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Unformatted text preview: MEEN 221 Summer 2009  Worksheet 8 Dr. A. Palazzolo (1) HWSS (Due: Tues. 30.1mm): Ch 7 (7, 9, 16, 43, 59, 68) (2) Attendance Mandatory for 10:00 am — 12:45 pm, unless excused by instructor.
Multiple Quizzes may be given anytime during this period. (3) Today’s Material: Truss Force Analysis By Joints and Sections, Sections 7.1 — 7.4 Analysis of Trusses for Member Forces and Support Reaction‘Forces . Trusses are load bearing structures which are composed of an
assemblage of two force “members” connected by “joints”. Assumptions used in truss analyses are: ' "—" ' a) members are connected only at their ends b) members are connected only by frictionless pins
0) truss structure is loaded only at joints (1) weight of members are neglected Note that the loads in the truss members may .all be solved for only if:
M = 2j  3 p
m = number of members a (1)
j = number of joints ‘ A FBDwis made for each joint to solve for the member loads. Therefore
 — ( Xi = 0 . . s . (2)
applies at each joint. . In some instances it may simpliﬂ the procedure to augment eqs. 2 with
, the eguilibrium egs. for the entire truss. structureI i.e. ~ : for Total Truss Static Equilibrium: 2F, =0 (3)
gr, =0 (4)
zr=0 (5) O When only two members form a noncollinear truss joint and
no external load or support reaction is applied to the joint,
then the members must be zeroforce members.
When three membertruss joint for which two of the
members are collinear and the third forms an angle with the
‘ﬁrst two, then the noncollinear member is a zeroforce
member provided no external force or support reaction is
applied to that ioint. The two collinear members carry equal
loads (either both tension or both compression). 0C . _ (b) 72.4 Example of a truss mummembers. 714* Determine the forces in
members CD, DE, and DF
of the truss shown in
Fig. P714; State whether
each member is in tension'
or compression. Example 3 R 712 (Similar to R 7—16) i712 @se the lethed 9f joints t9
determine the forcein eneh
member of the truss shown in
Fig. P712. State whether
each member is in tensidn ' ‘or compression, Fig. P712. as“: qua" — _‘ METHDD OF d‘EQ—CWMD (6) Truss Member Force Analysis by the Method of Sections.
This approach yields the forces in a subset of the truss members without
solving node by node, as in the method of joints. 744* Use the method of
sections to determine the forces in members
CD, DE, and EF of thele
truss shown in Fig.
P744. “3’ 3KN 4KN SKN ’1*ﬁﬂ¥'ﬁ§e the nathad sf ~é®¢t£ans ta ﬁatevniwa ‘ ﬁhé f6§Ee§.inmembérs
CB, CE, and EF of the
trusg shown in Fig.
P753. 1% ms 25 mm" 767* Use the method of ' ‘ 1 sections to determine
the forces in members
DE, EG, FG, and FH of the truss Shown in Fig.
P767. (20 ...
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 Spring '08
 McVay

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