Prof. Eng. Claudio Modena Full Professor of Structural Engineering

CRITERIA AND TECHNOLOGIES FOR THE STRUCTURAL REPAIR AND STRENGTHENING OF HISTORIC MASONRY

STRUCTURES: RESEARCH AND APPLICATIONS

Prof. Eng. Claudio Modena

Full Professor of Structural EngineeringDepartment of Civil, Architectural and Environmental Engineering (DICEA) University of Padova – [email protected]

Strenghtening and refurbishing of existing structures - Port of Spain, Trinidad & Tobago - 24-25 April 2014

Structural safety vs historical structures

Evidences exist that

no real PRESERVATION policies are possible of HISTORICAL BUILDINGS physical 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 techniques that are used to repair/strengthen historical structures most frequently provide inadequate performances

Structural safety vs existing 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

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

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 Guidelines for evaluation and mitigation of seismic risk to cultural heritage with reference to technical standard for construction (2006-2011)

- RILEM Recommendation 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”.

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.

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.

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

Recent advances

RECOMMENDATIONS FOR THE ANALYSIS,CONSERVATION AND STRUCTURAL RESTORATION OFARCHITECTURAL HERITAGE

Guidelines1. General criteria

2. Acquisition of data: Information and Investigation

2.2 Historical and architectural investigations2.3 Investigation of the structure2.4 Field research and laboratory testing2.5 Monitoring

3. Structural behaviour

3.1 General aspects3.2 The structural scheme and damage3.3 Material characteristics and decay processes3.4 Actions on the structure and the materials

4. Diagnosis and safety evaluation

4.1 General aspects4.2 Identification of the causes (diagnosis)

4.3 Safety evaluation4.3.1 The problem of safety evaluation

4.3.2 Historical analysis4.3.3 Qualitative analysis4.3.4 The quantitative analytical approach4.3.5 The experimental approach

4.4 Judgement on safety

5. Decisions on interventions - The Explanatory Report

Recent advances

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

Recent advnces

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;

removability of the interventions and the compatibility of traditional/modern/innovative materials and construction techniques.

Recent advances

- 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

A KEY ISSUE

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 buildingGeometrical surveyHistorical 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

The “knowledge level”

1 m

1 m

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

CONSTRUCTIVE DETAILS

MATERIAL PROPERTIES

connections, lintels, elements to counteract thrusts, vulnerable elements, masonry tipology

particularly aimed at the mechanical characterization of masonry, through inspections, NDT, MDT & DT

• by means of surveys

• limited in situ inspection• extended & comprehensive in situ inspection

• limited in situ testing (inspections)• extended in situ testing (MDT & NDT)• comprehensive in situ testing (DT)


> 15

St. Agostino

INSTALLED SENSORS (Sept 2010)2 Temperature sensors4 PDT (crack detection)4 String pot16 single axis accelerometers

Nagoya University, Japan


> 16

INSTALLED SENSORS (Sept 2010)2 Temperature sensors4 PDT (crack detection)4 String pot16 single axis accelerometers

Static sensors

accelerometers


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

Structural modelling and seismic analysis methods

The structural models

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.




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

Salò-Garda lake earthquake (24/11/2004)

Giuffrè, 1993



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)


Analytical approach procedures considering the modelling of the elementary failure mechanisms with the limit analysis of local rigid body kinematic mechanisms of structural macroelements (portions of the buildings with homogeneous constructive characteristics and structural behaviour) found a better match with the observed damage


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, global analytical procedures applied to historical masonry building can be misleading in the interpretation of the actual behaviour of the analyzed buildings.

AZIONI FUORI PIANO AZIONI NEL PIANO

MURATURE D’AMBITO

MURATURE INTERNE

DISCONTINUITA’ MURARIE

ORIZZONTAMENTI E COPERTURE

AGGETTI

IRREGOLARITA’ PLANO

VOLUMETRICHE

INTERAZIONE EDIFICIO-EDIFICIO

CLASSIFICAZIONE DEI MECCANISMI DI DANNO

AZIONI FUORI PIANO AZIONI NEL PIANO

MURATURE D’AMBITO

MURATURE INTERNE



AGGETTI


VOLUMETRICHE



Out of plane In plane

External walls

Discontinuity

Horizontal structures

Terraces and chimneys

Irregularities in plan and in elevation

Buildings interactions

Internal walls AZIONI FUORI PIANO AZIONI NEL PIANO

MURATURE D’AMBITO

MURATURE INTERNE



AGGETTI


VOLUMETRICHE



INTERAZIONE TERRENO-EDIFICIO

Building-soil interaction


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


XVIII Century church by Frigimelica with central plan and some irregularities due to following resets done in the first half of the XX Century

Example: the church of S. Maria del Pianto

Critical survey


Façade

Lateral Wall A

Western Bell Tower

Sacristy

Lateral Wall F

Eastern Bell Tower

Baptismal Font

Eastern Apse

Wall E

Wall C

Wall B

Western Apse

Wall D

Southern Apse

Identification of the macroelements



P4

P4

N2

N2 Gn2

P5

P5 G2

P3

P3 G1

N1

N1 Gn1

P1

P1 G1

P2

P2

P a r e te e s t P a r e te o v e s t

Mst = 52230 daN m

Minst = 3984900 daN m

c = 0,0131

CN1

N1 Gn1

P1

P1

G1

P2

P2

CN1

N1 Gn1

P1

P1

G1

P2

P2

Mst = 236220 daN m

Minst =4441250 daN m

c = 0,05319

Mst = 41137 daN m

Minst =1473034 daN m

c = 0,0279

Mst = 2125 daN m

Minst =148300 daN m

c = 0,0143



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.



y

zA

B

C

D

E

z

y

, , 0i x i i y i j ji i j

P P F

,

,

i y i j ji j

i x ii

P F

P

0 hv LL

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:

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.

The collapse limit acceleration a*0 is derived as: where e* is the participant mass factor and g is the gravitational acceleration. e

ga *

*

0

SIMPLIFIED PROCEDURE FOR THE SEISMIC ASSESSMENT OF MASONRY BRIDGESSTRUCTURAL CAPACITY TO HORIZONTAL LOADS


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).

The structural modelsSIMPLIFIED PROCEDURE FOR THE SEISMIC ASSESSMENT OF MASONRY BRIDGESCOLLAPSE 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.


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.


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.

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


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 experience of the Umbria-Marche earthquake shown the effect of stiffening the horizontal diaphragm by substituting original wooden floors with stiff reinforced concrete floors…

The masonry is not adequately

strengthened

Expulsion of the façade

The orthogonal walls are not adequately connected each other


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…

Jacketing

Poor quality

Montesanto (Sellano), 1997

Montesanto (Sellano), 1997

Reinforced injection

Building strengthened after the Bovec earthquake (Kobarid - Slovenia) in 1998, damaged again during the 12/07/2004 earthquake.

Injection


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


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. Arche Scaligere (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.


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 DURABILITYINTEGRATION / SUPPORT TO EXISTING ASSESSED BEHAVIOURCORRECT TYPOLOGICAL BEHAVIOUR OF THE BUILDING USE OF NON-INVASIVE TECHNIQUES IF POSSIBLE, REVERSIBILITY OR REMOVABILITY MINIMIZATION OF INTERVENTION


1. Interventions to improve the connections (walls – floors)1. Interventions to improve the connections (walls – floors)

2. Interventions to improve the behaviour of arches and vaults2. Interventions to improve the behaviour of arches and vaults

3. Interventions to reduce excessive floor deformability3. Interventions to reduce excessive floor deformability

4. Interventions on the roof structures4. Interventions on the roof structures

5. Interventions to strengthen the masonry walls5. Interventions to strengthen the masonry walls

6. Pillars and columns6. Pillars and columns

7. Interventions to improve connection of non-structural elements7. Interventions to improve connection of non-structural elements

8. Interventions on the foundation structures8. Interventions on the foundation structures

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.


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.

RESEARCH

Partnership

• 18 partners• 12 countries

• 9 Universities• 2 Research centres

• 6 Enterprises• 1 Public body

COORDINATOR:

RESEARCH

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

RESEARCH

CONSTRUCTION ELEMENT

WALL

FLOOR

ROOF

ARCH/VAULT

CONNECTION

SUB-ASSEMBLY

MATERIAL TYPOLOGY

EARTH MASONRY

ADOBE

RAMMED

COB

STONE MASONRY

SINGLE-LEAF

MULTI-LEAF

BRICK MASONRY

SINGLE-LEAF

MULTI-LEAF

IN-PLANE FAILURE

OUT OF PLANE OVERTURNING

OUT-OF-PLANE FLEXURE

LAYER SEPARATION

FAILURE MECHANISMS

INTERVENTION 1INTERVENTION 2



INTERVENTION 1INTERVENTION 1INTERVENTION 2

INTERVENTION 1

INTERVENTION 1 INTERVENTION 1 INTERVENTION 1


INTERVENTION 1 INTERVENTION 1INTERVENTION 1INTERVENTION 2







INTERVENTION 1

Property Symbol [Units] Description Range of values

Apparent density ρ [kg/m3]

Elastic Modulus E [N/mm2]

Shear modulus G [N/mm2]

Compressive strength fc [N/mm2]

Initial shear strength fv0 [N/mm2]

Tensile strength ft [N/mm2]

…. …

PRE-INTERVENTION PARAMETERS

RESEARCH


WALL

FLOOR

ROOF

ARCH/VAULT

CONNECTION

SUB-ASSEMBLY

MATERIAL TYPOLOGY

EARTH

ADOBE

RAMMED

COB

STONE

SINGLE-LEAF

MULTI-LEAF

BRICK

SINGLE-LEAF

MULTI-LEAF

IN-PLANE FAILURE



LAYER SEPARATION

FAILURE MECHANISM

In-plane failure

Performance Indicators Symbol Units Description Failure Scheme

Apparent density

Elastic modulus

Shear modulus

Compressive strength

…





INTERVENTION 1










INTERVENTION 1

Descriptive performance indicator Description

Section monolithism

RESEARCH


WALL

FLOOR

ROOF

ARCH/VAULT

CONNECTION

SUB-ASSEMBLY

MATERIAL TYPOLOGY

EARTH

ADOBE

RAMMED

COB

STONE

SINGLE-LEAF

MULTI-LEAF

BRICK

SINGLE-LEAF

MULTI-LEAF

FAILURE MECHANISM





INTERVENTION 1










INTERVENTION 1

IN-PLANE FAILURE



LAYER SEPARATION

INTERVENTION 1

Property Symbol [Units] Description Range of values

Apparent density ρ [kg/m3]

Elastic Modulus E [N/mm2]

Shear modulus G [N/mm2]

Compressive strength fc [N/mm2]

Initial shear strength fv0 [N/mm2]

Tensile strength ft [N/mm2]

…

Performance indicator Description

Section monolithism

…

POST-INTERVENTION PARAMETERS

RESEARCH

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 small size tie beams across the wall, with connective function between the wall’s leaves.

Injections technique: example of suitable execution and of problems related to uncorrected execution (e.g. lack of uniformity)

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.

Mortar repointing

Interventions to strengthen the masonry walls

Fluidity Stability Injectability

Grout injections research: grout selection through laboratory tests

0inf,infinf,0, )()( fVVfVVf kexexexwc

Grout injections research: injection on multi-leaf stone walls and calibration of models

Masonry walls

GROUT INJECTION OF STONE MASONRY WALLS:monotonic and cyclic compression tests of three-leaf stone masonry walls

Masonry walls

Increase of approximately 2 times of the compressive strength

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

Historic architectural heritage: Interventions to strengthen the masonry

walls

diatono

Application of transversal elements and ties to walls:

• Improvement in the strength of the wall• Reduction of the dilatancy of the walls

Direction of the

seismic actionShaking table tests on out-of-plane behaviour of single structural elements: stone masonry wall

Strengthened by:• Injections• Steel ties• Both; injections + steel ties

Historic architectural heritage: Interventions to strengthen the masonry

walls

Unstrengthenedcondition

Strengthenedusing ties

Strengthenedusing injection

Strengthened using ties and injection

0.25g 0.45g 0.60g 0.75g

• Failure mechanisms;• Variation of dynamic characteristics (frequencies, mode shapes);

Shaking table tests on out-of-plane behavior of single structural elements: stone masonry wall

Masonry walls

• Diagonal compression test;• Characterization of grout-original mortar interface.

Effect of six injection grouts, use to strengthen irregular stone masonry walls, damaged by April 6th 2009 earthquake

Masonry walls

Masonry walls

Soni

c Ve

loci

ty m

/s2

Soni

c Ve

loci

ty m

/s2

INCREASE SONIC VELOCITY ABOUT 2,7 TIMES

INCREASE SHEAR STRENGTH TO 2 TIMES

INCREASE SHEAR MODULUS G TO 5-10 TIMES

Effect of six injection grouts, use to strengthen irregular stone masonry walls, damaged by April 6th 2009 earthquake

Masonry walls

Town Walls, Cittadella:

• local rebuilding

• grout injection

• repointing

Masonry walls

Interventions aimed at the in-plane stiffening of existing floors must be carefully evaluated since the horizontal seismic action is transferred to the different masonry walls in function of the floor plane action, depending on its stiffness.

In plane and flexural floors stiffening with ‘dry’ techniques is obtained by providing, at the extrados of the existing floor, a further layer composed by wooden planks, with orthogonal direction respect the existing.

The use of metallic belts or FRP strips, disposed in a crossed pattern and fixed at the extrados of the wooden floor or the use of metallic tie-beams bracings, may improve the stiffening effect.

Axonometric views

Timber floors

• Different strenghetning systems (plankings, diagonals, nets, ..) and materials (wood, earth, FRP, Natural fibres) applied at the extrados, for a total of 35 laboratory tests

• High performance obtained for wooden planking (45°, single or double) both for strength and deformation capacity

• The shear stiffness of the joist ceiling is principally influenced by the planking thickness

• The shear capacity of the floors is linearly related with the strength of the fasteners

• Proper double planking provides stiffness capable to redistribute horizontal loads to bearing walls, comparable to the effect of more modern floors

Timber floors

Ducale Palace, Urbino

Timber floors

Reinforcement materials: CFRP, SRP, SRG, BTRM

Arches and vaults

STRIP POSITION

SETUP

GEOMETRY AND LOAD CONDITION

Arches and vaults

FAILURE MECHANISMSRigid block mechanism, opening of hinges without shear failure (VM, VC_BTRM VC_FR_SRG e VC_FR_SRP)

VC_FR_SRG/SRP

VC_BTRM

Arches and vaults

COMPARISON BETWEEN EXPERIMENTAL RESULTSThe different techniques showed different behaviour, brittle for the reinforcements with epoxy matrix, rather ductile for BTRM material and ductile for SRG and extrados stiffening diaphragm with composite materials.

Arches and vaults

S. Fermo Church, Verona

Sandro Gallo Bridge, Venezia

Bruni Villa Megliadino San Vitale (Padova)

Arco A1

0

50

100

150

0306090120150180210240270300330360390420450480510540

Ascisse arco (cm)

Ord

inat

e ar

co (c

m)

intradosso

estradosso

Linea delle pressioni

Application of FRP laminates to vaults: examples

Arches and vaults

C

C

Application of extrados elements and FRP laminates to vaults: examples

Ducale Palace, Urbino:

- Substitution of the thin “frenelli” (5 cm thick) with solid brick panels (16 cm thick).

- Application to the both sides of CFRP strips to make active the “frenelli” up to their ends.

- Realization of transverse ribs connected to the “frenelli” edges by thin solid brick panels and a CFRP strip on the top.

sezione A-Ascala 1:20

Arches and vaults

The goal is to allow the structure to manifest a satisfactory global behaviour, by improving the connections between masonry walls and between these and floors: this may be achieved via the insertion of ties, confining rings and tie-beams.

An effective connection between floors and walls is useful since it allows a better load redistribution between the different walls and exerts a restraining action towards the walls’ overturning. Considering wooden floors, a satisfactory connection is provided by fasteners anchored on the external face of the wall

Walls to floors connections

Connections and dissipative systems with early warning: intervention techniques, testing, modelling and design procedures


• Anchoring ties

• Reinforcing rings

• Floor/walls

connections

Residential buildings, Montesanto (Sellano)


Ducale Palace, Urbino (Italy): Positioning and design of ties in the façade

Intervention area: front on Rinascimento square

Existing anchors

Assicurare il perfetto contattopiastra-muratura con interposizionedi lamine di piombo

Barra Ø10 mmL. = 10 mmsaldataal paletto

cuneo econtrocuneo

cilindro con foro filettato

Saldaturadi prima classe

Barra Ø10mmL.=10mmsaldata al paletto

cilindro inox Ø70 mm filettato

Barra inox Ø36mm filettatainserita dall'esterno entro foropraticato con carotaggio


Characterization of the seismic behaviour of substructures and structures, original and strengthened with integrated interventions coming from previous tasks, by shaking table:

Th_7

-0,3

-0,2

-0,1

0

0,1

0,2

0,3

0 5 10 15 20

Time [s]

Ag

[g]

Systemic seismic response

Floor Dimensions:2.40m x 2.8m

Height: 3.60m

Regular openings

Masonry deepness: 0.33m(12cm external layers 9cm internal filler)

Double planking wooden floors

Additional masses (500kg per floor)

Penna et al. 2009

Montenegro earthquake (14/4/1979) was chosen and the signal was elaborated considering the scale factor of 2:3

Dynamic behaviour whole structures Building Models


URM Model SM Model RM Model

0.05g XY 0.05g XY 0.05g XY0.10g XY 0.10g XY 0.10g XY0.15g XY 0.15g XY 0.15g XY0.20g XY 0.20g XY 0.20g XY0.25gI XY 0.25g XY 0.25g XY0.25gII XY 0.30g XY 0.30g XY0.30g XY 0.35g XY 0.35g XY0.35g XY 0.40g XY 0.40g XY0.40g XY 0.45g XY 0.45g XY0.45g XY 0.50g XY 0.50g XY- 0.55g XY 0.55g XY- 0.55g X 0.55g XY- 0.60g X 0.60g XY- 0.65g X -- 0.70g I X -- 0.70g II X -

The dynamic behaviour of models was monitored using several systems simultaneously:

• 16 Sensors fixed externally at masonry;

• 6 Sensors fixed internally to the wooden beams.

Accelerations were recorded using two systems:

Experimental steps

Displacement monitoring systems:

• More than 100 points were optically monitored;

• Deformation of 3 panels;• Base Displacement.


1st PHASE (1361-1396): CONSTRUCTION OF THE BELL TOWER

The tower, built next to the church between 1361 and 1396, was originally conceived as a completely independent structure

The tower, built next to the church between 1361 and 1396, was originally conceived as a completely independent structure

It is 65 m tall, has a square base of about 9.5m and shows a double pipe brick masonry structure, supporting the internal staircase.

It is 65 m tall, has a square base of about 9.5m and shows a double pipe brick masonry structure, supporting the internal staircase.

Case study :BASILICA DEI FRARI (VENICE)

Campo dei Frari

1902: COLLAPSE OF THE BELL TOWER OF THE ST. MARK BASILICA

Monitoring of the venetian towers, including the “Frari” bell towerMonitoring of the venetian towers, including the “Frari” bell tower

DIFFERENTIAL SETTLEMENT BETWEEN CHURCH AND TOWER: 30 cm OUT-OF-PLUMB: 76cm ON A HEIGHT OF 42.5m

RESULTS OF THE MONITORING:

1903: Intervention on tower’s foundations1903: Intervention on tower’s foundations

Pavimentazione esterna

Cordolo incalcestruzzo

Fondazioneaggiuntiva

SECTION A-A

CONSEQUENCES: Reverse of tower’s rotation toward the church The new structural configuration caused the

formation of widespread cracks and extensive damages on structural elements of the church directly connected to the bell tower

STRUCTURAL INTERVENTION IN THE 20TH CENTURY

Cases study:BASILICA DEI FRARI (VENICE)

Experimental investigations and monitoring

1990 - fotogrammetric survey; - geotechnical investigations on the foundation’s soil; - endoscopies;- single and double flat-jack tests on the masonry elevation structures; - sonic tests on steel ties;- monitoring of the main cracks, by means of extensometers;- positioning of clinometers (detection of rotations of the bell-tower).

discrete stability of the tower structure; out of plumb of about 0.8 m

2000 - worrying sign of structural deterioration (new crack patterns; widening of already existing fissures; falling of small portions of plaster and bricks from the vaults).

- survey of differential settlements in different points of the complex

disconnectedness of the stone ashlars of the aisle arch adjacent to the bell-tower (differential settlement of the arch supports) installation of a timber prop

average subsidence of the structure of the church: - 10 ÷ - 20 mm average subsidence of the area of the bell-tower base: - 49.8 mm East corner

- 61.3 mm South corner- 93.3 mm West corner

settlements

250 cm

Timber frame

40 cm

40 cm

40 cm

6 ns

6 ns

6 ns

250 cm

Timber frame

40 cm

40 cm

40 cm

6 ns

6 ns

6 ns


2001 automatic monitoring system (check of the deformations):- 6 long base extensometers relative displacements

between the walls of the bell-tower and the adjacent structures of the basilica;

- 8 crack-gauges installed on the main cracks of the South-West side of the bell-tower and of the wall above

the stone arch.

the opening of the cracks is only partly caused by the settlement noticed at the foundations level

0 2.5 5m

A3 A4

A6

A5

A2A1

B4

y

x

B3y

x

B2

y

x

A : long-base extensometersB : crack-gauges

XV-XXXV XX-XXI The differential settlements and the comparison between the fotogrammetric survey of 1995 and 2000, indicated that the bell-tower is tilting in the opposite direction respect the “historical” tendency, meaning that it is going back towards its vertical.

250 cm

Timber frame

40 cm

40 cm

40 cm

6 ns

6 ns

6 ns


(0.00)

(0.09)

(0.00)

(0.56)

(0.72)

(0.63) (0.95)(0.00)

2003 investigation campaigns - analysis of the state of stress: flat jack tests

1.76 MPa1.76 MPa

3.12 MPa3.12 MPa

1.92 MPa1.92 MPa

1.44 MPa1.44 MPa

Values in MPa

Second Test CampaignSecond Test Campaign Third Test CampaignThird Test Campaign


EL3EL4

EL1

EL2EL7

T1PD1

y

x

SECTION A-ASECTION A-A SECTION B-BSECTION B-B

Direct Pendulum

Crack-gauges

Strain Gauges

Temperature sensors

Direct Pendulum

Crack-gauges

Strain Gauges

Temperature sensors

2003 extension of the automatic monitoring system


2003 extensive geotechnical investigation campaign

- analysis of the subsoil stratigraphy and geotechnical properties;- exploration of the exact geometry and typology of the foundation block;- definition of an accurate geotechnical model of the foundation finally completed;- in situ tests:

- 2 vertical boreholes: outside the church, to a depth of 25.50 m and inside the bell-tower, to a depth of 21.50 m;

- 5 inclined boreholes;- 4 continuous borings into the foundation block:

-EI1 and EI2 inclined of 30°, drilled for length of 4 m and located inside the basilica;

-SVE1 and SVE2 short vertical borings, carried out on the NE side of the bell-tower;

- 4 static penetrometer tests with monitoring of pore water pressure (piezocone tests – CPTU) pushed to variable depths (17.00 ÷ 19.20 m);

- Standard Penetration Tests (SPT), in boreholes;- Extractions of soil and foundation samples.


Geotechnical section and foundation geometry

Origin of continuous settlements and stability problems

Some progressive failure of the soft silty clay layer, squeezed between the piles end and the unit C, must be taken into account.

In addition, a possible increasing decay of the mechanical characteristics of the wooden piles under the foundation block could also be seen as concomitant cause.


Structural modeling

The modelled portion of structure includes the bell-tower and the adjoining parts of the church that were mostly affected by the interaction with the tower

The only load condition considered is the self weight. The load corresponding to some parts of the real structure not modelled (timber structure roof of the basilica, belfry), was imposed as external forces; the crossed vaults’ filling was included as surface load.

The mechanical properties chosen to describe the materials arise from the results of previous tests performed on the masonry structures. In particular:

- elastic modulus E = 3300 MPa (average of the results of double flat jack tests performed on the bell-tower masonry)

- density ρ = 2000 kg/m3

The material is considered homogeneous and isotropic, and the analyses performed are linear elastic.


Two previous models, calibrated with the available experimental data (historical drawings, surveys, monitoring and on site tests), were analyzed before implementing the actual one, by means of imposed rotations and translations at the base of the bell-tower: - after the construction (1450);- before the strengthening intervention on the bell-tower (1903).

In each model, after running the analysis, a higher deformability was assigned to the elements subjected to an excessive tension respect the assumed strength of the material, in the successive analysis.

A tensile stress concentration appeared in the model where a real crack pattern is evident. The propagation of some principal cracks was followed by the subsequent iterative process.

1450 model

1903 model


− preferential channels of compressive stress localized inside the masonry wall above the propped arch;

− high tensile stresses found in the same masonry wall, due to the settlements of the bell-tower wide crack patterns and loss of shape of the stone arch;

− high stress found below the capital of the column horizontal thrust determined by the movements of the bell-tower;

− tensile stress in correspondence of the bell-tower window opening on the transept presence of the main fissure on the external pipe of the bell-tower.

2002 model

compressivetensile

The final model reflects the tendency of the XX century. An “inverted” rotation was imposed to the bell-tower, with an average settlement of 84 mm.

Results:


XV-XXXV XX-XXIThe differential settlements and the comparison between the fotogrammetric surveys, indicated that the bell-tower is tilting in the opposite direction respect the “historical” tendency, meaning that it is going back towards its vertical.

compressivetensile

− preferential channels of compressive stress localized inside the masonry wall above the propped arch;

− high tensile stresses in the same masonry wall wide crack patterns and loss of shape of the stone arch;

− high stress below the capital of the column horizontal thrust determined by the movements of the bell-tower;

− tensile stress in correspondence of the bell-tower window opening on the transept presence of the main fissure on the external pipe of the bell-tower.


Realization of a provisional intervention for static control

Structural schemes considered for the design of the intervention


Realization of a provisional intervention for static control


CONSEQUENCES OF THE INTERNAL STATE OF STRESS CREATED BY THE MECHANICAL INTERACTION:

increase of the compression load on the columnincrease of the compression load on the column

decrease of the vertical load (equal to the increase on the column) on the towerdecrease of the vertical load (equal to the increase on the column) on the tower

a strong transverse bending stress on the column, due to both the eccentricity of the vertical load applied to it and the horizontal component of the thrust

a strong transverse bending stress on the column, due to both the eccentricity of the vertical load applied to it and the horizontal component of the thrust

Structural Diagnosis


BASIC PRINCIPLE OF THE INTERVENTION:

• Creation of a joint in order to separate the bell tower from the church and make them structurally more independent

• Reduction of the compressive forces that transfer part of the tower’s self weight to the column

BEFOREBEFORE AFTERAFTER

Structural Diagnosis



BEFOREBEFORE AFTERAFTER

The earthquake of 6th April 2009 destroyed the small village of Onna. So Onna became the symbol of the tragedy that struck the minor historical villages.

Cases study:St. Pietro Apostolo (Onna - L’Aquila)

The German government immediately signaled desire to help the local community, it especially financed the rebuilding of the church, dedicated to St. Pietro Apostolo, also severely damaged by the seismic action.

The 4th June 2010 an agreement for the reconstruction of the church has been signed between the Italian Ministry of Cultural Heritage and the Federal Ministry of Transportation, Building and Urban Development of the Federal Republic of Germany.


The church and annexed buildings survey began with the GEOMETRIC SURVEY of the structure and the decoratives.


The church is included in an AGGREGATE, that include some buildings with different history and structural typology.

CHURCHBELL TOWER“CONGREGA”SACRISTYPARSONAGE


The damage survey was performed to define the structural faults that, among the structural features, caused the collapses and the severe damages.

SCHEMATIZATION OF THE MAIN COLLAPSES


FAÇADE

The façade showed a double damage mechanism:-the global overturning;-the overturning of the upper part (that collapsed).


APSE AND BELL TOWERThe most severe damages are concentrated into the apse and bell tower, both totally callapsed; only a portion of about 1,5 m height survived.

BELL TOWER

APSE

R.C. BEA

M

Damages were amplified by the resence of the r.c. beam located between the church and the “congrega”.


LONGITUDINAL WALLS

The longitudinal walls show the damages due to their in plane behaviour. The presence of several niches and openings worsen the wall property.

LEFT LONGITUDINAL WALL – PRESENCE OF OPENINGS AND NICHES


The first historic documents about Onna dates 1178, in a bull of Papa Alessandro III.

The probable cistercian origin can be observed through the planimerty and the presence of several stone elements of the beginning of the XIII century.

The final shape of the church was realized after the reconstruction that followed the 1703 earthquake.

During the 50’s some intervention on the whole church were realized: the wall between the church and the “congrega” was demolished.


In the period betwen November 2010 and February 2011 some STRUCTURAL INVESTIGATIONS supported the restoraion project of the church:

Foundation investigations

Corings on the walls

Considering the heavy damages on the structures, only NDT or MDT were performed: these investigations were finalized to the qualitative and morphological evaluation of the structures.


Sonic Tests

Injections tests

FAÇADE LEFT LONGITUDINAL WALL

After the executions of the injections, the sonic tests were repeated.

AFTERBEFORE


To define the characteristic of the foundation soil some investigations were performed: geognostic surveyMASW tests

SEISMIC CLASSIFICATION OF THE SOIL:“C”


FAÇADE

LEFT LONGITUDINAL WALL


The architectural restoration design of the church and of the aggregate is based on two principles:1. The maximum conservation of the main valuable elements2. The rebuilding with similar shape of the collapsed portions

The architectural design choices were conditioned by structural considerations. Particularly the choice of the rebuilding of the wall between the nave and the “congrega”.


The STRUCTURAL DESIGN is based on the following considerations:

conservation of the more valuable portions (façade and North wall) using non invasive techniques, as recommended by the Sacred Art Commitions of the L’Aquila Curia. in any case the façade and North wall will be characterized by low values of the strength, because the walls are severely damaged. Moreover these values are not completely reliable because the efficiency of the performed interventions is not totally known. the ultimate resistance of the whole structure is determined by the resistance of the weaker element, that will surely be one of the repaired elements (low and not reliable strength).


So two interventions strategies were designed to increase the structural reliability:

1. Increase the capacity of the structure, acting on the structural configuration and the growing of the global behaviour;

2. Reduction of the input actions using base isolation system.

These two strategies are not alternative, but the second one is the extension of the first: so it is possible to choose between two intervention levels, with different impact but also two different protection degree, towards the ultimate state limit. Only the base isolation system can guarantee the full satisfaction of the “artistic” limit state.

RICOSTRUZIONE DEL CAMPANILE


Interventions on HISTORIC MASONRY WALLS: cracks repair with “scuci-cuci” technique consolidation with grout injections closing of niches and creation of connections creation of reinforced bricks horizontal layers


RECONSTRUCTION OF COLLAPSED MASONRY WALLS : repair and consolidation of remaining portions

realization of new stone masonry walls with reinforced bricks horizontal layers partial reconstruction of the wall between the church and the “congrega”


Maintaining of the ROOFING system with wooden trusses and positioning of a double planking to create a rigid plane.

The existing r.c. RING BEAM will be replaced with a masonry ring beam that will be connected with the wooden trusses. The ties will be placed inside the ring beam.


The seismic answer of the structure has been evaluated through kinematic verifications and through a Finite Element 3D Model

FE MODEL

FIRST VIBRATION MODE

KINEMATISM OF FAÇADE OVERTURNING


PLANE OF THE BASE ISOLATION DEVICES

A double line of isolators around the perimeter of the existing foundation is present

1- EXTERNAL ROW: elastomeric isolators (they characterize the behaviour of the isolation system in terms of stiffness and dissipation) and teflon-steel devices

2- INTERNAL ROW: simple teflon-steel slides characterized by a low friction coefficient (3%) and so by low stiffness and dissipation capacity.

The BASE ISOLATION SYSTEM design consider steel/teflon insulators.

The advantages in terms of "conservation" are:

• minimizing (20 cm) the thickness of the r.c. slab that collects the load transmitted to the base of the walls and transfer it to isolation system, thanks to the very close isolators;

• the slab doesn’t touch the top surface of the XIV century foundation, that remains intact;


LONGITUDINAL SECTION

• The bigger devices are kept outside the church. In fact, they must meet specific performance requirements (location of the stiffness center), and require greater freedom of access for maintenance and substitutions;

• simple teflon-steel "slides" are placed inside the church: they are characterized by high durability, small footprint, little maintenance needed and accessibility (through simple hatches) for manual operations that can occur also without direct access to a basement (planned in the project, but not strictly necessary);


ADAPTABILITY OF THE SYSTEM: the sledges and seismic isolators position may be modified according to the presence of archeological remains.

• thanks to the negligible horizontal forces absorbed by the slides, very small and very flexible support structures can be realized: in the project isolated pillars, that help to increase the awareness of the historical foundation are provided, but their number and position can be easily modified, linking the top of the pillars with beams that allow the accommodation of the slides, making them easily adaptable to the needs of preservation of what will be highlighted by the planned archaeological excavation within the church.


CASE STUDY : RIACE BRONZES

4. BENI MOBILIAssembling of anti-seismic devices

Acquisition of displacement data through 3DVision system

MESHINGHIGH-RESOLUTION LASER SCANNER: 3D RECONSTRUCTION OF THE GEOMETRIC MODEL WITH A HIGH LEVEL OF DETAIL

PREPROCESSING PHASE: WHERE NECESSARY,

MANUAL RECONSTRUCTION OF THE MESH

MESH IMPORT INTO STRAUS7 SOFTWARE AND TRANSFORMATION OF TRIANGULAR SURFACES INTO PLATE / SHELL ELEMENTS (3D MEMBRANE AND BENDING ELEMENT)

BRONZO A

BRONZO B

PRE-PROCESSING

1) CHOSEN TYPE OF ELEMENT • 3-NODE TRIANGULAR SHELL ELEMENT• 6DOF FOR EACH NODE – OUT OF PLANE

DISPLACEMENTS ASSOCIATED WITH THE BENDING BEHAVIOR ARE ALLOWED

2) DEFINITION OF MATERIAL CHARACTERISTICSLINEAR-ELASTIC MATERIAL• E = 113’000 MPA• Ρ = 8’500 KG/M3

• POISSON’S RATIO = 0,2

3) DEFINITION OF GEOMETRICAL CHARACTERISTICSASSIGNMENT OF THE THICKNESS ON THE BASIS OF A DETAILED GEOMETRIC SURVEY BRONZO A BRONZO B

PRE-PROCESSING

4) RESTRAINTS ASSIGNMENTFIXED RESTRAINTS AT THE BASE

5) LOADING CONDITIONS ASSIGNMENT TRUSS ELEMENTS INSERTION IN ORDER TO SIMULATE THE PRESENCE OF ANCHORED TIE RODS

INSERTION OF TIE RODS

TRUSS ELEMENTS

BEAM ELEMENTS

SIMULATION OF THEOLD SEISMIC ISOLATION

SIMULATION OF THENEW SEISMIC ISOLATION

BRONZO A

OLD SEISMIC ISOLATION NEW SEISMIC ISOLATION

PRE-PROCESSING

4) LOADING CONDITIONS ASSIGNMENT

BRONZO B


EXTERNAL SURFACE OF THE BRONZOOLD SEISMIC ISOLATION NEW SEISMIC ISOLATION

(I) STRESS DISTRIBUTIONS- VON MISES CRITERION (MPA)

EXTERNAL SURFACE OF THE BRONZO


ANALYSIS OF THE RESULTS – BRONZO A

MEDIAN SURFACE OF THE STATUE


(I) STRESS DISTRIBUTIONS- VON MISES CRITERION (MPA)

MEDIAN SURFACE OF THE STATUE


ANALYSIS OF THE RESULTS – BRONZO B

Tow case-studies of static and seismic retrofit of masonry road bridges are presented.In the S.Gallo Bridge the load bearing capacity of the existing structure has been increased through the thickening of the brick arch and the application of FRP laminates.In the GresalBridge the seismic vulnerability has been reduced through a new rc slab anchored to the piers with vertical ties and restrained at the abutments, collaborating with the existing structure in carrying horizontal loads.

SANDRO GALLO BRIDGE

GRESAL BRIDGE

Existing bridges - Design of intervention: cases study

The bridge was built in Venice in the XIX and widened in the first decades of the XX century, with a substantially homogeneous structural arrangement; before the intervention was used as vehicular bridge for light traffic (car, buses).

The Administration, in the framework of the improvement intervention of 1km bank sides of the Excelsior Canal, decided to increase the load bearing capacity of the bridge to the rank of 1st category bridges, as defined by the Italian standards (maximum double-axles load equal to 600 kN).

Cases study:Sandro Gallo Bridge

The bridge consists in a depressed brick arch with a clear span of about 9.10m and a rise of 2.15m (span to rise ratio=0.24), with a thickness of about 0.36 m (three brick layers) in the central part, and of 0.55 m (four brick layers) in the lateral part close by the springing.

The structural investigation, consisted in three core samples, three single and one double flat jack tests, performed on different points of the masonry arch (at 1,00, 1,70 and 1,90 m from the abutment). The results revealed a moderate state of stress in all tested points (0.25, 0.23 and 0.25 MPa respectively).

4. CONCLUSION4. CONCLUSION


Two more core samples were taken vertically at the abutments of the bridge, showing the presence of a 1.00-1.60 m layer of a gravel, sand and cobblestones filling under the road surface, then a difference in terms of foundations materials was found: abutments are made up of brick/trachyte masonry fixed with poor quality mortar, from -1.00m to -5.90 m below the road surface in the older part, and mainly by a massive concrete structure (thickness 2.70 m) in the more recent part corresponding to the widening of the bridge.


The intervention relies on the utilization of the existing structure, strengthened by the use of traditional technique (new brick layer) combined with innovative materials (CFRP).The central part of the arch span is strengthened by the insertion of one more layer of bricks. The thrust inside the vault is transferred from the new elements to the older structure in correspondence of the existing thickening of the arch (from three to four bricks). The connection between the new and the old masonry was obtained by positioning of brick units orthogonal to the axial line of the arch used as connectors, and positioning of steel bars, glued to the old structure with epoxy resin.


A further increase of the safety factor is found in the application, at the extrados of the masonry arch, of uni-directional high resistance CFRP stripes :The ends of the Carbon stripes are connected by epoxy-based adhesive to the new reinforced concrete abutments, and to the arch structure, whose surface is regularized by the presence of the new layer of bricks and smoothed through the application of a hydraulic-lime based mortar.

Ecfrp = 2,3E+05 MPa;ft, cfrp = 3430 MPa; e cfrp = 1,5%.


The intrados of the masonry arch has been restored in a “traditional” way (cleaning of the surface, removal of the plaster, excavation of the deteriorated part of the mortar joints, localized substitution of the most damaged bricks with new ones, repointing with proper hydraulic-lime based mortar.At the level of the abutments, a new foundationon micro-piles (diameter 200 mm, internal tubular reinforcement D= 101,6 mm, thickness 10 mm) was positioned aside the existing abutment, externally in respect of the canal: a beam was cast with shrinkage-compensated concrete adjacent to the old masonry structure, molded with a saw-tooth shape to allow a better transmission of the extra thrust coming from the increased live loads to the micro-piles, which are disposed in two rows, the internal line vertical and the external line inclined with a angle of 25°.


The Gresal bridge is located in the North-East of Italy , in the Belluno province; it was built in the XIX century and is currently used as a vehicular bridge.The structure is a three span stone masonry arch bridge, with a total length of 67.40 m: the three spans are almost equal, the single arch clear length being about 15m; their shape is almost semicircular with a radius of 7.39m, slightly increasing at the springers.The thickness of the arch, on the basis of the coring, was assumed variable from a value at the crown of 0.60 m, and 1.00m at the springing. The maximum height of the two piers, tapered between the base and the top, is 12.75m . At the base the pier section is 3.50x7.00m, with the longest dimension orthogonal to the bridge axis. The bridge was rated highly vulnerable to seismic action, mostly due to the slenderness of its high piers.

Cases study:Gresal Bridge

The structural investigation consisted in a geometrical survey and three core samples, one taken from the vault at the crown, the second taken from the pier and the third one drilled in the abutment, on an inclined plane. These investigations have allowed to determine the thickness of the brick stone, the layering of the material between the pavement and the masonry vault and to characterize the mechanical property of the infill material. The infill has very good mechanical characteristics and is made by stones and pebbles.

CORING

ARCH CROWN STRATIGRAPHY


-The internal infill layer and pavement has been removed only for a thin portion, with the aim of saving as much as possible the fill material with the best mechanical properties, acting with a stabilizing function, maintaining the vault voussoirs under compression;-a new 25 cm thick r.c. slab has been laid over the whole bridge length, anchored to the abutments; - New high strength bars (26 mm diameter) have been placed inside the two central slender piers, in vertical holes drilled from above and reaching the foundations. The bars are anchored at the top to the r.c. slab as well, and the combined action of the r.c. slab, vertical bars and “confined” infill allows the creation of a new resisting strut -tie scheme in longitudinal direction.


In the transverse direction the vertical reinforcement enhances the pier resistance to combined bending-compressive stress states. -New reinforced concrete plinths on micro-piles have been positioned out-side the existing masonry abutment. In the transversal section the micro-piles have been disposed in two inclined rows in order to transfer the action to the ground, and at same time oppose the abutment overturning.


MICRO-PILES POSITIONED IN TO THE MASONRY ABUTMENT

-The spandrel walls of the arches have been restored in a “traditional” way: the surface has been cleaned, damaged bricks have been substituted with new ones, the deteriorated part of the mortar joints has been excavated and re-pointed with proper hydraulic-lime based mortar while stainless steel bars 6mm in diameter have been inserted in the mortar joints. -Transversal stainless steel ties (D=24mm) which restrain the walls at the top and avoid out-of-plane overturning.

-It has to be noticed that the repair intervention has increased the structure dead loads only by about 1%.


High-strength bars placed inside the pier, act as tie when anti-symmetric deformation acts for the arches under horizontal forces, avoiding the uplift of the rc slab. A state of confinement of the infill can be realized, and strut -tie mechanisms can develop. Inclined micro-piles can absorb the horizontal action at the abutments .


Cases study

Thank you for your attention…!

Prof. Eng. Claudio Modena

Full Professor of Structural EngineeringDepartment of Civil, Architectural and Environmental Engineering (DICEA) University of Padova – [email protected]

Strenghtening and refurbishing of existing structures - Port of Spain, Trinidad & Tobago - 24-25 April 2014

Prof. Eng. Claudio Modena Full Professor of Structural Engineering

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Transcript of Prof. Eng. Claudio Modena Full Professor of Structural Engineering