The lifeMACS researchers submitted three contributions to the fib Congress 2022 in Oslo. These contributions were presented by the respective authors during the conference (12/06-16/06/2022).
THE RELATION BETWEEN CONCRETE CRACK WIDTH AND REBAR CORROSION LEVEL VALIDATED ON A LARGE SET OF EXPERIMENTAL DATA
C. Martens, H. Nasser, C. Van Steen, R. Caspeele & E. Verstrynge
Abstract: Reinforced concrete (RC) structures are subject to various degradation mechanisms, including reinforcement corrosion which impacts durability and structural safety. The effects of corrosion of reinforcing steel include a local reduction of the rebar’s cross-section and the formation of rust. As corrosion products occupy a greater volume than steel, this leads to internal stresses, concrete cracking, and eventually spalling.
The condition assessment of RC structures is often based on visual inspections, accompanied by hammer tapping and crack mapping. Consequently, crack width measurements serve as an important damage parameter and can be related to rebar corrosion level. However, no unambiguous relation has been established that is generally valid within certain modeling error limits for all types of layout cases.
In the present paper, the available empirical models which have been used to describe the relation between concrete crack width and rebar corrosion level are discussed and their applicability is validated on a large set of experimental data. The experimental data are obtained from various accelerated corrosion test programs at the Reyntjens laboratory of KU Leuven on RC specimens with varying dimensions, reinforcement layout, concrete cover thickness, reinforcement type and rebar diameter.
The aim of this research is to analyse the modeling error of the empirical relations in view of RC component layout including cover depth, rebar diameter and to investigate whether extrapolation towards other layout cases would be permitted within certain modeling error limits. Finally, the obtained empirical models are compared and classified according to their validity and modeling error.
Adjusted partial factor based assessment criterion for bridge management
K. Van Den Hende, S. Helderweirt, E. Vereecken, W. Botte, S. Matthys, G. Lombaert & R. Caspeele
Abstract: A large share of bridge inspections consists of regular measurements of deflections. As such, an evolution of the deflection over time is available, based on which a prediction of the future deflections can be made. Nevertheless, it is not clear if and how, based on these measured deflections and their possible future predictions, a reliability-based assessment can be made or hence an estimate on the remaining service life can be obtained. In this contribution, a deflection criterion is proposed which can be easily defined and applied for a large database of bridges. Based on the Design Value Method (DVM), adjusted partial factors are derived for an existing structure based on which the critical amount of reinforcement is assessed. Next, the deflection criterion is obtained based on a comparison of deflections in the initial design and deflections in the assessment state. In this contribution, the accuracy of the aforementioned DVM to determine the deflection criterion is assessed by means of full-probabilistic analyses. Results show that the load ratio has the highest influence on the probability that the criterion gives a safe prediction, i.e. the proposed deflection criterion is lower than the deflection limit in reality. Generally, the probability that the simplified criterion, using the DVM, gives a safe deflection limit compared to the full-probabilistic approach lies around 75%.
DEVELOPMENT OF A STEPWISE ADJUSTING DIRECT STIFFNESS METHOD APPROACH FOR THE ASSESSMENT OF EXISTING CONCRETE STRUCTURES
S. Helderweirt, K. Van Den Hende, W. Botte, E. Verstrynge & R. Caspeele
Abstract: Reinforced concrete (RC) structures are widely used in many industrialized countries. Because of the ageing patrimony in these regions, the assessment of time-dependent degradation effects on the structural behaviour is becoming more and more important. Hence, the incorporation of corrosion in a mechanical model predicting the structural performance is an important key necessity for an efficient life-cycle management.
In this contribution, the Direct Stiffness Method is modified in order to account for the time-dependent damage and degradation effects, through the incorporation of a stepwise updated and iteratively solved stiffness matrix. Effects such as the reduction of the rebar’s effective cross-section, the expansive nature of the corrosion product causing internal stresses, concrete cracking and spalling, and the degradation of the bond between the reinforcement steel and the surrounding concrete are added to the model. This results into a non-linear, second-order mechanical model of the deteriorated structural element which can be used to predict the structural performance. Applying this model to a corroded simply supported RC beam, it was found that the deflections increased by 8.3% and the ultimate bearing capacity decreased by 29% when the situation with no corrosion is compared to a situation with a corrosion degree of 10%. For a RC frame, it was found that the new model predicted deformations which are 138% higher compared to the original Direct Stiffness Method, and the ultimate horizontal load of the frame decreased by 35% when considering a corrosion degree of 10%.