Yield

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The yield point is the point on a stress–strain curve that indicates the limit of elastic behavior and the beginning of plastic behavior. Yielding means the start of breaking of fibers.

Yield strength or yield stress is the material property defined as the stress at which a material begins to deform plastically whereas yield point is the point where nonlinear (elastic + plastic) deformation begins. Prior to the yield point the material will deform elastically and will return to its original shape when the applied stress is removed. Once the yield point is passed, some fraction of the deformation will be permanent and non-reversible.

The yield point determines the limits of performance for mechanical components, since it represents the upper limit to forces that can be applied without permanent deformation. In structural engineering, this is a soft failure mode which does not normally cause catastrophic failure or ultimate failure unless it accelerates buckling.

Yield strength is the critical material property exploited by many fundamental techniques of material-working: to reshape material with pressure (such as forging, rolling, pressing, bending, extruding, or hydroforming), to separate material by cutting (such as machining) or shearing, and to join components rigidly with fasteners. Yield load can be taken as the load applied to the centre of a carriage spring to straighten its leaves.

The offset yield point (or proof stress) is the stress at which 0.2% plastic deformation occurs.

In the three-dimensional principal stresses ( sigma _{1},sigma _{2},sigma _{3}, an infinite number of yield points form together a yield surface.

It is often difficult to precisely define yielding due to the wide variety of stress–strain curves exhibited by real materials. In addition, there are several possible ways to define yielding:

True elastic limit

The lowest stress at which dislocations move. This definition is rarely used, since dislocations move at very low stresses, and detecting such movement is very difficult.

Proportionality limit

Up to this amount of stress, stress is proportional to strain (Hooke’s law), so the stress–strain graph is a straight line, and the gradient will be equal to the elastic modulus of the material.

Elastic limit (yield strength)

Beyond the elastic limit, permanent deformation will occur. The elastic limit is therefore the lowest stress point at which permanent deformation can be measured. This requires a manual load-unload procedure, and the accuracy is critically dependent on the equipment used and operator skill. For elastomers, such as rubber, the elastic limit is much larger than the proportionality limit. Also, precise strain measurements have shown that plastic strain begins at low stresses.

Yield point

The point in the stress–strain curve at which the curve levels off and plastic deformation begins to occur.

Offset yield point (proof stress)

When a yield point is not easily defined based on the shape of the stress–strain curve an offset yield point is arbitrarily defined. The value for this is commonly set at 0.1 or 0.2% plastic strain.The offset value is given as a subscript, e.g., Rp0.2=310 MPa.[6] High strength steel and aluminum alloys do not exhibit a yield point, so this offset yield point is used on these materials.

 Upper and lower yield points

Some metals, such as mild steel, reach an upper yield point before dropping rapidly to a lower yield point. The material response is linear up until the upper yield point, but the lower yield point is used in structural engineering as a conservative value. If a metal is only stressed to the upper yield point, and beyond, Lüders bands can develop.

 

 

 

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Stress

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In continuum mechanics, stress is a physical quantity that expresses the internal forces that neighbouring particles of a continuous material exert on each other, while strain is the measure of the deformation of the material. For example, when a solid vertical bar is supporting a weight, each particle in the bar pushes on the particles immediately below it. When a liquid is in a closed container under pressure, each particle gets pushed against by all the surrounding particles. The container walls and the pressure-inducing surface (such as a piston) push against them in (Newtonian) reaction. These macroscopic forces are actually the net result of a very large number of intermolecular forces and collisions between the particles in those molecules. Stress is frequently represented by a lowercase Greek letter sigma (σ).

Strain inside a material may arise by various mechanisms, such as stress as applied by external forces to the bulk material (like gravity) or to its surface (like contact forces, external pressure, or friction). Any strain (deformation) of a solid material generates an internal elastic stress, analogous to the reaction force of a spring, that tends to restore the material to its original non-deformed state. In liquids and gases, only deformations that change the volume generate persistent elastic stress. However, if the deformation is gradually changing with time, even in fluids there will usually be some viscous stress, opposing that change. Elastic and viscous stresses are usually combined under the name mechanical stress.

Significant stress may exist even when deformation is negligible or non-existent (a common assumption when modeling the flow of water). Stress may exist in the absence of external forces; such built-in stress is important, for example, in prestressed concrete and tempered glass. Stress may also be imposed on a material without the application of net forces, for example by changes in temperature or chemical composition, or by external electromagnetic fields (as in piezoelectric and magnetostrictive materials).

The relation between mechanical stress, deformation, and the rate of change of deformation can be quite complicated, although a linear approximation may be adequate in practice if the quantities are small enough. Stress that exceeds certain strength limits of the material will result in permanent deformation (such as plastic flow, fracture, cavitation) or even change its crystal structure and chemical composition.

In some branches of engineering, the term stress is occasionally used in a looser sense as a synonym of “internal force”. For example, in the analysis of trusses, it may refer to the total traction or compression force acting on a beam, rather than the force divided by the area of its cross-section.

Free body diagram

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In physics and engineering, a free body diagram (force diagram, or FBD) is a graphical illustration used to visualize the applied forces, movements, and resulting reactions on a body in a given condition. They depict a body or connected bodies with all of the applied forces and moments, as well as reactions, that act on that/those body. The body may consist of multiple internal members, for example, a truss, or be a compact body such as a beam. A series of free bodies and other diagrams may be necessary to solve complex problems.

Free body diagrams are used to visualize the forces and moments applied to a body and calculate the resulting reactions, in many types of mechanics problems. Most free body diagrams are used both to determine the loading of individual structural components as well as calculating internal forces within the structure in almost all engineering disciplines from Biomechanics to Structural. In the educational environment, learning to draw a free body diagram is an important step in understanding certain topics in physics, such as statics, dynamics and other forms of classical mechanics.

Construction law

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Construction law is a branch of law that deals with matters relating to building construction, engineering and related fields. It is in essence an amalgam of contract law, commercial law, planning law, employment law and tort. Construction law covers a wide range of legal issues including contract, negligence, bonds and bonding, guarantees and sureties, liens and other security interests, tendering, construction claims, and related consultancy contracts. Construction law affects many participants in the construction industry, including financial institutions, surveyors, architects, builders, engineers, construction workers, and planners.

Construction law builds upon general legal principles and methodologies and incorporates the regulatory framework (including security of payment, planning, environmental and building regulations); contract methodologies and selection (including traditional and alternative forms of contracting); subcontract issues; causes of action, and liability, arising in contract, negligence and on other grounds; insurance and performance security; dispute resolution and avoidance.

Construction law has evolved into a practice discipline in its own right, distinct from its traditional locations as a subpractice of project finance, real estate or corporate law. There are often strong links between construction law and energy law and oil and gas law.

Some of the major areas a construction lawyer covers are:

 

  • Alternative Dispute Resolutions
  • Arbitration
  • Dispute Review Boards (or other third party reviews)
  • Mediation
  • Structured negotiations
  • Bankruptcy issues for contractors, owners, suppliers, etc.
  • Bidding (tendering) disputes
  • Building and other permits
  • Building Information Modeling
  • Contract law
  • Change Orders (Variations)
  • Construction claims
  • Construction liens
  • Wage requirements (Davis-Bacon Act, etc)
  • Payment and Prompt payments acts
  • Extensions of time
  • Drafting construction contracts
  • Industry-standard construction contracts
  • Negotiating construction contracts
  • Negotiating a termination claim, whether for convenience or for default
  • Defective design or construction
  • Delays and acceleration
  • Employment Law including Immigration
  • Environmental matters in construction
  • False Claims Act(s)
  • Fire codes and regulations
  • Fulfilling regulations for non-discrimination or other social impact legislation
  • Insurances issues
  • Damage, liability
  • Indemnification
  • Surety Law (Payment and Performance Bonds)
  • Labor issues and strikes
  • Licensing construction professionals
  • OSHA, and other federal agencies
  • Overinspection
  • Project delivery systems, such as design-bid-build, Design-Build, Construction Manager (CM) at Risk or Agency CM
  • Provide defense to businesses facing administrative actions such as delisting (loss of bid listing)
  • Provide legal counsel
  • Public construction
  • Federal construction under FAR or other regulated procurements
  • State contracting procedures
  • State and local building codes
  • Sustainable construction, e.g. LEED
  • Litigation: trying construction cases in court
  • Violations, safety or other regulatory

 

 

 

Building regulations

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A building code or building regulations is a set of rules that specify the standards for constructed objects such as buildings and nonbuilding structures. Buildings must conform to the code to obtain planning permission, usually from a local council. The main purpose of building codes is to protect public health, safety and general welfare as they relate to the construction and occupancy of buildings and structures. The building code becomes law of a particular jurisdiction when formally enacted by the appropriate governmental or private authority.

Building codes are generally intended to be applied by architects, engineers, interior designers, constructors and regulators but are also used for various purposes by safety inspectors, environmental scientists, real estate developers, subcontractors, manufacturers of building products and materials, insurance companies, facility managers, tenants, and others. Codes regulate the design and construction of structures where adopted into law.

Examples of building codes began in ancient times. In the USA the main codes are the International Commercial or Residential Code [ICC/IRC], electrical codes and plumbing, mechanical codes. Fifty states and the District of Columbia have adopted the I-Codes at the state or jurisdictional level. In Canada, national model codes are published by the National Research Council of Canada.

The practice of developing, approving, and enforcing building codes varies considerably among nations. In some countries building codes are developed by the government agencies or quasi-governmental standards organizations and then enforced across the country by the central government. Such codes are known as the national building codes (in a sense they enjoy a mandatory nationwide application).

In other countries, where the power of regulating construction and fire safety is vested in local authorities, a system of model building codes is used. Model building codes have no legal status unless adopted or adapted by an authority having jurisdiction. The developers of model codes urge public authorities to reference model codes in their laws, ordinances, regulations, and administrative orders. When referenced in any of these legal instruments, a particular model code becomes law. This practice is known as adoption by reference. When an adopting authority decides to delete, add, or revise any portions of the model code adopted, it is usually required by the model code developer to follow a formal adoption procedure in which those modifications can be documented for legal purposes.

There are instances when some local jurisdictions choose to develop their own building codes. At some point in time all major cities in the United States had their own building codes. However, due to ever increasing complexity and cost of developing building regulations, virtually all municipalities in the country have chosen to adopt model codes instead. For example, in 2008 New York City abandoned its proprietary 1968 New York City Building Code in favor of a customized version of the International Building Code. The City of Chicago remains the only municipality in America that continues to use a building code the city developed on its own as part of the Municipal Code of Chicago.

In Europe, the Euro code is a pan-European building code that has superseded the older national building codes. Each country now has National Annexes to localize the contents of the Euro code.

Similarly, in India, each municipality and urban development authority has its own building code, which is mandatory for all construction within their jurisdiction. All these local building codes are variants of a National Building Code, which serves as model code proving guidelines for regulating building construction activity.

 

Brownfield land

 Image result for Brownfield LandBrownfield land is a term used in urban planning to describe any previously developed land that is not currently in use, whether contaminated or not or, in North America, more specifically to describe land previously used for industrial or commercial purposes with known or suspected pollution including soil contamination due to hazardous waste.

Generally, brownfield sites exist in a city’s or town’s industrial section, on locations with abandoned factories or commercial buildings, or other previously polluting operations like steel mills, refineries or landfills. Small brownfields also may be found in older residential neighborhoods, as for example dry cleaning establishments or gas stations produced high levels of subsurface contaminants.

Typical contaminants found on contaminated brownfield land include hydrocarbon spillages, solvents, pesticides, heavy metals such as lead (e.g., paints), tributyl tins, and asbestos. Old maps may assist in identifying areas to be tested.

Innovative remediation techniques used at distressed brownfields in recent years include in situ thermal remediation, bioremediation and in situ oxidation. Often, these strategies are used in conjunction with each other or with other remedial strategies such as soil vapor extraction. In this process, vapor from the soil phase is extracted from soils and treated, which has the effect of removing contaminants from the soils and groundwater beneath a site. Binders can be added to contaminated soil to prevent chemical leaching. Some brownfields with heavy metal contamination have even been cleaned up through an innovative approach called phytoremediation, which uses deep-rooted plants to soak up metals in soils into the plant structure as the plant grows. After they reach maturity, the plants – which now contain the heavy metal contaminants in their tissues – are removed and disposed of as hazardous waste.[citation needed]

Research is under way to see if some brownfields can be used to grow crops, specifically for the production of biofuels. Michigan State University, in collaboration with DaimlerChrysler and NextEnergy, has small plots of soybean, corn, canola, and switchgrass growing in a former industrial dump site in Oakland County, Michigan. The intent is to see if the plants can serve two purposes simultaneously: assist with phytoremediation, and contribute to the economical production of biodiesel and/or ethanol fuel.

The regeneration of brownfields in the United Kingdom and in other European countries has gained prominence due to Greenfield land restrictions as well as their potential to promote the urban renaissance. Development of brownfield sites also presents an opportunity to reduce the environmental impact on communities, and considerable assessments need to take place in order to evaluate the size of this opportunity.

Many contaminated brownfield sites sit unused for decades because the cost of cleaning them to safe standards is more than the land would be worth after redevelopment. However, redevelopment has become more common in the first decade of the 21st century, as developable land has become less available in highly populated areas, and brownfields contribute to environmental stigma which can delay redevelopment. Also, the methods of studying contaminated land have become more sophisticated and costly.

Some states and localities have spent considerable money assessing the contamination on local brownfield sites, to quantify the cleanup costs in an effort to move the redevelopment process forward. Therefore, federal and state programs have been developed to help developers interested in cleaning up brownfield sites and restoring them to practical uses.

In the process of cleaning contaminated brownfield sites, previously unknown underground storage tanks, buried drums or buried railroad tank cars containing wastes are sometimes encountered. Unexpected circumstances increase the cost for study and clean-up. As a result, the cleanup work may be delayed or stopped entirely. To avoid unexpected contamination and increased costs, many developers insist that a site be thoroughly investigated (via a Phase II Site Investigation or Remedial Investigation) prior to commencing remedial cleanup activities.

How we calculate of Sand, cement and aggregate of M20 ratio or other ratio

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Detailed analysis on M20  = 1:1.5:3 (Ratio)
As we know that  during concreting when we place wet concrete , it gets harden after certain standard time( 30 mins IST & 10hrs FST), considering same it had be decided upon by Civil design Engineers to take a factor of safety ranging from 1.54 to 1.57 to counter that shrinkage.
i.e volume of dry Concrete = 1.54 to 1.57 times Volume of wet concrete.
Now calculations is as follows for 1cum(assumed) of Concrete work
ratio Sum = 1+1.5+3=5.5
Shrinkage or safety Factor =1.57 (you can take 1.54 also)
So Total volume of wet concrete required is :- 1.57cum
Volume of broken stone Require = (3/5.5) x 1.57 = 0.856 m3
Volume of sand Require = (1.5/5.5) x 1.57 = 0.471 m3
Volume of cement = (1/5.5) x 1.57 = 0.285 m3
= 0.285 x1440 = 411 kg
For 1m3 of M20 (1:1.5:3)
Broken stone = 0.856 m3
Sand = 0.472 m3
Cement = 8.22 bag.
Some important conclusion from above
8 bag of Cement is required for 1cum of concrete