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1 
MEM202 Engineering Mechanics - Statics MEM 
7.2 Plane Trusses 
Examples for Method of Joints
2 
MEM202 Engineering Mechanics - Statics MEM 
7.2 Plane TrussesExamples for Method of JointsVehicle weight = mg = 9810 N 
A: AB, AE 
B: BC, BE 
E: CE, EF 
C: CD, CF 
D: Dx 
F: Fx, Fy 
Reactions not crucial 
Reactions must be obtained first
3 
MEM202 Engineering Mechanics - Statics MEM 
7.2 Plane Trusses 
Examples for Zero-Force Members
4 
MEM202 Engineering Mechanics - Statics MEM 
7.2 Plane Trusses 
Examples for Zero-Force Members
5 
MEM202 Engineering Mechanics - Statics MEM 
7.2 Plane Trusses 
Method of Sections 
Method of joints is more convenient when the truss is relatively simple and forces in all members are needed. 1F2F1R2RForce = ? 
Method of sections is more convenient when the truss is relatively complex and forces in only a few members are needed.
6 
MEM202 Engineering Mechanics - Statics MEM 
7.2 Plane Trusses 
Method of SectionsForce = ? 
1. If necessary, draw a free-body diagram of the entire truss and determine the reactions (if r = 3). 
2. Divide the truss into two parts by passing an imaginary section through member(s) whose member forces are needed. Draw a free- body diagram for each part. 000= = = ΣΣΣ MFFyx000= = = ΣΣΣ MFFyx 
3. Set up equilibrium equations for either free-body diagram and solve them to obtain the unknown member forces.
7 
MEM202 Engineering Mechanics - Statics MEM 
7.2 Plane Trusses 
Method of SectionsDGIFGDCDGTMTMTM⇒= ⇒= ⇒= ΣΣΣ 000FGDGCDyxTTTMFF,, 000⇒ ⎪⎪⎭ ⎪⎪⎬ ⎫ = = = ΣΣΣ
8 
MEM202 Engineering Mechanics - Statics MEM 
7.2 Plane Trusses 
Method of Sections 
K-TrussCDFFGDTMTM⇒= ⇒= ΣΣ 00
9 
MEM202 Engineering Mechanics - Statics MEM 
7.2 Plane Trusses 
Method of SectionsBAECHFKINLOTRWUDGJMPSV 
Q 
Reactions at Aand B 
Section 1: AC, BESection 2: CF, EH 
Section 3: IF, HKSection 4: LI, KN cdef 
Joint V: VL, VTJoint W: WN, WU 
Joint R: RO, RTJoint S: SQ, SU 
Joint T: TL, TOJoint U: UN, UQ 
Joint O: OL, OPJoint Q: QN, QP 
Joint P: PL, PNJoint L: LM 
Joint N: NMJoint M: MI, MK 
Joint I: IJJoint K: KJ 
Joint J: JF, JHJoint F: FG 
Joint H: HGJoint G: GC, GE 
Joint C: CDJoint D: DA, DB 
Joint A: ABJoint B: Check
10 
MEM202 Engineering Mechanics - Statics MEM 
7.3 Space Trusses2222222222223213232132323223232323++ −+− = ++ −−− = = + −− = + − = + + = kjiTFkjiTFjTFkiTFjiTFjiTFCDCDBDBDBCBCADADACACABABrrrrrrrrrrrrrrrrrrrkAjAiAAzyxrrrr++=kCjCCzyrrr+= kBBzrr= rjmjm−=−=3or 63()lb 30cos30sin125kjPrrroo−= 0=+++ADACABFFFArrrr0=+++BDDCABFFFBrrrr0=+++CDBCACFFFCrrrr0=+++CDBDADFFFPrrrr
11 
MEM202 Engineering Mechanics - Statics MEM 
7.2 Plane Trusses 
Forces in Straight and Curved Two-Force Members α r αααsincossinTrTdMTVTP====00===MVTP

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L14

  • 1. 1 MEM202 Engineering Mechanics - Statics MEM 7.2 Plane Trusses Examples for Method of Joints
  • 2. 2 MEM202 Engineering Mechanics - Statics MEM 7.2 Plane TrussesExamples for Method of JointsVehicle weight = mg = 9810 N A: AB, AE B: BC, BE E: CE, EF C: CD, CF D: Dx F: Fx, Fy Reactions not crucial Reactions must be obtained first
  • 3. 3 MEM202 Engineering Mechanics - Statics MEM 7.2 Plane Trusses Examples for Zero-Force Members
  • 4. 4 MEM202 Engineering Mechanics - Statics MEM 7.2 Plane Trusses Examples for Zero-Force Members
  • 5. 5 MEM202 Engineering Mechanics - Statics MEM 7.2 Plane Trusses Method of Sections Method of joints is more convenient when the truss is relatively simple and forces in all members are needed. 1F2F1R2RForce = ? Method of sections is more convenient when the truss is relatively complex and forces in only a few members are needed.
  • 6. 6 MEM202 Engineering Mechanics - Statics MEM 7.2 Plane Trusses Method of SectionsForce = ? 1. If necessary, draw a free-body diagram of the entire truss and determine the reactions (if r = 3). 2. Divide the truss into two parts by passing an imaginary section through member(s) whose member forces are needed. Draw a free- body diagram for each part. 000= = = ΣΣΣ MFFyx000= = = ΣΣΣ MFFyx 3. Set up equilibrium equations for either free-body diagram and solve them to obtain the unknown member forces.
  • 7. 7 MEM202 Engineering Mechanics - Statics MEM 7.2 Plane Trusses Method of SectionsDGIFGDCDGTMTMTM⇒= ⇒= ⇒= ΣΣΣ 000FGDGCDyxTTTMFF,, 000⇒ ⎪⎪⎭ ⎪⎪⎬ ⎫ = = = ΣΣΣ
  • 8. 8 MEM202 Engineering Mechanics - Statics MEM 7.2 Plane Trusses Method of Sections K-TrussCDFFGDTMTM⇒= ⇒= ΣΣ 00
  • 9. 9 MEM202 Engineering Mechanics - Statics MEM 7.2 Plane Trusses Method of SectionsBAECHFKINLOTRWUDGJMPSV Q Reactions at Aand B Section 1: AC, BESection 2: CF, EH Section 3: IF, HKSection 4: LI, KN cdef Joint V: VL, VTJoint W: WN, WU Joint R: RO, RTJoint S: SQ, SU Joint T: TL, TOJoint U: UN, UQ Joint O: OL, OPJoint Q: QN, QP Joint P: PL, PNJoint L: LM Joint N: NMJoint M: MI, MK Joint I: IJJoint K: KJ Joint J: JF, JHJoint F: FG Joint H: HGJoint G: GC, GE Joint C: CDJoint D: DA, DB Joint A: ABJoint B: Check
  • 10. 10 MEM202 Engineering Mechanics - Statics MEM 7.3 Space Trusses2222222222223213232132323223232323++ −+− = ++ −−− = = + −− = + − = + + = kjiTFkjiTFjTFkiTFjiTFjiTFCDCDBDBDBCBCADADACACABABrrrrrrrrrrrrrrrrrrrkAjAiAAzyxrrrr++=kCjCCzyrrr+= kBBzrr= rjmjm−=−=3or 63()lb 30cos30sin125kjPrrroo−= 0=+++ADACABFFFArrrr0=+++BDDCABFFFBrrrr0=+++CDBCACFFFCrrrr0=+++CDBDADFFFPrrrr
  • 11. 11 MEM202 Engineering Mechanics - Statics MEM 7.2 Plane Trusses Forces in Straight and Curved Two-Force Members α r αααsincossinTrTdMTVTP====00===MVTP