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Method to calculate the fire resistance of circular reinforced concrete
columns
Method to calculate the fire
resistance of circular reinforced
concrete columns
Lie, T.T.; Celikkol, B.
NRCC-34917
A version of this document is published in ACI Materials Journal, 88, (1), pp. 84-91, January-91:
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Les renseignements dans ce document sont protégés par la Loi sur le droit d’auteur, par les lois, les politiques et les règlements du Canada et des accords internationaux. Ces dispositions permettent d’identifier la source de l’information et, dans certains cas, d’interdire la copie de documents sans permission écrite. Pour obtenir de plus amples renseignements : http://lois.justice.gc.ca/fr/showtdm/cs/C-42
Risk-cost
assessment:
A PC tool
to lower
building costs
Dr. David Yung
In response to the growing need for and interest in the economic assessment of building-code provisions, the Institute for Research in Construction (IRC) of the National Research Council of Cana-da (NRCC) is developing analytical tools that should be of interest to design professionals. One such development is a PC-based model that can be used to assess the cost effectiveness of fire-safety provisions in buildings. At this stage, the risk-cost assessment model applies only to Canadian apartment buildings, but NRCC has a longer-tenn program to develop similar models for other types of buildings.
In 1986, a risk-cost assessment model was developed, the result of years of effort, by Dr. V. R. Beck oftheFootscray Institute of Technology (FIT) in
Mel-bourne, Australia. The model, which currently runs on a mainframe comput-er) assesses ｣ｯｳｴｾ･ｦｦ･｣ｴｩｶ･ｮ･ｳｳ＠ of ｦｩｲ･ｾ＠
safety provisions in the Australian build-ing code for office buildbuild-ings. In 1987, FIT and NRCC began collaborating to develop a similar risk-cost assessment model for Canadian apartment build-mgs.
The framework for the Canadian apartment model and preliminary sub-models has been developed. FIT and NRCC are working on improving the submodels and converting the main-frame model into a PC-based model for user-accessibility. A similar PC-based model is being developed for Australian apartment buildings. Office models for both Canada and Australia are in development.
Apartment model
The apartment model consists of a series of fire-and-smoke-spread, egress and cost sub models. The performance of any building design is characterized in tenns of two decision-making parame-ters, expected risk-to-life and fire-cost expectation.
The expected risk-to-life is the expected number of deaths over the lifetime of the building, divided by the total population of the building and its design life. The fire-cost expectation is the expected direct costs and losses, TABLE I- Normalized results for a six-storey apartment building with various oombinations of passive and active fire protection measures.
ill X Nominal FRR Nominal FRR I V1 X Nominal FRR No With No With No With Sprinklers Sprinklers Sprinklers Sprinklers Sprinklers Sprinklers (a) No Alann
f-'<pected Risk-to-Life (ERL) 1.80 0.84 1.62 0.83 1.62 0.83 Fire Cost Expectation (FCE) 0.78 1.31 0.84 1.42 1.06 1.63 (b) With Central Alarm
ｾ＠
0.60 1.00 0.600 1.57 1.21 1.79
Expected Risk-to-Life 1.08 0.60 Fire Cost Expectation 0.94 1.47 (c) With Higher Reliability Central Alarm
Expected Risk-to-Life
li\s2l
0.54 0.77 0.54 0.77 0.54Fire Cost Expectation ｾ＠ 1.47 1.00 1.57 1.21 1.79
Notes: The numbers have been normalized by ERL = 1.83 X
w-•
and FCE- 4.81 Xw-r,
which are the computed results for the reference building code option (nominal FRR) no sprinklers but with central alann). FRR = Fire Resistance Rating. Nominal are those indicative of building code requirements.26 a Canadian Consulting Engineer
including the capital cost of providing active and passive fire-safety and protec-tion facilities, maintenance and inspec-tion costs associated with active fire-safety and protection facilities, and expected monetary losses resulting from fire spread in the building, divided by the total cost of the building.
The present approach of separating life risks and fire costs avoids assigning monetary value to human life. It pro-vides a more explicit estimate of expected deaths from fires in apartment buildings and allows comparison, in terms of relative risks and costs, of designs other than those contemplated by building code requirements. An alternative design is considered cost-effective if the fire-cost expectation is lower than, and the expected risk-to-life value is similar to, or preferably lower than, the corresponding expected values based on current code requirements for a particular apartment building.
A simple six-storey apartment build-ing was used to show the model's potential application in assessing the cost effectiveness of fire-safety provi-sions. The building was assumed to have eight apartments on each floor, two exit stairshafts, and 144 residents, an average of three people per apartment. In this type of building, the National Building Code of Canada requires certain fire-resistance ratings (FRR) for certain building components, and installation of a fire-alarm and detection system but does not require sprinklers.
To determine the cost-effectiveness of these fire-protection measures, cases were considered encompassing all possi-ble combinations of the three fire-protection options. Another option, a central alann system with detection and warning reliability higher than the cur-rently-assumed 70 to 95 percent, was also considered. The results are tabu-lated in Table I.
The table shows that for a particular fire-resistance rating, the preferred active fire-protection system, in terms of relative risk and relative cost, is the one with a higher-reliability central alann and no sprinklers. A lower fire-resistance rating (1/2 x nominal FRR) does not signilicantly affect the life-safety of
occupants. The most cost-effective measure seems to be the one with 112 x
nominal FRR, a higher-reliability cen-.tral alarm, and no sprinklers.
Benefits
The PC-based, risk-cost assessment model will provide Canadian code-writing CDmmittees with a tool for better ensuring that new requirements in the National Building Code of Canada and other building codes are economical and provide the desired level of fire-safety. This approach could substantially reduce the capital cost of building construction without adversely affecting life-safety. Code committees, with the help of NRCC researchers, can use the model to assess the impact of proposed code changes on both the safety and cost of buildings.
Designers and code regulators will also benefit from the model as it is a means of determining whether innova-tive designs provide protection equiva-lent to that required by the CDdes. The possibility of analyzing design alterna-tives often leads to significant cost reductions and to greater freedom in choosing design parameters.
NRCC, itself, will use the risk-cost assessment model to identify areas of fire research that will have the greatest impact on fire safety and CDnstruction
costs. 11
Dr. David Yung is a senior researcher and program manager of the risk-cost assessment program at the Fire Research Section, Institute for Research in Con-struction, National Research Council of Canada, Ottawa.
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References
V.R. Beck, 1987, "A Cost-Effective Decision-Making Model for Building Fire Safety and Protection", Fire Safety
Journal, VoL 12, No.2, pp. 121-138.
V.R Beck and D. Yung, 1989, "A Cost-Effective Risk-Assessment Model for Evaluating Fire Safety and Protec-tion in Canadian Apartment Buildings",
Proceedings of the International Fire Protection Engineering Institute- V,
Ot-tawa, Canada, May 21-31.
D. Yung and V.R. Beck, 1989, "A Risk-Cost Assessment Model for Evalu-ating Fire Risks and Protection Costs in Apartment Buildings", presented at The
International Symposium on Fire Engi-neering For Building Structures and Safety, Melbourne, Nov. 14-15.
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