Hydration characteristics of cement pastes incorporating electric arc-furnace slag

This paper presents the results of a comparative study of the hydration characteristics of cement pastes incorporating steel slag or ground granulated blastfurnace slag (GGBS) as substitutes for ordinary Portland cement (OPC). The study looked at the physical and chemical characteristics of the starting materials. Various cementitious paste mixes were manufactured and cured under two separate curing regimes and a combination of thermogravimetric and X-Ray diffraction analysis used to identify the hydration products formed during the investigation. The study established that the partial replacement of OPC with Electric Arc-Furnace steel slag or GGBS leads to a slow rate of formation of hydration products at early ages. However, at later ages, mixtures containing GGBS and waste slag produced more hydration products than the control OPC mix, especially when cured under a hot humid (Mediterranean) climate. The results suggest the viability of application of such industrial waste products in concrete which, among others, is likely to have an important impact on waste utilisation strategy and a dual benefit of reducing the possible negative environmental impact and preservation of natural resources

Design, development and numerical analysis of honeycomb core with variable crushing strength

A honeycomb core with half-circular cut-away sections at the spine (the adjoining cell walls) is designed and developed and numerically tested under axial dynamic load condition. The parametric study is invoked to identify the effect of various circular cut-away dimensions. In one embodiment a half-circular shaped cuts are removed from the top of the cell where the cell is impacted and its radius decreases toward the trailing edge of the cell. Numerical (FE) analysis was performed using explicit ANSYS/LS-DYNA and LS-DYNA codes to investigate the crushing performance, where impact angles 30° and 90° was combined with velocity of 5:3 m/sec. The crushing strength and internal energy absorption of the modified honeycomb cores with cut-away sections are then monitored to define the design parameters. The representative Y-section (axisymmetric model) is used for numerical analysis which simulates the honeycomb crushing performance. The numerical results of these innovative models show cyclic buckling effect in which crushing strength increases linearly as the rigid wall passes through. The FE results are validated with corresponding published experiments of the original unmodified honeycomb core (without cut-away)

Procedural tool for analysing building energy performance: structural equation modelling protocol

Building energy performance assessment technique has become a new paradigm that plays a significant part in reducing world energy demand and greenhouse gas emissions. However, there exists a global proliferation of diverse models for assessing and benchmarking buildings. This paper proposes a single building energy performance assessment model that considered several factors that affect office building energy efficiency performances in two different countries. It aimed to develop a model that could identify building energy performance critical factors as a new technique for aggregating energy efficiency metrics for commercial buildings. It examined the relationship and interdependency between the variables as it affects buildings’ performance as a basis for developing its theoretical model. Survey questions were derived from variables obtained from the existing literature using this theoretical paper proposition. A self-administered questionnaire was used to gather data from occupants of office buildings in Nigeria and the UK. Exploratory factor analysis and structural equation modelling via confirmatory factor analysis were used to analyse the explanatory power of the measured variables and their constructs. The results identified management, strategic and operational issues as critical factors that affect building energy performance in both countries. It confirmed the relationships and interdependency of the study factors and developed a new strategy that gives them proper considerations in the operations and management of building energy. Data collected support the theoretical model, and the measurement model fits into the conceptual model. The model gives a quantitative approach that identified critical factors for improving energy management and auditing efficiency of buildings

Strength development of concrete made with recycled glass aggregates subjected to frost curing conditions

An experimental investigation was undertaken to study whether the strength behavior of concrete made with glass aggregate differed significantly from that made with natural aggregates when concretes cured in low temperatures. The aim of the research work presented is to examine the strength behavior of glass concrete when cured under freezing conditions at -15°C and -10°C. The results showed that when glass concrete is cured at low curing temperature, the 28 day compressive strength is higher than control concrete. Glass concrete that had been cured at low temperatures and subsequently allowed normal curing recovered 100% of its strength while the recovery for control concrete was of about 50%. These findings suggest that concrete made with recycled glass could have an important application, on cold temperature concreting

An investigation into the seismic base isolation from practical perspective

Isolation from the ground during a seismic excitation has been one of the challenging subjects for researchers for many years. From the review of current approach to date, the general principles are for buildings or structures to be decoupled from the horizontal components of the earthquake ground motion by interposing a layer with low horizontal stiffness between the structure and the foundation. The harmonious movement of the structural basement will cause a significant reduction of fundamental frequency that is much lower than its fixed-base frequency and also much lower than the predominant frequencies of the ground motion. In this paper the Base Isolation systems are investigated from the historical evidences up to now. The work presented herein is based on comparative perspective of different methods proposed to date based on their compatibility, efficiency, benefits and weaknesses of each system that are deliberated and analysed. Finally a five-storey building as a case study has been taken into consideration through simulated analysis for both, with and without base isolation systems. Numerical analyses are applied in order to observe dynamic behaviour of such structures under seismic loads. Brief review of the economy and practical effectiveness of base-isolation systems is reported for completeness

A validated low carbon office building intervention model based on structural equation modelling

Building energy performance in existing stocks via facilities management interventions for low carbon building has become expedient and relevant in global climate change discourse. It has raised the consciousness for the need for a unified decision-support model for Facilities Managers and Owners, which could be used for office buildings across countries in achieving cleaner building energy production and use. This paper aimed at examining the factors that affect office Building Energy Performance; their interdependencies; and identify the critical path for interventions. It filled this gap by presenting a combination of interrelated processes (operations, tactics, and strategies) needed to improve building energy performance, reduce costs and greenhouse gas emissions in buildings for organizations. An online questionnaire survey was used in gathering data on current study model variables from participants of case study office buildings in Nigeria and the UK. Structural Equation Modelling technique was used to examine the factors that contribute to improving the energy performance of heterogeneous office buildings in both countries. The result established a strong correlation among observed variables and constructs and high covariance between constructs. This indicates that dependency and interdependence relationships exist amongst constructs, and in between construct and indicators. The finding reveals that an organization needs Sustainability Policy, Facilities Management and Energy Management as a sub-set of Strategic policy incorporated into its core management policy and operations energy management to achieve low carbon building. It also reveals the most critical pathway in the overall model with Strategic Facilities Management discovered to underpin the optimal performance for office buildings

Application of operational-based strategic intervention model for evaluating office buildings energy efficiency performance

The operational management and strategic interventions for energy efficiency (EE) of facilities could be optimised if interventions and decision-making processes are well integrated. Hence, this study developed a conceptual dual model for building energy performance (BEP) as a composite model based on prior theories. The theoretical study variables were interventions (technical and operational) and decision-making (management) factors (manifest variables) derived from an extensive literature review. Likewise, the constructs (latent variables) were the aggregated data of the intervention/decision-making evident factors used in the composite scale model. These constructs define the identifiable EE (management) manifest factors and classify them for standardised EE management practices. This paper describes the effects and the causal relationship between constructs derived from these factors that impact BEP via the composite scale model. An online self-administered questionnaire was used in gathering information from the occupants of selected office buildings in two countries (Nigeria and the UK). Structural equation modelling was engaged in evaluating the structure of the composite scale model that serves as a merger of isolated critical factors that affect BEP improvement. The model has four parts: the strategic driver, management policy, operational and building energy performance constructs as distinct sub-models. The results of the model evaluation reveal that the collected data fit the hypothesised dual model and have good fits. The models are not significantly different; they help investigate the fundamental relationship between the constructs. The result also reveals a strong positive correlation of management policy with strategic drivers for EE; strategic drivers with the use of building energy performance model; and management policy with operational EE practices. Path evaluation shown on the dual model specified the hypothesised causal relationship amongst constructs and strategic driver as the only significant positive mediator. Furthermore, the study integrates interventions and decision-making in a new dual model for improving BEP for diagnostic and solution purposes. Facility managers and owners could use the dual model as a strategic and tactical decision-making implement in managing low-carbon office BEP

Design attributes for geometry optimization process of thin walled honeycomb structures

Thin walled cellular structures have the ability to absorb impact energy during crashing thus it is important to enhance the crashing efficiency and optimise the structural reliability. This paper discusses the honeycomb cell configuration optimization procedure. For the design optimization, the response surface method (RSM) is used to formulate the complex design where the energy absorption (EA) representing the structure’s ability of absorbing energy was selected as objective, the Y split side parting length w1 , w2 , and thickness T1 are defined as three design variables, and the maximum crushing force (Max.F) occurs as constraint. During this distinctive optimization, the (RSM) was combined with detailed geometrically simplified finite element (FE) model using ANSYS/LS-DYNA (pre-processor), LS-DYNA (solver) and LS-Opt (optimiser). RSM combined with (FE)model without user intervention, was the effective tool to optimize non-linear impacted cellular structures. Optimal design achieved through LS-OPT is compared to the validated results for accuracy and effectiveness

Hexagonal honeycomb cell optimisation by way of meta-model techniques

This paper presents the result of an optimisation study by linear, quadratic, Kriging and radial basis meta-models in order to augment the crashworthiness characteristic of cellular structures. Thin-walled cellular structures (honeycomb) have the ability to absorb impact energy during crashing, thus it is important to enhance the crushing efficiency and optimise the structural reliability. The optimisation carried out in this study is aimed at maximising the energy absorption characteristics using meta-models while considering some limitation on the maximum force as a constraint. Achieving these characteristics is an important factor in crashworthiness analysis, which minimises the damage in dynamic performance. The objective of using various meta-models is to qualify the meta-model in crashworthiness analysis using different point selection schemes and different number of points. The optimisation is performed in two stages; through experimental design methods in which a set of sampling points is selected from design space and polynomial fitting in order to optimise the objective. It is concluded that D-optimal best suits response surface method for model approximation. Kriging performed best by space filling and the best point selection scheme for radial basis surrogate is latin hypercube design. The results show that for optimising the crashworthiness characteristics of honeycomb, Kriging and quadratic response surface (RS) are best, in terms of accuracy and robustness point of view and the radial basis neural network would be the second best. During this optimisation, the RS was combined with detailed geometrically simplified finite element model of honeycomb cell using ANSYS/LS-DYNA, LS-DYNA and LS-opt packages. Approximated functions combined with the finite element analysis were an effective tool to optimise highly non-linear impact problems. This has led to the development of validated algorithm that enabled the development of the optimised solutions