THE TWO MOST IMPORTANT SENTENCES IN CRANE STEEL DESIGN

The following comes from Part 2, Section 19 of the AISC Steel Design Guide 7, 2nd Ed. 2016, by James M. Fisher. The words of the first paragraph are the writings of Jim Fisher, and the emphasis is mine. The important fact encompassed in this paragraph is that the critical differences between runway tolerances and building steel tolerances are understood by a few and acted upon by even fewer.

Buyers must understand that they cannot assume that the sellers will voluntarily accommodate this issue. It would be virtually impossible to be both the low bidder and the only bidder to quote “doing the job right.” Therefore, it is incumbent on the buyer to take the time and money to construct a comprehensive set of specifications to protect themselves against unethical low bidders or be prepared to suffer the consequences.

Crane Buyer Spoiler Alert:

Contrary to the overwhelming majority of buyer crane specs that I have seen, adequate protection for the buyer is not to simply writing, “cranes must conform to CMAA 70/74.” Crane runways are almost always fabricated by building steel fabricators and as Jim Fisher clearly states in Design Guide 7, “Crane runway fabrication and erection tolerances should be addressed in the project specifications because standard tolerances used in steel frameworks for buildings are not tight enough for buildings with cranes.”

In other words, “Buyer Beware,” you have one chance to write the rules of the transaction or forever hold your peace.

AISC DESIGN GUIDE 7:

PART 2:

SECTION 19. CRANE RUNWAY FABRICATION AND ERECTION TOLERANCES

AISC Design Guide 7, 2nd Ed, by James Fisher

Crane runway fabrication and erection tolerances should be addressed in the project specifications because standard tolerances used in steel frameworks for buildings are not tight enough for buildings with cranes. Also, some of the required tolerances are not addressed in standard specifications.

Tolerances for structural shapes and plates are given in the Standard Mill Practice section of the Manual of Steel Construction published by AISC. These tolerances cover the permissible variations in geometrical properties and are taken from ASTM Specifications, AISI Steel Product Manuals and Producer’s Catalogs. In addition to these Standards, the following should be applied to crane runways.

Sweep: not to exceed 1⁄4 in. in a 50-ft. beam length.
Camber: not to vary from the camber given on the drawing by plus or minus 1⁄4 in. in a 50-ft. beam length.
Squareness: within 18 in. of each girder end the flange shall be free of curvature and normal to the girder web.

Columns, base plates and foundations should adhere to the following tolerances.

Column anchor bolts shall not deviate from their theoretical location by 0.4 times the difference between bolt diameter and hole diameter through which the bolt passes.
Column base plates: Individual column base plates shall be within ± 1/16 in. of theoretical elevation and be level within ± 0.01 in. across the plate length or width. Paired base plates serving as a base for double columns shall be at the same level and not vary in height from one to another by 1/16 in.

Crane runway girders and crane rails shall be fabricated and erected for the following tolerances.

Crane rails shall be centered on the centerline of the runway girders. The maximum eccentricity of center of rail to centerline of girder shall be three-quarters of the girder web thickness.
Crane rails and runway girders shall be installed to maintain the following tolerances.

The horizontal distance between crane rails shall not exceed the theoretical dimension by ± 1⁄4 in. measured at 68 °F.
The longitudinal horizontal misalignment from straight of rails shall not exceed ± 1⁄4 inch in 50 ft with a maximum of ± 1⁄2 in. total deviation in the length of the runway.
The vertical longitudinal misalignment of crane rails from straight shall not exceed ± 1⁄4 in. in 50 measured at the column centerlines with a maximum of ± 1⁄2 in. total deviation in the length of the runway.

The foregoing tolerances are from the AISE Technical Report No. 13. The Table shown in Figure 19.1 is taken from MBMA’s Low Rise Building Systems Manual and gives alternate tolerances.