How to read shuttering drawings
Formwork drawings are hard to understand, there are alot of things which we have to look through for the execution of formwork, Whether it is level, line or area of the formwork. Even a small mistake can lead to many trouble such as uneven level, placement of beams/columns/slab etc.
In this article we are going to see what are the things we should check to make the shuttering drawing readable and understandable easily.
1) Grid Lines
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| Grid Lines |
The first question which arises is what are Grid Lines? They are the most important part of Building drawings.
They can be explained easily as these are the references lines which are distributed though out the structure of drawing at both X direction and Y direction at square or rectangular pattern of whose reference we can carry out for the layout or the positioning of different structures from each other.
The grid lines never changes from start of the building drawing till the end of the building drawing, So keeping the reference of these can help in maintaining the structure positioned. The engineer must always ensure checking of formwork with the reference to grid lines only.
Check with Grid Lines
(1) Position Of Columns with the help of measuring tape.
Once the slab is casted, we mark the reference line on the surface of the slab with help of which we do the layout of the building. After the layout is complete, the starter of Columns are fixed, Nowadays layout is done with the help of Total station as-well. To know exactly whether the layout is correct or not, they are cross-checked with the help of reference lines known as grids.
(2) Placement of Beam bottom with help of the plumb.
To fix the beam bottom, Layout is done with the help of grid lines on the slab surface, Than with reference of those markings the plumb is dropped from corner of the beam bottom and the beam bottom is placed.
(3) Positioning of Slab with the help of the Plumb.
The slab corners are checked by taking grid line references.
Note - For certain structures the dimensions are not given, so with help of grid lines they are easy to find out.
2) SSL - Structural Slab Level
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| SSL - Structural Slab Level |
This is the most important part of shuttering drawing which is level of the slab, beam etc which plays a very important and major role. If wrongly done can lead to re-work. SSL is the structural slab level, That means the top level of the slab which is not considered to be the Finished surface. It is only the concrete casted top surface.
How they are Referred in Drawings
Consider the above drawing,
The SSL which is given is +16.925 , so in this the structural top or the top after casting will be of Level +16.925. You must be wondering from where we got this level? Its is easy, when we start constructing a structure we take a reference point for our building level.
The easy example is consider i want to construct a house at road level, now the road lvl. will be +0m lvl. and same as my SSL/ground level will be +0m and if we consider the above drawing than the SSL will be +16.925 meter above from road level or the ground level.
Now I will tell you at what Level the beam bottoms and the Shuttering of slabs must be fixed.
(1) Fixing Of Slab
Lets consider the thickness of the slab is 150mm, and the SSL level we want to achieve is +16.925m
So, the slab shuttering we should fix for achieving the required SSL will be
16.925m - 0.150m = 16.775m
After pouring of concrete for 150mm, we will achieve required SSL of +16.925.
(2) Fixing of Beam Bottom
Assuming Beam depth of 450mm, and the SSL required is +16.925m
So beam bottom level will be,
16.925m - 0.450m = 16.475m
(3) Beam Sides
Here we will see what will be depth of the beam sides, they are really hard to find out so always we should find them with the help of levels.
We will not consider the thickness of the slab in this, So to find the side of beam we will Subtract the level of the slab to the level of the beam bottom.
So, Beam side depth
16.775 - 16.475 = 0.3m
So, here we can see how important is SSL.
3) FFL - Finish Floor Level
The FFL or finished floor level is the top level of the floor surface. It is the finished top level of the flooring we provide, let it be stone, wooden, Indian Patent Stone etc.
If in a drawing only FFL is given, than we can simply deduct the thickness of stone and the mortar mentioned in general detailed drawing and find out the SSL.
4) Cut-out
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| Cut-out |
They are provided for Shafts, Ducts etc which are generally used for the ventilation of building, or for MEP (mechanical, electrical, plumbing) work . In drawing they are shown as X symbol inside a box.
Cut-outs dimensions are checked properly by checking the diagonals and the plumb should be same for all floor cut-outs.
5) Stair-Case
There is always a separate drawing for Stair-case. For every new drawing we get, the number of steps should be cross-checked manually by calculating (landing level - Ground level)/thickness of steps [tread and riser] and counting the number of steps in detailed drawing. If they don’t match then it should be informed to the concerned person.
6) Dimensions
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| Dimensions |
The various terminologies for dimensions given in shuttering drawing are as follows
(1) Inner to inner face dimension - It is the length between both the inner faces of the structure consider it be a wall, beams etc.
(2) Inner to outer face - It is the length between one side from outer face and other side of inner face for beam, wall etc.
(3) Outer to Outer face - It is the outer to outer dimension of the structure.
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