Wire rope in civil engineering applications

J.P. Gourmelon
ODN 0725

As indicated during the previous OIPEEC General Assembly in Krakow, activity of WG4 "wire ropes in civil engineering applications" officially approved during in Delft on September 1993 covers in fact the research program initiated in LCPC. That programme was carried out in co-operation with several French universities namely: Ecoles Centrales Group (Paris, Nantes, Lyon), Joseph Fourier University (Grenoble).

The aim of the research program is to get a better understanding of the high cycle fatigue behaviour of cables used in civil engineering applications and particularly under free bending solicitations.

According to the main guidelines of the research program and following the organisation scheme as published in OIPEEC Bulletin 78 the main results of studies are as follows:

1. Collection of information and load effects

• The Burgundy cable-stayed bridge was equipped with a specific prototype instrumentation using "smart sensors" for service measurement of the forces and angular deviations of stay cables,  Extreme traffic effects were calculated as well as rain-flow histograms. A specific unit of "Castor-LCPC" software was set up allowing validation of calculation modelling for engineers.
• Wind and temperature effects are still pending.
• About vibrations of cables, vibrating method for tension measurement was improved and applied to several anchorage conditions; a universal damping curve was set up making easier the design of dampers.
• A new long-term measurement campaign is expected as well as industrial stage for the "smart sensors" equipment.

2. Local stress calculation

• Calculation models were settled for normal and contact stresses in wires under tension and free bending, taking into account inter-wire slipping effect on bending stiffness of the cables.

3. Theoretical study of fatigue

• Numerical models were developed for calculation of critical stresses in wires with line or cross inter-wires contact
• Use an uni-axial criterion for determining fatigue limits under fretting conditions was validated, allowing simpler hypothesis than for a multi-axial one.

4. Experimental study of fatigue and identification of damages

• All calculation models were validated by experimentation using fretting fatigue tests or free bending tests, as well for local stresses as for fatigue behaviour.
• Main phenomena affecting fretting fatigue behaviour were clarified such as change in contact surface due to wear or increase of friction coefficient.
• Critical configuration was determined, which corresponds to partial slipping (or full slipping with small range) at inter-wires cross contact.

For the time being, results of the research program make possible endurance limit prediction for multi-layers strands by comparison of a fatigue limit curve with "functioning points" conditions, those being situated at inter-wires cross contacts.

Some improvements are expected by more thorough exploitation of fretting fatigue tests results, so as to introduce accurate parameters in calculation models.

Further developments are also expected concerning vibration effects due to wind in order to establish links between wind speed and direction measurements on one side and tension or bending angle values at anchorage level.

For further information please contact:

Jean-Paul Gourmelon
37bis rue des Grands Noëls
F 44230
Saint Sébastien sur Loiren
France

E-mail: Jean-Paul Gourmelon