Date: April 18, 2000
Author/Local: J. Robertson/7522
CC File Nos. 3601/3603
Council: May 2, 2000
TO: Vancouver City Council
FROM: City Building Inspector in consultation with the General Manager of Community Services & the Director of Risk and Emergency Management.
SUBJECT: Seismic Hazard Abatement for Privately Owned Buildings
A. THAT Council endorse the development of a seismic hazard abatement program for privately owned buildings in the City of Vancouver.
B. THAT Council direct staff, in consultation with public stakeholders such as building owners and tenants, to report back in 18 months with recommendations and options, including time frame, upgrade triggers, extent of upgrade, costs, mandatory versus voluntary approaches, and public information strategies.
C. THAT Council approve a permanent position of Senior Seismic Specialist in the Permits and Licenses Department at an annual cost of approximately $92,000 plus a one time cost of $11,000 for work station setup to be funded from existing permit revenues currently allocated to the structural review program.
D. THAT Council approve continuation of the structural review program to permit independent third party reviews of structural designs with a budget allocation of $75,000 to be funded from existing permit revenues currently allocated to the structural review program.
E. THAT Council direct the Director of Legal Services to bring forward for Council's consideration, a revision to the fee schedule of the Building By-law to permit the City to recover the cost of a third party structural reviewwhere such reviews reveal significant structural or seismic deficiencies in the design.
GENERAL MANAGER'S COMMENTS
The General Manager of Community Services Group recommends the approval of A, B, C, D, and E.
Through the adoption of seismic requirements in the Vancouver Building Code and through proactive programs to monitor and assess seismic design in new and existing buildings, Council has consistently promoted seismically safe building standards in Vancouver.
Council has consistently promoted seismically safe building standards in Vancouver. These standards, reflected in Vancouver Building Code requirements, have continued to evolve over time as our collective knowledge of earthquakes and their effects grows. Currently there is sufficient research, understanding, and experience to support a more proactive approach to seismic upgrade. Many jurisdictions, in earthquake prone areas, have developed long term seismic hazard abatement programs to substantially reduce the life safety and financial risks associated with vulnerable structures. This report recommends that work commence to develop such a program in Vancouver.
The report identifies the need to create a permanent staff resource, funded from existing permit revenues. This senior seismic specialist will analyse the City's risk and develop recommended options for a comprehensive hazard abatement program and report back to Council in 18 months. In conjunction with that work the position would also support and improve the current structural review program for new buildings, which the report recommends be continued. To enhance the effectiveness of the structural review program, the report recommends that the building permit fee schedule be revised to permit recovery of the cost of third party reviews in instances of significant or repeated non-compliance.
The purpose of this report is to:
· Review current City initiatives to address seismic hazards in the City,
· Describe seismic hazard abatement progress in some other jurisdictions,
· Review potential options for a seismic hazard abatement program and seek Council direction for further policy development, and
· Recommend measures to strengthen the current structural review program for new buildings.
1. Seismic Risk
Vancouver is situated in a seismically active area. It is vulnerable to large destructive earthquakes resulting both from local crustal earthquakes and from a major subduction earthquake originating in the Cascadia subduction zone off the west coast of Vancouver Island. The last subduction earthquake in this area occurred three hundred years ago with an estimated Richter magnitude of M9+. Vancouver is also vulnerable to crustal earthquakes, which are shallower but can be more erratic and damaging than a subduction quake when located close to an urban centre such as the recent earthquakes in Taiwan, Turkey, and Greece. These more localised crustal earthquakes tend to occur in the Pacific Northwest every 20 to 40 years, the last one occurring in Seattle 35 years ago. Seismologists generally agree that Vancouver is overdue for a major earthquake - either a crustal or a subduction earthquake. Further information on the seismicity of the region is contained in Appendix A and Reference 1 (References on file in City Clerk's Office).
2. Vancouver Initiatives
Over the years Council has initiated By-law changes and programs to enhance seismic design in Vancouver. In 1967 Council adopted, as part of the Vancouver Building Code, the seismic requirements of the National Building Code (NBC). It continued, in subsequent years, to adopt successive editions of the NBC which have progressively improved and strengthened provisions for seismically resistant design in the City. In 1991 Council authorized a seismic risk assessment of privately owned buildings in the City (the Delcan study). In 1995, Council approved a pilot program to monitor the quality and adequacy of structural and seismic design of buildings submitted for building permit. This program has enabled the City to assess the level of structural and seismic compliance in buildings where detailed structural review by the City is replaced by a certificate of substantial compliance from the structural engineer of record. More recently, in December 1999, Council instructed the City Building Inspector to review the provisions of the Vancouver Building By-law for existing buildings.
The seismic vulnerability of buildings in the City varies depending on age, type of construction and degree to which they have been upgraded. The City commissioned a seismic assessment of all City owned buildings in 1991 and has embarked on a program of upgrades. A companion report describes the latest initiative to commission a detailed review of the seismic capacity of community centres and City Hall, buildings which may be required to play a significant role in the City's response to a major seismic event. City-owned buildings are subject to the same By-law requirements as private buildings. Many major corporations and utility companies have embarked on seismic upgrade programs with respect to their facilities. These include BC Hydro, BC Tel, BC Gas, GVRD, and the University of BC.
The City's Building By-law triggers seismic upgrading of private buildings when there is a renovation exceeding twice the assessed value of the property; a major addition; or a major change in occupancy (comprising at least the total floor area of a storey). In the absence of these triggers, seismic upgrade is not required. Generally the policy of the City has been that a building which legally conforms at the time of its construction and is properly maintained, may remain in service indefinitely. (An exception was the mandatory retrofitting of automatic sprinkler protection for rooming houses and older hotels in the mid 1970's).
3. Federal and Provincial Initiatives
The Federal government has adopted a comprehensive upgrading program and ultimately all federal buildings will be seismically upgraded. The Federal Government has also adopted a policy requiring that all buildings leased by Federal agencies meet a minimum level of seismic resistance.
The Provincial Government has recently announced a Seismic Mitigation Program which will extend over a 20-25 year time frame and will address Provincial buildings. The initial focus of the program is on non-structural hazards within buildings.
4. Other Jurisdictions
Many other jurisdictions have begun to grapple with the issue of seismically vulnerable buildings, particularly in the aftermath of earthquake experience. California, for example, halted construction of unreinforced masonry buildings in 1933, following the Long Beach earthquake. (By comparison Canada did not prohibit unreinforced masonry construction until 1965). Following the 1971 San Fernando earthquake, many California municipalities adopted ordinances mandating upgrade of seismically deficient buildings. In 1973, for example, the City of Los Angeles commenced public debate on a seismic retrofit ordinance. Nine years later, in 1982, it was finally approved and by 1994 most of the 8000 affected buildings had been either demolished or upgraded. The effectiveness of the Los Angeles program was dramatically demonstrated in the 1994 Northridge quake. There was no loss of life in retrofitted unreinforced masonry buildings and damage was limited. Los Angeles has since expanded its program to address tilt-up concrete and steel frame buildings. A seismic evaluation standard for wood-frame homes is being developed by the Applied Technology Council in the U.S. and an incentive to meet this standard is intended to be developed in the form of lower earthquake insurance rates.
Following the Hawkes Bay earthquake of 1931, New Zealand adopted seismic code requirements and prohibited unreinforced masonry structures. In 1964 it mandated seismic upgrading on change of use or major renovation. In 1968 municipalities began to mandate seismic upgrades of `hazardous' unreinforced masonry buildings and by 1999 the majority of these buildings had been addressed. New Zealand is now looking at expanding its program to other types of hazardous buildings. Further information may be found in Reference 2.
Although Japan adopted more stringent seismic Code requirements in 1971 and 1980, most of its building stock is non-conforming and only requires upgrade on major renovation or change of use. In the 1995 Kobe earthquake most of the 6300 deaths were caused by the collapse of non-conforming, seismically deficient buildings. Local governments throughout Japan are now reviewing and modifying their seismic upgrade policies and programs. Both Tokyo and Yokohama have implemented interest free loans for voluntary seismic upgrading of homes. Shizuoka Prefecture has implemented upgrading programs for public buildings and buildings located along emergency transportation routes. The City of Kobe is rebuilding with the stated intention to be the most seismically resilient City in Japan. Further information on the Japanese position may be found in Reference 3.
To date, no BC municipality has ordered retroactive seismic upgrading of existing buildings except where significant changes of use or renovations are proposed.
5. The Delcan Study
In 1991 the City undertook a review to assess the seismic vulnerability of building stock throughout the city. The `Delcan Study' reviewed 1150 older buildings, using the National Research Council's rapid screening methodology. The study results provide good statistical data on the extent of risk associated with different building types. (It does not provide reliable information on any particular address).
The study reviews various upgrade options and costs and provides a preliminarybenefit/cost analysis. Of the approximate 100,000 privately-owned buildings in the City, 80% are one and two family dwellings which, for the most part because of their size and construction, represent a low life-safety risk. While there is some concern about larger homes which embody complex structural layouts and incorporate large ground floor garages or carports, the critical area of vulnerability resides in the older commercial and multi-residential buildings which do not meet current code requirements and which have not been upgraded (estimated about 8000 buildings). The Delcan study showed that the biggest benefit/cost rewards are to be derived from upgrading old unreinforced masonry buildings. Because of the relatively low cost of upgrading wood frame buildings, these were also found to be a good benefit/cost investment. The results of the Delcan study are described in more detail in Appendix B.
6. Structural Review Program
In May 1996 the City initiated a pilot Structural Review Program, funded by a modest increase in building permit fees, which enabled City staff to retain consulting engineers to independently review the structural and seismic design of buildings submitted for building permit. These are projects which are certified by the structural engineer of record as being in substantial compliance with the structural and seismic provisions of the By-law. About 60 projects have been submitted for independent review over the past three years. The results are not encouraging, a significant number of the projects submitted for independent review were found to have significant structural or seismic deficiencies in their design. These results indicate a weakness in the current compliance rate and regulatory framework.
In June 1999, Council approved a number of changes to the Vancouver Building By-law including provisions to deal with upgrading requirements for existing buildings. At that time, a number of relaxations to existing policy were made including adoption of the Provincial Building Code Table for alternative methods of upgrading designated Heritage buildings. While this method offers some relaxations for the fire safety upgrading of buildings based on mandatory sprinklers, it offers little guidance on requirements for seismic and accessibility upgrades. It was indicated at the time that this would be an interim measure and that there would be a need in the future to review the basis on which upgrading requirements are determined for both heritage and non heritage older buildings.
In November 1999, Council instructed the City Building Inspector to implement a work program to complete a review of the Vancouver Building By-law for existing buildings at a cost not exceeding $30,000, funding to be provided in the year 2000 Operating Budget. That review is underway.
1. Buildings at Risk
The statement "Earthquakes don't kill people, buildings do" reflects the realities of seismic mitigation. In Vancouver, life-safety hazards posed by building failures arise from three sources:
_ Historic and heritage buildings built before the introduction of seismic design requirements in 1967. These include unreinforced masonry buildings constructed during or prior to the 1940's without reinforcing and positive ties between the floor, roof framing, and supporting walls.
_ More recent buildings built in accordance with earlier editions of seismic codes but which, in light of growing knowledge and experience, are now considered deficient. These include many concrete framed buildings (classified as non-ductile) and some multi-unit wood frame residential buildings.
_ Newer and upgraded older buildings which have seismic defects in their design or construction which were not detected by the regulatory system. While no regulatory system guarantees 100% compliance, studies conducted after the Northridge earthquake of 1994 indicated a positive correlation between the extent of seismic damage and the level of code enforcement. (See Reference 4).
The seismic upgrading specified under the Vancouver Building By-law is required to achieve at least 75% of current code seismic force levels, although some significant relaxations are offered for unreinforced masonry buildings. Applicants may phase the upgrading over a period of up to five years. The City's current upgrade requirements have been reasonably effective in the Downtown Peninsula, Broadway corridor and in other commercially vibrant parts of the City where about 1,000 older, non-conforming buildings have received significant levels of upgrading. In the older economically less-advantaged commercial areas, like parts of Gastown, Chinatown and the Victory Square area, the By-law has been less effective and many older non-conforming buildings remain under-utilized and are not upgraded. The By-law triggers come into play less frequently in newer non-conforming buildings, like those in parts of the West End and in False Creek.
2. A Seismic Mitigation Program for Existing Buildings
To address these building failure risks it is recommended that the City develop a comprehensive seismic hazard abatement program. It is recommended that over the next eighteen months the following elements of the program be analysed and that options be developed for Council's consideration:
_ Objectives: While the primary objective of any hazard abatement program is life-safety, other interests may warrant higher upgrade standards. For example, an interest to ensure continued functionality or occupancy of a building following an earthquake would result in a higher upgrade standard than if the objective were limited to the safe evacuation of the occupants. Objectives need to be examined to determine appropriate building performance levels.
_ Levels and Methods of Upgrading: Upgrading can be achieved in various ways to achieve different upgrade levels. These options need to be explored to prioritize building types and occupancies for upgrade and to identify upgrade methods that generate the highest benefit/cost ratios. Various levels of upgrading are available for structures, particularly unreinforced masonry and wood frame buildings. These levels are explored in more detail in the summary of the Delcan Report. Typical levels include:
- Restraint of non-structural components such as partitions, ceilings, mechanical and electrical equipment, tanks, piping, ductwork, storage racks etc.
- Restraint or removal of falling hazards such as slender chimneys, loose masonry or stone cladding, unrestrained parapets, cornices etc.
- "Bolts Plus" providing adequate connections between major structural elements such as floors, walls, roofs, stair shafts etc.
- Partial Upgrade to provide new lateral load resisting elements capable of resisting a prescribed percentage of design level earthquake forces.
- Full Upgrade to provide new lateral load resisting elements capable of substantially resisting the current code design level earthquake forces.
_ Costs of Upgrading: Based on experience locally and elsewhere, reliable estimates need to be developed for the various upgrade methodologies and construction types so that the program can be evaluated in terms of costs to owners. The Federal Government, in conjunction with the Insurance Bureau of Canada, is establishing a grant program for hazard abatement projects in various areas of Canada. As part of the research for the City's seismic hazard abatement program, staff will explore potential funding sources which may be used to support project development and incentive initiatives.
_ Socio-Economic Impacts: In addition to the direct financial costs of an upgrade program, there are socio economic costs that will need to be studied and analysed. These will include anticipated disruption costs to owners/ tenants, impacts on low rent housing stock and single room occupancies, impact on small businesses, and impact on neighbourhood planning and development.
_ Community Involvement: It is important to the success of any hazard abatement program that it receive public support. Experience in other jurisdictions has shown that hazard abatement programs are most successful when the community develops an appreciation for the risk exposure and supports a well-designed, proportionate program which addresses hazards over a reasonable time frame.
_ Incentives and Voluntary Upgrading: There are a variety of incentives which could be implemented to encourage voluntary upgrading of certain building types and occupancies (for example, one and two-family residences). These incentives need to be identified and explored to determine which are reasonably viable and would have the greatest impact.
_ Timing: Based on experience elsewhere, and the scale of the proposed undertaking, it is likely that the time frame for a comprehensive program would be of the order of twenty-five years, with more urgent work addressed in the early phases.
3. Structural/Seismic Review for New Buildings
The seismic hazard abatement program will be supported by, and developed in conjunction with, work underway to amend the seismic upgrade provisions of the Vancouver Building By-law. It will also be supported by the structural review program which should be continued but, in light of findings to date, should be modified to facilitate a higher level of compliance. Regulatory systems can never guarantee absolute compliance. Rather, through a combination of spot checks,education, and a cooperative approach among the regulator, building owner, designer, and constructor, an effective regulatory system facilitates an environment which generates a high level of voluntary compliance. With respect to the structural review program, it is recommended that further work be done in cooperation with the Association of Professional Engineers to strengthen their quality assurance role and to promote enhanced training and education specific to structural concept reviewers.
It is also recommended that to discourage inadequate or deficient design the City charge back the costs of the third party review where major design deficiencies are found. The engineer in charge would be responsible for the cost of any independent design reviews commissioned by the City where such a review indicates significant levels of non-compliance. Safeguards to ensure that these charges are not imposed unfairly, include:
· Advising the designer of the city's concerns with the structural design and inviting them to revise the design if required prior to proceeding with an independent review.
· Imposing the cost of the review only where major deficiencies are identified which, if uncorrected, would result in less than 90% compliance levels with current codes and standards.
· In the event of a technical dispute between the city appointed engineer and the designer, referring the dispute to the Structural Review Board of APEGBC for mediation.
It is anticipated that by this means, the costs and penalties associated with non-compliance will be raised significantly and will serve as a strong disincentive for those in the design and construction industries who might be otherwise tempted to evade the hard work required to achieve code compliance and a robust seismically resistant structure.
4. Senior Seismic Engineer
Staff recommend appointment of a Senior Seismic Engineer to assist with the development of a seismic hazard abatement program for the City. The funding for creating this new position would be derived from the current building permit fee revenues currently allocated to the structural review program and the work would be incorporated into the work of this program. The duties of this specialist position would include:
· To act as a strong technical resource to both staff and the design andconstruction communities.
· To develop an improved public information program on the earthquake hazard and to promote voluntary improvements to the seismic resistance of buildings and their contents.
· To assist with the development of a seismic hazard abatement policy for privately owned buildings in the City of Vancouver.
· To work cooperatively with the design community to facilitate an improved and flexible system for assuring compliance with structural and seismic codes and standards. It is proposed that this would be modelled on our current building envelope professional program wherein the building structural system would be required to be reviewed by a designated seismic specialist and subject to audit by City staff.
· To administer the structural review program with a budget allocation of $75,000 to be funded from existing permit revenues currently allocated to the Structural Review Program. This program would include a provision to recover the cost of a third party structural review where such reviews reveal significant structural or seismic deficiencies in the design.
· To assist with further development of our emergency response plans.
It is recommended that funding of $92,000 per annum plus a one time cost of $11,000 for the new position of Senior Seismic Engineer and $75,000 for the continuation of the Structural Review Program be funded from existing permit revenues currently allocated to the structural review program.
The development of a comprehensive seismic hazard abatement program, in conjunction with the current Building By-Law review and Structural Review Program will provide the City with a long-term strategy for minimizing seismic risks associated with buildings. To the extent that this program addresses this risk over time, it will substantially reduce the life-safety, economic and recovery impacts of a major earthquake.
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APPENDIX A. SEISMIC HAZARDS IN VANCOUVER.
SEISMIC HAZARDS IN VANCOUVER.
Vancouver lies in a seismically active area of the Pacific Northwest which contains active seismic faults and is adjacent to the offshore subduction zone between the Pacific and the North American tectonic plates. Although Vancouver has not experienced a major earthquake in recent years, the BC coastal region area has been subjected to significant seismic activity. The following diagram, prepared by the Pacific Geoscience Centre in Victoria, illustrates the location and intensity of the major seismic events that have been felt in the Vancouver and Victoria areas. A listing of known historic and recent earthquakes in the Pacific North-West is contained in Table 1.
Table 1 - Known Historic and Recent Earthquakes in the Pacific North-West
Crustal Earthquake in Puget Sound near the present city of Seattle. Surface rupture and tsunami deposits in Puget Sound.
Subduction earthquake off the west coast of Vancouver Island. Coastal native village destroyed and native houses on Vancouver Island may have been damaged.
Gulf Island region. Probably deep, no reported aftershocks. Felt strongly in the Lower Mainland and the Victoria area.
Washington State, south of Hope. Crustal earthquake, followed by many aftershocks. Location uncertain, based on felt reports. Felt strongly in the Lower Mainland and the Victoria area.
Gulf Island region. Probably deep, no reported aftershocks. Felt strongly in the Lower Mainland and on southern Vancouver Island.
West coast of Vancouver Island. Crustal earthquake, many aftershocks. Felt by most in the Lower Mainland and on Vancouver Island. Damage on the west coast of Vancouver Island.
Gulf Island region. Probably deep, no reported aftershocks. Felt strongly in the Lower Mainland and on southern Vancouver Island.
Central Vancouver Island. Crustal earthquake, very few aftershocks. Much damage in central Vancouver Island, and slight damage in the Lower Mainland. Felt strongly all over Vancouver Island, throughout the lower mainland.
Puget Sound area - at a depth of 54 km. Much damage in Seattle/Tacoma. Felt by most in Lower Mainland and southern Vancouver Island.
Beneath downtown Seattle - at a depth of 63 km. Much damage in Seattle. Felt by most in the Lower Mainland and southern Vancouver Island.
Beneath the Strait of Georgia. Shallow, many aftershocks. Felt by many in the Lower Mainland and on Vancouver Island.
Beneath Pender Island at a depth of 60 km, no aftershocks. Felt by most, and some damage (broken windows) in the Lower Mainland and southern Vancouver Island.
Northern Washington. Shallow, many aftershocks. Felt by many in the Lower Mainland.
East of Seattle. Shallow, many aftershocks. Felt by many in the Lower Mainland and on southern Vancouver Island.
Beneath the Strait of Georgia. Shallow, many aftershocks. Felt by many in the Lower Mainland and on Vancouver Island.
Vancouver is classified under the National Building Code of Canada (NBC) as Zone 4 with a design level firm ground acceleration of 0.21g. This classification corresponds roughly with Seattle and is less than Los Angeles and San Francisco. This acceleration is associatedwith an earthquake with a mean recurrence (return) interval of 475 years, or a 10% probability of occurrence over a fifty year period.
Awareness of the magnitude of the seismic risk in Western BC has increased significantly over the last 30 years. Seismic design provisions for new buildings were first included in the NBC in 1953 and adopted in Vancouver in 1967. Recent advances in seismic engineering have resulted in major improvements in North American seismic codes which are considered among the most comprehensive in the world. The recent earthquakes in San Francisco, (1989) Northridge (1994) Kobe (1995), Mexico (1995), Turkey (1999), Greece (1999) and Taiwan (1999) have further highlighted common design problems and served as a "wake up call" to other active seismic regions in the world.
Recent research has further highlighted the potential for a major earthquake occurring in the Cascadian subduction zone located approximately 125 km off Vancouver Island. The zone appears to experience a major earthquake on average every 600 years, but the interval between earthquakes has varied from 180 to 1800 years. The last recorded earthquake in this area occurred approximately 300 hundred years ago. The National Research Council of Canada (NRC) is currently preparing seismic zonation maps for BC and Canada which will more accurately reflect the seismic risk from this source. NRC are also considering utilizing a 1,000 year return period for seismic forces in lieu of the 475 year period currently employed. If adopted, this could result in a significant increase in the level of seismic design forces specified in our codes.
While the Cascadian Subduction Zone presents a major seismic hazard to Vancouver, a near field crustal earthquake may also have devastating results in an area close to its epicentre. In Kobe, the near field crustal earthquake of January 1995 of magnitude 7.2 on the Richter scale caused in excess of 5,000 deaths and $250 Billion in direct damages. This earthquake exposed significant vulnerability in local building practices and emergency planning which had been largely predicated on a major earthquake occurring in an offshore subduction zone approximately 150 km away. In Turkey, a similar near field earthquake of magnitude 7.4 occurred on the north Anatolian fault and caused 15,135 fatalities and 23,984 serious injuries. Damage is provisionally estimated in the range of $10 Billion to $40 Billion. This earthquake dramatically exposed the consequences of a lack of vigilance in the provision of Building Control services and has had a major impact on the assessment of earthquake hazards in seismically vulnerable areas of the world.
APPENDIX B - THE DELCAN STUDY
THE DELCAN STUDY
1. PHASE 1
For Phase 1 of this study, approximately 1150 buildings were short listed by staff from an inventory of approximately 8,000 older commercial and multi-unit residential buildings. These buildings were generally selected from pre-1975 buildings.
The Delcan study presented the results of a rapid screening of the seismically vulnerable buildings using the National Research Council (NRC) rapid screening methodology with some modifications to accommodate Vancouver's Heritage buildings and to reflect Vancouver's adoption of seismic design requirements.
This methodology is designed to provide tools for evaluating the average seismic vulnerability of a class or group of buildings but should not be relied upon to give an accurate assessment of the seismic performance of any specific building. The assessment is based on completion of a brief checklist for each building outlining general building type and characteristics. Evaluation time is typically 20 minutes per building.
The Phase 1 results are contained in the Volume II of Delcan's report which lists the buildings in order of hazard. The 1100 buildings evaluated on a seismic index in the range 2.34 to 168 where the higher value represented higher levels of hazard. In general, a modern seismically resistant building should achieve a seismic index of 3 or lower. Seismic indices of 4 - 7 represent low priority of risk, indices of 8 - 28 represent medium priority and indices of over 29 - 40 represent high priority. Indices of over 40 can be considered as hazardous. A summary of the results is shown in Figure 1 below.
Figure 1 - Summary of Seismic Hazard Ratings - The Delcan Report.
Further analysis of the results of the survey may be found in the Phase 1 report prepared by Delcan. It should also be noted that 84% of the buildings in the "Very High Priority" are unreinforced masonry buildings.
This has to be considered as an unacceptable level of risk, as the exposed occupantload of this group of buildings is 158,600 with 66,900 persons in unreinforced masonry buildings. In comparison to most major Californian Cities and Municipalities, this would be considered to present a very high exposure level both in terms of life safety and property damage. A large part of this vulnerability can be attributed to the relatively late introduction of seismic codes in Vancouver.
Phase II of the study investigated various potential upgrade scenarios, from doing nothing to requiring major upgrades of all buildings. Benefit/Cost analyses were developed for these scenarios to assist evaluate their effectiveness.
It should be pointed out that the Benefit/Cost analyses presented by Delcan, are based solely on direct repair or replacement costs. They do not include any factor for personal injuries or business interruption costs. Such costs are difficult to quantify in a Benefit/Cost analysis, but can be expected to exceed property damage costs in any major earthquake scenario. Similarly, the analyses do not include any costs due to providing emergency response teams or temporary food and shelter to displaced citizens.
It should also be noted that the inventory of 1100 buildings represents a sample of the approximately 8,000 older seismically vulnerable buildings in the City. This excludes consideration of one and two family wood frame dwellings in the City which are generally considered to provide an acceptable level of seismic performance.
Benefit/cost analyses of these scenarios indicated that significant benefits accrue from relatively low levels of upgrading and that the biggest "bang for the buck" is realised with seismically upgrading unreinforced masonry and wood frame buildings. (The latter reflects the relatively low cost of upgrading wood frame buildings.)
Further information can be found in Delcan's study which has been filed with the City Clerk's office. It is anticipated that the report will prove of significant use in evaluating the economic impact of the upgrading options presented in this report for consideration by the City.
APPENDIX C - REFERENCES
1. The Threat of a Great Earthquake in Southwestern BC. Clague, Bobrowsky and Hyndman. The BC Professional Engineer, November 1995.
2. Regulatory Issues in the Proposed Changes to the New Zealand Building Act. Cashin and Brunsdon. Twelfth World Conference on Earthquake Engineering, Auckland, New Zealand 1999.
3. Why were over 5,500 lives lost in Kobe? How to Protect in Future. Yamada. Twelfth World Conference on Earthquake Engineering, Auckland, New Zealand 1999.
4. Plans, Code Enforcement, and Damage Reduction: Evidence from the Northridge Earthquake. Burby, French and Nelson. Earthquake Spectra February 1998.
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(c) 1998 City of Vancouver