**8. Repair, rehabilitation and retrofit of historic masonry**

A large number of historical structures do not meet safety requirements because today's requirements are more demanding than those at the time of construction and because many years have passed by since their construction and structural safety has deteriorated due to use and time. To bring these historic buildings to a level of safety standards today, it is necessary to adapt its structure. However, historical value may be lost due to intervention; therefore, new approaches are needed to achieve sufficient safety.

The San Fernando, California, earthquake of 1971 demonstrated that the adaptation of the parapets to avoid their fall was effective. The 1994 Northridge, California, earthquake showed little damage to historic reinforced masonry with respect to URM that suffered damage and collapse [3].

The structural rehabilitation of historical buildings could be done by hiding those new structural elements or exposing them. Sometimes, the exhibition of new structural elements is preferred because alterations of this type may be reversible; in the future they can be changed without losing the historical character of the building [17].

The decision to hide or expose structural elements is complex, and there is to be a consensus with the preservation professionals who are participants of the project. In high seismic-risk area, it is difficult to strictly follow the principles of the different restoration charts (Venice, Athens, etc.), and the task is a challenge of structural engineering [17, 18].

The strengthening techniques depend on the building response to the earthquake. Different response leads to different strengthening methods. Three main groups could be:

• Interventions to obtain better global response of the building (in case of building box type behaviour and a prevailing in-plane response, **Figure 11**)


In the PERPETUATE project [18], both traditional and innovative intervention techniques have been evaluated. Some of the methods that are widely used in URM structures are insertion of horizontal tie rods; insertion of anchors between structural elements; adding new walls, buttresses and foundations; changing of weak mortar in joints of existing masonry (repointing); repair of cracks; jacketing of walls with reinforced concrete; grout injections of stone masonry walls; injections of cement or epoxy-based grout into cracks; and insertion of reinforced concrete "ring" beams or moment frames and reinforced concrete slabs. Each of these mentioned methods has its own advantages and disadvantages.

**Figure 11.**

*Reinforcement of foundations and reversible metallic structures in columns and lattice, Mitre school, 2012.*

**69**

**Figure 14.**

*rehabilitation [20].*

**Figure 13.**

*Support structure of masonry blocks, Saint Francis Ruins, 2011.*

*Evaluation of the change of the dynamic properties of the masonry building in the different stages of the* 

*Historic Masonry*

*DOI: http://dx.doi.org/10.5772/intechopen.87127*

Some innovative methods are strengthening brick masonry with attaching FRP fabric to the surface, restoration of stone masonry with compatible cement grouting, insertion of transversal connection in stone masonry walls, installing seismic isolation for single assets scale and installation of energy dissipation devices [18]. The choice of rehabilitation technique depends on the condition of the masonry,

the availability of local workmanship and the safety requirements [4, 9, 11].

**Figure 12.** *Bidirectional tensors for bracing of historic masonry walls, Fader House, 2013.*

#### *Historic Masonry DOI: http://dx.doi.org/10.5772/intechopen.87127*

*Heritage*

response, **Figure 12**)

• Interventions for the local mechanisms (in case of a prevailing out-of-plane

• Interventions on blocky structures (where the kinematic mechanisms must be

In the PERPETUATE project [18], both traditional and innovative intervention techniques have been evaluated. Some of the methods that are widely used in URM structures are insertion of horizontal tie rods; insertion of anchors between structural elements; adding new walls, buttresses and foundations; changing of weak mortar in joints of existing masonry (repointing); repair of cracks; jacketing of walls with reinforced concrete; grout injections of stone masonry walls; injections of cement or epoxy-based grout into cracks; and insertion of reinforced concrete "ring" beams or moment frames and reinforced concrete slabs. Each of these

prevented: obelisks, towers and also arches and vaults, **Figure 13**) [19]

*Reinforcement of foundations and reversible metallic structures in columns and lattice, Mitre school, 2012.*

mentioned methods has its own advantages and disadvantages.

**68**

**Figure 12.**

**Figure 11.**

*Bidirectional tensors for bracing of historic masonry walls, Fader House, 2013.*

Some innovative methods are strengthening brick masonry with attaching FRP fabric to the surface, restoration of stone masonry with compatible cement grouting, insertion of transversal connection in stone masonry walls, installing seismic isolation for single assets scale and installation of energy dissipation devices [18].

The choice of rehabilitation technique depends on the condition of the masonry, the availability of local workmanship and the safety requirements [4, 9, 11].

**Figure 13.** *Support structure of masonry blocks, Saint Francis Ruins, 2011.*

#### **Figure 14.**

*Evaluation of the change of the dynamic properties of the masonry building in the different stages of the rehabilitation [20].*

The effectiveness of a rehabilitation can be evaluated by system identification techniques. They measure the dynamic properties of the structure through environmental vibration before, during and after the structural reinforcement. The vibrations of low amplitude come from different sources, among them, the vehicular traffic, the micro-tremors, the wind, etc.

In the case of masonry, the parameter used to measure the efficiency of the structural reinforcement is the period of the walls measured at the top of them. Before starting the reinforcement work, the environmental vibration in the structure is measured in order to know the periods of the same with the existing level of damage. Once the foundations are consolidated and the walls reinforced, new measurements are taken, and in this way we can know the degree of recovery that the structure has had up to that stage as indicated in **Figure 14** [20].
