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Construction Concerns: Anchor Bolts in Concrete

Article and photos by Gregory HavelMarch 9, 2009

When a steel-framed structure is built, it usually features a steel frame that rests onconcrete foundations. The structural steel must be connected to the foundation or thebuilding will collapse before it is completed. The traditional way to set anchor bolts inconcrete is to embed long L-shaped bolts in the concrete foundation while it is beingpoured. When the concrete has set and cured, these bolts cannot be pulled out of theconcrete without destroying the foundation.

The structural engineer designs the concrete foundations dimensions and the length,diameter, and spacing of the bolts; he also specifies the size of the steel columns,flanges, and bolt holes.

Photo 1 shows four large anchorbolts prepared to be set in aconcrete foundation. The boltshave been assembled ontopiece of oriented strand board(OSB) that was made from thetemplate the steel fabricatorsupplied to match the bolt hon the columns bottom flanges.Wood bridging on the concreteforms holds the assembly at theproper elevation; sometimes tiewires to the steel rebar arAlthough the concretefoundation can be poured sothat it is close to the elevationneeded for the steel columoften isn

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Fire Engineering, March 9, 2009


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Photo 2 (left) shows the anchorbolts after the concrete

foundation has set. The OSBtemplate has been removedand replaced with a steelsetting plate from thestructural steel fabricator. Nutsthreaded onto the anchor boltssupport this plate. These nutswill be adjusted so that thesetting plate is level and atprecisely the elevation thestructural steel columnsrequire. The nuts on top will

lock the setting plate in place.

Photo 3 (right) shows the setting plateafter the space between it and theconcrete foundation has been packedwith quick-setting Portland-cementgrout for added strength. After thegrout has cured, the top nuts areloosened. The nuts will be removedcompletely to set the column,

replaced, and tightened to hold thecolumn in place. Usually, thiscompleted connection is not visible inthe completed building because it isbelow floor level and covered by apoured concrete floor, or embeddedinside a masonry wall.

This system provides a strong connection between column and foundation. Itsdisadvantage is that it leaves little room for error. The bolt holes in column flanges areusually large enough to compensate for an anchor bolt that is 1/8-inch out of alignment.

If the error is large enough so that the column flange does not fit, either the flange or theanchor bolt must be modified. Any modification of anchor bolts for structural steelrequires the written approval of the design structural engineer, according to consensusstandards and the requirements of the Occupational Safety and Health Administration(OSHA). If the anchor bolts are too far from their proper location or of the wrong size, theengineer may order them to be cut off and replaced with new anchor bolts epoxied orgrouted into holes drilled deep into the foundation.



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In the past, a too-frequent cause of structural collapse during construction was thesetting of structural steel before the concrete foundations or masonry walls weresufficiently cured. OSHAs 2001 revision of the Steel Erection Standard (29 CFR 1926Subpart R (1926.750 through 1926.761, plus Appendixes A-H) requires that contractorsfollow the procedures outlined to reduce the possibility of building collapse duringconstruction, providing a safe place for contractor employers to work, and a less-

hazardous environment for emergency responders who may be called.

OSHAs complete Steel Erection Standard can be found athttp://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=STANDARDS&p_id=10939

Section 1926.752 outlines the written notifications required before any steel is set,including the strength of foundations and masonry piers, and may be found athttp://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=STANDARDS&p_id=10788

Section 1926.755 discusses strength requirements for and modification of anchor bolts,and may be found athttp://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=STANDARDS&p_id=12746

Gregory Havel is a member of the Burlington (WI) Fire Department; a retired deputychief and training officer; and a 30-year veteran of the fire service. He is a Wisconsin-certified fire instructor II and fire officer II, an adjunct instructor in fire service programs atGateway Technical College, and safety director for Scherrer Construction Co., Inc. Havelhas a bachelor's degree from St. Norbert College and has more than 30 years ofexperience in facilities management and building construction.

CLICK HERE for more 'Construction Concerns' articles!

http://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=STANDARDS&p_id=10939http://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=STANDARDS&p_id=10788http://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=STANDARDS&p_id=12746http://www.fireengineering.com/training/categoryLanding.html?title=Construction%20Concerns&catId=CNSTChttp://www.fireengineering.com/training/categoryLanding.html?title=Construction%20Concerns&catId=CNSTChttp://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=STANDARDS&p_id=12746http://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=STANDARDS&p_id=10788http://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=STANDARDS&p_id=10939

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