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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Rate Analysis for Brick Masonry

Analyzing the rate for brick masonry can easily be calculated by referring the use of material, labor and required tools for the work. Not only that but also the transport cost of materials and tools should be considered along the costing. To evaluate a more precise figure for these types of construction work are mainly influenced by the field experience rather than the theoretical knowledge.

Use of Material

The materials use for brick masonry work are;

       1.      Bricks

       2.      Cement

       3.      Sand

       4.      Water

 Bricks

There are different sizes of bricks available in the construction market. Generally, the most commonly used type of brick is the Engineering brick which is in the size of 215mm in length, 102.5mm in width and 65mm in height. The bricks using for masonry work should be kept in a water tub for few minutes and then store them in clean place till the skin of the bricks get dried. Washing out bricks in water help removing unwanted sand and dust from the surface of the bricks. When the bricks are too dry, it will absorb the water contained in the mortar which is not healthy for the strength of the mortar bond in masonry work.   

Mortar

Mortar is the mix of cement, sand and water. The ratios of mixing of these elements can result; different strengths of the bond with an appropriate workmanship. The manufacturers specification and guidelines given for the cement must be referred and execute it accordingly to obtain the maximum expected quality and the strength. The sand using for the mortar should be cleaned and should not include oil and mud in it. Because, if the sand is not clean, the formation of the bond of cement and sand with water will not be formed properly and will lead a weak bond with the bricks. The water that is used to mix the mortar should be portable water if not it restricts the mortar bond to be formed properly due to the mud, dust particles and dirt.

Rate Analysis 

Assume we have to construct a 10m long and 3m high brick wall using Engineering bricks with the stretcher bond and the thickness of the mortar bond to be 10mm. The ratio of mixing the cement and sand for the mortar is 1:5. Since, the transportation cost of materials and tools cost various with the location, we will not consider about that in this analysis. Note that water is available at the site. 
   

Stretcher Bond

Rate Analysis for 90m2

First, let us find the area of the brick masonry work contains 4 bricks. The height and width can be calculated as follows.
Height = 10mm + 65mm + 10mm + 65mm 
            = 150mm

Width  = 10mm + 215mm + 10mm + 215mm
            = 450mm

Area of the unit = Width x Height

                          = 150mm x 450mm

                          = 67500mm2

                          = 0.0675 m2

Therefore Nr of bricks per 1m2 = (1 m2  / 0.0675 m2) x 4Nos

                                                   = 14.82 x 4 Nos

                                                   = 14.82 x 4 Nos

                                                   = 59.23 Nos

Hence, the required amount of bricks = 90 x 59.23

                                                             = 5330.70 Nos

Add 5 % Wastage for Bricks               = 266.54 Nos

Total Required bricks say                     = 5597.00 Nos

Now let's find the volume of mortar required for the above work.

Volume of mortar in a unit = (0.0675m2 x 0.1025m) - (4 x 0.215m x 0.1025m x 0.065m)
                                            = 0.007 - 0.005 m3
                                            = 0.002 m3
Therefore total required volume of mortar for the above job = 0.002m3 x (90m2 / 0.0675m2)
                                      Total Required Volume of Mortar   = 2.67 m3

After finding the required volume of mortar, we can calculate the required amount of cement, sand and water for the job. How to calculate the cement and sand quantity in mortar is explained here.  

Required amount of sand per 1m3 of mortar = (1.66 x 5) / (1+5)

                                                                       = 8.3 / 6

                                                                       = 1.38 m3

Therefore, Total Sand required for the job    = 1.38 x 2.67 m3

                                                                       = 3.69 m3

Required amount of Cement per 1m3 of mortar = [(1.66 x 1) / (1+5)] / 0.0347

                                                                             =  7.97 bags (50kg)

Therefore, Total number of cement bags required = 7.97 x 1.38

                                                                                = 10.90

                                                                   Say       = 11 Cement Bags 

                                                           

Cost of Material

         Bricks = 5597 Nos @ Rs.13 = Rs. 72,761.00

         Cement = 11 Bag @ Rs.900 = Rs.   9,900.00

         Sand      = 3.69 m3 @ Rs. 3800 Rs. 14,022.00

Total Cost of Material = Rs.72,761.00 + Rs.9,900.00 + Rs.14,022.00

                                     = Rs. 96,683.00

Labor Requirement 

Assume that 1 Mason and 1 helper required 8 hours to construct a 10m2 area of the brick wall, then we can calculate the required amount of labor hours for the above job. 

Therefore required amount of Mason hours = (90 m2 / 10m2) x 8 Hrs

                                                                      = 72 Hrs

Required amount of unskilled/helper hours  = (90m2 / 10m2) x 8 Hrs

                                                                      = 72 Hrs

Labor Cost

Mason = 72hr x Rs.190/hr 

            = Rs.13,680.00

Helper = 72hr x Rs.140/hr

            = Rs.10,080.00

Total Cost of Labor =  Rs.13,680.00 + Rs.10,080.00

                                 = Rs.23,760.00

Assume Tools & Equipment Cost is 3% of total labor cost = Rs.712.80

Hence the Total Basic Cost of the above Job = Rs.96,683.00 + Rs.23,760.00 + Rs.712.80

                                                                        = Rs. 121,155.80

Rate for the above work without OH & Profit per 1m2 = Rs.121,155.80 / 90 m2

                                                            Rate per 1m2       = Rs.1346.18

                             

Note: These calculations are only applicable for brick walls in stretcher bond with the standard Engineering bricks.

CALCULATION OF CEMENT AND SAND QUANTITY IN MORTAR

CALCULATION OF CEMENT AND SAND  QUANTITY IN MORTAR

In the building construction, we use cement mortar for civil works from the foundation up to the roof top.

Ex: Rubble Masonry, Brick Masonry, Plastering, etc.

The proportion of mixing of cement and sand will vary depend on the application of the particular work. Therefore, contractors must know what should be the mixing ratio according to the BOQ and specifications. If not required quality and strength will not be there with construction work.

Now let's go for the quantity of cement and sand calculation in mortar for 1 Cu of dry volume.

Assume that for 1 Cu of dry volume required 1.33 Cu of cement and 1.33 Cu of sand of wet volume. Which means to create a 1 Cu of a dry mortar volume is required 1.66 Cu of a wet mortar volume.

Shall take the proportion of cement and sand is 1:X

Therefore required volume of sand can be calculated from bellow equation;

Sand Quantity in Cement Mortar

Required Cement bags (50kg) can be calculated from bellow equation. 

Cement Quantity in Cement mortar

Note: Units are should be in Cu

Example: 

1. Calculate the required amount of cement and sand for 3.2 Cu of mortar in 1:5 mix.

    

How to Select an appropriate Air-Conditioning System for a Building

Select an Appropriate  Air-Conditioning System for a Building 

When we choose an appropriate air-conditioning system for a building there are particular factors to be concerned of as follows.

• - Type of the Building

• - Economical Feasibility

• - Likelihood Pollution of Air in the Particular Building Space

• - Exact Covering Volume of Particular Spaces

• - Maximum Expected Number of People for the Particular Space

• -Maximum Expected heat can be generated in the Particular Space

• -Reliability of Repairing and Maintenance    

What is Air-Conditioning?

It is the process of cleaning the air around and maintain the temperature in a particular place. The air-conditioners used to make a very pleasant and comfortable atmosphere for the dwellings. It also provides a healthy environment for users.

Why We need Air-conditioning?

We all know climates are changed and people are struggling to work under these conditions. Imagine if we have to work under the temperature of 32-40 degrees of celsius? how it would have been feeling? It is really scary even to think about it. isn't it? So we all need a better air-conditioning system to survive under these conditions and work without any problem. Therefore, the answer is to keep a comfortable and healthy atmosphere inside than actual blistering climate outside.

Types of Air-Conditioning Systems

Mainly air-conditioning systems can be divided into two categories as follows;

1. Centralised air-conditioning
2. De-centralised air-conditioning

Concrete Mixing Designs and Material Requirement

Concrete Mixing Designs and Calculations for 1 Cu

Description	Unit	1:1 ½:3 (G25)	1:3:6 (G15)	1:2 ½:5	1:2:4 (G20)	1:1:3 (G30)
		Quantity	Quantity	Quantity	Quantity	Quantity
Cement (50kg Bags)	Nr	23	13	14	18	31
Sand	Cu	0.47	0.53	0.6	0.5	0.44
Metal	Cu	0.82	0.92	0.9	0.88	0.76
Hire of Mixer	Day	0.333	0.333	0.333	0.333	0.333
Water	Gal	150	110	100	120	200
Skilled Labourer	Day	0.333	0.333	0.333	0.333	0.333
Unskilled Labourer	Day	2	2	2	2	2
Total for 1Cu of Concrete

There are different types of concrete we use in construction depend on the strength we need to achieve in the particular application. In order to meet the required strength of the structure, it is necessary to change the proportion of mixing of concrete elements (cement, sand, metal and water). The above table shows the commonly used concrete mixing designs in construction. It also provides the Labour and Material requirement for each mixing design. With the given data collection in the table, we should be able to calculate the required amount of the material, labor and plant for each mixing design.