New Seismic Design Requirements in Louisiana

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1 New Seismic Design Requirements in Louisiana Mohsen Shahawy, PhD., PE SDR Engineering Consultants, Inc. January, Louisiana Transportation Conference

2 Seismic Zones. Until relatively recently, seismic design criteria depended solely upon the seismic zone in which a structure was located. Zones were regions in which seismic ground motion, corresponding to a certain probability of occurrence, was within certain ranges. 20 Louisiana Transportation Conference

3 New design requirements recognized that structure performance during a seismic event depends not only on the severity of sub-surface rock motion, but also on the type of soil upon which a structure is founded 20 Louisiana Transportation Conference

4 20 Louisiana Transportation Conference

5 The soil condition at the site is the additional variable that must now be dealt with. While this adds another element to an already complicated procedure, it does incorporate established knowledge about the effect of soil properties during an earthquake into seismic design criteria. 20 Louisiana Transportation Conference

6 In general, the process leading to the classification of the Seismic Design Category involves several steps and clearly, the procedure for establishing the seismic classification of a structure has become more complex. 20 Louisiana Transportation Conference

7 Objectives Develop the Seismic Zone classification map for Louisiana based on a study of all parishes in the state and accounting for the existing soil classification for each Parish. 20 Louisiana Transportation Conference

8 Table. Basis for Seismic Design Criteria in Model Codes and Standards Procedure Step : Site Class Definitions A site shall be classified as A though F in accordance with the site class definitions. Seismic Zones Seismic Site Classification Classifications 0,, 2, 3, 4 A, B, C, D, E, F Criteria for Classification Location Location, Structure Use, & Soil Type 20 Louisiana Transportation Conference

9 20 Louisiana Transportation Conference

10 Procedure Step 2 : Determine Peak Ground Acceleration coefficient (PGA) and the short- and long period spectral acceleration coefficients (S S and S l, respectively) Step 3 : Determine zero, short, and long-period site factors, F PGA, F a, and F v 20 Louisiana Transportation Conference

11 Table. Basis for Seismic Design Criteria in Model Codes and Standards Procedure Step 4 : Calculate the Response spectrum 20 Louisiana Transportation Conference

12 For each Parish: Divide into 3 or 4 zones based on Zip code Perform analysis and determine S D =F v *S l Determine Zone Classification 20 Louisiana Transportation Conference

13 Seismic Performance Zones Each bridge shall be assigned to one of the four seismic zones in accordance with Table Table Seismic Zones Acceleration Coefficient, S D Seismic Zone S 0.5 D 0.5 < S D 0.30 < S D 0.50 < S 4 D 20 Louisiana Transportation Conference

14 Parish Acadia Allen Ascension Assumption Beauregard Bienville Bossier Zip Site PGA S code s S l Class F PGA F a F v S D =F v *S l As=F PGA *PGA Zone D D D D D D E* E* E* E* E* E* E* D D D D C C C C E E E Louisiana Transportation Conference

15 Parish Caddo Calcasieu Caldwell Cameron Catahoula Claiborne Concordia Zip code PGA S s S l Site Class F PGA F a F v S D =F v *S l As=F PGA *PGA Zone E E E E E E E E E E* E* E* E* E* E* E* C C C E* E* E* Louisiana Transportation Conference

16 Parish Desoto East Baton Rouge East Carroll East Feliciana Evangeline Franklin Grant Zip code PGA S s S l Site Class F PGA F a F v S D =F v *S l As=F PGA *PGA Zone C C C E E E E* E* E* D D D E E E E E D D D D Iberia E* E* E* Louisiana Transportation Conference

17 Parish Iberville Jackson Jefferson Jefferson Davis Lafayette Lafourche LaSalle Lincoln Zip code PGA S s S l Site Class F PGA F a F v S D =F v *S l As=F PGA *PGA Zone E* E* E* C C C C E* E* E* E* D D D E* E* E* E* E* E* E E E C C C Louisiana Transportation Conference

18 Parish Livingston Madison Morehouse Natchitoches Orleans Ouachita Plaquemines Zip code PGA S s S l Site Class F PGA F a F v S D =F v *S l As=F PGA *PGA Zone E E E E* E* E E E E E E E* E* E* D D D D D E* E* E* Louisiana Transportation Conference

19 Parish Pointe Coupee Zip code PGA S s S l Site Class F PGA F a F v S D =F v *S l As=F PGA *PGA Zone E* E* E* Rapides Red River Richland Sabine St. Bernard St. Charles E E E E E E E E E C C C E* E* E* E* E* Louisiana Transportation Conference

20 Parish St. Helena St. James St. John St. Landry St. Martin St. Mary St. Tammany Zip code PGA S s S l Site Class F PGA F a F v S D =F v *S l As=F PGA *PGA Zone D D D E* E* E* E* E* E* E* E* E* E* E* E* E* E* E E E Louisiana Transportation Conference

21 Parish Zip code PGA S s S l Site Class F PGA F a F v S D =F v *S l As=F PGA *PGA Zone Tangipahoa Tensas Terrebonne Union Vermilion Vernon Washington D D D E* E* E* E* E* E* C C C E* E* E* C C C D D D Louisiana Transportation Conference

22 Parish Webster Zip code PGA S s S l Site Class F PGA F a F v S D =F v *S l As=F PGA *PGA Zone D D Webster D West Baton Rouge E* West Carroll E E E West Feliciana D Winn C C C Louisiana Transportation Conference

23 The following Parishes are designated Seismic Zone 2: East Carroll Franklin Madison Morehouse Richland Tensas West Carroll All bridges located in these parishes shall be designed using the provisions under Extreme I. 20 Louisiana Transportation Conference

24 Seismic Zone Classification Map 20 Louisiana Transportation Conference

25 Summary: The structural analysis and design for the earthquake loads are specified in LRFD specification as for four seismic zones, i.e. seismic zone, zone 2, zone 3 and zone 4. Bridges in LA State shall be designed for seismic zone and zone Louisiana Transportation Conference

26 Summary: LA Bridges in seismic zone need not be analyzed for seismic loads, regardless of their operational classification and geometry except for the minimum requirements as specified in Articles and A Louisiana Transportation Conference

27 Summary: Bridges in Seismic Zone 2 shall be analyzed and designed in accordance with the minimum requirements specified in LRFD design specification, and the latest version of AASHTO guide specifications for LRFD seismic bridge design 20 Louisiana Transportation Conference

28 Summary: The structural analysis and structural design, respectively, shall be taken into consideration for bridges located in seismic zone 2. Bridges shall be analyzed and designed in accordance with the minimum requirements specified in LRFD design specification, and the latest version of AASHTO guide specifications for LRFD seismic bridge design 20 Louisiana Transportation Conference

29 Summary: The SEISMIC design requirements of Article (for Seismic Zones 3 and 4) shall be taken to apply to bridges in Seismic Zone 2 except that the area of longitudinal reinforcement shall not be less than 0.0 or more than 0.06 times the gross cross-section area, A g. 20 Louisiana Transportation Conference

30 Table Minimum Analysis Requirements for Seismic Effects Seismic Zone Single- Span Bridges Multispan Bridges Other Bridges Essential Bridges Critical Bridges regular irregular regular irregular regular irregular No seismic * * * * * * 2 analysis required SM/UL SM SM/UL MM MM MM * = no seismic analysis required UL = uniform load elastic method SM = single-mode elastic method MM = multimode elastic method Regularity is a function of the number of spans and the distribution of weight and stiffness. Regular bridges have less than seven spans; no abrupt or unusual changes in weight, stiffness, or geometry; and no large changes in these parameters from span to span or support-to-support. 20 Louisiana Transportation Conference

31 In general, the upper boundary for Zone 2 in the current edition is significantly higher than in the previous edition due to the increase in the return period for the design earthquake. 20 Louisiana Transportation Conference

32 Thank You 20 Louisiana Transportation Conference

TITLES I, II, and III

TITLES I, II, and III Chapter: 15 Chapter Title: Assignment of Cases and Preliminary Motions Appendix 15.1 Rule No: 15.1 Alternative Method of Service on District Attorney 1st Judicial District Caddo In