PE2113-Chapter 4 - Force System Resultants

PE2113-Chapter 4 - Force System Resultants - Chapter 4...

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1 Chapter 4 – Force System Resultants
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2 Objectives To discuss the concept of the moment of a force and show how to calculate it in two and 3-dimensions To provide a method for finding the moment of a force about a specific axis To define the moment of a couple To present methods for determining the resultants of non-concurrent force systems To indicate how to reduce a simple distributed loading to a resultant force having a specified location
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3 Moment of a Force - Scalar Formulation The moment of a force about a point or axis provides a measure of the tendency of the force to cause a body to rotate about the point or axis On the right figure, the force tends to cause the pipe to turn about the z-
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4 Moment of a Force - Scalar Formulation The tendency of the force to cause a body to rotate about the point or axis is called a TORQUE, but most often it is called the MOMENT of a FORCE or simply the MOMENT ( M O ) z The moment axis (z) is perpendicular to x- y plane
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5 • In figure b on the right, force F z will not rotate the pipe about the z-axis. Instead it tends to rotate it about the x-axis. However, it may not be possible, but there is a tendency to rotate. In figure c, no moment is produced about point O. The magnitude of the moment M o = F *d and it is a vector d = moment arm or perpendicular distance from the axis at point O to the line of Moment of a Force - Scalar Formulation
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6 The direction of Mo will be specified by using the “RIGHT-HAND RULE” The fingers of the right hand are curled such that they follow the sense of rotation which would occur if the force could rotate about point O The thumb then points along the moment axis so that it gives the direction and sense of the moment vector which is upward and perpendicular to the shaded plane Moment of a Force - Scalar Formulation
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7 Resultant Moment of a System of Coplanar Forces The resultant moment M R O of the system of coplanar forces can be determined by simply adding the moments of all forces algebraically since all the moment vectors are collinear. + M R O = Σ F *d Sign convention Clockwise is taken as negative Counterclockwise is taken as positive
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8 Bending during tonguing (avoidable) Observe max TJ height (refer API RP7G) (tongue jaw) Back up with winch and snatch block if tight breakout Always use two tongs When making or breaking connections, the pull on the tong lines exerts a bending force on the pipe, at the top of the slips. If this force is excessive the pipe will bend, which is seriously bad news. It’s also totally avoidable. There are two cases; tongs at 90
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This note was uploaded on 09/26/2011 for the course PE 2113 taught by Professor Staff during the Fall '11 term at The University of Oklahoma.

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PE2113-Chapter 4 - Force System Resultants - Chapter 4...

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