This study relates the structural stiffness and kinetic energy of impact (between 34 J and 136 J) to the resulting contact force and duration of force rise for a square tube with wall thickness between 12.7 mm and 25.4 mm. LS-DYNA3D, finite element program was used for the analysis. Two materials, AISI 4340 and AISI 301 steel, are used as examples. Regression equations for predicting the relationship between the structural stiffness, maximum force and duration of force rise are given for each material. Results indicate an increase in the force of impact and a decrease in the duration of force rise with the increase in structural stiffness; an increase in force and an increase in duration of force rise with the increase in kinetic energy of impact; under some conditions, significant plastic deformation results in only a moderate change in force of impact and significant increase in duration of force rise; under some conditions, lack of significant plastic deformation results in significant increase in force and only marginal increase in duration of force rise.