J. Maeck

Damage identification in reinforced concrete structures by dynamic stiffness determination

Service loads, environmental and accidental actions may cause damage to constructions. Regular inspection and condition assessment of engineering structures are necessary so that the early detection of any defect can be made and the structures remaining safety and reliability can be determined. When the structural damage is small or it is in the interior of the system, its detection cannot be carried out visually. A useful more elaborate non-destructive evaluation tool is vibration monitoring. It relies on the fact that the occurrence of damage or loss of integrity in a structural system leads to changes in the dynamic properties of the structure. In this paper, different techniques will be presented and compared to derive from experimentally determined modal characteristics of a reinforced concrete beam its dynamic bending stiffness. The degradation of stiffness, due to the cracking of the reinforced concrete, gives information on the position and severity of the damage that has occurred.

Comparison of techniques for modal analysis of concrete structures

Abstract This paper describes different experimental techniques for obtaining modal parameters of structures. Attention is focused on those techniques that may be applicable to in situ concrete structures (e.g. bridges). In a first stage, experiments are made on reinforced concrete beams of 6 meters length. The beams are excited using three types of excitation methods: impact hammer excitation and two different electromagnetic shaker signals: pseudo-random and swept-sine signals. The modal parameters are determined either by performing curve-fitting procedures on series of measured frequency response functions or by applying the stochastic subspace identification technique to the time response signals of the structure. The influence of the non-linear behaviour of the concrete beams is investigated by performing measurements at different excitation amplitudes. It appears that modal parameter estimates are affected by excitation techniques, data acquisition parameters and processing methods. The main cause of this is the non-linear behaviour which is observed even at very low vibration amplitudes. However, the influence on resonant frequencies and mode shapes is negligible. This is not the case for the modal damping ratios, so that the estimation of these parameters is unreliable.

A finite element model updating method using experimental modal parameters applied on a railway bridge

A finite element model updating method using experimental modal para- meters is presented. Such a procedure can be regarded as an optimisation problem. The objective function consists of the (weighted) sum of differ- ences between the experimental modal data (eigenfrequencies and mode- shapes) and the corresponding analytical predictions. The function can be completed with additional orthogonality conditions. The updating para- meters are the uncertainties of the model, which are changed locally until the objective function is minimised. A gradient-based algorithm is used to solve the optimisation problem. As a result a physically more correct model is obtained on which further analysis can be made. The presented proce- dure is applied on a railway bridge at Xntoing. Belgium, on which dynamic measurements have been made. Several variants of objective functions are minimised and the results are compared.

Facilitating the adoption of sustainable technologies in the asphalt sector

A need exists to bridge the gap between innovation in the bituminous materials sector and adoption of the new technologies by national road administrations (NRAs). The Evaluation and Decision process for Greener Asphalt Roads (EDGAR) enables NRAs to do this by providing an assessment methodology which makes sustainability information on new technologies readily accessible to the decision-making process, and therefore facilitates quick adoption of the technologies that offer the greatest sustainability benefits for the highways sector and society as a whole. EDGAR commenced with a wide-ranging review of the range of ‘green’ technologies in the bituminous materials sector and the sustainability benefits that they offer. Two methodologies to assist NRAs were then devised. The first acknowledged that the ability to recycle asphalt is its foremost environmental attribute, and devised a quick, qualitative method for the assessment of recyclability. The second devised a methodology for a more detailed assessment of the sustainability of any bituminous technology, considering all three facets of sustainability: environmental, social and economic, with particular attention given to how the information might be used in the decision process by NRAs, and the common challenges they might encounter when assessing a ‘novel’ technology.