Slip resistance of metalized–galvanized faying surfaces in steel bridge construction Charles-Darwin Annan ⁎, Albert Chiza Department of Civil and Water Engineering, Université Laval, Québec City, Québec, Canada abstract article info Article history: Received 7 April 2013 Accepted 18 December 2013 Available online 25 January 2014 Keywords: Metalizing Galvanizing Steel bridge construction Slip-critical bolted connections Slip resistance Faying surfaces Design standards The slip resistance of high strength bolted connections depends on the surface condition of the connected parts, also known as the faying surfaces. Metalizing and galvanizing are two commonly used corrosion protection solutions in steel bridge construction, providing physical barrier as well as sacrificial protection. Practical situa- tions exist where galvanized secondary structural components are joined to primary elements that are metalized in a slip-critical connection. Contemporary bridge design standards, such as the Canadian Highway Bridge Design Code, CAN/CSA S6-06, and the American Institute of Steel Construction (AISC) specifications, ANSI-AISC 360- 2010, however do not specify slip coefficient for slip-resistant connections with one faying surface metalized and the other face galvanized. Steel bridge fabricators are therefore compelled to mask off all connection faying surfaces before metalizing. This exercise is time-consuming, labor-intensive, and costly. In this investigation, the resistance of slip-critical joints having metalized–galvanized faying surfaces is characterized in view of the current North American design standards. The mean slip coefficient, determined from short-duration tension and compression test regimes, revealed slip resistance greater than the typical faying surface with roughened hot-dip galvanized finish, and in the majority of cases, greater than the typical uncoated blast-cleaned faying surfaces. © 2014 Elsevier Ltd. All rights reserved. 1. Introduction Exposed elements in steel bridge construction may be subjected to severe environmental conditions. The use of de-icing salt in certain countries (e.g. Canada) increases the vulnerability of such structures. Surface coatings are used to provide protection against wear and corro- sion. They have significant effect on the design life and cost of maintain- ing the structure over its life. In contemporary practice, two of the most effective surface protection solutions are metalizing [1,2] and galvaniz- ing [3]. Metalizing is a common term used to describe thermal sprayed metal coatings; for corrosion control of steel elements, it refers to the thermal spray of molten zinc or aluminum alloys as a direct coating on the steel surfaces [4,5]. This is accomplished by feeding the metal in either wire or powder form to a spray gun where it is melted and sprayed. Upon deposition, it cools and resolidifies almost instantly, interlocking into the surface angular profile and providing physical barrier between the environment and the steel surface as well as an effective sacrificial protection [6]. Since this is a mechanical bond, the angularity of the profile is very important. The required surface prepara- tion for metalizing, according to the Society for Protective Coatings specification, is a white-metal blast finish, or a near-white-metal finish as a minimum [5]. Hot-dip galvanizing, on the other hand, is a total immersion process where the steel element is dipped into a bath of molten zinc metal until it comes up to the bath temperature. Like all zinc metal coating, the zinc forms a physical barrier, and also acts as a sacrificial anode providing cathodic protection. Unlike metalizing, however, upon immersion the zinc and steel surface react metallurgi- cally. The total immersion method and the size of the bath containing the molten zinc impose size limitations on structural elements that can be galvanized. Thus, for practical reasons, primary bridge elements such as girders are often metalized and connected to secondary compo- nents such as cross frames that are hot-dip galvanized. High strength bolted connections in structures under significant load reversal or fatigue-type loading are designed as slip-critical. In this type of connections, slip is intolerable at any time during the service life of the structure, i.e. at the serviceability limit state. The performance of slip-resistant bolted connections depends on the friction between the planes of contact, also known as faying surfaces, developed by the clamping action of the pretensioned bolts. The condition of the faying surfaces therefore controls this resistance. Once the frictional resistance is overcome, the connected parts slip into bearing and this could lead to intolerable geometric changes and affect the stability of the structure. The resistance to slip in a slip-critical bolted connection is governed by the total clamping force provided by the pretensioned bolts and the Journal of Constructional Steel Research 95 (2014) 211–219 ⁎ Corresponding author. Tel.: +1 418 656 2542; fax: +1 418 656 3355. E-mail address: Charles-Darwin.Annan@gci.ulaval.ca (C.-D. Annan). 0143-974X/$ – see front matter © 2014 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jcsr.2013.12.008 Contents lists available at ScienceDirect Journal of Constructional Steel Research