Civil Engineering

Importance of Site Investigation

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Some types of rock/ sand

Importance of soil investigation in civil engineering

Civil engineering works have some form of foundation which is supported by the ground. The interaction between a civil engineering structure and the ground that holds it is complex. Hence it is appropriate that proper soil study and investigation is carried out before structure is built in it.

It is standard practice to examine any soil on which a structure is intended to be erected in order to determine the following:

  • The suitability of the soil site for the proposed work.
  • Adequate and economic foundation design.
  • Difficulties that may arise during construction.
  • Situations that may occur after construction.

Rock types

Rock types can be classified by their method of excavation. That is, whether blasting is required, by load bearing or other physical properties.

From a civil engineer’s point of view, A rock is a solid mass composed of soil material in a very stable position of which it’s removal is only possible after blasting, or breaking by compressed air and hydraulic tools or by breaking tools such a wedges or sledge hammer.

Rocks can be placed into 3 basic categories, the are:

Igneous, sedimentary and metamorphic.

Igneous rocks include basalt and granite. They are formed by the solidification of molten material from the hot lower levels of the earth crust which have ascended towards the surface. They have very high bearing capacities about 3 times that of sedimentary rocks and 40 times that of alluvial clays and sand.

Sedimentary rocks includes, Limestone and sandstone.They were formed by stratification and cementation of earth materials over time.Their strength depends on properties such as angle of stratification and cementation as well as behaviour under wet conditions.

Metamorphic rocks are any sedimentary or igneous rock deposits which after consolidation have become changed by heat and pressure. Examples of metamorphic rocks are gneisses, slates, schists.

The most suitable type of  rock for civil engineering  foundation work is the igneous rock. Sedimentary rocks have lower  load bearing capacity due to the presence of soft clay material in their deposits. However, the load bearing capacity of all types of rock is greatly reduced as a result of weathering and earth movements.

Soil types

Types of soil includes;

  • Residual soil ( too soil)
  • Detrital sediments ( sands, gravel, slits)
  • Organic deposits (peat)
  • Calcareous deposits ( shell, coral)
  • Uncemented volcanic dust.

Soil types are identified by;

  • Size and nature of soil particles
  • Density and structural properties

You can download the table of Field Identification and Description of Soils. (BS 5930:2015) HERE

The table can be found in page 110 of BS 5930: 2015.

8 reasons to build your own PC

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PC case showing components

Buy the exact parts you need to build your PC. When shopping for pre-built PCs in the market, finding the one that exactly suits you can be very hard.

Buying the PC components yourself and putting them together to make your PC is usually cheaper than a pre-built one of the same kind. You can also take advantage of deals when shopping for PC components.

You will be satisfied that you are really getting what you need for your business.

Building your computer yourself will help you understand how your PC works and rightly troubleshoot when necessary.

If you are really committed to building your PC you can spread the cost. That is, buying the components one by one until you get everything needed to build. You don’t have to borrow money.

Many prebuilt PCs come with software/Operating systems you don’t need or prefer. When you build your own PC, you install the software and the preferred operating system you need.

Better cooling for your PC is easily achieved by the careful choice of a PC case. You have a variety of PC cases to choose from. Some cases even come with multiple cooling fans That will better cool the processors making your PC work efficiently and last longer.

Its fun and a worthwhile experience when you build your own PC.

How to Calculate Design Load of a Concrete Slab (factored)

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In reinforced concrete design , there is what is called the factor of safety. The factor of safety is multiplied by the calculated load of the structural element. This is done to reduce the possibility of the structural element failing under its actual, or expected loadings.

When the factor of safety has been applied to the calculated load of a structural element, it is called design load. Note that Factored load is also the same as design load.

Determining the Design (factored) load of a Concrete Slab.

The formula for calculating the design load of a Concrete Slab is:

1.4gk + 1.6qk.

Where:

gk= dead load

qk= live load

1.4= factor of safety applied to dead load

1.6= factor of safety applied to live load.

Dead load is the same as the weight of the concrete slab element. 

Live load is the movable or variable load the slab will carry such as people, furniture,machinery and so on. 

The unit of the design load will be in kN/m².

The weight of concrete used in reinforced concrete design calculation is 24kN/m³

Example 1 calculating design load of slab

concrete slab panel

Let’s say a concrete slab panel is to be designed for a private dwelling. It  has a depth ( thickness) of 0.2m, a length of 5m, and a width of 3m as shown above, the design load can be calculated as follows:

The dead load of the slab panel is the weight of concrete multiplied by the slab thickness.

That is,

24kN/m³ × 0.2m = 4.8kN/m²

Therefore gk = 4.8kN/m²

Live loads for buildings are standardized. In page 2 of BS 6399 part 1, the live load for private dwellings is 1.5kN/m² (shown below)

Table minimum imposed floor loads.BS 6399 part 1

Therefore qk= 1.5kN/m²

Design load= 1.4gk+1.6qk=( 1.4×4.8kN/m²) + (1.6×1.5kN/m²) = 6.72kN/m² + 2.4kN/m²

=9.12kN/m²

Example 2. calculating design load of slab

Looking at part of a floor plan shown below, we will be calculating the design load for the floor plan labelled P8 as shown.Take live load for private dwellings as 1.5kN/m².

Part of general floor arrangement plan of a proposed building

Solution

The depth of the slab panel is 150mm or 0.15m

We know that the formula for  design load of slab panel is  1.4gk + 1.6qk and weight of concrete is 24kN/m³

Dead load, gk, = weight of concrete multiplied by panel thickness= 24kN/m³ × 0.15m = 3.6kN/m²

Live load , qk=1.5kN/m². (page 2 of BS 6399 part 1)

Design load is 1.4gk + 1.6qk=

(1.4×3.6kN/m²)+(1.6×1.5kN/m²)= 7.44kN/m²

Slab Design load is used for the calculation of the amount of steel reinforcement required for the slab panel.

How to calculate unfactored dead concrete slab load

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Slab panel

A slab in terms of its dimensions consists of a thickness(depth), length and width. Understanding this concept will correctly Enable you to calculate and apply slab loading.

In reinforced concrete design, the weight of concrete is usually taken as 24kN/m³. So let’s look at an example.

A reinforced concrete slab is to be constructed having a length of 5m, width of 3m and depth of 200mm. The slab loading can be calculated as follows.

Calculating slab load in kN/m²

Note that 200mm = 0.2m..

..and weight of concrete is 24kN/m³

In most design calculations the unit of the slab load is in kN/m². In this case the slab load is calculated by multiplying 24kN/m³ by thickness (depth) of slab which is 0.2m

So 24kN/m³ × 0.2m = 4.8kN/m²

(4.8kN/m² is the unfactored dead load of the slab)

Calculating slab load in kN

To represent the slab load in kN, just multiply the unit weight concrete which is 24kN/m³ by the volume of the slab. 

Note that the volume of the slab is length x width x depth

So 24kN/m³ × 0.2m × 5m × 3m = 72kN

In practice, you will be calculating slab loading from structural plan or floor panel arrangement. A typical structural plan is shown below.

Structural plan

The slab panels are label P and a number. Let’s take a look at one of the slab panels, panel P8.

The panel’s thickness is 150mm or 0.15m. Also it is a 2 way slab. You can also easily calculate the length and width of the slab from the dimensions shown.

To calculate the unfactored dead load of the slab in kN/m², ( which is what we have been doing so far), just multiply 24kN/m³ by the slab thickness which is 0.15m;

24kN/m³ × 0.15m = 3.6kN/m²

One and Two Way Slabs Simply Explained

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One Way Slab

In reinforced concrete design, a slab is said to be one way if the length of the longer side divided by the length of the shorter side is equal to or greater than 2. 

With reference to the diagram of the slab shown below, If the length of the longer side (Ly) = 5m, and the shorter side (Lx) is 2.5m then 

Ly/Lx = 5m/2.5m = 2

On structural plans, the symbol used to identify a one way slab panel is shown in the previous diagram (symbol that the arrow points at).

In a one way slab design, the main reinforcement steel spans along the shorter side of the slab, which is also the span of the slab

In a one way slab design, only the two long supporting beams along the the long side of the slab  is assumed to carry the slab load equally between them. The beams along the shorter side do not carry any slab load.

For instance with reference to this diagram of a one way slab, beam 1 carries half of the slab load and beam 2 takes the remaining half, none of the slab load is carried by beams 3&4. This makes beam 1&2 the critical beams. Beams 3&4 will not be carrying any slab load, but may carry wall load and part of roof load. 

Two Way Slab

If the length of the longer side divided by that of the shorter side is less than 2, the slab should be designed as a two way.

With reference to the diagram shown, the length of the longer side, Ly, =6, and that of the shorter side Lx = 4.75. Therefore, Ly / Lx = 6 / 4.75 = 1.26. 1.26 is less than 2 hence the slab should be designed as 2 way.

The symbol of a two way slab is as shown above (the symbol that the arrow points at);

In a 2 way slab design, the main steel reinforcement spans both directions.

All 4 supporting beams carry some part of the slab load but the beams along the longer side carry more of the slab load than the beams along the shorter side.

The loading on beams for a 2 way slab is as shown. Note that the beams 1& 2 carry more slab load than beams 3&4

How to determine the realistic cost of workmanship for a building construction work

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Sometimes paying high cost for workmanship doesn’t usually result in a good quality job. And too low a cost for workmanship can be an excuse for a shoddy job. You don’t also want to feel cheated by overpaying for workmanship.

There are standard rates of pay for workmanship in the building industry. It is determined by economic forces and so the rate changes from time to time.

Here are tips to help you get a good economy rate and quality workmanship.

You can ask a building contractor or someone who usually gets building construction jobs on  a regular basis. 

You can also look for or place an advert for professionals to come and access the work to be done and give their quotations. Make sure you ask each one of  them questions on areas of the work you need more clarity. Their individual quotations and how satisfied you are on how they will undertake the job will enable you to choose economically, the right professional for the job.

Beware of middle men, they pose as professionals but they are not. A middle man may charge incredibly higher fees so that if he gets the job, he passes it on to a professional who he pays the normal rates or even much lower. 

 Also, if you know a friend or someone who has done a similar project , you can ask him to get you the professional he or she used.