RECENT DEVELOPMENTS IN SEISMIC ANALYSIS OF BRIDGE SUBSTRUCTURES Mohiuddin A. Khan Ph.D., P.E. Manager Bridge Department, STV Inc., Trenton, NJ
What is an earthquake? • In New Jersey earthquakes usually occur when slowly accumulated strain within the Earth's crust is suddenly released along a fault. • Energy from this movement travels as seismic waves along ground surface and within the crust but away from the core. The arrival of this released energy is felt as an earthquake. • It’s intensity is determined by observing its effects at a particular place on Earth's surface. Intensity depends on • the earthquake's magnitude, • the distance from the epicenter, and • local geology. • The most commonly used scales in the United States are • Modified Mercalli Intensity Scale (usually reported in Roman numerals to distinguish them from magnitudes). • Magnitude - It is determined by using an instrument called a seismograph. • The best known magnitude scale is one designed by C.F. Richter in 1935.
Comparison of MM and Richter Scales • From Draft NJDOT LRFD Bridge Design Manual (Under Publication)
The Largest Earthquakes, Eastern States vs. CA The time periods varies from about three centuries in eastern states to slightly more than a century in some western states. Date ----- Magnitude --- Intensity Year Other Moment California 1857 7.6MS 7.92 IX 1906 7.80MS 7.68 XI Delaware 1871 VII Georgia 1914 4.50Mfa V Maine 1904 5.10Mfa VII Maryland 1990 2.5Mn V Massachusetts 1755 VIII New Hampshire 1940 5.50Mn 5.25 VII 1940 5.50Mn 5.60 VII New Jersey 1783 5.30Mfa VI New York 1944 5.80Mn 5.52 VIII North Carolina 1916 5.20Mfa VII Pennsylvania 1998 5.2Mn VI Rhode Island 1976 3.50Mn 2.07 VI South Carolina 1886 6.70Mfa 7.02 X Vermont 1962 4.2Mn V Virginia 1897 5.60Mfa VIII
Earthquake History of Pennsylvania • Limited information on effects in Pennsylvania until 1737. • A very severe earthquake centered in the St. Lawrence River region in 1663 • at Newbury, Massachusetts, in 1727 affected towns in Pennsylvania. • A strong earthquake on December 18, 1737 reported felt at Philadelphiaa. • Shocks with origins outside the State were felt in 1758, 1783, and 1791. • In 1800, two earthquakes (March 17 and November 29) were reported as "severe" at Philadelphia. • On November 11 and 14, 1840, earthquakes were felt at Philadelphia.. • Intensity V felt at Allentown by a strong shock on May 31, 1884. • West Chester, Pennsylvania reported shocks on August 10, 1884. • A tremor, on March 8, 1889, at Harrisburg, Philadelphia, Reading, York of intensity V. • An earthquake on May 31, 1908 at Allentown shook down a few chimneys (VI). • On October 29, 1934, a shock of intensity V was felt at Erie. • Southern Blair County on July 15, 1938. (VI) were reported at Clover Creek and Henrietta. • West of Reading experienced minor damage from an earthquake on January 7, 1954.. • On September 14, 1961, a moderate earthquake was centered in the Lehigh Valley. • On December 27, 1961, in the northeast portion and suburbs of Philadelphia. . • A strong local shock measured at magnitude 4.5, (VI) at Cornwall on May 12, 1964. • Intensity V effects at Darby, and Philadelphia on December 10, 1968. • On December 7, 1972, damage (V) was reported at New Holland. • Abridged from Earthquake Information Bulletin, Volume 8, Number 4, May - June 1973, by Carl A. von Hake.
10 Largest Earthquake in the World LocationDateMagnitude 1. Chile 1960 05 22 9.5 2. Prince William Sound, Alaska 1964 03 28 9.2 3. Aleutian Islands 1957 03 09 9.1 4. Kamchatka 1952 11 04 9.0 5. Off the Coast of Ecuador 1906 01 31 8.8 6. Aleutian Islands 1965 02 04 8.7 7. India-China Border 1950 08 15 8.6 8. Kamchatka 1923 02 03 8.5 9. Banda Sea, Indonesia 1938 02 01 8.0 10. Kuril Islands 1963 10 13 8.5
The 11 Largest Earthquakes in the Contiguous United States Location Date Time Magnitude 1. New Madrid, Missouri 1811 12 16 8:15 8.1 2. New Madrid, Missouri 1812 02 07 9:45 ˜8 3. Fort Tejon, California 1857 01 09 16:24 7.9 4. New Madrid, Missouri 1812 01 23 15:00 7.8 5. Imperial Valley, California 1892 02 24 7:20 7.8 6. San Francisco, California 1906 04 18 13:12 7.8 7. Owens Valley, California 1872 03 26 10:30 7.6 8. Gorda Plate, California 1980 11 08 10:27 7.4 9. N Cascades Washington 1872 12 15 5:40 7.3 10. CA - Oregon Coast 1873 11 23 5:00 7.3 11. Charleston South Carolina1886 09 01 2:51 7.3
Earthquake History of New York Strong earthquakes in 1638, 1661, 1663, and 1732 in the St. Lawrence Valley First notable tremor centered within the State was recorded on December 18, 1737 (intensity VII). Walls vibrated, bells rang, and objects fell from shelves (intensity VI) at Buffalo from a shock on October 23, 1857. A rather severe earthquake centered in northeastern New York area in 1877 (Intensity VII). On August 10, 1884, an earthquake caused large cracks in walls at Amityville and Jamaica (intensity VII). A shock reported as severe (intensity VI), occurred in northeastern New York on May 27, 1897. A very large area of the northeastern United States was shaken by a magnitude 7 earthquake on February 28, 1925. A maximum intensity of VIII was reached in the epicentral region, near La Malbaie, Quebec, Canada. Extensive damage occurred in the Attica area from a strong shock on August 12, 1929. On April 20, 1931, an earthquake centering near Lake George (intensity VII). On September 4, 1944, an earthquake centered about midway between Massena, New York, and Cornwall, Ontario, Canada, caused damage in the two cities. The shock was of Intensity VIII).
Quaternary Earthquakes are linked to geologic conditions. Precambrian Period is shown
Case Studies: Skew bridge Bridge curved in plan Bridge curved in elevation Railroad bridge Bridge with Integral Abutment
INTRODUCTION • 1. A number of bridges located in New Jersey, New York and • Pennsylvania were analyzed for acceleration factors between • 0.10 and 0.18, except for Long Island Railroad Bridge, which are . higher. The case studies of analytical procedures of five • bridges are presented here. Selection of suitable analytical, computational methods,bearing types, their locations and modeling techniques are discussed. • 2. Experience gained with analysis procedures contributed towards developing a chapter ‘ Seismic analysis and design’ in the proposed New Jersey LRFD Bridge Design Manual. • 3. Since the 1971 San Fernando earthquake FHWA published • “Seismic Design and Retrofit Manual for Highway Bridges” in • 1987. Further knowledge of seismic phenomenon was gained • from the 1989 Lorna Prieta and 1994 Northridge earthquakes.
Case Study 1 SKEW BRIDGE Route U.S. 322/N.J. 50 PRECAST CONCRETE PIERS
Case Study 1 Precast Pier
Case Study 2 - Curved Girders in Plan Route U.S. 23/ U.S. 80 (NJ)
Case Study 3- Girders Curved in Elevation Route U.S. 80 (NJ)
Case Study 4 - Replacement of Long Island R.R. Bridge (NY)
Case Study 5 – INTEGRAL ABUTMENTS AS PART OF SEISMIC RESISTING SYSTEM
Case Study 5 – INTEGRAL ABUTMENTS AS PART OF SEISMIC RESISTING SYSTEM
State of Art and Overview of Seismic Engineering Seismic Study/ Literacy Support Disciplines A. Seismology B. Geotech Eng. C. Disaster Managment D. Info. Links Seismic Disciplines E. Education F. Archives G. US Coord. Agencies H. International Coord. Agencies I. Earthquake Engineering J. Key Issues in Structural Engineering K. Structural Engineers Role a. Flow diagram for seismic study /seismic literacy
A. SEISMOLOGY • Geodesy • Earth’s Interior • Plate Tectonics / Location of Faults in NJ • Fault Maps • Wave Propagation • Seismometry, Seismographs • Intensity of Shaking/Strong Ground Motions • Acceleration, Velocity and Displacement Histories • Frequency and duration • Seismic Maps • B. GEOTECHNICAL ENGINEERING • Engineering Geology • Liquefaction • Site Effects • Soil Structure Interaction • Landslides • Micro-zoning
C. DISASTER MANAGEMENT • Vulnerable Populations • Risk Assessment • Loss Estimation (loss of life, property and commerce is the root of this problem) • Disaster Planning • Implementation • Mitigation (maintain Lifelines) • Recovery • Hazard Insurance • D. DISASTER MANAGEMENT LINKS/INFORMATION • Earthquake Information Network • Information Centers/Sites for Natural Hazards -Multidisciplinary Center for Earthquake Engineering Research, at SUNY Buffalo (MCEER) • National Information Service for Earthquake Engineering, at UCB (NISEE) • National Earthquake Information Center at USGS (NEIC) • Natural Hazards Research and Applications Inform. Center, CO (NHRAIC) • Databases
E. SEISMIC EDUCATION • College Curriculum • Laboratory Facilities/Shake Table Studies - 4 full size shake tables in USA and • smaller sizes in Ankara, Turkey, Imperial College London and Roorkee, India • Research Programs and Funding • Continuing Education • Seminar/Conference Funding • F. RELATED ARCHIVES ON SEISMIC LITERACY • News Archives of past earthquakes -Turkey, Iran, India, Mexico, California, Japan, Eastern Europe • Photos/Slides/ Videotapes • Library/Information Services • Natural Hazards Data Resources Directory • Abstracts/Journal Articles/Fact Sheets/Disaster Maps
G. US COORDINATING ENGINEERING AGENCIES/ASSOCIATIONS • Federal Emergency Management Agency (FEMA) • Government Agencies (Federal/State/Local) • National Agencies (USGS/FHWA/ACI/AISC/ASCE/PCA/SEI) • Civil/Structural Engineering Associations (SEAOC/NEHRP) • US Army Corps of Engineers/Red Cross • H. INTERNATIONAL SOURCES AND AGENCIES • ITALY (Universita degli Studi di Trieste) • JAPAN (Earthquake and Volcanic Disaster Prevention Laboratory, Tsukuba-shi) • MEXICO (Ciudad Universitaria, Coyoacan, Mexico/Seismology Lab. UNR, NV) • NEW ZEALAND (Institute of Geological and Nuclear Sciences, Lower Hutt, NZ) • RUSSIA (Center of Geophysical Data Studies and Telematic Applications, Moscow) • SWITZERLAND (Swiss Seismological Service)
I.EARTHQUAKE ENGINEERING • Basic Terminology / Glossary • Definition of Seismic Hazards • Deterministic and Probabilistic Seismic Hazard Analysis • Selection of Seismic Zone • Pseudo Velocity and Acceleration • Concepts of Quasi-static, Response Spectrum and Time History Analysis • Deformation Response Spectra • Importance of Ductility • Importance of Proportions / Sizing / Mass Distribution • Performance Characteristics of Lateral Load Resisting Systems • Condition Assessment of Damaged and Deteriorated Structures
J.KEY ISSUES IN STRUCTURAL ENGINEERING • Codes/Standards - Purpose of Seismic Code Lifelines • Critical Facilities • Structural Analysis - Quasi-static/Dynamic, D’Alembert’s Principle , Newton’s 2nd Law of motion, Non-linear matrices, Eigenvalues and Eigenvectors • Structural Design & Detailing • Theoretical Model, Multi-degree-of-freedom systems • Selection and application of Computer software for dynamic analysis • Computer Hardware requirements • Structural Repairs • Seismic Retrofit Concepts and Measures • Bearings, Restrainers, Shear Keys • Case Studies of past structural design • Earthquake Engineering Research and Development-Universities, Research Departments, Engineering Organizations
K.ROLE OF STRUCTURAL ENGINEER IN SEISMIC DESIGN • Advising the client on seismic criteria and costs • Structural planning, including locations and types of bearings (Rotational / Translational) • Compliance with relevant seismic codes • Selecting computer software for seismic analysis • Preparing construction drawings and guidelines for the contractor • Seismic detailing • Training design engineers in seismic design procedures • Following QA/QC procedures for the project • Keeping seismic design costs to a minimum • Solving any constructibility problems in the field • Maintain professional license and compliance with ethical requirements • Purchase liability insurance
Regular Draft LRFD Bridge Manual Selection of method of analysis for bridges
For any supplied response spectrum (either acceleration vs. period or displacement vs. period), joint displacements, member forces, and support reactions may be calculated. Time-History Analysis– This is an analysis of the dynamic responseof a structure when the base is subjected to a specific ground motion time history. This analysis is performed using the modal superposition method. Hence, all the active masses should be modeled as loads in order to facilitate determination of the mode shapes and frequencies. In the mode superposition analysis, it is assumed that the structural response can be obtained from the "p" lowest modes. The equilibrium equations are written as
Numerical Methods for solving differential equations • Solution of the Eigenproblem • The eigenproblem is solved for structure frequencies and mode • shapes considering a lumped mass matrix, with masses at active • d.o.f. included. • Two solution methods are available: • determinant search method, and • the subspace iteration method, • with solution selection based on problem size. • Modal responses may be combined using either the • Square root of the sum of squares (SRSS) or the • Complete quadratic combination (CQC) method to obtain the resultant responses. • Review Phase: Interpret and gain confidence with the analysis results. • Design Phase: Accomplish the AASHTO LRFD Code required design tasks. • Detailing Phase: Develop AASHTO LRFD required details.
Recent Developments in Methods of Analysis, Seismic Codes and Computer Software