Tall Stru_ppt1

MATERIALS USED IN TALL STRUCTERES Prepared by Sonawane Sandip P. 06MCL019 1

Materials Used in Tall structures    

RCC HPC FRC Prestressed concrete.

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RCC

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Although RCC began around the turn of century, it does not appear to have been used for multistory high rise buildings until 1930.

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After world war two the construction of High Rise Buildings commenced with radically new structural and Architectural solutions.

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In 1903 the first high rise building was built in Cincinnati.

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Start of R.C.C. in High rise Building 

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In 1903 the first high rise building was built in Cincinnati Cincinnati. Official name- Ingalls Building. City - Cincinnati. State - Ohio. Country - U.S.A. Height - 65m Floors - 16 Construction – 1903

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RCC •

What is RCC?

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Why it is used?

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Cost of reinforcement .

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Types of Reinforcement 

Upto 1960, Indian construction industry using 250 MPa mild steel for concrete reinforcement.

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Attempts to increase the yield strength by conventional method of increasing carbon content is result in reducing Ductility, Bendability of bars.

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In 1970, CTD bars introduced as product of cold Twisting technology to overcome strength, Ductility problem where carbon content restricted to low level and proof strength was increased from 250MPa to Guaranteed value of 415 MPA by cold twisting, bond strength was increased by ribbing pattern.

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TMT bars are recent technological advancement for production of High strength Deformed steel bars. Process of Thermomechanical treatment increases strength, ductility. 6

Classification and Identification of Bars 

HYSD bars have no clearly marked yield point & which exhibit brittle failure (ie. Failure occuring before reaching an elongation of less than (3-4)%

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Ribbed bars are in grades of Fe250, Fe 415, Fe 500 & Fe550

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The bar can be distinguished by surface deformation, grade marking by colour code is difficult.

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Bars less than 12mm dia. Are produced in two ribbed design while thw bars over 12 mm dia. Produced in four ribbed design.

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Grade Fe500 bars can be identified by presence of * after every 300mm,other bars do not have such marks.

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TMT bar

CTD bar

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Properties of steel reinforcement 1.Tensile strengthFe415- 10% higher than actual 0.2% proof stress or 485 MPa Fe500- 8% higher than actual 0.2% proof stress or 545MPa. 2. Bond strength-Bond between steel and concrete depend directly on the deformations over bars. Slipping chara. On HYSD bars indicate that slip of 0.1mm corrosponds to bond strength almost 3 to 4 times of plain round bar. 3. Ductility- Is very important criteria for desired performance of R.C. member especially during Earthquake. Elongation at rupture over standard gauge length is accepted to be an index for ductility quality, percentage elongation should never less than 14.5% for any steel. 4. Bendability- This is an important criteria for reinforcing bars in view of bending of bars,which are frequently required during fabrication.This in turn directly related to ductility of member. 9

Contd… 

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Fatigue strength- Reinforced concrete member subjected to alternating loads producing minimum and maximum stresses of sufficiently high intensity may fail due to fatigue in steel. Maximum repetitive stress that can be sustained by the steel section without failure for 2 million load cycles is commonly accepted as a measure of Fatigue strength. Fire resistance- RCC structures subjected to fire get severely affected when the temp of the reinforcing steel exceeds 500-600 deg. Celsius. around this temp proof strength of HYSD bars reduces to 250MPa

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Tall buildings 1.Name – Garden Towers Structural design- Taisei construction co. Date of completion- July 1992 No. of storey - 39 Height - 125.3m Max grade used - 60MPa

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Contd…

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Name- The scene Johoku Structural design- Shimizu construction co. No. of storey- 45 Height - 160m Grade used - M60 Completion - 1993

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Code of practice for concrete reinforcement 

IS 432 - mild steel and medium tensile steel bars (part1) and hard drawn steel wire (part 2).

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IS 1139- Hot rolled mild steel, medium tensile steel and high yield strength steel for concrete reinforce.

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IS 1786- High strength deformed steel bars with wires for for concrete reinforcement.

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IS 2502- Bending and fixing of bars for concrete reinforcement. IS 5525- Recommendations for detailing of reinforcement in R.C. work. IS 6461- Glossary of terms relating to cement concrete reinforcement. IS 1566- Hard drawn steel wire fabric for concrete reinforcement.

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High performance concrete 

Initially compressive strength of concrete is considered as the most important parameter to classify concrete.

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However it has been realized at a later stage with experience that the strength is not the only important parameter but Durability, workability of concrete are also important for structure.

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This led to the evolution of concept of H.P.C.

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HIGH PERFORMANCE CONCRETE

• As per ACI Concrete which meets special performance and uniformity requirements that can not be always achieved routinely by using conventional methods, normal mixing and curing practices. • According to Neville “ H.P.C. is concrete selected so far to meet for the purpose for which it is used. No unusual ingredients are needed and no special equipment has to used, all it requires is the understanding of the behavior of concrete and will to produce the concrete mix within close tolerances. 15

• What makes the concrete as H.P.C. is the very low w/c ratio. Always below 0.35, often around 0.25 & occasionally around 0.20. • High performance concrete requires low volume of pores. • Only way to have low volume of pores is for mix to contain particles grade down to finest size. • This is achieved by using admixtures.

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Quantities of cementitious materials 

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Determination of optimum quantity of cement and mineral admixture is extremely important in designing the HPC mix This is not only required for cost reduction but also for enhancement of the quality of concrete.

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Types of Admixtures used in H.P.C. 

Mineral Admixtures used in H.P.C. 1.Silica fume 2.fly ash 3.GGBS 4.Metakaoline

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M60 grade H.P.C.Mix with different mineral Admixtures

Sr. No.

Mix Descriptions

Aggregate

Cementitious

Water

Kg/M^3

materials (Kg/M3)

(Kg/M3)

Coarse

Fine

Cement

W/Cm

Mineral

SP

Colour

(% by wt of cement)

Admixture (%by wt of cement) 1H.P.C.- Control mix

1199.2

685.7

500

150.9

0.3

1.25Light grey

2H.P.C.- HRM

1188.2

679.4

425

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163.6

0.35

1.5Off White

3H.P.C.-SF

1162.5

676.3

425

10

163.6

0.35

1.25Light grey

4H.P.C.-PFA

1059.3

653

333.3

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166.7

0.325

1.25Off White

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Properties of H.P.C. mixes Parameters

mixes H.P.C.- CM

H.P.C.- HRM

H.P.C.-SF

H.P.C.-PFA

H.P.C.-GGBS

Fresh concrete Density (Kg/M3) slump (mm)

2579

2545

2531

2499

2534

150

165

170

200

180

73.5

77

70.5

69.3

73.3

0

4.5

4.55

3.68

4.36

Hardened concrete Strength( Mpa) Split Tensile Strength(Mpa)

Note: Properties at 28 days 21

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Chemical Admixtures used in HPC Superplasticizers 1.SMF 2.SNF 3.ASTM F-type  Optimum dosage of superplasticizer can be evaluated by flow consistency test using Marsh cone. The point at which the slope changes corresponds to the optimum dosage of admixture 

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Mixing Method

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Multistage mixing sequence is suitable for H.P.C.

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At Kaiga 1&2, RAPP-3&4 two stage mixing was found efficient.

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Silica fume was mixed dry along with aggregates, in the first stage for 5 seconds

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Final mixing of 45 seconds

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Placement and compaction 

Properly designed H.P.C.mix is more cohesive than NSC and does not tend to segregate but it loses strength rapidly compared to NSC.

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This makes H.P.C.more sensitive to temperature

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At kaiga 1&2 and RAPP-3&4 aggregates were precooled and about 90% water is replaced by ice flakes.

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High slump HPC mix may not seem to need compaction, but experience of Kaiga-1&2, RAPP-3&4 suggest that good vibration after placement of fresh mix is essential for structural elements having high congestion with reinforcement.

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Curing 

Performance of HPC at hardened state is rather more sensitive to Curing than that of NSC

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Loss of moisture from exposed surface of fresh concrete at early age cause plastic shrinkage.

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Protection against moisture loss from fresh HPC is crucial for development of strength and durability.

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Curing of HPC is carried out in two stages, initial curing and final curing.

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Design of H.P.C.

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No specific method of mix design of NSC, as presently prevailing in India, was found suitable for mix design of H.P.C.

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Absolute volume method has been adopted in mix design of HPC for containment domes of Kaiga-1&2 and RAPP-3&4 nuclear power plants

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In calculating the mix proportions, air content for concrete may be assumed to be 1 % and unit water content may not be less than 150Kg/m^3

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Target compressive strength may be taken as about 20% more than desired characteristic strength. 30

Case Study of Kaiga project.      

Slump 175 mm Silica fume 7.5% by wt of cement. Cement 475 Kg/m^3 Superplasticizer ASTM F- type Retarder 0.1 % of wt of cement W/Cm is taken as 0.32 for target split tensile strength of 4.37 MPa.

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Use of H.P.C.        

Bourke place Meilbourne, Australia Year of completion – 1991 No of storeys - 52 Height of building - 223m No of levels below ground- 3 Building use - office Type of structure - R.C.C. Concrete strength - 60MPa

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Fibre reinforced concrete 

Fibres are used through ancient times 3000 BC Egyptians Used mud mixed with straw to bind dried bricks. They also used gypsum mortars and mortars of lime in the pyramids.

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Portland cement association investigated FRC in 1950 with the surge in Fibre reinforcing, new materials other than steel were investigated

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Recently organic & synthetic fibres such as acrylic,aramid, carbon, nylon, polyster, polypropylene also been used. 33

Contd… 

Useful Improvements in the mechanical behavior of tension weak concrete (or mortar) can be achieved by incorporation of short discrete fibres

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Resulting composite generally termed as Fibre Reinforced Concrete

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FIBRE REINFORCED CONCRETE • Concrete containing a hydraulic cement, water, fine or coarse aggregate and Discontinuous fibres is called F.R.C. • Unlike plane concrete, a F.R.C. specimen does not break immediately after initiation of the first crack. • At the cracking section matrix does not resist any tension and fibres carry entire load of the composite. • With increasing load fibres will tend to transfer the additional stress to matrix through bending. If these bond stresses do not exceed the bond strength, then there may be additional cracking in matrix. • The process of multiple cracking will continue untill either fibres fail or there may be fibre pullout. 36

Constituent materials 

Commercially used mixes for matrix in FRC are often not very much different from what is used for conventional RCC.

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In applications when thin sections are tobe cast Maximum aggregate size limited to 9.5 to 19mm

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It is necessary to use superplasticizers with mixes containing larger fibre volume content (1% or more).

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Air entraining agents can also be used with FRC to improve its ability to resist freeze thaw cycling under load( especially in pavement)

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Fibre Aspect Ratio 

Mechanical properties of FRC are largely influenced by Fibre Aspect Ratio, fibre type, fibre orientation.

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F.A.R.- Is defined as the ratio of the length to equivalent fibre dia.

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To avoid the fibre balling in conventional and to provide uniform distribution of fibres in mix FAR taken as 100

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Practically used fibre volumes in conventional FRC range from (0.1 to2)%

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Types of fibres 1.Low modulus, high elongation fibres such as acrylic, aramid, nylon, polyster, polypropylene these are approx. 0.25mm in dia. & 12mm to 50mm length, with FAR=50-100 2.High modulus,high strength fibres such as steel, carbon, glass

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Properties of FRC 1. Tensile behavior

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Contd… 2.Compressive behavior-

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Contd… 3. Flexural behavior – In most practical applications FRC is likely to be subjected to flexural loads. There are two commonly reported strengths values associated with flexure, First crack strength & Ultimate flexural strength First crack strength- Is defined as the flexural tensile strength of the composite at a point where load- deflection curve deviates from linearity which is not influenced by incorporation of fibres. Ultimate flexural strength is evaluated as the flexural tensile strength at the peak load carrying capacity, which is greatly influenced by the fibre type, fibre aspect ratio and fibre volume content

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Toughness 

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Toughness is generally accepted as the energy absorbing capacity of the material. The energy absorbed by the specimen is computed from the area under the load deflection curve

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Fatigue resistance 

Experimental studies shows that for a given type of fibre there is a significant increase in Fatigue strength with increase in fibre content.

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Applications 

It can be used in both cast-in-place and precast applications where Durability and crack control are major considerations.

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In Tall buildings F.R.C. can be used for exterior panels, shear walls, floors that carry vehicle traffic (Parking level in tall buildings)

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Columns (Avoid congestion of reinforcement)

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Beams (Shear strength enhancement).

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Foundations and Footings (Shear resistance and dynamic loads).

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Beam column joints (Improve ductility and avoid congestion of steel)

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PRESTRESSED CONCRETE

• The development of the early cracks in Reinforced concrete due to incompatibility in the strains of steel and concrete is the starting point of the new material known as Prestressed Concrete. •Prestressing means intensional application of a predetermined force on a system for resisting the internal stresses, developed in system.

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System of Prestressing 

Pretensioned Prestressing.

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Post Tensioned prestressing

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Advantages of Prestressing

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Utilize the full section of concrete.

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To obtain the crack free concrete.

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Greater resistance to shearing forces due to effect of compressive prestress, which reduces the principle tensile stress.

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Size of member reduces which results in decreasing the dead load of structure and minimise the total height of the structure.

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For long span structures it is Economical 48

Disadvantages of Prestressed concrete 

For short span structures/ small structures it is uneconomical.

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Highly skilled labour is required.

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Material required for prestressing is not locally available at all places.

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High rise building Paramount building, Sanfrancisco  Post tensioned prestressing  No. of storey – 38 Concrete grade used M55 

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Thank you

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