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Plane Trusses. Plane Truss: Layout. joint[dʒɒɪnt] 节点. objective [əb'dʒektiv] n. 目的;. section ['sekʃən] n. 截面;. Objective - Determination of Internal Forces Definition/Properties Internally Static Determinacy The Method of Joints The Method of Sections. - PowerPoint PPT Presentation
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Plane Trusses
Plane Truss: Layout
Objective - Determination of Internal Forces
Definition/Properties Internally Static Determinacy The Method of Joints The Method of Sections
objective [ b'd ektiv] ə ʒn. 目的;
joint[d nt]ʒɒɪ 节点 section ['sek n] ʃən. 截面;
Bridge Truss Structures: Bridge
Truss Structures: Roof
Commonly Used Roof Trusses
roof [ru:f] n. 屋顶;
Truss: Definition
Straight Members Pin-jointed Loaded at JointsWeights ignored No-collapsible (rigid)
collapsible [k 'læps bl]ə əadj. 可折叠的;可变形的
Truss: Rigid or Collapsible
Basic Rigid Form(No-collapsible)
Collapsible Form(Mechanism)
Simple Truss
Two-Force Member & Internal Force
The Same Internal Force (T/C) at all sections
The Method of Joints
Determine the internal forces in all three members.
The Method of Joints: Procedures
Check Static Determinacy: Externally & Internally Determine the External Reactions (r=3)– FBD of the whole structure; Apply ΣFx=0; ΣFy=0; ΣM=0 Choose a Start Joint–Only two unknowns/members at the joint; – Apply Σ Fx=0; Σ Fy=0 Design a Joint Visit Order–Make sure no more than two unknowns need to be found
when visiting a particular joint;– Apply Σ Fx=0; Σ Fy=0 Check the Results by Employing Unused Joints or Equati
ons, if Possible.
The Method of Joints: Example II
Determinate the force in each member of the
loaded simple truss.
All triangles are equilateral
triangle ['traiæ ɡl] ŋn. 三角(形);
II: Find External Reactions
I: Check Static Determinacy
1. r=3, so externally s.d.2. m=7, j=5; m+r=2j; so internally s.d.
III: Joint Visit Order
IV: Joint Analysis (1)
IV: Joints Analysis (2)
The Method of Joints: Example III
Determinate the force in each member of the loaded simple truss.
The Method of Joints: Example IV
Determinate the force in each member of the loaded simple truss.
The Method of Joints: Example V
Compute the forces in members BC, BE and EF of the loaded truss.
Joints Visit Order
The Method of Sections
Method of sections
The Method of Sections: Example V
Example VI
Compute the force in member DJ.
Advanced Issues
Externally Static Determinacy (Refer to Example IV)
Use of Two or More Moment Equations
Choose a Local Coordinate System
local ['l uk l] ə ən. 局部;
adj. 当地的;局部的;
coordinate [k u' :dinit] ə ɔn. 坐标;
Advanced Issues: Example VII
Compute all member forces. All inclined members are at 300 or 600.
Local Coordinate Systems
Advanced Issues: Example VII