Vlatko Bosiljkov

PERPETUATE Project: The Proposal of a Performance-Based Approach to Earthquake Protection of Cultural Heritage

The paper describes the methodology proposed in the PERPETUATE Project (funded by the Seventh Framework Programme – Theme ENV.2009.3.2.1.1). The methodology proposed in PERPETUATE uses a displacement-based approach for the vulnerability evaluation and design of interventions. The use of safety verification in terms of displacement, rather than strength, orients to new strengthening techniques and helps in the comprehension of interaction between structural elements and unmovable artistic assets. The procedure is based on the following fundamental steps: definition of performance limit states, specific for the cultural heritage assets (considering both structural and artistic assets); evaluation of seismic hazard and soil-foundation interactions; construction knowledge (non-destructive testing, material parameters, structural identification); development of structural models for the seismic analysis of masonry structures and artistic assets and design of interventions; application and validation of the methodology to case studies. Two main scales are considered: the seismic risk assessment at territorial scale and at the scale of single historic building or artistic assets. The final aim of the project is to develop European Guidelines for evaluation and mitigation of seismic risk to cultural heritage assets.

Acquiring reference parameters of masonry for the structural performance analysis of historical buildings

The structural performance of historical masonry elements can be understood provided the following factors are known: geometry; the characteristics of its masonry texture and morphology, state of damage and decay, physical, chemical and mechanical characteristics of the components (units, infill, mortar); the characteristics of built masonry as a composite material. In order to quantify the mechanical properties of the masonry both laboratory and in-situ tests are required. However, in the case of cultural heritage assets, the setting up of an effective knowledge procedure is strictly related to the minimization of invasiveness on the structure, with the aim of its conservation, rather than the cost–benefit optimization: thus it is essential to have available reference parameters to be adopted for different masonry types. Within this context, this State-of-the-Art paper on this topic is organized with integrated outcomes from the test campaigns carried out through the PERPETUATE project, that are also briefly presented. Reference parameters for effective seismic assessment are provided both for brick and stone masonry together with their upper and lower bound values for both mechanical parameters and damage limits for which proper limit states (LS) may be associated. Apart from the LS for structural elements (SE), the relevant LS’s for artistic assets attached to the SE are also presented in this paper.

Sensitivity analysis for setting up the investigation protocol and defining proper confidence factors for masonry buildings

At present, the codified procedures for the seismic assessment of existing structures do not consider explicitly the use of sensitivity analysis that, on the contrary, is an essential tool due to the intrinsic and epistemic uncertainties involved. In particular, results of a sensitivity analysis allow, on one hand, to optimize the plan of investigations and tests, limiting it to what is really useful, and, on the other hand, to be aware of the propagation of uncertainties in the final outcome of the assessment. The paper proposes how to implement the sensitivity analysis in a systemic way, in order to define proper confidence factors, which are used within the semi-probabilistic approach of the performance-based assessment procedure. In relation to the procedures adopted by current standards, this method is aimed to overcome the following drawbacks: (1) the a priori definition of values for the confidence factor; (2) the a priori selection of parameters to which confidence factor has to be applied; (3) the weak connection between investigation and assessment. Despite the generality of most aspects of the proposed procedure, main attention is given in the paper to its application in the case of masonry existing buildings and, in particular, of those with a significant cultural value, where the minimization of invasiveness of investigations on the construction together with that of costs plays a crucial role for the aim of conservation.

Assessment of Structure Through Non-Destructive Tests (NDT) and Minor Destructive Tests (MDT) Investigation: Case Study of The Church at Carthusian Monastery at Žiče (SLOVENIA)

Increasing the knowledge of the structural behavior of existing masonry requires a multi-level approach, with proper application of diagnosis and assessment methodologies. The structural performance of a masonry wall structure can be understood provided that its geometry, the characteristics of its masonry texture and the general characteristics of masonry as a composite material are known. For the compilation of all required data, an effective on-site testing campaign is needed, including the application of different test methods by means of combination of minor destructive tests (MDT) and non-destructive tests (NDT). The case study presented herein, encompasses experimental work carried out at the Church of St. John the Baptist at the Carthusian monastery at Žiče, Slovenia. Within this project, on-site investigation was carried out in order to characterize wall cross-sections, to identify different types of masonry, and to collect the samples of mortars and stone particles for further laboratory tests. Methods that were applied for this case study were: crack pattern investigation, radar investigation of masonry walls and internal structure of the ground in the Church, thermography, coring, and boroscopy, as well as laboratory tests on cored samples.

In-plane shear tests on masonry panels with plaster: correlation of structural damage and damage on artistic assets

In the paper, possibilities of correlation of structural damage and damage of attached artistic assets on multi-leaf stone masonry walls by means of destructive and non-destructive testing (NDT) methods are investigated. Results from two testing campaigns carried out at the University of Genoa and University of Ljubljana are briefly presented. In particular, diagonal tests with different levels of pre-compression and shear tests under different boundary conditions were carried out in Genoa and Ljubljana, respectively. During the tests, different damage limit states (DL) of both masonry walls (SE) and attached plasters (AA) were investigated by means of NDT’s. Two different types of rubble stone masonry were considered (uncoursed random rubble vs. coursed squared rubble). For AA the results are presented in relative form in dependence from the DL of SE. Obtained results are influenced both by the type of test and tested masonry. Results of NDT revealed strong potential and a need for data fusing of both investigated methods for the evaluation of the state of the degradation behind the plaster.

In-situ and laboratory tests of old brick masonry strengthened with FRP in innovative configurations and design considerations

Worldwide cultural heritage and especially the heritage buildings in Europe are masonry buildings. Such buildings are generally capable to resist vertical loads but horizontal earthquake actions are often critical. The strengthening upgrade is generally required. One of the most promising methods for the strengthening of masonry walls is application of fibre reinforced polymers (FRP) to the surface of the wall. Three sets of the experimental research were performed recently with new innovative configurations of the fibre reinforcement placement on clay brick masonry. Within the framework of European FP7 research project PERPETUATE two sets of in-situ experiments were performed on 12 walls, belonging to two buildings approximately one hundred years old. Both buildings were made of solid bricks in low strength mortar. Third set of tests was performed in the laboratory on 16 specimens made of contemporary solid bricks in good lime-cement mortar. Tests were performed with different reinforcement configurations. Carbon FRP strips were epoxy-bonded horizontally, diagonally or combined (horizontally and vertically). Glass FRP grids were placed in the modified cement mortar over the entire surface of the wall. Specimens were tested under the constant vertical load and by a displacement controlled horizontal cyclic loading. The carbon fibre reinforced polymer strengthening significantly increased the ultimate displacement capacity in case of the horizontal and combined strengthening. The diagonal strengthening was not so effective because the failure of the diagonally strengthened specimens was governed by the peeling of strips from the masonry. The GFRP grid configuration greatly increased the load bearing capacity but not also the ultimate displacement. The shear strength of the strengthened and un-strengthened specimens was compared to the calculated values of the seismic shear load bearing capacity. For that the Triantafillou (J Compos Constr 2(2):96–104, 1998), Triantafillou and Antonopoulos (J Compos Constr ASCE 4(4):198–205, 2000), Marcari et al. (2011) and Wang et al. (Asian J Civil Eng Build Hous 7(6): 563–580, 2006) calculation models and the design guides ACI 440.7R-10 (2010) and CNR-DT 200/2004 were used.

Time Evolution of Properties of SCC Mixtures Produced Using Crushed Limestone Aggregate and High Content of Limestone Filler

The paper deals with time-dependent increase of compressive strength, splitting tensile strength and modulus of elasticity as well as with compressive stress-strain curves of self-compacting concrete (SCC) made with crushed limestone aggregate and high content of limestone filler. The characteristics under consideration were tested at the ages of 1, 3, 7, 28, 180, 360 and 720 days. Time evolution of the strength characteristics and modulus of elasticity was estimated with analytical models given in European code Eurocode 2. The study revealed that the models can adequately predict time evolution of the SCC characteristics, when coefficient s in the models is equal to 0.17, 0.08 and 0.25 for compressive strength, tensile strength and modulus of elasticity, respectively. These values of coefficient s are quite different from the value 0.2 proposed by Eurocode 2 for used cement strength class.

Seismic resistance of stone masonry building and effect of grouting

Injektiranje je jedan od najdjelotvornijih, a cesto i najprikladnijih postupaka za pojacanje zidova starih zidanih građevina. Da bi se ocijenio utjecaj raznih vrsta injekcijskih smjesa na mehanicka svojstva zidanih građevina, obavljeno je ispitivanje in situ postojece zidane građevine. Dobiveni rezultati koristeni su za ocjenu seizmicke otpornosti građevine pomocu metode postupnog guranja, uz primjenu pristupa katnog mehanizma i mehanizma globalnog odziva. Prihvatljivije vrste injekcijskih smjesa usporedive su s cementnim injekcijskim smjesama. Dobiveno je da se pristupom globalnog odziva postižu realniji rezultati cak i kod niskih zidanih građevina

NDT Data Fusion for the Enhancement of Defect Visualization in Concrete

Ground penetrating radar (GPR) and active thermography are well known non-destructive testing (NDT) methods for structural visualization and defect detection in concrete. However, for both methods, the probability of detection is strongly depth-dependent and each method suffers from an almost blind region at a specific depth. In this study we propose the use of unsupervised clustering techniques for the fusion of GPR and thermographic phase contrast data to enhance defect visualization in concrete. The evaluation was carried out on the basis of experimental data acquired on laboratory concrete test specimens, which contain inbuilt anomalies varying in shape, material and position. To achieve an optimal fusion of radar depth slices and thermographic phase contrast images along the depth axis, we derive sensitivity curves for both NDT methods and use the probability mass information to further improve the fusion results. Results show that the fuzzy c-means algorithm may contribute to an enhanced detection probability of defects below high density reinforcement. For defects with a concrete cover from 1.5 to 2 cm, the use of weighted clustering is particularly suggested. In general, complex defect types and shapes could be better resolved by using the Gustafson-Kessel algorithm or noise clustering. In addition, we demonstrate the application of the Dempster-Shafer theory to quantitatively evaluate the effectiveness of fused data on the basis of joint mass probability.

Lime Based Grouts for Strengthening of Historical Masonry Buildings in Slovenia

Most of the historical masonry buildings in Slovenia were built out of local stone or stone and brick with lime-based mortars. An efficient technique for improving the mechanical properties of stone or stone-brick walls is grout injection. In order to evaluate the quality and compatibility of commercially available injection grouts with materials present in historical masonry buildings, several types of hydraulic lime-pozzolana, lime-cement and cement grouts were tested. Chemical, physical and mechanical criteria to select optimal grout mixture for strengthening of historical masonry buildings were proposed, by which tested grouts were classified in three quality classes A, B and C. Only two commercial lime-cement grouts and one cement grout were able to meet the set requirements and were qualified in class B as medium quality grout (one lime-cement grout) or in class C as low quality grouts. Therefore, the design of hydrated lime-based grouts was carried out in continuation of our study, in order to obtain a grout that is highly compatible with the historical masonry in Slovenia. Among available limes, hydrated lime in powdered state and lime putty were used. Ground granulated blast furnace slag (GGBS), volcanic tuff, and limestone powder were used as mineral additives. It was found that the added combination of limestone powder and supplementary cementitious material (GGBS or tuff) has a beneficial influence on the properties of designed grout compositions.