and methods. The bonding of fibre reinforced plastics (FRP) with adhesives to timber structures for repair and strengthening has many advantages. However, the lack of established design rules has strongly restrained the use of FRP strengthening in many situations, where these could be a preferable option to most traditional techniques. A significant body of research has been carried out in recent years on the performance of FRP reinforced timber and engineered wood products. This paper gives a State of the Art summary of material formulations, application areas, design approaches and quality control issues for practical engineers to introduce on-site bonding of FRP to timber as a new way in design for structural repair and rehabilitation.

Mechanical properties of structures 3D printed with cementitious powders

The three dimensional (3D) printing technology has undergone rapid development in the last few years and it is now possible to print engineering structures. This paper presents a study of the mechanical behavior of 3D printed structures using cementitious powder. Microscopic observation reveals that the 3D printed products have a layered orthotropic microstructure, in which each layer consists of parallel strips. Compression and flexural tests were conducted to determine the mechanical properties and failure characteristics of such materials. The test results confirmed that the 3D printed structures are laminated with apparent orthotropy. Based on the experimental results, a stress-strain relationship and a failure criterion based on the maximum stress criterion for orthotropic materials are proposed for the structures of 3D printed material. Finally, a finite element analysis was conducted for a 3D printed shell structure, which shows that the printing direction has a significant influence on the load bearing capacity of the structure.