Types of Rebar Support in RCC Member

Liton Biswas | 9/02/2014 | | Be the first to comment!
RCC member is composed of reinforcement and concrete. Typically we use deformed steel bar as reinforcement. But the question is - what is Rebar support and why do reinforcements need them.

Reinforcement support, rebar support
Block

What is the "rebar support?

To prevent displacement of reinforcement during working and concreting we provide supports to them in RCC members. These are called rebar support. Not clear? Keep reading...


Why does reinforcement need supports?

In reinforced cement concrete (RCC) member, we provide concrete cover for all reinforcements. Because if the reinforcement exposes to weather it gets corrosion. And you know what the corrosion means for reinforcement.

Reinforcements need different thickness of concrete cover in different situation. Read this article "minimum concrete clear cover for reinforcement".

There is a possibility to displace the unsupported reinforcements during working and pouring concrete. To prevent the reinforcement from displacement, we need to give them support.

So far, we get the concept about rebar support. Now we'll see what kind of supports are used for steel bar in RCC member.

Typically used reinforcement supports in RCC member

We generally use the following types of rebar support -
  • Mortar Block
  • Steel chair
Mortar Block: This is the most common type of bar support. 1:3 cement-sand mortar is commonly used for making mortar block. The thickness of this block depends on the clear cover for steel bar. This type of bar support is generally used in edges of RCC member.

Rebar support, Support for reinforcement
Chair as "Rebar Support"
Chair: To separate top and bottom reinforcement in double reinforced RCC member this type of bar support is commonly used. Normally 10mm diameter steel bars are used for this purpose. Calculating the height of the chair is a bit tricky. I'll write about this later in a separate article. So subscribe by RSS or Email to get update when it is published.

Besides these common types of support, there is a plastic bar support which is used in the RCC member built on ground. This is nicely explained in "CRSI - Manual of Standard Practice" which is also refered by "ACI-315-99".

There are many sized and shaped of rebar supports available in the market ready for use. But in small RCC members like beam and slab of a building, you don't need to buy those expensive rebar supports.

Share your experience
Which types of rebar support have you used so far?
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Components of Superstructure of a Building BCT-5

Liton Biswas | 8/29/2014 | | | Be the first to comment!
I have seen many times in various question and answer website that a similar question asked repeatedly. That is "what is the superstructure?".

what is the superstructure?

As described in Dictionary, "Superstructure is the part of a building or construction entirely above its foundation or basement".

From the universal point of view, the definition is true.

From the civil engineers point of view, the superstructure is "the structure which is built on substructure".


That means, we can say, the structure built above plinth is the superstructure.

What is plinth?

Plinth is a layer of cement-sand mortar which sits in between substructure and superstructure to prevent ground floor dampness.

So far We have learnt what the superstructure is. Now we will figure out what are the components of the superstructure.

Consonants of superstructure

The components of superstructure are -
  • Column
  • Wall
  • Beam and Slab

Column: Columns that are built above ground-level are considered as the part of the superstructure.

Column can be two types based on their using purpose. Architectural and Structural.

Architectural column doesn't carry any vertical loads. It is just utilised to increase the aesthetic look of a structure.

On the other hand, structural columns are used to carry the loads to downward.

Sometimes structural column is decorated to give a structure an aesthetic look. That time it also acts as an architectural column.


Different types of materials are used to construct columns of a structure. The most common material is "reinforced cement concrete". Because it is economical and easy to form.

Wall: Wall can be a part of a superstructure. We are talking about structural walls here which carry the loads of structural parts. Such as a shear wall. Masonry wall can also be a part of a superstructure when it carries the structural loads.

Many of us consider masonry wall as a part of the superstructure. But I included them in the masonry work phase in this tutorial series. Because, it doesn't carry any structural loads.

Beam & Slab: To make the structure as useable space it's divided by slabs at different level.

Beam transfer the load coming from slab to column.

Read more: Types of RCC Beam

Both beam and slab are horizontal member which can be constructed with different kinds of materials.  But the most commonly used material is Reinforced cement concrete.
 
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Types of Mortar Joint Used to Make Masonry Wall

Liton Biswas | 8/21/2014 | | Be the first to comment!
Everyday we see the masonry wall here and there. Some appealed to us and some not. But did we notice how the joints are formed in wall?

When we make masonry wall we just combine bricks or concrete block with mortar. This mortar can be cement mortar or lime mortar etc. Whichever mortar you use no matter, the mortar joint should be strong, water-tight, good looking and weather resistant.

Read more: Traditional Brick Bond Patterns Used in Masonry Wall Construction 

The thickness of joint should be from 1/4" to 1/2". And it's done by a tool or a trowel.

Below are some common types of mortar joint used to build masonry wall -
  • Concave joint
  • V Joint
  • Struck joint
  • Weather joint
  • Raked joint
  • Flush joint
Concave joint: It is also called bucket handle joint. This joint is formed by a half-circular shaped jointing tool. This joint is globally accepted as the best joint for its resistance capability to water penetration.

mortar joint, masonry joint

V joint: Due to its "V" shape it's called "V" joint (see the pic). If the joint isn't properly compressed it can be the entry point of water.

mortar joint, masonry joint

Struck joint: In this joint, the top edge of the joint is finished flash with brick edge and the bottom edge is recessed.

masonry joint, mortar joint
 
Water resistance capability of this joint is very poor. Because the slope of the joint pulls water and allow to sit on a brick, which gives it more time to penetrate. So it is better to apply this joint on internal walls.

Weathered joint: This joint is similar as struck joint but the top edge is recessed instead of bottom edge of the joint. The water resistance capability of this joint is good due to its slope. But if the mortar isn't properly adhered with the brick water can penetrate running across the underside of the brick.

masonry joint, mortar joint

Raked joint: In this joint mortar is slightly recessed from the edges of the brick. It's why this joint is also called recessed joint. The surface of the joint is normally left roughened. But it is better to compact the surface to increase the water resistance capability.

It's not used in modern building due to its poor water resistance capability. But sometimes used to give a modern building a historic look.

masonry joint, mortar joint

Flush joint: The surface of the flash joint is left flush with brick edges. The resistance capability of water penetration of this joint is low. Because it is formed without compacting the surface.

Flush joint, type of mortar joint

Beside these, there are some other joints used to form masonry wall. These aren't normally used in building construction. For your knowing purpose these are given below -
  • Squeezed joint
  • Beaded joint
  • Grapevine joint

masonry joint, mortar joint

Whichever mortar joints you use to make masonry wall always remember one thing that exterior wall must be formed with tooled mortar joint. Such as "Concave" and "V" joint.
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Components of "Sub-Structure" of a building, BCT-4

Liton Biswas | 8/14/2014 | | Be the first to comment!
We have considered "Sub-structure" as 3rd work phase of building construction in our tutorial series. We left a "work-phase" that is "ground work". Because we discussed about that topic several times here in this blog. You can read them in following links -


In this post we'll discuss about sub-structure of a building.

First of all, we should know "what is sub-structure"?

"The structure below ground level can be defined as sub-structure".

Someone defined sub-structure as "the structure which can't be visible".

"The structure up to plinth level is defined as sub-structure" in many engineering books by specialists. 

From the definition of Sub-structure we can say it consists of the following parts of the building -

  • Foundation
  • Short/Neck column
  • Grade beam/Tie beam

Foundation: foundation also called base. A building completely stands on it. So it is the most important part of a building. There are many types of foundation we can make to build a building. Please see this post to know more about foundation.

Short/Neck column: Theoretically, short columns are those which effective length to least lateral dimension ratio don't exceed 12. Generally,  A column between foundation and grade beam is called short column or neck column.

Grade beam/Tie beam: grade beam doesn't carry any vertical load. It just ties columns to prevent lateral movement. That's why this beam is also called Tie beam. Sometimes ground slab rest on grade beam and thus carries vertical loads. Then it is called ground beam.

Dear reader, when I started this building construction tutorial series that time I expected to publish two or three posts in a week. But I was extremely busy on some of my projects. That's why I haven't published post for a long time. I'm sorry for that. From now I'll publish regularly, at least one post of this tutorial series in a week with some other important posts.

However, we already know from this post that ground floor slab can't be included in sub-structure as the ground floor slab is visible and ground floor slab is built above the plinth level, yet someone includes ground floor slab in sub-structure if it is build on the ground.

I've discussed briefly about sub-structure in this post. I'll discuss details about each item of sub-structure later in this tutorial series. Our next post of this tutorial series will be about super structure. So subscribe by email or RSS to get immediate update.
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Important Tasks of Construction Mobilization, BCT-3, PH-1

Liton Biswas | 10/31/2013 | | Be the first to comment!
Dear readers I'm extremely sorry for not publishing last posts in scheduled time. I was busy in some personal projects.

In previous post of this building construction tutorial series, we divided complete building construction works into 8 work-phases. In this post we are going to discuss the first phase of building construction that is mobilization.

Mobilization is the preliminary works of any construction project. In a board sense, construction mobilization refers to the processes and tasks that are undertaken before the actual groundwork begins. It needs the following important tasks to be performed -

  1. Temporary Fencing
  2. Labor shed making
  3. Power connection
  4. Water supply and Sanitation
  5. Site Office
  6. Storage
  7. Gathering tools and machineries
  8. Construction documents
  9. Other tasks, etc.

1. Temporary Fencing: The first task of starting construction project is to make fence all around the plot. It secures the plot. You can use signboard, banner, safety instruction, etc on this fence.

building construction tutorial, mobilization


2. Labor shed making: It is now common practice that labors who work on construction project stay in that project. So, it's essential to make a labor shed in the project. Choose a location carefully to make shed so that it doesn't hamper foundation work. Some big companies have permanent labor shed. So they don't need to make temporary labor shed on plot.

3. Power connection: For a construction project you must need continue power supply. So apply for power connection from electrical authority or arrange a generator to fulfill your need.

4. Water supply and Sanitation: As your workers will stay in project you will need pure drinking water and sanitation system for them. Pure drinking water also need for construction works. So, apply for water supply connection from national water supply authority or set a deep tubewell.

5. Site Office: Ofcourse, a project management team will work during the construction period of the project, there will be held meetings among clients, owners, contractors, sub-contractors and stackholders. For them you'll need a site office with proper sanitation and water supply facilities.

6. Storage: For storing building materials, construction equipments and tools you'll need a storage with lock and key.

7. Gathering tools and machineries: Gather necessary tools and equipments on project for construction works

8. Construction documents: Copies of all legal documents such as building permission, electricity, water and gas connection permissions from concerned authority, etc should be arranged and kept in project.

9. Other tasks: Keeping safe the passerby as well as the workers and stuffs from accident providing safety signboard is also included in mobilization. Arranging first-aid box and fire fighting equipments should be included in mobilization.

Sometimes cleaning and levelling the ground are included in mobilization phase of construction. I included those in ground-work phase.

This is the summary post of tasks of the mobilization phase. Some of these tasks need further explanation. I'll describe those in future posts.


Your Turn
Do you want to add any other task/tasks in mobilization phase of construction? Please share in comment...
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