ACI-COMPILATION-19-1992.pdf
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1、 A C 1 COMP*LS * O662949 0505886 968 CONCRETE FOU N DATIONS Compilation 19 American Concrete Institute Copyright American Concrete Institute Provided by IHS under license with ACI Licensee=IHS Employees/1111111001, User=listmgr, listmgr Not for Resale, 03/05/2007 19:08:47 MSTNo reproduction or netwo
2、rking permitted without license from IHS -,-,- - A C 1 COMPtL tt m Obb2i1 0505887 8T4 m 3 13 18 25 28 32 34 Concrete Foundations AC1 Compilation 19 Con tents Subgrade Reaction in Mat Foundation Design, by Edward J. Ulrich, Jr. 38 Underpinning Christ Church Cathedral, by Dirk J. Dressel, Joseph Galla
3、ccio, and Shahbaz Mavaddat Foundation Design in Florida Karst, by John E. Garlanger Building a Big Mat, by Myer Dimentberg Post-Tensioned Residential Foundations, by Jack W. Graves, Jr. Trench Wall Footings, by Purushottam Mehta 41 46 49 58 61 Massive Placement Melds Technology With Economy, by Emad
4、 Youssef 65 Machine Foundations -A Case Study, by H. Marzouk Building Pile Caps on Weak Soils, by W. Tiner, E.J. Ulrich, and P.D. Moore Concrete Foundations on Permafrost, by Alfred R. Mangus Design of Foundations in High Settlement Areas, by Thomas J. Tepper Pumping for Slurry Walls, by Gilbert R.
5、Tallard What Does a Soil Report Really Tell Us? by Robert L. Goeliring Casting a Large Concrete Slab in Hong Kong, by D.J. Sharpe, A.G. Ford, and M.G. Watson Copyright American Concrete Institute Provided by IHS under license with ACI Licensee=IHS Employees/1111111001, User=listmgr, listmgr Not for
6、Resale, 03/05/2007 19:08:47 MSTNo reproduction or networking permitted without license from IHS -,-,- A C 1 CONPUL9 *U E Obb2949 0505888 730 E Preface AC1 Compilations combine material previously published in Institute periodicals to provide compact and ready reference on specific topics. The materi
7、al in a compilation does not necessarily represent the opinion of an AC1 technical committee - only the opinions of the individual authors. However, the information presented here is considered to be a valuable resource for readers interested in the subject. Hugh S. Lacy Chairman, AC1 Committee 336
8、Combined Footings and Pier Foundations Erick N. Larson Chairman, AC1 Committee 351 Foundations for Equipment and Machinery Jerry A. Holland Chairman, AC1 Committee 360 Design of Slabs on Grade American Concrete Institute, Box 191 50, Redford Station, Detroit, Michigan 4821 9 Copyright American Concr
9、ete Institute Provided by IHS under license with ACI Licensee=IHS Employees/1111111001, User=listmgr, listmgr Not for Resale, 03/05/2007 19:08:47 MSTNo reproduction or networking permitted without license from IHS -,-,- long time ago, before man became enlightened as to the scientific mysteries of t
10、he A earth, the wise and foolish builders were identified: “. , . a wise man built his house on the rock. When the rains came down, the streams rose, and the winds blew . . . , yet it did not fall be- cause it had its foundation on the rock . . . a foolish man built his house on sand. The rain came
11、down, the streams rose, and the winds blew . . . and it fell with a great crash.” (Matthew, chapter 7). As man gained knowledge and expertise, wisdom seemed to degen- erate, and man began to build where ever a need arose, often on sand or “soil.” As a result, today we have the mat foundation and its
12、 relationship with the soil, a rela- tionship as complex and unpredict- able as that between a man and woman. Often an apparently com- patible relationship between mat and soil deteriorates due to the ever- present plague of construction de- tails and the design-construction re- lationship. Subgrade
13、 reaction, the most im- portant variable in designing mat foundations, is reviewed in four ac- companying case studies of four landmark buildings in Houston. Broad concepts related to mat foundation analysis using the finite element method will acquaint the practitioner with the related salient soil
14、-structure interaction concepts. A comprehensive examination of structural considerations in connec- tion with mat foundation design is furnished by Using an individual, uniform co- efficient of subgrade reaction will allow analysis of mat foundations; however, a uniform modulus of subgrade reaction
15、 as the soil model often is not rational and will mis- lead the designer. Past structural practice In the past, analyzing mat founda- tions included two major simplify- ing assumptions, an infinitely rigid mat and one-way bending.4 For very stiff mats with symmetrical geome- try and loading, these a
16、ssumptions may not introduce serious error. Assuming an infinitely rigid mat al- lows determination of a bearing pressure distribution by simple stat- ics, which ignores the high pressure concentrations in the load applica- tion areas and the low pressure con- centrations in areas distant from the l
17、oad applications. The second as- sumption provides for the mat be- havior to be approximated by a one-way, rather than a two-way, bending analysis. Two analysis methods used to address the limitations and errors of these simplifying assumptions are the successive approximations method and the method
18、 of finite differences. These are extremely te- dious and cumbersome procedures that do not lend themselves to an efficient general computer imple- mentation. The successive approxi- mations method addresses the mat flexibility relative to the bearing strata but does not include analyses for two-way
19、 bending. The method of finite differences appears to ade- quately address mat rigidity and two-way bending. Finite element method The finite element method (FEM) is easily implemented in a generalized computer code and eliminates the need for oversimplification. Some needed capabilities offered by
20、FEM which provide a more realistic ana- lytical model are: consideration of two-way bend- ing comprehensive mat and bearing stratum interaction using the beam-on-elastic foundation con- cept unusual and complex mat shapes mats of significant thickness dif- ferences mats accepting large moments and a
21、xial forces from laterally loaded shearwalls or frames mats in which structure rigidity affects mat behavior and stress distribution Although most engineers are aware of FEM, the method has not enjoyed widespread use. But due to the major advances in microcom- puter technology of the mid-l980s, whic
22、h have made vast computer ca- pabilities available and affordable to most users, FEM will be used in- creasingly on most projects requir- ing mat foundations. FEM analysis details and assumptions An FEM analysis is based on the theory of flat-plate bending with the mat supported by the soil. The soi
23、l is modeled as a dense liquid using Winkler springs. The mat is mod- eled as a mesh of discrete elements interconnected at the node points, and the Winkler springs are used as the soil-response model at each node. Some basic assumptions made using FEM include: the mat acts as an anisotropic or, iso
24、tropic, homogeneous, elastic solid in equilibrium the subgrade reactions are verti- cal vectors and are proportional to the deflection of the node the subgrade reaction is equal to the spring constant at a node multiplied by the deflection of that node CONCRETE FOUNDATIONS 3 Copyright American Concr
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