30-05-2013, 12:12 PM
AE2254 AIRCRAFT STRUCTURES-I
AIRCRAFT STRUCTURES.ppt (Size: 494 KB / Downloads: 76)
PLANE TRUSS ANALYSIS
Methods of Truss Analysis
method of joints
method of sections
Assumptions for Truss Analysis
Connections may be welded, nailed or
riveted but are modeled as pins
Loads are applied only at the joints
Weight of each member is small compared with the applied load
Loads are carried axially by members
Geometry is known.
Objective of Truss Analysis
Determine the force resisted by each
member so that the member can be
designed:
member material
member cross-section
Two Forms of Truss Analysis
Method of Joints:
consider the truss joint by joint, applying equilibrium equations to each joint.
Method of Sections:
consider a portion of the truss as a free body with three unknowns and apply equilibrium equations.
Analyzing a truss by Method of Joints
Use equations of equilibrium of whole
structure to determine reactions
Assume each joint is in equilibrium
Isolate each of the joints as a free body
Repeat, until all forces determined:
Identify joints that have only two unknowns
Determine member forces required at one of those joints to maintain equilibrium
Assumptions
Please note:
all unknown member forces are initially assumed to be tension forces at a joint
(see above)
if force turns out to be negative, then assumption of tension was incorrect and force is compression
a negative sign for a force means compression ONLY because we assumed the force was originally tension
Summary
Statically determinate trusses are analyzed
using two approaches:
method of joints
method of sections (fast for one member)
Method of joints finds forces in ALL
members
Method of sections is useful to find forces
in specific members, but not all