Uncoated Weathering Steel Reference Guide
Uncoated Weathering Steel Reference Guide
by
American Institute of Steel Construction
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The information presented in this publication has been prepared following recognized principles of designand construction. While it is believed to be accurate this information should not be used or relied upon for any specific application without petent professional examination and verification of its accuracy suitability and applicability by a licensed engineer or architect. The publication of this information is not a employees or mittee members or of any other person named herein that this information is suitableeseesseosaaosmaking use of the information presented in this publication assumes all liability arising from such use.
Caution must be exercised when relying upon standlards and guiclelines cleveloped by other bodies andincorporated by reference herein since such material may be modified or amendled from time to time sub-for such material other than to refer to it and incorporate it by reference at the time of the initial publicationof this edition.
Printed in the United States of America
Executive Summary
This manual is intended to provide guidance to bridgeowners and designers on when it is appropriate to (S) pas pn onconstruction and how to design detail fabricate con struct t e ta n ar woverview of the information contained in the manual. ing steel bridges. This summary document provides anReaders should consult the content of the manual fordetailed guidance.
Benefits of UWS
The primary benefit of using UWS is reduced cost both in terms of initial fabrication and constructioncosts). Additional benefits include reduced fabrication costs as well as long term maintenance costs (life cycletime for structural steel and potentially enhanced aes-thetics. Initial cost savings over painted systems are estimated to be approximately 10% while the savingsin life cycle costs may approach 30%. The elimination of the painting steps including drying time duringfabrication reduces the time needed to fabricate gird-construction schedule. ers and other structural ponents accelerating the
When to use UWS
In general UWS is appropriate to use in the vast ma-jority of locations. There are two main factors that in bination warrant further evaluation of use: highrides. Depending on the conditions present at a spe- atmospheric humidity and high concentration of chlo-cific site the usage remendations are:
to use UWS • to use UWS thoughtfully that is to carefullyfactors or consider the conditions and possible mitigation• to not use UWS at that site
extreme before UwS would no longer be a viable op- In general multiple factors need to be near theirtion for a site.
chloride concentration and moisture traps are a func- These main factors of atmospheric humidity tion of the general climate at the site (the macro-en- vironment) and the local conditions at the site (themicro-environment). The particular binations thatmay result in UWS not being remended are:
A coastal environment or one with an extreme-ly high time-of-wetness in bination with either:A low vertical clearance over water or close-inSup vegetation or shelter preventing the steel from
mended or remended to be used with some fore- For all other site conditions UWS is either re-thought. Coastal environments are defined as beingwithin 2 miles of the shoreline with average monthly relative humidity exceeding 75% for 8 or more monthsto isolated locations in the pacific northwest where of the year. High time of wetness locations are limitedrainfall rates can be extreme.
concern only when the amount of salt used in bi- Highway crossings with deicing salt use are of anation with the amount of traffic under the bridge ap- proach extreme values. For the vast majority of high-p m jo see ssso edesign remendations are followed. salts are used UWS should perform well provided the
Design Remendations
The most important design remendation is to pre-vent water from continuously flowing or ponding on the steel surfaces. A primary method to achieve thisgoal is to eliminate or minimize the number of joints ona bridge. Experience has shown drainage that directlyother material types) through a leaking or failed joint o senbape jep pue soueoad sood u snsanmaintenance cannot be reliably guaranteed. Elimina-tion of deck joints through the use of jointless bridges should be employed where possible. Long continuousgirder lengths link slabs and other methods can be utilized to minimize the number of deck joints. Whendeck joints must be present positioning them at abut-ments and locating them on the back side of the back- wall can prevent drainage from reaching the girdersand diaphragms.
Careful consideration of the drainage system ei-ther at joints or through scuppers is needed to ensuredoes not cause corrosion. Key considerations when the water is carried as desired off of the structure andging ease of inspection and cleaning and ensuring the designing drainage systems is the prevention of clog-bottom of any free-drop pipe is well below the loweststeel elevation.
For closed ponents like box girders or boxany moisture or water that enters the member should section truss members provision for drainage ofbe provided. Design approaches that minimize theamount of water entering box members should be uti- lized but should not be relied upon entirely. Past ex-member against all moisture ingress. perience has shown it is difficult to pletely seal a