|Shake table, seismic testing and performance evaluation of several innovative highway bridge columns designed to eliminate post-earthquake residual displacements and minimize column damage in strong earthquakes were presented to the “Bridge Resilience for Earthquakes and Other Natural Hazards” themed Seventh National Seismic Conference on Bridges & Highways (Oakland, California, May 20-22, 2013). Highway bridge column designs used pre-cast, Hybrid Fiber Reinforced Concrete (HyFRC) and post-tensioned steel strands (methods are elaborated in a 2011 PEER Report), or HyFRC with unbonded pre-tensioned steel strands, or prefabricated dual-steel shells. Carbon fiber reinforced polymer (CFRP) wrap was used to repair and strengthen the columns before subsequent testing. All tri-axial shake table tests of one-third scale specimens are reported with reference to a conventional reinforced concrete bridge column test specimen.|
Archive for May, 2013
Three experimental methods dominate laboratory research on the seismic performance of structural systems — shake table tests, quasi-static tests, and hybrid simulation. (See: M.S. Williams and A. Blakeborough, “Laboratory testing of structures under dynamic loads: an introductory review” in Theme Issue ‘Dynamic testing of structures’ compiled by M.S. Williams; Philosophical Transactions A of the Royal Society. September 15, 2001; 359 (1786). Costs of shake table tests (especially to avoid scaling problems) and the dynamic limits of most static testing procedures have propelled cost-effective hybrid simulation test methods. Hybrid simulation techniques combine physical, experimental testing of subassemblages (substructured components that can be full-scale) under simulated earthquake loadings with simultaneous numerical simulations of multiple other substructures into one model. Subassemblages tested experimentally are usually portions of the structure that are very difficult to model numerically, while components with predictable behavior are modeled on the computer.
The first operational hybrid simulated testing in earthquake engineering occurred 40 years ago at the University of Tokyo. (See – Takanashi, Koichi. Non-linear earthquake response analysis of structures by a computer-actuator on-line system (detail of the system); article first published in English in: Bulletin of Earthquake Resistant Structure Research Center (The Institute of Industrial Science, University of Tokyo), No.8, December, 1974. p.1-17., 1975; and subsequently, Takanashi, Koichi and Nakashima, M. “Japanese activities on on-line testing” Journal of Engineering Mechanics, ASCE, 113 (7) : July, 1987 p. 1014-1032.)
The hybrid simulation testing techniques of analytical simulation and substructure testing methods are rooted in the development of ‘pseudo-dynamic testing’ methods (See: Shing, Pui-shum B.; Mahin, Stephen A. Experimental error propagation in pseudodynamic testing. UCB/EERC-83/12, Earthquake Engineering Research Center, University of California, Berkeley, 1983-06, 175 pages. ; Shing, Pui-shum B.; Mahin, Stephen A. Pseudodynamic test method for seismic performance evaluation: theory and implementation. UCB/EERC-84/01, Earthquake Engineering Research Center, University of California, Berkeley, 1984-01, 162 pages ; Dermitzakis, Stavros N.; Mahin, Stephen A. Development of substructuring techniques for on-line computer controlled seismic performance testing. UCB/EERC-85/04, Earthquake Engineering Research Center, University of California, Berkeley, 1985-02, 153 pages ; Thewalt, Christopher R.; Mahin, Stephen A. Hybrid solution techniques for generalized pseudodynamic testing. UCB/EERC-87/09, Earthquake Engineering Research Center, University of California, Berkeley.) This continuous development of substructuring techniques, significant improvements in control technology, and repeated experimental implementation resulted in successful geographically-distributed hybrid simulation tests by early 2000s, (See – Mosqueda, Gilberto; Stojadinovic, Bozidar; Mahin, Stephen A. Continuous hybrid simulation with geographically distributed substructures. UCB/EERC-2005/02, Earthquake Engineering Research Center, University of California, Berkeley, 2005-11, 168 pages) as well as the emergence at UC Berkeley of the Open System for Earthquake Engineering Simulation – OpenSees - and the Open-source Framework for Experimental Setup and Control – OpenFresco - , open source software that support hybrid simulation for seismic performance testing.
Seismic performance testing using hybrid simulation techniques is now in wide use. Some widely drawn examples include : [US-Japan] Peng Pan, Hiroshi Tomofuji, Tao Wang, Masayoshi Nakashima, Makoto Ohsaki, Khalid M. Mosalam. “Development of peer-to-peer (P2P) internet online hybrid test system.” Earthquake Engineering & Structural Dynamics, Volume 35, Issue 7, pages 867–890, June 2006. [China] Jiang Wang, Jin-Ting Wang , Feng Jin, Fu-Dong Chi, Chu-Han Zhang. “Real-time dynamic hybrid testing for soil–structure interaction analysis.” Soil Dynamics and Earthquake Engineering. Volume 31, Issue 12, December 2011, Pages 1690–1702. [Europe] F. J. Molina, G. Magonette and B. Viaccoz . Linear Model of a Pseudo-Dynamic Testing System. European Commission, Joint Research Centre (JRC) Scientific and Technical Reports , IPSC, ELSA Laboratory, Ispra (VA), Italy. 2002; Santacana, Ferran Obón; Dorka, Uwe E. “Effects of large numerical models in continuous hybrid simulation.” Lisboa, Portugal. WCEE, 2012, paper presented at 15th World Conference on Earthquake Engineering; Tsitos, A. C.; Bousias, S.; Dimitropoulou, E. “Hybrid testing of bridge structures supported on elastomeric bearings.” Lisboa, Portugal. WCEE, 2012, paper presented at 15th World Conference on Earthquake Engineering; [USA] Nakata, Narutoshi; Elnashai, A. S.; Spencer, Billie F. “Multi-dimensional mixed-mode hybrid simulation control and applications.” University of Illinois at Urbana-Champaign, Newmark Structural Engineering Laboratory Report Series 005, 2007-12; [Canada] Kammula, V.; Erochko, J.; Kwon, O.; Christopoulos, Constantin. “Performance assessment of the self centering energy dissipative (SCED) bracing system using hybrid simulation.” Lisboa, Portugal. WCEE, 2012, paper presented at 15th World Conference on Earthquake Engineering.
Any semi-organized deployment of engineers, geologists, seismologists, sociologists, economists, and the other professionals attracted to immediate, post-damaging earthquake locales in California requires some planning and clear agency responsibilities to avoid chaos.
|A California Post-Earthquake Information Clearinghouse, established after the San Fernando earthquake in 1972 to coordinate observations and knowledge-sharing among emergency responders and the engineering and scientific communities, provides an organizational planning focus (See: 2013 ‘Golden Guardian’ exercise) for post-earthquake study and response. Although California law since at least 1971 requires municipalities to have seismic safety plans, coordination issues among cities and other levels of government in their quest for resources and assistance in post-earthquake scenarios are well-documented (See for example: Nigg, J.M. (1998) “Emergency response following the 1994 Northridge earthquake: intergovernmental coordination issues”). Training and coordination of non-emergency, post earthquake actions are continuously re-evaluated as engineering knowledge changes (See for example : Bazzurro, P. (2004) “Guidelines for seismic assessment of damaged buildings” or, Harthorn, R.W. (1998) “Temporary shoring & stabilization of earthquake damaged historic buildings : practical considerations for earthquake response & recovery in California” or the ongoing CalEMA – ATC20 training classes for post-earthquake inspections) and as new clearinghouse information-tools emerge for field use.|
The California Earthquake Clearinghouse provides a management platform for coordinated planning, discussion and review of local, state and federal agency responsibilities between earthquakes — and coordinated action immediately after larger earthquakes in California.
Extra credit: Musical relief for the California-earthquake-weary from the late, Warren Zevon or consideration of the potential flooding hazards in a predicted ARkStom for the state of California.
The ability of available, performance-based, analytical methods to predict reliably the performance of building structural systems in a major earthquake (mainshocks) and subsequent triggered aftershocks, (or other cascading hazard events) concerns earthquake engineering research. The possible damage to structures from cascading, shallow-focused, seismic events was provoked by the collapse of the CTV Building in the 22 February 2011, the Canterbury (Christchurch) region of New Zealand earthquake (Mw=6.3). That earthquake had followed the 4 September, 2010 Darfield earthquake (Mw=7.1) in the same region and a series of fairly strong aftershocks. (See: Forsyth Barr/CTV Building hearing:
Expert Panel Report: Structural Performance of Christchurch CBD Buildings in 22 February 2011 Aftershock.)
Analytically derived performance predictions (including “blind prediction competitions”) have achieved only mixed success with full scale experimental seismic testing results, — for example in Japan’s E-defense full-scale shaking table testing of steel moment frames –
Lignos, D.G., Hikino, T., Matsuoka, Y., and Nakashima, M., “Collapse assessment of steel moment frames based on E-Defense full-scale shake table collapse tests”, Journal of Structural Engineering, ASCE, 139:120-132; (2013)
Maison, B., Kasai, K., and Deierlein, G. “Study of building collapse for performance-based design validation.” Structures Congress 2008: Crossing Borders. pp. 1-10 (ASCE : 2008);
Lignos, D.G. (2012). “Modeling and experimental validation of a full scale 5-story steel building equipped with triple friction pendulum bearings: E-Defense blind analysis competition,” Proceedings 9th, International Conference on Urban Earthquake Engineering (9CUEE) & 4th Asia Conference on Earthquake Engineering, Tokyo, Japan; March 6-8, 2012.
Using reduced-scale models in shaking table testing at the University at Buffalo for validation, analytical performance predictions for four-story steel moment frames provided guarded success —
Lignos, D.G., Krawinkler, H., Whittaker, A.S. “Contributions to collapse prediction of steel moment frames through recent earthquake simulator collapse tests.” 3rd International Conference on Advances in Experimental Structural Engineering, October 15-16, 2009. San Francisco. (October, 2009).
A recent blind prediction competition using shake table testing of a full-scale, reinforced concrete bridge column subjected to six consecutive unidirectional ground motions at U.C. San Diego test facilities produced a wide variance in validity of performance predictions. —
Terzic, V., Schoettler, M., and Mahin, S.A. “Uncertainty in modeling seismic response of reinforced concrete bridge columns.” 9th International Conference on Urban Earthquake Engineering/ 4th Asia Conference on Earthquake Engineering, Tokyo Institute of Technology, Tokyo, Japan (2012).
For taller buildings (at least 160 feet in height), too large for reasonable laboratory shake table testing, the PEER/ATC-72-1 report : (Malley, J. et al) “Modeling and acceptance criteria … “ (2010), provides a near, ‘state-of-the-art’ compendium of recent available research, information, and recommendations on analytical modeling and acceptance criteria for the design and analysis of tall structural systems. Some methodologies for damage assessment of mid-rise building structural systems under cascading seismic events have also been elaborated in a variety of research studies — See for example:
Luco, N., Gerstenberger, M.C., Uma, S., Ryu, H., Liel, A.B., and Raghunandan, M. “A methodology for post-mainshock probabilistic assessment of building collapse risk.” Pacific Conference on Earthquake Engineering, Auckland, New Zealand (April, 2011).
Lee, K. and Foutch, D. “Performance evaluation of damaged steel frame buildings subjected to seismic loads.” Journal of Structural Engineering (ASCE), 130(4), 588–599. (April, 2004);
Li, Q. and Ellingwood, B.R. “Performance evaluation and damage assessment of steel frame buildings under main shock-aftershock earthquake sequences.” Earthquake Engineering & Structural Dynamics, 36(3), 405–427. (March, 2007).
M. Raghunandan, Liel, A.B.,Ryu, H., Luco, N., Uma, S.R. “Aftershock fragility curves and tagging assessments for a mainshock-damaged building.” Proceedings of the 15th World Conference in Earthquake Engineering (15WCEE), September 24-28, Lisbon, Portugal, 2012.
Eads, L., Miranda, E., Krawinkler, H., Lignos, D.G., (2012). “Improved estimation of collapse risk for structures in seismic regions,” Proceedings of the 15th World Conference of Earthquake Engineering (15WCEE), September 24-28, Lisbon, Portugal, 2012.
The complex challenges in accurately modeling the expected mainshock and aftershock seismic sequences for use in structural and non-structural damage analytical assessment prediction are recognized in recent work including –
Baker, J.W. “Probabilistic structural response assessment using vector-valued intensity measures.” Earthquake Engineering & Structural Dynamics, 36(13), 1861–1883; (9 May, 2007).
Ruiz-García, J. “Mainshock-aftershock ground motion features and their influence in building’s seismic response.” Journal of Earthquake Engineering, 16(5), 719-737; (26 June, 2012).
Work on improved analytical methods for reliable prediction of structural systems performance under realistic, cascading seismic events continues widely.
Most famous in earthquake mythology is the enormous subterranean catfish of ancient Japan whose sudden movements were reflected in surface ground movement until the fish could be subdued by superior force. (See images– NM0468, KZA63, KZA65, KZA66, etc.) Unveiling a modern earthquake view where great, unseen, natural forces of convection, gravity and friction act on large subterranean tectonic blocks in measureable and probabilistic ways may not have proved such a great phenomenological leap from the restrained catfish explanation for Japanese earthquake engineering. This opinion seems supported by the juxtaposition of the assembled contemporary warriors in business suits with the mythical catfish image offered in the printed version of the program at the March 2013, 10th International Conference of Urban Earthquake Engineering (CUEE – Tokyo Institute of Technology). Engineering technique now subdues natural forces.
Unrelated, recently the NISEE e-library received a request for a 1991 paper [International Workshop on Concrete Shear in Earthquake (University of Houston, TX) -- a solid workshop mysteriously absent of any California representation] in which Professor Michael P. Collins of the University of Toronto illustrated the engineering quest for a “rational model for shear [that] should make it possible to predict not only the shear strength but also the complete load-deformation response of elements subjected to shear… such a theory should be capable of being extended to the seismic situation of reversed, cyclic loading,” with a graphical representation of the number of technical papers dedicated to the shear design of concrete in one journal since the first paper on this topic in 1899.
Despite very considerable research accomplishment between 1899 and 1991 and subsequently (for example — M.P. Collins in 1996 (ACI) which re-uses this graphic), a cursory review of contemporary ACI Journals may suggest the quest and support for concrete shear design theory and practice continues apace.
Hospital reconstruction and seismic strengthening provided continuous demand for construction design and engineering services in recent years. (See NISEE, Dec 9, 2011) In California, compliance with mandatory seismic performance objectives for critical health care facilities is largely supervised through the California Office of Statewide Planning and Development (OSPD). A hospital’s ability to function adequately after a large earthquake is dependent on the building’s structural components (a building’s primary load carrying system of foundation, columns, beams, floors, walls and roof), non-structural components (building elements such as ceilings, partitions, pipes, mechanical and electrical, that are not part of the structural load-bearing system), occupants (staff and patients) and contents (equipment, supplies, furnishings, etc.) remaining largely undamaged. Hospital serviceability after natural disaster relies on robust interconnectedness of lifeline systems (water, power, transportation, etc.) that support hospital services. The constitution of structural, non-structural and contents may provide unique seismic strengthening challenges for hospitals.
For seismic strengthening of modern hospital buildings, reliable site-specific loss estimation techniques (e.g.: Blume-157) can account for structural and non-structural damage. Engineering building codes (e.g.: ICBO, FEMA, California Building Codes), applied research programs (e.g.: ATC-58, MCEER, Japan E-Defense) and sophisticated testing methodologies to analyze and strengthen structural and many non-structural systems to resist moderate to strong earthquake shaking or geotechnical damage are reasonably advanced. Video of recent shake-table testing at the University of California, San Diego (‘Building it Better: Earthquake-Resilient Hospitals for the Future’) confirms some ability to achieve both structural and non-structural hospital resilience after credible earthquakes in California.
More precise seismic fragility functions for hospital building contents and medical equipment (Zolfaghari, Porter, Furukawa) exist but experimental testing and verification of equipment fragility curves are confounded by prohibitive costs of testing very expensive medical equipment to a complete damage state (from high floor accelerations or from building displacements).
Similarly, analytical assessments of regional medical systems interconnectedness after natural disaster have been proposed (Lupoi, G. , Lupoi, A.) but can be fully tested only after a strong regional earthquake.