Abstract
Light weight superstructure is beneficial for bridges in remote areas and in emergency erection. In such weight sensitive applications, combination of fibre reinforced plastics (FRP) as material and box-girders as a structural system have great scope. This combination offers various options to tailor structure and its elements but this flexibility poses greater challenge in optimum design. In this paper a procedure is derived for a generalised optimum design of FRP box-girder bridges, using genetic algorithms (GA). The formulation of the optimum design problem in the form of objective function and constraints is presented. Size, configuration and topology optimization are done simultaneously. A few optimum design studies are carried out to check the performance of the developed procedure and to get trends in the optimum design which will be helpful to the new designers.
Key Words
box-girder; FRP; bridge; optimum design; genetic algorithms.
Address
Akhil Upadhyay: Department of Civil Engineering, IIT Roorkee, Roorkee 247667, India
V. Kalyanaraman: Department of Civil Engineering, IIT Madras, Chennai 600036, India
Abstract
Shallow fixed arches have a nonlinear primary equilibrium path with limit points and an unstable postbuckling equilibrium path, and they may also have bifurcation points at which equilibrium bifurcates from the nonlinear primary path to an unstable secondary equilibrium path. When a shallow fixed arch is subjected to a central step load, the load imparts kinetic energy to the arch and causes the
arch to oscillate. When the load is sufficiently large, the oscillation of the arch may reach its unstable equilibrium path and the arch experiences an escaping-motion type of dynamic buckling. Nonlinear dynamic buckling of a two degree-of-freedom arch model is used to establish energy criteria for dynamic buckling of the conservative systems that have unstable primary and/or secondary equilibrium paths and then the energy criteria are applied to the dynamic buckling analysis of shallow fixed arches. The energy approach allows the dynamic buckling load to be determined without needing to solve the equations of
motion.
Key Words
dynamic buckling; energy conservation; escaping-motion; lower dynamic buckling load; nonlinear equilibrium path; step loading of infinite duration; upper dynamic buckling load.
Address
Yong-Lin Pi: School of Civil and Environmental Engineering, Faculty of Engineering and Information Technology,
University of Technology, Sydney, Broadway, NSW 2007, Australia
Mark Andrew Bradford: School of Civil and Environmental Engineering, Faculty of Engineering and Information Technology,
University of Technology, Sydney, Broadway, NSW 2007, Australia
Weilian Qu: Key Laboratory of Roadway Bridge and Structural Engineering, Wuhan University of Technology, Wuhan 430070, China
Abstract
An energy-based fatigue life prediction framework was previously developed by the authors for prediction of axial, bending and shear fatigue life at various stress ratios. The framework for the prediction of fatigue life via energy analysis was based on a new constitutive law, which states the following: the amount of energy required to fracture a material is constant. In the first part of this study, energy expressions that construct the constitutive law are equated in the form of total strain energy and the distortion energy dissipated in a fatigue cycle. The resulting equation is further evaluated to acquire the equivalent stress per cycle using energy based methodologies. The equivalent stress expressions are
developed both for biaxial and multiaxial fatigue loads and are used to predict the number of cycles to failure based on previously developed prediction criterion. The equivalent stress expressions developed in this study are further used in a new finite element procedure to predict the fatigue life for two and three dimensional structures. In the second part of this study, a new Quadrilateral fatigue finite element is developed through integration of constitutive law into minimum potential energy formulation. This new QUAD-4 element is capable of simulating biaxial fatigue problems. The final output of this finite element
analysis both using equivalent stress approach and using the new QUAD-4 fatigue element, is in the form of number of cycles to failure for each element on a scale in ascending or descending order. Therefore, the new finite element framework can provide the number of cycles to failure at each location in gas turbine engine structural components. In order to obtain experimental data for comparison, an Al6061-T6 plate is tested using a previously developed vibration based testing framework. The finite element analysis is performed for Al6061-T6 aluminum and the results are compared with experimental results.
Key Words
cycles; equivalent stress; energy; fatigue; finite element analysis; structures; uniaxial.
Address
Wasim Tarar: Department of Aerospace Engineering, The Ohio State University, Columbus, OH 43210, USA
M.-H. Herman Shen: Department of Aerospace Engineering, The Ohio State University, Columbus, OH 43210, USA
Tommy George: Air Force Research Laboratory Wright-Patterson AFB, OH 45433, USA
Charles Cross: Air Force Research Laboratory Wright-Patterson AFB, OH 45433, USA
Abstract
The seismic performance of reinforced concrete (RC) bridge columns is a significant issue because the interaction of flexural ductility and shear capacity of such columns with varied amounts of lateral reinforcement is not well established. Several relationships between flexural ductility and shear capacity have been proposed by various researchers in the past. In this paper, a parametric study on RC bridge columns is conducted using a nonlinear finite element program,
Key Words
reinforced concrete; bridge columns; ductility; shear capacity.
Address
Rachel Howser: Department of Civil and Environmental Engineering, University of Houston, Houston, 77204-4003, USA
A. Laskar: WorleyParsons, Houston, 77094, USA
Y.L. Mo: Department of Civil and Environmental Engineering, University of Houston, Houston, 77204-4003, USA
Abstract
Different types of moment resisting connections are commonly used to transfer the induced seismic moments between frame elements in an earthquake resisting structure. The local connection behavior may drastically affect the global seismic response of the structure. In this study, the finite element and experimental seismic investigations are implemented on two frequently used connection type to evaluate the local behavior and to reveal the failure modes. An alternative connection type is then proposed to eliminate the unfavorable brittle fracture modes resulted from probable poor welding quality.
This will develop a reliable predefined ductile plastic mechanism forming away from the critical locations. Employing this technique, the structural reliability of the moment resisting connections shall be improved by achieving a controllable energy dissipation source in form of yielding of the cover plates.
Key Words
steel frames; moment connections; experimental testing; finite element analysis; earthquake resisting structures; rotational ductility.
Address
Hooman Farrokhi: Civil Engineering Department, KN Toosi University of Technology, Tehran, Iran
F. Ahmadi Danesh: Civil Engineering Department, KN Toosi University of Technology, Tehran, Iran
Sassan Eshghi: International Institute of Earthquake Engineering and Seismology, Tehran, Iran
Abstract
A numerical procedure for the geometrical and material nonlinear analysis of concrete beams prestressed with external tendons is described, where the effects of external prestressing are treated as the equivalent loads applied on the concrete beams. The geometrical nonlinearity is considered not only the eccentricity variations of external tendons (second-order effects) but also the large displacement effects of the structure. The numerical method can predict the nonlinear response of externally prestressed concrete beams throughout the entire loading history with considerable accuracy. An evaluation of second-order effects of externally prestressed concrete beams is carried out using the proposed analysis. The analysis
shows that the second-order effects have significant influence on the response characteristics of externally
prestressed concrete beams. They lead to inferior ultimate load and strength capacities and a lower ultimate stress increase in tendons. Based on the current analysis, it is recommended that, for simplysupported externally prestressed beams with straight horizontal tendons, one deviator at midspan instead of two deviators at one-third span be furnished to minimize these effects.
Address
Tiejiong Lou: Department of Structural and Geotechnical Engineering, Politecnico di Torino, Torino 10129, Italy
Yiqiang Xiang: Department of Civil Engineering, Zhejiang University, Hangzhou 310058, P.R. China
Abstract
In this study, the Differential Transform Method (DTM) is employed in order to solve the governing differential equation of a moving Bernoulli-Euler beam with axial force effect and investigate its free flexural vibration characteristics. The free vibration analysis of a moving Bernoulli-Euler beam using DTM has not been investigated by any of the studies in open literature so far. At first, the terms are found directly from the analytical solution of the differential equation that describes the deformations of
the cross-section according to Bernoulli-Euler beam theory. After the analytical solution, an efficient and easy mathematical technique called DTM is used to solve the differential equation of the motion. The calculated natural frequencies of the moving beams with various combinations of boundary conditions using DTM are tabulated in several tables and are compared with the results of the analytical solution where a very good agreement is observed.
