Contents lists available at ScienceDirect Soil Dynamics and Earthquake Engineering journal homepage: www.elsevier.com/locate/soildyn Seismic response of underwater fluid-conveying concrete pipes reinforced with SiO 2 nanoparticles and fiber reinforced polymer (FRP) layer Mohammad Sharif Zarei a , Reza Kolahchi b, ⁎ , Mohammad Hadi Hajmohammad c , Mostafa Maleki c a Faculty of Engineering, Ayatollah Boroujerdi University, Boroujerd, Iran b Department of Civil Engineering, Meymeh Branch, Islamic Azad University, Meymeh, Iran c Department of Mechanical Engineering, Imam Hossein University, Tehran, Iran ARTICLE INFO Keywords: SiO 2 nanoparticles Seismic response Fluid-conveying concrete pipes First order shear deformation theory (FSDT) Differential quadrature method (DQM) ABSTRACT This study aims at investigating the seismic response of the fluid-conveying concrete pipes reinforced with SiO 2 nanoparticles and fiber reinforced polymer (FRP) layer. The earthquake acceleration is consistent with the earthquake occurred in Tabas. It is assumed that the structure is subjected to external forces which exerted by inner and outer fluids. The force due to the inner fluid is evaluated using Navier-Stokes equation. Also, Mori- Tanaka model is employed to take into account the agglomeration effect of SiO 2 nanoparticles. The mathema- tical model of the structure is developed based on the first order shear deformation theory (FSDT) and the governing equations are derived using energy method and Hamilton's principle. Finally, the problem is solved employing differential quadrature method (DQM) and Newmark method and the effect of different parameters like SiO2 nanoparticles agglomeration and volume percent, inner and outer fluids, various boundary conditions and geometric parameters on the dynamic deflection of the structure is studied. The results indicate that with increasing the thickness to radius ratio and volume fraction of SiO2 nanoparticles and also employing the NFRP layer, the dynamic deflection of the structure decreases while considering the effect of inner and outer fluids and agglomeration of SiO2 nanoparticles and increasing the length to thickness ratio increases the dynamic de- flection of the structure. 1. Introduction Underwater pipelines can be used to carry oil, gas and water. The structure is often shielded against external corrosion by coatings such as epoxy, concrete or fiberglass. In addition, the concrete coating is also useful to compensate for the pipeline's negative buoyancy when it carries lower density substances. The underwater pipelines are exposed to seismic loads and however, the reinforce of these structure is very important. In this work, the SiO 2 nanoparticles and FRP layer are used for reinforcement of the underwater pipe subjected to earthquake load. The earthquakes in different parts of the world reveal the necessity of the seismic analysis of the structures which have a higher chance to be damaged and fractured. Therefore, many researchers investigate the seismic response of the various structures. For instance, Cai et al. [1] probed the seismic response of short circular reinforced concrete col- umns. They assumed that the structure is subjected to combined con- stant axial compression and lateral cyclic load. Chacon et al. [2] ex- amined the seismic response of the reinforced concrete free-plan structures. The seismic behavior of steel reinforced Ultra high strength concrete column and reinforced concrete beam connection is studied by Changwang et al. [3]. They discussed the influences of applied axial load ratio and volumetric stirrup on the strength degradation, ductility and rigidity degradation. Also, Chen et al. [4] investigated the seismic response of the Zipingpu concrete face rockfill dam employing finite element method (FEM). Experimental investigation of crumb rubber concrete columns (CRC) subjected to seismic loading is presented by Youssf et al. [5]. The pipelines are one of the most significant structures which affected by seismic waves dramatically. Bi et al. [6] analyzed the stochastic seismic response of buried onshore and offshore pipelines. Zhang et al. [7] developed nonlinear equations of three-dimensional motion to study dynamic behavior of straight fluid-conveying pipes with general boundary conditions. Also, He et al. [8] proposed a the- oretical investigation of an elastic and slender fluid-conveying pipe. Kjolsing and Todd [9] studied damping of a fluid-conveying pipe sur- rounded by a viscous annulus fluid. They used a hydrodynamic forcing function to simulate the annulus fluid and solved the problem using the spectral element method. Li and Hu [10] evaluated critical flow velo- city of fluid-conveying magneto-electro-elastic pipe. They assumed the structure resting on Winkler elastic foundation. They developed math- ematical formulation based on Timoshenko beam theory and derive the http://dx.doi.org/10.1016/j.soildyn.2017.09.009 Received 8 June 2017; Received in revised form 10 July 2017; Accepted 16 September 2017 ⁎ Corresponding author. E-mail address: r.kolahchi@gmail.com (R. Kolahchi). Soil Dynamics and Earthquake Engineering 103 (2017) 76–85 0267-7261/ © 2017 Elsevier Ltd. All rights reserved. MARK