IRAQI JOURNAL OF CIVIL ENGINEERING (2022) 016–002 Iraqi Journal of Civil Engineering Available online at https://www.iasj.net/ Journal homepage: https://www.iasj.net/iasj?func=issues&jId=141&uiLanguage=en * Corresponding author. Tel.: +0-000-000-0000 ; fax: +0-000-000-0000. E-mail address: sha19e1002@uoanbar.edu.iq Uniform Step Loading of a Partial Interaction Composite Beam Shaimaa Karem Mohammed Al-Joani 1* , and Nahidh H. Kurdi 2 1 MSc student at the Civil Engineering Department of the University of Anbar, Ramadi, Iraq 2 Lecturer at the Civil Engineering Department of the University of Anbar, Ramadi, Iraq A R T I C L E I N F O Article history: Received 01/ 10/ 2022. Received in revised form 22 / 10 / 2022 Accepted 25/10/ 2022. Available online 29/ 12 / 2022 Keywords: composite beams partial interaction uplift uniform step loading dynamic amplification factor finite elements A B S T R A C T In the present paper, a one-dimensional finite element model for the analysis of composite beams of partial interaction is constructed. This model was verified against some analytical results available in the literature and achieved very good agreement with the natural frequencies and the time histories it was compared to. Then it was utilised to analyse partial interaction composite beams under the effect of uniform step loads and provided important information about the expected dynamic amplification factors, which turned out to be particularly high, and the effects of the linear stiffness ratio of the interface and the boundary conditions of the lower layer of the beam. The results, in particular, showed that even for extreme cases the orders of magnitude of the slip and the corresponding uplift remain the same. This pointed out an important finding that the uplift in the researched context, at least, is not negligible as it is widely assumed in the literature. DOI: 10.37650/ijce.2022.160206 1. Introduction The structural performance of composite beams of partial interaction has been in the research interest in structural engineering since the pioneering work of Newmark (1951) in the 1950s in which he pointed out essential theoretical and experimental aspects of the subject in the static loading realm. Later on, many researchers expanded on that pioneering work and bifurcated it into several trends, some of which are analytical, some are numerical and the others are completely experimental (Plum and Horne, 1975; Hirst and Yeo, 1980; Oven et al., 1997; Taig and Ranzi, 2015; Turmo et al., 2015; Liu et al., 2016; Nguyen and Hjiaj, 2016; Bedon and Fragiacomo, 2019; Wang et al., 2020; Martinelli, 2021; Sun et al., 2022). The appearance of works in the literature that dealt with the dynamics of composite beams of partial interaction came much later. One pioneering work of those is that of Girhammar and Pan (1993) who extended the usual separation of variables analysis to the governing equation of the vibrations of a composite beam of partial interaction. They presumed that the only flexibility of the interface is the shear (or the tangential) one, neglecting any effects of the uplift (or the transverse) flexibility of the interface. This particular trend of neglecting the effects of uplift was, seemingly, inherited from the mainstream research dealing with the static of those composite beams.