Salani and Sims 1964

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The elastic and inelastic behavior of mortar-filled steel tubes in compression was investigated. Comparisons were made between the experimental values and theoretical values obtained from the tangent modulus formula.

Experimental Study, Results, and Discussion

The tubes in the study were composed of seamless, cold drawn, annealed steel and varied from 1 to 3 inches in diameter. Both hollow and mortar-filled tubes were tested. The ultimate load capacities of the 1 and 1.5 in. tubes were not augmented by the use of mortar. This may have been due in part to the low ratio of mortar to steel area. The 2 and 3 in. tubes showed an increase in strength when filled. All of the tubes failed by column buckling except for the 3 inch tubes which failed by local buckling.

Theoretical Discussion

The theoretical buckling loads for both the empty and mortar-filled tubes were computed by the tangent modulus formula.

where E is the effective modulus of elasticity, and I is the effective moment of inertia. For both the empty and filled tubes, this modulus of elasticity value was obtained from the experimental results of a stress-strain compression test of a stub column. A least squares polynomial curve fit was employed to express the stress-strain relationship. The concept of a transformed section was avoided here because Ec varied inversely with the load.

Comparison of Results

With the exception of the 3 in. tubes which buckled locally, the theoretical buckling loads for the empty and mortar-filled tubes were within 16% of the experimental values.

References

Salani, H. R. and Sims, J. R. (1964). “Behavior of Mortar Filled Steel Tubes in Compression,” Journal of the American Concrete Institute, Vol. 61, No. 10, pp. 1271-1283.