# Highway Defect

**EXAMINE W****HY A MANHOLE COVER JUMPED OUT OF ITS CASTING**

**THE TIDDLY WINK EFFECT**

**Review of the Event**

**Tire rolling over properly seated manhole**

*(opens in YouTube window)*

**Tire rolling over unseated manhole cover**

*(opens in YouTube window)*

When the Kinetic Energy exceeds the Potential Energy of the manhole cover, the cover will jump/slide out of its casting.

**Kinetic Energy vs Potential Energy of Improperly Seated Manhole Cover** *(opens in YouTube window)*

After the MH cover has been given the initial rotation because of the tire rolling over it, it is free to continue to rotate.What is the limit of rotation and what is the height that one end of the MH cover can attain as it raises up from the casting?

Procedure: Convert linear velocity to angular velocity: **V _{f}^{2 }= V_{o}^{2 }+ 2 × g × h** Where

**h**= Height that the MH cover must reach to clear the casting.

**ω**

_{f}^{2}

**× r**

^{2}

**= ω**

_{o}^{2}

**× r**

^{2}

**+ 2 × α × r × h**Where

**ω**= Final angular velocity of the MH Cover = 0 (Vertical Direction)

_{f}**ω**= Initial angular velocity of rotation of the MH cover in rad/sec.

_{o}**r**= Radius of the MH cover in inches, and;

**ω**If we estimate that the tire rolls over a section of the manhole equal to the radius then the equation reduces to:

_{f }= ω_{o }+ α × t; α = ω_{f }× t**ω**Where

_{f }=2 × h_{÷}r_{÷}t**t**is the time for the tire to roll over a portion (chord), of the MH cover equivalent to a function of the radius.

Resulting graph:

After the MH cover has been given the initial rotation because of the tire rolling over it, it is free to continue to rotate. What is the limit of rotation and what is the height that one end of the MH cover can attain as it raises up from the casting? Procedure: Convert linear velocity to angular velocity:

**V _{f}^{2} = V_{o}^{2} + 2 × g × h**

Where **h** = Height that the MH cover must reach to clear the casting.

**ω _{f}^{2} × r^{2} = ω_{o}^{2} × r^{2} + 2 × α × r × h**

Where;

**ω _{f}** = Final angular velocity of the MH Cover = 0 (Vertical Direction)

**ω**= Initial angular velocity of rotation of the MH cover in rad/sec.

_{o}**r**= Radius of the MH cover in inches and;

**ω**

_{f }= ω_{o }+ α × t; α = ω_{f }× tIf we estimate that the tire rolls over a section of the manhole equal to the radius then, the equation reduces to:

**ω _{f }=2 × h _{÷} r _{÷} t**

Where t is the time for the tire to roll over the MH cover.

Last update: 08/24/2012