Thursday, September 29, 2011

Re: Allowable flexural crack width


I believe the reinforcing steel has yielded because the crack extends the full height of the reduced beam height.  There is no concrete crushing damage present.  There is cracking (multiple cracks, 3 or 4 in some spots) in a classic flexural crack pattern on the tension side of the beams.  The bottom of the grade beams where the beam height reduces at the opening, and the top of the beam where it goes over the pier (still in the opening), and then at the bottom of the grade beam where the grade beam depth increases back up to the full wall height at the other edge of the opening.  Although the wall on one side could be designed to cantilever over the pier and support the load above (the wall is over 100 feet long in that direction) on the other side it cannot as there is a corner.  In my opinion, it was not a very good location for the pier being right in the middle of the opening.  In fact there are similar ventilation openings on the other walls that run parallel with the slab above and on those walls the piers are placed on each side of the openings even though the walls are loaded a lot less.  Looks to me like a drafting error or the openings were just added to the plans without looking at what was really going on.  Well, as you said what I am looking at is really a moot point because there is not near enough steel in the shorter section of the beam to accommodate what is going on.  It just got me thinking, what if the calculations showed that the section was adequate?  How large a crack would be expected to be normal based on the loading, etc.  If everything is detailed and constructed correctly would you expect to see cracks up to 1/8” wide? In many of the crawl spaces with grade beams I have been in I have never seen a crack 1/8” wide.  Obviously there could be a large variation in this due to how it gets constructed versus how it was calculated.  There are cracks in other portions of this structure that my client is concerned about.  If I had a way to calculate an expected crack width, it would be easier to convince them that the cracks are not a structural integrity concern, although we would still want to seal them to prevent corrosion.



Jeff Hedman , S.E.

L.R. Pope Engineering, Inc.

1240 East 100 South Suite # 15B

St. George, Utah  84790

Office: 435-628-1676

Fax: 435-628-1788



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