Tall Buildings

The aspiration to construct tall buildings is not something new. They have always been used to demonstrate control and wealth. In the world of tall buildings, the design and construction and life safety are the most important aspects of offering a fictional building. The life safety of the occupant of buildings is very essential as today most tenants are worried more and more about how safe the building is? Issues such as unplanned fire, earthquakes, floods and terrorist attacks are major concerns. Such disasters have proved to cost millions of economic, financial and human loss.

These disasters tend to have enormous effect on the construction industry; and professionals such as architects, fire engineers, structural engineers, insurers and emergency workers from all over the world were called to discuss the issue and find solutions. Their have been several procedures derived in order to attain security against fire It is not possible to attain the required level of safety by following one procedure. Thus several procedures if performed together prove to be helpful in attaining certain results against fire.

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Most of the fascinating tall buildings and there integrated systems that have reached a level of safety during several events such as the world trade centre1 and 2, the emirates tower in Dubai and many others. “Understanding the role, limitations and interface between systems is fundamental to system selection. Complementing to systems side of building design is the operating feature or human interface that supplements these sophisticated systems” (Craighead, 2003). To sustain the level of safety and quality it is necessary that security systems are designed with exceptional attention at the time when the design of the building is designed.

Then there is the maintenance to keep fire security up to date and in working conditions these systems are to be checked and tested from time to time on regular basis. This paper will offer a review and description of all of these aspects linked to high rise buildings. This study has been researched and developed in order to find requirements concerning fire safety in tall buildings, along with determining the relation between good designs and improving safety of tall buildings and occupants.

Aims and Objectives

Aims:

The aim of this paper is to provide an understanding of how a better informed design of tall buildings can address fire safety requirements. In particular, it seeks to identify how fire can affect the safety of a tall building and its occupants, It also examine the existing and emerging design solutions and legislation to address the problems and threats of fire safety in tall buildings. According to The New Civil Engineer, “The WTC disaster has caused us all to think hard about the best actions to take to make tall buildings safer,” (Forest and Wainwright 2002).

To improve the overall safety of tall buildings, this research will view a specific aspect of fire emergency in more depth. This aspect is related with the comparison of using stairs and elevators in case of an emergency.

Objectives:

The main objectives or topics of this paper that I have evaluated briefly and thoroughly as per requirement are as following:

1. Introduce fire behaviour in tall buildings and how it spreads.

2. Outline the consequences for human lives and physical resources.

3. Discuss how poor design of tall buildings has caused fire.

4. Examine how good design like a balanced approach in using stairs and elevators with respect to the number of floors is useful in minimizing losses during fires.

5. Synthesise the main points and outline the recommendations for the design of tall buildings.

Hence after evaluating and analysing the sub topics mentioned above in an organized manner it can be expected that we would achieve the desired aims. To thoroughly evaluate the every objective we need to conduct proper research and use appropriate methods to achieve the desired results.

Research Methodology

A number of sources have been used to compile this paper. The lists of references are outlined at the end of this paper. In main approaches were selected for this study, which includes:

1) Collection of secondary data about history, evolution, development of the design and safety issues in tall buildings and identify how they relate to each other. This included the analysis of books, journals, internet sources and other relevant publications. In addition, codes, standards and regulations which have impacted on fire safety in buildings were also reviewed.

2) Analysis of a case study illustrating examples of high rise buildings relating to their success and failure during a fire. This also entailed the examination of design solutions to fire safety.

Chapter #2: Literature Review

This chapter focuses on the analysis of existing literature on the good designs in relation to tall building. The chapter even revolves around fire behaviour and means of escape in case of fire from tall buildings. This chapter begins with the importance of tall buildings and what kind of threats pose these magnificent structure, the chapter moves on further with the concepts of good and bad design.

At the end of the chapter some legislations and laws are discussed. Tall Buildings Defining a building as being tall and magnificent can be done through the number of floors it has by general people. Then there are terms used that include ‘skyscraper’ and ‘high rise’ these terms are generally used to describe tall building therefore I researched to understand these terms and found meanings that were equally vague:

• “Very tall modern building, usually in a city” (Cambridge International Dictionary of English, 2003).
• “A very tall building with many storeys” (Word Net, 2003).
• “A tall modern building with a lot of floors” (Cambridge International Dictionary of English, 2003).
• After focusing on dictionaries I spend some time researching from books, Skyscrapers have fascinated mankind since the start of civilization.

It is not possible to define them by using specific terms linked just to the height or to the number of floors. “The height of a building is a matter of a person’s or community’s circumstance and their consequent perception” as Stafford-Smith said. Therefore, no definition of tall building can be generally applied.

However, the structural engineers define a tall building “as one that, because of its height, is affected by lateral forces due to wind or earthquake to the extent that the forces play an important role in their structural design” as Stafford-Smith said. (Tall Building Structures: Analysis and Design) Advantages of Tall Buildings Tall buildings are designed to supply the requirements of an intended occupancy such as residential, commercial or both together. They are not the only way to attain high density but they can in situations such as small areas of a city where land is limited.

Moreover, tall buildings are usually situated or placed near the public transport nodes which reduce the necessity for car use. many people agree that they are advantageous . They can as well take part in a positive part in the design of the city centre by marking places of public, commercial or cultural importance. Also, Refurbishing and reusing the actual unoccupied space can allow the positive flow-on effects of regeneration to be spread more all over the city centre, and as long as they are well designed and located, they can be a positive way to develop in urban areas. (Construction Technology for Tall Buildings)

In the early stages of planning a building, the whole design team has to agree on one form of structure to satisfy all the requirements considering the safety and fictional matters. Thus buildings not only help in developments and give accommodation to a huge number of people it gives employment opportunities during the construction of the building. (Tall Building Structures: Analysis and Design) Disadvantages of Tall Buildings With advantages tall buildings have many disadvantages, the disadvantages include the existence of too many occupied floors on top of each other means a big concentration of occupants, personal and business property.

Which result in a huge possible fuel weight of the building? The disadvantages that it has to face in case of accidental fire is the likelihood of a great uncontrolled fire rising presents danger in tall buildings as it is a vertical structure. There will be delays in reaching the area to provide assistance for example if there will be a fire in the upper floor of the tall building it will be difficult to reach that floor and provide help.

In a case of fire, it is difficult for all the occupants to leave the building by using lifts, staircases and emergency exits at once. The access of the fire department can be limited from both outside and inside the building. High rise buildings have natural forces that affect on the fire and smoke movements such as wind which increase the stack effect due to the height of the building, this stack effect can move a large amount of uncontrolled heat or smoke through the building.

Problems Faced By Buildings under Fire

The construction of tall buildings is much more important than before, as design safety is becoming paramount to avoid the unacceptable loss of lives and the collapse of buildings. Therefore, the construction of tall buildings needs a better approach, combining better design and technological solutions. These solutions should be designed to avoid the collapse of tall buildings, when the supports for one floor of the building fail, causing the failure of the lower floors.

To address this issue, recent studies suggest that tall buildings should include a ‘collapse’ floor every 10 storeys, this floor will be able to carry the weight of the floors on top. Modern buildings are at risk to fire because of the steel structural material that looses half its strength at 6000C, which can be easily reached when a building burns. To prevent this, we need to design strong and non-brittle buildings in order to absorb the shock without fracturing the structure of the building. . (Construction Technology for Tall Buildings)

Design Plan and Safety Precautions for Fire Safety

There are many fire life safety systems and equipments that can be used in order to make sure that the building is safe to use and that occupants can be evacuated safely and quickly, and that the right measures are taking at the right time. In order to understand what is required for a typical high rise building it is advised to review the laws, codes and regulations. The construction of skyscrapers necessitates more detailed planning to prevent errors from occurring in the lifecycle of it.

Since September 11th 2001 in New York, design teams are more conscious about the health and safety of the community. Buildings are growing taller to supply the demand for more space. It is evident that stairs provided in tall buildings as a means of escape are not sufficient. Consequently, there is a need for alternative means of escape from tall buildings in case of a fire. Architects and engineers must provide better solutions when designing tall buildings, as recent event such as 9/11 revealed that existing safety measures are inadequate.

For instance, major consideration should be given to how long it takes to get everyone out of a building on case of a fire, taking in consideration that the public cannot, in general, use lifts. . (Construction Technology for Tall Buildings) The planning of tall buildings is an essential procedure, particularly where the environment has old historic buildings. The process become so difficult in this case, and its not just to do with height, it is more to do with the difficulty of integration between the two different types.

Consequently, it is important to ensure that the building will have a nice effect on the environment and produce a relaxing surrounding. (Tall Building Structures: Analysis and Design) Tall buildings are difficult to build, not just for the safety issues, but also the required services such as elevators, plumbing, wiring, stairs, air-conditioning ducts. In addition to greater beams and columns, buildings require more elevators than short buildings. So, the construction of tall buildings makes business sense but necessitates huge architectural and engineering efforts.

(Tall Building Structures: Analysis and Design) The design and construction of future high-rise towers requires wide knowledge of good architectural principles; strong floor plates; Complex structural life-safety and building systems that have to be followed correctly. Key to this is through a well planned and better informed design process. According to the Triz journal Toru Nakagawa Staircases must be designed and built not just to be suitable, comfortable, and securely guarded for daily use, but also secure as emergency escaping ways in situations such as fire.

They should be designed in a way to prevent the chimney effects as well as flame, smoke, and toxic gases when fire occurs. Moreover, the staircase should be a kind of 'Internal Staircase' and of a 'Separated' type of 'Internal Staircase’; to avoid the rising of fire and to keep it as an escaping. In addition, the windows of the staircase should be opened widely in case of fire; these windows can be used as the entrance for rescuing activities. These windows should open remotely at the control centre of the tall building.

According to the Ingenta connect by J. Y. Richard Liew “Design codes for fire safety in buildings can be either a prescriptive type or performance-based type. It is recognized that performance-based codes provide greater advantages over the prescriptive codes which allow designers to use the fire engineering methods to assess the fire safety of the structure. However, as the assessment of the whole structure performance is not easy, most codes currently used are still prescriptive codes or a combination of prescriptive codes and performance-based codes.

The key feature for implementing the performance-based fire design codes is the assessment of the fire resistance of the structure”. (Liew, 2004) According to Will Pank, Maunsell Ltd Herbert Girardet, Urban Futures Greg Cox, Oscar Faber Ltd in practice, The Corporation of London,” Individual tall buildings are analysed in relation to their design to develop a rationale for fire engineering. The proposed fire solutions or requirements of the intent of the regulations. The main consideration is:

• The adequacy of means to prevent fire.
• Early fire warning by an automatic detection and warning system.
• The standard of means of escape.
• Provision of smoke control.
• Control of the rate of growth of a fire.
• The adequacy of the structure to resist the effects of a fire.
• The degree of fire containment.
• Fire separation between buildings or parts of buildings.
• The standard of active measures for fire extinguishment or control.
• Facilities to assist the fire service.
• Availability of powers to require staff training in fire safety and fire routines such as registration or licensing procedures.

Evacuation Process

When the raising of a fire alarm is occurred, the main entrance should receive the elevators according to the European evacuation plans. During an emergency, only stairs should be allowed for the evacuation purpose. Furthermore, the stairs may not be an efficient way of evacuation, especially for elderly and disabled persons. In this regard, three phases can be created from the time of an emergency until an area of safety is reached by all the people. In this regard, recognition time, reaction time, and egress time are the abovementioned three phases of an emergency.

When the building has not been egress by the people, the time has been referred as the pre-movement time. The signs of danger influence the length of this period. In addition, type of the building, as well as, alarms are some other factors that influence the pre-movement time of an emergency. For instance, long pre-movement time might be observed during the night time in an apartment building. Three times longer, as compared with the actual movement time has been considered for the determination of pre-movement time according to a number of studies.

After the recognition time, awareness of the emergency is attained by the occupants. Before the giving of fire alarms, one of the most critical parts of the emergency has been considered the recognition time. Information about the situation, as well as, source of the emergency is required by the people during the reaction time. The reaction time is often affected by the training for emergencies. Until the area of safety has not been reached by everyone, people move out of the building during the actual movement phase of an emergency.

Determination of the egress time has been concentrated by the evacuation studies due to the availability of its theoretical estimates. In this regard, figure 2 has illustrated the building filling, as well as, evacuation times with relation to the different up-peak handling capacities. For instance, thirty-three minutes was the building filling time, as the up-peak handling capacity was fifteen percent. At this stage, nineteen to twenty-two minutes was the average egress time. (Siikonen and Hakonen, 2003)

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