NATLINST.OFSTAND&TECHR.IC. NIST PUBLICATIONS A11103 Tb577D NIST BUILDING SCIENCE SERIES 170 Seismic Performance of Circular Bridge Columns Designed in Accordance With AASHTO/CALTRANS Standards -TA DEPARTMENT OF COMMERCE TECHNOLOGY ADMINISTRATION U.S. • ^ NATIONAL INSTITUTE OF STANDARDS AND TECHNOLOGY ,U58 70 //1 1993 The National Institute of Standards and Technology was established in 1988 by Congress to "assist industry in the development of technology . . . needed to improve product quality, to modernize manufacturing processes, to ensure product reliability . . . and to facilitate rapid commercialization ... of products based on new scientific discoveries." NIST, originally founded as the National Bureau of Standards in 1901, works to strengthen U.S. industry's competitiveness; advance science and engineering; and improve public health, safety, and the environment. One ofthe agency's basic functions is to develop, maintain, and retain custody ofthe national standards of measurement, and provide the means and methods for comparing standards used in science, engineering, manufacturing, commerce, industry, and education with the standards adopted or recognized by the Federal Government. As an agency of the U.S. Commerce Department's Technology Administration, NIST conducts basic and applied research in the physical sciences and engineering and performs related services. The Institute does generic and precompetitive work on new and advanced technologies. NIST's research facilities are located at Gaithersburg, MD 20899, and at Boulder, CO 80303. Major technical operating units and their principal activities are listed below. For more information contact the Public Inquiries Desk, 301-975-3058. Technology Services Manufacturing Engineering Laboratory • Manufacturing Technology Centers Program • Precision Engineering • Standards Services • Automated Production Technology • Technology Commercialization • Robot Systems • Measurement Services • Factory Automation • Technology Evaluation and Assessment • Fabrication Technology • Information Services Materials Science and Engineering Electronics and Electrical Engineering Laboratory Laboratory • Intelligent Processing of Materials • Microelectronics • Ceramics • Law Enforcement Standards • Materials Reliability' • Electricity • Polymers • Semiconductor Electronics • Metallurgy • Electromagnetic Fields' • Reactor Radiation • Electromagnetic Technology' Building and Fire Research Laboratory Chemical Science and Technology • Structures Laboratory • Building Materials • Biotechnology • Building Environment • Chemical Engineering' • Fire Science and Engineering • Chemical Kinetics and Thermodynamics • Fire Measurement and Research • Inorganic Analytical Research • Organic Analytical Research Computer Systems Laboratory • Process Measurements • Information Systems Engineering • Surface and Microanalysis Science • Systems and Software Technology • Thermophysics^ • Computer Security • Systems and Network Architecture Physics Laboratory • Advanced Systems • Electron and Optical Physics • Atomic Physics Computing and Applied Mathematics • Molecular Physics Laboratory • Radiometric Physics • Applied and Computational Mathematics^ • Quantum Metrology • Statistical Engineering^ • Ionizing Radiation • Scientific Computing Environments^ • Time and Frequency' • Computer Services^ • Quantum Physics' • Computer Systems and Communications^ • Information Systems 'At Boulder, CO 80303. ^Some elements at Boulder, CO 80303. NIST BUILDING SCIENCE SERIES 170 Seismic Performance of Circular Bridge Columns Designed in Accordance With AASHTO/CALTRANS Standards William C. Stone Andrew W. Taylor Structures Division Building and Fire Research Laboratory National Institute of Standards and Technology MD Gaithersburg, 20899 Issued February 1993 U.S. DEPARTMENT OF COMMERCE, Ronald H. Brown, Secretary NATIONAL INSTITUTE OF STANDARDS AND TECHNOLOGY Raymond G. Kammer,ActingDirector National Institute of Standards and Technology Building Science Series 170 Natl. Inst. Stand. Technol. Bldg. Sci. Ser. 170, 129 pages (Feb. 1993) CODEN: NBSSES U.S. GOVERNMENT PRINTING OFFICE WASHINGTON: 1993 For sale by the Superintendent ofDocuments, U.S. Government Printing Office, Washington, DC 20402-9325 ABSTRACT Limitations ofpresent procedures for the design of bridge columns to withstand seismic loads are discussed. An integrated seismic design procedure is developed which 1) allows the automatic selection and scaling of design earthquakes given the earthquake magnitude, the distance from the site to the fault, and the type of overlying soil strata; 2) predicts the inelastic behavior of reinforced concrete bridge columns when subjected to random lateral loads up to and including failure; and 3) calculates cumulative damage which can be directly correlated to observed states of damage in laboratory tests of bridge columns. Techniques for achieving the above capabilities are described and new design criteria, based on acceptable damage indices as functions of earthquake magnitude, distance, and structural importance, are proposed. Using the proposed procedure and criteria the performance of 72 representative bridge CALTRANS columns designed in accordance with 1992 specifications is analyzed. Analysis parameters included earthquake magnitude, distance from epicenter, subsurface soil characteristics, column aspect ratio, and normalized column axial load. Design charts, based on allowable damage index versus earthquake magnimde, are developed and retrofit strategies are discussed for those designs which do not meet the proposed design criteria. Key words: circular bridge columns; damage index; design; dynamic analysis; earthquakes; hysteretic damage model; inelastic modeling; reinforced concrete; seismic loads; site specific response; soil amplification; spiral reinforcement. iii On the cover: Proposed envelope for acceptable damage index, as a function ofearthquake magnitude and distance, for bridge piers deemed moderately important to seismic lifelines. See Chapter 6. Disclaimer Certain commercial equipment, instruments, or materials are identified in this paper in order to specify the experimental procedure adequately. Such identification is not intended to imply recommendation or endorsement by the National Institute of Standards and Technology, nor is it intended to imply that the materials or equipment identified are necessarily the best available for the purpose. iv ACKNOWLEDGMENT This project was funded in part by the Federal Highway Administration, Office of Research and Development. The authors gratefully acknowledge this support. The authors would also like to thank James Cooper of the Federal Highway Administration, James Gates of CALTRANS and Roy Imbsen of Imbsen and Associates for their helpful comments. V List of Symbols a = Peak ground acceleration, g's as = Cross section area of spiral bar, cm^ Ac = Spiral core cross section area, cm^ Ag = Gross cross section area, cm^ ARS = Response spectrum factor in CALTRANS design procedure, dimensionless db = Diameter of longitudinal bar, cm ds = Diameter of spiral bar, cm D = Overall diameter ofpier, cm Dc = Diameter of spiral core (out to out), cm D.I. = Damage index f = Concrete cylinder strength, MPa c fya = Longitudinal reinforcement yield stress, MPa fys = Spiral reinforcement yield stress, MPa F = Cumulative error between predicted and experimentally observed differential energy absorption for each point in an experimental record L = Length of pier, from base to first point of contraflexure, cm M = Earthquake moment magnitude N = Number of longitudinal bars in cross section _ 2asfygD^ p ~ S Per = Lateral load which causes first cracking of the column = Lateral load which causes complete collapse of the column Pfaii Puit = Maximum lateral load carried by the column Py = Lateral load which causes observable yielding of the longitudinal column reinforcement Pe = Axial load applied to pier, kN Q = 4p,Vf7V<^o -0.1 [Q = Oifa, <0.1] Ra Ac _S Rd D VI Rf f Rl D Rs S Rt f ^ ys f ^ ys Ry f~" ya Rn Pa S = Spacing (pitch) of spiral hoops, cm Sa = Response spectral acceleration, g's mm t = Thickness of steel retrofit shell, — o — — T = (in regressions equations for a, P and y) T = Fundamental period of structure (in CALTRANS design procedure) W = Superstructure dead weight in CALTRANS design procedure, kilo pounds Z = Risk and ductility factor in CALTRANS design procedure, dimensionless a = Stiffness degradation parameter for hysteretic failure rules, dimensionless P = Strength degradation parameter for hysteretic failure rules, dimensionless Y = Pinching behavior parameter for hysteretic failure rules, dimensionless % pa = Axial reinforcement content, areal % ps = Spiral reinforcement content, volumetric o = Standard deviation of spectral acceleration for target response spectrum ^lO—P Oo = ^ (kN MPa and cm^ Normalized applied axial load f^Ag , j vii List of Acronymns AASHTO = American Association of State Highway and Transportation Officials CALTRANS = State of California Department ofTransportation EARTHGEN = NIST interactive graphics program for selection and scaling of design earthquake records IDARC = Program for Inelastic Damage Analysis of Reinforced Concrete Frame-Shearwall Structures (Park et al., 1987) ISDP = NIST Integrated Seismic Design Procedure NIDENT = NIST interactive graphics program for system identification of cyclic behavior of reinforced concrete elements NIST = National Institute of Standards and Technology SAS/STAT = Commercial statitistical analysis package (SAS/STAT, 1987) viii