SEISMIC RETROFITTING OF MASONRY WALLS

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SEISMIC RETROFITTING

CONCRETE FRAMES FAILURE MODES

Column-Sway Mechanism

Plastic hinges are generated at columns at the ground level (dangerous)

 

Beam-Sway Mechanism

Plastic hinges are generated at beam ends in the different levels (desired target)

 

Other Collapse Mechanism

Flexural

 

Buckling

 

Strengthening Methods

Columns flexural reinforcement: and CFRP jackets for shear strengthening and to limit longitudinal steel rebars buckling.

Beam-Column joint retrofit to avoid fragile shear collapses

 


 

IN-PLANE SHEAR LOADS

SEISMIC RETROFITTING OF MASONRY PANELS

UN-REINFORCED WALLS

 

 

Initial (Usual) State

COMPRESSIVE FORCES

Masonry strains are due to in-plane compressions, therefore wall is working under suitable conditions.

 

a) DIAGONAL TENSION MODE

Brittle failure mode; diagonal cracks are propagated through mortar and masonry units.

 

FAILURE MODE: SHEAR

b) JOINT SLIDING MODE

Ductile mode, energy is dissipated through friction

 

Joint sliding does not significantly reduce the axial load capacity of the wall. It does, however, reduce the out-of-plane flexural load strength (dangerous)

 

 

 

 

 

Unreinforced walls requiring shear reinforcement are those whose failure mode is due to stepped joint sliding or diagonal tension

 

 

 

 

 

 

FRP STRENGTHENING

 

BONDED CARBODUR PLATES

System overview

Plates should be installed in diagonal or horizontal position over the wall.

End anchorage

Extending CFRP plates beyond the wall is not required, but it´s a good practice (risk of wall overturning is reduced in case of out-of-plane excitacions

Spacing limits

It´s recommended that the maximum clear spacing of externally bonded plates be limited to 3 x wall thickness.

 

 

End anchorage

Plates overlap on adjacent in-plane columns is possible by extending plates over the concrete´s surface (effective length)

 

 

 

 

 

 

 

 

 

 

System overview

Plates should be installed in diagonal or horizontal position over the wall.

End anchorage

Extending CFRP plates beyond the wall is not required, but it´s a good practice (risk of wall overturning is reduced in case of out-of-plane excitacions

Spacing limits

It´s recommended that the maximum clear spacing of externally bonded plates be limited to 3 x wall thickness.

 

 

End anchorage

Plates overlap on adjacent in-plane columns is possible by extending plates over the concrete´s surface (effective length)

 

 

 

 

 

 

 

 

 

 

 

 

End anchorage

In case of walls in rigth angles, grooves can be achieved in order to ensure the plate continunity.

 

 

 

 

 

 

 

 

 

Overview

SIKAWRAP can also be applied in horizontal strips; spacing limits are the same as in CARBODUR option.

Fabric overlap on adjacent in-plane columns is still possible by extending plates over the concrete´s surface (effective length)

 

 

 

 

 

 

 

 

Anchorage

SIKAWRAP can also be additionaly anchoraged using SIKAWRAP FX-50C through adjacent walls.

 

NSM main advantages

– Can be installed even on weak substrates
– Better behaviour under compressive forces
– Reduced surface preparation
– Invisible
– Easy anchorages through walls/slabs (cutting/drilling)

 

Installation

SIKA CARBODUR NSM Plates/Rods and plates can be easilly installed into grooves, using SIKADUR 330 or SIKA ANCHORFIX.

 

NSM Anchoring

Grooves can be homogeneous through the masonry walls and concrete adjacent colums.

In case of perpendicular walls, drills can be done to ensure the continuity.

 

 

 

 

 

 

 

 

 

Slots in masonry bed joints
Sika AnchorFix 3+ Adhesive
CarboDur BC 5 (5mm diameter)

 

 

 

 

 

 

 

 

 

 

Anchorage

SIKAWRAP can also be additionaly anchoraged using SIKAWRAP FX-50C through adjacent wall.

 

 

 

 

 

 

 

 

IN PLANE LOADS-SHEAR

TRM STRENGTHENING

 

Textile Reinforcement

SikaWrap-350G Grid
E-glass grid with special coating
Wide spacing for easy placement in mortar

+

Mortar

Sika MonoTop-722 Mur
Low E-modulus / High strength
Excellent adhesion to brick, stone, calcium silicate
Water vapor transmissible

=

Textile Reinforced Mortar

 

 

TRM main advantages

-Can be installed even on weak or wet substrates
-Fits on rough, curved or irregular surfaces
-High water vapour permeability
-Easy anchorage using SIKAWRAP FX-50C.

 

IN PLANE LOADS-SHEAR

FRP STRENGTHENING

X-frame is an efficient alternative that can be achieved using TRM, SIKAWRAP, SIKA CARBODUR or NSM methods.

 

IN-PLANE FLEXURAL LOADS

SEISMIC RETROFITTING OF MASONRY PANELS

Stress distribution

Compression and tension stresses are distributed according to a strain compatibility equilibrium.

 

IN PLANE LOADS-FLEXURE

FRP STRENGTHENING

Failure mode

Flexure-controlled failure mode is characterized by the formation of flexural cracks and crushing of the toe

 

Bonded Carbodur Plates

System overview

Vertical plates to be installed vertically along the wall

End anchorage

Extending CFRP plates beyond the wall is necessary (Ld)

Spacing limits

It´s recommended that the maximum clear spacing of externally bonded plates be limited to 3 x wall thickness.

 

End anchorage in slabs

Plates should be extended beyond the limits of the masonry to the adjoining concrete elements, inside a slot filled with SIKADUR 42. For a high-performance anchorage, CARBODUR ends are previously prepared by extending a slotted layer of SIKADUR 30 by both sides (Sika patented method)

 

Overview

SIKAWRAP fabrics can be displayed vertically; Surface smoothing is necessary by using SIKADUR 31. Fabrics are usually preferable in comparison to plates due to the lower shear stresses along the bond length.

End anchorage in slabs

SIKAWRAP fabrics can be rolled around a CARBODUR rod into a groove filled with SIKADUR 42.

 

Alternative anchorage

SIKAWRAP FX-50C anchors can be installed into drilled holes, spreading the carbon fiber tows over SIKAWRAP ends.

 

End anchorage

Anchorage can be obtained by drilling the slab and filling the hole using SIKADUR 300.

 

End anchorage

Anchorages are solved by drilling the slab/beam, and installing SIKAWRAP FX-50C

 

 

IN-PLANE LOADS: FLEXURE+SHEAR

SEISMIC RETROFITTING OF MASONRY PANELS

FRP STRENGTHENING

Grid Configuration

NSM, SIKAWRAP and CARBODUR options can be combined.

Vertical strips for flexural, horizontal strips for shear.

 

X-frame + Vertical Strips

NSM, SIKAWRAP and CARBODUR options can be combined.

Diagonal strips for shear, vertical strips for flexural.

 

TRM + Lateral TRM Strips

SIKAWRAP 350G GRID and SIKAWRAP FX-50C. Lateral GRID strips for additional flexural resistance.

 

MonoTop-722 Mur
SikaWrap-350G Grid
SikaWrap Anchor C

 

OUT-OF-PLANE LOADS

SEISMIC RETROFITTING OF MASONRY PANELS

 

Due to this forces, wall can develop tensional forces and flexural cracking (the contribution of masonry in tension is neglected)

 

“SEISMIC” Accelleration State

LATERAL ACCELERATION

Masonry vertical stress is altered due to an horizontal acceleration of the wall.

 

 

 

Reference Wall

Wall collapses

 

Wall reinforced 50cm on top by using Sika Monostop 722 Mur and 1 layer of SikaWrap 350G Grid

Textile Reinforced Mortar still intact
Failure mechanism in unstrengthened part of wall

 

Test Result

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