*J A El-Rimawi (J.A.El-Rimawi@lboro.ac.uk) . *

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- Calculate the degree of indeterminacy of the following pin jointed plane trusses, then determine whether each truss is stable. Start by identifying the triangulated (i.e. stiff/stable) parts of the structure and then examine how they are connected to each other and the supports.

- What do you understand by the term compound truss? How stable/determinate is this pin-jointed truss? Calculate the reactions and the axial force in each member.
- Analyse the truss shown qualitatively. Estimate the direction of the reactions, and deduce the sense of the axial force.
- Why is the truss shown statically determinate? Demonstrate this by hypothetical removal of members or reactions and in terms of equations v unknowns.
- An elevation and plan of a space truss is shown opposite. Analyse the structure by computer (QSE) using a suitable combination of support conditions at B, C and D to make the structure statically determinate.

(Answer: Reactions RB=250 , RC=50 ; Member forces: AD,DG=141.42(T); AB,BG =100(C); GH=100(T); BE,EH=212.13(C); HF,FC=70.71(C),BC=50(T); and zero.)

Calculate the reactions by careful choice of three equations of equilibrium and the equation of condition. Hence find the force in members BD and DC.

(Answer: VA= VG =75 ; HA = - HG = 12.5® , FBD = 19.3 (T); FDC= 45.7 (C))

Check the vertical reactions by taking moments about the z-axis through B. All the horizontal reactions should be zero.

Check the forces in members AB, AC and AD by resolving at joint A along each axis; each equation should sum to zero. Express the force of each member along an axis as a ratio of its projected to actual length (the lengths of members AB, AC and AD are 7.07, 10.49 and 7.55 m).

(Answer: FAB = 6.4; FAC = 4.9; FAD = 4.2 (all C)).

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