Sébastien Langlois

Strengthening of the net section of steel elements under tensile loads with bonded CFRP strips

AbstractThe use of carbon-fiber-reinforced polymer (CFRP) is an increasingly common solution for the strengthening of structures. However, the majority of research and applications have focused on the retrofitting of concrete structures. The applications of adhesively bonded CFRP to enhance the load-carrying capacity of metallic elements has been widely studied in the aeronautical industry, but it is also a promising technique for the area of civil engineering. This paper presents an experimental study that was designed to verify the effectiveness of the use of CFRP for the strengthening of the net section of steel elements under tensile loading. A series of tensile tests were conducted with different bond lengths, number of layers, and surface preparations of the steel. The specimens consisted of double lap joints and steel plates with various hole configurations. The ultimate load, the failure mode, and the effective bond length for CFRP-strengthened specimens were determined. The results showed that us...

Prediction of Aeolian Vibration on Transmission-Line Conductors Using a Nonlinear Time History Model—Part II: Conductor and Damper Model

Various numerical tools have been developed to predict the level of aeolian vibrations for a damped span of transmission-line conductors. In part I of this study, nonlinear time history models of two types of transmission-line dampers were developed. In this paper, a model for the complete conductor-damper system is presented. When combined with empirical equations for wind power input and conductor self-damping using the Energy Balance Principle, the direct integration time history model proposed allows the prediction of the vibration amplitudes expected on a damped span. The amplitudes predicted by the model compare well to experimental data sets available in the literature. Since the damper is modelled from its mechanical properties of geometry, mass, stiffness, and damping, the optimization of a conductor-damper system can be done easily with this model, without additional experimental tests. A sensitivity analysis is conducted to demonstrate the capabilities of the model.

Prediction of Aeolian Vibration on Transmission-Line Conductors Using a Nonlinear Time History Model—Part I: Damper Model

Stockbridge dampers, which consist of a clamp, a messenger cable, and two attached masses, have been successfully used throughout the world for many decades to provide additional damping to transmission-line conductors and reduce aeolian vibration amplitudes. An alternative damper, the Hydro-Québec damper, has a rotational joint with elastomer cylinders to provide stiffness and damping. The objective of this study is to develop a nonlinear model for both types of dampers that predicts their dynamic response for all expected amplitudes and frequencies. These models are built from simple experimental characterization tests to identify stiffness and damping properties. As a validation of the models, the force and phase shift with respect to frequency are obtained numerically and compared successfully to experimental results. These models will be fixed to a conductor model in Part II to predict aeolian vibration amplitudes of damped spans.

Time History Modeling of Vibrations on Overhead Conductors With Variable Bending Stiffness

Although bending stiffness of cables is small, it has a large influence on the deformed shape near constraints. A practical application where it is important is for the prediction of the deflection curve of transmission-line conductors during aeolian vibrations. These vortex-induced vibrations may cause fretting fatigue failure at or near the location of clamped devices. The objective of this paper is to model with a nonlinear time history finite-element analysis the deformed shape of conductors during aeolian vibrations using available bending stiffness models. The deformed shape obtained numerically is compared to laboratory measurements available in the literature. It was found that theoretical bending stiffness models can be used to predict the deformed shape of cables near the clamps. However, the results obtained with variable bending stiffness are not significantly more accurate than those for a constant bending stiffness equal to half of the maximum theoretical bending stiffness. In general, the variation of bending stiffness found experimentally is less important than the prediction of nonlinear models. The dynamic nonlinear numerical method presented here remains a powerful tool for the prediction of the deformed shape of vibrating conductors.

Experimental Study of Dynamic Bending Stiffness of ACSR Overhead Conductors

Aeolian vibrations of transmission-line conductors may cause fretting fatigue failure at or near the location of clamped devices. At these locations, the bending stiffness variation of the conductor has a large influence on its deformed shape and, hence, on its fatigue mechanics. Variable bending stiffness models could be integrated in nonlinear finite-element programs to obtain better mechanical behavior predictions. However, there is very little data available in the literature to validate such numerical models. The objective of this paper is to present experimental data for the deformed shape of two types of ACSR conductors undergoing vibrations. The tests were performed on a 5.83-m test bench for various tensions, displacement amplitudes, and frequencies. The displacement amplitude was measured at the vibration anti-node and at five locations near the square-faced bushing. The results suggest a large stiffness variation near the bushing. This experimental study provides valuable data to compare with a numerical model of a vibrating conductor that includes variable bending stiffness.

Numerical Analysis of ACSR Conductor–Clamp Systems Undergoing Wind-Induced Cyclic Loads

Submitted to wind-induced vibrations, overhead conductors are vulnerable to fatigue damage, especially at restraining fixtures such as the suspension clamp. This paper proposes an efficient finite-element modeling approach providing a full 3-D representation of both the conductor and suspension clamp. Validation based on experimental data shows the precision of the approach. An in-depth model response analysis also demonstrates its ability to describe inter-wire and conductor–clamp contact interactions. Finally, a study of conductor stress distributions reveals that in critical regions, conductor wires mostly sustain alternating bending loads.

Effect of geometric parameters on the behavior of bolted GFRP pultruded plates

This paper presents the effect of geometric parameters on the behavior of bolted glass fibre reinforced polymer (GFRP) pultruded plates for civil engineering applications. After a literature review, results of an experimental analysis investigating the behavior of GFRP-to-steel single-lap bolted connections are presented. Then, a finite element analysis validated by experimental data is used to evaluate the effects of the end-distance, side-distance, pitch, and plate properties on the strength and failure mode of the connection. A critical examination of geometric recommendations proposed in design references is presented. Bearing failure caused by contact of the bolt on the GFRP plate is usually defined as the preferred failure mode. With highly orthotropic plate, this type of failure was found to be less likely to occur when loading is applied in the pultruded direction. The investigation showed that the minimum end-distance and pitch-distance recommended by design references usually produce a connection with the maximum capacity. However, it was found that the minimum side-distance recommended by these references does not necessarily lead to the maximum capacity for one bolt and for two bolt in a column connections.

Vulnerability analysis of transmission towers subjected to unbalanced ice loads

This paper presents a probabilistic framework for vulnerability analysis of electric transmission towers subjected to unbalanced ice loads using the concepts of statistical learning theory (SLT). Based on SLT, the implicit limit state function of each element is replaced by an approximate polynomial function that has good prediction properties. The results are presented in the form of fragility curves for 3 different unbalanced loading scenarios of longitudinal, transverse and torsional loadings. Such fragility information provides us with a better understanding of the behavior of various components of the line under different climatic conditions. It can also be used to evaluate existing transmission towers and to optimize the design of new ones. This paper further studies the effect of various design parameters such as wind speed and direction, icing rate and location of ice formation on the fragility curves of tension and suspension towers. The results show higher failure probabilities for suspension towers than tension towers. The results also indicate that for most conditions, longitudinal loads are more important than other unbalanced loading scenarios. Finally, this study concludes that wind speed, wind direction and ice accumulation rate have notable effects on the fragility curves.

A probabilistic framework based on statistical learning theory for structural reliability analysis of transmission line systems

Abstract This paper describes a novel application of statistical learning theory to structural reliability analysis of transmission lines considering the uncertainties of climatic variables such as, wind speed, ice thickness and wind angle, and of the resistance of structural elements. The problem of reliability analysis of complex structural systems with implicit limit state functions is addressed by statistical model selection, where the goal is to select a surrogate model of the finite element solver that provides the value of the performance function for each conductor, insulator or tower element. After determining the performance function for each structural element, Monte Carlo simulation is used to calculate their failure probabilities. The failure probabilities of towers and the entire line are then estimated from the failure probabilities of their elements/components considering the correlation between failure events. In order to quantify the relative importance of line components and provide the engineers with a practical decision tool, the paper presents the calculation of two types of component importance measures. The presented methodology can be used to achieve optimised design, and to assess upgrading strategies to increase the line capacity.

Implementation of a Simplified Method in Design of Hysteretic Dampers for Isolated Highway Bridges

AbstractUsing seismic isolation systems for highway bridges modifies the structure’s principal vibration modes and effectively reduces the seismic base shear conveyed from the superstructure to the substructure. However, for some low-damping rubber isolation bearings, large displacements can be a problem. Supplemental hysteretic dampers can be introduced into the base-isolated bridge, which might nevertheless increase the structure base shear, and the merit of adding dampers has to be evaluated properly. In this paper, a simplified method was implemented for the design of a low-cost hysteretic damper, and the resulting isolator-damper system was tested experimentally. The design method used is based on an equivalent linearization approach. A full-scale elastomeric isolation bearing was characterized and used in the design of a hysteretic damper. Both the isolator and the damper went through cyclic testing and real-time dynamic substructuring (RTDS) methods to verify the capacity of the method to design ba...