Hollow and concrete filled steel hollow sections under transverse impact loads

Steel hollow sections are used extensively in the construction, offshore, mining and security industries. In many applications these sections are concrete filled in order to gain strength advantages under axial compression loads. These sections may be subjected to transverse impact loads from accidental or intentional impacts or explosive events. This paper reports an experimental and analytical investigation of hollow and concrete filled steel square hollow (SHS) section beams subjected to low velocity, large mass transverse impacts at the beam mid-span. Three different section sizes were tested as fully clamped beams, where the impact energy was sufficiently large so as to cause complete failure of the beam by tensile tearing. It is shown that non-compact hollow sections undergo local deformations beneath the impactor, and when concrete filled these sections can sustain greater transverse impact loads as the local deformations are restricted from forming. The effect is shown to be less pronounced for compact sections. An elastic-plastic theoretical method is developed to establish the force-displacement and energy absorption relationships for hollow and concrete filled sections, and is shown to compare well with the experimental results. The local reduction of the section at the point of load application is explicitly included. A design procedure is developed whereby the analyst may use a deflection, force or energy limit to design hollow and concrete filled steel SHS members for transverse impact loads.