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- To: seaint(--nospam--at)seaint.org
- Subject: Re: crack control
- From: "Bill Sherman" <SHERMANWC(--nospam--at)cdm.com>
- Date: 28 Jul 98 19:25:23 -0400
Roger Turk wrote: > I have a problem understanding the crack control requirements of the ACI code. I understand the stated theory about the crack control requirements, but don't understand why additional cover will require more reinforcing. If the width of the crack at the surface is the limiting factor, then increased cover should have less effect on the exposure of the reinforcing to corrosive environments...Since the crack control requirements do not apply if Grade 40 steel is used, that is the maximum amount of reinforcing that I will use in a footing, regardless of whether or not Grade 60 reinforcing is used. < The crack control formulas are based on limiting crack width at the concrete surface. Greater concrete cover correlates to greater crack width at the surface. Providing closer spaced, smaller diameter bars helps reduce crack width. More steel reduces service load stress, so reduces crack width. Design for Grade 40 bars was assumed to provide low enough stress to avoid special crack control design. Crack control for buildings is based both on corrosion protection and on aesthetics of cracks (wider cracks are less pleasing). Based on these facts, I would agree that if you use Grade 60 steel but base your design on Grade 40 steel, you should not need to calculate crack equations. Also, for water retaining structures, ACI 350R states that Z-values were established for cover less than 2-inches and when providing concrete cover greater than 2-inches the extra cover should not be used in the Z-equation but should be "regarded as added protection" (i.e., control the crack width at 2-inches from the steel and provide additional by judgement). Thus greater cover may provide wider looking cracks but should provide adequate corrosion protection. Hope this helps you.
- Re: crack control
- From: markah
- Re: crack control
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