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1、Steel Design Guide Series Column Base Plates Design of Column Base Plates John T. DeWolf Professor of Civil Engineering University of Connecticut Storrs, Connecticut Some Practical Aspects of Column Base Selection David T. Bicker Vice President, Engineering The Berlin Steel Construction Company, Inc
2、. Berlin, Connecticut A M E R I C A N I N S T I T U T E O F S T E E L C O N S T R U C T I O N Steel Design Guide Series Column Base Plates 2003 by American Institute of Steel Construction, Inc. All rights reserved. This publication or any part thereof must not be reproduced in any form without permi
3、ssion of the publisher. Copyright 1990 by American Institute of Steel Construction, Inc. All rights reserved. This book or any part thereof must not be reproduced in any form without the written permission of the publisher. The information presented in this publication has been prepared in accordanc
4、e with rec- ognized engineering principles and is for general information only. While it is believed to be accurate, this information should not be used or relied upon for any specific appli- cation without competent professional examination and verification of its accuracy, suitablility, and applic
5、ability by a licensed professional engineer, designer, or architect. The publication of the material contained herein is not intended as a representation or warranty on the part of the American Institute of Steel Construction or of any other person named herein, that this information is suitable for
6、 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 from such use. Caution must be exercised when relying upon other specifications and codes developed by other bodies and incorporated by referen
7、ce herein since such material may be mod- ified or amended from time to time subsequent to the printing of this edition. The Institute bears no responsibility for such material other than to refer to it and incorporate it by reference at the time of the initial publication of this edition. Printed i
8、n the United States of America Second Printing: September 1991 Third Printing: October 2003 2003 by American Institute of Steel Construction, Inc. All rights reserved. This publication or any part thereof must not be reproduced in any form without permission of the publisher. CONTENTS DESIGN OF COLU
9、MN BASE PLATES By John T. DeWolf INTRODUCTION LITERATURE REVIEW - DESIGN PROVISIONS Axially Loaded Base Plates . . . . . . . . . . . Base Plates with Moments . . . . . . . . . . . . Anchor Bolts for Tension . . . . . . . . . . . . Shear Loads . . . . . . . . . . . . . . . . . . . DESIGN OF AXIALLY L
10、OADED BASE PLATES Design Procedure . . . . . . . . . . . . . . . . Design for Lightest Plate . . . . . . . . . . . . . General Design Procedure . . . . . . . . . . . . Design Aid for Axially Loaded Base Plates . . . Base Plates Placed Eccentrically on the Concrete Foundations . . . . . . . . . . . .
11、 . . . . . . Determining the Design Load for Existing Base Plates . . . . . . . . . . . . . . . . . . . . . Design of Lightly Loaded Base Plates . . . . . . Base Plates for Uplift Loading . . . . . . . . . . Base Plates for Tube and Pipe Columns . . . . . Base Plates with Large Loads . . . . . . . .
12、 . . Details for Base Plates . . . . . . . . . . . . . . DESIGN OF BASE PLATES WITH MOMENTS General Behavior . . . . . . . . . . . . . . . . . Design for Small and Moderate Eccentricities Design for Large Eccentricities . . . . . . . . . Design Aid for Plates with Large Eccentricities . DESIGN OF AN
13、CHOR BOLTS FOR TENSION General Behavior . . . . . . . . . . . . . . . . Minimum Bolt Lengths and Edge Distances . . Design of Hooked Bolts . . . . . . . . . . . . . Design of Bolts and Rods with a Nut . . . . . . DESIGN FOR SHEAR General Behavior . . . . . . . . . . . . . . . . Proposed Design Appro
14、ach . . . . . . . . . . . APPENDIX A RESEARCH REVIEW Axially Loaded Columns . . . . . . . . . . . . Axial Load Plus Moment . . . . . . . . . . . . Anchor Bolts for Tension . . . . . . . . . . . . Shear Loads . . . . . . . . . . . . . . . . . . . REFERENCES NOMENCLATURE APPENDIX B SOME PRACTICAL ASPE
15、CTS OF COLUMN BASE SELECTION . . . . . . . By David T. Ricker APPENDIX C DESIGN OF SMALL BASE PLATES FOR WIDE FLANGE COLUMNS . . . . . . . By W.A. Thornton 1 2 .2 .2 .3 .3 4 .4 .5 .6 .8 12 12 13 15 15 16 17 18 18 19 21 23 25 25 25 25 26 30 30 31 33 33 36 36 37 38 42 43 52 2003 by American Institute
16、of Steel Construction, Inc. All rights reserved. This publication or any part thereof must not be reproduced in any form without permission of the publisher. PREFACE This booklet was prepared under the direction of the Committee on Research of the American Institute of Steel Construction, Inc. as pa
17、rt of a series of publications on special topics related to fabricated structural steel. Its purpose is to serve as a supplemental reference to the AISC Manual of Steel Construction to assist practicing engineers engaged in building design. The design guidelines suggested by the author that are outs
18、ide the scope of the AISC Specifications or Code do not represent an official position of the Institute and are not intended to exclude other design methods and proce- dures. It is recognized that the design of structures is within the scope of expertise of a competent licensed structural engineer,
19、architect or other licensed professional for the application of principles to a particular structure. The sponsorship of this publication by the American Iron and Steel Institute is gratefully acknowledged. The information presented in this publication has been prepared in accordance with recognized
20、 engineering principles and is for general information only. While it is believed to be accurate, this information should not be used or relied upon for any specific application without competent professional examination and verification of its accuracy, suitability, and applicability by a licensed
21、professional engineer, designer or architect. The publication of the material contained herein is not intended as a representation or warranty on the part of the American Institute of Steel Construction, Inc. or the American Iron and Steel Institute, or of any other person named herein, that this in
22、formation is suitable for any general or particular use or of freedom infringement of any patent or patents. Anyone making use of this information assumes all liability arising from such use. 2003 by American Institute of Steel Construction, Inc. All rights reserved. This publication or any part the
23、reof must not be reproduced in any form without permission of the publisher. INTRODUCTION This report contains a compilation of existing informa- tion on the design of base plates for steel columns. The material is taken from reports, papers, texts and design guides. The intent is to provide enginee
24、rs with the re- search background and an understanding of the behavior of base plates and then to present information and guidelines for their design. The material is intended for the design of column base plates in building frames, though it can be used for related structures. Bearing plates for be
25、ams would be based on similar principles. Three cases are covered, each involving different loads. These are shown in Fig. 1. The first is the axially loaded column, shown in Fig. 1 (a). The load is perpendicular to the plate and through the column centroid. It is used in frames in which the column
26、bases are assumed pinned. A layer of grout is used for leveling of the plate and setting it at the specified elevation. Anchor bolts are also used to stabilize the column during erection, and the fixity which results is neglected in design. The column and base plate are normally centered on the conc
27、rete foundation. If the column load is relatively small, the required base plate size determined from the concrete bearing capacity only will be approximately equal to, or smaller, than the actual column size. These base plates are referred to as lightly loaded column base plates, and they require a
28、 modified design approach. The second case, shown in Fig. 1 (b), includes both an axial load and a moment. This kind of connection would be used at the base of moment resistant frames where moment capacity is needed. It is also used where the load is applied eccentrically to the column and the resul
29、ting moment must be resisted by the base connection. If the moment is relatively small, the connection can be designed without the use of anchor bolts, other than those provided for stability during construction. The more common case involves the use of one or more bolts to resist the tension result
30、ant from the moment. The third case, shown in Fig. 1 (c), is a base plate with a horizontal, or shear load. This will occur in rigid frames. Often the shear component is small in relation to the friction developed. Shear is sometimes important when bracing is connected to the base of the column. The
31、 shear can be resisted through friction or the development of bearing in the horizontal direction. Many variables influence the behavior and load resisting capacity of base plates. While some of these have been studied extensively, others have only received nominal study. The following material is b
32、ased on the best avail- able information, and some of it represents suggested guidelines based on the authors judgement. The design approaches given here are not intended as the only ac- ceptable methods. Provisions for the design of base plates have generally been developed in the Allowable Stress
33、Design (ASD) format, as reflected in the AISC Manual of Steel Con- struction (AISC 1989a) and AISC Specification (AISC 1989). The AISC Load and Resistance Factor Design (LRFD) Manual (AISC 1986) and Specification (AISC 1986a) have translated these provisions into equivalent limit state design format
34、 which may be used as an alter- native to ASD. Since the provisions were initially developed in the ASD format, the discussions in the design chapters are based on this format, with appropriate references to LRFD design. The design procedures and examples which fol- low the discussions are given fir
35、st in ASD format and then repeated in LRFD format. The design methods chosen for this document are based on the listed references and the authors judgement but they are not the only approaches possible. Other rational design methods based on engineering judgement may also be adequate. See Appendix B
36、 for some practical aspects on column base selection. (a) Axial Load (b) Axial Load plus Moment (c) Axial Load plus Shear Fig. 1. Base Plate Design Cases 1 2003 by American Institute of Steel Construction, Inc. All rights reserved. This publication or any part thereof must not be reproduced in any f
37、orm without permission of the publisher. LITERATURE REVIEW - DESIGN PROVISIONS The review of the research work is given in the Appen- dix. What follows is a review of applicable design provisions. This includes specification requirements, suggested approaches and design aids. The details are discuss
38、ed more fully in the subsequent chapters. Axially Loaded Base Plates Axially loaded base plates, those with the load applied by a wide flange column to the center of the base plate, are designed according to the method in the ASD Manual of Steel Construction (AISC 1989a). This method is based on an
39、allowable bearing stress defined in the ASD Specification (AISC 1989), which is a function of the concrete compressive strength and the ratio of the con- crete to the plate areas. This allowable bearing stress has been increased from that in earlier Specifications to agree with the more liberalized
40、value in the ACT Code (ACI 1983). This had been changed following the results of the studies by Hawkins (1967,1967a, 1968,1968a). The allowable bearing stress has been put in terms of load and resistance factor design (AISC 1986, ACI 1983a). DeWolf (1978) and Narus (1976) have shown that the method
41、in the Manual of Steel Construction is conserva- tive. They have also noted that it does not consider the effects of reinforcement or the relative depth of the concrete foundation, nor does it allow for different plate thicknesses. Thus, plates designed under old specifica- tions cannot be evaluated
42、 under the new one. Design aids for the method in the Manual of Steel Con- struction have been developed by Blodgett (1966), Sandhu (1973), Dixon (1974), Stockwell (1975), Bird (1976, 1977) and Douty (1976). Good sources of detailing infor- mation are the Manual of Steel Construction, Detailing for
43、Steel Construction (AISC 1983), Engineering for Steel Construction (AISC 1984) and Blodgett (1966). Base plates with especially large loads require more than a simple plate. This may result in a double layer of plates, a grillage system, or the use of stiffeners to reduce the plate thickness. The de
44、sign of these plates is covered by Blodgett (1966) and noted in Engineering for Steel Con- struction (AISC 1984). Lightly Loaded Base Plates in which the plate size is approximately equal to the column size, were initially treated by Fling (1970) using an elastic plate bending approach and the assum
45、ption that the full plate is in contact with the concrete. The approach has been used in the 8th Edition Manual of Steel Construction. This has been shown to be conservative. Stockwell (1975), with modifications by Murray (1983), developed a method which is based on the assumption that bearing occur
46、s only under the column flanges and web. Murray also treats base plates subject to uplift. This approach has been adopted for the 1st Edition Load and Resistance Design Factor Manual (AISC 1986). Base Plates with Moments Base plates with both axial loads and moments are not covered in the AISC Speci
47、fication or the Manual of Steel Construction. Engineers must refer to textbooks for design information, though not all texts cover this case. Two general approaches exist for design, one based on the elastic behavior and one based on the ultimate capacity. For each of these approaches, different ass
48、ump- tions are made. The elastic approach is covered in the majority of texts which treat moments, including those of Ballio and Maz- zolani (1983), Blodgett (1966), Gaylord and Gaylord (1972), McGuire (1968), and Salmon and Johnson (1980). Soifer (1966) has noted that the design can be based on tha
49、t for reinforced concrete columns. He has stated that the anchor bolt force determination is the most important design element, and that the precise deter- mination of the concrete bearing stress distribution is not essential. He based his discussion on the elastic ap- proach. The approach based on the ultimate capacity, much like that used for the design of reinforced concrete columns today, is based on the study of Salmon, Schenker and Johnston (1957). The method is presented by Gaylord and Gaylord (1972) and McGuire (1968). Both used it to calculate the ultimate load for plate
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