Study and investigation of stainless steel – lightweight concrete – stainless steel composite wall

This project seeks to design and create a sustainable sandwich construction with a lightweight concrete core built from coal waste spheres, stainless-steel rigid face and shear studs embedded into the concrete to enable the combined action of the concrete foam and the stainless-steel profile to improve the fatigue strength through experimental, numerical and FEM studies. The main objective of this research is to study and investigate a composite wall consisting of stainless-steel face plates, concrete foam and shear studs to contribute to understanding of the behavior of the shear connector in the lightweight concrete and the stainless-steel face plates. This study intends to investigate and compare the mechanical properties of lean duplex stainless steel grades 2001, austenitic stainless-steel grades 304D, and grade 304 to mild steel for the face plate of the composite wall. In addition, to the three grades of stainless steel, ten lightweight concrete mixes are studied, designed and casted to achieve the floatable density of the concrete, the mixes are further investigated based on the filler diameter, kind, and percentage of fibre content for the foam of the composite structure. Various researchers’ investigation on composite walls are studied and in-depth analysis is done on the axial loading and equations are proposed. American Standards AISC360, Korean Standards KEPIC-SNG and Japanese Standards JEAG 4618 are extensively studied, and suggestions are made on the validity of the standards. A three-dimensional finite element model of the axial loading test is developed using the general-purpose finite element program ABAQUS and the load test is analyzed using different concrete material models, and analysis procedures. To assess the accuracy and reliability of the developed finite element model, it is validated against steel – concrete – steel composite walls modelled by researcher. The results obtained from the finite element analysis showed excellent agreement with the experimental studies proving that the stainless-steel concrete steel depicted larger axial load bearing capacity in comparison to steel concrete steel composite wall. The results of the parametric study are evaluated, and findings are used to propose the design equations for shear connector resistance considering the position of the shear stud and thickness of the profiled sheeting. The coefficient of correlation between experimental and predicted results is nearly equal to one, which indicates that the predicted results are accurate, and the proposed equations are suitable for future predictions

Optimal control of the heave motion of marine cable subsea-unit systems

One of the key problems associated with subsea operations involving tethered subsea units is the motions of support vessels on the ocean surface which can be transmitted to the subsea unit through the cable and increase the tension. In this paper, a theoretical approach for heave compensation is developed. After proper modelling of each element of the system, which includes the cable/subsea-unit, the onboard winch, control theory is applied to design an optimal control law. Numerical simulations are carried out, and it is found that the proposed active control scheme appears to be a promising solution to the problem of heave compensation

Hybrid cold-formed steel structural systems for buildings

Cold-formed steel (CFS) shear walls or strap-braced walls are the primary lateral load resisting components in light-weight steel framed (LSF) structures. Despite the increasing demand on the application of CFS systems in mid-rise construction, the relatively low lateral load resistance capacity of these systems has remained one of the major obstacles for further growth, as this low resistance becomes problematic in their use in cyclonic wind regions or highly seismic zones. In this thesis, in order to address this issue, a new Hybrid CFS wall composed of CFS open sections and square hollow sections (SHS) is developed and investigated. The proposed hybrid system is suitable for light-weight steel structures for mid- to high-rise construction, due to its satisfactory lateral load resistance. The thesis presented provides the results of the study which contains experimental and numerical investigation as outlined in the following. In the first stage of this study, a comprehensive literature review was conducted to reveal the existing gaps in the previous studies on CFS structures under lateral loads. In the second stage, a series of full-scale experimental tests were performed on seventeen hybrid CFS wall panels in order to investigate their lateral performance, shear resistance, failure modes and energy absorption. In the third stage of this thesis, a comprehensive study was performed on the theories and applications of the numerical models for analysis of the lateral behaviour of CFS wall systems during the past several decades, and all existing numerical methods for simulating the behaviour of CFS shear walls were accordingly classified. In stage four of this study, proposed hybrid wall panel was further developed, and twenty new wall configurations were evaluated using non-linear finite element analysis, aiming to further investigate the seismic performance of CFS hybrid walls. Finally, in the last stage, a sustainability analysis was performed which could be of interest to all stakeholders including owners, builders and investors, when assessing the potential use of hybrid CFS systems, in particular for mid-rise buildings

In-plane shear behaviour of composite walling with profiled steel sheeting

This thesis introduces a novel form of double skin composite walling with profiled steel sheeting and an infill of concrete. This is a logical extension of research on composite slabs with profiled steel sheeting currently known as popular "Fastrack" construction. The composite walling is thought to be specially applicable as shear or core walls in steel frame buildings. The profiled steel sheeting will act as a temporary shear bracing to stabilise the frame against wind and destablising forces during construction and also act as a form work for infill of concrete. In the service stage, they will act as a reinforcement to carry axial, lateral and in-plane forces. This thesis investigates the behaviour of composite walls under in-plane shear so that they can be used as shear elements in buildings. The investigation includes analytical, numerical and small scale model tests. Design recommendations for the composite walls are the final aim of the research. The investigation is based on the concept that the in-plane shear strength and stiffness of the composite wall will be derived from the individual sheeting, concrete core and from the interaction between the two. Based on above, individual behaviour of the sheeting and concrete core was studied before considering the composite wall as a whole. A shear rig has been designed and fabricated to carry out the model tests of approximately 1/6 th scale using very thin sheeting (profiled in house) and microconcrete. Analytical equations for the shear strength and stiffness of the sheeting, profiled concrete and composite wall are derived. These equations are validated by model tests and finite element analysis. Finite element analysis included modelling of composite walling with full composite action and some parametric studies using interface elements. The stiffness of the composite wall is found to be greater than the individual summation of stiffness of the sheeting and concrete core. The profiled steel sheeting will provide sufficient shear bracing to the frame during construction. The composite wall is capable of taking high in-plane shear loads which is greater than the summation of individual capacity of the sheeting and concrete and confirms its potential to be used as shear elements in buildings. Simple equations for the calculation of shear strength and stiffness of the composite wall are derived which can safely be used for design purposes. Further research directions are also outlined.This thesis introduces a novel form of double skin composite walling with profiled steel sheeting and an infill of concrete. This is a logical extension of research on composite slabs with profiled steel sheeting currently known as popular "Fastrack" construction. The composite walling is thought to be specially applicable as shear or core walls in steel frame buildings. The profiled steel sheeting will act as a temporary shear bracing to stabilise the frame against wind and destablising forces during construction and also act as a form work for infill of concrete. In the service stage, they will act as a reinforcement to carry axial, lateral and in-plane forces. This thesis investigates the behaviour of composite walls under in-plane shear so that they can be used as shear elements in buildings. The investigation includes analytical, numerical and small scale model tests. Design recommendations for the composite walls are the final aim of the research. The investigation is based on the concept that the in-plane shear strength and stiffness of the composite wall will be derived from the individual sheeting, concrete core and from the interaction between the two. Based on above, individual behaviour of the sheeting and concrete core was studied before considering the composite wall as a whole. A shear rig has been designed and fabricated to carry out the model tests of approximately 1/6 th scale using very thin sheeting (profiled in house) and microconcrete. Analytical equations for the shear strength and stiffness of the sheeting, profiled concrete and composite wall are derived. These equations are validated by model tests and finite element analysis. Finite element analysis included modelling of composite walling with full composite action and some parametric studies using interface elements. The stiffness of the composite wall is found to be greater than the individual summation of stiffness of the sheeting and concrete core. The profiled steel sheeting will provide sufficient shear bracing to the frame during construction. The composite wall is capable of taking high in-plane shear loads which is greater than the summation of individual capacity of the sheeting and concrete and confirms its potential to be used as shear elements in buildings. Simple equations for the calculation of shear strength and stiffness of the composite wall are derived which can safely be used for design purposes. Further research directions are also outlined

Innovative hybrid coupled wall systems to resist seismic action – HYCAD

This article summarizes the research carried out in the ongoing HYCAD project, which aims to improve the performances of a hybrid coupled wall (HCW) system for buildings in seismic areas, by further developing the HCW originally studied in the RFCS project INNO-HYCO. This HCW system consisted of a reinforced concrete (RC) wall coupled with two steel side-columns via steel coupling links. Encouraging outcomes were obtained such as: controlled post-elastic ductile behaviour under medium- and high-intensity earthquakes, suitable lateral stiffness, seismic energy dissipation concentrating in the easily-replaceable steel links and very limited damage in the RC wall. However, advanced studies were required to bring this system into practice, addressing issues and develop advancements in the analysis, design, and detailing. This article summarizes the primary steps taken towards that purpose. Five new components were chosen in order to improve the performance of the HCW system: (1) Link-to-wall connections using post-tensioned tendons; (2) Composite walls with encased steel profiles instead of a conventional RC wall; (3) Rocking coupled wall system; (4) Dissipating devices as links and (5) Precast double slab wall systems. Combining these components, four new HCW systems were developed, pre-designed and analysed through numerical and experimental studies. Advanced yet simple techniques were proposed for the numerical analyses while test specimens are used to characterize local and global behaviour

Numerical modelling strategies and design methods for timber structures

Over the last years timber constructions are gaining back a primary role in the building industry after decades in which they were almost abandoned in favor of concrete and steel structures. A sign of this change is the appearance in the last years in many Italian universities of courses dedicated to the design of timber structures. One of the main reasons behind this success must be sought in the development of new engineered timber materials, such as glued-laminated and cross-lam timber, that allowed to wooden structures to reach structural potentialities that until some decades ago were prerogative of concrete or steel building materials. Tests recently carried out on full-scale buildings have also proven the excellent capabilities of these new timber technologies in providing reliable and highly-performant multi-storey building able to withstand high seismic intensities. Since the employment of timber to build multi-storey buildings in seismic-prone areas is quite recent, many aspects relating the understanding of their structural behavior and their correct design are still to be sought, as demonstrated by the lack of provisions in current building codes and standards and the still ongoing great amount of research activity on seismic behavior of timber structures. Modern timber technologies also allow to cover very large spans with long glued-laminated timber beams, satisfying the need of large open spaces and architectural flexibility required by modern building design approaches. These bulky big-size elements anyway result quite expensive in production, transportation and installation phases undermining the economic competitiveness of timber structures. To cope with this problem, the prototype of an innovative timber-steel composite beam consisting of sub-elements assembled on-site to create longer members has been ideated at KTH Royal Institute of Technology of Stockholm in Sweden. One of the objectives of this thesis is therefore to provide an advance in the state of knowledge of timber building technology adopted for seismic-prone areas, focusing in particular on both numerical modelling strategies and design methods for cross-laminated timber buildings, illustrated respectively in the first and second part of the thesis. The other goal is the development of an analytical tool for the enhancement and the investigation of the structural performances of the innovative composite beam ideated at KTH Royal Institute of Technology, and it will be exposed in the third and last part of the thesis

Behaviour of Reinforced Concrete and Composite Conical Tanks Under Hydrostatic and Seismic Loadings

Conical liquid storage tanks are widely used to store different liquids and to provide water supply at cities and municipalities. However, no comprehensive guidelines currently exist in the codes of practice for the structural analysis and design of such tanks. The walls of a conical tank can be made of steel, reinforced concrete, or a combination of the two materials in a composite type of construction in which steel and concrete walls are connected using steel studs. The research conducted in this thesis provides a comprehensive understanding of the structural behaviour of reinforced concrete and composite conical tanks under hydrostatic and seismic loadings. Finite element models for both reinforced concrete and composite tanks are developed and validated. In these models, a 3-D consistent shell element that accounts for the material nonlinear effect is used. The composite model also includes a 3-D contact element simulating the steel studs. The numerical models are utilized to study different behavioural aspects of reinforced concrete and composite conical tanks. An Equivalent Cylinder Method (ECM) is introduced and assessed for the analysis and design of reinforced concrete conical tanks. A set of charts that can be used to determine the adequate thickness and the straining actions for reinforced concrete conical tanks under hydrostatic pressure is developed. An Equivalent Section Method (ESM) for the analysis of composite tanks, which is based on using an equivalent single wall, is introduced and assessed. Both the ECM and ESM are found to be inadequate for the analysis of reinforced concrete and composite conical tanks, respectively. The composite finite element model is extended to include an optimization routine for minimization of the cost of composite conical tanks. The optimization of the design of a real composite conical tank using the developed scheme resulted in a reduction of 32% in the material cost. The study is proceeded by examining the seismic behaviour of composite conical tanks. This is done by extending a previously developed numerical model that takes into account the fluid-structure interaction that occurs during the seismic vibration of a conical tank. A simplified procedure for the analysis of composite conical tanks under seismic loadings is introduced. The procedure is found to be adequate for preliminary design as the differences in the prediction of the natural frequencies and seismic forces are shown to be less than 17% compared to those predicted by the sophisticated numerical model

The mechanics of composite corrugated structures: A review with applications in morphing aircraft

Corrugation has long been seen as a simple and effective means of forming lightweight structures with high anisotropic behaviour, stability under buckling load and energy absorption capability. This has been exploited in diverse industrial applications and academic research. In recent years, there have been numerous innovative developments to corrugated structures, involving more elaborate and ingenious corrugation geometries and combination of corrugations with advanced materials. This development has been largely led by the research interest in morphing structures, which seek to exploit the extreme anisotropy of a corrugated panel, using the flexible degrees of freedom to allow a structure’s shape to change, whilst bearing load in other degrees of freedom. This paper presents a comprehensive review of the literature on corrugated structures, with applications ranging from traditional engineering structures such as corrugated steel beams through to morphing aircraft wing structures. As such it provides an important reference for researchers to have a broad but succinct perception of the mechanical behaviour of these structures. Such a perception is highly required in the multidisciplinary design of corrugated structures for the application in morphing aircraft