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Explain Negative Super elevation with neat sketch and find the speed on main curve if a 50 curve diverges from a 30 main curve on a BG yard assuming the speed of branch line is 35 kmph.
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  • Negative Superelevation Figure,

Negative Superelevation

  • When main line is on a curve and a branch line takes off from a main line with a curve which is in contrary flexure to the main line, the outer rail of the branch line instead of being raised, has to remain lower than the inner rail upto a certain distance from take off point.
  • The amount by which outer rail of branch line is lower than the inner rail is called negative superelevation.

    Problem:-

  • Vmax,BT=35kmph

  • Theoretical Cant, eth =GV2max127R

  • ethBT =1.676×352127×17205=4.7 cm

Since,

eth,BT=eact,BT+CD

  • 4.7 cm= eact, BT +7.6 cm eact, BT =2.9 cm
  • As, For negative Superelevation,

  • eact, MT= - eact, BT=2.9 cm

th,MT = eact, MT+C D e_{th,MT}=2.9+7.6=10.5 \mathrm{~cm}

  • eth, M T=\frac{G V_{\operatorname{max}}^{2}}{127 R}

\Rightarrow \quad 0.105=\frac{1.676 \times V_{\text {max,MT }}^{2}}{127 \times \frac{1720}{3}} V_{\max ,MT}=67.54 \mathrm{kmph}

Check, As per martin's formula,

\begin{aligned} V_{\text {max, } M T} &=4.35 \sqrt{R-67} \\ &=4.35 \sqrt{\frac{1720}{3}-67} \\ &=97.88 \mathrm{kmph}\gt67.54 \mathrm{kmph} \\ (OK\mathrm) \end{aligned}

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