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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
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Page 1: Masonry Retrofitting System - TU Dortmund...Retrofitting of load bearing masonry walls in earthquake regions Background - Concept of retrofitting Effect on wall performance under seismic

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

Page 2: Masonry Retrofitting System - TU Dortmund...Retrofitting of load bearing masonry walls in earthquake regions Background - Concept of retrofitting Effect on wall performance under seismic

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

Page 3: Masonry Retrofitting System - TU Dortmund...Retrofitting of load bearing masonry walls in earthquake regions Background - Concept of retrofitting Effect on wall performance under seismic

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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)

Page 4: Masonry Retrofitting System - TU Dortmund...Retrofitting of load bearing masonry walls in earthquake regions Background - Concept of retrofitting Effect on wall performance under seismic

Figure2: Retrofittingsystem[W1]

Anchor head

Textile reinforced retrofittingelement

Masonry

Anchor boltInjection ring

2

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].

Page 5: Masonry Retrofitting System - TU Dortmund...Retrofitting of load bearing masonry walls in earthquake regions Background - Concept of retrofitting Effect on wall performance under seismic

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Figure 3: Installation [W1]

Page 6: Masonry Retrofitting System - TU Dortmund...Retrofitting of load bearing masonry walls in earthquake regions Background - Concept of retrofitting Effect on wall performance under seismic

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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.

Page 7: Masonry Retrofitting System - TU Dortmund...Retrofitting of load bearing masonry walls in earthquake regions Background - Concept of retrofitting Effect on wall performance under seismic

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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

Page 8: Masonry Retrofitting System - TU Dortmund...Retrofitting of load bearing masonry walls in earthquake regions Background - Concept of retrofitting Effect on wall performance under seismic

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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%

Page 9: Masonry Retrofitting System - TU Dortmund...Retrofitting of load bearing masonry walls in earthquake regions Background - Concept of retrofitting Effect on wall performance under seismic

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Figure8: Ductilebehaviourofretrofittedwallcomparedwiththebrittlefailureofunretrofittedwall

(3) sliding mechanism (4) after testing under earthquake action

Figure 7: RetrofittedMasonrywallundersimulatedseismicaction/Testresults[W1]

Page 10: Masonry Retrofitting System - TU Dortmund...Retrofitting of load bearing masonry walls in earthquake regions Background - Concept of retrofitting Effect on wall performance under seismic

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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

Page 11: Masonry Retrofitting System - TU Dortmund...Retrofitting of load bearing masonry walls in earthquake regions Background - Concept of retrofitting Effect on wall performance under seismic

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.

9

Page 12: Masonry Retrofitting System - TU Dortmund...Retrofitting of load bearing masonry walls in earthquake regions Background - Concept of retrofitting Effect on wall performance under seismic

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