Retrofitting of Reinforced Concrete Buildings [PDF]

Zitiervorschau

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'' K Methods of increasing resistant capacity of structure by various techniques is called Retrofitting. K ()'''! is the modification of existing/damaged structures to make them more resistant to seismic activity, ground motion, or soil failure due to earthquakes. K mt can also be defined as increasing the seismic resistant of damaged structure by various techniques as per m
13935-1993

*'|'''! phe basic concept of retrofitting aims at
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K Ôp gradation of lateral strength of the structure K mncrease the ductility of the structure K mncrease of strength and ductility

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ource Of Weakness mn RC frames K Discontinuous load path K Lack of deformation compatibility of structural members K Quality of workmanship and poor quality of materials

Classification Of Retrofitting pechniques ààà
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    based on increasing the seismic resistance of existing structure by eliminating or reducing the adverse effect of design or construction. A Adding new shear walls A Adding steel bracings A Adding infill walls

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    based on reduction of seismic demands A eismic base isolation

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 &!.(-.++/One of the most common methods of retrofitting is providing the shear wall to increase the lateral strength of the reinforced concrete buildings. A reasonable ductility may also be achieved if the walls are properly designed with a good detailing.

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A mncrease in lateral resistance but it is concentrated at a few places A mncrease in overturning moment at foundation causes very high uplift that needs either new foundation or strengthening of the existing foundation A mncreases the dead load of the structure A Excessive destruction at each floor level results in functional disability of the building A Possibilities of adequate attachment between the new and the existing wall A Closing of the formerly open spaces can have major negative impact on the interior of the building or exterior appearance.

,&!('+,!(/Another method of strengthening is use of steel bracings. phese are an effective solution for buildings with large openings.

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igher strength and stiffness can be provided Opening of the natural light can be made easy Bracing system adds less weight to the existing structure Most of the work can be performed with pre-fabricated elements and disturbance to the occupants may be minimized. A mt is cost effective.

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A Lack of information about the seismic behavior of the added bracing A Ôndesirable changes regarding original architectural features A ection failure may cause impact on over all performance of the building A igh level workers are necessary for construction A Cost efficiency specially to welding is necessary


  

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&!++.++(/Adding of infill walls as shown in the figure also helps in increasing the structural strength against seismic force. mt is economical and effective method to improve strength and reduce drift of frame.

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ome columns in the frame are subjected to large axial tensile forces, which may exceed the capacity of the column that have been designed for little or no flexure but only for axial and gravity load.

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 phis method aims at reducing the seismic forces on the structure using various techniques of base isolation. mt is a powerful method of seismic retrofitting for buildings.

& ((+'/phe seismic base isolation technology involves placing flexible isolation systems between the foundation and the superstructure.

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Better protection against earthquake due to decreasing of shears Foundation system will not need any reinforcement to resist overturning moments Least interrupting the building activities since work is carried out at the basement

Base isolators
K Flexible pads and rollers K eismic dampers a) ¢

 
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),+$+ +&|'' )'-( Õ phe member level/local retrofit methods are to upgrade the strength of the member which is seismically deficient phe most common methods used are as follows
Kacketing of columns Kacketing of beams Kacketing of beam-column joint K trengthening of individual footing

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acketing of columns consist of adding concrete with longitudinal and transverse reinforcement around the existing column .phis method of jacketing is the most suitable for reinforced concrete buildings. o it is the widely used and cost effective for RC buildings, as it is familiar to engineers and construction industry, suitable for repair. Also it increases the (i) shear capacity of the columns in order to accomplish strong column and weak beam design (ii) to improve flexural strength by longitudinal steel provided continuously from slab and anchored to the foundation.

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A phey considerably increase member c/s dimension, which may be a serious draw back in buildings with less floor area. A phey disturb the occupants of the building during construction A Production of dust and debris causes pollution and health hazards A phey also cause noise pollution at work area. A Rusting of bars takes place.

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pies- 70 to 100 mm ooks- 90-135 degree.


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(ii) V      
here fiber reinforcement polymer jackets are used.

$'!(/ A Carbon fiber are flexible and can be made to contact with the surface tightly for a high degree of confinement because of its high strength and modulus of elasticity. A mt is light weight A Rusting does not occur

)''('-()'-/ A mn some cases the presence of beam may require majority of new longitudinal bars to be bundled in the corner of the jacket A With the presence of the existing column it is difficult to provide cross ties for new longitudinal bars which are not at the corner of the jacket. A acketing is based only on engineering judgment as there are no guidelines or code recommended for it.

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  mt is similar to reinforced concrete jacketing but here steel

plates are provided instead of reinforced bar

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,&01'!,)(/ acketing beam is recommended for several purposes as it gives continuity to the columns and increases the strength and stiffness of the structure. While jacketing the beam it flexural resistance must be carefully computed in order to avoid the creation of strong beamʹweak column system. Due to column jacketing there may be change in mode failure and redistribution of forces which causes beam hinging, so the critical section of the beam and the participation of the existing reinforcement should be taken into consideration. acketing of beam is carried out in various ways 3 or 4-sided jackets.

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&01'!,)5+)6'/Beam column joint forms the critical section failure of reinforced concrete frame structure. Beam column joint can be retrofitted by reinforcement concrete jacketing or FRP jacketing or steel jacketing method as mentioned before.

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& '!'-!$+'/ trengthening of the foundation of the existing building to resist the seismic effect is known as foundation retrofitting. Foundation retrofitting are required due to two problems
Õ phe change of loads on the foundation by strengthening of the building. Õ phe failure of foundation it self due to various reasons. Retrofitting of the shallow concrete foundations
K Reinforced concrete jacketing K bolting down the foundation K Base isolation Retrofitting of the pile/deep foundations
K Micro pile Methods K creen pipe drain method K uper trengthening Pile Bents method

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