Design Of Such Type Research Articles

Stability of tapered and stepped steel columns with initial imperfections

The elastic stability of eccentrically loaded steel columns with tapered and stepped cross-section and initial imperfection is studied herein. The stability problem is formulated in a manner covering most cases met in design applications. The formulation presented herewith is based on the exact solution of the governing equation for buckling of columns with variable cross-section. A parabolic shape is assumed for the initial imperfection according to EC3 provisions. A plasticity criterion is applied to determine material failure in the buckled configuration. Nonlinear finite element analyses are performed to verify the analytical results. The findings presented in this study can be used for the design of such type of imperfect steel columns.

Response of fiber reinforced plastic chimneys to wind loads

Due to their high corrosion and chemical resistance, fiber reinforced plastics (FRP) are becoming widely used as the main structural material for industrial chimneys. However, no national code currently exists for the design of such type of chimneys. The purpose of this study is to investigate analytically the response of FRP chimneys to wind loads. The classical lamination theory is used to substitute the angle-ply laminate of a FRP chimney with an equivalent orthotropic material that provides the same stiffness. Dynamic wind loads are applied to the equivalent chimney to evaluate its response to both along and across wind loads. A parametric study is then conducted to identify the material and geometric parameters affecting the response of FRP chimneys to wind loads. Unlike the across-wind response, the along-wind tip deflection is found to be highly dependent on the angle of orientation of the fibers. In general, the analysis shows that FRP chimneys are very vulnerable to across-wind oscillations resulting from the vortex shedding phenomenon.

Launched bridges: prestressed concrete bridges built on the ground and launched into their final position

This book is designed to merge the static, organizational, and economic aspects of construction techniques for the launch of monolithic bridges, as these aspects are related to each other and must be considered as a whole in the design of such types of structures. The book is geared toward building contractors, technical and design engineers, and owners, as it can benefit all involved with bridge building.

A Methodology for the Design of Rule-Based Supervisors

This work deals with the introduction of heuristics on the design of digital control systems, so as to combine rule-based techniques with conventional control methods. The heuristics is implemented by means of a rulebased supervisor designed from the expert knowledge about the process. From the expert knowledge about the process it is possible to divide the process operation into a set of so called ‘states’. These ‘states’ may include for instance different operating points in which the system can be considered linear or zones where the system is operating under some type of nonlinearity. For each particular state it is possible to select and tune an appropriate control algorithm (e.g. a linear control algorithm for the former states and fuzzy, neural or rule-based controller for the zone with nonlinear-specific behaviour). The goal of the supervisor, which is executed at each sampling period, is then to track the system operation, detect a system state change and switch to the control algorithm associated to the state reached. A methodology for the design of such type of supervisors is presented. It addresses how the information acquired from the process has to be organized in a simple manner in order to be used to track process transitions between states. In particular, the idea of detector modules, whose function is to establish the tendency of the relevant process signals, is proposed. This information is combined in what is called ‘propositions’. Particular combinations of such propositions control the transitions between states. Finally, the complete state transition diagram is implemented as a set of rules of type if-then-else.

Design of a compliant-cylinder-type fiber-optic accelerometer: theory and experiment

Experimental and theoretical research was carried out in order to establish the dependence of the performance of a compliant-cylinder-based fiber-optic accelerometer on the geometry and elastic properties of the transducer cylinders. The sensitivity and the natural frequency of the sensor were measured as a function of the ratio ε = (inner cylinder diameter)/(outer cylinder diameter). Two transducer materials with different elastic properties, a silicone rubber (Ecosil) and a polyetheretherketone polymer (PEEK 450G), were examined. It was found that with decreasing ε the sensitivity increases in the case of Ecosil and decreases in the case of PEEK. In both cases the natural frequency increases with decreasing ε. A simple analytical model was developed in order to explain this behavior qualitatively. The model takes into account the contributions to the effective stiffness from both the cylinder material and the fiber wrapped around the cylinder. The model is useful for the design of such types of accelerometer.

Discrete-time variable structure control systems

This paper presents a treatment of discrete variable structure control systems. The purpose is to lay a foundation upon which design of such type of systems can be made properly. Phenomena of switching, reaching, and quasi-sliding mode are investigated thoroughly. Terms pertaining to discrete variable structure control are defined. A method of quasi-sliding mode design is given. The inherently existing quasi-sliding mode band is analyzed. A recently introduced "reaching law approach" is conveniently used to develop the control law for robust control. Comments are given regarding chattering. The design technique is illustrated by a simulated system.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>