Prof. Eng. Claudio Modena Full Professor of Structural Engineering

1. CRITERIA AND TECHNOLOGIES FOR THE STRUCTURAL REPAIR AND STRENGTHENING OF HISTORIC MASONRY STRUCTURES: RESEARCH AND APPLICATIONS Prof. Eng. Claudio Modena Full Professor of Structural Engineering Department of Civil, Architectural and Environmental Engineering (DICEA) University of Padova – Italy claudio.modena@unipd.it Strenghtening and refurbishing of existing structures - Port of Spain, Trinidad & Tobago - 24-25 April 2014

2. Structural safety vshistorical structures • Evidences exist that • no real PRESERVATIONpolicies are possible of HISTORICAL BUILDINGSphysical testimony of intangible assets and values • if not compatible with their • socially/economically sustainable use • unsustainable preservation with no valorisation • PRESERVATION ↔ STRUCTURAL SAFETY ↔ USE • the sophisticated and highly conventional procedures that are used to verify modern structures are inadequate when applied to assess the structural safety of historical structures; • the techniquesthat are used to repair/strengthen historical structures most frequently provide inadequate performances

3. Structural safety vsexisting structures Conventional procedures that are in use to verify new structures not applicable to assess the safety of existing structures In spite of being the structure already “physically” exiting NO REAL CONSISTENT PROBABILISTIC APPROACH IS FEASIBLE STRUCTURAL MODELS NORMALLY IN USE NOT RELIABLE WHEN EVALUATING THE RESPONSE OF HISTORIC MATERIALS AND COSTRUTION SOLUTIONS TO BOTH STATIC AND DYNAMIC ACTIONS

4. Recent advances RILEM International Union of Laboratories and Experts in Construction Materials, Systems and Structures ICOMOS International Council on Monuments and Sites - ISCARSAH International Scientific committee for Analysis and Restoration of Structures of Architectural Heritage CEN European Committee for Standardization - Technical Committee TC 346 (Conservation of Cultural Property) ISO International Organization for Standardization ISO 13822 – bases for design of structures – assessment of existing structures (first edition 2001) UNI Ente Italiano di Unificazione - “Cultural Heritage” committee

5. Recent advances • CODES • ISO 13822 – bases for design of structures – assessment of existing structures (first edition 2001) - ANNEX I (Informative) Historic Structures • ISO/DIS 13824 General principles on risk assessment of systems involving structures • Italian Building Code for design, assessment and seismic retrofitting – Chapter 8: existing buildings (NTC 2008) • prEN 1998-3 Eurocode 8 – Design of structures for earthquake resistance Part 3: assessment and retrofitting of buildings • GUIDELINES • ICOMOS – ISCARSAH Recommendations for the analysis, conservation, and structural restoration of architectural heritage • Italian Guidelinesfor evaluation and mitigation of seismic risk to cultural heritage with reference to technical standard for construction (2006-2011) • RILEMRecommendation 1996, TC 127-MS. MS.D.1. • CEN TC346 Conservation of cultural property – WG1: “Condition survey of immovable heritage”; WG2N 018: “Diagnosis of building structures”.

6. Recent advances • ISO 13822 • The continued use of existing structures is of great importance because the built environment is a huge economic and political asset, growing larger every year. The assessment of existing structures is now a major engineering task. • The structural engineer is increasingly called upon to devise ways for extending the life of structures whilst observing tight cost constraints. • The establishment of principles for the assessment of existing structures is needed because it is based on an approach that is substantially different from the design of new structures, and requires knowledge beyond the scope of design codes. • The ultimate goal is to limit construction intervention to a strict minimum, a goal that is clearly in agreement with the principles of sustainable development.

7. Recent advances ISO 13822 – § 7.4 The conclusion for the assessment shall withstand a plausibility check. In particular, discrepancies between the results of structural analysis (e.g. insufficient safety) and the real structural condition (e.g. no signs of distress or failure, satisfactory structural performance) shall be explained. Note: many engineering models are conservative and cannot always be used directly to explain an actual situation.

8. Recent advances • ISO 13822 – § 8.1 • Safety assessment: structures designed and based on earlier codes, or designed and constructed in accordance with good construction practice when no codes applies, may be considered safe to resist actions others than accidental actions (including earthquake) provided that: • Careful inspection does not reveal any evidence of significant damage, distress or deterioration • The structural system is reviewed, including investigation of critical details and checking them for stress transfer • The structure has demonstrated satisfactory performance for a sufficiently long period of time for extreme actions due to use and environmental effects to have occurred • Predicted deterioration taking into account the present condition and planned maintenance ensures sufficient durability • There have been no changes for a sufficiently long period of time that could significantly increase the actions on the structure or affect its durability, and no such changes are anticipated

9. Recent advances RECOMMENDATIONS FOR THE ANALYSIS,CONSERVATION AND STRUCTURAL RESTORATION OFARCHITECTURAL HERITAGE Guidelines 4. Diagnosis and safety evaluation 4.1 General aspects 4.2 Identification of the causes (diagnosis) 4.3 Safety evaluation 4.3.1 The problem of safety evaluation 4.3.2 Historical analysis 4.3.3 Qualitative analysis 4.3.4 The quantitative analytical approach 4.3.5 The experimental approach 4.4 Judgement on safety 5. Decisions on interventions - The Explanatory Report 1. General criteria 2. Acquisition of data: Information and Investigation 2.2 Historical and architectural investigations 2.3 Investigation of the structure 2.4 Field research and laboratory testing 2.5 Monitoring 3. Structural behaviour 3.1 General aspects 3.2 The structural scheme and damage 3.3 Material characteristics and decay processes 3.4 Actions on the structure and the materials

10. Recent advnces GUIDELINES FOR THE ASSESSMENT AND THE REDUCTION OF SEISMIC RISK OF CULTURAL HERITAGE • CHAP. 1: OBJECT OF THE GUIDELINES • CHAP. 2: SAFETY AND CONSERVATION REQUIREMENTS • CHAP. 3: SEISMIC ACTION • CHAP. 4: BUILDING KNOWLEDGE • CHAP. 5: MODELS FOR SEISMIC SAFETY ASSESSMENT • CHAP. 6: SEISMIC IMPROVEMENT AND INTERVENTION TECHNIQUES CRITERIA • CHAP. 7: RESUME OF THE PROCESS

11. Recent advances • Carefully considering what has be learned from the past and • ongoing experiences, new concepts and tools are entering into codes • and structural design practice: • mechanical properties of structures and materials defined with no real statistical evaluations (estimation based on limited data); • combined use of different possible global and local structural models; • extensive use of “limit analyses”, i.e. based on pure equilibrium of forces, according to kinematic approaches; • combination of “quantitative” ( results of models) and “qualitative” approaches (expert judgments - observational approach: the existing structures as a model of itself); • limitation of interventions at the minimum possible level, mostly depending on the level of knowledge of the structure and on the use of appropriate investigations/monitoring techniques; • removabilityof the interventions and the compatibility of traditional/modern/innovative materials and construction techniques.

12. A KEY ISSUE • MINIMUM INTERVENTION • STEP BY STEP MEASURES AND CONTROL OF EFFICIENCY/NECESSITY • LOCAL ACTIONS THAT DO NOT AFFECT THE STRUCTURAL RESPONSE • REMOVABILITY • ALLOWING / MAINTAINING REPAIRABILITY • DURABILITY • RELIABLE IN ITSELF 'AND INTERACTION WITH THE REST OF THE STRUCTURE • USE MORE ALTERNATIVE MODELS AND ANALYSIS, VALIDATION / CALIBRATIONS • EXPERTS JUDGEMENTS • -------------------------- • ASSESSMENT - IMPROVEMENT - instead of - VERIFICATION – RETROFITTING • FORCES-EQUILIBRIUM - in addition to, and rather than - STRESSES-RESISTANCE

13. The “knowledge level” The knowledge of the masonry historical building, using particular techniques of analyses and interpretation, is the basis for a reliable appraisal of the seismic safety and for the choice of an effective improvement. Steps: Building identification Functional characterisation of the building Geometrical survey Historical analyses of events and past interventions Material and structural survey and conservation state Mechanical characterization of materials Ground and foundations Monitoring Different knowledge levels and confidence factors CF

14. The “knowledge level” To carry out the structural analyses, it is necessary to gain proper knowledge by means of surveys, historical researches, in-situ and laboratory tests: geometry, particular elements (such as chimneys, niches, etc), crack pattern & out of plumbs BUILDING GEOMETRY • by means of surveys connections, lintels, elements to counteract thrusts, vulnerable elements, masonry tipology 1 m CONSTRUCTIVE DETAILS 1 m • limited in situ inspection • extended & comprehensive in situ inspection MATERIAL PROPERTIES particularly aimed at the mechanical characterization of masonry, through inspections, NDT, MDT & DT • limited in situ testing (inspections) • extended in situ testing (MDT & NDT) • comprehensive in situ testing (DT)

15. The “knowledge level” St. Agostino INSTALLED SENSORS (Sept 2010) 2 Temperature sensors 4 PDT (crack detection) 4 String pot 16 single axis accelerometers Nagoya University, Japan

16. The “knowledge level” Static sensors INSTALLED SENSORS (Sept 2010) 2 Temperature sensors 4 PDT (crack detection) 4 String pot 16 single axis accelerometers accelerometers

17. The structural models Structural modelling and seismic analysis methods • For existing masonry buildings it is possible to consider various analysis methods, according to the considered appropriate model which describe the structure and its seismic behaviour. • It is possible to consider: • Macro-elements models • Equivalent frame models • Finite elements models

18. The structural models Structural modelling and seismic analysis methods The Finite Element Method (FEM) is a powerful tool to study stresses and displacement in solids. A mathematical description of the material behaviour, which yields the relation between the stress and strain tensors in a material point of the structural element, is necessary for this purpose. Constitutive models of interest for practice are normally developed according to a phenomenological approach in which the observed mechanisms are represented in such a manner that simulations are in reasonable agreement with experiments. Several examples of non linear relatively simple 2D or 3D models can be found (e.g. structural elements as churches’ triumphal arches, vaults, or structures as chimneys, bell towers). Relatively few studies considering full scale complex structures, for their seismic assessment, are on the contrary available.

19. The structural models Structural modelling and seismic analysis methods The effective response of an existing masonry building to horizontal actions can be hardly defined, in the majority of cases, by just considering the global behaviour of the structure Main causes: - Lack of connection between walls - Lack of connection between walls and floors - Reduced in plane stiffness of floors - Masonry composition - Existing crack pattern Giuffrè, 1993 Salò-Garda lake earthquake (24/11/2004)

20. The structural models Structural modelling and seismic analysis methods It is necessary to evaluate the response of individual portions of the structure that can manifest an independent behaviour in occasion of a seismic event (local structural models). Local damage is particularly related to out-of-plane actions, as denounced by the observation of local damage, with partial collapse of masonry panel, that are not able to redistribute the seismic forces to the rest of the building, and the rest of the building still standing. Salò-Garda lake earthquake (24/11/2004)

21. The structural models Structural modelling and seismic analysis methods A wide research was performed to appreciate the reliability of the proposed models, also in comparison with “traditional” global assessment methods used for masonry buildings: in general, globalanalytical procedures applied to historical masonry building can be misleading in the interpretation of the actual behaviour of the analyzed buildings. Analytical approach procedures considering the modelling of the elementary failure mechanisms with the limit analysis of local rigid bodykinematic mechanisms of structural macroelements (portions of the buildings with homogeneous constructive characteristics and structural behaviour)found a better match with the observed damage External walls Discontinuity Out of plane In plane Horizontal structures Terraces and chimneys Internal walls Irregularities in plan and in elevation Building-soil interaction Buildings interactions

22. The structural models Structural modelling and seismic analysis methods The adoption of suitable interpretative models can not disregard the structural typologies of the considered buildings (isolated or aggregate buildings, churches…). Several abaci graphically depicting the more common failure modes, based on a vast damage mechanism classification work after the recent seismic events and referred to specific constructive typologies, were defined. Further input data: - the construction of the building following “correct” empirical rules - the historical response of the building to past seismic events Local models Aggregate buildings

23. The structural models Example: the church of S. Maria del Pianto XVIII Century church by Frigimelica with central plan and some irregularities due to following resets done in the first half of the XX Century Critical survey

24. The structural models Example: the church of S. Maria del Pianto Identification of the macroelements Western Apse Southern Apse Wall C Wall B Wall D Lateral Wall A Western Bell Tower Sacristy Eastern Apse Lateral Wall F Eastern Bell Tower Baptismal Font Wall E Façade

25. The structural models Example: the church of S. Maria del Pianto

26. The structural models Example: the church of S. Maria del Pianto Mst = 52230 daN m Minst = 3984900 daN m c = 0,0131 Mst = 236220 daN m Minst =4441250 daN m c = 0,05319 Mst = 2125 daN m Minst =148300 daN m c = 0,0143 Mst = 41137 daN m Minst =1473034 daN m c = 0,0279

27. The structural models Example: the church of S. Maria del Pianto From the analyses carried out, it was pointed out that the most vulnerable element is the façade, in case of overturning with partial involvement of the lateral walls. This is also a possible mechanism, due to the presence of corresponding crack pattern close by the façade.

28. The structural models Simplified procedure for the seismic assessment of masonry bridges Structural capacity to horizontal loads Determination of the collapse mechanism (Heyman 1982; Clemente 1998); application of the principle of virtual work for the determination of the ground acceleration that activates the collapse mechanism, which is the horizontal load multiplier a in the capacity curve: The collapse limit acceleration a*0 is derived as: where e* is the participant mass factor and g is the gravitational acceleration. This is a simplify method order to calculate the seismic longitudinal capacity of the masonry bridges and the transversal capacity of spandrel wall. Kinematic analyses were used for estimate the seismic vulnerability for the homogeneous classes.

29. The structural models Simplified procedure for the seismic assessment of masonry bridges Collapse mechanisms for different classes of masonry arch bridges 1) Single span bridges with squat abutments: Single span masonry arch bridges are generally characterized by massive abutments, which in most cases can be schematized as an infinitely rigid constraint. The most vulnerable element in the longitudinal direction is the masonry, which can collapse when subjected to horizontal accelerations developing an antimetric collapse mechanism through the formation of three rigid voussoirs and four hinges. 2) Single span bridges with high abutments: In single span bridges, if the abutments are high (h/L>0.75), the longitudinal mechanism can involve both the arch and the abutments, becoming a global mechanism (da Porto et al., 2007).

30. The structural models Simplified procedure for the seismic assessment of masonry bridges Collapse mechanisms for different classes of masonry arch bridges 3) Multi-span bridges with squat piers: for these classes the strong abutments continue to represent a fixed restraint for the arch. 4) 2-3 Spans and Multi-span bridges with high abutments:the seismic vulnerability is affected by the slenderness of the piers, and influenced by the ratio H/B. In the longitudinal direction a global mechanism Arch-Piers, with formation of plastic hinges at the pier bases. In transverse direction, not only the local mechanism related to the out-of-plane rotation of the spandrel wall has to be considered, but also a global mechanism, involving both arch and piers, which can only be identified with F.E. analysis.

31. The structural models Simplified procedure for the seismic assessment of masonry bridges Collapse mechanisms for different classes of masonry arch bridges 5) Out of plane rotation of the spandrel wall:The spandrel walls are subject to out of plane overturning. This collapse is a local mechanism, and generally does not involve the structural safety of the arch, but it can compromise the support of the ballast and the rail tracks, and in the end the serviceability of the bridge.

32. Criteria for the selection of interventions Restoration was in the past reserved to monumental buildings. Restorers were few experienced professionals who took care for years and sometime for their professional life of the same monument or group of monuments. After the second world war the historic centers in Italy were left to the poorest and to the immigrants lowering the level of maintenance of historic building. On the other hand in high schools and universities, teaching of old traditional materials as masonry and wood was substituted by concrete, steel and new high-tech materials. As frequently happened in the recent past, due to lack of knowledge and of appropriate analytical models, masonry was simply treated as a material as homogeneous as concrete, steel, or wood.

33. Criteria for the selection of interventions The assumption for masonry structures, especially, in seismic areas were that, they should behave like a “box” with stiff floors and stiff connections between the walls, no matter which was their geometry or material composition. The strengthening project implied the use of the same intervention techniques: substitution of timber-floors and roofs with concrete ones, wall injection by grouts, use of concrete tie beams inserted in the existing walls. Collapse of a repaired walls Separation of leaves in a repaired stone masonry

34. Criteria for the selection of interventions The experience of the Umbria-Marche earthquake shown the effect of stiffening the horizontal diaphragm by substituting original wooden floors with stiff reinforced concrete floors… Traditional techniques, aimed only at reducing excessive deformability of the floors, are now proposed. The tie-beam is supported only by the internal leaf of a multi-leafs masonry: load eccentricity and reduction of the resisting area The masonry is not adequately strengthened Expulsion of the façade The orthogonal walls are not adequately connected each other

35. Criteria for the selection of interventions Poor quality Reinforced injection Montesanto (Sellano), 1997 Montesanto (Sellano), 1997 Jacketing The earthquake pointed out problems related to poor masonry quality but also to the use of non-effective intervention techniques, of strengthening intervention badly executed, of intervention techniques that can worsen the local/global behaviour… Injection Building strengthened after the Bovec earthquake (Kobarid - Slovenia) in 1998, damaged again during the 12/07/2004 earthquake.

36. Criteria for the selection of interventions A “to do list” in case of strengthening intervention is not viable, since specific and effective intervention in one case can be ineffective or, even worst, detrimental to the seismic capacity of the structure in other cases. In order to respect the existing features of the considered constructions special care has to be paid in order to limit in any case as much as possible variations not only of its external appearance, but also of its mechanical behavior. Attention has to be focused on limiting interventions to a strict minimum,avoiding unnecessary strengthening, a goal that is clearly in agreement with the principles of sustainable development. Tomaževič, ZRMK, Ljubljana, Slovenia

37. Criteria for the selection of interventions Efforts are needed to respond to “conservative” design criteria while intervening to ensure acceptable structural safety conditions of existing historic constructions. This requires that it is necessary to analyze, theoretically and experimentally, the resisting properties of the considered construction, prior and after interventions are made, in order to avoid over-designing approaches. ArcheScaligere (Verona, Italy) before and after intervention The actual contribution of any traditional/innovative material and techniques, and of their possible combinations, can be adequately and scientifically exploited in order to ensure durability, compatibility and possibly removability of repair/strengthening interventions.

38. Criteria for the selection of interventions The criteria for the intervention are the same already mentioned, but specific attention has to be paid to conservation principles. Besides, a clear understanding of the structural history of the building (type of action, causes of damage, etc.) should set its mark on the design. So, intervention should not only be aimed at reaching appropriate safety level of construction, but they should also guarantee: Compability and durability Integration / support to existing assessed behaviour Correct typological behaviour of the building Use of non-invasive techniques If possible, reversibility or removability Minimization of intervention

39. Criteria for the selection of interventions Interventions have to be regular and uniform on the structures. The execution of strengthening interventions on limited portion of the building has to be accurately evaluated and justified by calculating the effect in terms of variation on the stiffness distribution. Particular attention has to be paid also to the execution phase, in order to ensure the actual effectiveness of the intervention, because the possible poor execution can cause deterioration of masonry characteristics or worsening of the global behaviour of the building. 1. Interventions to improve the connections (walls – floors) 2. Interventions to improve the behaviour of arches and vaults 3. Interventions to reduce excessive floor deformability 4. Interventions on the roof structures 5. Interventions to strengthen the masonry walls 6. Pillars and columns 7. Interventions to improve connection of non-structural elements 8. Interventions on the foundation structures

40. RESEARCH Development of integrated and knowledge based methodologies for the protection of Cultural Heritage assets from earthquakes on the basis of optimization and minimum intervention approach.

41. RESEARCH COORDINATOR: Partnership • 18 partners • 12 countries • 9 Universities • 2 Research centres • 6 Enterprises • 1 Public body

42. RESEARCH NIKER catalogue: https://niker.isqweb.it/

43. RESEARCH CONSTRUCTION ELEMENT FAILURE MECHANISMS PRE-INTERVENTION PARAMETERS

44. RESEARCH CONSTRUCTION ELEMENT FAILURE MECHANISM

45. RESEARCH FAILURE MECHANISM CONSTRUCTION ELEMENT POST-INTERVENTION PARAMETERS

46. Interventions to strengthen the masonry walls Interventions aimed at increasing the masonry strength may be used to re-establish the original mechanical properties lost because of material decay or to upgrade the masonry performance. Techniques used must employ materials with mechanical and chemical-physical properties similar to the original materials. With opportune cautiousness, suggested techniques are the “scuci-cuci”, non cement-based mortar grouting, mortar repointing, insertion of “diatoni” (masonry units disposed in a orthogonal direction respect the wall’s plane) or smallsize tie beams across the wall, with connective function between the wall’s leaves. Mortar repointing Injections technique: example of suitable execution and of problems related to uncorrected execution (e.g. lack of uniformity)

47. Masonry walls Grout injections research: grout selection through laboratory tests Fluidity Stability Injectability Grout injections research: injection on multi-leaf stone walls and calibration of models

48. Masonry walls GROUT INJECTION OF STONE MASONRY WALLS: monotonicand cyclic compression tests of three-leaf stone masonry walls

49. Historic architectural heritage: Interventions to strengthen the masonry walls GROUT INJECTION OF STONE MASONRY WALLS: monotonic and cyclic compression tests of three-leaf stone masonry walls Increase of approximately 2 times of the compressive strength

50. diatono Historic architectural heritage: Interventions to strengthen the masonry walls Direction of the seismic action Shaking table tests on out-of-plane behaviour of single structural elements: stone masonry wall • Strengthened by: • Injections • Steel ties • Both; injections + steel ties Application of transversal elements and ties to walls: • Improvement in the strength of the wall • Reduction of the dilatancy of the walls