Contents lists available at ScienceDirect Thin-Walled Structures journal homepage: www.elsevier.com/locate/tws Full length article Buckling and post-buckling behavior of various dented cylindrical shells using CFRP strips subjected to uniform external pressure: Comparison of theoretical and experimental data Mahyar Maali a , Mahmut Kılıç a , Zeynep Yaman b , Elif Ağcakoca b , Abdulkadir Cüneyt Aydın a, ⁎ a Engineering Faculty, Department of Civil Engineering, Ataturk University, 25030 Erzurum, Turkey b Faculty of Engineering and Architecture, Department of Civil Engineering, Sakarya University, Sakarya, Turkey ARTICLE INFO Keywords: Cylindrical shell CFRP Dent shape Theoretical and experimental External pressure ABSTRACT Thin-walled circular cylindrical shells are used in many civil engineering applications. Any initial geometric imperfections and the type of applied load determine the buckling and the post buckling of cylindrical thin- walled shell structures. Fourteen thin-walled cylindrical shell models in two groups (labelled without CFRP and with CFRP) with different dent directions (H= horizontal, V= vertical and D= 45° diagonal direction) and dent depths (2t c and 4t c ) subjected to external pressure were tested in the present research (t c is the thickness of the cylindrical shell). The results of testing under different theories and codes are compared. Moreover, the results are identified and investigated in the present experimental research. 1. Introduction Any initial geometric imperfections and the type of applied load determine the buckling and the post buckling of thin-walled shell structures [1–3]. Eurocode 3 ECCS and DINI 18,800 [4,5] have all set limitations for rolling and welding-induced imperfections. Most re- cently, the effect of longitudinal stiffening on cylindrical shells under external pressure was investigated and the relevant literature show that the buckling capacity increased as a result of the stiffening [6–9]. Ghanbari Ghazijahani et al. [7] investigated the effect of circular openings on the fatigue behavior of circular hollow sections. They ex- perimented with 8 specimens of different cutout diameters but did not study different positions of the circular hollow sections. Also, Ghanbari Ghazijahani et al. [8] studied tubes with door-shaped cutouts under axial loading. Different buckling modes as well as the effect of geo- metric parameters of a cutout were examined in this study. A stiffening method was also used to reduce the effect of the cutout on the capacity of such structures. Ghanbari Ghazijahani et al. [9] conducted an ex- perimental study on such corrugated thin-walled structures under uniform peripheral pressure. They experimented with 5 specimens with relatively small initial geometrical imperfections. They experimented with constant vertical initial geometrical imperfections over the whole of the cylindrical shell with constant thickness. Moreover, Ghanbari Ghazijahani et al. [10] conducted an experimental study on externally pressurized, stiffened and thickened cylindrical shells, and they showed that the effect of strengthening provided by local thickening was slightly less but comparable to that provided by the stiffeners. In this research, the effect of partial and full length stiffening of shells was studied in which the stiffeners were attached without welding to avoid the adverse effects of the residual stresses. They studied 9 laboratory cylindrical shell specimens, With the thickness of the cylindrical shell being constant. Ghanbari Ghazijahani et al. [11] investigated timber filled carbon fibre reinforced polymer (CFRP) jacketed circular steel tubes under axial compression. They discussed the structural behavior of an innovative composite column through an experimental study. The new composite comprised steel cylindrical hollow sections, solid timber infill and CFRP confinements. Ifayefunmi [12] conducted an experi- ment on the buckling of short mild steel cylindrical shells subjected to axial compression. He studied two sets of nominally identical cylinders (1 mm and 2 mm wall thickness) that failed at almost the same mag- nitude of collapse force. The cylinders were joined together using a Metal Inert Gas welding process with a radius-to-thickness ratio, R/t, ranging from 25 to 100. Moreover, Ghanbari Ghazijahani et al. [13] conducted an investigation on a dented cylindrical shell under per- ipheral pressure. They did not use CFRP on the dent section. In addi- tion, their dent depth was different. Vakili and Showkati [14] studied elephant foot type buckling and retrofitting of cylindrical shells by fibre-reinforced polymer (FRP). Their study examined inelastic buck- ling behavior of cylindrical shells near the base, known as elephant foot buckling. This form of buckling occurs under high internal pressure https://doi.org/10.1016/j.tws.2018.12.042 Received 16 April 2018; Received in revised form 12 December 2018; Accepted 31 December 2018 ⁎ Corresponding author. E-mail address: acaydin@atauni.edu.tr (A.C. Aydın). Thin-Walled Structures 137 (2019) 29–39 0263-8231/ © 2018 Elsevier Ltd. All rights reserved. T