Shaking Table Experiment on Seismic Performance of a Scaled-Down Arch Dam with Initial Crack Mohammed Noori Hussein * , Ahmed Alkadhimi, Wisam Abdullah Najim, Hashim A. Almousawi Civil Engineering Department, Iraq University College, Basra 61001, Iraq Corresponding Author Email: mohammed.alhashimi@iuc.edu.iq https://doi.org/10.18280/ijdne.160610 ABSTRACT Received: 20 August 2021 Accepted: 8 December 2021 Seismic responses of cracked scaled-down arch dams were investigated by experiment on a shaking table. Two different curvature models (M1 and M2) were cast by using a plan concrete. Dams properties, including materials and dimensions, were carefully simulated. A significant earthquake magnitude with (7.7M) and water pressure were applied on the dam's models. Considering water and seismic loadings, the dynamic reactions of the arch dam's system were investigated. Both models showed crack overstresses or propagation on the dam's model as a result of seismic excitations. The arch dam with a higher degree of curvature was recorded 44 Mpa of stress evaluation which less by 30.7% of the arch dam with the lowest degree of curvature. The results indicated that raising the degree of curvature led to raising the dam's stability, earthquake resistance, less displacement, and less growth of tensile cracks. Keywords: cracked arch dam, earthquake, degree of curvature, XFEM 1. INTRODUCTION An arch dam is a solid concrete dam that is arch upstream in form. The arch dam is built so that the force of the water behind it, known as hydrostatic pressure, pressures against the arch as it pushes through its base or abutments, compressing and reinforcing the structure. An arch dam is most fitting for narrow gorges or canyons with steep walls of solid granite to sustain the framework and pressures. Since they are thinner than any other form of the dam, they need far less building material, rendering them in remote areas economic and functional. The body is usually built of concrete, but in the past, stone rubble masonry was also utilised. It has two structural functions: one as a cantilever retaining wall lifted from its foundation, and the other as a horizontal arch movement, with the load passing to the two ends [1, 2]. Because many large- scale hydro projects are situated in deep valley locations, a concrete arch dam is a good option. This is especially true in a region with an abundance of hydropower. Nonetheless, earthquakes are common in the area, and their severity is considerable, making the performance of big dams and their security during earthquakes a major issue for construction [3]. Following previous earthquakes, concrete arch dams have performed well. An arch dam has never failed as a consequence of earthquake deterioration. However, it should be noted that only a few large earthquakes have happened near an arch dam because the number of arch dams is very few compared to other dams, because arch dams are subject to several determinants and requirements for their establishment [4]. The purpose of this study is to use shaking table tests to evaluate the seismic behavior of an arch dam having an initial crack. An arch dam's safety assessment should determine all major failure mechanisms and undertake suitable judgements and analyses to guarantee that the dam's structural stability is preserved. Many finite element method (FEM) numerical studies have been published [5-10]. Even though FEM can hypothetically examine even the failure or damage of a complex arch dam system, the computational time required to do so restricts its practical application. More importantly, because no failure due to the earthquake has yet been detected, the parameters for nonlinear responses, numerical models and numerical processes of an arch dam have not been verified or calibrated. The extended finite element method (XFEM) encompasses substantial advantages of crack propagation numerical modelling. Moreover, this method does not require the finite element mesh to correspond to the presence of cracks. Likewise, there is no requirement for remeshing techniques for crack growth. This is a consequence of the displacement vector function approximation, which is appended to model the crack's existence. When the damage is modelled using XFEM, the classical displacement is predicated on the finite element approximation in conjunction with the partition of unity method (PUM) paradigm, as per Melenk and Babuška [10, 11]. This permits the easy incorporation of local enrichment functions into the finite element approximation. Specifically, enrichment functions generally comprise near-tip asymptotic functions which apprehend the uniqueness encircling the crack tip and an intermittent role that signifies the displacement leap across the surfaces of cracks. Currently, the XFEM method represents the crack initiation, while proliferation manifests in concrete gravidynamics for pliant or brittle components, including the concrete gravity dams represented in the current project, according to ABAQUS/CAE [12, 13]. Using the (XFEM) technique, Zhang et al. [14] researched seismic cracking analysis of concrete gravity dams with initial cracks and found that the XFEM protocol would effectively forecast the crack propagation mechanism and the cracking profile under seismic conditions in concrete gravity dams. The XFEM has a slight mesh effect on the growth path of the crack and the final crack sequence, but due to the highly nonlinear issue, International Journal of Design & Nature and Ecodynamics Vol. 16, No. 6, December, 2021, pp. 683-689 Journal homepage: http://iieta.org/journals/ijdne 683