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1、NCHRP 24-31 LRFD DESIGN SPECIFICATIONS FOR SHALLOW FOUNDATIONS Final Report September 2009 APPENDIX C QUESTIONNAIRE SUMMARY Prepared for National Cooperative Highway Research Program Transportation Research Board National Research Council Samuel G. Paikowsky and Mary Canniff Geosciences Testing and
2、Research, Inc. 55 Middlesex Street, Suite 225, North Chelmsford, MA 01863 and Geotechnical Engineering Research Laboratory University of Massachusetts Lowell 1 University Avenue, Lowell, MA 01854 LIMITED USE DOCUMENT This Appendix is furnished only for review by members of the NCHRP project panel an
3、d is regarded as fully privileged. Dissemination of information included herein must be approved by the NCHRP and Geosciences Testing and Research, Inc. Geotechnical Engineering Research Laboratory Samuel G. Paikowsky, Sc.D. One University Avenue Professor Lowell, Massachusetts 01854 Tel: (978) 934-
4、2277 Fax: (978) 934-3046 e-mail: Samuel_Paikowskyuml.edu web site: http:/geores.caeds.eng.uml.edu DEPARTMENT OF CIVIL AND ENVIRONMENTAL ENGINEERING C-1 June 18, 2007 RE: NCHRP Project 24-31 LRFD Design Specifications for Shallow Foundations Dear DOT and FHWA Engineer; The Geotechnical Research Labor
5、atory at the University of Massachusetts Lowell in cooperation with Geosciences Testing do you use rock cores? No 5% Yes 90% do you evaluate RQD? No 8% Yes 88% do you conduct uniaxial (unconfined) compressive strength tests? No 8% Yes 88% do you conduct point load strength index tests? No 63% Yes 33
6、% If you conduct other tests, please specify 15 responses (38%) Alabama Determine size and spacing of discontinuities Georgia split tensile tests Illinois Percent recovery and detailed description, and coring time Iowa We do evaluate RQD and conduct uniaxial compressive strength tests for drilled sh
7、afts. Minnesota Split tensile Mississippi Very little, if any, shallow rock in MS. - Section for design on rock will be left blank. Nevada X-ray diffraction Ohio Pressuremeter Oklahoma Texas Cone Penetrometer (TCP) Oregon Unit weight Pennsylvania Rock cores are always taken, RQD is always evaluated.
8、 Compressive strength tests are generally performed. Point loads tests are rarely done. South Dakota The type of field investigation and lab testing conducted depends upon the structure Texas Texas DOT uses deep foundations exclusively. Texas Cone Penetrometer (TCP) is our primary evaluation tool. C
9、ores, RQD and UU tests may also be utilized. Wisconsin Unconfined compression tests are only performed on a limited basis. CA Alberta SASW, geophysical tests 2. When evaluating bearing resistance of rock, which do you use? (can be both) Only Presumptive values 19.4% Only Engineering Analysis 22.2% U
10、se Both 58.3% a. For presumptive values, do you use AASHTOs Table C10.6.2.6.1-1? No 38% Yes 53% If in addition or alternatively you use other presumptive values, please specify 14 responses (35%) Alabama ASD methodologies 17th Edition Section 4.4.8.1 Arizona We currently use AASHTO 2002 17th Edition
11、 and have not transioned to AASHTO 2004 3rd Edition, so most of the following questions do not apply. Arkansas Based on knowledge of geological conditions in our area we use reduced values in table C10.6.2.6.1-7 Iowa We use historic Iowa DOT allowable bearing values for rock Kansas Utilize experienc
12、e derived values also Maine We also consult Canadian Foundation Engineering Manual, 2006, Section 9.3 New Hampshire used as a guide New York NYC Building Code, Appendix A, Article 26; NAVFAC D.M. - 7.2 Oregon In combination with engineering judgment Pennsylvania Presumptive tables were permitted in
13、the past, bearing resistance is now calculated. South Dakota For in-situ rock we have pre-determined values from experience over the years. Wisconsin Temper values based on local conditions/experience. Wyoming Hough CA - Alberta Canadian Foundation Engineering Manual, Ed. 4 and as modified for local
14、 experience. All references are made to AASHTO LRFD Interim 2006 or 2007 edition C-9 b. For engineering analysis or bearing resistance on rock, the AASHTO specifications (section 10.6.3.2) provide guidelines to use analytical and semi-empirical correlation to Rock Mass Rating (RMR). Would you like a
15、 specific method to be presented? No 18% Yes 70% If you currently use a semi-empirical design method, do you use Carter and Kulhawy (1988) mentioned in the commentary (C10.6.3.2.2)? No 35% Yes 33% Please specify if other (including computer programs) 10 responses (25%) Indiana We use presumptive val
16、ues. Maine We use Kulhawy and Goodman (1980) International Conf. on Structural Foundations of Rock, May 1980, Pells “Design of Foundations on Discontinuous Rock“ and Bowles, 5th Ed, Section 4-16, based on Stagg re FHWA NHI-01-023 Washington We do this so infrequently, we would likely check all three
17、. CA Alberta Sigma/W c. Do you evaluate failure by sliding for footings on rock? No 23% Yes 60% If no, please specify the reason, if yes please specify the method of calculation and factors (F.S. or resistance factor) you are applying 20 responses (50%) Alabama Typically key footings into the rock o
18、ne to two feet. Arkansas Footings are typically keyed into rock 1.5ft to 2.0ft Connecticut It could be either, depending on the code that is being used AASHTO Standard Spec-ASD, AREMA, or AASHTO-LRFD Idaho Use resistance factor of about 0.5 (Note that Table 10.5.5.2.2-1 in AASHTO does not have resis
19、tance factor for sliding for rock). Illinois per AASHTO LRFD Indiana We use AASHTO Table 10.4.6.5-2 to get Poissons ratio. We use a Factor of Safety of 1.5 Iowa The Bridge Design Manual requires that spread footings be notched into rock. For typical bridges the notching provides adequate sliding res
20、istance. C-10 Maine Sliding calculated for Strength I using min vert load and max horiz loads, and a resistance factor of 0.80 based on reliability theory analysis for footing on sand, but also have used RF of 0.90 which translates to a FS of 1.5 Maryland We will seat footing into rock Minnesota Foo
21、tings are typically dowelled to rock with enough dowels to resist the lateral force. Nevada We use limit equilibrium method as discussed in FHWA Module 5 “Rock Slopes“ with a superimposed foundation loading. Factor of Safety against sliding failure should be at least 1.5 for static condition and 1.1
22、 for seismic condition. New Hampshire SF = 1.5 per Working Stress, Resistance factor = 0.8 per LRFD North Carolina Note: This is done by our Structure Design Unit. We determine bearing capacity and settlement. Most of our footings are keyed or carried into rock, therefore, sliding is a major concern
23、. Ohio FS 1.5 Oregon as described in FHWA NHI-01-023 Pennsylvania Currently the designer has the option to evaluate sliding for footings on rock. Historically, sliding is not checked if the footing is embedded below the top of rock one foot. South Dakota Footings are usually doweled and/or neatlined
24、 into the rock Utah We havent yet had a need to do a sliding evaluation with the LRFD code, but if we did, wed have to determine a design method and a resistance factor for rock (not provided in code). Washington 1.5 or 0.67 CA Alberta Using LRFD if the sliding is based on friction use resistance fa
25、ctor of 0.8, if the sliding is based on cohesion use resistance factor of 0.6 Do you limit the eccentricity of footings on rock? No 10% Yes 75% If yes, please specify criteria (i.e. e/B , section 10.6.3.3 or others) 29 responses (73%) Arizona AASHTO 2002 Arkansas section 10.6.3.3 Connecticut AASHTO
26、Hawaii Per AASHTO LRFD Bridge Design Specifications Idaho section 10.6.3.3 Illinois per AASHTO LRFD Indiana We use e/B 1/4 from section 8.4.3.1 of FHWA NHI 06-089 “Soils and Foundation Manual“ Iowa Less than or equal to 1/4 footing dimension in any direction (AASHTO Std. 4.4.8). We plan to use the 3
27、/8 limit under LRFD. Kansas e/B 1.5 then the lateral displacements are generally acceptable. Oklahoma We only use shallow foundations on very competent rock. Oregon usually key footings into solid rock Tennessee We presume fixity on rock. Utah Shallow foundations have been on single span bridges. La
28、teral analysis hasnt been required. South Dakota The foundation unit is keyed into the rock Wisconsin Displacements have not been an issue. III. Design Considerations Foundations on Soils 1. Do you follow the AASHTO LRFD Specifications (section 10.6)? No 33% Yes 50% If no, please specify what guidel
29、ines/code/procedure you follow in the Geotechnical design of shallow foundations 16 responses (40%) Alabama Have not converted to LRFD yet, still using 17th Edition Section 4.4 Arizona We currently use AASHTO 2002 17th Edition and have not transitioned to AASHTO 2004 3rd Edition, so most of the foll
30、owing questions do not apply. Arkansas We do not use footings founded in soil. Connecticut Generally follow AASHTO guidelines; however as in working stress designs there will always be some exceptions that require you to depart from the code. Georgia Empirical values to limit settlement to 0.5” Indi
31、ana We follow the old AASHTO. We will use LRFD starting in January 2008 Iowa We do not use spread footings on soil for bridges. Spread footings on soil for other structures such as sign trusses and light towers are designed by the AASHTO standard specifications. Kansas We do not use shallow foundati
32、ons with soil as the foundation medium for bridge footings Maryland AASHTO Allowable Stress Design Mississippi AASHTO ASD Standard Spec. Will use LRFD Spec. for future designs. North Carolina Not yet, we are in the process of using LRFD Pennsylvania AASHTO LRFD as modified by PennDOTs Design Manual
33、Part 4 South Dakota AASHTO Standard Specification for Highway Bridges Wisconsin Still using ASD, but moving to LRFD Wyoming AASHTO Working Stress Design used in this timeframe. CA Alberta National Building Code of Canada, National Bridge Code 2. Do you use the LRFD AASHTO specification for bearing p
34、ressures at the service limit state (section 10.6.2.6)? No 38% Yes 35% C-13 If yes, do you use the presumptive values of Table C10.6.2.6.1-1? No 43% Yes 13% If no, do you calculate the service limit procedures based on limit displacements? . No 15% Yes 40% If no, please explain your procedure 4 resp
35、onses (10%) Illinois Use factored resistance and estimate service settlement Nebraska ASD New York Question is unclear South Dakota Experience and unconfined compression strength test results Do you apply any safety margin (F.S. or R.F.) to a foundation determined on the basis of settlement calculat
36、ions? No 55% Yes 8% As the specifications do not address this issue, please explain 7 responses (18%) Connecticut We are applying the FS or RF; however the value is 1 Illinois Resistance factor on nominal bearing resistance controlled footing and check settlement not excessive to structural engineer
37、. Nevada If the settlement is within structure tolerable limit, we do not apply further F.S. or R.F. to the allowable bearing capacity. New Hampshire The settlement calcs are based on service load. New York Service limit bearing pressure is applied to soil, settlements calculated. Settlement must be
38、 structure tolerable settlement. Oregon Resistance factor is 1.0 at service limit state - settlement determined based on allowable structure settlement criteria Utah Specs do address the issue, the RF is 1.0 for service limit sate used in settlement calculations. 3. If instead of 8% or in addition t
39、o 18% the above you use other procedures or computer software for the evaluation of bearing capacity of shallow foundations, please specify: 12 responses (30%) Connecticut Various published techniques for estimating settlement. No formal practice established. Georgia CBEAR Illinois We have a spreads
40、heet to calculate nominal bearing pressure and elastic settlement Maine CBEAR Massachusetts FHWA and/or Text books Mississippi ASD Standard Spec. (FS bearing capacity = 3.0); settlement not a problem on sand/gravel (no shallow foundations on clay) - will use LRFD Specification for future designs. Re
41、maining questions deal mainly with the LRFD Spec. After some experience with this code, MS will gladly update the unanswered sections. New Hampshire Use procedures in AASHTO 10.6.3 North Carolina none Pennsylvania PennDOTs Pier and Abutment/Retaining Wall programs calculate the bearing resistance fo
42、r spread footings on soil. Bearing resistance for rock is determined using a hand calculation and the bearing resistance for rock is a program input. South Dakota SDDOT runs unconfined compression strength tests Wisconsin Use AASHTO ASD guidelines CA - Alberta Sigma/W, in-house spreadsheets 4. Do yo
43、u use the theoretical general bearing capacity estimation presented in section 10.6.3.1.2? . No 15% Yes 58% C-14 If no, please elaborate on any bearing capacity factors, shape factors and inclination factors you are using that are different than those specified by AASHTO 4 responses (10%) Iowa We do
44、 not use the formula and thus have no need for special factors. Massachusetts Not all the factors (s, d, and i) are used. North Carolina use the usual Meyerhof equations CA - Alberta We use the Canadian Foundation Engineering Manual, Which provides a general bearing capacity equation which may be id
45、entical to 10.6.3.1.2 Do you find it reasonable to omit the load inclination factors as explained in C10.6.3.1.2a? No 13% Yes 53% Do you limit the eccentricity of the footing? No 5% Yes 63% If yes, please specify criteria (i.e. e/B , section 10.6.3.3 or others) 22 responses (55%) Alabama As noted in
46、 Section 10.6.3.3 Arizona AASHTO 2002 Connecticut AASHTO guidelines Idaho section 10.6.3.3 Illinois 10.6.3.3 Indiana We use e/B 1/6 with ASD Method. After January 2008, we will use e/B with LRFD Iowa Less than or equal to 1/6 of the footing dimension (AASHTO std. 4.4.7). Maine e/B Michigan Follow cr
47、iteria of section 10.6.3.3 Minnesota As per LRFD 10.6.3.3 Nevada Same criteria as addressed in Section 10.6.3.3. For static loading, the location of the bearing pressure resultant on the footings should be within B/4 of the center of the footings on soils. For seismic loading, the location of the re
48、sultant force should be within B/3 of the center of the footings. New Hampshire 10.6.3.3 New York e/B Ohio e/B Oregon e/B Pennsylvania The resultant must fall in the middle half of the footing. South Dakota Keep the resultant in the middle of the footing Utah Section 10.6.3.3 Vermont 10.6.3.3 Washin
49、gton AASHTO th Wisconsin e/b CA Alberta e/B 1/6 Please comment on the above 8 responses (20%) Iowa AASHTO Standard Specifications for Structural Support for Highway Signs, Luminaires and Traffic Signals has not yet been converted to LRFD. Massachusetts Load inclination factors must be used in the Final Design of footings. New Hampshire Use of these limits have produced satisfactory designs for years. North Carolina above and below done by structures Oregon more reasonable than FOS against overturning approach
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