repair and retrofit techniques

DANIEL STOICA

REPAIR AND RETROFIT TECHNIQUES FOR MASONRY BUILDINGS STRUCTURES

BUCHAREST

0. INTRODUCTION

The suggestions and the economic estimates reported in this manual refer to

little masonry buildings of about 1000 m3 volume, which are typical of rustic

semi-detached or detached houses placed in small towns and villages or even

isolated from urban contexts.

The suggestions on building reinforcement techniques, construction methods,

dimensioning of elements, etc., provided in the text refer to typical general

conditions and suit buildings of regular shape and dimensions.

Their application to every single case should therefore carefully evaluated and

eventually adapted, also through calculations, to the real conditions and

characteristics of the building to be reinforced.

The goal of the described interventions is to improve the seismic resistance of

buildings trying to make the interventions as effective, simple and economic

as possible.

The improvement of the efficiency and the reliability of the connections

between the various building elements has therefore carefully considered,

especially for what concerns the connections between the walls and the walls

and the slabs.

The principle that the slabs, through their rigidity, must distribute the

horizontal forces to the various vertical bearing elements has widely been

applied. Many experiences have shown, in fact, that when there is a lack of

structural organization and of overall fastening (that is when there is not a

box-like behavior) the main damages are due to:

collapse of walls perpendicular to the horizontal loads, slabs slipping from the

walls and roofs collapse, while the walls parallel to the horizontal loads still

maintain their strength capacity.

When there is a good structural scheme and efficient connections high

intrinsic strength it is not necessary. Usually, the need of intrinsic strength is

satisfied by medium and homogeneous quality masonry.

The principle that partial interventions are generally not sufficient to assure an

effective seismic resistance has also been observed. The proposed

interventions are in fact intended to face problems in a global way, thus

stimulating a good construction response under seismic load.

Underpinnings are mentioned but not treated in this manual because they

refer to each intervention special needs and local rules of practice.

Nevertheless, for any of the above mentioned works the safety measures

required to grant the worker safety must be arranged.

The manual has been divided in five chapters developed according to the

following main structure:

1. General information

2. Criteria for the adoption and the execution

3. Construction phases

4. Work item list for the analytical estimate of quantities and prices

For some interventions, to avoid iterations with other sections or cards, the

section 3 has not been developed and the description of the construction

phases has been included directly in section 4.

Chapter 1 1. FOUNDATION REINFORCEMENT BY CURBS

1.1 GENERAL INFORMATION

The curbs must perform a continuous connection and toothing of the

masonries foot (foundation connection) in order to avoid the development of

cracks in the masonries upwards from the soil.

As second function the curbs improve the loads transfer to the soil thus

allowing extra loads due to new building elements (for seismic reinforcements,

and/or reorganization of the inner spaces) or due to higher operating loads

because of a change in the buildings use.

The connection among foundations can be carried out on the external side

only or, when possible, on both sides.

In all cases a special attention should be paid in creating a good homogeneity

with the old masonry, by reinforced concrete connections or the use of

cemented steel bars (passing through in the case of reinforcement on both

sides) as linking elements (see figs. 1.1, 1.2, 1.3).

1.2 CRITERIA FOR THE ADOPTION AND TILE EXECUTION

The connection and toothing of the foundations by reinforced concrete curbs

not seldom it is possible only from the external side. For example, when there

is an internal floor that cannot be totally or partially demolished.

In the case of cracks or cavities or lacks of continuity in the existing

foundation structure, the curbs construction should be made after the

consolidation of the foundation structure. For such consolidation different

techniques can be used like, for instance, cement grout injections, local

toothings by two curbs (one on each side) linked with transversal connecting

steel bars, cemented steel bars, etc.

When the intervention foresees also the construction of a new floor at ground

level, it will be very useful to connect the reinforcement (generally steel net) of

the base course to the reinforcements of the curb. This connection makes the

foundation structure much more monolithic.

If new internal walls are built their foundations should also be joined to the

reinforcing curbs in a monolithic way.

When surface slips or settlements have happened and might still occur

interventions of soil consolidation should be also defined.

The interventions considered in this card are:

1. External foundation curb and connections in reinforced concrete.

2. Internal and external foundation curbs and connections in reinforced

concrete.

3. Foundation curb in reinforced concrete and connections in cemented

steel bars.

Here below the description of their construction phases is given.

1.3 CONSTRUCTION PHASES

1.3.1 Formation of the curb seats

The excavation depth should not be lower than the foot of the masonry, taking

into account the thickness of the curbs subfloor in concrete with low cement -

aggregate ratio.

Before performing the excavation it will be necessary to underpin all the

elements affected by stability problems.

If the foundations are very deep the excavation can be stopped at the level

where the soil has a good solidity and resistance.

If the connection is made in r.c., the holes must be made one or two stone or

brick level above the foundation base layer. This to preserve the continuity of

the masonrys impression on the ground.

In order to establish the correct excavation depth, the 10 -15 cm of thickness

of a subfloor in concrete with low cement - aggregate ratio and the possibility of

overlying the curb with a walkway or protection pavement of proper thickness

should be taken into account.

The excavation is generally made by hand or little diggers. Usually, it is better

to make it large enough to place a lateral formwork, thus avoiding casting on

one side the curb directly against the ground.

1.3.2 Preparation of the seats for the curb(s)/masonry connectors

The curb/masonry connection can be made by reinforced concrete cast

connectors or by cemented bars

Preparation of the r. c. connector seats

After the excavation, the partial or passing connecting holes should be

prepared in the masonry according to the use of single or double curbs.

This work requires local demolitions, and has to be performed very carefully in

order to avoid disconnections in the masonry near the hole. If this happens, it

will be necessary to restore the link within the masonrys bricks or blocks

before the casting of the curb and its connectors.

If the curb is only external, the demolition depth will affect a wide portion of

the wall thickness or even the whole thickness if the wall is rather thin.

In stone masonries the seats of the connectors can have a not perfectly

regular shape only if this does not allow, after the casting, the formation of

voids within the concrete or between this and the stones.

The suggested average distance between the connections in reinforced

concrete is about 1.5 m for the external curbs and about 2 m for the internal

and external curbs.

Preparation of the cemented bars connector seats

The use of curb/masonry connections made of cemented steel bars calls for

higher curbs section (the recommended height is two or three times the base

span), so that at least three connectors will result vertically aligned. The

suggested density is 6 to 10 connectors per square meter. The suggested

diameters are: 16 mm for the bars and 30-35 mm for the holes

1.3.3 Preparation of the masonry surface for casting

Before the casting of the curb(s) and type 2.1 connectors, the masonry

surfaces that have to adhere to the new concrete elements should be cleaned

and wetted. Incoherent and cracked portions (if any) must also be taken away

in order to achieve an optimal connection between masonry and curb(s)

1.3.4 Curb casting

First of all, a subfloor made of concrete with low cement - aggregate ratio

should be prepared. Then lateral formworks are to be set, along with the steel

reinforcements that should be disposed to have a wide concrete cover and

linked to the reinforcements of the connectors 2.1 or 2.2.

Then the casting will be made with a controlled shrinkage concrete mix in

order to facilitate the complete physical contact with the masonry also inside

the 2.1 type connectors cavity, that must be completely filled with concrete.

If after the casting there should remain cavities in the masonry (above the

curb) due to the preparation of the connectors seats, these have to be filled

and sealed.

1.3.5 Interment and finishing

The last phase is the interment of the excavation and the construction of a

protecting pavement where possible.

Chapter 2 2 SETTING OF NEW MASONRY INTERNAL WALLS


The masonry compactness and constructive regularity in plan and section

represent safety factors for the building good response to seismic actions.

Asymmetry in plan and position of openings represent hazard factors because

they can lead up to dangerous torsion effects.

The square plan is the best one. If the plan is rectangular it is a good rule that

the side dimensions have a ratio not greater than 1 to 4.

The projections of the various building portions should be of a maximum of 2

m and not greater than the 20% of the building depth of the nearby portions

as well (see fig. 2.1 a, b).

In the case of wider projections and/or significant asymmetries, the possibility

to use joints in order to subdivide the building in two or more structurally

independent units should be taken into account (see fig. 2. 1c).

Also when the choice of an asymmetric plan or of a very long rectangular

shape it is not avoidable, the use of structural joints to subdivide the building

in more units it is absolutely necessary. Each one of such units will have to

meet the above mentioned geometric characteristics. In existing buildings this

requires the construction of connecting transversal walls.

The joints have to be at least 3 cm wide for the up to 8 m high buildings. For

higher buildings the joint width has to be increased 1 cm every 3 m (for

example, for an 11 m high building the joint width has to be 4 cm)

Usually, the distance among the internal walls should not be greater that 7 m.

Table 2.1 shows the minimum percentage of resisting wall area with respect

to the total plan area. Those values must undergo to the usual necessary

controls.

SEISMIC ZONE

I II III

Reinforced brick walls: Aw/A x 100 4.50 4.00 3.00

Brick walls: Aw/A x 100 6.00 5.00 4.00

Aw = wall resistance area A = building plant area

Table 2.1

As already pointed out, construction irregularities in the vertical building shape

also represent a hazard factor. Sharp variation in stiffness and strength

should be therefore avoided (see fig. 2.3 a, b) and if existing they should be

eliminated or at least controlled by ad hoc local strengthening of the building

elements involved.

From this point of view it is important that the ratio between the shorter plan

dimension and the building height should be greater than 0.5.

Moreover, the presence of thin and isolated internal walls should be avoided,

since they may cause a dangerous blow with a lash effect, even able to

cause the collapse of the whole building or of its parts (see fig. 2.4).

The following rules apply to the openings:

they must have moderate slenderness, with a base/height ratio less than

1.5 (for the doors a greater slenderness may be admitted, but always less

or equal than 2 2.5);

they must be at least 1.5 m away from the perimeter wall connections and

0.8 m from internal wall connections;

in the same wall the sum of the openings width cannot exceed the 50% of

the width of the wall itself;

the height of the wall strip localized between the openings of two

subsequent floors should be as constant as possible, not less than the

30% of the height between two floors and anyhow greater then 1 m (see

fig. 2.5).

2.2 CRITERIA FOR THE ADOPTION AND THE EXECUTION

The addition of new internal walls is necessary wherever the required strength

is not sufficient or where the distribution and strength of internal walls have to

be regularized, the asymmetries in plant and/or height have to be eliminated,

collapsed or damaged walls have to be substituted.

The new walls can be reinforced or not and have to be coupled to curbs

located at the foundation levels and between floors.

The intervention effectiveness depends on the proper connection between the

existing walls and the newly built integrating ones. For this purpose:

base curbs must be joined to the foundation reinforcement curbs of the

existing masonry;

the curbs between floors must be linked to the existing masonry by

reinforced dovetail cement inserts (see figs. 2.6);

in the case of reinforced walls, their reinforces (steel reticular trestles)

should be placed, spaced each one at circa 50 cm in height, in the mortar

between two brick levels and linked to the old masonry by dovetail passing

bars (see figs. 2.6);

in the case of new not reinforced walls their extremes should be connected

to the existing masonries by indentations disposed in the latest in order to

assure the mutual transfer of the shear actions. Such indentations should

be disposed every two or three brick levels and filled with a piece of brick

and mortar;

when a new wall has to be built at the building header, transversally to the

main fronts, the link among walls should be made by reinforced concrete

corner pillars.

The pillars reinforcements have to be connected to those of the new wall

and to the dovetail tie bars placed in the existing masonries. The concrete

of the pillars must fill the voids between the bricks levels of the new

masonry.

The pillars should be also connected to the foundation curb, the roof curb

and the curbs displaced at each floor level (see fig. 2.7);

the openings in the internal walls (for example doors) should be reinforced

on their perimeter by a r.c. frame. This frame should be rather thin and

linked to the stone/brick masonry, through the connection of its

reinforcements to the masonrys and filling with concrete the voids between

the bricks or stone levels at the interface frame - masonry.

The frame vertical reinforcements have to be extended downward and

upward, to be connected respectively to those of the lower and upper curb

(see fig. 2.8).

The interventions considered in this chapter are:

1 - Construction of an unreinforced brick cross wall to be connected to

the main fronts stone walls.

2 - Construction of a reinforced brick cross wall to be connected to the

main fronts stone walls (see fig. 2.6).

3 - Construction, at the building header, of a reinforced brick cross wall

to be connected to the main fronts stone walls (see fig. 2.7).

Here below the description of their construction phases is given.

2.3 CONSTRUCTION PHASES

2.3.1 Construction of the wall foundation curb

The excavation depth should equal that of the building foundations reinforcing

curbs to which the wall foundation curb has to be connected.

Before the excavation the floor and its base course have to be demolished

mainly by hand or with the help of a pneumatic hammer.

The excavation is mainly carried out by hand or little diggers.

Usually, it is better to make it large enough to place lateral formworks, thus

avoiding casting the curb directly against the ground.

The curb should be cased on a subfloor made of concrete with low cement -

aggregate ratio. The linkage between the wall foundation curb and the

building foundations reinforcing curbs should be made by cemented bars,

whose suggested diameters are 16 mm for the bars and 30 - 35 mm for the

holes.

As to the curb cast see the indications given in chapter 1 Foundation

reinforcements.

2.3.2 Preparation of the existing masonries for the connection to the new cross wall

According to the type of masonry (reinforced or unreinforced) and its location

(inside the building, at one header) one of the following interventions 2.1, 2.2

or 2.3 has to be adopted.

In any case it is important to perform a preliminary lay-out of the necessary

local demolitions or drillings in order to obtain the correct alignment between:

the cross wall reinforcements (if any) and the dovetail passing bars; the curbs between floors and their anchorages at the existing masonries

The drillings and the local demolitions have to be carried out with special care

in order to avoid disconnections among the stones around them and the

consequent, obvious local structural weakening.

Once the above-mentioned works have been carried out the stone masonries

surfaces will be properly prepared for the connection to the cross wall

eliminating their incoherent parts and re-consolidating the weakened parts if

necessary and, finally, cleaning and wetting them by a water jet.

When the existing masonries are plastered, the plaster has to be removed

near the connection zones.

Indentation preparation for the connection with unreinforced brick cross walls

Local removal of the plaster (if any) from the existing walls along a vertical

band corresponding to the connection with the new wall. Local demolition of

the existing stone walls (three subsequent stone levels out of six) in order to

achieve a good shear connection with the new cross wall.

Preparation of the dovetail passing cemented bars for the connection with

reinforced brick cross walls (except header walls)

Diagonal drilling of the existing walls (every 50 cm height) in order to insert

the dovetail passing bars. Such bars have to be cemented and linked to the

cross walls steel reinforcement trestles (see fig. 2.6).

Preparation of the r. c. corner pillars for the connection with header brick cross walls

Drilling of the existing walls heads (every 50 cm height) in order to insert the

dovetail connecting bars. Such bars have to be directly connected to the

reinforcements of the corresponding pillar. The latest have to be connected to

the header brick cross wall reinforcements (see fig. 2.7).

2.3.3 Brick cross wall construction

The new brick cross wall has usually a thickness of about 25 cm (2 brick

modulus) when it is not inserted at the building header and of about 37.5 cm

(3 brick modulus) if it is inserted at the building header.

The new brick walls should be built according to the usual rules of practice

and, in particular:

the bricks have to be wetted before their setting with mortar;

both the vertical and horizontal joints between bricks must be filled with

mortar, the same for the lateral joints against the existing stone walls;

where the reinforces in steel reticular trestles have to be settled, the mortar

layer should have a higher thickness in order to cover the trestle itself

the header cross walls extremes, nearby the r.c. corner pillars, should be

toothed, because of the usual staggering of the subsequent brick levels,

and filled with concrete, to make the connection between the brick masonry

and the r.c. pillars more efficient (see fig. 2.7).

2.3.4 Reinforcement and cast of the r.c. corner pillars

The casting of the corner pillars should be carried out after having set their

reinforcements (bars and stirrups), connected them to the cross walls steel

trestles and to the dovetail connectors with the existent stone walls and set

the necessary formwork.

The casting should be made of concrete and anti-shrinkage additives and

then compressed in order to get the best adherence and mechanical

connection with the existing walls and with the toothed cavities of the brick

cross wall extremes. Cavities formation in the concrete must be absolutely

avoided.

2.3.5 Preparation and cast of the r.c. curbs between floors

At each floor level the vertical continuity of the cross wall should be

interrupted by a strengthening r.c. curb, whose position corresponds to that of

the slab. The curb should be connected with the existing stone walls by

dovetail r.c. elements or, in the case of header walls, by r.c. corner pillars. In

both cases the curb bears the cross wall upper part, if any, which will be

overlaid by a strengthening curb as well (see fig. 2.6).

After the formworks setting, the curbs reinforcements should be set and

linked to those of the connectors with the existing stone walls.

For the casting a controlled shrinkage concrete has to be used and accurately

compacted in order to get good adherence and mechanical collaboration with

both the existing walls (through the dovetail or pillar anchorages), and the

underlying cross wall. Cavities formation in the concrete must be absolutely

avoided.

The preparation of the curb seat involves the partial demolition of the slab and

its floor. Such demolition has to be carried out in a way depending on the slab

type (wooden, wooden and concrete, bricks and concrete, brick and steel,

etc.), its thickness, and its parallel or perpendicular main orientation with

respect to that of the curb.

The curbs seat preparation should be therefore established case by case,

together with the necessary underpinning.

Whenever after the casting cavities should remain over the curb, between the

curb itself and the existing stone walls (that is over the dovetail anchorage

elements), they should be filled by stone pieces and cement mortar, or by

further controlled shrinkage concrete.

2.3.6 Finishing

In the end, the finishing works are undertaken if needed. Generally those

works include: internal and/or external plastering of walls, finishing of both the

ceiling and floor sides of the slab to eliminate the traces of the construction of

the cross wall and its curbs.

Chapter 3

3. LOCAL REINFORCEMENT, REPAIR AND SEALING OF LOCAL

DAMAGES


In principle, the local interventions are absolutely not recommended to be the only step to take for the reinforcement or repair of damaged walls. As a matter of fact, they should be part of a global, systematic approach to the

improvement of the buildings seismic resistance regarding the connections between the various elements, the dynamic loads distribution and the proper reinforcements and repairs of the various building components.

3.2 TYPES OF THE REINFORCEMENT INTERVENTION

The interventions considered in this chapter are:

a - cement grout injections.

b - reinforced cemented drillings.

c - closing of openings.

d - framing of openings.

e - steel net and cement grout binding render.

f - addition of a reinforced concrete slab.

g - insertion of concrete reinforcement components.

In the following sections the description of their construction phases is given together with the criteria for their adoption and execution.

3.3 LOCAL CONSOLIDATION OF MASONRIES BY CEMENT GROUT INJECTIONS

3.3.1 Criteria for the adoption and the execution

This intervention is suitable to fill voids in masonries due to the absence or lacks of mortar, diffused cracks, presence of cavities, etc., and wherein it is possible to inject and spread the cement grout m a controlled and homogeneous way. This intervention is therefore mainly suggested for stone walls, especially when they are quite old, to fill the voids among the stones and the numerous cavities that often weaken their resistance. To this goal the completeness and homogeneity of the injections it is basic. Such result should he obtained through a sufficient number of injections and maintaining the - injection pressure on moderate values: the holes density should be at least 6 holes/m2. A partial or not homogeneous masonry consolidation would be dangerous because it would concentrate stresses in the masonry much higher than those it could bear!. The injection technique, if properly applied, has the advantage of restoring the mechanical resistance of the masonry without modifying its look and its geometry, and with just a little increase of its weight. For such reasons this techniques fits particularly the consolidation of masonries in buildings that have an high environmental, historical or cultural value. As to its application, if the masonry is rendered or plastered, the render or the plastered has to be struck by a pickaxe in order to find out the joints between the stones or bricks, where the injection holes should be drilled. Before the injection all the joints, cracks and holes (door frames, electric sockets, chimney-flues, sockets for the support of wooden beams, etc.) the cement grout could leak out have to be sealed.

In the case of masonries to be aesthetically preserved (especially in buildings with a high environmental, historical or cultural value) the use of a temporary, single layer plaster can be requested. A plaster made of clay powder, sand, meal brick powder and water, it is easily removable after the consolidation and then suitable as a temporary one. Before the cement grout injection, water must be injected in the holes to take away the incoherent parts among the stones and ease the cement grout adhesion to the stones. The injection should be started from the bottom to the top layers of the wall, using low pressure at the beginning and then increasing it gradually since when the exceeding cement grout will leak through the holes overlaying the injection level. Only jet pumps that allow the regulation of the pressure and the grout volume injected should be used.

3.3.2 Construction phases

Masonry preparation and injection If the masonry is rendered or plastered, its injection front has to be struck by a pickaxe until when the joints between the stones or bricks can be seen. In the whole masonry: sealing of all joints, cracks or other possible holes the cement grout could leak out. Only in the case of masonries to be aesthetically preserved, execution of a temporary plaster to be removed after the injections. Generally the minimum number of holes per m2 has to be 6, but it can be higher (9 or 12) when the masonry characteristics and the completeness and the homogeneity of the work call for extra injections. In particular, the hole density has to be increased around the connections with cross walls or other structural components.

The holes, all realized by a corer, should have a diameter of about 25 mm and

a minimum depth of 15 cm.

Once they are prepared the 3/4 jets will be setting in each one of them.

Water must then be injected in the holes, from the upper to the lower wall

levels or layers, to take away the incoherent parts among the stones and ease

the cement grout adhesion to the stones.

Immediately after the cement grout injection should start from the bottom to the top layers of the wall. Each injection should stop when the cement grout leaks out from the overlaying jets. The injections have to be carried out gradually, layer after layer, by jet pumps increasing the low initial pressure up to 2 -4 atm since when the exceeding mortar will appear through the holes overlaying the injection level. According to the specific needs the cement grout might be added with very fine or fine sand, fluidifier (for thin connections) or expansive additives (for big cavities). Finishing After the injections and the jets removal are completed, the wall cleaning, the sealing of the injections holes, the repair of the old plaster, if any, or the new plastering, if requested, or the removal of the temporary plastering have to be performed.

3.4 REINFORCED CEMENTED DRILLINGS


The intervention is suitable for (see fig. 3.1, 3.2, 3.3):

the repair of cracked walls;

the strengthening of curb - wall connections; the strengthening of connections between walls;

the reinforcement of walls by a steel net and cement grout binding render applied only on one or on both wall sides. In this case the reinforced

cement drillings work as connectors between the masonry and the

reinforcing render (see fig. 3.6).

Before choosing it, the following analyses should be performed:

exam of the masonry conditions in the interested area; evaluation of the shear and traction strength to be achieved;

need for other reinforcement works.

In this manual the cemented networks are not taken into consideration.


A precise tracing of the holes position is always requested. Sometimes it must be preceded by some preparing steps like, for instance, the local removal of the plaster by a pickaxe, the local removal of damaged wall elements, the cracks borders cleaning, underpinning of unstable components, etc.. The drilling of the masonry should be carried out by a corer; the resulting holes diameter should be from 30 to 50 mm. After the holes have been drilled they must be cleaned and wetted. An embedded steel bar can then be inserted in each hole (for example C516 mm bar within a 30 - 35 mm hole). The holes must be completely filled afterwards by a controlled shrinkage grout casted or pumped. If necessary, the grout can be added with a fluidifier additive. After the grout hardening steel bars sticking out from holes (if any) can be cut.

3.5 CLOSING OF OPENING


The closing of wall openings, such as niches, doors, windows, etc., if compatible with the buildings plant, contributes to the elimination of structural weaknesses (see fig. 3.4).


After the plaster or render removal from the surfaces delimiting the opening to close, indentations have to disposed in the latest in order to assure a proper connection between the new closing masonry and the wall. Such indentations should correspond to the brick or stone layers. At the same time the wooden lintel, if any, has to be removed. In the niches, the wall delimiting their thickness has to be demolished. The construction of the closing wall can then be performed. Its thickness should be the same of that of the existing wall. Special care should be paid to the filling of both the horizontal and vertical bricks joints with mortar, included those with the existing masonry. If the existing wall needs also cement grout injections, these will follow the foreseen closing of openings. In this case some injections should be carried out also around the closed openings. In the end the finishing work is undertaken. Generally it consists of the plastering of the new wall portions (trying to make it as similar as possible to that of the old wall) and in the repainting of the whole wall.

3.6 FRAMING OF OPENINGS


The framing is generally made of thin reinforced concrete frames, connected to the nearby wall by reinforced cemented drillings. It allows the strengthening of a wall without closing its opening/s (see fig. 3.5). This technique is therefore suitable when, for functional reasons, openings

weakening the wall structure can not be closed.


The first step is the plaster or renders removal from the surfaces delimiting the opening to be framed. If the net opening dimensions can not be reduced a local demolition of the wall around the openings perimeter is needed.

At the same time wooden lintel or vaults are removed. Then the necessary reinforced cemented drillings are carried out as shown in fig. 3.5 (The description of this intervention is provided in previous section 3.4). The cemented steel bars should be bent at their free end to make their connection with the frame reinforcements more efficient. At this point the masonry surfaces that have to adhere to the concrete frame should be cleaned and wetted. Incoherent and cracked portions (if any) must also be taken away in order to achieve an optimal connection between the masonry and the concrete frame. The frames reinforcements should then be placed and linked to the cemented steel bars and the formwork is set. The frame cast follows made of a controlled shrinkage concrete possibly added with fluidifier additives in order to get a complete and good adherence with the wall and avoid cavities formation. The base portion is casted first, then the two side portions and the frame head at the end. For the frame head casting two or three sockets must be prepared on the overlaying wall, as shown in fig. 3.5.

Whenever after the casting cavities should remain over the frame head or between the other frame portions and the wall, they should be filled by further controlled shrinkage concrete. If the wall has to be reinforced also by cement grout injections, this should be done after the openings framing. In this case injections have to be carried out around the frame. In the end the finishing work is undertaken. Generally it consists of the plastering of the frame (trying to make it as similar as possible to that of the old wall) and in the repainting of the whole wall.

3.7 STEEL NET AND CEMENT GROUT BINDING RENDER


This intervention is suitable for the stone or brick walls binding and, by this, for the improvement of their stiffness and their resistant section.

It consists of the wall binding, by a steel net reinforced cement grout render

applied on both the wall fronts. On each front the steel net should be

accurately anchored to the wall and connected with that on the opposite front

by passing metal strips. The cement grout can be set by hand or spraying and

then carefully pressed (see fig. 3.6).

In the case of poor quality or widely cracked stone masonry, the insertion of passing metal strips and the wall consolidation by cement grout injections must be performed first. The intervention here considered can also be used for local repair or strengthening of cracked or weak elements and connections, also in combination with other reinforcing techniques (see the following paragraph 3.8).

In these cases, however, the local thickening and improvement in the static

behavior should be carefully taken into account.


In any case it is necessary to fill voids and/or cracks that can weaken the masonry resistance by cement grout and, if necessary, also by the progressive repositioning or substitution of the unbound elements (bricks or stones). The steel net (suggested 0 3 - 4 mm spaced at 15 cm in each direction) should be applied on each wall front, fastened to the masonry by nails (stainless steel nails are suggested) and connected to the net applied on the opposite wall front by steel metal strips (suggested 0 4 - 6 mm, density from 2 to 4 per m2). The steel net should be folded and fastened on the nearby masonry for at least 50 cm. It should be connected with the curbs between floors as well.

After having well cleaned and wetted the wall surfaces, the cement grout render should be set by hand or spraying and then carefully pressed. The spray rendering can be carried out when the masonry is able to withstand the high pressure that this technique implies. The perfect adherence of the binding render to the masonry should be in any case achieved. The cement grout render should be thick from 3 up to 5 cm; it has therefore to be set in at least two layers. The last layer should be vigorously hand smoothed by a darby. The cement grout adherence should not be weakened by shrinkage, for this reason a controlled shrinkage grout should be used. In the first days the rendered surfaces should be properly protected and eventually also wetted in order to achieve a correct hardening.

3.8 ADDITION OF A REINFORCED CONCRETE SLAB


This intervention is suitable to consolidate decayed walls, whose thickness is

not sufficient to withstand seismic loads and that are therefore affected by

crushing, eccentric loading, wide diffused cracks, etc.

It consists of the considerable integration of the wall resistance by the addition of a reinforced concrete slab to be casted against one of the existing wall fronts. The connection and mechanical collaboration between slab and wall have to be granted by a sufficient number of proper connectors. The slab should be moreover connected with the nearby structural components too, i.e. reinforced curbs and other structural reinforced components of the upper and lower floors, vertically aligned with the slab (see fig. 3.7 and 3.8). This in order to make the structural behavior of the whole more efficient.

In average, the slab suggested thickness is about 15 cm. In any case the r.c.

slab has to be dimensioned, starting from the foundation and up to the roof,

as a self-sufficient bearing component, like it substituted the existing wall.

In the case of much damaged walls the slabs cast should be done after the wall underpinning (to be carried out on the opposite side with respect to that of the slabs cast) and its eventual local consolidation (by cement grout injections, progressive repositioning or substitution of the unbound elements, etc.). The relevant load increasing this intervention implies calls for an adequate analysis of the foundations bearing capacity and eventually also for its strengthening. As to the above mentioned mechanical connection between slab and wall, the adoption of dovetail r.c. connectors it is advisable, though in the case of brick walls the use of steel cemented bars is allowed. The perfect connection with the existing wall is necessary to grant the due mechanical collaboration between the two coupled elements, thus preventing the risk of disconnection. To this purpose it is necessary to prepare and wet carefully the wall front and use a controlled shrinkage concrete. If the existing wall was made of reinforced concrete, it would be useful to prepare its front by specific primer. In any case the concrete cast should be properly protected and eventually wetted in order to achieve a correct setting and hardening.

3.9 INSERTION OF CONCRETE REINFORCEMENT COMPONENTS


This intervention consists of the insertion of reinforced concrete pillars within the existing masonry structure, in a proper position of the walls actual section and/or at their corners (sees fig. 3.9 and 3.10). In such way it allows the building of a r.c. frame within the existing masonry structure. Such frame has to be mechanically connected with the other nearby structural components: curbs located at the foundation levels and between floors, lower and upper floors pillars, cross reinforced masonry, etc.. The expected result is a relevant increasing in the whole building strength

especially with respect to the seismic actions. The perfect link between each single pillar and the masonry it is inserted in has to be reached: inside the wall thickness, by the use of a controlled concrete shrinkage

concrete accurately compacted in order to get good adherence and mechanical collaboration with the wall. To this purpose it is necessary to prepare and wet carefully the wall surfaces. If the existing wall was made of reinforced concrete,, it would be useful to prepare its surfaces by specific primer. Cavities formation in the concrete must be absolutely avoided;

outside the wall, by a local steel net and cement grout binding render on

both wall fronts. This link implies a local increase in the wall thickness to be taken into account.

The preparation of the pillar seat involves also the drilling of the lower and upper slab curbs to allow the connection and linking of its reinforcements with those of the lower and upper pillars, if any, or simply with those of the curb. The pillars seat preparation should be established case by case, together with the necessary underpinning. In the case of poor quality or widely cracked stone masonry, the wall consolidation by cement grout injections must be performed afterwards (see paragraph 3.3). The steel net (suggested 3 - 4 mm spaced at 15 cm in each direction) should be applied on each wall front, fastened to the masonry by nails (stainless steel nails are suggested) and connected to the net applied on the opposite wall front by two vertical rows of steel metal strips, one at each side of the pillar, at about 30 cm from it (suggested 6 mm, average spacing between the metal strips 40 cm). On the internal side/s the steel net should be folded on the slab and fastened to upper raw surface for at least 1 m (see fig. 3.9).

After having well cleaned and wetted the wall surfaces, the cement grout

render should be set by hand or spraying and then carefully pressed. The spray rendering can be earned out when the masonry is able to withstand the high pressure that this technique implies.

The perfect adherence of the binding render to the masonry should be in any case achieved. The cement grout render should be thick from 3 up to 5 cm; it has therefore to be set in at least two layers. The last layer should be vigorously hand smoothed by darby. The cement grout adherence should not be weakened by shrinkage, for this reason controlled shrinkage grout should be used. In the first days the reinforced concrete and the rendered surfaces should be properly protected and eventually also wetted in order to achieve a correct hardening.

Chapter 4 4 WOODEN SLABS STIFFENING AND CONNECTION TO THE SUPPORTING WALLS


A wooden slab badly connected to its supporting walls can slip off them and collapse in the case of seismic action. In order to avoid this it is necessary, after having verified and eventually improved or accomplished the mutual connection of the supporting walls (see the previous chapters), to carry-out the slabs stiffening and its connection to the bearing masonry. To this purpose, the building of a horizontal curb around the slab improves the slab/wall connection. Furthermore it strengthens the building perimeter at each floor when applied to each floors slab. For such reasons this intervention is the most suitable to improve the slabs performance and the building seismic resistance at the same time (see intervention 4.4). When the reinforced curbs construction is not possible, the building should be hoped by tendons anchored to plates or keys (see intervention 4.7). In this case the connection to the supporting walls and the wooden slabs stiffening can be carried out, respectively by: steel metal straps and plates and the addition of new floorboards perpendicularly to the existing one (see intervention 4.4). Otherwise the casting of a steel net reinforced concrete slab can be considered as an alternative. In this case the added slab and the relevant steel net should be connected to the curbs built around the slab, if any. Otherwise it is necessary to connect them directly to the walls by cemented bars (see the interventions 4.4 and 4.5). After the preparation of the slab/wall connection and before the slab stiffening, the local consolidation of the supporting walls is needed. It can performed by cement grout injections and or reinforced cemented drillings (see the

interventions 3.3 and 3.4). The choice of a wooden slabs stiffening techniques involves the evaluation of its residual load-bearing capacity together with that of its flexibility when loaded and its capability to withstand the foreseen higher permanent and cycling over-loads after the intervention. Whenever the slab conditions are really too bad to allow its stiffening or strengthening, its substitution should be considered. In that case the choice between rebuilding it according to the original technique or a new one has to be performed. When the latest is allowed, the construction of a brick hollow tiles and r.c. slab like that indicated at paragraph 4.7 might be a proper solution.

4.2 TYPES OF THE INTERVENTION

The interventions considered in this chapter are: a. - connection by steel metal straps and plates - stiffening by new floorboards. b. - connection by a reinforced concrete curb and stiffening by a reinforced concrete slab c. - connection by steel stirrups and pins - stiffening by a r.c. slab. d. - hooping of the building by horizontal steel tendons. e. - substitution of the wooden slab by a brick hollow tiles and r.c. one. In the following sections the description of their construction phases is given together with the criteria for their adoption and execution.

4.3 CONNECTION BY STEEL METAL STRAPS AND PLATES- STIFFENING BY NEW FLOORBOARDS


First of all the state of the slab has to be examined. The conservation state and the consequent residual load-bearing capacity of the slab should fit its use. Deteriorated elements like for instance joists or boards, if any, should be previously consolidated or substituted by a proper technique. The sole connection to the supporting walls does not require the demolition of the floor, if any. Such demolition becomes necessary instead when the stiffening intervention is also to be carried out. The connection intervention follows. It includes: the main joists anchorage to the supporting walls to be carried out one joist

out of two by (see fig. 4.1):

- the insertion of passing steel metal straps in the wall (dimensions mm: 5x80x1300-1500, properly drilled to be nailed and with a slit at one end);

- the insertion, upon the metal straps end sticking out the wall, of a slit plate (plate dimensions mm: 10x200x250 mm), and of a steel grip wedge;

- the metal straps nailing on the joists side by forged nails, suggested average distance between the nails 150 mm.

the anchoring of the floorboards to the supporting walls parallel to the joists by (see fig. 4.2):

- the insertion of passing steel metal straps in the wall (dimensions mm:

5x80x1400-1600, properly drilled to be nailed and with a slit at one end) 30 V-like placed with respect to the perpendicular to the wall;

- the insertion, upon the metal straps end sticking out the wall, of a double slit V-like plate (plate dimensions mm: 10 x 250 x 250 x 200 mm), and of two steel grip wedges;

- the metal straps nailing on the floorboards by 2 forged nails per board. Then the stiffening intervention, where required, is carried out setting over the old floorboards the new floorboards, perpendicularly to the existing one (see fig. 4.3).

The connection and mechanical collaboration between the new and the old floorboards have to be granted by a proper nailing. Two nails for each new/old board crossing point are suggested. Before the setting of the new floorboards the nailing of the existing boards to the joists has to be revised

4.4 CONNECTION BY A REINFORCED CONCRETE CURB AND STIFFENING BY A REINFORCED CONCRETE SLAB


This intervention allows higher stiffening and a better load distribution with respect to the previous intervention 4.3. It can be adopted when a wooden slab is in good condition and, at the same time, it can withstand the overload due to the concrete slab weight. Furthermore the higher final thickness of the slab (i.e. the final height of the floor surface) is acceptable. The intervention includes: the slab underpinning, the demolition of the floor and of its base course, if any, the consolidation or substitution of deteriorated elements like joists or boards, if any, by a proper technique. The connection intervention consists of: the building of a reinforced concrete curb around the slab, to be integrated in

the wall thickness and connected to the supporting walls by dove tail reinforced concrete connectors (see fig. 4.4).

The intervention requires the local demolition of the walls surrounding the slab to prepare the curbs and the dove tail connectors seats. Such demolition allows the check of the joists and beams ends state. This important control should be careflil performed. The stiffening intervention consists of: the casting of a thin concrete slab (4 - 5 cm thick) reinforced by a steel net

(suggested bars diameter 4 mm, bars spacing 15 cm in each direction and possibly electrically welded) over the existing floorboards, to be connected

to the underlying wooden structure by steel nails (see fig. 4.4). In order to achieve a more efficient connection between the reinforced concrete slab and the underlying wooden structure (that is for the better stiffening and load distribution) the steel net should be connected to the joists by steel pegs or steel screw connectors and epoxy resins glue.

4.5 CONNECTION BY STEEL STIRRUPS AND PINS - STIFFENING BY A R.C. SLAB


The connection to the supporting walls can be carried out also by steel stirrups and pins inserted in passing drillings and then cemented by injections of cemented grout (see fig. 4.5 and 4.6). Thus the partial demolition required by the construction of a curb inside the thickness of the walls supporting the slab (see previous intervention: 4.4) can be avoided. This intervention therefore provides an alternative to be considered in all those cases the masonry conditions and/or thickness dont recommend any demolition. As well as the previous one, this intervention requires the slab underpinning, the demolition of the floor and of its base course, if any, the consolidation or substitution of deteriorated elements, if any, by a proper technique. Furthermore it can require the supporting walls strengthening to be carried out after the slab has been connected to the walls and before it has been stiffened. Generally the wall strengthening consists of cement grout injections (see the previous intervention 3.3) carried out around the connecting stirrups and pins. The injection density should be sufficient to anchor such elements and grant the mutual slab/wall mechanical connection. The connection intervention consists of:

the accomplishment of dove tail anchorages made of cemented steel stirrups, one every of 2 m, and pins made of cemented steel bars, one every 1,5 m as shown in fig. 4.5.

Both types of connectors have to be realized by passing drillings in the supporting walls (suggested diameter 35 mm) and steel bars (possibly of the embedded type, suggested diameter 16 mm) to be connected to the slab reinforcement steel net by welding or accurate links. After the bars have been inserted in, the holes should be filled by a controlled shrinkage cement grout casted or pumped;

the upward folding (about 40 cm) around the slab perimeter of the steel net setted on the slab and its anchorage to the walls by pegs made of 10 steel bars (see fig. 4.6);

the accomplishment of horizontal tendons anchored by properly dimensioned plates or keys, allowing an efficient hooping of the building (see fig. 4.6). The horizontal tendons have to be tightened before the casting of the slab. The details of this intervention are presented at the following paragraph 4.6 and in figs. 4.7-4.12). The stiffening intervention consists of:

- the casting of a thin concrete slab (4 - 5 cm thick) reinforced by a steel net (suggested bars diameter 4 mm, bars spacing 15 cm in each direction and possibly electrically welded) over the existing floorboards, to be connected to the underlying wooden structure by steel nails (see fig.s 4.4 and 4.6). In order to achieve a more efficient connection between the reinforced concrete slab and the underlying wooden structure (that is for the better stiffening and load distribution) the steel net should be connected to the joists by steel pegs or steel screw connectors and epoxy resins glue.

4.6 HOOPING OF THE BUILDING BY HORIZONTAL STEEL TENDONS


Whenever the connections adopted in a building between its slabs and the supporting walls do not include existing or new reinforced concrete curbs, the accomplishment of tendons anchored by proper plates or keys it is advisable, like in the case of the previous intervention 4.5. It allows in fact, the improvement of the efficiency and the reliability of the

connections between the walls and the walls and the slabs. In other words it contributes to give the building a box-like behavior. Furthermore it gives the walls an advantageous horizontal compressive constraint. The horizontal tendons have to be tightened after the supporting walls repair or strengthening have been carried out if needed (using the techniques indicated in the previous chapter N.3: sealing of cracks, cement grout injections, progressive repositioning or substitution of the unbound elements, etc.) and before the casting of the reinforcing slabs or of other concrete elements, if any. The above mentioned tendons can be made of:

one or two steel bars threaded at both ends, to be tightened by bolts acting on anchoring plates (straight, cross or L shaped, etc.) properly dimensioned and eventually stiffened, and stacked to the wall by mortar;

a pre-stressed steel strands, inserted in a protective sheath or pipe, generally applied underneath the slabs and anchored to the supporting walls by steel plates and steel grip wedges. The possible application schemes are very many, those presented in fig.s from 4.7 to 4.11 are among the most frequently used in practice. All of them require the accomplishment of passing holes through the bearing walls for the setting and the anchoring of the tendons. The choice of the most suitable solution should be carried out case by case according to the walls, the slabs, the joints, connections, etc., characteristics and conservation conditions. In any case, the anchorage devices should be properly protected against the outdoor environment, once the tendons have been tightened. In the case of tendons made of steel bars, the holes they are passing through have to be filled and sealed by cement grout. Instead if strands have been used, the passing holes should be cemented only when the strands post-tightening is not to be foreseen.

4.7 SUBSTITUTION OF THE WOODEN SLAB BY A BRICK HOLLOW TILES AND R.C. ONE


Whenever the slab conditions are really too bad to allow its stiffening or strengthening, its substitution should be considered. In that case the choice between rebuilding it according to the original technique or a new one has to be performed. When the latest is allowed, the construction of a brick hollow tiles and r.c. slab might be a proper solution. In particular this solution might be suggested when:

the wooden elements are too decayed;

the residual load bearing capacity is too low with respect to the permanent and cycling loads required for the building use and its structural safety;

the slab should highly contribute to the stiffening of the building structure;

the slab should take on or integrate the load bearing capacity of other components: arches, vaults, etc.;

there are new or higher fire safety needs. The intervention includes: a proper building underpinning to be defined case by case, the complete demolition of the wooden slab and relevant upper and lower finishings (floor and its base course, ceiling, etc.), the consolidation of the bearing walls, the construction of the new slab, the required finishings. In any case, a basic problem to solve is that of the connection between the new slab and the bearing walls. A solution generally fitting this goal in practice consists of the building of a reinforced concrete curb around the new slab to be partially inserted in the bearing walls thickness and anchored to them by dove tail r.c. connectors (one every 2 m at least). This connection requires the local demolition of the

new slabs supporting walls to form a track whose depth should be defined case by case also according to masonry type, thickness and conservation condition. However, on each side perpendicular to the slab main direction (i.e. the joists direction) the curb should be inserted in the wall for at least 15 cm (see figs. 4.12 and 4.13). The building of dove tail connectors involves the whole wall thickness (see fig. 4.13). Furthermore it can require the supporting walls strengthening to be carried out especially around the tracks and holes for the new slab connection. Generally the wall strengthening consists of cement grout injections (see the previous intervention 3.3). The injection density should be sufficient to anchor the curb and the dove tail r. c. connectors and grant the mutual slab/wall mechanical connection. The upper concrete layer (over the brick hollow tiles) of the new slab should be reinforced by a steel net (possibly electrically welded) connected to the reinforcements of the concrete joists and curbs. The slab resistant sections: structural thickness, brick hollow tiles and upper concrete layer thickness, joists width and pitch, curb width, joists, upper layer and curb reinforcements should be defined case by case according to the required dimensions in plant and load bearing capacity.

Chapter 5

5. RIDGED ROOFS: STIFFENING AND CONNECTION TO THE BEARING WALLS


The ridged roofs usually cause significant horizontal stresses on the external bearing walls (see Fig. 5.1). In the case of earthquake, such stresses can cause the roof damage and even its collapse. If this should happen, the consequences would be obviously related to the roof density (kg per m2): higher the roof density is worse the consequences will be. In buildings located in seismic zone it is then essential to revise the static and the stability of their roofs through the control and the eventual consequent improvement of the following static behaviors:

vertical forces distribution on the bearing walls; restriction of the horizontal stresses on the bearing walls; roofs connection to the bearing walls; roofs stiffening.

The interventions techniques depend upon the roof structure and, in particular, on the material it is made of. Here considered are the wooden and the brick hollow tiles and reinforced concrete structures only. The eventual substitution of wooden structures by prefabricated r. c. rafters and hollow flat blocks it is not generally advantageous for it implies a relevant increasing of the permanent load and a difficult connection to the supporting walls. Therefore it is not here considered. In the following, cases referring to typical ridged roofs of little buildings, like gable and gambrel roofs, are considered. Their structure consists of:

a ridge pole placed on the triangular end of header and intermediate (if any) bearing walls;

rafters which extend from the ridge pole to the eaves leaning upon the ridge pole a front wall.

Their structural scheme is then the one shown in fig. 5.1, which causes horizontal stresses on the external bearing walls. These stresses can highly increase because of excessive deflection under load and/or development of a permanent bowing in the ridge pole. As to the roofs made of a brick hollow tiles and reinforced concrete structure, the damages in case of earthquake depends generally on their heavy weight and their feeble anchorage to the bearing walls as well as on a lack of mutual linking within the elements they are made of, especially when they are made of prefabricated r.c. rafters and hollow flat blocks.

5.2 TYPES OF THE INTERVENTION

The interventions considered in this chapter are: a. wooden roofs: construction of garret reinforced concrete curbs. b. wooden roofs: control of the pushing actions. c. insertion of transversal steel tendons after the construction of the garret r.c. curbs. d. construction of transversal r.c. curbs associated with the construction of garret r.c. curbs and bearing cross walls. e. insertion of wooden tendons. f. connections by steel anchor ties. g. wooden roofs: stiffening of the structure in the slope plane. As for the brick hollow tiles and reinforced concrete roofs the interventions described are:

- raising of the existing garret reinforced concrete curbs. - construction of intermediate transversal reinforced concrete curbs.

In the following sections the description of their construction phases is given together with the criteria for their adoption and execution. In all cases, the need of a preventive strengthening of the bearing walls, especially at their top should be evaluated. Generally the wall strengthening consists of cement grout injections (see the previous intervention 3.3). The injection density should be sufficient to anchor the curbs and/or the connectors and grant their mutual mechanical connection to the wall.

5.3 WOODEN ROOFS: CONSTRUCTION OF GARRET REINFORCED CONCRETE CURBS


This intervention is in order to improve the transfer of the loads and the consequent stresses from the roof to the bearing walls and to hoop the building top. The intervention is carried out on the existing bearing walls as well as on those inserted to reinforce and stiffen the whole wall structure (sees figs. 5.2 .a and 5.2 .b). In the first case, in order to decide the choice and the size of the curb a preliminary check of the structure solidity and the conservation state of both the wall top and the roof structural components is required. The decision about the choice and size of the curb should be consistent with the eaves and with the detail of the eventual cornice, especially in the case of historical and artistic value buildings. After the intervention a steel tendon should be installed in order to control the horizontal forces (pushing actions) (see the following intervention 5.4). In the areas corresponding to the ridge pole and in that of the knuckle pole (gambrel roofs) or of the eventual intermediate pole (gable roofs) the curb section should be varied in order to englobe the pole section and properly distribute its load on the wall. In the second case, the curb construction could be coordinated to the new wall one; the function of absorbing the pushing actions will be then carried out by a curb (see fig.s 5.3.a and 5.3 b and the following intervention 5.6). Also in this case, in the areas corresponding to the ridge and the eventual knuckle pole (gambrel roofs) or intermediate pole (gable roofs) the curb section should be varied in order to englobe the pole section and distribute its load on the wall (see fig. 5.3 b). In any case the construction of the curb should be carried out after:

the roof propping up (by proper underpinning);

the partial dismantling of the shingles or tiles and of the eventual underneath boards; the local demolition of the walls (n. of layers corresponding to the curb minimum height) in order to allow the preparation of the curb seat and its cast.

Before casting the curb, the stirrups should be put in the proper position for the necessary connections between the curb and the rafters (the connections will be completely englobed in the concrete - see the following intervention 5.6) and, where necessary, the holes where the connecting bars have to pass through should be drilled.

5.4 WOODEN ROOFS: CONTROL OF THE PUSHING ACTIONS

5.4.1 General information

The pushing actions can be controlled by several techniques according to the building conservation state, the amount of the stresses and the risk of damage involved, the other interventions already foreseen for the building top and its roof The choice of the most suitable type of intervention should be done therefore case by case on the basis of the variable factors mentioned above. Among the variety of possible techniques those described in the following are suitable and easy to use for the control of the pushing actions in the type of buildings studied in this referees. They consists of

the insertion of transversal steel tendons combined with the construction of garret r.c. curbs (see fig.s 5.2.a, 5.2.b, 5.4, 5.5, 5.6);

the construction of transversal r.c. curbs associated with the construction of garret r.c. curbs and the construction of new tympanum-shaped walls with close inter-axes (see fig.s 5.3.a, 5.3.b, 5.4, 5.5, 5.6);

the insertion of wooden tie beams.

The association of the garret curb with the transversal steel tendons or r.c. curbs provides an advantageous hooping effect on the top of the bearing walls.

In those cases the construction of the perimeter r.c. curbs it is not foreseen or not consistent with the eaves and with the detail of the eventual cornice, the need to accomplish anyhow the hooping of the building top by other techniques should be considered, especially in the case of historical and artistic value buildings. Not seldom it can be done by steel tendons anchored by steel plates or keys (as shown in the former chapter 4, intervention 4.6).

5.5 INSERTION OF TRANSVERSAL STEEL TENDONS AFTER THE CONSTRUCTION OF THE GARRET R.C. CURBS


The association of the garret curb with transversal steel tendons, or with transversal r.c. curbs, provides a favorable hooping of the masonry top. When the connection of the ridged roof to the walls has to be improved by the construction of a garret r.c. curb (see the previous intervention 5.3), it is suitable to install also a steel tendon along the internal side of each transversal bearing wall. Such steel tendons should pass through the garret curbs (through previously drilled holes) and then anchored to them by steel plates or keys. In this way it is possible to get an effective hooping of the building top. Such hooping effect contributes to give the building a box-like behavior. Furthermore it gives the transversal bearing walls an advantageous horizontal compressive constraint. The horizontal tendons have to be tightened after the supporting walls repair or strengthening have been carried out if needed (using the techniques indicated in the previous chapter N.3: sealing of cracks, cement grout injections, progressive repositioning or substitution of the unbound elements, etc.). The above mentioned tendons can be made of one or two steel bars threaded at both ends, to be tightened by bolts acting on anchoring plates (straight, cross or L shaped, etc.) properly dimensioned and eventually stiffened, and stucked to the wall by mortar.

They should be installed at the front garret curbs level (see figs. 5.2.a and 5.2.b) The possible application schemes are very many, those presented in figs. 5.4, 5.5 and 5.6 are among the most frequently used in practice. All of them require the accomplishment of passing holes through the front garret curbs for the setting and the anchoring of the tendons. The choice of the most suitable solution should be carried out case by case according to the top wall thickness, the bearing walls conservation conditions, the location of the steel tendon: beside an header or intermediate transversal wall, the length of the transversal walls (i e the building depth) and the distance between the various transversal walls (i e the width of the front walls between two transversal walls). In any case, the anchorage devices should be properly protected against the outdoor environment, once the tendons have been tightened. The passing holes have to be filled and sealed by cement grout only when the tendons post-tightening is not to be foreseen, other ways a polymeric sealant should be used.

5.6 CONSTRUCTION OF TRANSVERSAL R.C. CURBS ASSOCIATED WITH THE CONSTRUCTION OF GARRET R.C. CURBS AND BEARING CROSS WALLS


This intervention is in order to improve the transfer of the loads and the consequent stresses from the roof to the transversal bearing walls and to hoop the building top. The intervention is carried out on the walls inserted to reinforce and stiffen the whole wall structure (see the intervention in previous Chapter 2). The transversal r.c. curb construction should be coordinated to the new wall one. Once it has been built, a triangular or otherwise properly shaped wall should be built together with its upper curb (see fig.s 5.3.a and 5.3%). This will be the intermediate support to the ridge pole and to the other eventual intermediate poles of the roof

5.7 INSERTION OF WOODEN TENDONS


This intervention is in order to avoid the horizontal stresses due to the deflection or to the permanent bowing of the ridge pole. The intervention consists in the mutual connection of facing rafters by wooden tendons made of 2 planks 4 x 15 cm each one, anchored at the facing rafters feet by bolts, washers, nuts and nailed hooping strips of sheet steel. The planks are also mutually connected at the half of their span by a wooden block and a bolt, a washer and nut (see fig. 5.7). This intervention is suitable when the loft is not used to live in, the roof is not particularly heavy and the rafters are well proportioned and in good conservation conditions. The suggested wooden tendons rate is about 1,5 to 2,5 m, that is every 2 - 3 rafters.

5.8 CONNECTIONS BY STEEL ANCHOR TIES


This intervention is in order to achieve a reliable connection between the rafters and the garret r.c. curbs. (see fig. 5.8). It should be envisaged when the garret r.c. curb preparation is carried out (see the previous intervention 5.3).

5.9 WOODEN ROOFS: STIFFENING OF THE STRUCTURE IN TILE SLOPE PLANE


The stiffening of the ridged roof structure is useful to increase the roof stability and improve the transfer of the dynamic loads to the ground. This intervention should be therefore combined with those of the construction of garret r.c. curbs and transversal tendons or curbs (see the previous

intervention n. 5.3 and the relevant interventions n. 5.4 and 5.6) as well as with that of the improvement of the connection between the rafters and these curbs (see the previous intervention n. 5.8). The possible application schemes are very many, those presented in fig.s from 5.9 to 5.10 are among the most frequently used in practice. The first one is for the mutual connection between the rafters, while the second is for the anchorage of the ridge pole. The first solution consists of the setting of new roof boards under the tiles, perpendicularly to the existing rafters (see fig. 5.9). The connection and mechanical collaboration between the new roof boards and the rafters have to be granted by a proper nailing. Two nails for each board/rafter crossing point are suggested. The second one consists of the installation of St. Andrews cross steel tendons between the ridge pole and the garret curbs, having a width of 4 - 6 m measured on the ridge pole and garret curbs (see fig. 5.10). In many cases the first solution itself is effective to grant the roof enough stability. On the contrary, the second one generally requires also the accomplishment of the first solution. Furthermore it should be applied only when the ridge pole free inflection span is not exceeding 4 - 6 m (or if it has been reduced at this fig.s by the construction of cross bearing walls). The first solution is quite easy to carry out and requires the complete dismantling of the roof covering and of the underneath roof sheathing. It also implies the increasing of the permanent load (in the range of 15 - 20 kg/rn2), modifies the roofs wind and moisture behavior and does not give the possibility to inspect and change the tiles from the loft anylonger. It is therefore suggested to place over the roof boards a membrane working as air barrier and to insure watertightness made of asphalt cardboard, for example. In order to preserve the roof boards over time their protection by a anti-fungi and anti-mould paint is suggested. Whatever solution is going to be adopted the previous check of the ridge poles and rafters conservation state and residual load bearing capacity is requested also with reference to the increasing in the permanent load

because of the roof boards setting. Eventual deteriorated wooden members should be previously consolidated or substituted. Whenever the roof members conditions are really too bad to allow their stiffening or strengthening, its substitution should be considered. In that case the new roof should not be significantly heavier than the old one and its anchorage to the bearing walls should not be feebler. Therefore the choice of not rebuilding it by wooden members has to be carefully evaluated.

5.10 BRICK HOLLOW TILES AND R. C. ROOFS: RAISING OF THE EXISTING GARRET R. C. CURBS


For the roofs made of a brick hollow tiles and reinforced concrete structure, the damages in case of earthquake depends generally on their heavy weight and their feeble anchorage to the bearing walls as well as on a lack of mutual linking within the elements they are made of, especially when they are made of prefabricated r.c. rafters and hollow flat blocks. This intervention is therefore in order to improve the transfer of the loads and the consequent stresses from the roof to the bearing walls as well as to improve the mutual linking between the roof structure members. The intervention can be carried out when the conservation state of both the wall top and the roof structural components is good enough. After the intervention a steel tendon should be eventually installed in order to control the horizontal forces (pushing actions) (see the previous intervention 5.4). In any case the construction of the garret curb should be carried out after (see fig. 5.11):

the roof propping up (by proper underpinning); the partial dismantling of the shingles or tiles and of the eventual

underneath horizontal strips; the local demolition of the concrete layer and the brick hollow tiles upon

the wall in order to allow the preparation of the extra curb seat and its cast;

the existing curb drilling to prepare the hollows for the insertion of the steel stirrups connectors.

5.11 BRICK HOLLOW TILES AND R. C. ROOFS: CONSTRUCTION OF INTERMEDIATE TRANSVERSAL R. C. CURBS


This intervention is in order to improve the mutual linking between the roof structures members (see fig. 5.12). It should be always carried out together with the previous intervention 5.10.

Repair and retrofit techniques.pdf (p.1)Introducere.pdf (p.2-3)Capitolul 1.pdf (p.4-10)Capitolul 2.pdf (p.11-29)Capitolul 3.pdf (p.30-49)Capitolul 4.pdf (p.50-71)Chapter 5.pdf (p.72-93)

repair and retrofit techniques

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