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Turbo Pascal Chain module | 1987-10-26 | 46.2 KB | 352 lines |
- DATA AREA FOR BUILDEXE FOLLOWS
- GBIGTURBO - Large Code Model. Copyright (c) 1985 by TurboPower Software.
- "All Rights Reserved. Version 1.08D
- 0123456789ABCDEFLL
- module:
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- _Vector Mechanics for Engineers_U
- _Explanatory Comment:_
- j>\The direction of the reaction at a pin or hinge is unknown.
- i#(See Section 4.3 and Figure 4.1 in
- \Read section 4.3 of
- and look at figure 4.1.
- )i@\The force exerted by a short link is directed along that link.
- hE(See sections 4.3 and figure 4.1 in _Vector Mechanics for Engineers_)
- h/\The reaction at D therefore forms an angle of
- Nh degrees
- >h?with the horizontal. However, we do not yet know whether this
- g1reaction is directed away from or toward point D.
- g=\Such an equation would involve two unknown force components
- fg>and could not be solved independently. On the other hand, we
- !g?can eliminate two unknowns by summing moments about a properly
- selected point.
- fA\Point A is the only point known to lie on the line of action of
- gf@two of the unknown forces, namely ~A~x and ~A~y. Both of these
- f=forces will be eliminated by computing moments about point A.
- e7\A force component which tends to rotate the structure
- eB_counterclockwise_ about point A has a _positive_ moment, and one
- ?e9which tends to rotate it _clockwise_ a _negative_ moment.
- \Consult Figure 5.8 of
- for the area of the
- d<component. NOTE: The sign is negative if the area is to be
- subtracted.
- \Consult Figure 5.8 of
- d for the
- location of the centroid.
- cB\ IF THE MEMBER _PUSHES_ IF THE MEMBER _PULLS_
- ` ` \
- bcA IT IS IN _COMPRESSION_ IT IS IN _TENSION_
- b9At this point, none of the forces exerted by the various
- members are known.
- {bAThere are: 2 unknown forces, F(AB) and F(AC), acting on joint A;
- (bI 4 unknown forces, F(AB), F(BC), F(BD), and F(BE), on joint B;
- aB 3 unknown forces, F(AC), F(BC), and F(CE), on joint C;
- ya, 3 unknown forces on joint D; and
- ;a' 5 unknown forces on joint E
- `?Since the force exerted by the member on the joint is directed
- `<\ _TOWARD_ THE JOINT,
- X`B\ THE MEMBER _PUSHES_ ON THE JOINT
- `B\ THE MEMBER IS IN _COMPRESSION_
- _?Since the force exerted by each member on the joint is directed
- C_!\ _AWAY FROM_ THE JOINT,
- _%\ THE MEMBER _PULLS_ ON THE JOINT
- ^#\ THE MEMBER IS IN _TENSION_
- At this point, there are:\
- \^@ 3 unknown forces, F(BC), F(BD), and F(BE), acting on joint B;
- ^2 2 unknown forces, F(BC), and F(CE), on joint C;
- ]# 3 unknown forces on joint D; and
- 5 unknown forces on joint E
- At this point, there are:\
- *]8 2 unknown forces, F(BD) and F(BE), acting on joint B;
- \= 3 unknown forces, F(BD), F(DE), and F(DF), on joint D; and
- 5 unknown forces on joint E
- M\Q A _positive_ answer means that our A _negative_ answer means that our
- [O assumption was correct: the force assumption was incorrect: the force
- [N exerted by the member on the joint exerted by the member on the joint
- )[M is directed _away from_ the joint. is directed _toward_ the joint.
- ZC THE MEMBER _PULLS_ ON THE MEMBER _PUSHES ON
- uZB THE JOINT; THE MEMBER THE JOINT; THE MEMBER
- !ZA IS IN _TENSION_. IS IN _COMPRESSION_
- At this point, there are:\
- uY< 2 unknown forces, F(DE) and F(DF), acting on joint D; and
- 3 unknown forces on joint E
- X@Since the two forces you wish to eliminate are not parallel, at
- XAleast one of them will have a component in any direction you may
- `XAchoose. Therefore, only one of the two forces may be eliminated
- X8by writing an equilibrium equation involving components.
- WBSince the two forces you wish to eliminate are parallel, at least
- zW=one of them will have a moment different from zero about any
- 6WApoint you may choose. Therefore, only one of the two forces may
- V7be eliminated by writing an equation involving moments.
- VQ A _positive_ answer means that our A _negative_ answer means that our
- &VO assumption was correct: the force assumption was incorrect: the force
- UN exerted by the member on the joint exerted by the member on the joint
- eUM is directed _away from_ the joint. is directed _toward_ the joint.
- UC THE MEMBER _PULLS_ ON THE MEMBER _PUSHES ON
- TB THE JOINT; THE MEMBER THE JOINT; THE MEMBER
- ]TA IS IN _TENSION_. IS IN _COMPRESSION_
- SA\The force you wish to determine will not be the only unknown in
- S?the equation obtained in this way. To eliminate the other two
- RS<unknown forces, you must compute moments about the point of
- S8intersection of the lines of action of these two forces.
- R8We could solve the problem by considering the free-body
- {RAdiagrams of members AKC and BLD. However, this would lead us to
- 3R=writing 6 equilibrium equations to be solved simultaneously.
- Q9It is better to draw the free-body diagram of the entire
- Q?frame and determine from it as many of the reactions as we can.
- EQ>The direction of the reaction at a pin-and-bracket support is
- QCknown _only if the member attached to that support is a two-force_
- P%_member_. This is not the case here.
- (See Section 4.6 of
- ]P( for the definition of a two-force body)
- P<When the direction of a reaction is not known, the reaction
- O9should be represented by 2 unknowns, usually its x and y
- O!components. (See Section 4.3 of
- COC\In the case of the equilibrium of a rigid body in two dimensions,
- N8we can write only 3 _independent_ equilibrium equations.
- NA\Any additional equation that we would write would only _repeat_
- jN>information already obtained from the previous equations. It
- %N$would _not add_ to this information.
- MB\The unknowns consist of the components Cx and Cy of the reaction
- M>at the support C and the components Dx and Dy of the reaction
- at the support D.
- %MA\Writing the equation ~
- Fx = 0 would involve the two unknowns Cx
- L=and Dx. Writing the equation ~
- Fy = 0 would involve the two
- unknowns Cy and Dy.
- iL>The computation of the moments of the forces about that point
- 'L5would involve at least 2 of the 4 unknown components.
- K@We can eliminate Cx and Dx either by summing y components or by
- K=summing moments about a point on their common line of action.
- 1K@Summing moments about that point will not eliminate both Cx and
- J.Such an equation would involve both Cx and Dx.
- J>To eliminate Cx we may either sum y components or sum moments
- =J>about a point on the line joining C and D. In either case Dx
- I@will also be eliminated. Conversely, if we try to eliminate Dx
- we will also eliminate Cx.
- wICIt is recalled that a _two-force member_ is a member acted upon by
- 0IGforces at _only two points_ (see Section 4.6 of _Vector Mechanics for_
- H?_Engineers_). Any other member is referred to as a multiforce
- member.
- uHAIn a two-force member, the two forces exerted on the member must
- 0HAhave the same line of action, same magnitude, and opposite sense
- (see Section 4.6 of
- GQTherefore, the forces exerted on member AB are directed along AB, and the forces
- WG+exerted on member KL are directed along KL.
- GAWe cannot eliminate 2 of the 3 unknowns by summing moments about
- F1one of the points shown in the free-body diagram:
- F-Summing moments about B eliminates only F(AB)
- BF-Summing moments about L eliminates only F(KL)
- F*Summing moments about D eliminates only Dx
- E8The equation ~
- Fx = 0 would contain all of the unknowns.
- gE<A positive sign indicates that our assumption regarding the
- 'E@direction of F(KL) was correct, that is, that F(KL) is directed
- away from point L.
- DAA negative sign indicates that our assumption was wrong and that
- tD!F(KL) is directed toward point L.
- 3D:The equation ~
- Fx = 0 would contain both of the remaining
- CAunknowns and the equation ~
- Fy = 0 would contain neither of them.
- C?Summing moments about point L does not eliminate either of the
- two remaining unknowns.
- C<A positive sign indicates that our assumption regarding the
- B:direction of Dx was correct, that is, that Dx is directed
- to the right.
- wBAA negative sign indicates that our assumption was wrong and that
- Dx is directed to the left.
- A<A positive sign indicates that our assumption regarding the
- A@direction of F(AB) was correct, that is, that F(AB) is directed
- to the left.
- OAAA negative sign indicates that our assumption was wrong and that
- F(AB) is directed to the right.
- @<We are computing RB, so we should sum moments about point A.
- r@.For the maximum bending moment, dM/dx = V = 0.
- '@2Check where the shear crosses the horizontal axis.
- ?BSince the floor is not frictionless, we need 2 components, one to
- ?<represent the normal force N and the other to represent the
- friction force F.
- ?@Writing ~
- Fx = 0 eliminates only N and leaves 2 unknowns, F and
- >?P; writing ~
- Fy = 0 eliminates only F and leaves 2 unknowns, N
- and P.
- n>2The equation you suggest would involve 2 unknowns.
- >ASince the value found for F is not larger than the maximum value
- ==Fm that the static-friction force can reach, our solution is
- valid.
- p==Since the value found for F is larger than the maximum value
- /==Fm that the static-friction force can reach, our solution is
- not valid.
- Check Figure 9.12 of
- ; we want the _centroidal_
- p< moment of inertia of the square.
- Check Figure 9.12 of
- ; we must use the
- length of a side of the square.
- ;:For this triangle Ix is moment of inertia with respect to
- s;2the _base_ of the triangle. Check Figure 9.12 in
- Check Figure 9.12 in
- . The cubed dimension
- :5is the dimension that is perpendicular to the x axis.
- :AThe parallel-axis theorem can be used only with the _centroidal_
- axis.
- Check Figure 9.12 in
- . We now seek the
- 98moment of inertia with respect to the _centroidal_ axis.
- Check Figure 9.12 in
- . The cubed dimension
- ?95is the dimension that is perpendicular to the y axis.
- Check Figure 9.12 in
- . We
- 8Iseek the moment of inertia of the semicircle about the transverse axis y.
- Check Fig. 5.18 in
- . We
- #8"seek the centroid of a semicircle.
- Check Fig. 9.12 in
- 7 for the
- 71moment of inertia of a semicircle about its base.
- _7<Point X should be plotted _above_ the horizontal axis since
- its ordinate Ixy is positive.
- 6<Point X should be plotted _below_ the horizontal axis since
- its ordinate Ixy is negative.
- e6@Since Ixy is positive, the ordinate -Ixy of point Y is negative
- !6:and point Y should be plotted _below_ the horizontal axis.
- 5@Since Ixy is negative, the ordinate -Ixy of point Y is positive
- 5:and point Y should be plotted _above_ the horizontal axis.
- )5=ED is obtained by subtracting OE from OD. Since OD = Ix and
- OE = Iy, we have ED = Ix - Iy.
- 4=The length DX is equal to Ixy if Ixy > 0, or to the absolute
- value of Ixy if Ixy < 0.
- 148When the coordinate axes xy rotate through an angle ~
- 37the corresponding diameter XY of Mohr's circle rotates
- 34through twice that angle, that is, through 2~
- (see
- Section 9.10 of
- D3:It follows that to bring the axis Ox to coincide with the
- 3:principal axis Oa, we should rotate it through _half_ the
- 2$angle XOA measured on Mohr's circle.
- 26The x and y axes and the corresponding diameter XY of
- G2.Mohr's circle always rotate in the same sense.
- 26\Since in this case the rotation bringing X into A on
- 15Mohr's circle is clockwise, the rotation bringing Ox
- into Oa will also be clockwise.
- O17\The x and y axes and the corresponding diameter XY of
- 1.Mohr's circle always rotate in the same sense.
- 06\Since in this case the rotation bringing X into A on
- 09Mohr's circle is counterclockwise, the rotation bringing
- W0)Ox into Oa will also be counterclockwise.
- 0=DE is obtained by subtracting OD from OE. Since OD = Ix and
- Oe = Iy, we have DE = Iy - Ix.
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