Thin–Walled Structures 148 (2020) 106601 Available online 25 January 2020 0263-8231/© 2020 Elsevier Ltd. All rights reserved. Full length article Experimental and numerical investigation of ultimate shear strength of unstiffened slender web-tapered steel members Mohamed Mostafa Ibrahim, Ihab Mohamed El Aghoury * , Sherif Abdel-Basset Ibrahim Department of Structural Engineering, Faculty of Engineering, Ain Shams University, Cairo, Egypt A R T I C L E INFO Keywords: Tapered beams Shear buckling Slender tapered web Unstiffened web Ultimate shear strength Experimental shear strength ABSTRACT This study investigates the ultimate shear strength of unstiffened slender web in prismatic tapered steel beams using newly proposed buckling coeffcients raised in the preceding research conducted by the authors [1]. An experimental program is performed using three specimens that are selected to fail in shear without any signif- icant fexural deformations. A three dimensional numerical fnite element model is established considering both material and geometrical non-linearities. The fnite element model is successfully calibrated to simulate the experimental tests. New procedures are proposed to predict the ultimate shear strength which is validated against the existing experimental results. The developed fnite element models are used to expand the validation range of the proposed method to include the practical ranges within the relevant specifcations limits. 1. Introduction and state-of-the-art Web tapered members are widely used in steel buildings and bridges due to their tendency to be highly optimized under the applied straining actions and forces. This optimization results in fully functional material consumption but usually leads to highly slender web plates. These highly slender unstiffened webs are more subjectable to the shear buckling phenomenon. Since the AASHTO [2] limits the depth to thickness ratio of web plate without longitudinal stiffeners to the value of 150, it would save a lot of fabrication costs to eliminate these stiffeners if not affecting the web strength. For the shear buckling limit state of unstiffened webs, the AISC Design Guide 25-“Frame design using web tapered members” [3] re- quires checking the members on a section-by-section basis along its length using the AISC specifcations for prismatic members. This pro- cedure ignores any gain in strength resulting from the stiffness provided by the “higher stiff zone” at the smaller plate width to the “less stiff zone” at the larger width. The EN 1993-1-5 Eurocode 3: Design of steel structures - Part 1–5: General rules - Plated structural elements [4] states that rules of rectangular web panels can be applied to non-rectangular web panels with an inclination angle (between non-parallel fanges) not greater than 10 � . Otherwise, panels can be assessed assuming it to be rectangular based on the larger panel width or fnite element methods. Historically, Basler’s model [5,6] served as the basis for the shear buckling strength evaluation in both the AASHTO [2] and the AISC [7] specifcations. Basler’s model recognizes the post-buckling shear strength only for stiffened web plates and considers the elastic shear buckling strength as the limit state for unstiffened webs. Simply sup- ported condition is used for the fange-to-web connection. The nominal shear strength V n is given by equation (1). V n ¼ 0:60F y A w C v (1) where F y is the web yield stress, A w is the web area and C v is the ratio of shear buckling stress to shear stress and is given by equation (2). C v ¼ 1:00 if h , t w < 1:1 ffffffffffffff k v E � F y q C v ¼ 1:1 ffffffffffffff k v E � F y q h=t w if 1:1 ffffffffffffff k v E � F y q < h , t w < 1:37 ffffffffffffff k v E � F y q C v ¼ 1:51k v E F y ðh=t w Þ 2 if 1:1 ffffffffffffff k v E � F y q < h , t w < 1:37 ffffffffffffff k v E � F y q (2) where h is the web depth, t w is web thickness, E is the modulus of elasticity of steel and k v is the shear buckling coeffcient of simply supported prismatic web given by equation (3). * Corresponding author. Department of Structural Engineering, Ain Shams University, Egypt. E-mail address: ihab.elaghoury@eng.asu.edu.eg (I.M. El Aghoury). Contents lists available at ScienceDirect Thin-Walled Structures journal homepage: http://www.elsevier.com/locate/tws https://doi.org/10.1016/j.tws.2020.106601 Received 29 August 2019; Received in revised form 19 November 2019; Accepted 4 January 2020