Benefits of crank bars in slab & beam

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Why is curing made exactly 28 days for concrete?

Types of Shear Reinforcement

The following three types of shear reinforcement are used

• Vertical stirrups

• Bent up bars along with stirrups.

• Inclined stirrups.

Vertical stirrups

• These are the Steel Bars Vertically placed around the Tensile Reinforcement at suitable spacing along the length of the Beam. Their Diameter varies from 6mm to 16mm.

• The free ends of the Stirrups are anchored in the Compression Zone of the Beam to the Anchor Bars (Hanger Bar) or the Compressive Reinforcement.

• The Spacing of Stirrups near the Supports is less as compared to spacing near the Midspan since Shear Force is Maximum at the Supports.

Type of vertical stirrups:

• Single Legged Stirrup

• Two Legged Stirrup

• Four Legged Stirrup

• Six Legged Stirrup

Bent up Bars along with Vertical Stirrups

• These Bent up Bars resist Diagonal Tension. These Bars are usually Bent at 45°.

Inclined Stirrups

• Inclined Stirrups are also provided generally at 45° for resisting Diagonal Tension. They are provided throughout the length of the Beam.

Waterproofing solution for concrete

The Economic Analysis of Fire Sprinkler System in a High-Rise Building

What is meant by Bar Bending Schedule (BBS)?

Bar Bending Schedule, commonly referred to as “BBS” is a comprehensive list that describes the location, mark, type, size, length and number, and bending details of each bar or fabric in a Reinforcement Drawing of a Structure.

This process of listing the location, type and size, number of and all other details is called “Scheduling”. In context of Reinforcement bars, it is called bar scheduling. In short, Bar Bending Schedule is a way of organizing rebars for each structural unit, giving detailed reinforcement requirements.

General guidelines to be followed in preparing BBS:

• The bars should be grouped together for each structural unit, e.g. beam, column, etc.
• In a building structure, the bars should be listed floor by floor.
• For cutting and bending purposes schedules should be provided as separate A4 sheets and not as part of the detailed reinforcement drawings.
• The form of bar and fabric schedule and the shapes of bar used should be in accordance with BS 8666.
• It is preferable that bars should be listed in the schedule in numerical order.
• It is essential that the bar mark reference on the label attached to a bundle of bars refers uniquely to a particular group or set of bars of defined length, size, shape and type used on the job.
• This is imperative as a bar mark reference can then point to a class of bar characteristics. Also, this helps steel fixers and laborers keep track of the type and number of bars needed to complete a certain work.

Bar Bending Schedule is used by the:

• Detailer
• person checking the drawing
• contractor who orders the reinforcement
• organization responsible for fabricating the reinforcement
• steel fixer
• clerk of works or other inspector
• the quantity surveyor

Quantity surveyor is responsible for estimation and costing operations of a project. This kind of surveying demands a high level of precision. Bar Bending Schedule helps the quantity surveyor to consolidate the number of bars required of each bar type.

This leads to an estimation of the quantity of steel, which translates to the cost requirements for steel work.  Hence, BBS is used by the contractor who orders the reinforcements as well. Unit cost of steel is charged by weight of steel purchased.

Clerk of works and other inspectors refer to the BBS to make sure that the reinforcement work in the site is in tandem with the design requirements as per drawings. It is used as a frame of reference by the steel fixers firsthand. They can easily make note of the number and kind of rebar needed for a structural unit.

In essence, Bar Bending Schedule subsumes all necessary information on reinforcements, used by professionals at various stages of the construction process, right from procurement to finish.

How to prepare a BBS?

Necessary Columns

• Bar number/Bar Mark Reference
• Bar shape
• Diameter
• Spacing
• Length of bar
• Cutting Length
• Number of bars

Most of the information in a BBS can be found in reinforcement drawings of the structural unit. Bar shape, diameter, length and spacing is directly entered in the schedule just by looking at the drawings, which will have detailed dimensioning.

What are crack repair techniques?

Crack Repair Techniques:

1. Sealing with epoxies
2. Routing and sealing
3. Stitching
4. External stressing
5. Overlays
6. Grouting
7. Blanketing
8. Autogenous healing

Sealing with epoxies :

• Injection epoxy bonding compounds in high pressure in to cracks

PROCEDURE

Sealing with epoxies

1. Drill into the cracks
2. Flush out cracks by injecting water/ other solvents
3. Dry the surface
4. Epoxy injection in to holes
5. Curing of epoxy
6. Remove surface seal by grinding

Routing and Sealing

Routing and Sealing

• Simplest, most common, inexpensive method
• For both fine and larger isolated cracks
• This method involves enlarging the crack along its exposed face and sealing it with a suitable joint sealant
• Most used for floors and pavements
• Side effects-
  • Chemical attack
  • Corrosion of rebar
  • Swelling

Stitching

Stitching

Stitching may be used when tensile strength must be reestablished across major cracks.

• Stitching involves
  • drilling holes on both sides of the crack
  • grouting in U-shaped metal units with short legs called staples or stitching dogs

External Stress

• The development of cracking is due to the tensile stress, thus can be arrested by suppressing this stress
• Cracks can be closed by inducing a compression force to over come the tensile stresses
• The compressive force is applied by
  • Pre- stressing wires or rods
  • Wedging- by opening the cracks and filling with expanding mortar, by jacking and grouting or by actual driving wedges.

Blanketing

• Blanketing is similar to routing and sealing
• used on a larger scale and is applicable for sealing active as well as dormant cracks.
• Following are the types of blanketing joints
  • Type I
  • Type II
  • Type III
  • Type IV
    • Type I
    • The first type of blanket joints use elastic sealants
    • They return to their original shape, when not under an externally induced stress
    • A bond breaker should be used at the bottom of the chase, so that the sealant is free to deform.
    • Type II
    • use sealant materials that are known as mastic sealants
    • their details are similar to that of an elastic sealant, except that the bond breaker is omitted and the sealant is bonded to the bottom as well as to the sides of the chase.
    • Type III
    • It is a mortar plugged joint
    • A recess in the form of a trapezoid to accomodate the mortar plug is made
    • This recess is filled with mortar
    • Type IV
    • A water cripped bar is used

Overlays

• Used to seal cracks
• Used when large no of cracks, treating each crack is expensive
• Active cracks- overlays done with materials which are extensible but not flexible. Eg: Polymeric membrane with top coat of tar
• Dormant cracks- any type of overlays may be used

Eg: polymer modified Portalnd cement mortar or concrete, or by silica fume concrete

Grouting

• Similar to epoxy injection
• Epoxy not used where fire resistance and cold weather
• Grouting is effective alternative
• When the crack is straight line- drill out the length of crack- grout it to form a key
• This method is effective in shopping water leaks.

Autogenous Healing

• It is the natural process of crack repair that can occur in concrete in the presence of moisture
• The repair is by a combination of mechanical blocking by particles carried into the crack with the water and the deposition of calcium carbonate from the cementitious material
• Mechanism
• Autogenous healing occur by the carbonation of calcium oxide and calcium hydroxide present in the cement by CO2 present in the air and water

The resulting CaCO3 and Ca(OH)2 crystals precipitate accumulate and grow through and out from cracks.

Core Cutting In Reinforced Cement Concrete Structures

Cores are generally cut with the use of a rotary cutting tool having diamond bits. In this way, a cylindrical specimen is acquired normally with its ends to be unequal, parallel and square and occasionally with embedded pieces of reinforcement.

Core cutting is performed for the following reasons :-

• To detect firmness and density of concrete
• To find out depth of carbonation of concrete
• Chemical analysis
• Water/gas conformity
• Petrographic analysis
• ASHTO Chloride permeability test

How to calculate cutting length of Rings of rectangular column?

Example: Consider Rectangular Column 450mm x 300mm having cover to reinforcement 40mm.


 Size of the stirrup on 450mm side= 450-40-40 = 370mm
 Size of the stirrup on 300mm side= 300-40-40 =220mm          

Total cutting length of ring for 8 dia bar = Periphery + hook length.                         
                                                                  =2*370+2*220+2*8*10=1340mm

hook length= 10D

What type of test should perform for Concrete work, M.S High strength deform bars, Brick work?

What type of test should perform for Concrete work?

-Setting time of cement

-Compressive strength of cement

-Gradation of Coarse aggregates.

-FM of fine aggregates.

-Water absorption of coarse aggregates.

-Loss angels abrasion test

-Concrete cylinder casting & testing

What type of test should perform for M.S High strength deform bars?

-Tensile strength, Elongation and unit wt.

What type of test should perform for Brick work?

-Setting time of cement

-Compressive strength of cement

-FM of fine aggregates

-Compressive strength of brick

-Water absorption of brick

-Efflorescence of brick

What is Structure

What is Structure

Structure is assembly of number of members such as Slabs, Beams, Columns, Walls etc. Structure is design so it can transmit self weight and imposed load to foundation and can withstand climate changes.

 

Designer

Designer should estimate load and forces depending upon type of structure, climate conditions.

Assessment of loading  

Assessment of loading unless structure will be unsafe if load assessment is underside. It can be uneconomical if load are assessed on higher side.

Aim of Design (IS 456:200, Clause 18)

Structure  is so designed do it can perform satisfactorily during its life. It can sustain all the loads and deformation of normal construction and have adequate durability and adequate resistance to the effects of misuse and fire.

Types of Load

Types of Load

1. Dead Loads
2. Live Loads
3. Dynamic effects
4. Wind Loads
5. Seismic Loads
6. Erection Loads
7. Temperature effects
8. Soil and Hydro static pressure

Dead loads IS 875 (Part 1 ):

 It consist of weight of the RCC and all the material supported by it permanently. Example self weight of wall, floor , roof , beam etc. It is calculated on the basis of unit weights of material as given in IS 875 (Part 1 ).

Live Loads IS 875 (Part 2 ):

 Loads which are temporarily rest at one place. Example furniture, snow load on roof, moving load on bridges.

Dynamic effects:

Live loads which produce vibrations by impact such as moving trains, trucks and cranes, produce greater effects than would be produced by the same loads if stationary. The additional effect is called the dynamic effect.

Wind Loads IS 875 (Part 3 ):

Liability of structure to high wind pressure depend not only on geographical location but also on characteristic of structure. 

Types of Beam Section

Types of Beam Section

The three common types of Reinforced Concrete Beam section are

1. Rectangular section with tension steel only (this generally occurs as a beam section in a slab).

2. Rectangular section with tension and compression steel.

3. Flanged sections of either T or L shape with tension steel and with or without compression steel.

Design Steps

 Typical design steps in any design include:

• First step in any design is the preparation of the architectural drawings.
• In these drawings the architect marks tentative structural beams and columns and specifies their size and marks their approximate location as per his knowledge.
• Then these drawings are passed to the structural engineer whose first step is to study these drawings and notice the marked position of the beams and columns. Generally a structural engineer tries to follows the things as given by architect so that there is no change in the elevation and other drawings prepared by him.
• But when its not possible the engineer has to change the size of the beams and the column. These drawings are known as Preliminary Architectural Drawings.
• After this both engineer and the architect discuss whether the proposed plans are feasible in field or not.
• If the changes are acceptable to both, then the architect incorporates the changes in his drawings and prepares the plan, elevation and section drawings according to finally decided position of the beams and columns.
• After this drawing is sent to field for execution. These drawings are known as construction drawings. Then these drawings are sent to structural engineer for structural design.

Steps involve in designing any structure

Design of any structure involves following steps:

 

• Estimation of the loading on the structure
• Soil investigation to be decided on the basis of tentative loads and type of structure/ foundations, as per the architectural layout plan
• Co-ordination/ incorporation of requirements of other building services like public health, electrical, lifts, air conditioning, fire fighting etc into architectural drawings
• Structural analyses ( computerized or manual, as the case may be)
• Structural design of various components (columns, beams, slabs, secondary beams- not included in frame analysis, staircases, load bearing brick walls and foundations).

Depending on the analyses/ design software being used some structural components may require manual design taking into consideration various provisions of ductility detailing from seismic considerations etc. The structure has to be so designed so as to satisfy all the requirements of safety, durability and economy.


Finally preparation of working structural drawings.

Rapid hardening portland cement

Rapid hardening portland cement

Initial and final setting time of this cement are the same as those of ordinary cement. But it attains high strength in earlier days. This is due to increased lime content in cement composition and very fine grinding. It is light in weight. It requires short period of curing.

Cement

Cement

Cement is a hydraulic binder and a finely ground inorganic material. When mixed with water, it forms a paste, which sets and hardens by means of hydraulic reactions.

Types of Cement:

There are various types of cement in use and the latest revised edition of IS:456-2000 permits the use of 10 different types of cement. These are:

1. 33 grade- ordinary Portland cement, conforming to IS 269.
2. 43 grade- ordinary Portland cement, conforming to IS 8112.
3. 53 grade- ordinary Portland cement, conforming to IS 12269.
4. Rapid hardening Portland cement conforming to IS 8041.
5. Portland slag cement conforming to IS 455.
6. Portland pozzolana cement (fly ash based) conforming to IS 1489 (Part 1).
7. Portland pozzolana cement (calcined clay based) conforming to IS 1489 (Part 2).
8. Hydrophobic cement conforming to IS 8043.
9. Low heat Portland cement conforming to IS 12600.
10. Sulphate resisting Portland cement conforming to IS 12330.  

Ordinary Portland Cement (OPC)

Ordinary Portland Cement (OPC)

33 grade-OPC, 43 grade- OPC, 53 grade- OPC are three different grades of OPC. Ordinary Portland Cement (OPC) is a product obtained by intimately mixing together calcareous and argillceous materials, with or without other materials containing silica, alumina or iron oxide, burning them at a high temperature, and grinding the resulting intermediate product, clinker with gypsum.

Oil well cement

Oil well cement

OWC is specially manufactured for use while drilling oil wells to fill the space between the steel castings and the wall of the well. It has controlled setting under high temperature and pressure conditions.


However, once setting takes place it develops strength rapidly and remains stable at high temperatures. It also has resistance to sulpahte attack because of its intrinsic chemical composition.

White cement

White cement

This is just a variety of ordinary cement and it is prepared from such raw materials, which are practically free from colouring oxides of iron, manganese or chromium. White cement is so called because the raw materials are so called that the maximum iron oxide content is strictly limited to 1 percent.


It is used primarily for decorative purposes like plaster work, ornamental work. But most white cements can be used as a replacement for ordinary portland cement for structural work. A variety of colours can be obtained by the addition of pigments. It should not set earlier than 30 minutes.