The role of steel fibres on the compressive and tensile properties of concrete

Concrete being a widely used structural material due to its good compressive strength and versatility under harsh conditions; it does suffer from weak tensile strength. Concrete tends to develop cracks which weakens its structural performance and leads to a reduction of its durability and failure in some cases. One of the ways to sort out this problem is to incorporate reinforcement bars and fibers. This study is on steel fiber reinforced concrete and the role of those steel fibers in the strength of concrete and which dosage level is both appropriate and economical in concrete production. The study has followed an experimental approach guided by the outcome of the comprehensive literature review. Cylindrical specimens of size 100mm diameter and 200 mm high are utilized. Uniaxial comprehensive and splitting tensile strength were investigated through test of 72 concrete cylinders. The tests were conducted for plain concrete 3 cylinders which are tested at 7 days, 14 days and 28 days; the same is repeated for 0.5% steel fibers, 1% steel fibres and 2% steel fibres both for compressive and splitting tensile tests. Regressions are done in MS-Excel and linear models developed which can be used to predict compressive and tensile strength of concrete with different dosages of steel fibres. It is established that the steel fibres have an effect on concrete strength development whereby they contribute 36.5% at 2% steel fibres and 81.2% for splitting tensile strength enhancement

Error control techniques for satellite and space communications

Two aspects of the work for NASA are examined: the construction of multi-dimensional phase modulation trellis codes and a performance analysis of these codes. A complete list is contained of all the best trellis codes for use with phase modulation. LxMPSK signal constellations are included for M = 4, 8, and 16 and L = 1, 2, 3, and 4. Spectral efficiencies range from 1 bit/channel symbol (equivalent to rate 1/2 coded QPSK) to 3.75 bits/channel symbol (equivalent to 15/16 coded 16-PSK). The parity check polynomials, rotational invariance properties, free distance, path multiplicities, and coding gains are given for all codes. These codes are considered to be the best candidates for implementation of a high speed decoder for satellite transmission. The design of a hardware decoder for one of these codes, viz., the 16-state 3x8-PSK code with free distance 4.0 and coding gain 3.75 dB is discussed. An exhaustive simulation study of the multi-dimensional phase modulation trellis codes is contained. This study was motivated by the fact that coding gains quoted for almost all codes found in literature are in fact only asymptotic coding gains, i.e., the coding gain at very high signal to noise ratios (SNRs) or very low BER. These asymptotic coding gains can be obtained directly from a knowledge of the free distance of the code. On the other hand, real coding gains at BERs in the range of 10(exp -2) to 10(exp -6), where these codes are most likely to operate in a concatenated system, must be done by simulation

Computer Aided Reliability Based Hydro-Structural Response Analysis of Tension Leg Platforms

The TLP technology has gained credibility with the offshore industry and the associated engineering community. The TLP concept covers a number of areas where there is a great need for research. The developments associated with the TLP technology are briefly reviewed in Chapter 1. For numerical demonstrations, a TLP model is selected which was originally chosen by the Derived Loads Committee 1.2 of the 1985 LSSC. The principal particulars of the ISSC TLP are discussed in detail. Some important design parameters that influence significantly the configuration of TLPs are outlined in Chapter 1. A complete global analysis of a TLP includes many analytical and empirical methods where some of them are fairly standard but some other may not be well defined. The problem areas involved in the analysis and the future trends in design are also discussed. Chapter 2 examines different components of the environmental loading. Second order effects are included. Drift forces are estimated from simplified analytical solutions. The calculation of external forces described in Chapter 2 are used in the next chapters. Some closed-form expressions are derived that are particularly important for transforming complicated external forces into equivalent nodal loads. A step-by-step procedure combining transformation matrices and results from standard load cases is proposed which deals with complex member loads on a 3-D beam, arbitrarily oriented in space. Chapter 3 describes the development of a rigid body motion analysis program, RBRA. The dynamic equation of motion which takes account of all six rigid body degrees of freedom and the associated coefficient matrices are discussed. A solution technique is proposed which is found quite effective to estimate the linearised rigid body responses. The results from RBRA are compared with the published results from 17 organisations who have used boundary element formulations and diffraction-radiation analysis for their calculations. Chapter 4 discusses the development of a computer program, DCATLP which can bring hydrodynamic and structural aspects together in the dynamic coupled analysis of a TLP. The TLP is modelled as a 3-D frame structure with internal hinges to account for the hull-tether connections. However, main particulars of a TLP are not enough for any structural analysis. For numerical demonstration, the ISSC TLP components are designed realistically with stiffeners to estimate their scantlings. In DCATLP, the global mass and stiffness matrices are stored in skyline arrays. The dynamic equilibrium equations are solved in the time domain. The non-linear time integration algorithm belongs to the Newmark-beta family but it is a modification and combination of a number of existing algorithms. DCATLP can calculate internal member forces in each beam element under the action of environmental loading. The structural displacements, velocities and accelerations at each and every FE node are calculated. The static, quasi-static and dynamic components of the environmental forces are applied simultaneously in DCATLP to include the inertia effects. A different type of model for the ISSC TLP is developed in LUSAS where tethers are replaced by linear springs at each corner. Responses of two different ISSC TLP models (one for DCATLP and the other for LUSAS) under sinusoidal loads are compared. The structural and hydrodynamic responses of the ISSC TLP in a peak storm event are also presented. Chapter 5 presents a step-by-step calculation procedure to find failure probabilities of TLP column structures after assigning appropriate coefficients of variation to the strength and load variables. The calculation of longitudinal and hoop stresses from maximum axial compression, torsion, shear forces, bending moments and hydrodynamic pressure is also shown. The uncertainty modelling is mainly based on the previous work carried out in the author's Department. The failure surfaces for TLP columns are formulated according to API Bulletin 2U and the Model Code of TLP RCC. The chapter also describes some improvements achieved in developing a program BCCNNV, based on the AFOSM method. The program is sufficiently accurate for non-normal correlated variables and it is validated by considering a few classic cases. The main objective in Chapter 6 is to carry out a detailed FE analysis of a part of a TLP structure with the help of the results obtained from a 3-D beam element based global analysis. One ring only stiffened and three orthogonally stiffened cylinders, similar to TLP columns are modelled in LUSAS to compare the numerical predictions with the experimental results available from other researchers' work. To get an initial "feel' for the structure, the buckling loads of the FE models are estimated by eigenvalue buckling analyses. The author also attempts to capture the post-buckling phase of the FE models through rigorous non-linear FE analyses. Chapter 7 contains the final discussion and conclusions and ends with some recommendations for future research work

The design and application of associative memories for scene analysis

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.This thesis investigates a novel scene analysis system that determines the identity and the relative positions of unconstrained objects within a natural three dimensional grey scale image. Images may be of 'block filled' or 'line drawn' occluded shapes. It utilises the occluding information to discover the relative depth of objects in the scene. The system incorporates associative memories, the N tuple pattern recognition process, movable multiple resolution windows and edge detection. The structure and performance of the system and its subsystems is reported. The associative memory incorporates a novel recall procedure which has uses outside the application given here. The work incorporates ideas from the neurophysiology of the human visual system to overcome some of the problems encountered.Funding was obtained from the South Eastern Regional College (SERC)

MIMO Systems

In recent years, it was realized that the MIMO communication systems seems to be inevitable in accelerated evolution of high data rates applications due to their potential to dramatically increase the spectral efficiency and simultaneously sending individual information to the corresponding users in wireless systems. This book, intends to provide highlights of the current research topics in the field of MIMO system, to offer a snapshot of the recent advances and major issues faced today by the researchers in the MIMO related areas. The book is written by specialists working in universities and research centers all over the world to cover the fundamental principles and main advanced topics on high data rates wireless communications systems over MIMO channels. Moreover, the book has the advantage of providing a collection of applications that are completely independent and self-contained; thus, the interested reader can choose any chapter and skip to another without losing continuity

CEAS/AIAA/ICASE/NASA Langley International Forum on Aeroelasticity and Structural Dynamics 1999

The proceedings of a workshop sponsored by the Confederation of European Aerospace Societies (CEAS), the American Institute of Aeronautics and Astronautics (AIAA), the National Aeronautics and Space Administration (NASA), Washington, D.C., and the Institute for Computer Applications in Science and Engineering (ICASE), Hampton, Virginia, and held in Williamsburg, Virginia June 22-25, 1999 represent a collection of the latest advances in aeroelasticity and structural dynamics from the world community. Research in the areas of unsteady aerodynamics and aeroelasticity, structural modeling and optimization, active control and adaptive structures, landing dynamics, certification and qualification, and validation testing are highlighted in the collection of papers. The wide range of results will lead to advances in the prediction and control of the structural response of aircraft and spacecraft

Space Programs Summary No. 37-36

Research in systems, guidance and control, space sciences, engineering, telecommunications and propulsion for space exploration program

Correlated uncertainty arithmetic with application to fusion neutronics

his thesis advances the idea of automatic and rigorous uncertainty propagation for computational science. The aim is to replace the deterministic arithmetic and logical operations composing a function or a computer program with their uncertain equivalents. In this thesis, uncertain computer variables are labelled uncertain numbers, which may be probability distributions, intervals, probability boxes, and possibility distributions. The individual models of uncertainty are surveyed in the context of imprecise probability theory, and their individual arithmetic described and developed, with new results presented in each arithmetic. The presented arithmetic framework allows random variables to be imprecisely characterised or partially defined. It is a common situation that input random variables are unknown or that only certain characteristics of the inputs are known. How uncertain numbers can be rigorously represented by a finite numerical discretisation is described. Further, it is shown how arithmetic operations are computed by numerical convolution, accounting for both the error from the input's discretisation and from the numerical integration, yielding guaranteed bounds on computed uncertain numbers. One of the central topics of this thesis is stochastic dependency. Considering complex dependencies amongst uncertain numbers is necessary, as it plays a key role in operations. An arithmetic operation between two uncertain numbers is a function not only of the input numbers, but also how they are correlated. This is often more important than the marginal information. In the presented arithmetic, dependencies between uncertain numbers may also be partially defined or missing entirely. A major proposition of this thesis are methods to propagate dependence information through functions alongside marginal information. The long-term goal is to solve probabilistic problems with partial knowledge about marginal distributions and dependencies using algorithms which were written deterministically. The developed arithmetic frameworks can be used individually, or may be combined into a larger uncertainty computing framework. We present an application of the developed method to a radiation transport algorithm for nuclear fusion neutronics problems

Sensing and real-time expert system for a masonry building robot

The construction industry is striving to eliminate dangerous and repetitive work, as well as increase quality and productivity in the various tasks. For this reason, there is growing interest in the use of automation and robotics. However, the requirements of robots for construction are different from those of industrial robots, due to the characteristics of the construction tasks and the relatively unstructured working environment. The main objective of this research is to investigate the enabling technology for a masonry tasking robot, utilising an experimental robot cell. To truly automate the masonry construction task, there is need to utilise the advancement in robotic technology, especially to deal with the unstructured environment. This view is in-line with this research, which attempts to solve part of the complex problems of automating the building task, by using forms of sensing and intelligence. Concentration on this is the main distinguishing difference between this work and the few other attempts at physical realisation and experimentation in masonry automation. In terms of research and development of masonry tasking machines and robots, there is much activity on an international scale. Concerning the provisions for machine intelligence in this, it appears that the work reported has the most advanced provisions for computer intelligence. This work is of general relevance to construction robots because imprecision, dynamic performance, unplanned events and cell component relocation are considered. The experimental robot cell, built at City University, is used in the research. Standard construction materials have been adopted with imprecise dimensions. Using a CAD/CAM facility, building project designs are translated into robot’s ‘theoretical task’. However, because the masonry material is unpredictable, this can not be directly implemented without real-time adjustments derived from sensing. Not withstanding, advantage is taken of pre-processing, with real-time accommodation of discrepancies, obstacle avoidance and un-planned events. In this, the robot cell performs intelligent processing using rule-based expert systems to carry out the masonry building tasks. Such a process contributes to the fundamental basis for the automation of all stages of building, from architectural planning through to execution of the construction work. A further complication is that the form of a move influences the dynamic response of the robot structure. Therefore, the structural dynamics response of the robot is taken into account in order to optimise performance. Rule based expert systems are investigated to enable a goal driven, intelligent planning approach to be implemented, that can provide an effective dynamic plan for the building task, as well as real-time adjustments to the automatically generated ‘theoretical task’. XXVI