The retrofit of historic buildings invariably requires a variety of conservation approaches. Any retrofit scheme must be consistent with, and fully integrated with, the chosen approach. For example, if the form and materials of an existing building are to be preserved, retrofitting techniques might need to be concealed. This may require the use of more innovative and sophisticated retrofit methods than normal. On the other hand, full or partial exposure of retrofit systems and details may be acceptable where a building's rehabilitation involves more general preservation of architectural, cultural and historical values, possibly including former alterations and additions. Total concealment of retrofit structure may or may not be required when restoring a building to its original condition.
Whatever one's attitude towards conservation, far greater architectural sensitivity to the retrofit process and outcome is needed. Technical strengthening requirements need to be balanced with principles of architectural conservation. Look, Wong and Augustus recommend adopting the following three principles:
• Historic materials should be preserved and retained to the greatest extent possible and not replaced wholesale in the process of seismic strengthening;
• New seismic retrofit systems, whether hidden or exposed, should respect the character and integrity of the historic building and be visually compatible with it in design; and
• Seismic work should be "reversible" to the greatest extent possible to allow removal for future use of improved systems and traditional repair of remaining historic materials.17
The three authors do not insist that retrofit structure be concealed, nor recommend as some do, that strengthening elements be located in spaces of least historic value. After all, if retrofit structure is well-designed and respectful of the existing fabric, it can add another layer of historical intervention and avoid perpetuating the myth that the original construction is earthquake-resistant. This unconventional approach, which was investigated in a design project where exposed retrofit structure enriches the interior architecture of a historic unre-inforced masonry building, was discussed in the introduction to this chapter (Fig. I2.3).4
Whereas the main seismic performance goal for most buildings requiring retrofit is to preserve life and minimize injuries to occupants, the conservation plan prepared prior to an historic building retrofit may require designers to consider a second goal - to protect the building fabric. Although each historic building has to be treated individually, there may be a desire to control or limit the amount of damage suffered in the design-level earthquake. It might be inappropriate to adopt a lower performance criterion of life safety, where, although no lives are lost during a quake, a building is so badly damaged it requires demolition. However, as Randolph Langenbach points out, if seismic performance standards are too high, ironically the ensuing retrofit interventions may compromise or even destroy the very fabric to be protected. He argues for an approach to seismic retrofit that is far more sensitive to preservation ideals than much current practice:
Unlike maintenance and rehabilitation from decay, a seismic project may tear apart a building which was otherwise in good repair and make it almost entirely new. In such an instance, only the image, rather than the substance, of much of the historic fabric is preserved.18
1 Seismic Safety Commission (1995). Status of the Unreinforced Masonry Building Law: 1995 Annual Report to the Legislature. Seismic Safety Commission, California.
2 Look, D.W., Wong, T. and Augustus, S.R. (1997). The Seismic Retrofit of Historic Buildings: Keeping preservation in the forefront, Preservation Brief 41. National Park Service USA. Available at www.cr.nps.gov/hps/tps/briefs/ brief4I.htm.
3 Charleson,A.W. and Taylor, M. (1997). Architectural implications of seismic strengthening schemes. In Structural Studies Repairs and Maintenance of Historic Buildings, Sanchez-Beitia, S. and Brebbia, C.A. (eds.). Computational Mechanics Publications , pp. 477-786.
4 Taylor, M., Preston , J. , and Charleson,A.W. (2002). Moments of Resistance. Archadia Press, Sydney.
5 SF DBI (2001). What you should know about unreinforced masonry buildings. San Francisco Department of Building Inspection.
6 Bruneau. M. et al. (2005). Review of selected research on US seismic design and retrofit strategies for steel structures. Progressive Structural Engineering Materials, No. 7, 103-114.
7 Applied Technology Council (1988). Rapid visual screening of buildings for potential seismic hazards: a handbook. ATC-21. Federal Emergency Management Agency.
8 NZSEE Study Group on Earthquake Risk Buildings (2006). Assessment and improvement of the structural performance of buildings in earthquakes: prioriti-sation, initial evaluation, detailed assessment and improvement measures. New Zealand Society for Earthquake Engineering.
9 FEMA (1997). NEHRP guidelines for the seismic rehabilitation of buildings: FEMA-273, Federal Emergency Management Agency.
10 WCC (2005). Draft Earthquake-prone Buildings Policy. Wellington City Council.
11 For example, CSSC (2005). Homeowner's Guide to Earthquake Safety. California Seismic Safety Commission.
12 San Leandro City (2005). Earthquake Retrofit Programs. http://www.ci.san-leandro.ca.us/cdearthretro.asp.
13 NZSEE Study Group on Earthquake Risk Buildings (2006). Assessment and improvement of the structural performance of buildings in earthquakes: prioriti-sation, initial evaluation, detailed assessment and improvement measures. New Zealand Society for Earthquake Engineering, pp. 13-16.
14 Sherstobitoff, J., Rezai, M. and Wong, M. (2004). Seismic upgrade of Lions Gate Hospital's Acute Tower South. Proceedings 13th World Conference on Earthquake Engineering, Paper No. 1423. 12 pp.
15 Comerio, M.C., Tobriner, S. and Fehrenkamp, A. (2006). Bracing Berkeley: A guide to seismic safety on the UC Berkeley Campus. Pacific Earthquake Engineering Research Centre, University of California.
16 FEMA (1992). NEHRP handbook of techniques for the seismic rehabilitation of buildings: FEMA-172, Federal Emergency Management Agency.
17 Look, D.W., Wong, T. and Augustus, S.R. (1997). The seismic retrofit of historic buildings: keeping preservation in the forefront, Preservation Brief 41. National Park Service USA. Available at www.cr.nps.gov/hps/tps/briefs/ brief4l.htm.
18 Langenbach, R. (1994). Architectural issues in the seismic rehabilitation of masonry buildings. Proceedings of the US-Italy Workshop on Guidelines for Seismic Evaluation and Rehabilitation of Unreinforced Masonry Buildings; University of Pavia, Italy, June 22-24. Also in NCEER Report 94-0021. National Center for Earthquake Engineering Research, State University of New York at Buffalo, 1994, 1-3 to 1-16.
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