Strengthening under Load: The Effect of Preload Magnitudes
Abstract
Strengthening existing structures under load by welding plates is often conducted but little research into this subject was presented. Some researchers claim that the column strengthened under load has the same ultimate capacity as the column welded without preloading. Others disagree and recommend safe design not allowing the steel to yield. The paper presents the parametric study of wide flange columns HEA 100 strengthened under load via two plates parallel to flanges conducted on numerical models validated by experiment. The varying parameters are thickness of strengthening flange, column length, initial bow imperfection, preload magnitude and direction of the axis which is pinned while the other axis is fixed. The experimental research consisted of two columns welded without preload and two columns strengthened under preload ratios (preload magnitude divided by base column ultimate strength) equal to 0.5 (200 kN) and 0.75 (300 kN). All columns were 3 m long and the boundary conditions were determined by knife-edge bearings which ensured pinned supports in the direction perpendicular to the strong axis and fixed perpendicular to the weak axis. All strengthening plates were welded to columns with intermittent welds. All columns failed via flexural buckling. The numerical models used for the parametric study were created in ANSYS software. Design values and procedures recommended by EN 1993-1-5, Annex C were used. The most commonly used steel grade S235 was selected for all plates. Shell 181 element type was used for mapped meshing of steel plates. Element birth and death feature was convenient to simulate strengthening under load. Equivalent initial bow imperfection of the first Eigen buckling shape was included, the model was loaded by force and geometrical and material nonlinear analyses were performed. From provided results some conclusions can be reached. The load under which the column is strengthened slightly weakens the column but not by far to the extent of design recommendations used in the Czech Republic. The reduction ratio (ultimate load capacity of column strengthened under load divided by ultimate load capacity of column welded without preloading) decreases with increasing preload magnitude and column slenderness. Surprisingly, the initial geometrical imperfection, while affecting ultimate capacity greatly, has almost no effect on the reduction ratio.
Full text
Procedia Engineering 161 ( 2016 ) 343 – 348 Available online at www.sciencedirect.com 1877-7058 © 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of WMCAUS 2016 doi: 10.1016/j.proeng.2016.08.570 ScienceDirect :RUOG0XOWLGLVFLSOLQDU\&LYLO(QJLQHHULQJ$UFKLWHFWXUH8UEDQ3ODQQLQJ6\PSRVLXP :0&$86 6WUHQJWKHQLQJXQGHU/RDG7KH(IIHFWRI3UHORDG0DJQLWXGHV 0DUWLQ9LOGD0LURVODY%DMHUD aBrno University of Technology, Faculty of Civil Engineering, Institute of Metal and Timber Structures, VeveĜí 331/95, 602 00 Brno, Czech Republic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eywords:)LQLWHHOHPHQWDQDO\VLVIOH[XUDOEXFNOLQJVWHHOFROXPQVWUHQJWKHQLQJZHOGLQJ &RUUHVSRQGLQJDXWKRU7HO E-mail address:YLOGP#IFHYXWEUF] © 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of WMCAUS 2016
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