Posts Tagged structural design
Load Calculations | Design of Buildings
In our earlier article, we discussed “Different types of loads” and their importance in Structural design.
Now we will move on with our further discussion on the following points:
- Design principle assumption and notation assumed
- Design Constant
- Assumptions regarding Design
- Loads on Beams
- Loads on slabs
Design principle assumption and notation assumed:
The notations adopted throughout are same as given in IS:456:2000
Density of material used in accordance with reference to IS:857-1987s
|1||Plain concrete||24 KN/m3|
|2||Reinforced cement concrete||25 KN/m3|
|3||Flooring material (cement mortar)||1.00 KN/m3|
|4||Brick masonry||19 KN/m3|
Using M20 and Fe415 grade of concrete and steel respectively for columns and footings
Fck – i. e. Characteristic strength for M15 – 15 N/mm2
Fck – i. e. Characteristic strength for M15 – 15 N/mm2
Fck – i. e. Characteristic strength for M20 – 20 N/mm2
Fy – i. e. Characteristic strength for steel – 415 N/mm2
Building Construction | Civil Engineering and Design
Construction of buildings can be divided into three main categories:
- Load bearing construction
- Composite construction
- Framed construction
But among the three types, framed construction is widely used for all kinds of constructions.
An engineering structure is an assembly of number of elements transferring the loads and providing a form space to serve the desired function.
The structural design is a science and art of designing, with economy and elegance, a durable structure is that which can safely carry the forces and can serve the desired function satisfactorily during its expected service life span.
The entire process of structural planning and designing requires not only imagination and conceptual thinking but of practical aspects, such as relevant design codes and byelaws, backed up by aple experience, institution and judgement.
The process of design commences with planning of a structure, primarily to meet the functional equipment of the user or client. The functional requirements and the aspects of the aesthetics looked into normally by an architect while the aspect of safety, serviceability, durability and economy of the structure for its intended use over the life span.
What is a building?
A building can be defined as a structure consisting of walls, floors, education, business, manufacturing, storage, hospitalization, entertainment, worship etc.
Normally all building are constructed according to drawings and specifications prepared by architects. Each city has prescribed building bye-laws to which building must confirm. The building bye-laws lay down norms like minimum front, side and rear backs, minimum height and area of habitable rooms, kitchen, bath, minimum area of windows, width of staircase etc, apart from respecting the bye-laws the building design should ensure optimum utilization of built-up space, thermal comfort, proper ventilation, desirable illumination and acoustical characteristics and it should satisfy the functional requirements of people who live and work in the building.
A lesson for all the Civil Engineers and Designers to learn
I got a project of designing (Architectural Design) a Hostel in Lucknow, India. The Structural design that is, column positions and wall construction was already done. The client wanted me to design a Hostel keeping the column positions and exterior wall construction intact. I have written this article to address all the Civil engineering students as well as Civil Engineers to avoid making such blunders while they design. Please do read this article because understanding the intensity of the job of a Civil Engineer is must for every student and professional. I guess this realization has been washed away and forgotten in the wave of commercialism.
Hostel Design, Lucknow, India
The client mailed me the layout of the existing construction. After I studied the layout, I figured out that the Column layout was pathetic. I wonder what kind of Civil Engineer must have made the layout or if at all any Civil Engineer has done it.
Errors in Construction
Wrong size of the Columns
The size of the columns was 9”x9” and the building is supposed to be constructed upto G+2 floors which is really disastrous for the structure.
It could lead to structural failure and ultimately structural collapse.
(The duty of the Civil Engineer is to understand and not make such dramatic blunders. The consequences of this kind of structural design could be disastrous.)
9”x9” size columns are only preferred if you were to construct only a ground floor structure using M15 grade concrete. If you are to construct another floor that is (G+1), the minimum size of the column should not be less than 9”x12” using M15 grade concrete.
If the client insists on using smaller columns (9”x9”); in that case, use of M20 grade concrete should be done mandatorily and the construction should not be initiated before the client agrees to do so.
Guidelines to be followed for making a column layout
In this article, we will go through the essential thumb rules to be followed for giving a column layout. Ofcourse columns have to be designed in accordance to the total forces acting on the structure, but apart from that, it is essential for every Civil engineer and Architect to remember a few thumb rules so that they are prevented from making mistakes.
Three thumb rules to be followed are as follows:
- Size of the Columns
- Distance between Columns
- Alignment of columns
Minimum Size of RCC columns
The size of the columns depends on the total load on the columns. There are axial loads and lateral loads. Large beam spans induce bending moment not only in the beams, but also in columns which are pulled by the stresses in the beams. It is important to use advanced structural design software like ETabs or Staad pro. I highly recommend every structural designer learn these software. The thumb rules are for general designing in very small projects.
For this general thumb rule, we will assume a structure of G+1 floors high, using standard 6″ walls.
Minimum size of an RCC column should not be less than 9”x 9” (225mm x 225mm) with 4 bars of 12 MM Fe500 Steel.
These days the minimum I use in my projects is 9″ x 12″ (225 mm x 300mm) with 6 bars of 12 MM Fe500 steel. You can never go wrong with strong columns. I also recommend use of M20 grade concrete for the structure (ratio 1 part Cement : 1.5 parts Sand : 3 parts Aggregate with 0.5 parts water by volume). I recommend use of 8 MM stirrups at a distance of 150 MM center to center throughout the length of column.
This setup of 9″ x 12″ RCC columns is safe for G+1 Floors. There are a lot of other considerations, but this is just a thumb rule.