Frédéric Légeron

BEHAVIOR OF HIGH-STRENGTH CONCRETE COLUMNS UNDER CYCLIC FLEXURE AND CONSTANT AXIAL LOAD

In this study, six large-scale columns made of high-strength concrete (HSC) were subjected to constant axial loads corresponding to target values of 15%, 25%, and 40% of the column axial-load capacity and a cyclic horizontal load-inducing reversed bending moment. Results reveal that tie spacing, and therefore tie volumetric ratio and axial-load level, have significant effects on the flexural behavior of HSC columns. The need to include the axial-load level in code requirements for confinement reinforcement is pointed out.

PREDICTION OF MODULUS OF RUPTURE OF CONCRETE

Tensile strength of concrete is an important parameter for determining deflection and minimum flexural reinforcement. Many design codes use the modulus of rupture as the cracking strength. Relations giving the modulus of rupture as a function of concrete compressive strength are based on tests on concrete with a compressive strength lower than 40 MPa. This study presents a statistical study on 395 data points from a large number of research programs with concrete compressive strength ranging from 20 MPa to 130 MPa. It further reveals that the data are largely scattered and that minimum, mean, and maximum values for the modulus of rupture should be defined. New relations are proposed by giving the modulus of rupture as a function of the square root of the compressive cylinder strength of concrete and the compressive cylinder strength of concrete raised to the 2/3 power. The use of the new relations in design codes is illustrated.

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.

A Checking Method for Multiple Seismic Performance Objectives of Bridge Piers Designed According to Code Provisions

Seismic bridge design codes require that bridge piers designed according to prescribed design rules should attain specified multiple seismic performance objectives. However, design codes do not explicitly require checking the attainment of specified performance objectives for designed bridge piers. In this article, seismic performance levels have been correlated with engineering damage parameters. A checking method for multiple seismic performance objectives of bridge piers has been outlined and validated with experimental results. The application of the method has been demonstrated by checking the performance of a bridge pier designed according to a code provision for a wide range earthquake ground motions.

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.

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.