Week 1 Challenge
Ability of the material to support loads through more than one path.
Prevents progressive collapse.
Failure in a member will not fall the entire structure.
Highly desirable in structural system.
Pratt truss:
Is one of the most common forms of truss and is made up of vertical and diagonal members that form an N shape or pattern.The diagonal members are arranged so that they only develop tensile forces.As such they canbe designed to resist axial tension only, avoiding the need for a compression buckling analysis.The vertical members in a pratt truss develop compression forces.This means they will typically be more robust and capable of resisting buckling.
It is composed of alternate vertical and inclined members.
It has diagonal members that slant down towards the middle.
Howe trusses: Are essentialy the opposite of pratt trusses in terms of geometry.In fact looking at a pratt truss upside down will visualize a Howe truss of sorts.The entire structure is still relatively the same, but the diagonal braces are now occupying the opposite or the unoccupied joints.This switch in position of the diagonal members has a very important effect structurally.
It consist of alternate vertical and inclined members.
It has diagonal members that slant down away from the middle.
Final observation:
The main differences are that the pratt truss has no force on the ends and the compression members are vertical.
The Howe truss has no force on the centre and the tension members are vertical instead.
CONCLUSION: Pratt trusses have their vertical members in compression and diagonal members in tension upon the application of gravityloads at the jointsof the top chord.For Howe trusses the reverse becomes true as diagonal members are now in compression while the vertical loads are in tension.
As they are similar in structure to pratttrusses,their uses are generally the same.To maximize the efficiency of the truss, the truss can be loaded at the joints of the bottom chord.
Pratt trusses can have more unloaded members than Hawe trusses.
Hence Pratt trusses is most trusses efficient in carrying gravity loads.