Retrofitting of Existing RCC Buildings b

Retrofitting of Existing RCC Buildings by Method of Jacketing

CHAPTER 1 INTRODUCTION 1.1 SEISMIC STRENGTHENING Seismic strengthening is defined as the actions taken to upgrade the seismic resistance of an existing building so that it becomes safe under earthquakes. This can be in the form of providing seismic bands, eliminating source of weakness or concentrations of large mass and opening in walls, adding shear walls or strong column points in walls, bracing roofs and floors to be able to act as horizontal diaphragms adequately connecting roofs to walls and columns and also connecting between walls and foundations. 1.2 CONCEPT OF RETROFITTING Retrofitting is technical interventions in structural system of a building that improve the resistance to earthquake by optimizing the strength, ductility and earthquake loads. Strength of the building is generated from the structural dimensions, materials, shape and number of structural elements. Ductility of the building is generated from good detailing, materials used, degree of seismic resistant etc. Earthquake load is generated from the site seismicity, mass of the structures, important of buildings, degree of seismic resistant etc. Due to variety of structural condition of building, it is hard to develop typical rules for retrofitting. Each building has different approaches depending upon the structural deficiencies. Hence engineers are needed to prepare and design the retrofitting approaches. In the design of retrofitting approach, the engineers must comply with the building codes. The results generated by adopting retrofitting techniques must fulfill the minimum requirements on the building codes such as deformation, detailing strength etc. 1.3 CAUSES OF FAILURE Damage of buildings was caused by a combination of affects: 

Old decaying buildings predating modern construction practices.



New buildings not being designed to Indian Earthquake codes.

MLMCE

1

Civil Engineering


CHAPTER 2 STRENGTHENING OF RCC STRUCTURES 2.1 INTRODUCTION Structure repair and rehabilitating is a process whereby an existing structure is enhanced to increase the probability that the structure will survive for a long period of time and also against earthquake forces. This can be accomplished through the addition of new structural elements, the strengthening of existing structural elements and/or the addition of base isolators. Deterioration of concrete and corrosion of embedded reinforcement structure might make the R.C.C structure structurally deficient. Corrosion can be controlled to some extent by fixing of chloride or protective coating Before any repair work is put in hand, the cause of damage must be identified as clearly as possible. This principle may seem self-evident but it is surprising how often it is disregarded, with the result that further repairs have to be carried out within a short time. Sometimes the cause is obvious as, for example, in many cases of accidental damage but, more often than not, careful investigation is required. The next step must be to consider the objective of the repair, which will generally be to restore or enhance one or more of the following: 

Durability



Structural strength



Function



Appearance.

Of these four requirements, restoration of durability is by far the most common in repair work. One must also consider whether the repair is to be permanent or temporary. Only after deciding on the most likely cause of damage, whether it is likely to occur, and the purpose of the work, should the method of repair be chosen. 2.2 CONVENTIONAL STRENGTHENING METHODS These are the conventional strengthening methods adopted to rehabilitate RCC 

Grouting process



Guniting Process

MLMCE

2

Civil Engineering




Application of Epoxy Resins



Section Enlargement or Jacketing



Post Tensioning



Bonded Steel Plates



Carbon Fiber Reinforced Plastics(CFRP) for Repair & Strengthening

2.2.1 Grouting It is the process of placing a material into cavities in concrete for the purpose of increasing the load bearing capacity of the structure, grouting restores the monolithic nature of the structure. Primary grouting materials and their common uses are: Table 2.1 Primary grouting materials

MLMCE

CHEMICAL

CEMENTITIOUS

Control Seepage

Mass Placement

Shut-off Seepage

Structural (high strength)

EPOXY

POLYURETHANES

Seal Cracks

Building Envelope Insulation

Acidic Environments

Acoustical Sealant

POLYSTERS

SILICONES

Bolt Anchoring

Smoke Seals

3

Civil Engineering


2.2.2 Guniting Process Guniting is an effective method, which has been extensively used in the rehabilitation of structurally distressed RC members. There have been cases of heavy rusting of the mesh in the form of powder or in the form of sheets coming out. The Guniting process suffers from drawbacks like dust and noise nuisance. 2.2.3 Application of Epoxy Resins In this method of strengthening, an epoxy adhesive normally consisting of two components –a resin and a hardener is used to bond steel plates to overstressed regions of RC members. Normally, the steel plates are located tension zone of concrete to enhance the flexural capacity. The plates can also be placed at the compression and shear regions to enhance the axial and shear capacities of the RC structural elements 2.2.4 Section Enlargement or Jacketing In this method the entire height of the column section is increased and a cage of additional main reinforcement bars with shear stirrups is provided right from the foundation as per the requirement of additional load, etc. However, there are many instances where the column section is increased with additional reinforcement bars only on one face, and that too starting from the floor slab level of a particular floor and only up to the height of deterioration of the column .The enlargement should be bonded to the existing concrete to produce a monolithic member .Cement mortar is used for these enlargements. The section enlargement method is relatively easy to construct and economically effective. The disadvantages of this method are a high risk of corrosion of embedded reinforcing steel and concrete deterioration. These problems are associated with relative dimensional incompatibility between existing and new concrete. The restrained volume changes of new material are inducing tensile stresses that may lead to cracking and delaminating when the induced tensile stresses are greater than tensile strain capacity of tile new material The way to make this strengthening technique effective in the future is to use materials with higher tensile strain capacity, with low shrinkage properties

MLMCE

4

Civil Engineering


Figure 2.1 Additional Reinforcement & Micro concreting

2.2.5 Post Tensioning External prestressing is now widely developed for concrete strengthening in the United States, Japan &Switzerland. External prestressing techniques have been employed with great success to correct excessive and undesirable deflections in existing structure. They have also been used to strengthen existing concrete structures to carry additional loads It can be used on tile inside of box girders or the outside of „I‟ girders to increase the capacity of existing bridges and to provide improved resistance to fatigue and cracking. 2.2.6 Bonded Steel Plates In this method of strengthening steel plates or other steel elements are glued to the concrete surface by a two component epoxy adhesive creating a three-phase concrete glue steel composite system. The wide acceptance and at the same time attractiveness is due to negligible changes to overall dimensions of the structure and minimum disruption to its use. At the same time, adequate design, specification and execution of the job will ensure the necessary composite action for the designed loading range. It was demonstrated that steel plates bonded to the tension

MLMCE

5

Civil Engineering


face of the concrete beams can lead to increase in flexural capacity, along with increase in flexural stiffness and associated decreases in deflection and cracking. 2.2.7 Carbon Fiber Reinforced Plastics (CFRP) for Repair & Strengthening CFRP has high strength, lightweight, excellent strength to weight ratio, resistant to chemicals (acids and bases), good fatigue strength, and nonmagnetic, non-corrosive and nonconductive properties. As with any composite system, bond of the strengthening plate the existing concrete is very critical. Therefore, the surface preparation of both phases of tile system, concrete and CFRP plates is very important .The plates should be ground on tile bonding side, immediately before bonding, the surface should be cleaned with acetone. After mixing the epoxy glue component should be placed oil tile plate without delay, after assembling the plate in the design position, a slight pressure is applied to squeeze out excessive adhesive

MLMCE

6

Civil Engineering


CHAPTER 3 JACKETING 3.1 INTRODUCTION Jacketing is one of the most frequently & popularly used techniques to strengthen reinforced concrete (RC) columns. With this method, axial strength, bending strength, and stiffness of the original column are increased. It is well known that the success of this procedure is dependent on the monolithic behavior of the composite element. To achieve this purpose, the treatment of the interface must be carefully chosen. The common practice consists of increasing the roughness of the interface surface and applying a bonding agent, normally an epoxy resin. Steel connectors are also occasionally applied. These steps involve specialized workmanship, time, and cost. Concerning the added concrete mixture and due to the reduced thickness of the jacket, the option is usually a grout with characteristics of self-compacting concrete (SCC) and high strength concrete (HSC). The most common types of jackets are steel jacket, reinforced concrete jacket, fiber reinforced polymer composite jacket, jacket with high tension materials like carbon fiber, glass fiber etc. The main purposes of jacketing are: 1. To increase concrete confinement by transverse fiber reinforcement, especially for circular cross-sectional columns 2. To increase shear strength by transverse fiber reinforcement 3. To increase flexural strength by longitudinal fiber reinforcement provided. 3.2 TECHNICAL CONSIDERATIONS The main objective of jacketing is to increase the seismic capacity of the moment resisting framed structures. In almost every case, the columns as well .as beams of the existing structure have been jacketed. In comparison to the jacketing of reinforced concrete columns, jacketing of reinforced concrete beams with slabs is difficult yielding good confinement because slab causes hindrance in the jacket. In structures with waffle slab, the increase in stiffness obtained by jacketing columns and some of the ribs, have improved the efficiency of structures. In some cases, foundation grids are strengthened and stiffened by jacketing their beams. An increase in strength, stiffness and ductility or a combination of them can be obtained. Jacketing serves to

MLMCE

7

Civil Engineering


improve the lateral strength and ductility by confinement of compression concrete. It should be noted that retrofitting of a few members with jacketing or some other enclosing techniques might not be effective enough to improve the overall behavior of the structure, if the remaining members are not ductile. 3.3 JACKETING OF COLUMNS Jacketing of columns consists of added concrete with longitudinal and transverse reinforcement around the existing columns. This type of strengthening improves the axial and shear strength of columns while the flexural strength of column and strength of the beam-column joints remain the same. It is also observed that the jacketing of columns is not successful for improving the ductility. A major advantage of column jacketing is that it improves the lateral load capacity of the building in a reasonably uniform and distributed way and hence avoiding the concentration of stiffness as in the case of shear walls. This is how major strengthening of foundations may be avoided. In addition the original function of the building can be maintained, as there are no major changes in the original geometry of the building with this technique. The jacketing of columns is generally carried out by two methods: (i)

Reinforced concrete jacketing

(ii)

Steel jacketing.

3.3.1 Reinforced Concrete Jacketing Reinforced concrete jacketing can be employed as a repair or strengthening scheme. Damaged regions of the existing members should be repaired prior to their jacketing. There are two main purposes of jacketing of columns:  Increase in the shear capacity of columns in order to accomplish a strong column-weak beam design  To improve the column's flexural strength by the longitudinal steel of the jacket made continuous through the slab system are anchored with the foundation. It is achieved by passing the new longitudinal reinforcement through holes drilled in the slab and by placing new concrete in the beam column joints as illustrated in figure 3.1. Rehabilitated sections are designed in this way so that the flexural strength of columns should be greater than that of the beams. Transverse steel above and below the joint has been provided with details, which consists of two L-shaped ties that overlap diagonally in

MLMCE

8

Civil Engineering


opposite corners. The longitudinal reinforcement usually is concentrated in the column corners because of the existence of the beams where bar bundles have been used as shown in figure 3.1

Figure 3.1 Construction Techniques for Column Jacketing

MLMCE

9

Civil Engineering


Table 3.1 Details of Reinforced Concrete Jacketing

Properties of jackets

Minimum width of



Match with the concrete of the existing structure.

 

Compressive strength greater than that of the existing structures by 5 N/mm2or at least equal to that of the existing structure. 10 cm for concrete cast-in-place and 4 cm for shotcrete.



If possible, four-sided jacket should be used.



A monolithic behavior of the composite column should be assured.

jacket 

Narrow gap should be provided to prevent any possible increase in flexural capacity.

Minimum area of transverse reinforcement



Designed and spaced as per earthquake design practice.



Minimum bar diameter used for ties is not less than 10 mm or 1/3 of the diameter of the biggest longitudinal bar. The ties should have 135-degree hooks with 10bar diameter



anchorage

Minimum area of longitudinal reinforcement



3Afy, where, A is the area of contact in cm2 and fy is in kg/cm2



Spacing should not exceed six times of the width of the new elements (the jacket in the case) up to the limit of 60 cm.



Percentage of steel in the jacket with respect to the jacket area should be limited between 0.015and 0.04.



At least, 12 mm bar should be used at every corner for a four sided jacket



Provide adequate shear transfer mechanism to assured monolithic behavior.



the jacket and the existing element) should be prevented.

Shear stress in the interface

A relative movement between both concrete interfaces (between



Chipping the concrete cover of the original member and roughening its surface may improve the bond between the old and the new concrete.



MLMCE

For four-sided jacket, the ties should be used to confine and for

10

Civil Engineering


shear reinforcement to the composite element



Connectors

  

Connectors should be anchored in both the concrete such that it may develop at least 80% of their yielding stress. Distributed uniformly around the interface, avoiding concentration in specific locations. It is better to use reinforced bars (rebar) anchored with epoxy resins of grouts.

3.3.2 Steel Jacketing Local strengthening of columns has been frequently accomplished by jacketing with steel plates. A general feature of steel jacketing is mentioned in Table 3.2

Figure 3.2 Construction Techniques for Steel Jacketing

MLMCE

11

Civil Engineering


Table 3.2 Details Of Steel Jacketing.

Steel plate thickness



At least 6 mm



1.2 to 1.5 times splice length in case of flexural

Height of jacket

columns. 

Full height of column in case of shear columns



Rectangular jacketing, prefabricated two L-shaped panels The use of rectangular jackets has proved to be successful in case of small size columns upto 36 inch width that have been successfully retrofitted with %" thick steel jackets combined with adhesive anchor bolt, but has been less successful on larger rectangular columns. On larger columns, rectangular jackets appear to be incapable to provide adequate confinement



Welded throughout the height of jacket, size of weld



38 mm (1.5 inch), steel jacket may be terminated above the top of footing to avoid any possible bearing of the steel jacket against the footing, to avoid local damage to the jacket and/or an undesirable or unintended increase in flexural capacity.



25 mm fill with cementations grout.



25 mm in diameter and 300 mm long embedded in 200 mm into concrete column. Bolts were installed through pre-drilled holes on the steel jacket using an epoxy adhesive. Two anchor bolts are intended to stiffen the steel jacket and improve confinement of the splice.

Shape of jackets

Free ends of jackets bottom clearance.

Gap between steel jacket and concrete column Size of anchor Number of anchor bolts

 

3.4 BEAM JACKETING Jacketing of beams is recommended for several purposes as it gives continuity to the columns and increases the strength and stiffness of the structure. While jacketing a beam, its flexural resistance must be carefully computed to avoid the creation of a strong beam-weak column system. In the retrofitted structure, there is a strong possibility of change of mode of failure and redistribution of forces as a result of jacketing of column, which may consequently causes beam

MLMCE

12

Civil Engineering


hinging. The location of the beam critical section and the participation of the existing reinforcement should be taken into consideration. Jacketing of beam may be carried out under different ways, the most common are one-sided jackets or 3- and 4-sided jackets. At several occasions, the slab has been perforated to allow the ties to go through and to enable the casting of concrete. The beam should be jacketed through its whole length. The reinforcement has also been added to increase beam flexural capacity moderately and to produce high joint shear stresses. Top bars crossing the orthogonal beams are put through holes and the bottom bars have been placed under the soffit of the existing beams, at each side of the existing column. Beam transverse steel consists of sets of U-shaped ties fixed to the top jacket bars and of inverted Ushaped ties placed through perforations in the slab, closely spaced ties have been placed near the joint region where beam hinging is expected to occur (figure no. 3.3). The main features of reinforcement details of beam jacketing are given in table 3.3 although those guidelines can give a rational basis for practical design; research still needs to address critical aspects in the behavior of jacketed elements. The change in behavior in jacketed elements, whose shear span/depth ratios are significantly reduced, due to their jacketing, needs to be clarified.

Fig 3.3 Construction Technique for Beam Jacketing

MLMCE

13

Civil Engineering


Table 3.3 Reinforcement of beam jacketing.

 Minimum width for jacket Longitudinal reinforcement

  

Shear reinforcement

 

8 cm if concrete cast in place or 4 cm for shotcrete Percentage of steel on the jacket should be limited to 50 of the total area of the composite section Ignore the effect of existing shear reinforcement New reinforcement should have 135 hooks and at each corner of the tie there must be at least one longitudinal bar. The bar used for the tie should have at least 8 mm diameter Multiple piece ties can be used, as discussed before for columns

Depth of jacketed beam

MLMCE

  

Span/depth ratio Storey height Ductile behavior

14

Civil Engineering


CHAPTER 4 RETROFITTING OF HEALTH BUILDING AT NASIK A CASE STUDY 4.1 GENERAL In order to overcome the future disorders that may have occurred due to unwanted and no predicted disasters it was decided to strengthen the existing Health building located in the central part of Nasik city. This building was proposed in 1984 and accordingly was designed for B + G + 4 stories. The building during its life span at the end in 2008 found completely deteriorated and was not capable to sustain further loads and was predicted that it may fail due to the following reasons. a) Higher ground water table in the locality. b) Faulty workmanship during the stage of execution at initial stage. c) The columns were not centered properly in their position. d) Improper methods of compaction to the concrete. e) Insufficient cover to the steel reinforcement. In addition to this it may also have caused failure due to the non predicted disasters as was caused too many buildings in the past which are listed in the next bit. 4.2 CAUSES OF FAILURE AND DAMAGES TO THE BUILDING IN PAST FEW EARTHQUAKES Following were the main causes of failure and damages to the buildings in Gujarat & Maharashtra; causes to buildings same in rest part India. 

Damages to buildings were caused by a combination of affects:



Old decaying buildings predating modern construction practices



New Buildings not being designed to Indian earthquake codes



Lack of knowledge, understanding or training in the use of these codes by local engineers



Unawareness that Gujarat and some part of Maharashtra is a highly seismic region



Buildings erected without owners seeking proper engineering advice

MLMCE

15

Civil Engineering




Improper detailing of masonry and reinforced structures



Poor materials, construction and workmanship used, particularly in commercial buildings



Alterations and extensions being carried out without proper regard for effects on structure during an earthquake.



Buildings having poor quality foundations or foundations built on poor soils.



Little or no regularity authority administering or policing the codes.

It‟s necessary to every civil engineer to have knowledge of proper repairs and strengthening of earthquake damaged buildings. Indian standards exist but are not used by local engineers or builders in urban or rural areas, mainly due to lack of knowledge and training. As a result, many of the owner-occupiers have unknowingly been carrying out bad repairs in Gujarat. Many buildings have been severely weakened, and the experts are concerned to that there could be another disaster in waiting from a future earthquake. Good repairs, using well-recognized seismic standards may reduce this vulnerability. This project aims in simple terms to explain to the engineers why earthquakes happen in India, which regions are seismically active, how buildings respond in an earthquake; and how to safely carry out good repair and strengthening techniques to damaged and low strength buildings.

Fig.4.1 Some damages those were occurred after earth quake at Gujarat in non engineered R.C.C building construction

The inset shows large deformations were concentrated at column heads, which caused many soft storey failures, as per picture. Buildings if designed with uniform deflections of insert would have survived without collapse.”

MLMCE

16

Civil Engineering


4.3 RETROFITTING OF R.C.C BUILDING BY METHOD OF JACKETING As it‟s shown in above part of chapter no five, that Nasik and some part of Maharashtra is along the border part of Gujarat, Gujarat has suffered from severe earth quake in last two decades, nobody knows which would be the next time of future earth quake & its intensity. Like Gujarat many constructions in Maharashtra and at Nasik are found as non engineered unsafe & quality compromised constructions, this would be future risk for coming days. So it is necessary to carry out the non destructive tests of all construction in Nasik and rest part of India, to save valuable lives and properties, nowadays many advance retrofitting techniques are available in the world, those can be used to repair & strengthen the unsafe and damaged buildings. Here the paper has its focus on a Health building which is under execution (for re modification and strengthening of existing structure). 4.4 HISTORY OF HEALTH BUILDING A group proposed to start a hospital in Nasik in 1984. And as per the decision the detail plan & the structural details for the same were prepared. It was proposed to construct a Basement + G + 4 storey structure and the designs were prepared so. The site for the hospital was near Dwarka circle. Nasik: 11. Though it was planned to construct 6 storey in all, only 2 storey ( i. e. Basement + G) structure was constructed in actual when structural details were for 6 storey. The built up area for basement is 1236 sq.mt. And that of the ground floor is 1178 sq. mt. This group had a smooth functioning up to 2004. Then in 2005 the administration of the hospital was changed. New administrative body utilized the same infrastructure up to 2008. Then in 2009 was decided to extend the building as per the initial plan and structural details and for the same had the structural audit in that respect. From the audit it was found that all the defects were at the execution stage. The faults that were concluded were as below. a) The high ground water table in the region. b) Eccentricity of all the columns was a serious problem observed. c) Improper techniques that were followed during mixing, placing & compacting the concrete. d) There were many loose pockets found in the concrete. e) Sufficient concrete cover at different stages to the steel reinforcement was not maintained. f) The terrace slabs are provided with unwanted thickness of IPS flooring at the top. MLMCE

17

Civil Engineering


From the NDT test results it was suggested that the management should demolish the entire existing structure instead of extending it and go for complete new structure. The management refused to do so and asked to suggest such a measure so that the existing infrastructure at least can withstand and be utilized for 5 – 7 years more. As the final conclusion and the requirement of the management it was decided to go for „Retrofitting of the Structure‟. 4.5 THE STEPS THAT WERE SUGGESTED AND ARE ADOPTED  The entire flooring at the basement to be removed & to be provided again with a raft below it. To overcome the uplift pressure that could be generated due to the higher ground water table it was suggested to provide a raft below the basement floor.  All the columns should be jacketed. In the existing structure it was found that the columns were not centered properly in their position, due to which they were subjected to unwanted eccentric loads. Also the concrete in columns, beams, slabs was not compacted properly which created loose pockets & honey combs in the components. Suitable cover for the reinforcement was not maintained. To overcome the above difficulties it was decided to jacket all the columns such that the eccentricity of loading will be reduced, the loose pockets of concrete will be capable to sustain the load to which the column is subjected & all the steel get the required concrete covering.  The loose pockets in the concrete in the beams are also removed and recasted in M25 grade.  The unwanted heavy loading of water proofing (IPS flooring) damaged the slab to greater extent. Therefore, five slabs are entirely opened, strengthened with additional reinforcement and are casted with 150 mm thick M25 grade concrete layer. The estimated cost of retrofitting the existing structure is 4.5 crore. To meet the further requirement of infrastructure the management now is constructing additional new building with G + 2 storey, instead of razing the existing building.

MLMCE

18

Civil Engineering


Fig 4.2 Column jacketing at basement stage

Fig 4.3 Beam column junction strengthening in basement

MLMCE

19

Civil Engineering


4.4 finished Column after jacketing work

Fig 4.5 Rusting condition of existing slabs reinforcement

MLMCE

20

Civil Engineering


Fig 4.6 Replaced slab reinforcement for existing rusted steel reinforcement

Fig 4.7 Application of chemical admixtures at the joint of new and old concrete

MLMCE

21

Civil Engineering


Fig 4.8 Compaction of concrete by needle vibrator and placement of cover blocks

Fig 4.9 Finished slabs - ready to cure

MLMCE

22

Civil Engineering


As discussed above all works those were carried out on strengthening of the Health building at Nasik, will definitely increases the strength of existing building, this practice would be necessary for many buildings at Nasik and rest of India, it will save the many lives, when any natural disasters will occur.

MLMCE

23

Civil Engineering


CHAPTER 5 CONCLUSIONS The analysis of results of this experimental study led to the following statements: 1) All models behaved monolithically independent of the adopted interface preparation method, 2) Whether the strengthening operation was carried out with or without an axial load applied had no significant influence for the adopted conditions; 3) The resistance of the strengthened models was considerably higher than that of the original column and slightly higher than that of the monolithic model; 4) The stiffness of the strengthened models was considerably higher than that of the original column; 5) The transverse reinforcement strain of the original column was significantly higher in the no strengthened model than in the strengthened models, although the horizontal force applied in the first case was less than half the corresponding value in the other cases; and 6) The contribution of the adherent jacket to the horizontal force resistance varied between 86 and 90%. Thus it was also confirmed that RC jacketing is a very effective strengthening technique, leading to values of resistance and stiffness of the strengthened column considerably higher than those of the original column.

JOURNAL MLMCE

24

Civil Engineering


REFERENCE 1. Bhavar Dadasaheb, “Retrofitting of existing RCC buildings by method of jacketing” IJRMEET-Volume 1,Issue 5 (June 2013) 2. E S Julio, “Structural rehabilitation of columns with reinforced concrete jacketing” Prog Structural Engineering Mater, Volume 5 (2010) 3. Eduardo N B, “Reinforced concrete jacketing interface influence on monolithic loading response” ACI Structural Journal (2007) 4. Gnanasekaran Kaliyaperumal, “Seismic retrofit of columns in buildings for flexure using concrete jacket” SET Journal of Earthquake Technology, Volume 46 (June 2009) 5. Hamidreza Nasersaeed, “Evaluation of behavior and seismic retrofitting of RC structures by concrete jacket” Asian Journal Of Applied Sciences, Volume 4(2011) 6. Pravin B Waghmare, ”Materials and jacketing techniques for retrofitting of structures” IJAERS(2012) 7. Ramirez Ortiz J L & Barcena Diaz J M, ”Strengthening effectiveness of low quality reinforced concrete columns strengthened by two different procedures” Informes De La Construction, Volume 272(July 2008)

MLMCE

25

Civil Engineering

Retrofitting of Existing RCC Buildings b

Recommend Documents