Methods of Joints | Structural Analysis - Civil Engineering (CE) PDF Download

 Page 1


Method of Joints
Note the direction of the forces in 
the members acting on the joints
Page 2


Method of Joints
Note the direction of the forces in 
the members acting on the joints
Problem 27  
Determine the forces in the members  in the following truss
15
Page 3


Method of Joints
Note the direction of the forces in 
the members acting on the joints
Problem 27  
Determine the forces in the members  in the following truss
15
F
AB
=8.84kN (T)	
F
BC
=10.62kN (C)	
F
AC
=2.13kN (C)
We assumed that all the forces in the members were tensile. 
But we got some of them negative. So, the negative sign 
indicates that the forces in the members are compressive.
18
10.62	kN
8.84	kN
2.13	kN
Page 4


Method of Joints
Note the direction of the forces in 
the members acting on the joints
Problem 27  
Determine the forces in the members  in the following truss
15
F
AB
=8.84kN (T)	
F
BC
=10.62kN (C)	
F
AC
=2.13kN (C)
We assumed that all the forces in the members were tensile. 
But we got some of them negative. So, the negative sign 
indicates that the forces in the members are compressive.
18
10.62	kN
8.84	kN
2.13	kN
Joints Under Special Loading Conditions
• F o r c e s i n o p p o s i t e m e m b e r s 
intersecting in two straight lines at a 
joint are equal.
• The forces in two opposite 
members are equal when a load is 
aligned with a third member.  The 
third member force is equal to the 
load P.
• Zero force members
• Recognition of joints under special 
loading conditions simplifies a truss 
analysis.
• When a joint connects only two 
members, the forces in two 
members are equal when they lie in 
the same line.
19
Page 5


Method of Joints
Note the direction of the forces in 
the members acting on the joints
Problem 27  
Determine the forces in the members  in the following truss
15
F
AB
=8.84kN (T)	
F
BC
=10.62kN (C)	
F
AC
=2.13kN (C)
We assumed that all the forces in the members were tensile. 
But we got some of them negative. So, the negative sign 
indicates that the forces in the members are compressive.
18
10.62	kN
8.84	kN
2.13	kN
Joints Under Special Loading Conditions
• F o r c e s i n o p p o s i t e m e m b e r s 
intersecting in two straight lines at a 
joint are equal.
• The forces in two opposite 
members are equal when a load is 
aligned with a third member.  The 
third member force is equal to the 
load P.
• Zero force members
• Recognition of joints under special 
loading conditions simplifies a truss 
analysis.
• When a joint connects only two 
members, the forces in two 
members are equal when they lie in 
the same line.
19
Problem 30 and 31
•
For the given loading, determine the zero force 
members in the trusses shown 
20