Dxgj Essay

Design of Metal Structures

Prof. S. R. Satish Kumar and Prof. A. R. Santha Kumar

7. three or more Factors of safety and cargo 7. several. 1 Elements of protection and Allowable deflections Elements of protection of conductors and ground wires The factor of safety ( f. to. s ) of a conductor ( or perhaps ground cable ) is definitely the ratio with the ultimate durability of the director ( or perhaps ground line ) for the load made under believed loading condition. Rule seventy six (1)(c) of the Indian Electricity Rules, 1956, stipulates as follows:

The minimal factor of safety intended for conductors will probably be two, based upon their best tensile strength. In addition , the conductor tension at 32oC with no external fill shall not go over the following percentages of the greatest tensile strength in the conductor:

Intial unloaded anxiety 35 percent Final unloaded tension 25 %

The secret does not identify the packing conditions that the lowest factor of safety will need to correspond. Generally, these packing conditions happen to be taken as the minimum heat and the optimum wind in the area concerned. However , meteorological data display that minimal temperature takes place during the winter when, generally speaking, weather can be not disrupted and dermatose and storms are unusual. It therefore appears that the possibility of the event of maximum wind challenges, which are connected with gales and stromy wind gusts and prevail for appreciable periods of hours at any given time, simultaneously with the time of incident of the lowest minimum temperatures is small , with the effect that the

Of india Institute of Technology Madras

Design of Steel Structures

Prof. S. L. Satish Kumar and Prof. A. L. Santha Kumar

conductors may be subjected almost never, if at all, to loading circumstances of minimum temperature and the maximum blowing wind.

However , zero no data are available for various combinations of temperatures and wind conditions, for the purpose of determining the most severe loading circumstances in various regions. The problem is as well complicated by the fact that the combination of temp and wind to produce the worst loading conditions differs with the size and materials of the conductor. Furthermore, it is found that in a number of situations the governing conditions is definitely the factor of safety essential under 'everyday' condition (or the average contion of 32oC, with a little or any wind to which the caudillo is put through for most in the time) as opposed to the factor of safety within the worst launching conditions because illustrated in Table 7. 9 Desk 7. on the lookout for Factors of safety underneath various conditions Al St Al Saint Al Street Al St 30/3. 00+7/3. 00 30/2. 59+7/2. 59 6/4. 72+7/1. 57 mm 30/3. 71+7/3. 71mm logistik Panther millimeter Wolf Doggie Panther seventy five kg/sqm 5-60 C 335m o

Conductor size Breeze pressure Temperature. range Period Factors of safety

seventy five kg/sqm 5-60 C 335m 2 . 66 4. 01

o

75 kg/sqm 5-60 C 245m 2 . twenty eight 4. 02

o

one hundred and fifty kg/sqm 5-60oC 300m 2 . 29 4. 00

Underneath the worst installment payments on your 76 launching condition Under everyday 4. 00 state

Factors of safety to towers The factors of safety implemented in the patterns have a great bearing around the cost of structures prove cost effective as well as safe and dependable.

Rule seventy six (1)(a) in the Indian Electric powered Rules, 1956, specifies this factors of safety, being adopted inside the design of steel transmission range towers:

American indian Institute of Technology Echarpe

Design of Metal Structures

Prof. S. L. Satish Kumar and Prof. A. Ur. Santha Kumar

1 . underneath normal conditions

2 . zero

2 . underneath broken-wire circumstances 1 . your five

It is interesting to assess this practice with that followed in the USSR. In the USSR, while for normal conditions the f. to. s. is 1 . five, that intended for the broken-wire condition is definitely 1 . two for suspension tower, and 1 . 33 for core towers. When it comes to transmission lines at 500kV and previously mentioned, in addition of the factors of safety, an effect condition is usually imposed. If the conductor fails, there is a abrupt impact on the tower occuring for zero. 4 to 0. six second. The effect factor is definitely assumed because 1 . three or more in the case of suspension tower with rigid clamps and...

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