Similar to trusses, frames are generally fixed, load carrying structures.

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2 Similar to trusses, frames are generally fixed, load carrying structures. The main difference between a frame and a truss is that in a frame at least one member is a multi force member (çoklu kuvvet elemanı). A multi force member supports three or more forces or at least two forces and one or more couples.

3 In contrast with a truss, the force or moment can be exerted to any point on the frame member; it does not have to be applied the joint as in trusses.

4 Machines are structures which contain moving parts and are designed to transmit input forces or couples to output forces or couples. Therefore a machine is an assembly of rigid and sturdy members that are capable of generating work by means of some kind of motion. A mechanism is a term used to describe the physical devices which enable the parts of a machine to conduct the intended movements.

5 A machine may contain several mechanisms. Machines are designed to change forces, enhance and amplify their magnitudes and transmit them. Whether a machine is as simple as a hand tool or as complex as an airplane, the main aim is to convert input forces into output forces.

6 The main difference between a frame and a machine is that although frames are rigid structures, machines are not. Machines may be fixed to some supporting surface or body, but they will always consist moving parts.

7 The forces acting on each member of a connected system are found by isolating the member with a FBD and applying the equations of equilibrium. The principle of action and reaction must be carefully observed when we represent the forces of interaction on the separate FBDs.

8 If the structure contains more members or supports than are necessary to prevent collapse, then, the problem will be statically indeterminate. Because frames and machines contain multi force members, the forces in these members in general will not be in the directions of the members as in two force members.

9 In order to determine the forces in a frame or machine, it is divided into a sufficient number of members or groups of members, but initially the support forces to be used in the analysis must generally be determined from the equilibrium of the whole frame.

10 It would be appropriate to identify the two force members in the frame, if there is any, before starting with the solution. The structure is then, dismembered and the equilibrium of each member is considered separately. The equilibrium equations for the several parts will be related through the terms involving the forces of interaction.

11 It should be kept in mind that when going from one member to the other, the direction of the interaction force must be changed in accordance with Newton s third law. In most cases, the analysis of frames and machines is facilitated by representing the forces in terms of their rectangular components. The advantage of this representation is that the calculation of moment arms is simplified.

12 It is not always possible to assign the proper sense to every force or its components when drawing the FBDs, and it becomes necessary to make an arbitrary assignment. In any case, it is absolutely necessary that a force be consistently represented on the diagrams for interacting bodes which involve the force in question.

13 In general the FBDs of pins in the structures are not drawn; pins are considered as a complementary part of one of the two members it connects. It must be clearly decided which member the pin will belong to. Whereas, the FBD of a pin will be considered if: It connects three or more members, It connects a support and two or more members, A load is directly applied to the pin.

14 Mechanical Efficiency h work output energy input Machines are considered as ideal machines when the work output is equal to the energy input. It is impossible to build such machines. In a real machine friction forces always generate useless work which causes loss of energy; therefore, work output is always less than the energy input. In other words, the mechanical efficiency is always less than one, h < 1.

15 Mechanical Advantage: Output Input Force Force Çikti Girdi Kuvveti Kuvveti Mechanical advantage is the ratio of the output force of a machine to the input force necessary to work the machine. This concept is totally different from the mechanical efficiency and should not be mixed with it. Mechanical advantage is generally greater than one.

16 SAMPLE FRAMES AND MACHINES

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