Pierre Léger

Polytechnique Montréal · Department of Civil, Geological and Mining Engineering

Concrete spillways are three-dimensional structures that are particularly vulnerable to earthquakes with a strong component occurring in the direction of the weak axis of the piers. This paper presents a progressive three-dimensional structural analysis methodology to assess the seismic stability of spillway piers. The methodology is based on four...

The presence of uplift pressures in cracked plain concrete hydraulic structures is a major concern for their durability, serviceability and stability. To assess the performance of cracked structures several mechanical and hydraulic response parameters must be computed. This paper presents the development, implementation and application of a new non...

The presence of uplift pressures in cracked plain concrete hydraulic structures is a major concern for their durability, serviceability and stability. To assess the performance of cracked structures several mechanical and hydraulic response parameters must be computed. This paper presents the development, implementation and application of a new non...

XFEM animation of the propagating crack in the Alqueva arch dam

This paper presents a novel and robust three-dimensional plain concrete cracking model applicable to the study of structural stability of large structures, such as dams, while considering the presence of pressurized water in propagating cracks. When leaving the elastic range, there is a transition from a continuum approach to a XFEM approach. This...

This paper presents a new higher order 3D fiber element using beam theory leading to a 18x18-stiffness matrix including shear and torsional warping. This element is used to analyze the structural response of concrete spillway piers with deep variable cross-sections subjected to 3D loads. The element stiffness matrix is computed from numerical integ...

Several hydraulic concrete structures suffer from severe tridimensional (3D) discrete cracking, producing an assembly of concrete blocks resting one on top of the other. It is important to consider the 3D particularities of the cracked surfaces in the nonlinear sliding safety evaluation of these structures. A methodology to assess a sliding safety...

To evaluate the modulus of rupture and the shear strength of mass concrete repaired by grout injection, six 400 x 400 x 1250 mm (16 x 16 x 49.2 in.) concrete specimens with a maximum aggregate size of 100 mm (4 in.) were tested following ASTM C78, third-point bending test, and a loading configuration promoting large shear stresses along a vertical...

This paper presents the effectiveness of seven ground motion scaling methods and two spectral matching methods to achieve compatibility with the Canadian National Building Code (CNBC) 2005 uniform hazard spectrum for Montreal to perform nonlinear seismic analysis. Databases of 30 historical records and 30 Eastern North America simulated records hav...

This paper presents a crack model that couples the benefits of the damage mechanics approach and the extended finite element method (XFEM). A crack-tracking technique is developed to propagate the crack path along a single row of finite elements as a function of the stress-based nonlocal method. The level sets are computed to predict the crack path...

In several northern regions around the world, concrete dams are subjected to severe seasonal temperature variations, with up to 75 degrees C changes from summer to winter. Those variations contribute to the degradation of the stiffness, strength, and durability of concrete dams. Thermal stresses and related concrete cracking also need to be evaluat...

This paper presents a crack model that couples the benefits of the damage mechanics approach and the extended finite element method (XFEM). A local crack-tracking technique is developed to propagate a crack pattern along a single row of finite elements as a function of the equivalent principal stress direction. The level-sets are computed to predic...

Factors of safety are applied to accommodate uncertainties in the assumptions for load, resistance, and model parameters. The sources of uncertainty are physical variability inherent in nature, statistical uncertainty of input data, and limited knowledge. This paper analyses the effect on safety when curbing uncertainly. It argues that deterministi...

Seasonal thermal stresses have been found to contribute significantly to the long-term degradation of strength and stiffness of concrete dams located in northern regions. Temperature variations and the associated thermal stress and strain must be evaluated to define the initial loading conditions for safety analyses and develop defensive measures t...

The thermal response of a typical dam–foundation–reservoir system, using the methodology described in part 1, is presented. Extensive parametric analyses are performed to determine the relative influence, on the thermal and stress–strain responses of the system, due to (i) the geometrical, thermal, and mechanical properties of the dam, (ii) the res...

Nonlinear seismic analyses of a 90 m high concrete gravity dam, assumed to be located in eastern Canada, have been conducted using a smeared crack finite element model. Reduced frequency-independent added matrices have been used to represent the hydrodynamic and foundation interaction effects. Parametric analyses have been performed to assess the e...

The seismic safety of concrete dams is a matter of serious concern around the world. During severe ground motions, the dams are likely to experience cracking due to low tensile resistance of concrete. Several analytical methods have been proposed in the literature for finite element crack propagation analysis of concrete structures. Due to lack of...

This paper presents elastic and inelastic response spectra of strong motion accelerograms recorded during the 1988 Saguenay earthquake. Comparisons are made with the National Building Code of Canada (NBC) 1990 lateral forces requirements for the seismic resistant design of short-period structures. The use of a period-dependent force modification fa...

Seasonal temperature displacements are an important component of the total displacements recorded by pendulum measurements at gravity dams located in northern regions. A hybrid dam displacement model is presented in this paper to interpret these displacements and extrapolate the response for an extreme thermal event not yet experienced by the dam....

Microcomputers are currently used to solve linear problems in structural dynamics. However, realistic engineering applications require a large amount of processing operations such that computer execution time and storage requirements can become critical. It is shown in this paper that the solution of large three-dimensional linear dynamic problems...

This paper develops a methodology to perform seismic response analyses of concrete gravity dams considering aftershocks, and reduced drainage efficiency due to disruption of the drainage system. A database of earthquake records has been assembled to characterize main shocks and aftershocks. A drain finite difference hydraulic model considering lami...

Grouting is often considered to reinstate water tightness and displacement continuity in cracked concrete dams. Grouting alters the state of stress, deformation, and the strength of a dam in many ways. The state of stress prior to grouting is altered by the injection pressure that often increases the crack opening. This new state of stress will be...

A semi-continuum structural analysis methodology is developed to evaluate the seismic response of shear soil–building systems. The method of dynamic substructuring and closed-form continuum formulation of modal properties of shear media is used to directly construct the soil–building system matrices. The structural behaviour of the complete system...

Structural models of large space structures have a substantial number of degrees of freedom (DOF) and possess semi-positive-definite stiffness matrices. The paper presents an efficient co-ordinate reduction procedure for structural dynamic analysis of large space structures. The method is based on the superposition of load-dependent Ritz vectors, w...

A method is presented for evaluating the fatigue of offshore structural steel members based on structural component reliability procedures coupled with spectral analysis methods. The approach is based on formulating a nonlinear performance function that expresses the cumulative fatigure damage in the form of Miner's rule. Uncertainties in the cumul...

The response of offshore structures subjected to wave loading is generally dominated by pseudo-static behaviour which is not efficiently expressed in truncated modal co-ordinates. In this paper, a new and efficient method has been developed to reduce modal truncation error in the numerical evaluation of transfer functions for the wave response of o...

The purpose of this Note is to discuss practical implementation aspects of dynamic substructuring method related to the algorithm used to generate transformation vectors and the corresponding evaluation of error norms. A new computational variant that combines the subspace generation of load-dependent vectors and the static condensation technique i...

Analytical methods for the seismic analysis, design and safety evaluation of dam-foundation-reservoir systems require the solution of large systems of dynamic equilibrium equations. Efficient coordinate reduction procedures are presented for this purpose. It is shown that a new method of solution based on a Ritz transformation to a reduced system o...

A generation procedure of Ritz vectors to control the inclusion of static effect and the number of vectors in mode superposition dynamic analysis is presented. The original algorithm of the Ritz vectors15 is modified to improve stability in the generation procedure and to include the use of static residual. To reject unimportant Ritz vectors, cut-o...

The rate of convergence of the conventional mode superposition method can be significantly improved for systems subjected to relatively low frequency loadings by adding static correction terms to approximate the contribution of higher modes neglected by the use of a truncated eigenbasis. Two computational variants of the classical mode-acceleration...

The evaluation of linear dynamic response analysis of large structures by vector superposition requires, in its traditional formulation, the solution of a large and expensive eigenvalue problem. A method of solution based on a Ritz transformation to a reduced system of generalized coordinates using load dependent vectors generated from the spatial...

This paper presents the results of an experimental investigation aimed at the development of moment connections for precast reinforced concrete members. Two types of moment connections were tested. Type 1 moment connections are made by welding reinforcing bars protruding from the column to a steel plate welded to the tension reinforcement of the be...

Thesis (Ph. D. in Engineering)--University of California, Berkeley, May 1986. Includes bibliographical references (leaves 233-243).