How to design Doubly Reinforced Beams

Concrete has quite high compressive strength, but low tensile strength. However, steel has very high tensile strength. That is why we insert steel reinforcements in the tension zones of a structure.

Now, you can provide reinforcements in concrete beams in two ways - single reinforcement (commonly used) and double reinforcement. Today, we will talk about doubly reinforced beams.

In case of doubly reinforced beams, steel reinforcements are inserted into both the tensile and compression zones of a beam. Meaning, at the top and the bottom of the beam. In contrast, the singly reinforced beams have reinforcements only at the bottom, where it needs tensile support.

Further, in singly reinforced beams, there are two steel bars to be provided, but you need not consider the moment of resistance. However, when you do need to consider this, you have to provide additional bars to reduce the tension in the over-reinforced section.

In case of doubly reinforced beams, though, the matter is quite different. In this case you will have to find out the moment of resistance first! Then, you need the area of tension steel (Ast) and area of compression steel (Asc). Combined, they would overcome the Excess Bending Moment (Mu2).

Designing doubly reinforced beams

When we begin designing a doubly reinforced beam, we need to be careful about some factors. For example, the depth of the beam may need to be limited to given values, be it for architectural reasons or otherwise.

If that is the case, you will have to implement the doubly reinforced beam with the requirement to resist more than standard limiting moment in that confined space you have for it. As a general rule of thumb, we design doubly reinforced beams when the go-to design moment of resistance is higher than that of the limiting moment of resistance.

The beam can be defined as a structural member that carries all vertical loads and resists bending. There are several types of materials used for beams, such as steel, wood, fibers, etc. But the most common material is reinforced concrete.



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Relocation of Structures

Sometimes, it is required to move a building from one place to another location. This can be required for a number of reasons, like change of land, replanning of facility or even natural causes. In such situations, a process called Structure Relocation comes into play.

Relocation of a structure essentially involves three steps. The first is to disassemble the existing structure - you need to tear the building down systematically, preserving as much material and objects as you can. The second step is transporting the disassembled building blocks to the intended target location.

This may need the involvement of heavy transport support if the location is far away. Of course, if the location is within the same property then this step reduces next to zero. The last and the most important step is to reassemble the building back again at the target location using the same building blocks from the previous structure and maybe some extra materials.

Sometimes if the building is small enough and light enough, it can be picked up as a whole and transported to the new location with minimal disassembly and reconstruction necessary. If the move is within the same piece of property, the move can be done by rolling it on temporary rails or rollers. For long distance moves, generally heavy-duty flatbed trucks are used. Though in that case many complications may arise on the way, like roadside obstacles like narrow zones, and overhead obstacles like low-hanging branches and cables.

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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.

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Types of Cranes Used in the Construction Industry

From as far back as the Mesopotamian civilization, cranes have been used for lifting objects that are too heavy or too repetitive to be done manually. Since this type of work is very much used in the construction industry, the use of cranes in it has been invaluable and indispensable since the ancient era. From the ancient Shadouf to roman Polyspastos to modern mobile telescopic cranes, they were used pretty much everywhere on earth.

What is a Crane?

A crane is a machine, comprised of beams, cables, and pullies, which is used to lift or lower heavy objects. An appropriately equipped crane may also move objects horizontally as well as vertically. The mechanism can be supported by a tower or a derrick.

Most cranes used in construction are temporary structures or even mounted on mobile platforms so that they can be moved around the construction site as necessary. They can be taken away when construction finishes in order to leave the site for normal usage. In some cases, where the building in question requires constant maintenance, the engineers may choose to rig a permanent crane with the building.

Modern cranes are powered by means of hydraulics that are driven by an electric motor or a combustion engine driven by fossil fuel. Operating (and driving, in case of mobile cranes) the crane is possible from an operators cabin that may be mounted on crane vehicle or rig itself, or a control station beside the crane, or by means of portable radio-operated controllers that gives the crane operator the freedom to move around and see the loading and unloading operation from any reasonable point of view. Taking that flexibility to a newer level, there are some modern cranes available that can even be controlled via mobile phone apps.

Types of Cranes in Building

Depending upon their usage, flexibility, and mobility, there can be several types of cranes to choose from to use in a construction site. The varieties of choices enable the constructor to adapt to any load-lifting requirements on site. Let us see what they are.

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Advantages & Disadvantages of Flat Slab

Normal process of design and construction is to support the slabs with beams and support the beams with column. It is known as beam-slab construction.

The beams help in minimizing the existing net clear ceiling height. Often, in warehouses, offices and public halls, the slabs are used as a substitute of beams and they are directly supported with columns. These types of slabs are known as flat slabs.

A flat slab stands for a one-way or two-way system with solidities in the slab at the columns and load bearing walls are known as ‘drop panels’ Drop panels function as T-beams over the supports. They raise the shear strength and the rigidity of the floor system against vertical loads, thus the economical span range becomes greater.

Normally, the height of drop panels remains about two times the height of slab. The plan dimensions of the drop panels are a minimum of 1/3 of the distance in the direction being considered, normally rounded to the nearest 100 mm.

Flat Slabs are useful for most of the construction and for irregular column layouts like floors having curved shapes and ramps etc.

Types of Flat Slab Construction - Following types of flat slabs are commonly used in construction:

1. Simple flat slab
2. Flat slab with drop panels
3. Flat slab with column heads
4. Flat slab with both drop panels and column heads

The major features of a flat slab floor are a flat soffit, simple formwork and smooth construction. The economical span ‘L’ of a reinforced concrete flat slab is roughly D x 28 for simply supported, D x 32 for an end span and D x 36 for an interior span. Pre-stressing the slab raises the economical span to D x 35, D x 40 and D x 45 respectively, where D stands for the depth of the slab without the drop panel.

Benefits and Drawbacks of Flat Slabs

Benefits:

• Easy formwork
• No beams—streamlining under-floor services outside the drops
• Least structural depth
• Normally, shear reinforcement is not necessary at the columns.
• Saving in the height of the building
• Construction time is reduced
• Application of prefabricated welded mesh

Drawbacks:

• Medium extents
• Normally not ideal for supporting brittle (masonry) partitions
• Drop panels may obstruct with larger mechanical ducting
• Vertical penetrations should circumvent area around columns
• For reinforced flat slabs, deflection at the middle strip becomes important.

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Variations among framed structures & load bearing structures

Structures are available with several models like solid, framed, shell, load bearing, membrane, composite, trusses, cables and arches, surface structure etc. They are categorized depending on the geometry so as to obtain strength and withstand various types of loads.

Under a framed structure system, a framework or ‘skeleton’ comprising beams and columns is applied to bear the structural loads down the building to the foundations. Generally, the framework is made of steel or reinforced concrete, but in very small (normally single-storey) structures, it is built with timber or aluminium.

Under a non-framed structure system, the wall itself becomes load-bearing. These load-bearing walls are normally constructed by masonry, but reinforced concrete is also used to build up them. Here, the loads are transferred to the foundations through walls.

Given below, the points of variations among framed structure and load bearing structure.

1. Framed Structure: A framed structure integrates different structural components like beam, column and slab which are attached together to defend the gravity and various lateral loads. The purpose of these structures is to control the large forces, moments caused by the applied loads.

Load Bearing Structure: In Load bearing structure, the loads of the roofs along with lateral loads are carried by walls, and through walls they are delivered to lower floor and finally to foundations.

2. Framed Structure: Framed structure contains beam, column, and slab.

Load Bearing Structure: Load bearing structure contains heavy masonry walls with brick or stone that provides support to the whole structure.

3. Framed Structure: In framed structure, vertical load transfer path directs from slab/floor to beam, beam to column and column to footing and then to soil.

Load Bearing Structure: In load bearing structure, vertical load transfer path directs from slab/floor to walls and walls to footing.

4. Framed Structure: Multi storey buildings with various heights are built up. These buildings are normally suitable for office, hotel, residential apartment and provide the vertical circulation in the form of stairs and lifts which engross up to 20% of the floor area.

Load Bearing Structure: Limited storey buildings are built up. For load-bearing construction, in several countries, even 14 storied buildings are constructed only with masonry.

5. Framed Structure: Framed structure has strong resistance capacity against Earthquake.

Load Bearing Structure: Load bearing structure is not very effective to withstand Earthquake due to its limitations. But for low rise buildings, it functions equally well.

6. Framed Structure: In framed structure all the walls are leaner.

Load Bearing Structure: In load bearing structure walls are denser.

7. Framed Structure: In these types of structures, there are lots of carpet areas and they are leaner.

Load Bearing Structure: In these types of structures less carpet area is available, as walls are thicker and hence carpet area efficiency of planning is less.

8. Framed Structure: Less excavation is required for this type of construction.

Load Bearing Structure: Higher excavation is required for this type of construction.

9. Framed Structure: It is less material intensive.

Load Bearing Structure: It is more material intensive and as a result the dead load is increased

10. Framed Structure: Thickness of wall is unchanged during the construction. Thickness of wall is not changed if the height is raised.

Load Bearing Structure: Thickness of wall remains inconsistent during the construction. The thickness of the wall is raised when the height is higher.

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Some useful methods to work out ideal column spacing for pallet racking

While placing warehouse pallet racking, it becomes difficult to adapt building columns. Although the layout drawing is adjusted properly but collapsing of columns in the middle of a drive aisle or in the racking itself can’t be avoided.

In this civil engineering article, you will be familiar with a perfect building column spacing to get rid of this complicated method and increase the number of storage locations inside a building.

Building Columns: These are vertical members which provide support to the facility ceiling. They are available with different types of sizes and designs.

Uprights: These are vertical supports in a pallet racking system. To develop a pallet racking structure, two upright frames are required on each side to support the horizontal beams.

Beams: They provide horizontal weight-bearing supports in a pallet racking system which attaches the upright frames to each other.

Flue Space: These are spaces among back to back rows of pallet racking. These back-to-back rows are attached with row spacers. 12” is the most recommended row spacer length to facilitate minor overhang of the pallets in the back as well as fire suppression if required inside the racks.

This flue space also facilitates the typical building columns (10” x 10”) to be hidden inside the racking devoid of losing any pallet storage locations.

Purpose of building columns: The architects and structural engineers place building columns by keeping 40 or 50 feet distance owing to standard steel mill member lengths. However, when the building is designed around the proposed use and equipment inside, these lengths can be adjusted to obtain the best use of the space investment.

To maximize your pallet rack layout, two things can be done to get rid of the building columns falling outside of the racking and inside fork truck drive aisles:

Place racking properly in order that the building columns land in the flue spaces of the pallet racking as well as inside the racking itself.

If possible, the pallet racking should be placed in order that the building columns fall inside flue spaces to get rid of losing storage locations. Given below the ideal building column spacing for a various single-deep pallet racking designs. Here, 12” x 12” building columns and 48” deep pallets (therefore no pallet overhang) are taken.

To determine the best building column spacing for your preferred rack layout, the following formula should be applied :-

[(Rack Depth x 2) Flue Aisle] x # Bays = Column Spacing

The process is complicated for placing and configuring pallet racking specifically when it is not possible to work with the general contractor to maximize the building column spacing inside your new building, or moving into an existing building.

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Some important checklists for RCC slab and beams

The following checklists are extensively utilized for RCC slab and Beams.

1. Examine the bottom line, level & width of beam properly.
2. Examine the side line, level & plumb of beam properly.
3. Beam to beam measurements should be examined according to architectural drawings.
4. Individual level & diagonal of each slab bay should be examined properly.

5. The thickness level of slab should be marked with nails on the peripheral beam’s exterior sides.
6. Examine the thickness of slab and depths of beam properly.
7. Support props for slab & beam bottoms should arrange in line & plumb. Bamboo bracing should be accomplished at around 4′ ht from floor level. Support props for double staging terraces should be examined cautiously.
8. Line of external /peripheral beam’s sides should be examined & cross supported to get rid of buldging out of sides.
9. Junctions of columns & beam should be verified to make them water resistant.
10. De-shuttering oil should be provided to beam/slab shuttering.

11. Formwork of stair case should be examined for dimensions of tread and riser, level of treads, plumb of risers.
12. Reinforcement should be examined for beams and slab as per R.C.C drawing
13. Ensure to provide exact cover for bottom /sides of beams.
14. Proper cover should be provided for slab.
15. Electrical points, electrical piping (conduits)/fan hooks should be examined as per drawing.
16. Reduction of column according to drawing should be performed if any.
17. There should be exact numbers of chairs should be arranged for slab.
18. Dowels (if any) should be arranged for elevational feaures / future expansion.
19. Parapet (Pardi) bars should be provided for balconies/staircase etc.

20. Ring (stirrups) should be arranged at the free end of each column reinforcement.
21. Distances among plates /planks should be filled. Taping should be performed at ply joints for the protection of ply shuttering.
22. Before starting pouring work, consent of the architect and R.C.C Consultant should be obtained.
23. Prior to start concreting work, verify the accessibility of necessary labour strength, mixer, lift, vibrators, masons, weigh batcher, diesel/petrol and plastic sheets etc before start of concreting.
24. Hidden beams /inverted beams/cantilever beams should be examined properly.
25. Based on the approved drawings, verify the sunk.
26. Packing underneath support props should not be provided. As an alternative, single wooden plank should be inserted as packing.
27. For large slabs, exact location of concrete joints should be determined beforehand as per approval of RCC consultant.
28. Accessibility of raw material for concrete /RMC per grade of concrete, water , electricity should be examined beforehand prior to start concreting work.

29. Initially, concreting should be performed for the beams & then slabs.
30. Compaction of concrete should be accomplished with vibrators & tamping rods.
31. The top level of the slab should be completed with mason & there should be restrictions to walk on the fresh finished concrete.
32. Carpenter should be provided under the slab shuttering throughout concreting to keep the form work tight.
33. For protection against rains, large plastic sheets should be used to wrap finished concrete.
34. Cast 6 cube moulds for testing.
35. Curing of slab should be accomplished with ponding method by making ponds in cement & sand mortar (1:10) of size around 5′ X 5′. Curing of beams and slabs should be performed for 7 to 10 days or as suggested by the consultant.
36. Deshuttering of the exterior sides of the beam should be accomplished after 24 hours . Deshuttering of the inner sides of beam should be accomplished after 48 hours . Deshuttering of the beam bottoms should be accomplished after 14 days for beam lengths up to 3 M or as per suggestions of the consultant. Deshuttering of the slab should be performed after 7 days for slabs up to 3 M span or as directed by the consultant.
37. Finishing of honeycomb should be accomplished cautiously in front of engineer the next day.
38. Hacking of the beam sides, beam bottoms, slab bottoms should be accomplished within 1 or 2 days from deshuttering.
39. Date of casting and the number of slab should be painted on the front side beam.

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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.

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Construction Method Of Concrete Slab On Grade

Slab on grade belongs to concrete floor slabs which are poured at grade or ground level to develop a foundation for a home. Prior to start the construction, contractors excavate the soil adjacent to the area where the foundation should be constructed and ensure that the ground has sufficient strength to support the structure.

Normally, the periphery of the slab is very dense as compared to the rest of the surface. This section has similarity with footer that facilitates to circulate the weight of the exterior walls uniformly over the soil underneath the structure. Slab on grade foundations are suitable for the areas where the soil is unusable for crawl spaces or basements.

Grade slabs are provided in areas where the ground is not solidified. This type of slabs may or may not include reinforcement in it. The inclusion of reinforcement depends on the floor loads and local building codes.

The thickness of Grade Slab should be at least 4 inches. If porosity exists in soil, the thickness of the slab should be raised. To maintain safety, a layer of gravel & bitumen should be placed on earth prior to arrange concrete slab to stop the penetration of moisture content into the slab.

Slab on Grade is categorized as follow:

1. Supported Slab on Grade
2. Monolithic Slab on Grade

Supported Slab on Grade / Grade Slab: Supported grade slab or slab on grade foundation should be used when the conventional footings are already set up on site to uplift the columns. Under this system, the wall is laid on a footing and the grade slab stands on a layer of gravel and moisture barrier.

The formwork applied for plinth beams operates as batter boards for slab mould. There is an expansion joint among concrete slab and wall to reduce the stress throughout high-temperature days. Control joints are set in a planned grid with chalk lines to manage occasional cracking on the slab.

Monolithic Slab on grade: There are no footings for monolithic grade slab, the concrete slab itself functions as a footing for the building; and the columns, walls are uplifted from the grade slab. This type of slab is structured with batter boards around the slab based on the plan and the concrete is poured inside batter boards. These batter boards operate as a mould to detect the slab corners.

Grade slabs normally stand on the layers of gravel and moisture barrier. These layers can resist penetration of water into the slab to develop surface cracks.

The periphery of the grade slab is very dense as compared to the rest of surface. This dense section operates as a mini footing and facilitates to circulate top loads more consistently over the adjacent soil.

Construction Method: Prior to cast slab on grade, the excavation of earth is done to the desired depth along with compaction to drive out air voids. Batters are leveled and provided in exact location based on the plan prior to concrete pour. These boards function as a concrete mould to facilitate detecting the slab corners.

After that, soil investigation is performed to design the thickness of the slab. After obtaining the results, the layers of gravel and moisture barriers (bitumen) is again poured on the ground. These layers are used as a sub-base for slab and resist the infiltration of moisture into the slab.

The thick concrete is poured at the edges to form an solid footing and reinforcement rods are placed to increase the strength of the edges.

To reduce random cracking on the surface, the concrete should be cured and dried for long times.

The expansion joint should be arranged among the wall and slab. The control joints on the slab are leveled with chalk lines prior to pouring which can check random cracking.

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Guidelines for making perfect structural design

This civil engineering article focuses on the least standards which should be maintained for the design of various RCC structural elements like the columns, beams, slab and foundation as well as the least safe standards for the reinforcing bars to be applied for making the design of the above mentioned structural elements.

Minimum cross-sectional dimension for a Column should be 9″x 12″ (225 MM x 300 MM). It is the minimum approved size.

It is always recommended to utilize M20 grade concrete for construction as per IS 456:2000. The least steel in a 9″ x 9″ column should be 4 bars of 12 MM with stirrups of 8 MM steel rings at a spacing of 150 MM centre to centre. In a 9″ x 12″ column, more bars (6 bars with 12 mm diameter) should be added to sustain the total efficiently.

Least RCC beam size should not be lower than 9″x 9″ (225MM X 225MM), with an supplementary slab thickness of 125 MM.

Normally, there should be minimum of 4 bars, with 2 bars having 12 MM thickness in the bottom of the beam, and 2 bars having 10 MM at the top of the beam.

A concrete cover of 40 MM should also be provided. It is suggested to utilize M20 grade of concrete (1 part cement : 1.5 parts sand : 3 parts aggregate : 0.5 parts water).

Minimum thickness of RCC slab should be 5″ (125MM) since a slab may comprise of electrical pipes which are implanted into them which could be 0.5″ or more for internal wiring and as a result the depth of slab is decreased at specific places that lead to cracking, weakening and water leakage throughout rains. Therefore, a least thickness of 5″ should be retained.

Minimum size of foundation for a single storey of G+1 building should be 1m x 1m, where safe bearing strength of soil is 30 tonnes per square meter, and the anticipated load on the column does not surpass 30 tonnes.

The depth of footing should be minimum 4′under ground level. It is suggested to get to depths up to had strata.

Minimum Reinforcing bar details:

1. Columns: 4 bars of 12mm steel rods FE 500.
2. Beams: 2 bars of 12 mm in the bottom and 2 bars of 10 mm on the top.
3. Slab

a) One Way Slab: Main Steel 8 MM bars @ 6″ C/C and Distribution Steel of 6 mm bars @ 6″ C/C
b) Two Way Slab: Main Steel 8 MM bars @ 5″ C/C and Distribution Steel of 8 mm bars @ 7″ C/C

4. Foundation: Initially, there should be 6″ of PCC layer. Over it, a tapered or rectangular footing with minimum 12″ thickness should be arranged. Steel mesh of 8 mm bars @ 6″ C/C should be placed. In a 1m X 1m footing, there should be 6 bars of 8 mm on both segments of the steel mesh.

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Common thumb rules for civil engineering works

Thumb Rules is very important for any civil engineer, Site engineer or civil supervisor to obtain instant decisions on the construction site. By applying thumb, the engineers can get the solution with a simple mathematical formula and take proper decisions wherever required. Before applying these thumb rules, it should be kept in mind that the thumb rule can only provide fairly accurate results never the correct results.

The following types of thumb rules for civil engineers are commonly used in construction work :-

Thumb rule for measuring the Concrete Volume relating to the area:
The volume of concrete necessary = 0.038 m3/square feet area.

As for instance, if Plan Area = 40 x 20 = 800 Sq. m., total necessary volume of concrete will be as follow :-
= 800 x 0.038m3 = 30.4m3

Thumb rule for Steel quantity necessary for Slab, Beams, Footings & Columns:
Essential quantity of steel in residential buildings = 4.5 Kgs – 4.75 Kgs / Sq. Ft.
Essential quantity of steel in commercial buildings = 5.0 Kgs-5.50 Kgs/Sq. Ft.

Thumb Rules For Civil Engineers recommended by B N Datta for the Steel quantity that will be applied for several members of the building :-

Proportions of Steel in Structural Members:

1) Slab – 1% of the total volume of concrete
2) Beam – 2% of the total volume of concrete
3) Column – 2.5% of total volume of concrete
4) Footings – 0.8% of the total volume of concrete

As for instance, suppose the length, width and depth of the slab are 5m, 4m and 0.15m. Now, the quantity of steel for the slab will be computed as follow :-

Initially, it is required to work out the concrete volume.
The total volume of concrete for the slab = 5x4x0.15 = 3m3

Secondly, work out the quantity of steel with formula as follow :-
Based on the guidelines provided in B. N. Dutta reference book, the quantity of steel in slab is 1% of the total volume of concrete used.
Thumb rule to work out the quantity of steel in above slab = Volume of concrete x density of steel x % of steel member.

The weight of steel necessary for above slab = 3x7850x0.01 = 235 kgs

To make perfect calculation, use bar bending schedule.

To learn how thumb rules are applied to calculate the shuttering area and the quantity of cement, sand, course aggregate in several grades of concrete, click on the following link civiconcepts.com

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Advantages of cross wall construction

Cross wall construction stands for a building construction method. Under this system, the precast load-bearing walls are arranged perpendicular to the lateral axis of the building.

In cross wall construction, the load-bearing walls provide support to the floors, roofs and the beams. The structures built up with the cross wall method are structurally strong and cost-effective.

Given below, the construction details and the features of cross wall construction :-

Features of Cross Wall Construction: Under cross wall construction, the prefabricated walls are arranged in series. These load-bearing walls transmit the structural loads securely to the foundation devoid of any concrete or steel frame. They also serve as shear walls and safeguard the building against lateral movement.

Cross wall construction is ideal for the buildings which contain maximum of 5 stories where all the floors come with similar plans. The intermediate floor span among the load-bearing walls offers adequate lateral control.

If both the load-bearing walls and the floors belong to precast members, then a series of boxes should be created. This type of construction is normally defined as box frame construction.

Cross Wall Construction Systems:

1. Precast materials can be sent at the right moment.
2. The precast wall components are arranged both horizontally and vertically. They are grouted and attached according to the plan through hidden joints and ties.
3. Prior to finish the complete structure, mechanical & electrical installation works, finishing works and other multifaceted works on the walls should be finished.

The cross walls are attached with any of the following key connections:

1. Wall-to-wall by Horizontal Joints
2. Wall-to-wall by vertical joints
3. Wall to the base foundation

When the cross walls are placed along the floor, the front and the rear walls can be non-load bearing claddings. The connections among the non-load bearing walls and the cross walls should be designed and built up with a proper care to avoid moisture infiltration and other issues.

Advantage of Cross Wall Construction:

1. Cross wall construction forms a long-lasting structure.
2. The initial construction cost is fewer.
3. With regard to conventional construction method, cross wall construction method save huge time and cost.
4. The building built up is structurally strong that contains greater fire and acoustic separation among the nearby rooms.
5. The construction achieves good thermal mass.
6. Site co-ordination is simple at the time of providing cross wall construction.
7. The structure ensures superior security.
8. The maintenance cost of the structure developed with cross wall construction method is fewer.
9. No scaffoldings are required for cross wall construction.
10. The structure remains monolithic with good air tightness.

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Detail guidelines on Structural Design Codes And Standards

Design of RCC Structural Components: In this civil engineering article, you will be familiar with the minimum standards necessary for the design of RCC structural elements of a structure like columns, beams, slab and foundation.

Besides, the information is also given on the minimum safe standards for the reinforcing bars which should be applied for the design of the above mentioned structural elements.

Minimum cross-sectional dimension for a Column: Minimum standard size should be 9″x 12″(225 MM x 300 MM). It is recommended to use M20 grade concrete for construction as per IS 456:2000. The minimum steel in a 9″ x 9″ column should contain 4 bars of 12 MM containing stirrups of 8 MM steel rings at a spacing of 150 MM centre to centre. In a 9″ x 12″ column, two more bars can be added to make the total to 6 bars of 12 MM diameter. This design will be secured for up to G+1 floors.

Minimum RCC beam size : It should not be under 9″x 9″(225MM X 225MM), containing a extra slab thickness of 125 MM.

A minimum of 4 bars can be used containing 2 bars of 12 MM thickness in the bottom of the beam, and 2 bars of 10 MM at the top of the beam. The required concrete cover should be 40 MM. It is recommended to utilize M20 grade of concrete (1 part cement : 1.5 parts sand : 3 parts aggregate : 0.5 parts water).

Minimum thickness of RCC slab : It should be minimum 5″ (125MM) as a slab may comprise of electrical pipes implanted into them with thickness 0.5″ or more for internal wiring, which in fact minimizes the depth of slab at specific areas. It leads to cracking, decay and water leakage during rains. So, there should be a minimum thickness of 5″.

Minimum size of foundation : A size of 1m x 1m should be ideal for a single storey of G+1 building, where the safe bearing strength of soil should be 30 tonnes per square meter, and the impending load on the column does not be in excess of 30 tonnes,. Minimum depth of footing should remain 4′ underneath ground level. It is recommended to retain deepness up to had strata.

Reinforcing bar details (minimum):

1. Columns: 4 bars of 12mm steel rods FE 500.
2. Beams: 2 bars of 12 mm in the bottom and 2 bars of 10 mm on the top.
3. Slab

a) One Way Slab: Main Steel 8 MM bars @ 6″ C/C and Distribution Steel of 6 mm bars @ 6″ C/C
b) Two Way Slab: Main Steel 8 MM bars @ 5″ C/C and Distribution Steel of 8 mm bars @ 7″ C/C

4. Foundation: Initially, 6″ of PCC layer should be provided. Over it, there should be a tapered or rectangular footing with minimum 12″ thickness. Steel mesh of 8 mm bars @ 6″ C/C should be placed. In a 1m X 1m footing, it should comprise of 6 bars of 8 mm on both portions of the steel mesh.



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Published By
Rajib Dey
www.constructioncost.co
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