# Salani and Sims 1964

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.

## Contents

## 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.