Development of an experimental system to apply high rates of loading

Purpose – The purpose of this paper is to develop an experimental system to apply high rates of loading, in order to characterize the behaviour of bolted steel connections subjected to accidental loads, such as impact. The work presented in this paper is part of an ongoing research project at the University of Coimbra IMPACTFIRE PTDC/ECM/110807/2009. Design/methodology/approach – The experimental set-up was designed to test under tension T-stubs and is capable to apply high strain rates. The test rig comprises a series of beams and steel elements placed horizontally, providing resistance and stiffness for the proposed tests. The loading system is operated by high-pressure nitrogen and it comprises three main components: pneumatic reservoir, pneumatic cylinder and a rapidly opening valve, which and allows the instantaneous nitrogen flow from the reservoir to the cylinder. This paper presents a detailed description of the experimental components developed, designed and fabricated at University of Coimbra. Furthermore, the data acquisition system, the methodology for analysis of the results and the results of preliminary tests are also reported. Findings – The results of the tests showed that the developed system is capable to apply an impact force in the specimens, the shape of the force and acceleration, in terms of duration and magnitude provided by the system showed that the system is capable to apply and simulate an impact force in specimens under tension. Moreover, the results reached under high rates of loading are compared with those reached under quasi-static loading; an increase of the plastic and ultimate resistances and a decrease of the deformation capacity are noticed. Originality/value – The value of this paper is to describe the development of a new experimental system to perform tests at high strain rates. The results of the experimental tests of T-stub under tension are presented herein.