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:8. Four steel bars jointly support a mass of 15 Mg as shown below. Each bar has a cross sectional area of 600 mm. Find the load carried by each bar after a temperature rise of 50°C. assume a = 11.7 x 10°C and E = 200 GPa[PA-Po = 21.02 kN; P = Pc = 66.63 kN) Figure P-276 15 MG
There are different grades and thicknesses of bars and based on the application and construction criticality, an engineer chooses the right one. Bars are generally laid in a grip pattern with certain spacings of the grid. The spacing of the grid is very crucial in deciding the strength of the overall construction. Bars with variable thicknesses provide different strengths. The ridges provided on the periphery of the bars are provided to improve the bonding between the concrete and the bar.
There are various types of reinforcement bars used, based on the applications, some of them are outlined below.
Mild steel bars are characterized by their circular-cross section and plain periphery, they are very easy to bend and shape. These bars are available in a variety of thicknesses ranging from 6 mm to 50 mm and are specially used as dowels in expansion joints, for contraction joints in roadways and runways, and for making column spirals.
These bars are not suitable for the construction of heavy structures such as bridges and heavy buildings due to their plain periphery, which provides a very poor bond between the concrete and the bar.
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There are generally three grades of mild steel bars, Grade I or Grade 60, Grade II or Grade 40, and medium tensile bars, designated as Grade 75.
The TMT bars have ribs, patterns, or lugs on their periphery which helps in securing a superior bond between the concrete and the bar. These bars eliminate the problems faced by mild steel bars. These bars are available in thickness ranging from 6 mm to 50 mm.
TMT bars are popularly used in reinforced concrete cement (RCC) works to provide superior strength. These bars are heat treated and provide high strength characteristics. Some of the properties of TMT bars are outlined below:
Epoxy-coated bars are similar to TMT bars in terms of strength and durability, but they are coated with epoxy resins which make them corrosion-resistant, which is 70 to 1,700 times more than ordinary TMT bars.
These bars are the most expensive. They provide 1,500 time more corrosion resistance than other bars. These bars are made of stainless steel having high chromium and vanadium content with little carbon. These are the best choice for most civil engineering projects.
These bars are known as black bars due to their high carbon content. They provide the best tensile strength to the concrete but are usually poor in providing resistance to corrosion.
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