Friday 15 August 2014

ASSESSMENT OF BLAST LOADING

ASSESSMENT OF BLAST LOADING (due to vibration from bomb explosion) ON BRIDGES
Aim of the Study
Ø  Analyze the structures under the effects of blast loading.
Ø  Including; the threat definition, blast wave parameters, dynamic properties of materials and damage assessment.
Definition of Blast Loading
Ø  Blast loading may result from the detonation of high Explosives, chemical ammunitions.
Ø  Type of extraordinary dynamic load and it has to be described by two parameters; peak overpressure and duration.
Ø   Blast loading is a function of: Distance of the structure from the explosion, and the charge weight or a weapon size.

Bomb explosion create a loading effect on the bridges, bridges are made up of element such as columns or piers, slab and beams, each of this element undergo stresses that need to be assessed to prevent a future failure of structures.
Columns can be under a pure compression, if all load are transferred axially along it centred, but loads affecting a column can be along x-x axis or y-y or even both, columns can be bi-axially loaded, uni-axially loaded and axially loaded, which ever form of loading, there are instance of the unexpected loading that occur during the structural life span, at preliminary design stage, bending reinforcement is provided and checks are done, such as deflection. shear and crack are checked for to ensure that the building material meet the design permissible limit. area of steel bars required are calculated with respect to the expected loading but live and dead load, but impact load (loading due to bombs) are usually not inclusive in preliminary design stage, so it is imperative that impact assessment is carried out on columns to prevent axial failure.
Basic checks in column include, the following the designer needs to check present degree of plumb deviation from the initial design specification before the explosion, and the displacement due to differential or tilt settlement must be checked if it is still within a permissible limit. If there is need for replacement of columns, racking or flying shore can be used to make alterations or replacement, for the foundation jack piles can be used to replace pile foundation if the piers used as foundation have failed axially.
Slabs are under the influence of bending stresses this stress can cause hogging or sagging, the excessive stresses caused by the bomb can cause any of the above defect mentioned above, assessing the bridge will require checks that include levels and degree of tilt from level, need to ask what is the required slope base on design prescription, if there is any case of sag, beams can be introduced at the point where bending is at the peak, the point of inflection should be checked also to ensure that bending is kept zero, the depth of slab can also be increase to with stand the instantaneous effect of the bomb blast, as far as there is no total failure of structure the tensile strength of steel is still within the permissible limit.
Beams transfer loads from slab to the columns, they are  constantly under the influence of shear and bending stresses, the beam must be checked for if there is any form of deflection and this is done by making sure that the depth of beams can still withstand the present stresses, check for cracks to ensure that the spacing of reinforcement can still prevent cracks due to the present blast loading(explosive),
Threat Definition
·         Charge Weight or weapon size (W): W is expressed in weight or mass of TNT; the equivalent W of any other explosive material is based on experimentally determined factors or the ratio of its heat of detonation to that of TNT.
·         Stand-off Distances (R): R measures how close to the building a bomb could explode and is therefore a function of the physical characteristics of the surrounding site.


Thursday 7 August 2014

PROBLEMS OF URBANIZATION IN CONTEMPORARY NIGERIA

PROBLEMS OF URBANIZATION IN CONTEMPORARY NIGERIA
Viewed Through Reflections on the Standards of the livable City.
1. INTRODUCTION.
Nigeria is the country with the largest population on the continent of Africa; by 2004 estimates, she has a current population of 137,253,130. Nigeria’s population growth rate of 2.45 significantly exceeds the continental average population growth rate for Africa that is estimated at 2.02 ,Newman et al, (2005), and additionally, the projected population figures are 206,397,510 and 307,420,055 for the years 2025 and 2050 respectively; about 50 percent of the national population is presently located in cities, Microsoft Encarta Reference Library, (2005)a, Stock, (2005). All these add up to the fact that, like many other nations of the Third World, Nigeria is poised to face very dramatic dimensions of population growth and equally dramatic manifestations of the process of urbanization; as already evidenced throughout the second half of the 20th century. Thus, issues of urbanization and a well ordered urbanization process deserve to be considered as the most topical and also the most urgent national issues at policy level in Nigeria of today. As issues of urbanization emerge as top priority national issues in Nigeria and the Third World, the need to adequately prepare the architect to face the ensuing challenges also emerges; the need thus emerges to elevate human settlement studies (and research) and also urban design studies (and research) to higher priority levels in the architectural education curricula of universities and polytechnics in Nigeria, in particular, and the Third World, in general.
Urbanization is, essentially, the shift of populations from rural areas to cities and the concomitant phenomenon of the growth of cities. In this paper the subject of urbanization is discussed, in general, and also with specific reflections on the prevailing situations in Nigeria. The conceptual framework adopted is the livable city, the theme of the Third World Urban Forum, WUF3, just concluded in Vancouver City, Canada, in June 2006. The goal of urbanization has been established; it needs not be at the expense of the “quality of life”. Thus, the premise of this paper is to address urbanization as an inevitable and also desirable process in Nigeria’s national development process in the 21st century. According to citiesPLUS (2003), cited in Timmer and Seymoar, (2005), the principle of equity in city development demands a fair allocation of scarce resources among all competing users and also the responsibility for the cost of pollution must be borne by the beneficiaries.
Thus, the premise of this paper is to address urbanization as an inevitable and also desirable process (and also a possible asset) in Nigeria’s national development process in the 21st century; Another very important aspect of the urbanization is that it must be controlled in order to preserve a sustainable environment for the present and future generations, and also to address (in policies that are proactive) the interests of the currently marginalized city dwellers. However, if uncontrolled, rapid urbanization could develop into one of the major threats of the millennium; according to the records of UN-Habitat from the 2nd World Urban Forum – WUF2, Barcelona, (2004):
Ø  “The Second World Urban Forum opened in Barcelona on Monday with warnings from world leaders and mayors that rapid urbanization was one of the greatest challenges facing humanity in the new Millennium.  Speaker after speaker at the opening plenary called for more backing for local authorities from the United Nations system and governments. They called for a renewed drive for decentralization. And all expressed concern that millions of people in cities around the world still lacked access to safe water and sanitation, health care, education, shelter, security of tenure.”                                  
2. Urbanization.
2.1 The Rise of Urban Culture. Two groups of fundamental changes, which have resulted in very dramatic alterations in the general ways of life and the means of existence of mankind, have occurred in the course of the history of mankind, they have both universally been described as revolutions. The first occurred in the latter part of the Stone Age; anthropologists call it the Neolithic Revolution. The Stone Age is dated in human history as beginning about 2.5 million years ago, and beginning to come to an end in some parts of the world about 5000 years ago. The Neolithic period of the Stone Age is dated as having begun about 9000 years ago in some parts of the world and spanning to the beginning of the Bronze Age about 5000 years ago. In the course of the Neolithic Revolution, man evolved out of the primitive existence of hunting animals and gathering food in the wilds of the forest and established more complex communities in permanent settlements, based on the domestication of animals and formal agriculture. In the end, the Neolithic Revolution eventually led to the establishment of small urban communities and the beginning of urban civilization; one of the earliest known of the human settlements of the Neolithic period is Jericho Schick and Toth, (2005). The Industrial Revolution, which began in Britain in the 18th century, led to a widespread shift from manual labour to machines as the means of production, Porter, (2005). In consequence it also led to a shift from agricultural economies to (urban based) industrial economies; resulting in massive shifts of human populations from rural areas to urban areas and the rapid growth of cities in sizes and numbers to accommodate the ever increasing numbers of city dwellers – a phenomenon that is known as urbanization. It is significant to observe here that these revolutions had intricate relationships and/or impacts on human settlements and urban culture; underscoring the inevitable and inalienable relationships between all affairs of human development and shelter.

2.2 The Intensification of Urbanization Culture. The Industrial Revolution dramatically changed the orders of human societies in Europe and America, resulting in massive influxes of people into existing cities and, at the same time, leading to the emergence of new cities, out of previously rural areas. Another factor that created similar effect of urbanization is the liberation of nations (developing nations) from the yoke of colonization.
All these have resulted in the intensification of urbanization in various parts of the world, raising significant global concerns towards the end of the 20th century. Within the 20th century, humanity experienced the intensification of urbanization in a dimension that surpassed the combination of all the previous experiences (in urban development) of all the several centuries before it. At the advent of the 20th century, 15 percent of the world’s population (of 1.5 billion people) lived in cities; by the close of the century 50 percent of the world’s population (of 6 billion people) had taken up residence in cities. Furthermore, while in 1800, London was the only city with a population of over 1 million people, by 1990, the 100 largest cities of the world accommodated 540 million people and 20 megacities (of population over 10 million people each) accommodated 220 million people, Deelstra and Girardet, (2005). According to Deelstra and Girardet, by the close of the 20th century, mankind was already transforming into “an urban species”. Also, according to UN-Habitat, urbanization intensified more dramatically within the second half of the 20th century: beginning from 30 percent of humanity being resident in cities, the century came to a close with the figure 50 percent, World Urban Forum – WUF II, (2004). In the course of these 50 years also, there was a significant shift in the theatres where the scenarios of the intensification of urbanization were playing out. According to Einsele (1995), while in 1950, two out of ten largest cities of the world were located in the Third World, by the close of the century, eight out ten of the largest cities of the world were being located in the Third World. Within this period also, Lagos in Nigeria, had emerged as one of the largest cities (one of front-line megacities) of the world; placing urbanization as one of the most urgent national issues for Nigeria in the 21st century. In the course of these challenges, cities are constantly faced with the risk of losing their classical definition as “safe havens and cases of comfort for the inhabitants” ,Cunningham and Saigo (1992). This danger has informed the United Nations Organization, to address urbanization as one of the most significant challenges facing humanity in the 21st century. At the 2001 General Assembly of the United Nations Organization (Istanbul+5) that deliberated on the Habitat Agenda of the world for the 21st century, urbanization was identified as one of the greatest challenges facing humanity, in general, today:
Ø  “…Wish to stress that this is a special moment in the development of human settlements, when half of the world's six billion people will be living in cities and the world is facing unprecedented growth of urban population, mainly in the developing world ………”

2.3 The Challenge of Urbanization in the Third World. With more megacities emerging in the Third World than the rest of the world by the close of the 20th century, the global urban challenge appears to be focused on the Third World; Eimsele (1995)
Today, Lagos, in Nigeria, with an estimated population of 13,427,000 (2000 estimate), is the largest city in Africa, and has already surpassed the population of India’s largest city, Calcutta, estimated at 13,216,546 (2001 estimate), (Microsoft Encarta Reference Library (2005)b). Already, by the beginning of the 21st century, more than fifty percent of the world’s population is located in cities. Consequently, the city has become the arena where human destiny (and by implication, the destinies of nations) and where the future of the biosphere will be determined in the 21st century, Deelstra and Girardet (2005).
The major challenges of these third world cities are in the areas of providing livelihood for the ordinary people and making the cities ecologically sustainable. Reliance by cities, on the hinterlands, for daily supply of foods will not be a viable perspective as the hinterlands are also rapidly turning into cities. Furthermore, the issues of waste disposal, which are being taken for granted in the most Nigerian cities of today, will pose serious ecological problems if not promptly checked. In virtually every international forum where questions or issues of human settlements are discussed, the principal focus is placed on Third World cites, and always the major concerns are environmental degradation and urban poverty. Presently it is estimated that about thirty percent of the developing world’s urban population lives below official poverty line, The Cities Alliance (2005)

2.4 Tragic Consequences of Default. Since the 20th century, urbanization has been proceeding with a very high impetus in the Third World, demanding timely responses and appropriate control; in the absence of appropriate and timely responses and controls rapid urbanization could result in environmental degradation and/or urban poverty, as a result of default. Although these scenarios have become familiar with the rapid urbanization processes of the second half of the 20th century (particularly in the Third World), studies have confirmed that they are indeed, symptoms of gross deficiencies in the mechanisms of control of urbanization. According to Evans (2002), cited in Timmer and Seymoar, (2005), livelihood and ecological sustainability constitute two faces to the same coin; and livelihood comprises the “jobs close enough to decent housing with wages commensurate with rents, and access to services that make for a healthful habitat”; thus livelihood must be sustainable and should therefore not be permitted to result in environmental degradation: “To be livable, a city must put both sides of the coin together, providing livelihoods for its citizens, ordinary as well as affluent, in ways that preserve the quality of the environment” Evans (2002). Unfortunately, where urbanization is now proceeding at the fastest rate ever in human history (the Third World), the mechanisms for proper control of urbanization have been weak and inefficient; uncontrolled urbanization has resulted in gross distortions, like slums, where the dreams and talents of useful and decent citizens (who have enormous potentials for building up the city and the nation) are buried, because they lack access to the basic necessities of life or to the requisite “quality of life”. In the Background Paper to the Third World Urban Forum – WUF3, Vancouver (2006), the looming tragedy associated with uncontrolled urbanization is summarized with the following words:
Ø  “….The world’s urban population is likely to reach 4.2 billion by 2020, and if no serious action is taken, the urban slum population is expected to increase to 1.4 billion in 2020…….
Can we accept this projected state of the world whereby, in just 14 years, one out of every three people living in cities will live in impoverished, overcrowded and insecure living conditions?”                  

The issues of environmental degradation and urban poverty constitute the real challenges that are threatening to turn urbanization into a crisis in the 21st century: the key issue is the enablement of appropriate mechanisms for the control of urbanization and city development, in order to enhance and also sustain the “quality of life” of the citizens, in general. Thus, the central theme of the twin concepts of the livable city and the sustainable city is the “quality of life” of the “citizens, ordinary as well as affluent, in ways that preserve the quality of the environment” for the enhancement of the general economic advancements of nations. The measures of success, so far attained in some cities and urban regions of the developed nations, confirm that these goals do not exist in utopia; they are feasible and attainable; according to UN-Habitat (2005):
Ø  “Cities play a vital role in the social and economic development of countries. Efficient and productive cities are essential for national economic growth and equally, strong urban economies are essential for generating the resources needed for public and private investments in infrastructure, education and health, improved living conditions, and poverty alleviation………   Environmental degradation brings with it enormous costs, resulting in significant inefficiencies in the use of local resources. It also compounds inequities, and threatens the sustainability of development. Yet environmental degradation is not inevitable and is often caused by inappropriate urban development policies and ineffective planning and management.”
                                                                                      

3. Livability as a Goal in Urbanization.
Under the current philosophical context of human civilization, every human process ought to have a goal; the current global interpretation of the goal of urbanization is the livable city. In this paper we shall attempt to investigate how the lessons derivable from the concept of the livable city can apply to the current state of city development in Nigeria.
Livability is generally defined as the “quality of life” experienced by the residents of the city, which in turn is defined by the ability of the residents to gain appropriate access to “infrastructure (transportation, communication, water and sanitation); food; clean air; affordable housing; meaningful employment; and green space and parks”, Timmer and Seymoar (2005). The concept of the livable city as a family that shares its resources among contending stakeholders is further expounded by Halhweg (1997): a place that is common space, with easy access to green spaces, open spaces and other common facilities for all and also a place that “should be attractive, worthwhile, safe for children, for older people, not only for people who earn money there and then go and live outside in the suburbs and in the surrounding communities”.  The concept of the livable city, as a continuity within the continuum of time, is expressed by Salzano (1997);  place where, not only the demands of the present generations are addressed, but also the demands of future generations as well as the heritage of past generations: “The livable city as a link between the past and the future: the livable city respects the imprint of history (our roots) and those who are not yet born (our posterity)”, Salzano, (1997). The perspective of future generations brings up the issue of sustainability of cities; sustainability is defined as the capability of the city to continue to provide for and maintain the “quality of life” of its residents, by implication, the pursuit of livelihood by the current generation must not foreclose the access of present and future generations of residents of the city to good and appropriate “quality of life”.

Thus, urbanization is not the simple relocation of masses of people from the rural areas to the city; it should result in cities that are livable and sustainable and such undesirable attributes of urbanization as urban poverty and environmental degradation must be constantly addressed and eliminated by policy. In attaining these goals for the Nigerian cities, there is the need to depart from the present policy position of meliorism (the belief that human societies have a natural tendency to improve, on their own, and that the members of the society can consciously assist the process) and recognize that human processes must, of necessity, be guided by appropriate policies towards the desired goals. In the place of meliorism, what will be demanded will be proactive policies in urban governance and urban development, backed up with timely and appropriate professional inputs and consultations.     

4. The Metaphor of the Livable City.
The metaphor of the city as a living organism, presented in Timmer and Seymoar (2005), provides a good conceptual framework for appraising urbanization. By this metaphor, the city comprises systems that are likened to the parts of a living organism (similar to the human body). Thus, there are components of the urban system that are likened to the brain and nervous system, the heart, the circulatory systems and the organs. Our fair understanding of the human body, guides us into a better understanding of the critical roles played by each of the significant components of the urban system; this leads us to a better appreciation of the important fact that one cannot expect a livable and sustainable city through the development of certain components of the urban system at the expense of other components; a holistic approach is demanded.  

4.1 The Mechanisms for Control. In the metaphor livable city the mechanisms for development control, active involvement of diverse groups of stakeholder in urban governance, professional consultations and also monitoring and feedback processes are group together as representing the brain and the central nervous system of the body. The fundamental importance of good professional consultations in monitoring, control and feedbacks, and also interactions with a wide spectrum of stakeholders is thus underscored. In Nigeria, outside Abuja, there is hardly a city where urban development is guided by a functional master-plan, a properly constituted full compliment of professional teams, effective and modern digital monitoring processes (like Land Information Systems - LIS and  Geographic Information Systems – GIS etc), and also appropriate incorporation of a wide spectrum of stakeholders in urban governance. This constitutes one of the most fundamental errors in the current urbanization processes in Nigeria. With reference to the metaphor of the livable city as a living organism, the interpretation of this omission is extremely bizarre; we are probably developing cities that may be likened to living organisms, with malfunctioning brains and central nervous systems; that presents a picture of general clumsiness and total lack of co-ordination. In his introduction to Abuja Geographic Information Systems, the Minister of the Federal Territory, Mallam Nasir Ahmad Ee-Rufa’i observed the critical importance of proper monitoring and control in the face of the rapid urbanization that is ensuing in Abuja (and, by extension, also in Nigeria generally) today:
Ø  With this rapid expansion, manual record-keeping became inefficient, time-consuming and prone to abuses. Several unsuccessful attempts were made in the past to solve the problems. The attempt failed because of the gross under estimation of the gravity of the problems and the ill-defined scope of the project.”
                                       Abuja Geographic Information Systems, webmaster@abujagis.com
Thus, there is already the proven case that the dimensions of urbanization ensuing in our cities, has completely defied manual record-keeping”, and thus everywhere (not only in Abuja) there is the need for modern digital monitoring techniques; it is, therefore, a very serious danger to continue to underestimate the currently ensuing urbanization scenarios all over Nigeria today. The ultimate goals must be handing over livable and sustainable cities to the future generations; that demands that, in this generation, we must accord proper importance to urban development processes and the control of urbanization. This will also demand new perspectives in the training of professionals in architecture and for the built environment generally.

4.2 Infrastructural Networks and Grids. The “quality of life” in the livable city is also defined by the ease of flow of resources that are necessary to sustain livelihood activities: energy, water, materials, waste and sewage disposal, transportation networks, communication networks etc. In the metaphor of the livable city as a living organism, infrastructural networks and grids are grouped together to represent the circulatory system of the living organism. In our present state of urbanization these systems do not usually keep pace with housing; owing principally to ineffective development control processes and poor public housing policies. Current strategies in city development demand a holistic approach; the designs and implementation of infrastructural networks and services grids must develop alongside with well planned housing and other urban facilities. Phase delays between the development of housing and urban facilities, on the one hand, and the infrastructural networks and services grids, on the other hand, usually result in cities in which the flows of resources and materials are chocked up in critical positions and at critical periods of times; agencies responsible for infrastructural networks and services grids must be involved at the outset, not long after housing development has advanced significantly. This perspective is the concept of the city as one integrated system, contrary to the old paradigm of the city as a combination of discrete elements, functions and elements; Timmer and Seymoar (2005):

In addition, it must also always be remembered walking is also a means of transportation; the majority of the users of the urban space (in Nigeria and also in the city centres of most major cities in the world) are pedestrians. The quality of life in the urban space thus also depends very much on the provisions made, within the transportation infrastructure of the urban space, for safe and pleasurable pedestrian traffic; “Transportation for a Livable City” (2002):

4.3 New Paradigms in Urban Development: The Complete Community. For much of the 20th century, the principal paradigm for urban planning and development was based on the concept of zoning; that is the regulation of land development and land use by designating specific uses or functions (like housing, commerce and business, industry etc) to specific areas (or sectors) of the city. The new worldview is that (in the face of rapid urbanization) zoning has resulted in urban sprawl; with housing progressively located farther away (in suburbs and satellite settlements) from jobs located strictly within the commercial and business districts and also the industrial sectors of cities.  Thus, people are compelled to travel very long distances daily, to and fro, across cities and megacities, in order to arrive at their places of work (or business), and also to return home. Apart from long daily travel distances, sprawl has also been observed to result in rapid depletion of periurban forests and agricultural lands; and thus increasing ecological footprints of cities, Wackernagel and Rees (1996).
In the last two decades of the 20th century, new paradigms (promoted principally by the Congress for the New Urbanism) have emerged to challenge the concept of zoning; the new paradigms are based on the concept of the complete community, which offers residents easier access to jobs, recreation, commerce etc alongside with housing. According to Timmer V. and Seymoar, N. K. (2005):
In essence, the new paradigms discourage sprawl, proposing complete communities where people can live well-rounded lives; and creating out of the city, a “community of communities”, Timmer. and Seymoar, 2005); contrary to old concept of the city, which being partitioned into zones that are strictly defined by functions, compels people to travel several kilometers, by automobile, daily: the auto-dependent city, Nebel & Wright, (1993).

5. Conclusion.
In conclusion we recommend that city development and human settlement development, in general, deserve to be considered as the top priority issues in national policy, and also in training of professionals in architecture and the built environment in 21st century Nigeria. If the mistakes of Lagos are not to be repeated, then it must be realized that livability of Abuja is tied to the livability of the state capitals, other regional cities and the local government headquarters also.
 References
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