Chapter 9: Repair Restoration and Strengthening of Buildings

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REPAIR, RESTORATION AND STRENGTHENING OF BUILDINGS

Chapter 9

REPAIR, RESTORATION ANDSTRENGTHENING OF BUILDINGS

9.1 INTRODUCTIONThe need to improve the ability of an exist-ing building to withstand seismic forcesarises usually from the evidence of dam-age and poor behaviour during a recentearthquake. It can arise also from calcula-tions or by comparisons with similar build-ings that have been damaged in otherplaces. While in the first case the ownercan be rather easily convinced to take meas-ures to improve the strength of his build-ing, in the second case dwellers that havemuch more stringent day-to-day needs areusually reluctant to invest money in theimprovement of seismic safety. The prob-lems of repairs, restoration and seismicstrengthening of buildings are brieflystated below:

(i) Before the occurrence of the probableearthquake, the required strengthen-ing of seismically weak buildings isto be determined by a survey andanalysis of the structures.

(ii) Just after a damaging earthquake,temporary supports and emergency

repairs are to be carried so that pre-cariously standing buildings maynot collapse during aftershocks andthe less damaged ones could bequickly brought back into use.

(iii) The real repair and strengtheningproblems are faced at the stage afterthe earthquake when things start set-tling down. At this stage distinctionhas to be made in the type of actionrequired, that is, repairs, restorationand strengthening, since the cost,time and skill required in the threemay be quite different.

The decision as to whether a givenbuilding needs to be strengthened and towhat degree, must be based on calculationsthat show if the levels of safety demandedby present codes and recommendations aremet. Difficulties in establishing actualstrength arise from the considerable uncer-tainties related with material properties andwith the amount of strength deteriorationdue to age or to damage suffered from pre-vious earthquakes. Thus, decisions are fre-

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quently based on gross conservative as-sumptions about actual strength.

The method of repair and strengthen-ing would naturally depend very largelyon the structural scheme and materials usedfor the construction of the building in thefirst instance, the technology that is feasi-ble to adopt quickly and on the amount offunds that can be assigned to the task, usu-ally very limited. Some methods like�splints and bandages�, �wire mesh withgunite�, �epoxy injection,� etc., have al-ready been tried and applied in a few coun-tries for repairing as well as strengtheningearthquake damaged buildings. These aswell as other possible methods will be dis-cussed in this chapter.

9.2 REPAIR, RESTORATIONAND STRENGTHENINGCONCEPTSThe underlying concepts in the three op-erations are stated below:

9.2.1 RepairsThe main purpose of repairs is to bring backthe architectural shape of the building sothat all services start working and the func-tioning of building is resumed quickly. Re-pair does not pretend to improve the struc-tural strength of the building and can bevery deceptive for meeting the strength re-quirements of the next earthquake. The ac-tions will include the following:

(i) Patching up of defects such as cracksand fall of plaster.

(ii) Repairing doors, windows, replace-ment of glass panes.

(iii) Checking and repairing electric wir-ing.

(iv) Checking and repairing gas pipes,water pipes and plumbing services.

(v) Re-building non-structural walls,smoke chimneys, boundary walls,etc.

(vi) Re-plastering of walls as required.

(vii) Rearranging disturbed roofing tiles.

(viii) Relaying cracked flooring at groundlevel.

(ix) Redecoration � whitewashing,painting, etc.

The architectural repairs as stated abovedo not restore the original structuralstrength of cracked walls or columns andmay sometimes be very illusive, since theredecorates building will hide all the weak-nesses and the building will suffer evenmore severe damage if shaken again by anequal shock since the original energy ab-sorbing capacity will not be available.

9.2.2 RestorationIt is the restitution of the strength the build-ing had before the damage occurred. Thistype of action must be undertaken whenthere is evidence that the structural dam-age can be attributed to exceptional phe-nomena that are not likely to happen againand that the original strength provides anadequate level of safety.

The main purpose of restoration is tocarry out structural repairs to load bearingelements. It may involve cutting portionsof the elements and rebuilding them or sim-ply adding more structural material so thatthe original strength is more or less restored.The process may involve inserting tempo-rary supports, underpinning, etc. Some ofthe approaches are stated below:

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(i) Removal of portions of cracked ma-sonry walls and piers and rebuild-ing them in richer mortar. Use of non-shrinking mortar will be preferable.

(ii) Addition of reinforcing mesh onboth -faces of the cracked wall, hold-ing it to the wall through spikes orbolts and then covering it suitably.Several alternatives have been used.

(iii) Injecting epoxy like material, whichis strong in tension, into the cracksin walls, columns, beams, etc.

Where structural repairs are considerednecessary, these should be carried out priorto or simultaneously with the architecturalrepairs so that total planning of work couldbe done in a coordinated manner and wast-age is avoided.

9.2.3 Strengthening of existingbuildingsThe seismic behaviour of old existing build-ings is affected by their original structuralinadequacies, material degradation due totime, and alterations carried out during useover the years such as making new open-ings, addition of new parts inducing dis-symmetry in plan and elevation, etc.

The possibility of substituting themwith new earthquake resistant buildingsis generally neglected due to historical, ar-tistic, social and economical reasons. Thecomplete replacement of the buildings in agiven area will also lead to destroying anumber of social and human links. There-fore seismic strengthening of existing dam-aged or undamaged buildings can be a defi-nite requirement in same areas.

Strengthening is an improvement overthe original strength when the evaluation

of the building indicates that the strengthavailable before the damage was insuffi-cient and restoration alone will not be ad-equate in future quakes.

The extent of the modifications must bedetermined by the general principles anddesign methods stated in earlier chapters,and should not be limited to increasing thestrength of members that have been dam-aged, but should consider the overall be-haviour of the structure. Commonly,strengthening procedures should aim atone or more of the following objectives:

(i) Increasing the lateral strength in oneor both directions, by reinforcementor by increasing wall areas or thenumber of walls and columns.

(ii) Giving unity to the structure by pro-viding a proper connection betweenits resisting elements, in such a waythat inertia forces generated by thevibration of the building can betransmitted to the members that havethe ability to resist them. Typical im-portant aspects are the connectionsbetween roofs or floors and walls,between intersecting walls and be-tween walls and foundations.

(iii) Eliminating features that are sourcesof weakness or that produce concen-trations of stresses in some members.Asymmetrical plan distribution ofresisting members, abrupt changesof stiffness from one floor to the other,concentration of large masses, largeopenings in walls without a properperipheral reinforcement are exam-ples of defect of this kind.

(iv) Avoiding the possibility of brittlemodes of failure by proper reinforce-

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ment and connection of resistingmembers. Since its cost may go to ashigh as 50 to 60% of the cost of re-building, the justification of suchstrengthening must be fully consid-ered.

The extent of modification must befound using the principles of strengthen-ing discussed in Chapters 2, 3 and 4 andin accordance with the local factors appli-cable to each building.

9.3 REPAIR MATERIALSThe most common materials for damagerepair works of various types are cementand steel. In many situations non-shrink-ing cement or an admixture like aluminiumpowder in the ordinary portland cementwill be admissible. Steel may be requiredin many forms, like bolts, rods, angles,channels, expanded metal and weldedwire fabric. Wood and bamboo are the mostcommon material for providing temporarysupports and scaffolding etc., and will berequired in the form of rounds, sleepers,planks, etc.

Besides the above, special materials andtechniques are available for best results inthe repair and strengthening operations.They are described below:

9.3.1. ShotcreteShotcrete is a method of applying a combi-nation of sand and portland cement whichmixed pneumatically and conveyed in drystate to the nozzle of a pressure gun, wherewater is mixed and hydration takes placejust prior to expulsion. The material bondsperfectly to properly prepared surface ofmasonry and steel. In versatility of appli-

cation to curved or irregular surfaces, itshigh strength after application and goodphysical characteristics, make for an idealmeans to achieve added structural capa-bility in walls and other elements. Thereare some minor restrictions of clearance,thickness, direction of application, etc.

9.3.2 Epoxy resinsEpoxy resins are excellent binding agentswith high tensile strength. There are chemi-cal preparations the compositions ofwhich can be changed as per requirements.The epoxy components are mixed just priorto application. The product is of low vis-cosity and can be injected in small crackstoo.

The higher viscosity epoxy resin can beused for surface coating or filling largercracks or holes. The epoxy mixture strengthis dependent upon the temperature of cur-ing (lower strength for higher temperature)and method of application.

9.33 Epoxy mortarFor larger void spaces, it is possible to com-bine epoxy resins of either low viscosity orhigher viscosity, with sand aggregate toform epoxy mortar. Epoxy mortar mixturehas higher compressive strength, highertensile strength and a lower modulus ofelasticity than Portland cement concrete.Thus the mortar is not a stiff material forreplacing reinforced concrete. It is also re-ported that epoxy is a combustible mate-rial. Therefore it is not used alone. The sandaggregate mixed to form the epoxy mortarprovides a heat sink for heat generated andit provides increased modulus of elasticitytoo.

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9.4.1 Small cracksIf the cracks are reasonably small (openingwidth = 0.075 cm), the technique to restorethe original tensile strength of the crackedelement is by pressure injection of epoxy.The procedure is as follows, Fig 9.1 (a) and(b).

The external surfaces are cleaned ofnon-structural materials and plastic injec-tion ports are placed along the surface ofthe cracks on both sides of the member andare secured in place with an epoxy sealant.The centre to centre spacing of these portsmay be approximately equal to the thick-ness of the element. After the sealant hascured, a low viscosity epoxy resin is injectedinto one port at a time, beginning at the low-est part of the crack in case it is vertical or atone end of the crack in case it is horizontal.

The resin is injected till it is seen flow-ing from the opposite sides of the memberat the corresponding port or from the nexthigher port on the same side of member. Theinjection port should be closed at this stageand injection equipment moved to the nextport and so on.

The smaller the crack, higher is the pres-sure or more closely spaced should be theports so as to obtain complete penetrationof the epoxy material throughout the depthand width of member. Larger cracks willpermit larger port spacing, depending uponwidth of the member. This technique is ap-propriate for all types of structural elements� beams, columns, walls and floor unitsin masonry as well as concrete structures.Two items should however be taken care ofin such type of repair:

9.3.4 Gypsum cement mortarIt has got rather limited use for structuralapplication. It has lowest strength at fail-ure among these three materials.

9.3.5 Quick-setting cementmortarThis material is patented and was origi-nally developed for the use as a repair ma-terial for reinforced concrete floors adjacentto steel blast furnaces. It is a non-hydrousmagnesium phosphate cement with twocomponents, a liquid and a dry, which canbe mixed in a manner similar to portlandcement concrete.

9.3.6 Mechanical anchorsMechanical type of anchors employ wedg-ing action to provide anchorage. Some ofthe anchors provide both shear and ten-sion resistance. Such anchors are manu-factured to give sufficient strength.

Alternatively chemical anchors bondedin drilled holes polymer adhesives can beused.

9.4 TECHNIQUES TO RESTOREORIGINAL STRENGTHWhile considering restoration work, it isimportant to realise that even fine cracksin load bearing members which areunreinforced, like masonry and plain con-crete reduce their resistance very largely.Therefore all cracks must be located andmarked carefully and the critical ones fullyrepaired either by injecting strong cementor chemical grout or by providing externalbandage. The techniques are described be-low along with other restoration measures.

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(i) In the case of loss of bond betweenreinforcing bar and concrete, if theconcrete adjacent to the bar has beenpulverised to a very fine powder, thispowder will dam the epoxy from

saturating the region. So it shouldbe cleaned properly by air or waterpressure prior to injection of epoxy.

(ii) It has been stated that cracks smallerthan about 0.75 mm may be difficult

Fig 9.1 Strengthening of existing masonry (continued on next page)

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to pressure inject. So cracks smallerthan this should not be repaired bythis method.

9.4.2 Large cracks and crushedconcreteFor cracks wider than about 6 mm or forregions in which the concrete or masonryhas crushed, a treatment other than injec-

tion is indicated. The following proceduremay be adopted.

(i) The loose material is removed andreplaced with any of the materialsmentioned earlier, i.e., expansive ce-ment mortar, quick setting cement orgypsum cement mortar, Fig 9.1 (c).

Fig 9.1 Strengthening of existing masonry

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(ii) Where found necessary, additionalshear or flexural reinforcement isprovided in the region of repairs.This reinforcement could be coveredby mortar to give further strength aswell as protection to the reinforce-ment, Fig 9.1 (d).

(iii) In areas of very severe damage, re-placement of the member or portionof member can be carried out as dis-cussed later.

Fig 9.2 Roof modification to reduce thrust of walls

(iv) In the case of damage to walls andfloor diaphragms, steel mesh couldbe provided on the outside of the sur-face and nailed or bolted to the wall.Then it may covered with plaster ormicro-concrete, Fig 9.1 (d).

9.4.3 Fractured, excessivelyyielded and buckledreinforcementIn the case of severely damaged reinforcedconcrete member, it is possible that the re-inforcement would have buckled, or elon-

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enclose the longitudinal bars to preventtheir buckling in future.

In some cases it may be necessary toanchor additional steel into existing con-crete. A common technique for providingthe anchorage uses the following proce-dure:

A hole larger than the bar is drilled. Thehole is filled with epoxy, expanding cement,or other high strength grouting material.

gated or excessive yielding may have oc-curred. This element can be repaired by re-placing the old portion of steel with newsteel using butt welding or lap welding.

Splicing by overlapping will be risky. Ifrepair has to be made without removal ofthe existing steel, the best approach woulddepend upon the space available in theoriginal member. Additional stirrup ties areto be added in the damaged portion beforeconcreting so as to confine the concrete and

Fig 9.3 Details of new roof bracing

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The bar is pushed into place and held thereuntil the grout has set.

9.4.4 Fractured woodenmembers and jointsSince wood is an easily workable material,it will be easy to restore the strength ofwooden members, beams, columns, strutsand ties by splicing additional material.The weathered or rotten wood should firstbe removed. Nails, wood screws or

steelbolts will be most convenient as con-nectors. It will be advisable to use steelstraps to cover all such splices and jointsso as to keep them tight and stiff.

9.5 MODIFICATION OF ROOFS(i) Slates and roofing tiles are brittle and

easily dislodged. Where possiblethey should be replaced with corru-gated iron or asbestos sheeting.

Fig 9.4 Integration and stiffening of an existing floor

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(ii) False ceilings of brittle material aredangerous. Non brittle material likehesian cloth, bamboo matting, orlight ones of foam substances maybe used.

(iii) Roof truss frames should be bracedby welding or clamping suitable di-agonal bracing embers in the verti-cal as well as horizontal planes.

(iv) Anchors of roof trusses to support-ing walls should be improved andthe roof thrust on walls should beeliminated.

Figs 9.2. and 9.3 illustrate one of themethods.

(v) Where the roof or floor consists ofprefabricated units like RC rectangu-

Fig 9.5 Details of inserted slab

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lar, T or channel units or woodenpoles and joists carrying brick tiles,integration of such units is neces-sary. Timber elements could be con-nected to diagonal planks nailed tothem and spiked to an all roundwooden frame at the ends. RC ele-ments may either have 40 mm cast-in-situ-concrete topping with 6 mmφ bars 150 mm c/c both ways or ahorizontal cast-in-situ RC ring beamall round into which the ends of RCelements are embedded.Fig 9.4.shows one such detail.

(vi) Roofs or floors consisting of steeljoists and flat or segmental archesmust have horizontal ties holdingthe joists horizontally in each archspan so as to prevent the spreadingof joists. If such ties do not exist, theseshould be installed by welding orclamping.

9.6 SUBSTITUTION ORSTRENGTHENING OF SLABS(a) Insertion of a new slabA rigid slab inserted into existing wallsplays an important role in the resistingmechanism of the building keeping thewalls together and distributing seismicforces among the walls.

The slab has to be properly connectedto the walls through appropriate keys.Fig 9.4 shows typical arrangement to beadopted while in Fig 9.5 some details areshown.

(b) Existing wooden slabsIn the case in which the existing stab is notremoved the following actions have to beundertaken:

Stiffening of the slabThis can be achieved either by planks nailedperpendicularly to the existing ones, Fig 9.6or by placing a RC thin stab over the oldone, Fig 9.7.

In this case a steel network is nailed tothe wooden slab and connected to the wallsby a number of distributed steel anchors.These can be hammered into the intersticesof the wall and a local hand cement grout-ing has to be applied for seating.

Connection of the slab to the wallsA proper link can be obtained by means ofthe devices shown in Figs 9.8. and 9.9.

They consist of flat steel bars nailed tothe wooden supporting beams and to thewooden slab. Holes drilled in the walls toanchor them have to be infilled with ce-ment. If a steel mesh has been used, the con-nection can be made as shown in Fig 9.5,i.e., inserting a small RC band into the ex-isting walls, the band has to be keyed atleast each 3 m.

9.7 PLANNAR MODIFICATIONSAND STRENGTHENING OFWALLS9.7.1 Inserting new wallsIn the case the existing buildings showdissymetries which may produce danger-ous torsional effects during earthquakes,the center of masses can be made coinci-dent with the center of stiffness by separat-ing parts of buildings, thus achieving indi-vidual symmetric units and/or, insertingnew vertical resisting elements such asnew masonry or reinforced concrete wallseither internally as shear walls, or exter-nally as buttresses. Insertion of cross wall,

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Fig 9.6 Stiffening of wooden floor by wooden planks

Fig 9.7 Stiffening wooden floor by reinforced concrete slab and connection to wall

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will be necessary for providing transversesupports to longitudinal walls of long bar-rack type buildings used for various pur-poses such as schools and dormitories.

The main problem in such modifica-tions is the connection of new walls withold walls. Figs 9.10. and 9.11. show twoexamples of connection of new walls to ex-isting ones. The first case refers to aT-junction, the second figure to a cornerjunction. In both cases the link to the old

walls is performed by means of a numberof keys made in the old walls. Steel is in-serted in them and local cement infilling ismade. In the second case however connec-tion can be achieved by a number of steelbars inserted in small length drilled holeswhich substitute keys.

9.7.2 Strengthening existingwallsThe lateral strength of buildings can beimproved by increasing the strength and

Fig 9.8 Connection of floor to wall

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stiffness of existing individual wallswhether they are cracked or uncracked.This an be achieved (a) by grouting; (b) byaddition of vertical reinforced concrete cov-erings on the two sides of the wall (c) bypre-stressing walls.

(a) GroutingA number of holes are drilled in the wall,Fig 9.1. (2 to 4 m2). First water is injected inorder to wash the wall inside and to im-

prove the cohesion between the groutedmixture and the wall elements. Secondly acement water mixture (1:1) is grouted at lowpressure (0.1 to 0.25 MPa) in the holes start-ing from the lower holes and going up.

Alternatively, polymeric mortars may beused for grouting. The increase of shearstrength which can be achieved in this wayis considerable. However grouting cannotbe relied on as far as the improving or con-

Fig 9.9 Connection of floor with wall

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Fig 9.10 (a) Connection of new and old brick walls (T-junction) (b) Connection of new brick wall with existing stone wall

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nection between orthogonal walls is con-cerned. Note that pressure needed for grout-ing can be obtained by gravity flow fromsuper-elevated tanks.

(b) Strengthening with wire meshTwo steel meshes (welded wire fabric withan elementary mesh of approximately50 × 50 mm) are placed on the two sides of

the wall, they are connected by passingsteel each 500 to 750 mm apart, Fig 9.12. A20 to 40 mm thick cement mortar or micro-concrete layer is then applied on the twonetworks thus giving rise to two intercon-nected vertical plates. This system can alsobe used to improve connection oforthogonal walls.

Fig 9.11 Connection of new and old walls (corner junction)

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(c) Connection between existingstone wallsIn stone buildings of historic importanceconsisting of fully dressed stone masonryin good mortar effective sewing of perpen-dicular walls can be done by drilling in-clined holes through them, inserting steelrods and injecting cement grout, Fig 9.13.

(d) PrestressingA Horizontal compression state induced byhorizontal tendons can be used to increasethe shear strength of walls. Moreover thiswill also improve considerably the connec-tions of orthogonal walls, Fig 9.14. The easi-est way of affecting the precompression isto place two steel rods on the two sides of

Fig 9.12 Strengthening with wire mesh and mortar Fig 9.13 Sewing transverse walls withinclined bars

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the wall and strengthening them byturnbuckles. Note that good effects can beobtained by slight horizontal prestressing(about 0.1 MPa) on the vertical section ofthe wall. Prestressing is also useful tostrengthen spandrel beam between tworows of openings in the case no rigid stabexists.

9.7.3 External bindingOpposite parallel walls can be held to in-ternal cross walls by prestressing bars asillustrated above, the anchoring being doneagainst horizontal steel channels insteadof small steel plates. The steel channels run-ning from one cross wall to the other will

Fig 9.14 Strengthening of walls by prestressing

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hold the walls together and improve theintegral box like action of the walls.

Fig 9.15 Splint and bandage strengthening technique

Fig 9.16 Strengthening an arched opening in masonry wall

The technique of covering the wall withsteel mesh and mortar or micro-concretemay be used only on the outside surface ofexternal walls but maintaining continuityof steel at the corners. This wouldstrengthen the walls as well as bind themtogether. As a variation and for economy inthe use of materials, the covering may be inthe form of vertical splints between open-ings and horizontal bandages overspandrel walls at suitable number of pointsonly, Fig 9.15.

9.7.4 Other points(i) Masonry arches If the walls have

large arched openings in them, it willbe necessary to install tie rods acrossthem at springing levels or slightlyabove it by drilling holes on bothsides and grouting steel rods inthem, Fig 9.16 (a). Alternatively, a lin-

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tel consisting of steel channels or I-shapes, could be inserted just abovethe arch to take the load and relievethe arch as shown at Fig 9.16 (b). Injack-arch roofs, flat iron bars or rodsmay be provided to connect the bot-

tom flanges of I-beams, connected bybolting or welding.

(ii) Random rubble masonry walls aremost vulnerable to complete collapseand must be strengthened by inter-

Fig 9.17 Strengthening of long walls by buttresses

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nal impregnation by rich cementmortar grout in the ratio of 1:1 as ex-plained in 9.7.2 (a) or better still cov-ered with steel mesh and mortar asin 9.7.2 (b). Damaged portions of thewall, if any, should be reconstructedusing richer mortar.

(iii) For bracing the longitudinal wallsof long barrack type buildings, a por-tal type framework can be inserted

Fig 9.18 Jacketing a concrete column

Fig 9.19 Increasing the section and reinforcement of existing beams

transverse to the walls and con-nected to them. Alternatively, ma-sonry buttresses or, pillasters may beadded externally as shown inFig 9.17.

(iv) In framed buildings, the lateral re-sistance can be improved by insert-ing knee braces or full diagonalbraces or inserting infill walls.

9.8 STRENGTHENING RCMEMBERSThe strengthening of reinforced concretemembers is a task that should be carriedout by a structural engineer according tocalculations. Here only a few suggestionsare included to illustrate the ways in whichthe strengthening could be done.

(i) RC columns can best be strengthenedby jacketing, and by providing addi-tional cage of longitudinal and lat-eral tie reinforcement around the col-umns and casting a concrete ring,Fig 9.18, the desired strength andductility can thus be built-up.

(ii) Jacketing a reinforced concrete beamcan also be done in the above man-ner. For holding the stirrup in thiscase, holes will have to be drilledthrough the slab, Fig 9.19.

(iii) Similar technique could tie used forstrengthening RC shear walls.

(iv) Inadequate sections of RC columnand beams can also be strengthenedby removing the cover to old steel,welding new steel to old steel andreplacing the cover.

In all cases of adding new concreteto old concrete, the original surfaceshould be roughened, groves made

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Fig 9.20 Improving a foundation by inserting lateral concrete beams

in the appropriate direction for pro-viding shear transfer. The ends of theadditional steel are to be anchoredin the adjacent beams or columns asthe case may be.

(v) RC beams can also be strengthenedby applying prestress to it so that op-posite moments are caused to thoseapplied. The wires will run on bothsides of the web outside and an-chored against the end of the beamthrough a steel plate.

9.9 STRENGTHENING OFFOUNDATIONSSeismic strengthening of foundations be-fore or after the earthquake is the most in-volved task since it may require careful un-derpinning operations. Some alternativesare given below for preliminary considera-tion of the strengthening scheme.

(i) Introducing new load bearing mem-bers including foundations to relievethe already loaded members. Jackingoperations may be needed in thisprocess.

(ii) Improving the drainage of the areato prevent saturation of foundationsoil to obviate any problems of liq-uefaction which may occur becauseof poor drainage.

(iii) Providing apron around the build-ing to prevent soaking of foundationdirectly and draining off the water.

(iv) Adding strong elements in the formof reinforced concrete strips attachedto the existing foundation part of thebuilding. These will also bind thevarious wall footings and may beprovided on both sides of the wall,Fig 9.20. To avoid digging the floor

inside the building, the extra widthcould be provided only on the out-side of external walls. The extrawidth may be provided above the ex-isting footing or at the level of the ex-isting footing. In any case the rein-forced concrete strips and the wallshave to be linked by a number of keys,inserted into the existing footing.

Note: To avoid disturbance to the in-tegrity of the existing wall during thefoundation strengthening process,proper investigation and design iscalled for.

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Chapter 9: Repair Restoration and Strengthening of Buildings

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Transcript of Chapter 9: Repair Restoration and Strengthening of Buildings