Strengthening of aluminium and stainless steel tubular sections with fibre-reinforced polymer

Abstract

Strengthening of aluminium and stainless steel structural tubular sections using

adhesive bonded fibre-reinforced polymer (FRP) subjected to web crippling has been

investigated. Aluminium and stainless steel tubular sections may experience web

crippling failure due to local concentrated loads or reactions. The web crippling

strength can be enhanced by strengthening the webs of the sections in localized

regions. The current international specifications of aluminium and stainless steel

structures do not provide web crippling design rules for strengthening of tubular

sections. Therefore, there is a need to develop safe and reliable web crippling design

rules for FRP strengthened aluminium and stainless steel structures.

An extensive test program was performed on FRP strengthening of aluminium and

cold-formed stainless steel tubular sections subjected to web crippling. The test

specimens consisted of 6061-T6 heat-treated aluminium alloy, ferritic stainless steel

type EN 1.4003 and lean duplex type EN 1.4162 square and rectangular hollow

sections. A total of 254 web crippling tests was conducted in this study. The tests

were performed on eighteen different sizes of tubular sections which covered a wide

range of web slenderness (flat portion of web depth-to-thickness) ratio from 6.2 to

62.2.

The web crippling tests were conducted under the four loading conditions according

to the American Specification and Australian/New Zealand Standard for cold-formed

steel structures, namely End-Two-Flange, Interior-Two-Flange, End-One-Flange and

Interior-One-Flange loading conditions. The investigation was mainly focused on the

effects of different adhesive, FRP, surface treatment, widths of FRP plate and web

slenderness of tubular sections for strengthening against web crippling. Six different

adhesives, six different FRPs, two different surface treatments, three different widths

of FRP plate were considered. It was found that the web crippling capacity of

aluminium tubular sections are significantly increased due to FRP strengthening,

especially for those sections with large value of web slenderness. The web crippling

strength can be increased up to nearly 3 times using the appropriate adhesive and

FRP for aluminium tubular sections, whereas the web crippling strength can be

increased up to 51% and 76% for ferritic and lean duplex stainless steel tubular

sections, respectively.

The finite element models for FRP strengthened aluminium and stainless steel

tubular structural members subjected to web crippling were developed and calibrated

against the experimental results. The debonding between FRP plate and aluminium

or stainless steel tubes was carefully modelled using cohesive element. It is shown

that the calibrated model closely predicted the web crippling strengths and failure

modes of the tested specimens. An extensive parametric study included 212 web

crippling specimens was carried out using the verified finite element models to

examine the behaviour of strengthened aluminium and stainless steel tubular sections

subjected to web crippling.

Design equations are proposed to predict the web crippling strengths of FRP

strengthened aluminium and stainless steel tubular sections based on the

experimental and numerical results. The web crippling strengths obtained from the

tests and numerical analysis were compared with the design strengths calculated

using the proposed equations. The reliability of the proposed design rules was

evaluated using reliability analysis.