Lecture 4 part I

Lecture 4 part I - LECTURE 4 RIDIG BODIES EQUIVALENT...

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1 LECTURE 4 RIDIG BODIES: EQUIVALENT FORCE/MOMENT SYSTEMS PART I Contents: Introduction to nonconcurrent force systems Rigid bodies: equivalent force/moment systems Moments and their characteristics

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2 Introduction to nonconcurrent force systems In a body with negligible size and shape, the rotation of the particle is not important, nor of interest. The equilibrium of the particle is guaranteed by the vanishing of the resultant force R . This idealization of infinitely small size and shape usually neglects the rotation effect on the particle. However, the rotation of the body can not be neglected in engineering practice . To understand the rotation, for instance, in a building structure, when an earthquake hits the building site, not every part of the building will move at the same time with the same amplitude. The foundation will move with the ground first , followed by the low part of the building. Since the upper part of the building will remain at rest at the beginning, the accommodation of the moving part of the building and the still part of the building will produce the mandatory rotation in between. In engineering practice, we are mostly dealing with nonconcurrent force systems since the body has definite size and shape . What does that mean by saying definite size and shape? It means the force systems applied on the rigid body not only can have different directions , but Rotation Ground motion Ground Building
3 also different point of application . When the force system has different points of application on a body with definite size and body, it is called a nonconcurrent force system. In other words, the points of application of applied forces may not intersect at the same point. What will happen if not all forces is concurrent. One of the possibilities is the rotation of rigid body. As the counterpart of the rotation tendency , moment is needed to maintain the equilibrium of the rigid body.

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This note was uploaded on 04/20/2009 for the course CVEN 221 taught by Professor - during the Summer '08 term at Texas A&M.

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Lecture 4 part I - LECTURE 4 RIDIG BODIES EQUIVALENT...

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