Performance Based Design

http://www.ukessays.com : Building regulations are legal instruments intended to ensure that buildings, when constructed in accordance with the regulations, provide socially acceptable levels of health, safety, welfare and amenity for building occupants and for the community in which the building is located. This is typically accomplished through regulatory controls on the design, construction and operation of buildings, covering such diverse areas as structural stability, fire safety, heating, lighting, ventilation, plumbing, sanitary facilities, indoor air quality and energy (Meacham,2005)

The role of the Building Codes is to establish minimum acceptable standards for new buildings and building work, without preventing higher standards. The standards for buildings that are set in building codes balance quality, cost, affordability and accessibility. Building codes cannot eliminate risk. They are set to provide basic protection for the people who use buildings and to achieve national goals.(Department of building and housing, New Zealand, 2007)

1.2Classification of building codes

Building codes may be classified as prescriptive or performance-based in nature. Prescriptive codes obtain their names from the fact that they prescribe specifically what to do in a given case. Performance codes express the desired objective to be accomplished and allow the designer to use any acceptable approach to achieve the required results. ( Kruppa,2000)

1.3 Background building codes

The oldest known Performance requirements are found in Hammurabi's Code (c. 1795 to 1750 BC), where is stated that

“228. If a builder build a house for some one and complete it, he shall give him a fee of two shekels in money for each sar of surface.

229 If a builder build a house for someone, and does not construct it properly, and the house which he built fall in and kill its owner, then that builder shall be put to death.

230. If it kill the son of the owner the son of that builder shall be put to death.

231. If it kill a slave of the owner, then he shall pay slave for slave to the owner of the house.

232. If it ruin goods, he shall make compensation for all that has been ruined, and inasmuch as he did not construct properly this house which he built and it fell, he shall re-erect the house from his own means.

233. If a builder build a house for someone, even though he has not yet completed it; if then the walls seem toppling, the builder must make the walls solid from his own means.”

(Hooker,R)

In the first half of the 20th century the standards, guidelines and recommendations shape the current specifications used for design, construction and evaluation of buildings and bridges. They were formulated by technical committees. The first committee was the American concrete institute that recommended practice and standard specification for concrete and reinforce concrete. Other committees are (ASCE, ACI, AISC, ASTM, AASHO and currently AASHTO).(ASCE SEI Technical committee,2004; Bukowski,1996):

The Prescriptive approach to civil engineering facilitated the design and evaluation practice, because of its rationale and heuristic knowledge b. From a design point prescriptive approach is easier to be used than performance-based approach. (ASCE SEI Technical committee,2004) Moreover, prescriptive codes have the advantage in that they enable a straightforward evaluation of determining whether or not the established requirement has been met. Furthermore(Buchanan,2002), it includes many factors of safety to account for unknown in both the loading and resistance and to account for simplifications in the analytical techniques (ASCE SEI Technical committee,2004). On the other hand ‘’In a traditional, prescriptive-based regulatory system, the performance objectives are often implicitly embodied in specific requirements that vary by building use or occupancy type’’(Filiente,2000,p.14) .

In addition, these codes have evolved over many decades, with newer requirements being imposed over existing ones. As a result, prescriptive codes have become complex and are often difficult to use for new technologies and change in practices. (Beyler andIwankiw,2005)

Many civil engineering professionals believe that implicit design construction evaluation may possibly in the case of many modern civil engineering projects (ASCE SEI Technical committee,2004)

‘‘A hallmark of performance-based building regulation is the explicit statement of goals and objectives that reflect societal expectations and desires, along with functional statements, operative requirements and in some cases

Performance criteria, which are to be used for demonstrating that goals and objectives have been met ’(Mecham,2005,p.92) .That is why many countries are in the process of introducing performance based building regulations and some countries have already introduced them. (Mecham, 2005)

It is very obvious from the above information that the move to performance based regulations began for many reasons. In addition to above ,in some cases, dramatic changes to the existing regulations are needed in respond to the stakeholder’s concerns, while in others there is a belief that one has to regulate

More intelligent policy directions for governments. Performance based codes offer the ability to have the right people involved in the right type of discussion. For example specialists must to be involved during the development of new scope of codes, while technical specialist need to examine how to meet the objectives expressed by policy decisions. (Meacham,2005)

Taking into consideration the above , the present framework cannot explain explicitly the real building performance and is becoming increasingly inappropriate for new technologies and performance indications. So it is necessary to establish a new <<performance-based structural design framework>>. This framework would also encourage the communication between clients and engineers in order to make a consensus on building structural performance, and the application of new material new technologies , by its rational performance requirement and its flexibility in evaluation of performance.

Table 1: The main advantages and disadvantages of the prescriptive codes Retrieved from :(Tavares ,2008,p.8)

Performance based design of structures,

what is the state of the art?

Table 2 : Historial prescriptive codes. Retrieved from (Chrisanthopoulos,2009)

1.4 Differences between a prescriptive approach and a performance based approach.

A prescriptive approach “describes means as opposed to ends, and is concerned with type and quality of materials, method of construction, workmanship, etc" Moreover

“In some parts of the building materials industry, performance specifications are known as “end result” specifications, while prescriptive specifications are known as “recipe” specifications ” (Gibson, 1982 )

A clear example of the difference between prescriptive code and performance criterion can be found in the spacing of guardrail elements. Prescriptive requirements in international building codes specify that rail elements must be spaced so that a sphere of 102 mm cannot pass through any opening up to a height of 864mm.This requirement was developed specifically for the safety of children. However, A performance code developed by the international code council in 2001 , does not mandate this narrow spacing, instead of that , it specifies << That the opening shall be of an appropriate size and configuration to keep people from falling through based on the anticipated age of the occupants>>. If it can be shown that children are not expected to visit the structure (e.g. manufacturing facility), then the spacing of the guardrail element can vary (Harmon, 2005, p.18)

2.The Concept of Performance based design

There are plenty definitions of performance based design. However, most researchers agree that a proper and clear definition was given in 1982 by Gibson. Gibson defined that: <<The Performance Approach is the practice of thinking and working in terms of ends rather than means. It is concerned with what a building or a building product is required to do, and not with prescribing how it is to be constructed>>

(Deru and Torcellini,2005,p.4)

Moreover Gibson added that “It is concerned with what a building or a building product is required to do, and not with prescribing how it is to be constructed.” (Gibson,1982)

One has to consider the experience the experience gained over time on the concept performance based design, without ignoring the basics and the first principles on design .Moreover, one must also taking into account laboratory experiment and observations about the non-linear of structural elements and components

2.1 Key Characteristics of the performance Concept

Two key characteristics of the performance concept are:

• The use of two languages, one for the demand for the performance and the other for the supply of the performance.


• The need for validation and verification of results against performance targets

(Szigeti and Davis, 2005)

Chieling in 1986 used the ‘Hamburger model’ in order to explain both characteristics. The model distinguishes a Solution Concept’ on the supply side of e.g. a built facility and ‘Functional Concept’ on the demand side.The solution concept has to primarily comply with the functional concept, however, the two concepts are expressed in two different languages, that make it difficult . The Functional concepts state in ‘user language’ what the facility should do for the users and why.(PeBBu,2005A)

The solution concept basically states in ‘technical language’ how a facility could and/or should be constructed. Moreover users and clients need to be able to verify that what they get is wanted, asked and paid for(PeBBu,2005)In addition to the above (Szigeti and Davis P3)stated that evaluation and reviews need to refer back to explicit statements, as they are part of design, construction and commissioning. Otherwise they are based on perceptions, intuitions and guess work. Furthermore according (PeBBu,2005) There is a need for making functional (user) needs and requirements more explicit and for linking those to the objectives for the project. Furthermore, there is a need for checking whether or not proposed solutions comply with the requirements. But, because of the different languages that are inherent to the different viewpoint mentioned above, this is quite a difficult thing to do

The Performance approach offers a solution here, once the functional and the solution concepts are translated into ‘performance language’ as it is explained below, it is possible to compare and match demand and supply sites: The ‘performance language’ can be used as an intermediate between functional needs and requirements and then as intermediate between requirement and between technical solutions. Analyzing the subject further, on the demand site ‘performance language’ translates functional needs into performance requirements. In details, these are expressing what properties the built facility should have in order to facilitate the intended use. The technical specification on the supply side, are translated into performance specifications. These are expressing the measures or predicted properties of the offered solution. The tools for this translations are validation and/or assessment methods. (PeBBu,2005A)

2.2 The Nordic Model/ And the two languages of performance approach

The Nordic Model is currently being applied in the U.S. in the development of two codes, the ICC Performance Building Code and the ICC Performance Fire Code. For purposes of this paper, the Nordic Model is that which appears in the ICC Building Performance Code Committee Preliminary Report dated August 199 . Originally articulated as five levels(Figure 5), it has been compressed in the US into four levels, and appears in the form of a pyramid, as in Figure 3. This provides the structure of the code provision ( Hattis and Becker,1999,p.7)

OBJECTIVES: The objectives express what is acceptable from the society. An example could be safeguarding people during escape and/or rescue.

FUNCTINAL STATEMENTS: Explain In wide ranging terms, what function the building and and/or structural element must be provided in order to meet the objective. For instance, the structure must be constructed to give to people an appropriate length of time to reach a place of safety without exposure to untenable conditions).

PERFOMANCE REQUIREMENTS are detailed accomplish the objectives of the constrains of the functional statements

ACCEPTABLE METHODS using the performance approach are the explicit verification methods which may be operated in order to achieve the performance requirements that in particular order, meet the performance objectives

Additionally, the following expressions are used:

MAJOR TOPIC AREAS are the topics of particular

Chapters of the code for instance, fire safety and safety of occupants.

PERFORMANCE PROVISIONS supply a set of objectives, functional statements and performance requirements for main topic areas that should be provided the aim of the design code. > >( Hattis and Becker,1999,p.7)

‘‘The development of performance-based and objective-base codes is based on key characteristics of the Performance approach,

the this model and links easily to one of the dialog between the WHY + WHAT and the HOW’’. (Source: Szigeti and Davis, 2005)

3.Performance Based Fire Design

Fire safety and seismic design are mainly the two civil engineering areas in which performance based design is becoming accepted. In both , a client can demand a certain performance objective and expect to get it.(Kolarevic,2003)

The state of art of performance based fire safety is a main part of the particular report because earthquake activities in the U.K are very limited .

Design fire safety teams argue that progressive design is the main characteristic of performance based design. This characteristic offers safety and flexibility. However , a special challenge to facility executives(e.g. maintaining fire protection features during future operations) is presented as the performance based design which is becoming more common. ( Begley,2004)

A logical and easy way to understand the concept of performance based fire design is to start with the traditional prescriptive based fire design. A very simple and easy example is given below as introduction to the particular chapter . A similar reasoning is used in the following in the following sub-chapters

Prescribed specific design criteria is the main commitment of traditional prescriptive building codes. An example could be, the number of exits or the number of feet to an emergency exit: These criteria are numerical and they can without difficulties measured. On the other hand, Performance based fire code allows the use of different designs that are able to demonstrate compliance with the fire safety objectives .( Begley,2004)

3.1Fire Safety Requirements

The two main components of fire safety requirements are:

• General building fire safety. That is achieved with an insulation of the structure due to a proper compartmentation of the building.


• structure/structural members stability. That it can be achieved with a proper fire resistance of the structural members.


•  

The main aspect of the first component is to maintain structural and thermal barriers in order to prevent spreading for a sufficient time which will allow the occupant to leave the building safely.

The key characteristic of the second component is he length of time for which the structural member is required to exposure to the fire regime given in the standard fire without the load capacity falling below the fire limit state factored load or loss of its insulation and or its integration. (Usmani,2009).

The majority of t organizations and researchers who deal with fire safety issues, seem to agree with the above approach. The only difference is that some of them explain the fire safety requirement in a different way, as it can be seen below.

Considerations addressed to minimize the risk of failure model including structural collapse is a special fire design treatment because the fire is not a loading condition but an environmental condition which may have a negative impact on load carrying capacity of a structural element and therefore ,may affect the safety of the structure. Maintaining structural integrity during the fire for long enough so that all the occupants may safely evacuate the building. It is the main objective of fire resistance design. Moreover, the design confines any potential fire with statically placed fire stops in order to provide the appropriate conditions to the fire fighters to put out the fire and minimize property loss. (Cramer and white, 1997)

3.2 Current Prescriptive codes approach to fire safety

The prescriptive Codes and standards prescribe fire resistance and safety for general use and application and typically these documents do not achieve fire safety objectives because: Fire resistance and protection are achieved by specifying the main and important construction characteristics. Moreover, by limiting dimensions and adding protection systems. However, they do not provide mechanisms how these requirements can achieve a desired fire safety.(NFPA, 1997)

The presumed temperature profile and duration of standard fire are the mainly requirements for fire resistance in building codes. (Deru and Torcellini, 2005).

Pr Usmani (2009) illustrated some very key examples of current prescriptive codes approaches on fire safety

As it can be seen A and V are the key factors for the section heating rate, When the ratio of A/V is high the rate of the heating is fast conversely when the ratio is small the section heating rate is slow. the determination of A/V for profiled and box protection is illustrated above and it is very simple.

The figure 6 illustrates the appropriate fire resistance rating of ( 30,60.90 and120 minutes) in terms of the building type , height of the top story and occupancy.

3.3Prescriptive codes , example of fire resistance test with uncertain outputs

In USA building codes a fire resistance test is described in ASTM 119. The test determines the structural members bearing capacity(The ability of the structural element to withstand exposure to fire regime in length of time without collapse).Moreover they determines the integrity (the flames or/and gases passage , hot enough to ignite cotton waste) and insulation (assuring the temperature on the unheated side of the element does not exceed 250°F). ( Lane,2000)

In a test ,a column ,a beam ,a wall or a floor under its calculated design load can withstand when exposed under a given fire defined by prescribed temperature/time curve. One can achieve this curve by programming the temperature of a test furnace by controlling the rate of fuel supply .Moreover, the time to the nearest minute , between the beginning of heating and failure under (load bearing capacity, insulation or/and integrity), is taken as the fire resistance of the element ( normally one-two hours). ( Lane,2000)

This test was developed between 1900-1981 when there was very little knowledge of fire safety issues. The standard fire test has been criticized negatively. Since it is very inaccurate (see figure 8) . (Lane,2000)

The above graph shows the temperature/time curve for the standard test compared to different real fires with various areas of windows. The differences are obvious , the duration and severity of real fire scenarios is not well defined .Moreover, as it can be seen ,periods of fire resistance in many cases, are over-specified where the standard results are applied.(Lane,2000)

In addition, the above graph shows clearly that, the standard fire test is not valid, since the maximum fire temperature depends on the ventilation condition of the fire compartment and the building covered area from windows.

3.4 Risk assessment

The use of risk assessment as the method to determine acceptable solutions is possible .The estimation of the consequences of the event has been the main effort or risk assessment But the quantification of risk depends on the ability to describe detailed scenarios and their likelihood of occurrence(severity of events: disastrous, extreme, serious, significant, minor, negligible).

Furthermore the losses from hazard can be :fatalities and injuries with direct and indirect economic loss ( Bukowski, 1996B).

Figure: BS EN 1991-1-7;Risk Assessment. Retrieved from (Chryssanthopoulos,2009)

According to A guide for the use of BS EN 1991-1-7 for Qualitative Risk Assessment:

‘‘ A systematic risk assessment of the building should be undertaken taking into account both foreseeable and unforeseeable hazards.

This is not an exact science and the primary gain is obtained through a systematic examination and recording of the potential hazards, of the vulnerability of the structure’s to these hazards, and the measures that can be taken to minimize any undesirable consequences.

The results of the risk analysis should be presented as a list of consequences and probabilities and their degree of acceptance should be discussed.

The report may need to be peered and reviewed and periodically reevaluated.”

(Chryssanthopoulos,2009)

3.5 Fire Hazard Assessment and computers models key concepts and tools For Building Fire Safety Performance Evaluation

The majority of the developed countries have expressed great interest in the use of fire risk assessment, in order to judge performance against the code’s explicit objective.

However, risk assessment is very complicated because it needs a huge amount of historical data which is very difficult to select. That is why, fire hazard assessments is the main method that is used by designers for evaluating performance. Fire Hazard assessments measure performance, in a specific set of conditions presume to represent the most significant dangers. Because experience has proved that the most dangerous fires occur as a result of many things going wrongly at the same time. It is useful to have in mind of situations which are characterized by multiple failures in providing safety of the public . ( Bukowski, 1996A, 1996C)

Better knowledge of structural fire performance and the development of better computation tools of fire endurance are demanded in order to emerge performance-based codes. Moreover the emergence of the performance-based codes demands the improvement of the current understanding of the fire growth, heat transfer process and material property changes. Moreover, significant advantages will be given to scientist and designers by using computer based models. (Harmon, 2005, p.18)

Performing a FHA

Performing a fire hazard assessment is a fairly straightforward, engineering analysis. The steps include:

• Selecting a target outcome,


• determining the scenario(s) of concern that could result in that outcome,


• selecting an appropriate method (s) for prediction,


• evaluating the results, and


• examining the uncertainty.

( Bukowski,1996C)

In performing a calculation to assess equivalency to code provisions for safe evacuation of building occupants in cooperation with computer models several steps are required to assure a valid result. These include:

• Establish the acceptance criteria.


• Select appropriate fire models/methods.


• Select design fire(s).


• Perform an evacuation calculation.


• Account for uncertainty.


• Reality check.

( Bukowski, 1995C)

In the following sections each of these steps will be discussed in detail so that the objective of each as well as the overall process can be evaluated.

3.5.1Establish the acceptance criteria

The primary purpose of fire safety code requirements is to allow for safe exit by all the occupants of the building, thus, egress analysis is required in the majority of alternative design calculations. This is classically in two parts: The time available for safe egress is calculated by estimating the fire development and smoke filling time; and an estimation of the time which is needed in order to evacuate the maximum population expected in the exposed area.. The occupants are safe and the building complies the intention of the code if the available time is more than the time needed. Traditional assumption is normally used for the first part of the calculation. This assumption is that the escape in no longer possible once the smoke layer fills down to the head height ( average 1.5 m from the floor). In fact, the models countermand the above assumption. The smoke level or visibility distance can be specified, as the model has the ability to predict the increase in smoke density within the layer (either upper or lower).

However, egress is not always the main objective. For example, in some industrial occupancies (for instance nuclear power station),the main objective is the public from fire consequences. Therefore, code requirements are established in order to prevent exposure of critical systems or processes. (Cornell,2002; Bukowski, March 15-16, 1995)

Moreover, ‘‘ protection in place’’ is the main objective in occupancies where person have limited mobility. In both of these instances only the filling time calculation is necessary in order to make some estimate of the susceptibility of the critical equipment or people to damage. It must be also mentioned that models that do this are available. ( Bukowski, 1996C)

3.5.2DETERMINING THE SCENARIO(S) OF CONCERN

Once the outcomes to be avoided are established, it is important to identify any scenarios which may result in these objectionable outcomes. It is very crucial to use the correct type of scenario .if wrong scenario is used then the analysis may lead to false results.

Using hazard analysis in Performance based design , The key fire scenarios are limiting state. They correspond to the most crucial and dangerous fires for which the building design is expected to meet the fire safety objectives.( (NFPA, 1998)

In order to use the appropriate scenarios the best is the experience .In order to identify conditions leading to wrong result, Records of past fires, either for the specific structures or for similar structures or class of occupancy can be used.

( Bukowski,1996C)

For more information See appendices A and B

3.5.3Select appropriate models/methods

The key to the decision of the appropriate model ,is taken through understanding of the assumption and limitation of this individual model or calculation and their relation to the situation being assessed.

The prediction of fire is very difficult due to its nature. The predictive method represents at best and estimates very important uncertainties. MQH upper layer temperature correlation and flashover correlation, are some of the examples which under the right circumstances are generally useful engineering tools for estimates.

Where public safety is at stake, it is appropriate to use models instead to rely solely on such estimation techniques for the calculation of development/smoke and filling calculations. Multiple compartment models are appropriate where the area of the interest involves more than one space, and mainly where they are more than one floor. (Bukowski,1995C)

On the one hand, where a single compartment exists, single compartment models are appropriate since there is not enough mixing between the layers in a room . On the other hand, where mechanical systems exist and/or doorways, multiple compartment models are appropriate.

However, for a single compartment model, limitation of burning by the available oxygen is very crucial, as well as, for multiple compartment models it is equally important for the model to track unburned fuel and allow it to burn when there is sufficient temperature and oxygen.

Heat transfer calculation takes up a lot of computer time, as a result, many models take a shortcut. The problem is that significant errors occur as a consequence of the shortcut. ( Bukowski,1996C)

The major source of gas expansion and energy and mass dilution is entrainment of ambient air into the fire flame. In very high flames, this entrainment is constraint, however, the majority of models do not include this. The consequences are very crucial for the correct estimation of egress time. Models CFAST (6) solve the above issue.

Input Data

it is inappropriate to rely solely on model. Most critical is the proper specification of the fire. Next in importance is specifying sources of air supply to the fire

(see section 3.3)

Wall materials and ceiling and heat transfer parameters are also important characteristics.

3.5.4Select design fire(s)

The purpose of the design

The purpose of the assumed loading in a structural analysis is very similar to the design fire. The purpose is to answer the question of whether the design will perform as intended under the assumed challenge. Keeping in mind that especially in a sprinklered building, the greatest challenge is not necessarily the largest fire. (Bukowski, March 15-16, 1995)

Figure (14) illustrates a design fire by giving a rate of heat release as a function of:

• The fire growth rate measured by the parameter to.


• The fire load density by the parameter qf


• The fire area by the parameter Afi


• The ventilation and fuel conditions

The fire area Afi in large spaces(e.g airport concourses and exhibition halls) can be easily calculated by the layout of the compostable. If not the area Afi is equivalent to the fire-compartment area Af.

Usually, When the temperatures are below 100°C at the first stage of the fire, is neglected in the design fires used for the evaluation of fire resistance because the can affect the structural elements. Therefore, temperatures more than 400°C are considered in the design fired used for the evaluation of fires because they can affect the structural elements.(Cramer and white,1996)

<<Flashover is the transition from the growth stage of a fire to the fully developed stage (full room involvement). It is widely accepted that flashover occurs when the temperature in the hot gas layer of a compartment reaches 500°C to 600°C or radiation from this layer reaches 20 kW/m2 to 25 kW/m2. After flashover, all pyrolysis gases cannot burn inside the compartment due to lack of oxygen, and flames appear through openings in the boundaries>> (CIB W014,2001)

For any item the fire growth (heat release) rate can be represented by an exponential curve. There are several experimental curves can be shown to be roughly proportional to time squared, where the curve is defined by the time needed for the heat release rate to reach a meticulous value. ( Bukowski,1994)

It is helpful to think of the design fires in terms of their growth phase, steady-burning phase, and decay phase.

For more information see appendix C

It is very obvious that, the selection of design fire is related to the determination of the scenarios of concern and to the selection of appropriate models and methods.

3.5.5Evacuation calculations

As it is explained similarly above the prediction of the needed by the building occupants to a safe area is performed next .whether the evacuation calculation is done by hand or by model calculation it must account for several crucial factor, . An excellent discussion of this factor is found in Pauls' (14) and Bryan's (15) chapters in the Society of fire Protection Engineers (SFPE) Handbook.

For more information see appendix C

(Bukowski,1995C)

3.5.6Account for uncertainty

This refers to dealing with the uncertainty which is inherent in any prediction. During the calculation procedure wrong input and models give uncertain output. In building design and codes the classic method of treating uncertainties in evacuation calculations is the use of safety factors( safety 2 is generally recommended in present codes). A sufficient safety factors is used in order to give safe result. In the prediction of fire development/filling time the worst scenarios is selected. Thus, a safety factor is needed only when assumption or data are used to which the predicted result is very sensitive. The analysis report should include a discussion of uncertainties. The sensitivity of the results to data and assumption made must be discussed.

For more information see appendix C

( Bukowski,1996C)

3.5.7Reality check

The reality check is the last step in any calculated analysis. If the result look logic (sense and experience) it is probably correct. Convulsively, If a model or calculation produces a result which is not logical there is probably something wrong. However , cases have been seen where it initially looked wrong but was not. A good example is that. The cold air from outdoor been drawn in an open door cause to drop temperature in a space adjacent to a room with a growing fire.

For more information see appendix C

(Bukowski,1995C)

3.5.8Obtaining help

For high profile project higher demand of confidence is demanded. The code official may need another independent opinion about the appropriateness of the analysis. Qualified engineering firms and universities can be appropriate advisers.

For more information see appendix C

(Bukowski, 1995C)

3.5.9Certification of methods

the majority of the code official will not be comfortable with making decisions about the appropriate of a model’s physics or some complex assumption(see also above). (Bukowski, 1995C)

4 .Ongoing Developments in Structural Fire Protection Design Methods

In the area of engineered structural fire protection, there are numerous ongoing efforts of organization in order to develop the required design method infrastructure. The National Fire Protection Association(NFPA), meanwhile, is developing a standard for fire loads for structural fire protection design. The Society of fire Protection Engineers(SFPE),meanwhile, have a committee which work on a standard in order to determine the design of fire exposure. Moreover SFPE is in the process of constituting a committee to develop a standard on the transfer of thermal/heat portion of the design process. These committees are coordinating their efforts in order to develop a set of documents that reinforce cooperatively support Performance Based Structural Fire Engineering. At the same time the American society of Civil Engineers(ASCE) have published their purpose to develop a structural document of the design process, As it is known the process of (ASCE Committee for Structural Design for Fire Conditions is charged with development of a Performance-Based Fire Design Standard) which has not yet materialized. It is very obvious that the use of current test methods is not appropriate in order to give the required date for the development of SFPE efforts on the heat-transfer portion and ASCE’s effort on the structural portion. In that vein, a guidance document for conducting non-standard furnace tests are being developed by a task group within ASTM E 05.11(fire resistance) . All these activities have European counterparts generally encompassed by the Eurocode suite of documents.

Means for integrating standardized fire resistance test results into the performance-based structural fire are needed to develop upon the various ongoing performance based related activities. (National institute of standards and technology,2007)

NOTE << Many current NFPA codes and standards are not strictly performance-based or prescriptive-based: technically, they can be referred to as prescriptive documents containing some performance provisions. For example, a requirement for a one-hour door sets a measurable performance criterion, going beyond prescription of the door's construction, but does not link the criterion explicitly to a fire safety goal>> (NFPA , 1997A)

5. Ongoing Development in structural Fire Protection around the world

Currently, most developed countries such as Australia, New Zealand, Scandinavia, UK, Japan, Canada and the USA started to focus on performance – based regulations, especially regarding fire safety codes. This mainly happens because the performance based regulations seem to provide a more comprehensible guidance than the prescriptive codes, concerning the growing complexity of the architectural designs, which create more fire risks (Tavares, 2008; Hadjisophocleous and Bénichou, 2000).

On the other hand, a number of developing countries seem to have some level of involvement with performance-based building codes. These are Belgium, Greece, Denmark, Norway, Finland, Spain, France, Italy, Poland, Netherlands and many more. Nevertheless, the establishment of performance-based regulations in their Building Codes is still at an embryonic stage.

(Tavares, 2008; Hadjisophocleous and Bénichou, 2000).

5.1 Three main categories

Taking into consideration the development and the implementation of performance-based codes, the countries could be divided in three categories. The three main categories derived could be: a) The countries that are supported from their government and have the economic resources and the technical knowledge to develop their national Building Code, b) The countries that have limited economic resources, neither the technical capacity. These countries seem to be willing to introduce performance-based building code, but gradually and in combination with the existing prescriptive codes, and c) The countries with the will to change their own Building Code to one that is performance-based. Nevertheless, changes in their building regulatory system will be done from existing work accomplishes by other countries that can be adopted with minor adaptations (PeBBu, 2005B).

The implementation strategies in the development and establishment of performance-based building and fire codes of four developed countries were chosen to be displayed in the current report. These countries are Australia, New Zealand, the USA and the United Kingdom and, among others, are the countries that have shown some significant progress towards the shift to performance-based regulations.

5.2Australia

Australia was the first country that began to work with performance-based fire codes in 1989. The Australians formed a non-profit organization called as the Fire Code Reform Centre Ltd (FCRC), in an attempt to help the Australian Building Codes Board (ABCB), which was established in 1994, to reform the Building Code of Australia. Their findings appear to be similar with the UK and New Zealand approach. Nevertheless, the purpose of the reform was to present a performance-based approach of alternative designs rather than replace the existing requirements (Bukowski, 1995A)

KPMG (as cited in Newhouse, 2001)) investigated whether ABCB and the reform have delivered benefits and value for money for the Australian government. For this purpose, 12 major projects which were constructed in Australia were used as case studies. As cited in Newhouse (2001), the benefits from reform the Building Code of Australia from ABCB were, among others, that the level of life safety was extended, new products and materials were more easy to be used and costs related to efficiency of design and construction were reduced. Moreover, reform has increased functionality for owners and end users, since designs met their requirements. Also, the reform has offered the ability to maintain heritage elements of building.

See some case studies of the report in Appendix D

In addition, Pebbu (2005B), reports that this reform succeeded in reducing costs, supporting skill attainment and encouraging innovation. However, the same report stated that regulatory reform is still incomplete. A number of changes that need to be done are suggested in Pebbu (2005B) and Newhouse (2001) as listed below:

• Further reduction of jurisdictional variations and the corrosion of the codes uniform application by local planning decisions.


• Re-evaluation of the approach to protect property from fire.


• A more clear and coherent explanation of performance based regulations.


• The enrichment of local government and enforcements.


• The addition of environmental requirements in the Code.


• More technical provisions which are closer to latest building technology.


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5.3 New Zealand

Likewise Australia, New Zealand is also in advanced stage of developing and implementing the performance- based regulations. Prescriptive codes were replaced from the performance- based codes since 1991. Actually, the Building Act 1991 introduced for the first time a national building code for New Zealand, a Code which became mandatory in 1993. The Act was partially modified by the Building Act 2004, known as the New Zealand Building Code. The major changes occurred in fire engineering, where any detailed limitations, such as the maximum number of floors for timber buildings, from previous codes were removed (Buchanan et al., 2006).

The New Zealand Building Code regulations can be demonstrated by the use of any one of the three following methods:

• Verification Model – a method with specified calculations.


• Acceptable Solution- prescriptive requirements that satisfied the Building Code regulations. It is mainly used for the design of building for fire safety.


• Alternative Solution- a solution for special designs (Buchanan et al, 2006).


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The establishment of New Zealand Building Code 1991 offered freedom and innovation in design the use of contemporary construction systems. However, because of this freedom, some problems made their appearance, such as different levels of enforcement across the country and poor workmanship (Buchanan et al.,2006). In addition, New Zealand Building Code provides that the protection of property at the regulated occupancy is not an issue of the Code but it is an issue between the owner and the insurance company. Nevertheless, insurance companies seemed to be rather upset with this regulation and tried to enforce their own requirements along with the Code regulation (Bukowski,1995A).

For the above reasons, the New Zealand Building Code 2004 tried to eliminate the freedom from innovative design regarding finished product and shift the focus to the process, proof and the details of a structure (Buchanan et al., 2006). What is more, The Building Act 2004 stated some further requirements for New Zealand Building Code. Its main principle, among others, is to focus on the needs of consumers, who are the occupiers of housing, and ensure that a building will maintain the durability and its standards throughout its life (Department of Building and Housing, New Zealand, 2007).

5.4United Kingdom

UK’s building regulatory system was prescriptive until 1985. In 1985, the government published new regulations, in an attempt to increase the flexibility in design and create a more intelligent system. Some years after, in 1994, 15 new fire safety engineering principles regarding the design of fire safety in building were published (Hadjisophocleous and Bénichou, 2000). The current building regulatory system is based on 15 performance-based “approved documents”. However, these “deemed to satisfy” solutions are still more prescriptive than performance-based (PeBBu, 2005).

5.5United Stated of America

USA started to shift from prescriptive code regulations to performance-based codes in the early 1970’s. USA building codes were introduced from three private organizations, which altogether formed the International Code Council, in order to develop the International Building Code (IBC). Although initially the IBC appeared to be a prescriptive building code, a set of tasks and performance-based requirements are included. Also, a fire risk assessment method and a performance-based fire safety guide have been ongoing in USA,in an effort to develop a performance-based analysis and design in buildings (Hadjisophocleous and Bénichou, 2000).

USA has mainly contributed to the international research for the fire safety of buildings, especially through their research centers and universities. Among others, the NFPA (National Fire Protection Association), the SFPE (Society of Fire Protection Engineers) and the NIST (National Institute of Standards and Technology) offered essential outcomes for the fire safety standards (Tavares, 2008). More specifically, the SFPE has organized a number of Engineering Seminars on performance-based design and on performance-based Fire Safety Engineering (Bukowski,1995A)

However, the USA still have some problems regarding the successful implementation of performance-based codes. Particularly, among others, the establishment of fire safety codes is the responsibility of public and private organizations and differs from state to state (Tavares, 2008; Hadjisophocleous and Bénichou, 2000). In addition, the USA do not have a wide government support for the fire safety in buildings. That is why USA, despite the fact that is a developed country, still lacks I the development and implementation of the performance-based regulations, although fires are a significant problem in the USA (Tavares, 2008).

5.6 Summary of chapter five and some extra comments

As it can be concluded from PeBBu report (2005B), performance based building regulations have a wide support globally. Most of the countries seem to mix prescriptive codes with performance based requirements according to their needs and understanding. Moreover, the majority of the countries agree that an international cooperation would be beneficial, although they do not agree with the idea of an international performance based building code.

Regarding the effective change of a building regulatory system, PeBBu (2005B) assumes that, in order for a building code to work effectively, key stakeholders need to be supportive. Otherwise, any resistance in the process would end any attempt of establishing performance based building regulations.

6.A Survey of code officials on performance based codes and risk assessment

A Survey was administered in 1995 at the annual conferences of Building Officials and code administrations. The questionnaires were distributed at the life and fire safety code development hearing for all the groups

The survey was structured to estimate the status of the performance based codes and risk analysis.

The key outputs from the survey were:

• There was strong agreement on the necessity of both performance and prescriptive codes


• Building and fire official regarding the role of risk base analysis at that time, were not comfortable specifying a number of acceptable life.


• The use of fire prediction computer models at that time was very limited. A main reason was, the lack of awareness of the availability or adequacy of computer models at that time.(Charles and Rickley,1996)


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(for more information see appendix E)

On the one hand, someone can be argue that for the above survey it has to be considered that it was 15 years ago. When the people were not that much aware about Performance based design and computer models. On the other hand, according (PeBBu,2005B) design professionals (architects and engineers) are generally not very aware of Performance based design .

7.Advandages and disadvantages of Performance based design

Table (3): BARRR I E R S AND INCENT IVES FOR PERFORMANCE BASED DESIG. Retrieved from (PeBBu,2005A,p.51)

8.It is not all one or the other

The use o prescriptive specifications do not exclude the use of Performance based design. Similarly, the use of Performance based approach does not reject the use of prescriptive specifications. The experience is not yet enough with the performance approach in building. Consequently, solely the use of Performance based document at each step of the design is not efficient .On the one hand, prescriptive specifications will possibly still be used when they offer more effective, efficient, faster and more economical constructions. In many situations they continue to be useful. On the other hand, prescriptive documents are based on the experience of what has been done in the past. It can be argued that prescriptive documents are essentially expressions of the performance embedded in the chosen solution, as well as of the knowledge and the experience of their users. That is the negative side of any prescriptive document. Some effective solutions are their regular update and the consideration of feedback from the field in order to avoid the risk of codifying mistakes or misunderstandings by freezing solutions. Furthermore, they have to take into account the real client’s needs and benefits. Blending Performance and prescriptive approach often has the best of both approaches (Szigeti and Davis, 2005).

9.Perfomance based engineering/other areas and methods

• Performance based seismic design


• Performance based blast design


• Performance based Ship impact design


• Performance based Corrosion design


• Performance based Fatigue design


• Performance based Extreme vehicular loading in bridge engineering design


• Performance Based robustness design


• Other methods

Probabilistic risk Assessment

10.Discussion

The role of the Building Codes establish minimum acceptable standards for new buildings and building work, without preventing higher standards. The standards for buildings that are set in building codes balance quality, cost, affordability and accessibility. Building codes cannot eliminate risk. They are set to provide basic protection for the people who use buildings .

Building codes may be classified as prescriptive codes or performance based. In Prescriptive codes obtain their names from the fact that they prescribe specifically what to do in a given case. Performance codes express the desired objective to be accomplished and allow the designer to use any acceptable approach to achieve the required results.

The Prescriptive approach to civil engineering facilitated the design and evaluation practice, because of its rationale and heuristic knowledge b. From a design point prescriptive approach is easier to be used than performance-based approach. Moreover, prescriptive codes have the advantage in that they enable a straightforward evaluation of determining whether or not the established requirement has been met. Furthermore it includes many factors of safety to account for unknown in both the loading and resistance and to account for simplifications in the analytical techniques. On the other hand in traditional prescriptive design objectives are usually implicitly.

Many countries are in the process of introducing performance based building regulations because the main advantage of performance based design isthe explicit statement of goals and objectives that reflect societal expectations and desires, along with functional statements, operative requirements and in some cases

Performance criteria, which are to be used for demonstrating that goals and objectives have been met . Moreover in some cases, dramatic changes to the existing regulations are needed in respond to the stakeholder’s concerns, while in others there is a belief that one has to regulate.

There are many definition of performance based design but he best is :The Performance Approach is the practice of thinking and working in terms of ends rather than means. It is concerned with what a building or a building product is required to do, and not with prescribing how it is to be constructed.

Furthermore the two main characteristics of the performance concept are:

• The use of two languages, one for the demand for the performance and the other for the supply of the performance.


• The need for validation and verification of results against performance targets


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As it can be seen from section 2.2 and 2.3 the ‘performance language’ can be used as an intermediate between functional needs and requirements and then as intermediate between requirement and between technical solutions. Analyzing the subject further, on the demand site ‘performance language’ translates functional needs into performance requirements.

Fire safety is one of the two civil engineering areas in which performance based design is becoming accepted. In both , a client can demand a certain performance objective and expect to get it.

The two main components of fire safety requirements are:

• General building fire safety. That is achieved with an insulation of the structure due to a proper compartmentation of the building.


• Structure/structural members stability. That it can be achieved with a proper fire resistance of the structural members.


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The prescriptive Codes and standards prescribe fire resistance and safety for general use and application and typically these documents do not achieve fire safety objectives because: Fire resistance and protection are achieved by specifying the main and important construction characteristics. Moreover, by limiting dimensions and adding protection systems. However, they do not provide mechanisms how these requirements cannot achieve a desired fire safety.

It is obvious from section 3.3 is that the tests of fire resistance from Prescriptive codes give uncertain outputs

As it can be seen in section 3.4 the use of risk assessment as the method to determine acceptable solutions is possible .The estimation of the consequences of the event has been the main effort or risk assessment But the quantification of risk depends on the ability to describe detailed scenarios and their likelihood of occurrence (severity of events: disastrous, extreme, serious, significant, minor, negligible). Moreover according section 3.5 and 6 risk assessment is very complicated because it needs a huge amount of historical data which is very difficult to select. Moreover the building and fire official regarding the role of risk base analysis are not comfortable with some aspect of risk assessment. That is why, fire hazard assessments is the main method that is used by designers for evaluating performance. Fire Hazard assessments measure performance, in a specific set of conditions presume to represent the most significant dangers. Because experience has proved that the most dangerous fires occur as a result of many things going wrongly at the same time.It is useful to have in mind of situations which are characterized by multiple failures in providing safety of the public.

As It can be seen from section 6 the use of fire prediction computer models is very limited. A main reason is the lack of awareness of the availability or adequacy of prediction computer models . According section 3.5 Better knowledge of structural fire performance and the development of better computation tools of fire endurance are demanded in order to emerge performance-based codes.

According section 4 In the area of engineered structural fire protection, there are numerous ongoing efforts of organization in order to develop the required design method infrastructure. Moreover according Currently, most developed countries such as Australia, New Zealand, Scandinavia, UK, Japan, Canada and the USA started to focus on performance – based regulations, especially regarding fire safety codes .Furthermore as it can be seen from section 5.6 and 4 performance based building regulations have a wide support globally. Most of the countries seem to mix prescriptive codes with performance based requirements according to their needs and understanding. Moreover, the majority of the countries agree that an international cooperation would be beneficial, although they do not agree with the idea of an international performance based building code.

Performance base design and prescriptive design have many advantages and disadvantages. . Blending Performance and prescriptive approach often has the best of both approaches.

11.Conclusion

Performance based design place responsibility and accountability back into the designer’s hands. Moreover in order for a building code to work effectively, key stakeholders need to be supportive. Otherwise, any resistance in the process would end any attempt of establishing performance based building regulations.