L. Schueremans

Conservation and New Construction Solutions in Rammed Earth

The conservation and rehabilitation of several sites of cultural heritage and of the large housing stock built from rammed earth requires adopting intervention techniques that aim at their repair or strengthening. The present work discusses the main causes of the decay of rammed earth constructions. The intervention techniques used to repair cracks and lost volumes of material are also discussed. Regarding the strengthening of rammed earth walls, the discussion is focused on the techniques that improve the out-of-plane behaviour. Special attention is given to the injection of mud grouts for crack repair in rammed earth walls, including the presentation of the most recent developments on the topic, namely regarding their fresh-state rheology, hardened-state strength and adhesion. Finally, the use of the rammed earth is discussed as a modern building solution. In addition, several typical techniques for improving rammed earth constructions are discussed, aiming at adequate those to modern demands. In addition, the alkaline activation of fly ash is presented and discussed as a novel improvement technique.

Strengthening of Concrete Structures using Steel Wire Reinforced Polymer

SYNOPSIS: This paper deals with a new material for external reinforcement: Steel Wire Reinforced Polymer (SWRP). It consists of thin high-strength steel fibres embedded in a polymer laminate. This innovative material combines the advantages of steel plates and CFRP, which are already used today. The material cost of SWRP is relatively low, and the laminate is quite flexible. In the feasibility part, the practical use of SWRP is studied. Further, the available design model for externally bonded reinforcement for concrete elements is confronted with the results of an experimental program, carried out at the Reyntjens Laboratory of KULeuven. The model is adapted accordingly.

Triaxial testing of historic masonry, test set-up and first results

In 1998 the Reyntjens Laboratory acquired a big size triaxial cell testing device for the testing of heterogeneous materials. The goal of the triaxial test set-up is to gather information about the material behaviour under a multi-axial stress state. In that it simulates the confining pressure of the surrounding material. In 1998 and 1999 the test set-up was developed. Meanwhile the first test results on the triaxial behaviour of lime mortar and masonry have been acquired. In the case of masonry cores, special attention is paid to the resulting biaxial yield-criterion. as this is of major importance for an assessment of the structural safety of the masonry. The study on lime mortar aims at determining its deformability in the case of a triaxial compression state. Especially the influence of the pore structure is evaluated. The research goal is the better understanding of the mechanical behaviour of ancient masonry, seeking for scientific explanation about the relative high mechanical strength of masonry built up with lime mortar that is considered to be a weak material. The test set-up is illustrated, the first test results and the resulting biaxial yield criterion for masonry based on cores are presented. Triaxial tests on both hydrated and hydraulic lime mortars as well as the mutual influence between the triaxial behaviour of the mortar and its pore structure are studied and discussed.

Konstruktive Injektion von historischem Mauerwerk mit mineralisch- oder polymergebundenen Mörteln / Structural injection of historical masonry using mineral or polymer based grouts

Abstract Recent developments in injection grouts used for consolidation are proposed. Special compositious have been developed, made out of lime, cement and pozzolan. The stability, the viscosity and the mechanical properties are illustrated. Comparison is made with polymer grouts and with double injections using mineral and polymer grouts consequently. The influence of injections on the load-bearing capacity of the masonry is calculated. Some elements for the judgment of the safety and reliability of masonry structures are pointed out.

Safety assessment of masonry arches using probabilistic methods / Bestimmung der Sicherheit eines Mauerwerkbogens unter Anwendung probabiiistischer Methoden

Safety, reliability and risk are key issues in preservation of the built, cultural heritage. Structural collapses such as the Basilica of San Francis (Italy, 1997) and the Civic Tower in Pavia (Italy, 1989), make us aware of the vulnerability of our technical and natural environment and demand an adequate engineering response. The architectural preservation process is generally based on a sequence of analysis, diagnosis, therapy and control. In the analysis phase, an objective way to assess the safety of the structure is essential. The present raises the need for a reliability based assessment framework for existing masonry structures. As it is a major concern of engineers, the notions of reliability and risk and related theory and practice are no longer working topics for specialists only. Powerful methods are available for the calculation of structural safety values. These permit to calculate the global failure probability of complex structures, relying on deterministic techniques able to calculate the stability state for a prescribed set of parameters. The safety of arches is a typical example of new fields for these methods. Traditionally their stability is assessed using a deterministic approach, resulting in safety factors. To relate these safety factors to an absolute safety requires a great deal of engineering judgement. In case of an existing arch, this judgement depends on a variety of uncertainties such as on the accuracy of the geometry measurements, the uncertainty on the material properties, support conditions and the constructional history of the structure. This article will deal with the methodology of reliability methods and their applicability for safety assessment in practice. The method will be outlined using an illustrative example. The example of the masonry arch demonstrates the applicability in practice.

Long-term Behaviour of Low Quality Sandstone Masonry: Assessment Methodology and Case Study / Langzeitverhalten von Sandsteinmauerwerk mit niedriger Qualität: Erfassungsmethodologie und Fallstudie

The long-term behaviour of a soft natural stone, Diestian ferruginous sandstone, has been analysed and modelled. This type of sandstone has been used for the construction of many monuments in the central region of Belgium and, at present, a considerable part of these historical monuments show significant decay and, in two recent cases, even collapse of the structure. The analysis is based on a methodology which combines experimental research, modelling, monitoring and risk assessment. All steps are outlined and illustrated on a case study. Experimental research has shown that the sandstone has a very low compressive strength and large scatter on its strength characteristics. Monitoring of a church tower was performed with strain gauges and acoustic emission sensors. The church tower was modelled with a previously calibrated creep model and risk assessment was performed with a probabilistic analysis, based on Monte Carlo simulation. These techniques indicated that the structural safety was insufficient and strengthening actions were taken by confining the base of the church tower. The effects of these confinements on the long-term creep deformations in the masonry are discussed.

Application of the Acoustic Emission Technique for Assessment of Damage Accumulation in Masonry / Anwendung der Messung der akustischen Emission zur Bestimmung der Schadensakkumulierung in Mauerwerk

The interest in acoustic emission (AE) as a monitoring technique to assess the damage evolution in masonry structures is recently gaining field. The AE technique detects transient energy waves emitted by a material as a result of stress redistributions. Energy waves are excited by external loads as well as by internal movements in the structure or the materials. In this paper, the focus is on long-term monitoring and the use of AE-monitoring to assess damage evolution under sustained stresses, such as damage-accumulation during creep phenomena in masonry. A laboratory test campaign is set up, during which long-term creep tests are performed on masonry specimens at different stress levels. The latter are increased at specific time intervals. In addition to stress-strain and crack monitoring, AE-monitoring is performed at discrete moments in time. Both sources of data arc used to validate the AE-monitoring technique to assess the damage accumulation. Hereby, both damage initiation due to load increment and the damage accumulation due to time-dependent deformation under sustained loading are addressed. In this paper, focus is both on the added value and limitations of the AE for damage assessment. The results indicate that the acoustic emission technique is able to detect the damage-accumulation in the masonry, in particular the instable damage increase during the tertiary creep phase, thereby predicting the failure of the test specimen.

New Trends in Rehabilitation and Consolidation of Historical Concrete and Masonry Constructions / Neue Wege beim Instandsetzen und Festigen historischer Gebäude aus Beton und Mauerwerk

New trends in structural consolidation and strengthening techniques are based on the true nature and stress-strain behaviour of the concrete and masonry material, as well as on the understanding of the load distribution and deformation mechanisms acting in such structures. Safety, reliability and risk are key issues in rehabilitation as well as in the preservation of the built, cultural environment. Powerful methods are becoming available for the calculation of structural safety values, and they allow to calculate the global probability of failure of complex structures. These methods need appropriate analysis models as input, as well as reliable design models for strengthening of structural elements by means of externally bonded steel plates or fibre reinforced laminates, or design models for the effect of grouting on strength and stiffness of ancient brick or block masonry. Such models are derived from research, which combines investigation and development of new materials, non-destructive testing, laboratory and site investigation. This global approach, as it is practiced in the Reyntjens Laboratory of K.U.Leuven, and applied in rehabilitation and restoration projects by Triconsult n.v., is presented and documented with case-studies.

Sicherheitsanalyse und Planung einer verstärkenden und festigenden Maßnahme durch Injizieren / Safety Assessment and Design of Consolidation and Strengthening by Means of Injections

Safety, reliability and risk are key issues in the preservation of our built, cultural heritage. Several structural collapses make us aware of the vulnerability of our technical and natural environment and demand an adequate engineering response. The architectural preservation process is generally based on a sequence of anamnesis and analysis, diagnosis, therapy, control and prognosis. In the analysis phase, an objective way to assess the safety of the structure is essential. The present raises the need for a reliability based assessment framework for existing masonry structures. As it is a major concern of engineers, the notions of reliability and risk and related theory and practice are no longer working topics for specialists only. Powerful methods are available for the calculation of structural safety values. These permit to calculate the global probability of failure of complex structures, relying on deterministic techniques able to calculate the stability state for a prescribed set of parameters. This paper explains how these techniques can be a valid tool to evaluate the bearing capacity of existing structures. The applications focus on the assessment of existing masonry structures and on the reliability increase obtained by consolidation and strengthening by means of injections.

Probabilistische Zustandsanalyse von tragendem Mauerwerk / A Probabilistic Evaluation Method for Structural Masonry

Abstract A probabilistic method to evaluate the reliability of structural masonry elements is presented. Local probability of failure, different failure modes and corresponding limit state functions, probability distributions of basic variables and model uncertainty are discussed. A graphical probability mapping is presented as an easilyaccessible, visual evaluation instrument in the restoration decision process. The proposed methodology is illustrated on tested shear panels, reported in literature.