A 1000 inch span truss has six flexible supports. The four interior supports are misaligned. The truss is subjected to four point loads at the lower chord.

Determine the vertical displacements at the joints along the bottom chord of the truss and the final gap widths.

Truss elements of constant cross section are used to model the structure. The material and section property of the truss is:

Modulus of Elasticity = 30,000,000 lb/in2

Poisson's Ratio = 0.00

Area = 10 in2

The misalignments of the interior supports are modeled using compression-only foundation spring with built-in gap element.

K = 1,000,000 lb/in

Gap Distance @ Joint 2= 0.80 inch

Gap Distance @ Joint 3= 0.90 inch

Gap Distance @ Joint 4= 1.20 inch

Gap Distance @ Joint 5= .50 inch

The exterior supports have no misalignment and the gap distance is specified as zero.

K = 1,000,000,000 lb/in

The joint at the top center of the truss is restrained from moving in the horizontal direction. Only the vertical movement is allowed at the center supports.

Concentrated forces of 40,000 lbs each are applied at the interior joints of the bottom chord of the truss.

Tested Features

Sources

W.R. Marks, "Solution of Frictionless Contact Problems by a Conjugate Gradient Technique,", M.Sc. Thesis, University of Wisconsin, Milwaukee (1979).
EMRC, "NISA II Verification Problems Manual", 1991.
LARSA 4D

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