Environmental impact of modern agriculture by Dr.S.Charles Ruskin Kumar

 Stress and Strain

Stress

Stress is the ratio of applied force F to a cross section area - defined as "force per unit area".

                                                          

• 
  tensile stress - stress that tends to stretch or lengthen the material - acts normal to the stressed area
• compressive stress - stress that tends to compress or shorten the material - acts normal to the stressed area
• shearing stress - stress that tends to shear the material - acts in plane to the stressed area at right-angles to compressive or tensile stress

Tensile or Compressive Stress - Normal Stress

Tensile or compressive stress normal to the plane is usually denoted "normal stress" or "direct stress" and can be expressed as

σ = F_n / A                                    

where

σ = normal stress (Pa (N/m²), psi (lb_f/in²))

F_n = normal force acting perpendicular to the area (N, lb_f)

A = area (m², in²)

• a kip is an imperial unit of force - it equals 1000 lb_f (pounds-force)
• 1 kip = 4448.2216 Newtons (N) = 4.4482216 kilo Newtons (kN)

A normal force acts perpendicular to area and is developed whenever external loads tends to push or pull the two segments of a body.

Shear Stress

Stress parallel to a plane is usually denoted as "shear stress" and can be expressed as

τ = F_p / A                              

where

τ = shear stress (Pa (N/m²), psi (lb_f/in²))

F_p = shear force in the plane of the area (N, lb_f)

A = area (m², in²)

A shear force lies in the plane of an area and is developed when external loads tend to cause the two segments of a body to slide over one another.

Strain (Deformation)

Strain is defined as "deformation of a solid due to stress". 

• Normal strain - elongation or contraction of a line segment
• Shear strain - change in angle between two line segments originally perpendicular

Normal strain and can be expressed as

ε = dl / l_o

   = σ / E                             

where

dl = change of length (m, in)

l_o = initial length (m, in)

ε = strain - unit-less

E = Youngs Modulus (Modulus of Elasticity) (Pa , (N/m²), psi (lb_f/in²))

• Young's modulus can be used to predict the elongation or compression of an object when exposed to a force

Note that strain is a dimensionless unit since it is the ratio of two lengths. But it also common practice to state it as the ratio of two length units - like m/m or in/in.

• Poisson's ratio is the ratio of relative contraction strain

Strain Energy

Stressing an object stores energy in it. For an axial load the energy stored can be expressed as

U = 1/2 F_n dl

where

U = deformation energy (J (N m), ft lb)

 

Deflection 

Deflection is the degree to which a structural element is displaced under a load (due to its deformation). It may refer to an angle or a distance. The deflection distance of a member under a load can be calculated by integrating the function that mathematically describes the slope of the deflected shape of the member under that load. Standard formulas exist for the deflection of common beam configurations and load cases at discrete locations. Otherwise methods such as virtual work, direct integration, Castigliano's method, Macaulay's method or the direct stiffness method are used. The deflection of beam elements is usually calculated on the basis of the Euler–Bernoulli beam equation while that of a plate or shell element is calculated using plate or shell theory. An example of the use of deflection in this context is in building construction. Architects and engineers select materials for various applications.

The deformation of a beam

The deformation of a beam is usually expressed in terms of its deflection from its original unloaded position. The deflection is measured from the original neutral surface of the beam to the neutral surface of the deformed beam

Thermal Stress and strain

Thermal stress is mechanical stress created by any change in temperature of a material. These stresses can lead to fracturing or plastic deformation depending on the other variables of heating, which include material types and constraints.[1] Temperature gradients, thermal expansion or contraction and thermal shocks are things that can lead to thermal stress. This type of stress is highly dependent on the thermal expansion coefficient which varies from material to material. In general, the greater the temperature change, the higher the level of stress that can occur. Thermal shock can result from a rapid change in temperature, resulting in cracking or shattering.

 

Thermal strains are strains that develop when a material is heated or cooled, they can be the bane of an engineer’s existence if they are not considered Materials that fit perfectly at one temperature can rupture or fall out when their environmental temperature changes.

TRUSSES

 

Trusses are structures made of up slender members, connected at joints which can be approximated to pinned connections. It is typically assumed that loads are applied to the joints of the truss, not directly to the members. Because of this, the members only carry axial forces - they do not carry bending moments. The internal force in each member is constant, and a member can be either in tension or in compression. It is important for engineers to be able to determine the axial force in the members of a truss, so that they can be designed appropriately. In this video I cover the two main methods for doing this, which are the Method of Joints and the Method of Sections. The Method of Joints involves applying the equilibrium equations to solve the internal forces acting on every joint within the truss. The Method of Sections involves creating an imaginary cut through the members of interest, and applying the equilibrium equations to the external and internal forces.

BUCKLING IN TRUSSES

A vision towards sustainable concrete prepared by Mr. G.Jein Jenish 

Concrete is the most used man-made material on earth. It forms the foundations of cities and connects communities. Without it, many of the elements of modern life we take for granted today wouldn’t be possible – safe buildings and homes, roads, tunnels and bridges, clean water, and clean energy. Concrete will also play a vital role in providing solutions to the challenges of the future and in building a sustainable world of tomorrow. Concrete has amazing sustainability benefits and we are working hard to make it even more sustainable.

Three-phase soil system

Three-phase soil system Prepared by Mr.Bright Winsley

Soil is a three-phase system consisting of solid particles (called soil grains), water, and air. The void space between the soil grains is filled partly with water and partly with air. However, if we take a dry soil mass, the voids are filled with air only. In the case of perfectly saturated soil, the voids are filled completely with water.

  

 

wind rose diagram

A wind rose diagram is a tool which graphically displays wind speed and wind direction at a particular location over a period of time. The diagrams normally comprises of 8, 16 or 32 radiating spokes, which represent wind directions in terms of the cardinal wind directions (North East South West) and their intermediate directions. Meteorologist use wind rose diagrams to summarise the distribution of wind speed and direction over a defined observation period. Data is taken from a weather station, which should be a near as possible to your project /site.

What do the Spokes Represent?

Each ‘Spoke’ shows:

1. How often the wind blows from each direction
2. How often the wind blows within each pre-defined wind speed range (bins). This is shown by the colour bands on each spoke.

A wind rose diagram uses a polar coordinate system, whereby data is plotted a certain distance away from the origin at an angle relative to north.

It is possible to create these plots using costly purpose-made software or, alternatively, very basic wind rose diagrams can be made using Microsoft Excel. Wind Rose Excel also provides 2 paid options:

1. WRE Web App – allows users to fetch data from 30,000 different weather stations and create wind rose diagrams within a web application.
2. WRE v1.7 – allow users to copy their own data into a macro-enabled excel workbook in order to produce wind rose diagrams.

 

Interpreting an Example Wind Rose Diagram

 

In Diagram 1 the westerly spoke and its colour bands provides the following information:

• The wind blows from the west (a “westerly”) 12% of the time at location x
• Westerly wind speed distribution for location x:
• 1% of total time the wind blows at 0-2 knots from the west
• 1% of total time the wind blows at 2-3 knots from the west
• 1.5% of total time the wind blows at 4-6 knots from the west
• 3.5% of total time the wind blows at 7-10 knots from the west
• 3% of total time the wind blows at 11-66 knots from the west
• 1% of total time the wind blows at 17-22 knots from the west
• 1% of total time the wind blows at >23 knots from the west

What is Possible using Excel?

 

PREFABRICATED STRUCTURES

Prefabricated construction is the practice of assembling a variety of components of a structure at a manufacturing site and transporting those sub-assemblies to the location of the construction jobsite. Prefabricated construction is sometimes thought of as a low-end and mass produced mode of construction. In reality however, it is quite the opposite. Prefabricated construction is becoming more common, improving in quality and has become available in a variety of budgets. Despite the perception of prefabrication, there are numerous benefits to this type of construction. This article assesses the advantages that prefabricated construction presents for both businesses and customers.

 

Eco-Friendly

Modular construction is often commended for energy efficiency and sustainable construction. Traditional construction methods require extra materials that lead to increased waste. However, since prefabricated sub-assemblies are constructed in a factory, extra materials can be recycled in-house. This is a considerable improvement over sending waste directly to a landfill from a traditional construction site. Also, the controlled environment of a factory allows for more accurate construction, tighter joints and better air filtration, which in turn allows for better wall insulation and an increase in energy efficiency.

Financial Savings

One of the greatest advantages of prefabricated construction would be financial savings. Although the perception of custom-made pieces may seem expensive, with prefabricated or modular construction, this is not the case. Modular construction targets all budgets and price points, creating an affordable option. Prefabrication manufacturers often receive bulk discounts from material suppliers which then trickles down to the cost of a construction project. Modular construction also sidesteps the possibility of unreliable contractors and unproductive staff. Additionally, the reduction in construction time can significantly save on construction financing costs.

Flexibility

Modular construction can be easily be disassembled and relocated to different sites. This significantly reduces the demand for raw materials, minimizes expended energy and decreases time overall. Also, modular construction allows for flexibility in the design of the structure allowing for a limitless number of opportunities. Since prefabricated construction units can be used in different spaces, its neutral aesthetics is able to blend in with almost any building type.

Consistent Quality

Since prefabricated construction occurs in a controlled manufacturing environment and follows specified standards, the sub-assemblies of the structure will be built to a uniform quality. Construction site-built structures are dependent upon varying skill levels and the schedules of independent contractors. These all contribute to the craftsmanship and overall quality of given structure. With prefabrication, each sub-assembly is built by an experienced crew in a weather-resistant factory, with multiple quality checks throughout the entire process. Some components of the building are constructed using precise machine equipment to ensure conformity to building code.

Reduced Site Disruption

Since many components of a building are completed in the factory, there is significantly less truck traffic, equipment and material suppliers around the final construction site. This limits the disruption of traditional jobsites that suffer from noise, pollution, waste and other common irritants. This streamlined approach to construction provides a far more efficient atmosphere for productivity, and eliminates unnecessary distractions and interference that are typical of construction sites.

Shorter Construction Time

Portable construction takes significantly less time to build than on-site construction. In many instances, prefabrication takes less than half the time when compared to traditional construction. This is due to better upfront planning, elimination of on-site weather factors, subcontractor scheduling delays and quicker fabrication as multiple pieces can be constructed simultaneously. Shorter construction times allows construction companies to take on multiple projects at once, allowing businesses to grow rather than putting all their focus and resources on one or a few projects at a time.

Safety

Since sub-assemblies are created in a factory-controlled environment utilizing dry materials, there is less risk for problems associated with moisture, environmental hazards and dirt. This ensures that those on the construction site, as well as a project’s eventual tenants are less likely to be exposed to weather-related health risks. Also, an indoor construction environment presents considerably fewer risks for accidents and other liabilities. There are strict factory processes and procedures that protect the worker from on-the-job injury. At a construction site, although safety is of utmost importance, workers are subjected to weather-related conditions, changing ground conditions, wind and other crew members who are at the site.

Final Thoughts

With the continued popularity of prefabricated construction, it is likely that it will only continue to grow in popularity. Customers who choose this option are able to enjoy a high quality, quicker, cost-effective, and eco-friendly construction method. Furthermore, construction companies may soon increase their investment in modular construction processes, benefiting both their business and customer relationships. Prefabricated construction is proving to be an extremely viable option, and as manufacturing technology continues to improve, expect to see its benefits and advantages rise in the future.