Capítulo 3: Validación de la propuesta
3.2. Método para la validación de la propuesta
A sudden change in the earth’s crust thousands of metres deep generates waves in rock, which then propagate to the surface as an earthquake. As the ground shakes, buildings are brought into motion. By Newton’s laws of motion, forces are generated from within the building by its own weight.
There are already well-established calculation procedures for determining the
magnitude of forces that can be generated for a given ground motion intensity. Similarly, there are already methods for determining if the soil would experience liquefaction or spreading when subject to a certain degree of shaking. Ground shaking intensity is mainly a function of the magnitude (size) of the earthquake, and distance measured from the building to the earthquake source. Had it not been for recent major events, few experts would have predicted that the epicentre of a magnitude 6.3 earthquake would have originated so close (10 kilometres) to Christchurch, New Zealand. Likewise, experts from Japan itself would have considered the chance of having a magnitude 9 earthquake in northern Japan to be very remote. Clearly, the world is still on a steep learning curve when it comes to predicting future earthquake events. When a natural phenomenon is not well understood, experts resort to the use of statistics to make predictions in probabilistic terms.
In regions of high seismic activity, it is common practice to design a building for ground shaking corresponding to a return period of 500 years. This means that, on average, there is one such event every 500 years. So, there is a 1/500 chance of this level of ground shaking being exceeded in any given year, which means a roughly 10 per cent chance of it being exceeded at some time during a design lifespan of 50 years. While 500 years appears to be a very long period of time, ground motions recorded in Christchurch during the February 2011 earthquake were found to be more severe than that predicted for a 2500-year return period event, as per the
78 design standard currently used in New Zealand. Thus, predictions based on current statistics were shown to be inadequate.
The destruction in Christchurch.
The probability of these occurrence values are based on a building in isolation and should not be confused with the probability of a country experiencing a disaster, which is characterised by much higher values. The level of seismic loading stipulated for the design of buildings in Christchurch will have to be increased in the future (as for many cities that have experienced a disaster). The philosophical question is do we simply increase design requirements when prompted by a disaster? It is preferable to prevent damage resulting from disasters before they occur, but what level of loading should we anticipate when data is lacking?
Does Australia too have destructive earthquakes? The most serious in Australia’s history was in Newcastle in 1989 with a magnitude of 5.7, which resulted in loss of life.
A 5.0 earthquake was recorded in Kalgoorlie, Western Australia, on 20 April 2010. A slightly higher magnitude earthquake occurred roughly a year later — 5.3 on 16 April 2011 in a remote part of northern Queensland; and on 5 July 2011 there was a minor but widely felt 4.4 magnitude earthquake just outside of Melbourne (Geoscience Australia).
No damage was reported in these recent instances, but there is no guarantee of the same in the future. Could these earthquakes be used as ‘statistics’ to predict when and where the next earthquake strikes? Common sense tells us this would be impossible.
Even more research is warranted in developing earthquake-resistant design of
buildings that are also economical and practical to their environment. Improving design methods alone would not mitigate a future disaster; retrofitting
79 existing infrastructure is just as important. A good knowledge of the relative risks of existing buildings is required to assist with prioritising, given that retrofitting every building would be too costly.
Since the Christchurch earthquake in February 2011, the New Zealand government has outlined the goal of developing an earthquake-resilient community. Accomplishing this goal requires substantial input from the disciplines of engineering, social science, financial planning and public health, as well as individual citizens. Engineers will have to play a pivotal role in making this major interdisciplinary undertaking a success. In the future, Christchurch can be used as a case study to guide other countries in formulating their own disaster mitigation plan.
Source: Associate Professor Nelson Lam, University of Melbourne.
Critical thinking
1. Can you think of other natural phenomena that are rare enough to require a national statistical approach (that is, it is not enough to rely on data from just a single site)?
2. Find some data on:
(i) the value of current building stock in Christchurch’s CBD
(ii) the cost of repairing some comparable damaged buildings following the earthquake.
If you were a Christchurch CBD building owner, how could you decide whether retrofitting greater structural strength is worthwhile, in terms of the cost versus the risk?
Let us consider another example. It is interesting to look at the potential risk-management strategies for major water storages such as Wivenhoe Dam in Queensland, which was subject to a commission of inquiry over its operations during the 2011 Queensland floods (discussed further in the introduction to chapter 4). Each storage has a spillway that allows very large floods to be passed downstream without damaging the dam wall. If the spillway is of inadequate capacity, the water level might overtop the dam wall itself and begin to erode it due to extreme turbulence, leading to catastrophic failure of the dam wall. Under such conditions, a huge flood wave could pass down the river, potentially destroying any towns or cities in its path. Engineers must carefully decide the capacity of any dam spillway. A smaller spillway is a cheaper option but it comes with a higher risk of failure, as the following
discussion illustrates.
Consider a spillway designed for a 100 000-year flood, which might cause damage of $5 billion if it caused the dam to fail (including the cost of civilian deaths, damage to towns and cities and the cost of replacing the dam). A 100 000-year flood is one that occurs on average once every 100 000 years. The expected damage in any one year is $5 billion/100 000 = $50 000. If the dam is designed to last 200 years, the expected damage is 200 × $50 000 or $10 million.
The spillway of the dam could be upgraded so that it safely handles a 1 million-year flood.
If this upgrade costs $100 million and it will reduce the likely cost of the dam failure to $1 million spanning its 200-year life, is it worth investing $100 million
80 (a certainty) to reduce estimated damages over 200 years from $10 million to $1 million? This would suggest the spillway be designed for the 100 000-year event. This is a risk–cost trade-off.
Similarly, buildings are often designed for 50- or 100-year wind events or to survive an earthquake of a particular magnitude. If a building lasts for 200 years (this is not uncommon), there is a chance its design conditions will be exceeded. Fortunately, other excess capacity is built into most structures, so — even under these extreme conditions — the building is likely to survive. If a building is designed to a 100-year wind standard, the probability of failure will be much less than 1 per cent, perhaps 0.1 per cent, given the excess capacity in most
structures. This means the structure has a survival probability of 0.999 in any one year. Over a 200-year life, this equates to a survival probability of 0.999200 = 0.812; or a 19 per cent chance of failure. Is this reasonable?
You may not be estimating probabilities for structural behaviour or spillway behaviour just yet. However, completing a risk assessment of your own work is an important process, using these four steps:
risk assessment A process of identifying impacts, their likelihood and consequences. The risk is the product of likelihood and consequences.
1. Identify potential impacts (e.g. unavailability of key people, information, equipment or skills).
2. Assess the likelihood of each impact (e.g. are they almost certain, likely, possible, unlikely or rare?).
3. Compare the potential consequences of each impact on a scale (e.g. grouping them as insignificant, minor, moderate, major or catastrophic).
4. Calculate risk as the product of likelihood and consequence of each impact.
Table 2.7 outlines a qualitative risk analysis matrix based on the Australian and New Zealand Standard. Extreme risk can be the result of catastrophic consequence and unlikely likelihood, as well as major consequence and possible likelihood, moderate consequence and almost certain likelihood. The impacts in the extreme range are the ones to pay particular attention; the high-risk ones should also get your attention.
Table 2.7 Qualitative risk analysis matrix (AS/NZS 4360: 1999)
In the dam spillway example above, dam failure due to over-topping is unlikely, but its consequence is catastrophic. This presents an extreme risk, which needs careful attention. In vehicle safety, a frontal collision is possible and the consequences are
81 major (injury or death), so again this extreme risk needs special attention by vehicle designers.
In the design of playground equipment, a child falling off a piece of equipment is likely at some point during a year, and the injury could be moderate to major. Again, risk management is essential, which could include soft surfaces beneath the equipment.
Reporting and documentation
Formal documentation is necessary as it marks key stages in the development of a project. The project starts with a document, usually a client brief. The data collection and research stage produces many documents, such as data sheets, spreadsheets, catalogue data and discussion summaries of various kinds. The alternative solutions are documented through sketches, data sheets and summaries of advantages and disadvantages. The analysis and evaluation of each alternative solution stage will involve calculations, modelling and other assessments that are summarised in a design report. All of the important processes and conclusions in the design report are revised to make sure the preferred alternatives meet the original client specification.
These checks are carefully documented for future reference. This guarantees appropriate quality assurance processes are enacted.
The final report describes recommendations of what is required. This is usually a summary of everything achieved to date, which is written in sufficient detail for the client. This is normally presented to the client in a meeting; some follow-up work or revisions may be required.
When you work as an engineer, it is likely you will formally review projects to consider how you and your team might improve your performance in the future. This leads to continuous improvement and lifelong learning. This is akin to the performance review, or
‘discussion’ between a coach and members of a sporting team after a competition.
In addition to needing to have access to documentation, engineers need to have good writing skills so they can communicate recommendations.
Writing and speaking skills
Regular written reporting, such as the documentation required for engineering problem-solving, is required in the field of engineering. As a professional, you will need to be able to write simply and concisely; simple sentences are usually more effective than longer sentences.
Write in the active voice (e.g. ‘I submitted my report to the client’) rather than in the passive voice (e.g. ‘My report was submitted to the client’). Define terms, abbreviations and acronyms which may not be familiar to your readers. Provide supporting evidence for your assertions.
Writing skills are discussed in more detail in chapters 6 and 11.
As an engineer, you will be required to formally present your work to clients and to discuss it. This will require personal confidence as well as presentation skills. The project work you do throughout your degree will provide you with opportunities to improve and develop your communication skills.
In the car-buying example, you would sit down with your client and outline the range of solutions you have identified, and the criteria you have used to assess them, and finally describe how you have arrived at your recommendations. It is quite possible that your client will then have new insights, which might lead to additional work for
82 you. There may be new criteria to consider or different weights of the existing factors that could change the recommendations. When all such changes have been finalised, the final report, in written form, can be transmitted to the client.
Improving practice
On any project, most professionals review what they are doing and think about how they might improve their results. Sports coaches are experts at this. These coaches review how the team is playing and make recommendations, such as changing the players on the field and the plays made in games, as well as helping individuals improve their kicking, catching and throwing skills by encouraging them to train regularly. Likewise, you need to get into the habit of being your own coach, both as a student and in your future career, and engage in thinking about your own practice as a means of personal and professional growth.
A systematic way to engage in this kind of reflective practice is to keep a diary or a journal for jotting down ideas, so when you are employed as an engineer, you will be able to look up ideas you had last week or last month.
A formalised process of doing this is action learning (or action research). Action learning is the process of continual improvement or learning through action. There are four basic steps:
plan, act, observe, and reflect (plan to improve). For example, you may draft plans to improve the efficiency of a process in a chemical processing plant. Your plans are enacted through the installation of some new equipment. You then observe the performance of the process by collecting data over the following weeks, and reflect on whether the changes have been successful. Perhaps the process needs further adjustment, such as an increase in temperature.
action learning The process of continual improvement or learning through action. The four basic steps are: plan, act, observe, and reflect (plan to improve).
Dick (2002) shows continuing cycles of action and reflection — action, reflection, action, reflection and so on. As tasks are completed, reflection needs to take place. Can a project be completed more efficiently, more quickly, more cheaply or with less environmental impact?
As better solutions are developed, they should be implemented; then even better solutions can be created, and the cycle continues. This process has allowed humans to move from caves to satellites in about 7000 years. The transition from the first powered flight to a moon landing took just 65 years — a truly remarkable achievement. Such is the power of continual reflection and improvement. You will learn more about reflective practice in chapter 4.
Team management and improvement
When you work in teams, it is easy for things to go wrong — work is not done, members do not meet and you may be unsure of what needs to be done. You may begin to panic, with too much work to do and not enough time to do the work well to meet the deadline. Rather than procrastinate and proceed to panic, the purpose of project management is to ‘plan, proceed and perform’ (Turbit 2005). The project management processes discussed earlier in the chapter provide the tools for team organisation. Once a project is underway, regular progress checks are needed to keep the plan on track.
At each meeting, team members should check off what has been done and decide what will be done next. This process is backed up by an action plan. These meetings may be
uncomfortable discussions. You may need to tell a colleague that they need to put in more effort or improve their attendance at meetings. A team member may be
83 holding others up. Questions may need to be asked, such as ‘Does everyone understand the task required? Is the project too large? Can someone else help? Can a group brainstorm be conducted to scope out the task (work out the real engineering problem) so it can be completed more quickly?’
action plan A documented process of tasks that need to be completed, when and by whom.
In these discussions it is advisable to focus on the task rather than on the person. How can the task be moved forward? It may be necessary to re-allocate certain tasks, or for the whole group to provide input to the task. It is easy to get caught up in blaming others for not getting work done; however, there may be a range of reasons why tasks have not been completed.
People respond to positive feedback much more than they do to negative feedback. If you can provide team members with a helping hand, it is much more likely that they will respond positively to you. Negative criticism tends to lead to team members putting in less work rather than more work. The team dynamic will be discussed in greater detail in chapter 6.
In addition to being aware of the importance of participating in reflective practice, engineering students should pursue and engage in lifelong learning.
Lifelong learning
As a reflective engineering practitioner, you will always be learning and improving. This will be essential to the development of your career. In the Engineers Australia Stage 1 Competency Standard (2011), the need for professional development and lifelong learning is expressed as:
Orderly management of self and professional conduct.
Demonstrates commitment to critical self-review and performance evaluation against appropriate criteria as a primary means of tracking personal development needs and achievements.
Understands the importance of being a member of a professional and intellectual community, learning from its knowledge and standards, and contributing to their
maintenance and advancement.
Demonstrates commitment to life-long learning and professional development.
Manages time and processes effectively, prioritises competing demands to achieve personal, career and organisational goals and objectives.
Thinks critically and applies an appropriate balance of logic and intellectual criteria to analysis, judgment and decision making.
Presents a professional image in all circumstances, including relations with clients, stakeholders, as well as professional and technical colleagues across wide ranging disciplines.
Source: Engineers Australia (2011).
The importance for engineers to undertake ongoing professional development is discussed in the following Spotlight.
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