How to prepare a BOQ

Step 1

When preparing a BOQ, there are certain steps to be carried out in order to make a proper BOQ. Mainly, it can be Quantity and Rate for each work. As the first step in preparing a BOQ is taking off quantities from the given drawings.Therefore, we need record these taking off measurements properly in a particular order which we can easily edit and recognize the measurements for each work. This measurement recording sheet is called TDS. The sheet arrangement will look like the following document.

TDS - Sheet

Timesing:- In this column, we fill the number of repetitions of same work. for an example if we have same size columns 10 nos. we put it in this raw as 10.

Dimension :- In this column, we put the dimensions of the work. When we enter the dimensions, we should first add the length, width, and depth.

Sums:- In this column, we calculate the sums of work multiplying the Timesing & Dimensions.

Description:- In this field, we describe the work of the BOQ prior to the measurements we enter.

Completing the TDS is the first step when preparing a proper BOQ. because we can edit and adjust quantities easily if we maintain a TDS sheet. Not only that but also we can justify how we estimate the quantities to a senior or someone who's responsible for checking the quantities.

If a part of the drawing need to be changed, we need to estimate the quantities again. Even the changes like this can easily be re-estimated easily, quickly and accurately by using a TDS sheet. Once we complete the TDS sheet next step is preparing the abstract sheet which I am going to explain in my future articles.

How to Allocate Money for Construction work

When allocating money for a construction project, we should know what could be the approximate project budject and provisions for each work. The amount of these provisions will vary depending on the specification of the materials and technology use. Below the rough figure about the provision of money for a project based on BOQ itemes. This could be changed easily so consider these percentages as only to have an approximate idea and not the exact values.

• Exacavation -  2.5 - 4.5 %

• Concrete Work (Including R/F & Formwork)        -  23 - 27 %

• Masonry Work                                                       -  11 - 13 %

• Floor/ Wall/ Celing/ Roof Finishes                        -  25 - 30 %

• Doors & Windows Installation                               - 14 - 18 %

• Plumbing & Sanitary Installation                           -  4 - 6 %

• Electrical Installation                                             - 2.5 - 3.5 %

• Drainage System                                                   - 1 - 2%
• 
  

For small projects Labour cost will be 30-35% from the total project cost while Material cost take upto 65-70%  from the total project cost.

Cantilever Beams & Bending Moment

Cantilever Beams

Cantilever beam is a type of beams that one end of the beam is fixed and the other end is completely free. Therefore, the fixed end should be able to bear the rest of the load of the beam itself. In that case, supported end must be stiff and rigidly fixed. Though this is not a structurally proficient method, it is being used   In order to achieve some purposes in certain  construction. Ex: improve the space requirement & quality, the aesthetic of the buildings, etc.

          

Maximum Bending Moment

I am going to explain the maximum bending moment theory with an example situation. Assume that the part of a balcony design is supported by cantilever beam that is carrying a “w” uniformly distributed load per unit. Length of the cantilever beam is “L”.

Now we will consider a point on the beam (c) where the vertical displacement is “x” from the free end of the beam (B).

Let’s take the momentum force (M) around the point “C” considering the section “CB”.

Hence,  M_max where the x = L

M_max = -wL²/2

You can draw the graph for the maximum bending moment.  We can consider  the above equation as y = mx2

where, y = M, m = -(w/2), and x = L

Application of Differentiation for Construction Work

This section of mathematics helps us to improve the construction especially when we design a particular building, road, service, etc. In fact, this knowledge will be beneficial when you analyse the most constructive method for a particular work that leads toward a lesser cost while producing the most effective outcome. This form of application can be used not only in the construction field but also in any type of productions.

Now let’s see how this knowledge is applied when designing something cost effective. For an example, If we assume that we need to construct a water supply plant to distribute water for 3 cities, and the 3 cities are A, B & C, when cities are located as follows where distance between AB and AC are exactly the same. We need to identify the most suitable location to construct it which has the shortest lengths of supply lines.

From the geometry of these 3 cities, we can decide the proposed plant should be somewhere inside the triangle and vertically going through city “A” and Midpoint of BC. We will name the location of the plant as “D”.

Now measure the required lengths of supply line regarding the above figure.

Require lengths of supply line (L) = z + 2y

Let’s convert this equation as follows.

To get the shortest length for supply line, it is required dL/dx to be zero.

Hence, the water supply plant (D) should be located on the vertical line from the city "A" by a distance of (16 - x) km.

Therefore, plant should be placed by a distance of 12.54 km from city "A".

Density, Weight & Specific Gravity

Density is described as the heaviness/ mass of an object for a unit volume. It is directly proportion to its weight. The weight of an object can be changed due to the gravity, but mass does not change. For an example if you measure the weight of a same object on the earth and moon you will have different readings from the both ends. 

Gravity of the earth = 9.78 m/s2
Gravity of the moon = 1.622 m/s2

If we apply newton's third law for the situations, F=ma, here "m" is a constant as we use the same object.

Weight of the object on the earth = m * 9.78

Weight of the object on the moon = m* 1.622

From the above equations,  you can understand that how the weight is being changed.

Density is calculated by bellow equation.

m = v.d  (m = mass/ v = volume/ d = density)

hence, d = m/v (kg/m3)

Therefore, weight can be calculated for a particular material by bellow equation.

Weight = (volume of material) x (Density) x (Gravity)
             
Specific gravity of a material = d.g  (g=gravity)

Therefore; Weight = (volume) x (specific gravity)

You can find the specific gravity of few of the materials bellow.

        Aluminium Foil   = 2700 - 2750
        Beryllium             = 1840
        Brace                    = 8400 - 8730
        Cast Iron              = 6800 - 7800
        Copper                 = 8930
        Gold                     = 19320
        Iron                      = 7850
        Lead                     = 11340
        Magnesium          = 1738
        Mercury               = 13593
        Nickel                  = 8800 
        Platinum              = 21400
        Silver                   = 10490
        Tin                       = 7200
        Titanium              = 4500
        Tungsten              = 19600
        Uranium               = 18900
        Zinc                      = 7135

Example questions:

[1] Calculate the weight of a solid iron cylinder dim. of 0.25m and height of 3m. (Find the specific gravity of iron in the above table)

Volume of cylinder = (22/7) x (0.25)^2 x 3
                      
                                = say 0.6 m3

Weight of the cylinder = V. (specific gravity)

                                     = 0.6 x 7850

                                     = 4710 kg

How to Set a Rate for the Construction Work.

Rate Analysis for the Construction Work

Setting a rate for a particular building work is very important. Because the rate we give should be able to handle the total cost and overheads. Not only that but also that rate should be able to give the expected profit after completing the job. Therefore, it is necessary for us to do a method study (Work Study) of that particular work in order to determine the actual cost. 

Realisation of the scope work and construction method is the key to set the correct rate for a particular work. Otherwise, after the contract agreement, we can not change the agreed rate. The cost is two-way as the direct cost and indirect cost.

Direct Cost: 

The cost that directly affect the work. This would be the main cost for a particular work which is normally same for every site.  

1. Material
2. Labour
3. Plant & Equipment

Indirect Cost:

The cost that indirectly affect the work which depends on the site and it's location. Because with the location construction cost can be considerably changed.

1. Transport Cost
2. Accessibility
3. Material wastage
4. Safety
5. Food & Beverages
6. Water & Electricity
7. etc.

Analysis about above factors will make us come to a more accurate figure which covers the overall cost (Direct cost + Indirect Cost). After the realisation of all possible cost to be involved with the rate then only we are going to decide the profit that we expect from the work.  

Direct Cost = Material + Labour + Plant & Equipment

Indirect Cost = Transport + Accessibilty + Material wastage + Safety + etc.

Total Cost = Direct Cost + Indirect Cost

Rate for the Work = Total Cost + Total Cost x (X%)

X% = Expected profit percentage

Recommendations :- 

• First write a work breakdown
• Keep a Checklist for rates
• Refer similar site information  

How to Calculate the Required Number of Bricks in Brick Masonry Work

Total Area of a Unit = x.y

x = 450mm = 0.45m

y = 150mm = 0.15m

xy = 0.0675 m2

Total Area of Brick Per Unit

(x-20)(y-20) = 0.43 x 0.13 = 0.0559 m2

Let's find the Nr of units per 1m2

Nr of Units = (1/0.0675) = 14.8

Hence, Nr of Bricks Per 1m2

= 14.8 x 4

= 59.2 Nr

We can Calculate Required amount of mortar per 1m2 by below equation.

Requires Amount of Mortar = 14.8 x 0.1025 x (0.0675-0.0559)

                                              = 1.517 x 0.012

                         

                                              = 0.02 m3 

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