René Tinawi

Evolution of seismic design provisions in the National building code of Canada

The purpose of this paper is to provide a summary of the evolution of seismic design in Canada. This paper presents the significant changes to the approach taken in determining seismic hazards and seismic hazard maps, and describes the evolution of the seismic design provisions of the National building code of Canada. The introduction of important parameters in determining the seismic base shear such as the period of vibration of the structure, the influence of type of soil, and the concepts of ductility and energy dissipation capacity of elements and structures are presented. The levels of seismic design base shears, determined from different versions of the National Building Code of Canada, are compared for reinforced concrete frame and wall structures to illustrate the changes.

Computer aided stability analysis of gravity dams: CADAM

This paper presents the main features and organisation of CADAM, a computer program, freely available, that has been developed for the static and seismic stability evaluations of concrete gravity dams. CADAM is based on the gravity method using rigid body equilibrium and beam theory to perform stress analyses, compute crack lengths, and safety factors. Seismic analyses could be done using either the pseudostatic or a simplified response spectrum method. CADAM is primarily designed to provide support for learning the principles of structural stability evaluation of gravity dams. It could also be used for research and development on stability of gravity dams. In adopting several different world-wide published dam safety guidelines, a large number of modelling options have been implemented. These include (i) crack initiation and propagation, (ii) effects of drainage and cracking under static, seismic, and post-seismic uplift pressure conditions, and (iii) safety evaluation procedures using deterministic, allowable stresses and limit states probabilistic analyses (Monte-Carlo simulations). Structural stability evaluation of a 30 m dam is presented to illustrate the use of CADAM.

Mathematical modeling of the transient response of electric transmission lines due to conductor breakage

Abstract Nonlinear dynamic analyses are performed using ADINA with four idealizations of a smallscale model of a transmission line section subjected to a conductor breakage condition. Results indicate that higher frequency components of the response must be filtered out in order to achieve numerical stability. Accuracy is obtained provided the effect of the propagating stress wave is integrated frequently enough, both in time and space. Comparisons of the transient response with experimental results reported by Mozer et al . ( IEEE Trans. Power Apparatus Systems 100 , 938–947, 1981) confirm the validity of the proposed mathematical models.

On the computation of seismic energy in inelastic structures

Abstract The explicit computation of energy balance for structures subjected to seismic excitation is useful to assess the accuracy with which dynamic equilibrium is achieved in each time-step. Examples on the use of the energy balance concept are presented in the first part of this paper for simple inelastic structures excited by various ground motions. It is shown how the energy approach can guide the designer in appreciating the nonlinear behaviour of the structure, the hierarchy of mechanisms that occur in time, and the ductility requirements of the various components. This was achieved using an unconditionally stable time marching algorithm with no algorithmic damping. A parametric study is then presented on the influence of algorithmic damping on seismic energy response of multi-degree-of-freedom structures. Finally, the Newmark-Beta method, with and without algorithmic damping, and the Alpha method are used in comparative analyses to evaluate the response of bilinear hysteresis models of multi-degree-of-freedom structures.

Finite element stress tensor fields interpolation and manipulation using 3D dual kriging

Abstract Three-dimensional dual kriging theory, commonly applied in geostatistics, is used in a novel way for the interpolation and manipulation of 3D stress tensor fields. The application of this technique provides a designer with a way of visualizing the results and an appreciation of the errors in the finite element model. Applications of this technique are described using simple as well as complex structures.

ORTHOTROPIC BRIDGE DECKS WITH CLOSED STIFFENERS - ANALYSIS AND BEHAVIOUR

Abstract The behaviour of stiffened bridge decks is investigated. The deck is treated not as an equivalent continuum but as a monolithic unit in which all the interactions are considered. A rectangular shell finite element is developed which is suitable for the idealization and efficient analysis of closed type stiffeners. Solutions are compared with three experimental tests of closed type stiffeners of trapezoidal shape. These and other examples show excellent agreement with the analysis. An investigation of the effect of one of the principal parameters entering the problem is presented. This concerns the rib spacing for torsionally stiff ribs, and results obtained indicate that present design methods are conservative in some areas, but are slightly unconservative in others.

Comportement d'un cadre rempli soumis à un chargement cyclique: modélisation pour une analyse dynamique non linéaire

This paper presents the results of an experimental program investigating the behavior of a steel frame with masonry infill panels subjected to cyclic loadings. Three types of masonry frequently use...

Experimental and Numerical Predictions of Critical Cooling Temperature for Crack Propagation in Concrete Structures

This paper describes an experimental program to induce thermal fracture in notched unreinforced concrete wall specimens subjected to severe cooling thermal gradients. The variations of the compressive and tensile strengths, the elastic modulus, the fracture energy Gf, and the coefficient of thermal expansion of concrete over a temperature range varying from 20 deg C to -40 deg C have been determined from tests on standard cylinders and three-point bending tests of notched beams. Correlations between experimentally determined critical temperature conditions to propagate a crack from an existing notch and linear elastic, elastobrittle, and Gf-type smeared cracked thermomechanical finite element analyses are presented. It is shown that a good correlation between the experimental and numerical cracking predictions from the thermoelastic response could be obtained using a thermal stress relaxation factor of the order of 0.35. Nonlinear finite element analyses using Gf-type crack models have indicated that there is a large difference between the tensile softening initiation temperature state and the temperature state for complete cracking. The tensile stress-temperature postpeak response is strongly influenced by the magnitude of the fracture energy selected for the analysis.

Response Spectra For Structures On Soft Soils In Eastern Canada

INTRODUCTION Transactions on the Built Environment vol 3,

Comportement dynamique d'une éolienne à axe vertical (application pratique)

The dynamic behaviour of the vertical axis wind turbine of the EOLE Project is examined using a special purpose program developed for extracting the complex frequencies and mode shapes of the structure. The precise evaluation of the frequencies is an important step in the design process, to detect any dynamic instabilities of the rotor for a given speed. Gyroscopic effects and geometric nonlinearities due to centrifugal and gravity forces as well as the vertical compression due to the tension of the guys are also considered. Nonlinear behaviour of the guys is also accounted for. The influence of the variation in the stiffness of the guys on the dynamic behaviour is examined specifically for the EOLE Project. Results indicate that this effect is not important if the initial tension in the guy is high. Key words: Vertical axis wind turbines, guys, complex frequencies, complex mode shapes, centrifugal forces, Coriolis forces, Campbell diagrams, numerical software.