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Cold-formed steel sections have become competitive structural components in the modern building construction due to their inherent favourable characteristics over conventional hot-rolled steel members. A wide range of products, with a multiplicity of shapes, sizes, and applications typically manufactured with perforations to facilitate various services: electrical, plumbing, and heating, etc., are produced using simple and cost-effective industrialised processes. Cold-formed members are thin, light, and economically efficient. However, the advantages of these members are often limited due to the presence of perforations and susceptible to various buckling modes such as local, distortional, flexural, and torsional-flexural buckling which sometimes are not predicted. This research work provides a general insight into cold-formed steel and buckling, and investigates the influence of perforations on the buckling behaviour of cold-formed column members of lipped channel cross-section using experimental study, finite element analysis, and design code predictions.

No description available.

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The use of virtual experiments of welded steel plate girders are commonplace in modern structural research. One key factor in the success of using such numerical analysis is the availability and reliability of input data including imperfections such as initial deformations and residual stresses. In this research a methodology combining experimental and numerical work is developed in order to use virtually fabricated welded specimens, which include the imperfections as a result of the manufacturing process, in virtual experiments. A series of experiments are performed to calibrate and validate the numerical models. Temperature measurements are conducted in a steel structure factory during the welding of plate girders. The measurement methodology developed combines two types of measurements using an infrared thermometer without disturbing the fabrication process itself. The residual stresses are measured using a modified hole drilling method. Geometrical imperfection measurement results are also available from other related projects. For the numerical simulation of welding a mixed time integration scheme is proposed. For the modelling of the heat source of welding an “equivalent prismatic heat source model” is developed, which is very robust and allows for very simple calibration. Both thermal and thermal stress analyses of the welding process are performed including a large number of parametric studies. The residual stress measurements are also numerically investigated and calibration tables are developed to evaluate the measurements considering inaccuracies in their execution. The fabrication of full size plate girders is simulated. The calculated and measured web deformations are compared and reasonable agreement is found. Finally, to demonstrate and summarise the achievements of this research, a virtual specimen is used in a virtual experiment in which the ultimate behaviour of a plate girder is studied.

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No description available.

Exploitation of thermogeology energy in heating and cooling of buildings starts to spread worldwide as an alternative renewable source of heat energy. The thermal conductivity of soils is among the critical parameters required to achieve a proper design of ground heat exchangers or any underground systems that involve thermo-active processes. This research is a part of study related to the laboratory measurements of thermal conductivity of soils and thermal grouts used for borehole heat exchangers. The first part of this project involves a design of a new thermal cell that can be used to measure the thermal conductivity of soils. The design of the apparatus is based on the application of Fourier’s law at steady state condition where unidirectional heat flux is generated through two identical specimens. A new concept of minimizing the radial heat losses that occur due to the ambient temperature interface (ATI) using a thermal jacket as a heat insulation barrier has been introduced in the design and experimentally performed. The obtained results and the analysis of the heat flow reveal that the longitudinal heat flow can be maximized and the radial heat flow can be minimized when the thermal jacket is used with proper temperature control. Also, it has been revealed that the measured thermal conductivity of soils is sensitive to further boundary conditions such as thermocouples and temperature of sink disks. In addition to its simplicity, the new cell can be used for undisturbed field samples (U100 samples) as well as laboratory-prepared specimens. The sample preparation and the test procedure for the two different soil conditions highlighted the simplicity of using the new apparatus in measurement of the thermal conductivity of soils. The second part of this research concerns a production of new thermal grout for borehole heat exchangers using unwanted industrial and domestic materials (PFA and ground glass-low cost) and the commodity fluorspar, all of which have relatively high thermal conductivity. The thermal conductivity of different PFA based grouts that comprise different enhancing materials at different mix proportions has been measured dry and at saturation using the new thermal call. The results highlighted the effect of mineralogy and the particle size distribution of the mix constituents on the thermal conductivity of the grout. The results showed that a combination of fluorspar with coarse ground glass can provide good thermal enhancement in both dry and saturated conditions. The grout that consist of 20% cement, 30% PFA, 15% coarse ground glass and 35% fluorspar by weight with dry and saturated thermal conductivity of 1.283 and 1.985 W/m respectively can be considered as a suitable grout that can be used successfully in UK. Comparing with thermally enhanced bentonite (1.46 W/m.K), it is expected that with London Clay Formation optimal performance of borehole heat exchangers and cost savings would be achieved using the selected grout. The work done in the final part can be considered as an application of the new steady state thermal cell in the estimation of the thermal conductivity of sandy soils. Also, it can be considered as a case study where the thermal conductivity was measured for soils that have not been previously thermally tested (Tripoli sand). The effects of the porosity and degree of saturation on the thermal conductivity of Tripoli sand were investigated. The results of twenty experimental tests showed that the effect of the saturation degree is significant compared with the effect of dry density especially at saturation degree less that 10%. Also, the results revealed that the thermal conductivity is approximately linearly proportional to the dry density at all levels of saturation. The validation of some existing selected prediction models showed that none of the selected models is able to correctly match the thermal conductivity of Tripoli sand at all conditions. However, some models were more accurate than others in certain conditions. It is also concluded that all presented models failed to estimate the thermal conductivity of such soil in low or partially saturated conditions where convection started to play a role in the heat transfer mode. On the other hand, the variation of thermal conductivity of Tripoli sand can be fittingly described as logarithmic function of the water content at all levels of porosity with R2 value ranges between 0.9694 and 0.9732. As a result, an empirical model based on the experimental results expressing the thermal conductivity in terms of water content and porosity has been obtained and validated.

X-ray computed tomography (XRCT) enables the non-destructive analysis of samples internal structures down to a sub-micron resolution and has been used to examine the macrostructure of unstabilized soil based construction materials (SBCMs) alongside experiments on the materials unconfined compressive strength. SBCMs are manufactured mixtures of clay, sand and gravel which should be considered as highly unsaturated compacted soil where suction is the key source of strength. The use of XRCT in geotechnical literature is comprehensively reviewed before three laboratory investigations are described. Firstly crack propagation in SBCMs following unconfined compression is investigated and key lessons about XRCT scanning highlighted. Secondly the impact of altering sample size to match optimum XRCT scanning conditions is explored through experiments on void size distribution and unconfined compressive strength. Finally the effects of adding expansive clay to SBCM mixes on macrostructure are investigated and insights on how the unconfined compressive strength develops as SBCM dries are given. Conclusions from this thesis have applicability to both the SBCM industry, as the insights into the fundamental behaviour of SBCM can be used to inform building practice, and geotechnical researchers where the extensive use and development of XRCT can be applied to investigate the internal structure of a wide range of geotechnical materials.

Civil engineering structures are subject to a wide variety of loads during their life span, either due to natural hazards or everyday use. The vibrations that are generated by these actions affect the performance of the structure. In extreme cases, especially during strong wind or earthquakes, excessive vibrations may lead to structural failure, resulting in economic losses and even loss of human life. It is therefore very important to study, understand and then act towards limiting these vibrations. Various types of devices can be attached to structures to limit unwanted vibration. Traditional passive systems, that resist motion within the structure, are the most widely used due to their simplicity. More complex devices include semi-active ones which allow closed-loop variation of parameters within a device. While these devices still only resist motion, and so retain the desirable property that they are inherently stable, this control arguably allows better vibration suppression. Active devices, such as actuators, generate motion as well as resist it, allowing potentially better control, however at the cost that they require higher power. As they can feed energy into the structure, they are not inherently stable. The research presented in this thesis focuses on the use of passive control for mitigating vibration of multiple degrees of freedom systems and the development of novel passive control systems, able to ensure good structural performance. Initially, the possibility of emulating the performance of an active control system by using equivalent semi-active and passive devices is studied. Then, a novel type of passive vibration control system, based on the inerter is proposed. The principal advantage of the inerter is that a high level of vibration suppression can be achieved with low amounts of added mass. Several layouts and installation possibilities are studied, the most efficient system being the one that preserves the layout of a tuned mass damper (TMO) where the mass element is replaced by an inerter. This is named a tuned inerter damper (TIO). A design methodology for TIOs used in earthquake and wind-excited structures is developed, while showing that the new system is most efficient when installed at the bottom storey level. This feature is one advantage of the TIO when compared to a more traditional TMO. In addition, given the inerters capacity of generating high apparent mass from small devices masses through gearing, an improved level of vibration suppression can be obtained by using a reduced dimension and economical device. The application of TIOs is then extended to stay cables, where a TIO is attached transversally to the cable, similar to the use of viscous dampers. A design methodology based on contour plots, aimed at choosing the optimal viscous damper or TIO to be connected at a given location along the cable length is proposed. It is shown that the TIO represents a viable alternative to viscous dampers, being more efficient and also economical.