How to calculate timber works in concrete lintel

A lintel in architectural terms is defined as a structural horizontal element/block/material that spans the space or opening between two vertical supports.
Is a loadbearing member of part of a building that is usually placed over entrances, windows,arcs and other openings in the building.
Lintel can be of wood,concrete,bamboo,steel etc depends on the materials for construction, for our study we are working on concrete lintel which is commonly used in the tropical region like nigeria.
The lintel must bear loads that rests on it as well as its own load without deforming or breaking. Brick stone or ordinary concrete are weak in tensile strength, so they can only be used for a limited span 6meters maximum ideally, but iron/steel can be used for longer lintels. Reason you need to introduce adequate iron rods in the concrete lintel to be able to resist the compressive stress of concrete and span longer openings.
To cast the concrete lintel in a building you’ll need to consider the doors,windows, beam by the entrances, beam by the entrance porch between two or more columns, ars in the interior and exterior.
Now knowing the numbers of planks you are going to use, you must first have at the back of your mind the length and breadth of each plank which is 3.6m or 12ft by 0.3m or 1 foot.

For the plan above, we have two options, for a building with a lot of openings you can simply run the lintel as a beam round the entire perimeter blocks, but for others with less openings the conccrete lintel should be placed ontop of openings giving allowances on right and left for the beam to rest on the supports thereby transmitting load through the blocks or whatever the vertical supports to the ground.

OPTION-A
Calculating for windows and doors openings only, check opening in sides A,B,C and D dimensions.
A -1200mm or 1.2m, 2400mm or 2.4m
B-2.4m
C-1.2m,1.2m and 2.4m
D-1.2m,0.6m and 1.2m
For each openings remember there must be an extension to allow the concrete lintel to overlap both ways. The longer the openings the longer the space you should provide for the concrete to overlap. From experience 30% of the opening should be be used for the two sides overlap.

For our calculation 2(30% of window)+window
For side A
– 1.2m will be taken as 2(30% of 1.2)+1.2=1.92
– 2.4m will be taken as 2(30% of 2.4)+2.4=3.84
For side B
– 2.4m will be taken as 2(30% of 2.4)+2.4=3.84
For side C
– 1.2m will be taken as 2(30% of 1.2)+1.2=1.92
– 1.2m will be taken as 2(30% of 1.2)+1.2=1.92
– 2.4m will be taken as 2(30% of 2.4)+2.4=3.84
For side D
– 1.2m will be taken as 2(30% of 1.2)+1.2=1.92
– 0.6m will be taken as 2(30% of 0.6)+0.6=0.96
– 1.2m will be taken as 2(30% of 1.2)+1.2=1.92
Now planks will be used to support the concrete both sides and under the concrete which is the top of the opening.
For ease of calculation. Add all lengths i.e 1.92+3.84+3.84+1.92+1.92+3.84+1.92+0.96+1.92=22.08
Divide the sum by a length of plank which is 3.6m
22.08/3.6=6 planks
Now multiply by 3 because you need the planks for two sides and under
=18 planks for the windows.

OPTION 2
Is to run the lintel round the perimeter, so calculate the perimeter from plan.
A=9.4m+1.35m(wall that leads to front entrance door)
B=9.0m
C=9.4m+1.2m+1.2m (walls that leads to door behind- both sides)
D=9.0m
Add all the dimensions 9.4+1.35+9.0+9.4+1.2+1.2+9.0=40.55m
Divide by 3.6m as a length of plank=11 planks
multiply by 2 for both sides of lintel=22 planks
Now you need to add the base of the windows which the sum is 22.08m from previous calculations, we use this because planks will also be used to brace the planks at the base of concrete.
22.08 divide by 3.6m =6 planks
Total planks=22+6=28 planks

For the door follow same process,
All doors are taken to be 0.9 (900mm)
2(30% of 0.9)+0.9=1.44
Doors are 8 in numbers
1.44 x 8=11.52m
Divide by 3.6m (remember 3.6m or 12 feet is the length of a plank=3.2 planks
Then multiply by 3 =10 planks for the doors.
TOTAL ALL add 28 plus 10=38 planks if the concrete must run round.
OR 18 plus 10=28 planks if the lintel will only be restricted to window areas.