Water distribution in beams damaged by alkali-silica reaction: global weighing and local gammadensitometry

International audienceWithin the framework of an experimental programme developed by the Laboratoire Central des Ponts et Chaussees (LCPC) and Electricite de France (EDF), in the aim of increasing knowledge on Alkali-Silica Reaction (ASR) and understanding the effect of water on ASR development in structures, two techniques have been designed to measure water content vs. time in large-scale concrete specimens. Global weighing variations are monitored on six 900 kg beams; and the gammadensitometry measurement allows evaluating water content profiles in the beams. These two complementary measurements serve to validate water content models and correlate the moisture gradient with measured deformations. The measurement principle, execution and qualification are first described. The accuracy of the weighing device is thus evaluated at 10 g, and the uncertainty of the gammadensitometry method is close to 0.4% of relative mass. The paper then presents the results of one-year monitoring conducted on one of these beams and proves the consistency of these methods. At last, it is shown that the square root of time kinetics allows a good representation of the global mass variations of the beams, and that the drying depth reaches between 80 and 100 mm after one year exposure

Unimodal optimal passive electromechanical damping of elastic structures

In this paper, a new electromechanical damper is presented and used, made of a pendulum oscillating around an alternator axis and connected by a gear to the vibrating structure. In this way, the mechanical energy of the oscillating mass can be transformed into electrical energy to be dissipated when the alternator is branched on a resistor. This damping device is intrinsically non-linear, and the problem of the optimal parameters and of the best placement of this damper on the structure is studied. The optimality criterion chosen here is the maximum exponential time decay rate (ETDR) of the structural response. This criterion leads to new design formulas. The case of a bridge under construction is considered and the analytical results are compared with experimental ones, obtained on a mock-up made of a vertical tower connected to a free-end horizontal beam, to simulate the behavior of a cable-stayed bridge during the erection phase. Up to three electromechanical dampers are placed in order to study the multi-modal damping. The satisfactory agreement between the theoretical model and the experiments suggests that a multi-modal passive damping of electromagnetic type could be effective on lightweight flexible structures, when dampers are suitably placed

Experimental determination of the stress evolution in a prebent steel-VHPC composite beam by means of an active stressmeter

info:eu-repo/semantics/publishe

Détermination expérimentale de l’évolution des contraintes dans une poutre mixte acier-BTHP préfléchie au moyen d’un contraintemètre actif

info:eu-repo/semantics/publishe

Détermination expérimentale de l’évolution des contraintes dans une poutre mixte acier-BTHP préfléchie au moyen d’un contraintemètre actif

info:eu-repo/semantics/publishe

Experimental determination of the stress evolution in a prebent composite steel-VHPC beam by means of an active stressmeter

info:eu-repo/semantics/publishe

Experimental damage identification in a post tensioned concrete beam

The paper deals with the results of an experimental campaign carried out on a post tensioned concrete beam with the aim of investigating the possibility to detect early warning signs of deterioration based on static and/or dynamic tests. The beam was tested in several configurations aimed to reproduce 5 different phases of the ‘life‘ of the beam: the original undamaged state, under increasing loss of tension in the post tensioning cables, during and after the formation of cracks at mid span, after a strengthening intervention carried out by means of a second tension cable, during and after the formation of further cracks on the strengthened beam. Responses of the beam were measured by an extensive set of instruments consisting of accelerometers, inclinometers, displacement transducers, strain gauges and optical fibers. The paper presents the test program and the dynamic characterization of the beam in the different damage scenarios in terms of the first modal frequency identified from dynamic tests. The evolution of the bending stiffness monitored during static tests is also reported and a simplified mechanical model of the cracked beam was proposed to interpret the correlation between the two parameters

Static and dynamic testing of a damaged post tensioned concrete beam

In this paper are reported the results of an experimental campaign carried out on a post tensioned concrete beam with the aim of investigating the possibility to detect early warning signs of deterioration basing on static and/or dynamic tests. The beam was tested in several configurations aimed to reproduce several different phases of the ‘life’ of the beam: the original undamaged state, increasing loss of tension in the post tensioning cables, a strengthening intervention carried out by means of a second tension cable, formation of further cracks on the strengthened beam. Responses of the beam were measured by an extensive set of instruments consisting of accelerometers, inclinometers, displacement transducers, strain gauges and optical fibres. The paper discusses the tests program and the dynamic characterization of the beam in the different damage scenarios. The modal properties of the beam in the different phases were recovered basing on the responses recorded on the beam during sine-sweep and impact hammer tests. The variation of the first modal frequency was studied to investigate the sensitivity of this parameter to both the cracking of the concrete section and the tension in the cables and also to compare results given by different types of experimental tests