1、1Steel Design GuideBase Plate and Anchor Rod DesignSecond Editioncover_DG1_2ndPrint_cover.indd 1 4/8/2010 7:34:49 PM1Steel Design Guideamerican institute of steel constructionBase Plate andAnchor Rod DesignSecond EditionJAMES M. FISHER, Ph.D., P.E. computerized structural Design, s.c.milwaukee, Wisc
2、onsinandLAWRENCE A. KLOIBER, P.E. leJuene steel companyminneapolis, minnesota00i-0vi_DG1_titlePage_acknow_TOC.indd 1 3/31/10 11:54:20 AMAISC 2006byAmerican Institute of Steel ConstructionAll rights reserved. This book or any part thereof must not be reproduced in any form without the written permiss
3、ion of the publisher. The AISC logo is a registered trademark of AISC.The information presented in this publication has been prepared in accordance with recognized engineering principles and is for general information only. While it is believed to be accurate, this information should not be used or
4、relied upon for any specific application without competent professional examination and verification of its accuracy, suitability, and applicability by a licensed professional engineer, designer or architect. The publication of the material contained herein is not intended as a representation or war
5、ranty on the part of the American Institute of Steel Construction or of any other person named herein, that this information is suitable for any general or particular use or of freedom from infringement of any patent or patents. Anyone making use of this information assumes all liability arising fro
6、m such use.Caution must be exercised when relying upon other specifications and codes developed by other bodies and incorporated by reference herein since such material may be modified or amended from time to time subsequent to the printing of this edition. The Institute bears no responsibility for
7、such material other than to refer to it and incorporate it by reference at the time of the initial publication of this edition.Printed in the United States of AmericaFirst Printing: May 2006Second Printing: March 201000i-0vi_DG1_titlePage_acknow_TOC.indd 2 3/31/10 11:54:20 AMiacknowledgmentsThe auth
8、ors would like to thank Robert J. Dexter from the University of Minnesota, and Daeyong Lee, Steel Structure Research Laboratory, Research Institute of Industrial Science consistent with the approach used in the AISC Specification. Many of the equations shown herein are independent of the load approa
9、ch, and thus are applicable to either design method-ology. These are shown in singular format. Other derived equations are based on the particular load approach and are presented in a side-by-side format of comparable equations for LRFD or ASD application.The typical components of a column base are
10、shown in Figure 1.1. This figure shows anchor rods that are threaded and nutted at the embedded end. Anchor rods also may be headed or have hooked ends.Material selection and design details of base plates can significantly affect the cost of fabrication and erection of steel structures, as well as t
11、he performance under load. Rel-evant aspects of each of these subjects are discussed briefly in the next section. Not only is it important to design the column-base-plate connection for strength requirements, it is also important to recognize these connections affect the behavior of the structure. A
12、ssumptions are made in struc-tural analysis about the boundary conditions represented by the connections. Models comprising beam or truss elements typically idealize the column base connection as either a pinned or fixed boundary condition. Improper characteriza-tion can lead to error in the compute
13、d drifts, leading to un-recognized second-order moments if the stiffness is overes-timated, or excessive first-floor column sizes if the stiffness is underestimated. If more accurate analyses are desired, it may be necessary to input the stiffness of the column-base-plate connection in the elastic a
14、nd plastic ranges, and for seismic loading, possibly even the cyclic force-deformation relations. The forces and deformations from the structural analyses used to design the column-base-plate connection are dependent on the choice of the column-base-plate con-nection details.Fig. 1.1. Column base co
15、nnection components.001-064_DG1_2nd_Ed.indd 1 3/31/10 11:55:03 AM2 / BASE PLATE AND ANCHOR ROD DESIGN / AISC DESIGN GUIDE 1, 2ND EDITIONalong with practical suggestions for detailing and installing anchor rod assemblies. These guidelines deal principally with cast-in-place anchors and with their des
16、ign, installation, inspection and repair in column-base-plate connections.AISC Design Guide 7, Industrial Buildings: Roofs to Col-umn Anchorage (Fisher, 2004), hereafter referred to as AISC Design Guide 7, contains additional examples and discus-sion relative to the design of anchor rods.2.0 MATERIA
17、LS, FABRICATION, INSTALLATION AND REPAIRS2.1 Material SpecificationsThe AISC Specification lists a number of plate and threaded rod materials that are structurally suitable for use in base plate and anchor rod designs. Based on cost and availability, the materials shown in Tables 2.1 and 2.2 are rec
18、ommended for typical building design.2.2 Base Plate Material SelectionBase plates should be designed using ASTM A36 material unless the availability of an alternative grade is confirmed prior to specification. Since ASTM A36 plate is readily available, the plates can often be cut from stock material
19、. There is seldom a reason to use high-strength material, since increasing the thickness will provide increased strength where needed. Plates are available in 8-in. increments up to 1-in. thickness and in -in. increments above this. The base plate sizes specified should be standardized during de-sig
20、n to facilitate purchasing and cutting of the material.When designing base plate connections, it is important to consider that material is generally less expensive than labor and, where possible, economy may be gained by using thick-er plates rather than detailing stiffeners or other reinforce-ment
21、to achieve the same strength with a thinner base plate. A possible exception to this rule is the case of moment-type bases that resist large moments. For example, in the design The vast majority of building columns are designed for axial compression only with little or no uplift. For such col-umns,
22、a simple column-base-plate connection detail like that shown in Figure 1.1 is sufficient. The design of column-base-plate connections for axial compression only is presented in Section 3. The design is simple and need not be encumbered with many of the more complex issues discussed in Appen-dix A, w
23、hich pertains to special structures. Anchor rods for gravity columns are often not required for the permanent structure and need only be sized to provide for column sta-bility during erection.Column-base-plate connections are also capable of transmitting uplift forces and can transmit shear, includi
24、ng through the anchor rods if required. If the base plate remains in compression, shear can be transmitted through friction against the grout pad or concrete, thus the anchor rods are not required to be designed for shear. Large shear forces can be resisted by bearing against concrete, either by emb
25、ed-ding the column base, or by adding a shear lug under the base plate.Column-base-plate moment connections can be used to resist wind and seismic loads on the building frame. Moment at the column base can be resisted by development of a force couple between bearing on the concrete and tension in so
26、me or all of the anchor rods.This Guide will enable the designer to design and specify economical column base plate details that perform adequate-ly for the specified demand. The objective of the design pro-cess in this Guide is that under service loading, and under extreme loading in excess of the
27、design loads, the behavior of column base plates should be close to that predicted by the approximate mathematical equations in this Design Guide.Historically, two anchor rods have been used in the area bounded by column flanges and web. Recent regulations of the U.S. Occupational Safety and Health
28、Administra-tion (OSHA)Safety Standards for Steel Erection (OSHA, 2001) (Subpart R of 29 CFR Part 1926)require four an-chor rods in almost all column-base-plate connections, and require all columns to be designed for a specific bending mo-ment to reflect the stability required during erection with an
29、 ironworker on the column. This regulation has essentially eliminated the typical detail with two anchor rods except for small post-type structures that weigh less than 300 pounds (e.g., doorway portal frames).This Guide supersedes the original AISC Design Guide 1 Column Base Plates. In addition to
30、the OSHA regulations, there has been significant research and improved design guidelines issued subsequent to the publication of Design Guide 1 in 1990. The ACI Building Code Requirements for Structural Concrete, ACI 318-08 (ACI, 2008), has improved provisions for the pullout and breakout strength o
31、f anchor rods and other embedded anchors. Design guidance for an-chor rods based on the ACI recommendations is included, Table 2.1. Base Plate MaterialsThickness (tp) Plate Availabilitytp 4 in.ASTM A36aASTM A572 Gr 42 or 50ASTM A5884 in. 6 in.ASTM A36aASTM A588aPreferred material specification001-06
32、4_DG1_2nd_Ed.indd 2 3/31/10 11:55:03 AMAISC DESIGN GUIDE 1, 2ND EDITION / BASE PLATE AND ANCHOR ROD DESIGN / 3of a crane building, the use of a seat or stool at the column base may be more economical, if it eliminates the need for large complete-joint-penetration (CJP) groove welds to heavy plates t
33、hat require special material specifications.Most column base plates are designed as square, to match the foundation shape and more readily accommodate square anchor rod patterns. Exceptions to this include moment- resisting bases and columns that are adjacent to walls.Many structural engineers have
34、established minimum thicknesses for base plates for typical gravity columns. For posts and light HSS columns, the minimum plate thickness is typically 2 in., and for other structural columns a plate thickness of w in. is commonly accepted as the minimum thickness specified.2.3 Base Plate Fabrication
35、 and FinishingTypically, base plates are thermally cut to size. Anchor rod and grout holes may be either drilled or thermally cut. Sec-tion M2.2 of the AISC Specification lists requirements for thermal cutting as follows:“thermally cut free edges that will be subject to calculated static tensile str
36、ess shall be free of round-bottom gouges greater than x-in. (5 mm) deep and sharp V-shaped notch-es. Gouges deeper than x in. (5 mm) and notches shall be removed by grinding and repaired by welding.”Because free edges of the base plate are not subject to tensile stress, these requirements are not ma
37、ndatory for the perimeter edges; however, they provide a workmanship guide that can be used as acceptance criteria. Anchor rod holes, which may be subject to tensile stress, should meet the requirements of Section M2.2. Generally, round-bottom grooves within the limits specified are acceptable, but
38、sharp notches must be repaired. Anchor rod hole sizes and grouting are covered in Sections 2.6 and 2.10 of this Design Guide.Finishing requirements for column bases that bear on steel plates are covered in Section M2.8 of the AISC Specification as follows:“Steel bearing plates 2 in. (50 mm) or less
39、in thickness are permitted without milling, provided a satisfactory contact bearing is obtained. Steel bearing plates over 2 in. (50 mm) but not over 4 in. (100 mm) in thickness are permitted to be straightened by pressing or, if presses are not available, by milling for bearing surfaces to obtain a
40、 satisfactory contact bearing. Steel bearing plates over 4 in. (100 mm) in thickness shall be milled for bearing surfaces .” Two exceptions are noted: the bottom surface need not be milled when the base plate is to be grouted, and the top surface need not be milled when CJP groove welds are used to
41、connect the column to the base plate. AISC Specification Section M4.4 defines a satisfactory bearing surface as follows:“Lack of contact bearing not exceeding a gap of z in. (2 mm) regardless of the type of splice used is permitted. If the gap exceeds z in. (2 mm), but is less than in. (6 mm), and i
42、f an engineering investigation shows that sufficient contact area does not exist, the gap shall be packed out with non-tapered steel shims. Shims need not be other than mild steel, regardless of the grade of the main material.”Table 2.2. Anchor Rod MaterialsMaterialASTMTensile StrengthFu(ksi)Nominal
43、 Tensile StressaFnt= 0.75Fu(ksi)Nominal Shear Stress (X type)a, bFnv= 0.50Fu(ksi)Nominal Shear Stress (N type)a, cFnv= 0.40Fu(ksi)Maximum Diameter(in.)F1554 Gr 36d58 43.5 29.0 23.2 4Gr 55 75 56.3 37.5 30.0 4Gr 105 125 93.8 62.5 50.0 3A449120 90.0 60.0 48.0 1105 78.8 52.5 42.0 190 67.5 45.0 36.0 3A36
44、 58 43.5 29.0 23.2 4A307 Gr Ce58 43.5 29.0 23.2 4A354Gr BD150 112 75.0 60.0 2140 105 70.0 56.0 4aNominal stress on unthreaded body for cut threads (based on major thread diameter for rolled threads)bThreads excluded from shear planecThreads included in the shear planedPreferred material specificatio
45、neSee F1554 Gr 36001-064_DG1_2nd_Ed.indd 3 3/31/10 11:55:03 AM4 / BASE PLATE AND ANCHOR ROD DESIGN / AISC DESIGN GUIDE 1, 2ND EDITIONWhile the AISC Specification requirements for finishing are prescriptive in form, it is important to ensure that a satisfac-tory contact bearing surface is provided. B
46、y applying the provisions of Section M4.4, it may not be necessary to mill plates over 4-in. thick if they are flat enough to meet the gap requirements under the column. Standard practice is to order all plates over approximately 3 in. with an extra 4 in. to 2 in. over the design thickness to allow
47、for milling. Typically, only the area directly under the column shaft is milled. The base elevation for setting the column is determined in this case by the elevation at the bottom of the column shaft with the grout space and shims adjusted accordingly.2.4 Base Plate Welding The structural requireme
48、nts for column base plate welds may vary greatly between columns loaded in compression only and columns in which moment, shear and/or tension forces are present. Welds attaching base plates to columns are often sized to develop the strength of the anchor rods in tension, which can most often be achi
49、eved with a relatively small fillet weld. For example, a c-in., 22-in.-long fillet weld to each column flange will fully develop a 1-in.-diameter ASTM F1554 Grade 36 anchor rod when the directional strength increase for fillet welds loaded transversely is used. Alternative criteria may be advisable when rod diameters are large or material strength levels are high.A few basic guidelines on base plate welding are as follows: Fillet welds are preferred to groove welds for all but large moment-resisting bases. The use of the weld-all-around
