Reinforcement of Concrete Slabs

The determination of a formwork framework ought to be made based on the chosen floor framework that satisfies the basic stacking conditions. Floor slabs in concrete structures are classified into two essential sorts, in view of the heap appropriation applied on the Reinforced Concrete slab:

Two-way slab, in which the rectangularity proportion (slab length/width) is somewhere in the range of 1 and 2, and the slab load is moved to the supporting pillars in two directions.Two-way development incorporates flat plate, flat slab, waffle slab, and two-way slabs bolstered by drop shafts.

Single direction slab, in which the rectangularity proportion (slab length/width) is more than 2, and the slab load is moved to the supporting bars a single way. Single direction development as a rule remembers strong slabs for shafts or dividers, single direction joist (ribbed) slabs upheld on bars or bearing dividers.

Two-Way Flat Plate: Such slabs might be cantilevered at the outside of the structure to allow the utilization of outside balconies.The supporting segments for flat plates are normally similarly dispersed to encourage the plan and development of such slabs.

This framework is prudent for ranges of up to 23 ft (7.0 m) with mellow reinforcing.Flat plates can be built in least time since they use the easiest conceivable formwork. Level plates have been utilized effectively in multi storey inn, lodging, medical clinic, and high rises.

Two-Way Flat Slab: A flat slab basic framework comprises a steady thickness of Reinforced Concrete slab with drop boards at the sections areas. Note that the framework is normally appropriate for square or about square boards.

In prior years, section capitals were utilized alongside drop boards, but since of the higher formwork cost, segment capitals are less preferred in the present development practice. Level slabs are utilized to oppose heavier burdens and longer ranges than flat plates. Generally, the framework is generally appropriate for square or about square boards.


~~~~~~~~~~~~~~~~~~~~~~~~~~
Published By
Rajib Dey
www.constructioncost.co
~~~~~~~~~~~~~~~~~~~~~~~~~~

5 Important Points About Preparing Slabs

Concrete Floor Slab is a basic component that comes in numerous structures. The most common ones are the slab-on-grade and suspended slabs. Slab on grade or commonly called SOG is a concrete slab put on the head of completely compacted earth materials.

Suspended slabs, on the other hand, are elevated slabs that structure the tales on each building and rooftop decks. Appropriate elevations and leveling must be done on throwing concrete slabs. Along these lines, settlement because of self-weight loads and other outer power incited by the structure must be considered before the genuine throwing of the slabs, particularly for suspended slabs.

1. Estimating steel bars to deliver on-site

Setting up an estimate to convey on-site must be planned relying upon the need on-site. Venture engineers base the estimate to convey on a list pre-orchestrated by the quantity surveyors. Some venture engineers want to have their individual site engineers check the assessments of the quantity surveyors and contrast it with the real number of steel bars required on-site.

More often than not, the information given by the site engineers wins and is utilized by the obtainment group on acquiring the all out number of steel bars. Besides, engineers consider including at any rate 10% of the genuine assessments as a wastage factor.

As a custom on site, venture engineers and directors have a few steel bar providers; should one provider come up short, the individual has the second provider to deal with.



~~~~~~~~~~~~~~~~~~~~~~~~~~
Published By
Rajib Dey
www.constructioncost.co
~~~~~~~~~~~~~~~~~~~~~~~~~~

Standards of Reinforcements Detailing in Slabs and Beams

Reinforcement Detailing in Slabs and Beams performs a vital role in a construction process to provide durability and strength to the structure. It also helps out in the cost optimization for the project. A structure’s cover to reinforcement, length of the reinforcement, it’s curtailment, number and diameter should all be clearly defined by the detailing of the reinforcement of the concrete beams and slabs.

Consider a generic concrete slab or beam, supported via simple means. This structure would experience the maximum bending moment at the center of the span. The shear force will come at a distance of d/2 from the face of the support (where d = effective depth of the slab or the beam).

This indicates clearly that the bending reinforcement is required at the center of the span, where the bending moment occurs, not at the support. Whereas the support should be reinforced to withhold the shearing forces.

Therefore, it would not be necessary to cover the full length of the structure in tension reinforcement. In fact, as much as 50% of the reinforcement can be curtailed at suitable locations. They can also be repurposed as shear reinforcements by bending them upwords.

Read more

~~~~~~~~~~~~~~~~~~~~~~~~~~
Published By
Rajib Dey
www.constructioncost.co
~~~~~~~~~~~~~~~~~~~~~~~~~~

Some vital tips to control cracking with Reinforce Concrete Slab on Ground

Steel reinforcing bars and welded wire reinforcement are used to check crack width in nonstructural slabs-on-ground.

Most slabs-on-ground are unreinforced or minimally reinforced for crack-width control. If steel reinforcement is arranged in the upper or top portion of the slab thickness, it restricts the widths of random cracks resulting from concrete shrinkage and temperature restraints, subbase settlement, applied loads or other issues. This type of reinforcement is normally defined as shrinkage and temperature reinforcement.

Shrinkage and temperature reinforcement is not same as structural reinforcement. Structural reinforcement is generally arranged in the bottom section of the slab thickness to enhance the load bearing strength of the slab. Most structural slabs-on-ground contain both top and bottom layers of reinforcement for managing crack-widths and improving load capacities. Due to constructability issues and costs regarding two layers of reinforcement, structural slabs-on-ground are not regularly used as nonstructural slabs.

The basics: Steel reinforcing bars and welded wire reinforcement can’t control cracking. Reinforcement mainly remains inoperative unless the concrete cracks. Once cracking happens, it gets activated and manages crack widths by limiting the expansion of crack.

When the slabs are provided on greater quality sub bases with uniform support and include low shrinkage concrete with joints perfectly installed at a gapping of 15 feet or less, reinforcement is normally is not required. Seemingly, there exist few random or out-of-joint cracking. In case of random cracks, they should remain moderately tight due to the restricted joint spacing and low concrete shrinkage thus future serviceability or maintenance issues will be reduced.

If slabs are arranged on difficult sub bases with risks of non-uniform support or comprise of medium to high shrinkage concrete or joint spacing surpassing 15 feet, then reinforcement should be provided to control the widths of cracks. Since crack widths expand and become about 35 mils (0.035 inches), the effectiveness of load transfer via aggregate interlock is reduced and differential vertical movements over cracks or slab "rocking" can happen.

Due to this, crack edges remain uncover and edge spalling takes place, particularly when the slab is uncovered to wheeled traffic and especially hard-wheeled lift trucks. As soon as spalling begins, crack widths at the surface get expanded and slab deterioration along cracks is raised considerably.

When contraction joints are inappropriate and not installed, shrinkage and temperature reinforcement is necessary. This design approach is sometimes called as continuously reinforced or joint-less slabs and produces several closely spaced (3 to 6 feet) fine cracks all through the slab.

Crack control options: Normally, the cracks in slabs-on-ground are controlled with the following ways -

1) check the location of cracking by installing contraction joints (does not control crack widths) or 2) Installation of reinforcement (does not control crack location).

With Option 1, we can know where to crack in the slab and widths of contraction joints or cracks in the joints are mostly managed by the joint spacing and concrete shrinkage. When joint spacings and concrete shrinkage are raised, joint widths also expand. Similar to cracks, when joint widths turn out to be about 35 mils, the effectiveness of the aggregate interlock to transmit loads and resist differential vertical movements across joints is considerably decreased. Because of this, several load-transfer devices like steel dowels, plates or continuous reinforcement through contraction joints are used to keep positive load transfer and control differential vertical movements across joints.

With Option 2, the slabs are allowed to crack indiscriminately but crack widths are controlled through steel reinforcing bars or welded wire reinforcement. Normally, contraction joints are not installed with this option rather cracking happens indiscriminately that develop several, tightly held together cracks.

Read more

~~~~~~~~~~~~~~~~~~~~~~~~~~
Published By
Rajib Dey
www.constructioncost.co
~~~~~~~~~~~~~~~~~~~~~~~~~~

Details about Composite Slabs & Columns and their benefits

Composite slabs:

1. It comprises of profiled steel decking with an in-situ reinforced concrete topping.
2. The decking(profiled steel sheeting) perform as permanent formwork to the concrete as well as offers adequate shear bond with the concrete in order that when the concrete has attained strength, the two materials function mutually & compositely.

3. Distance among 3 m and 4.5 m onto supporting beams or walls.
4. When the slab is unpropped throughout construction, the decking single-handedly withstands the self-weight of the wet concrete and construction loads. Subsequent loads are delivered to the composite section.
5. When the slab is propped, all of the loads should be combated by the composite section.
6. These are normally designed as simply supported members in the normal condition.

Profiled steel sheeting:

1. Depths vary from 45 mm to over 200 mm.
2. Yield strengths vary from 235 N/mm2 to minimum 460 N/mm2.
3. The thickness vary from 0.8 mm to 1.5 mm.
4. The different shapes offer Interlock among the steel and concrete.
5. Decking is also applied to make the beams stable against lateral torsional buckling throughout construction.
6. Improve the stability of the building entirely by behaving as a diaphragm to transmits the wind loads to the walls and columns.
7. Temporary construction load normally manages the choice of decking profile.

Composite Columns:

A steel-concrete composite column stands for a compression member that contains either a concrete encased hot-rolled steel section or a concrete filled tubular section of hot-rolled steel. The existence of the concrete is granted for two ways.

1. Safeguard from fire.
2. It may also withstand a small axial load.
3. To minimize the effective slenderness of the steel member, that raises its resistance capacity against axial load.

The bending stiffness of steel columns of H-or I-section is superior in the plane of the web (‘major-axis bending’) as compared to a plane parallel to the flanges (‘minor-axis bending’).

The ductility performance of circular type of columns is considerably superior as compared to rectangular types. There is no need to offer extra reinforcing steel for composite concrete filled tubular sections.

Protection from erosion is arranged by concrete to steel sections in encased columns.

When the local buckling of the steel sections is removed, the reduction in the compression resistance of the composite column caused by overall buckling should definitely be permitted. The plastic compression resistance of a composite cross-section shows the maximum load that can be employed to a short composite column.

Read more

~~~~~~~~~~~~~~~~~~~~~~~~
Published By
Rajib Dey
www.constructioncost.co
~~~~~~~~~~~~~~~~~~~~~~~~

Advantages of Plinth beam and proper height of plinth in residential buildings

Plinth beam belongs to a RCC member. The purpose of plinth beam is to detach the superstructure and the substructure and it functions similar to a tie beam to retain columns, walls etc.

Superstructure is located over ground level that comprises of columns, beams, slabs, masonry walls etc. Substructure is located underneath the ground level that comprises of foundation.

Advantages Of Plinth Beam In House Construction :-
1. To sustain the masonry load at ground floor level
2. The objective of plinth beams is to bear the dead weight of the masonry wall (brick/block wall over it) on ground floor level

Maintain Backfilled soil: Houses are normally built up 150-300 mm over the adjoining road level(s). Plinth functions as a retaining structure for the compacted soil that is applied to fill the empty space from foundation level to top of plinth

To check/circumvent differential settlement

Foundations are exposed to differential settlement when the soil underneath is not compacted perfectly. A differential settlement leads to cracks in the masonry walls. Plinth beam belongs to an integrated structural member and it facilitates minimizing the differential settlement in the structure.

To function as a Tie-beam: Load bearing strength of columns is based on slenderness ratio. Slenderness ratio is obtained from unsupported length of column to cross sectional area of column. If the length of column is increased, the slenderness ratio is also raised to reduce the load bearing strength of the building. In order to reduce the effective length of column, tie beams are arranged and in such a situation if foundation is very deep then RCC plinth beam should be arranged. For foundations below or equivalent to 6 feet, plinth also functions as a tie beam.

Suitable Height Of Plinth:

Plinth level should remain over the adjoining road level to stop the penetration of your house in the rainy season.

Sometimes, local municipalities re-carpet the existing roads devoid of extracting old road strata at the time of repairing or building up the roads. Under such situation, nearby properties may set out under ground level and it is not recommended for practical purposes and for vastu.

To stop penetration of water or storm water into the house from outside, plinth is built up in such a manner that the top of the plinth remains adequately over road level.

If the plinth is built up too high over the road level, then the adjoining parking area level will also be raised and problems will arise.

With proper height only 3-4 stairs are necessary to get to plinth level and the bikes can be easily driven, cars can be easily parked and throughout rainfall it will safeguard property from storm and drainage water.

Because of these problems, plinth height should retain very cautiously neither too high nor too low.

The perfect plinth height should be 1.5ft to 2ft high as compared to road level.



Read Continue
~~~~~~~~~~~~~~~~~~~~~~~~
Published By
Rajib Dey
www.constructioncost.co
~~~~~~~~~~~~~~~~~~~~~~~~

Use and benefits of self compacting concrete

Self-consolidating concrete alias self-compacting concrete (SCC) is a concrete mixture that can flow into very complex forms with various reinforcing bars (rebar congestion) and leaves no voids.

It can be arranged with its own weight devoid of any mechanical vibration. SCC retains all the conventional mechanical and durability characteristics of concrete.

With extremely fluid nature of SCC, it becomes possible to arrange it in complicated conditions and in sections with congested reinforcement. It can also reduce hearing-related damages on the worksite due to vibration of concrete. In SSC, the required time is curtailed significantly for arranging bigger sections.

In some cases, the superplasticizers and viscosity modifier are provided to the mix to minimize bleeding and segregation.

A well designed SCC mix never segregates because it contains extreme deformability and outstanding stability characteristics.

Self-Compacting Concrete Properties: Self-compacting concrete has good resistance capacity against segregation as it applies mineral fillers or fines as well as special admixtures. Self-consolidating concrete is essential to flow and fill special forms under its own weight. It is flown adequately to travel over extremely reinforced areas, and should have capability to circumvent segregation of aggregate.

Self-compacting concrete contains an equivalent water cement or cement binder ratio that provides normally a slightly higher strength with regards to conventional vibrated concrete and because of non-existence of vibration, a better interface among the aggregate and hardened paste is created.

The concrete mix of SCC should be arranged at a comparatively greater velocity as compared to regular concrete. Self-compacting concrete is placed from heights longer than 5 meters exclusive of aggregate segregation. It is also useful for areas having normal and congested reinforcement, with aggregates as large as 2 inches.

Self-Compacting Concrete Uses - Self-compacting concrete is mostly utilized in bridges and even on pre-cast sections. This type of concrete is suitable for the following:

• Drilled shafts
• Columns
• Earth retaining systems
• Areas with high concentration of rebar and pipes/conduits

To know about the benefits of self consolidating concrete, go through the following link thebalance.com



~~~~~~~~~~~~~~~~~~~~~~~~
Published By
Rajib Dey
www.constructioncost.co
~~~~~~~~~~~~~~~~~~~~~~~~