masonry retrofitting system - tu dortmund...retrofitting of load bearing masonry walls in earthquake...
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Retrofitting of load bearing masonry walls in earthquake regions
Background - Concept of retrofitting
Effect on wall performance under seismic actions
Effect on building performance under earthquakes
Faculty of Architecture andCivil EngineeringChair of Structural DesignUniv.-Prof. Dr.-Ing. Atilla ÖtesTU Dortmund UniversityAugust-Schmidt-Straße 844227 Dortmund
in cooperation with:
Hering Bau GmbH & Co. KG, SystemeNeuländer 157299 Burbach
© 2018 Chair of Structural Design, TU Dortmund University - Faculty of Architecture and Civil Engineering
[EP1] European Patent EP 2 722 466 B1 “Composite system for reinforcing building elements” EuropeanPatentOffice[W1] Wertenbroch, A. Verstärkung von Mauerwerkswänden mit textilbewehrten Betonelementen
zur Verbesserung der Trageigenschaften unter Erdbebenbeanspruchung Technische Universität Dortmund – Dissertation Schriftenreihe Tragkonstruktionen Heft 5 - 2017 (in German)[01] DIN EN 1998-1 Eurocode 8: Design of structures for earthquake resistance - Part 1 National Annex: DIN EN 1998-1 NA 01/2011
DIN Deutsches Institut für Normung e.V. – 12/2010
Further Information:https://www.bauwesen.tu-dortmund.de/tk/de/Forschung/Forschungsprojekte/Erdbebensicheres_Bauen/Verstaerken_von_Mauerwerk
References
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Background
Masonry wall V7Masonry wall V7
Unreinforced masonry walls show brittle failure mechanisms when
subjected to increasing horizontal loads in case of earthquakes.
Typical squat masonry walls stiffening the building exhibit diagonal
cracks leading to a loss of their structural integrity accompanied by
a reduction of their load carrying capacity.
Finally with the propagation of cracking in the corners the entire
wall fails (Fig. 1).
Figure 1: Tests on masonry walls under simulated seismic action (TU Dortmund University)
Figure2: Retrofittingsystem[W1]
Anchor head
Textile reinforced retrofittingelement
Masonry
Anchor boltInjection ring
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Concept of retrofitting
In order to overcome the brittle failure of a masonry wall, the wall
is retrofitted with textile reinforced concrete elements fastened
on both sides. For a durable fastening of these elements on the
masonry wall mechanical connectors are used (Fig. 2).
Sizing of the prefabricated retrofitting elements allows an easy
transportation and application on site by two persons. The installation
can be performed quickly and with high precision (Fig. 3). As a
major advantage, the intervention into the existing building and its
service life remains very limited.
Theretrofittingsystem is registered as European Patent [EP1].
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Figure 3: Installation [W1]
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Effect on wall performance under seismic action
The concept of supplying the masonry wall with stiff tension
elements via shear connectors leads to a composite system with
favourable properties.
Textile reinforced elements act as horizontal reinforcing with high
stiffness. They limit very effectively the relative displacements in
the masonry wall. Furthermore, keeping the wall together they
distribute the forces along the entire wall section.
In this way, the local stresses can be reduced and the global load
carrying capacity can be increased (Fig. 4).
As shown in Fig.5theexperimentwiththeretrofitted wall exhibits
an initial increase of the resistance compared with the reference
masonrywallwithoutretrofitting.
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Hmax = 145 kN
Figure4: PrincipalStresses-Masonry/RetrofittingElement
Figure5: RetrofittedMasonrywallundersimulatedseismicaction/Testresults[W1]
Tests on walls with calcium silicate bricks(corr. vertical load: σN = 0,5 N/mm²)
Masonry wall Retrofitted Masonry wall
maximum horizontal initial resistance 102 kN 145 kN + 42 %
(1) before testing (2) maximum resistance force
Hmax = 145 kN
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With increasing earthquake action on the wall, the system develops
a sliding mechanism between the two top blocks (Fig. 7). With the
high level of the friction resistance the system is able to perform
fully reversible plastic deformations.
This corresponds to a perfect ductile behaviour with a very high
capability of plastic deformations (Fig. 8).
Theretrofittingmeasuretransformsthebrittlemasonrywallintoa
ductile system with large energy dissipation capability providing an
excellent potential for damping.
Figure6: RetrofittedMasonrywallundersimulatedseismicaction/Testresults[W1]
Tests on walls with calcium silicate bricks(corr. vertical load: σN = 0,5 N/mm²)
Masonry wall Retrofitted Masonry wall
available horizontal resistance in ductile regime - 116 kN
Ductility - elasto-plastic behaviour
Energy dissipation / damping5 %
(basic damp-ing ratio)
pronounced energy dissipation due to sliding
mechanism equivalent damping ratio
up to 50%
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Figure8: Ductilebehaviourofretrofittedwallcomparedwiththebrittlefailureofunretrofittedwall
(3) sliding mechanism (4) after testing under earthquake action
Figure 7: RetrofittedMasonrywallundersimulatedseismicaction/Testresults[W1]
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Effect on building performance under earthquakes
Based on the large potential for ductility and damping of the retro-
fittedwalls,buildingswithsuchwallscanresisthigherearthquake
actions.
As an example, the structural system of a two-storey terraced
building with only two stiffening walls in one direction, has been
analysed (Fig. 9).With retrofittedmasonrywalls, the building is
able to withstand earthquake actions which are roughly three times
higherthanthecasewithoutretrofitting.Thereby,thelimitationsof
the Eurocode 8 for the storey displacements are considered.
Figure 9: Results of structural analysis - Increase of resistance against earthquakes
sustainable ground acceleration ag
Design for maximum strength
Design utilizing ductilityallowable storey displacement
0,3 % (7,5 mm) 0,4 % (10 mm) 1,0 % (25mm)withoutretrofitting 0,8 m/s² - - -retrofitted 1,0 m/s² 1,2 m/s² 1,5 m/s² 2,35 m/s²
Summary
- Theeffectivenessoftheretrofittingconceptformasonrywallsis
confirmedbyexperimentsoncalciumsilicatemasonrywalls.
- With prefabricated stiff tension elements mounted on the
masonry wall via shear connectors, the composite wall system
ensures the structural integrity of the masonry wall.
- Withtheretrofittingsystemthehorizontalbearingcapacityofthe
masonry wall can be increased.
- Theretrofittingsystemovercomes the brittle failure mechanisms
of masonry walls and introduces a ductile behaviour.
- The plastic deformability of the system leads to a remarkable
increase of damping properties.
- Based on these advantages masonry buildings with the
application of the retrofitting system can withstand higher
earthquake actions without failure.
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