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Opinions of Saturday, 8 May 2010

Columnist: Allotey, Nii Kwashie

Wake Up Ghana; We Could Go The Way Of Haiti: Series #5

Building Design Process: A Change is Necessary

Summary: This article is the fifth in the series and builds on the previous discussion on the concepts of seismic design. Among other seismic safety issues, this article takes a look at various aspects of the building design process and discusses the role they play in increasing seismic risk. It points to the need for various aspects of the process to be revamped, and stresses the fact that modern day seismic codes really do work, if adhered to.

Introduction: All over Accra buildings are springing up everywhere. There seems to be a boom in all types of construction: residential, commercial and public. With Ghana’s average five percent increase in GDP, this trend is certain to continue. The question however is: how many of these buildings are designed to be earthquake-resistant? Recently the news media carried an article to the fact that the Vice President had struck a deal with a Korean company for the construction of a large number of houses to help alleviate the shortfall of housing in the country. Nothing was mentioned about these being earthquake-resistant. At a time such as this, when earthquake disasters are occurring all around us, should not this have been a highlight of such a deal? One can only hope that this has been taken into account.

Consider all the infra-structure being constructed in the metropolis: flyovers, high-rise buildings, shopping malls, multi-storey car parks, etc. Are seismic provisions taken into account in the design of these structures? In addition, what seismic input is being used? As a country, we still have not answered or agreed upon the fundamental issue of seismic input. Structures that are designed for earthquakes could thus be over-designed or under-designed. One can only hope most are over-designed!

Is Change Necessary?: The need for earthquake-resistant buildings appears to be on the lips of some public commentators. Most of these commentators point to the increase in illicit construction all over the metropolis. These buildings are in most cases not designed at all, and when they are, they are designed by unqualified professionals, without any, or limited professional oversight. To make things worse, these building are constructed with substandard materials and under the supervision of unqualified personnel. This is a major contributory factor to seismic risk increase, and demands serious attention. But wait a minute, is it only the illicit buildings in the metropolis that are at risk?

Recently, the Ghanaian Times carried a center page story on fallouts from the earthquakes in Haiti and Chile. They interviewed a director of a Ghanaian engineering services company about the way buildings are designed in Ghana. He was quoted as saying that in Ghana the British building code is used for building design, and that many buildings are not earthquake-resistant, since they are designed by unqualified personnel, e.g., draughtsmen. Is this statement wholly true? The author does not believe this to be so! Why? The simple reason is that British codes such as BS 8110 do not have seismic design provisions. Hence, designs based solely on this code would by default not include any seismic design features. Secondly, seismic design is based on principles that are different from non-seismic design, and is just not an extrapolation of vertical load design. Change in the way buildings are designed and constructed is therefore necessary, if the metropolis is to witness any increase in earthquake-resistant construction. The question then becomes: are our professionals in the building and construction industry ready for such a change?

The Clarion Call for Change: The Earthquake Engineering Research Institute of the US, the globally accepted premier professional association of earthquake-related specialists publishes a “Learning from Earthquake Series”. This is based on submissions from expert teams that pay reconnaissance visits to regions struck by earthquakes. A common thread between most of these reports is that the predominant failures observed are due to design and construction flaws that are well understood, and for which mitigation measures are known and well-established. This has led to a catch phrase in the technical community that says, “earthquakes don’t kill, poorly built buildings do”. It is important to stress that these failures occur in buildings with and without permits. Some of the common architectural, structural and geotechnical causes of these failures are listed below:

• Collapse of buildings due to poor conceptual and architectural layout. This is related to irregular and unsymmetrical layout of buildings in plan and in elevation. These situations result in buildings that have eccentric lateral force resisting systems, resulting in them experiencing significant torsional forces, for which they are not designed. Examples of plan-wise irregularity are L-shaped, C-shaped and U-shaped buildings that are not separated into different rectangular blocks. Examples of height-wise irregularity are the irregular arrangement of infill masonry (masonry refers to blockwork) along the height of the building, and walls and columns that do not go all the way to the ground. • The collapse of soft stories, many of which are mostly ground floor storeys. A soft storey is one with considerable less lateral stiffness than the storeys above it. • Column failures due to excessive horizontal forces imposed on them by infill masonry walls. This is due to inadequate shear strength of columns to resist horizontal forces imposed on them as a result of column and infill wall moving separately under earthquake action. • Column failures as a result of the captive column syndrome (also called the short column syndrome). This is due to an amplification of the shear force imposed on a column as a result of it being attached to a partial storey height wall on its side. Such walls are normally masonry infill walls. • The pancake collapse of frame buildings due to beams that are stronger than the columns they are attached to. This is regarded in the technical community as the main cause of death in recent quakes in developing countries. This is the result of buildings being designed mainly for vertical loads. • Poor confinement of concrete columns and beam-column joints, resulting in concrete crushing and the buckling of steel under cyclic action. This is linked to the large spacing of ties (steel rings), and the wrong approach to anchorage and curtailment of steel bars. This is also due to the fact that column ties are not allowed to continue through the beam-column joint. • Poor lateral bracing of buildings and structures. In fact, in choosing to be specific, one cannot just avoid noticing the rows of slim steel tube columns that are used to support the roofs of the sheds at the new Achimota lorry station. No lateral cross-bracing is provided in any bay; one can only hope that the combined moment capacity of these columns is enough to resist any imposed lateral loads. • Bearing capacity failure! This is the result of the provision of inadequate foundation. This is normally the result of foundations being designed considering vertical loads only. No horizontal load, vertical load and moment interaction is taken into account in assessing the bearing capacity of the foundation. Furthermore, foundations are generally not tied together. • Liquefaction failure. This is one failure that is easily noticed; entire buildings are precariously tilted to one side, or even flat on their backs. This is the result of buildings being built on saturated loose silty-to-sandy soils.

The frustration faced by such experts is summed up in a statement by a New Zealand Earthquake Engineer who was part of a reconnaissance trip to Indonesia after the 2009 Magnitude 7.6 Padang Earthquake. He gives a clarion call for professionals in the building industry, to in all humility, accept that there is a need to change the way we design and build.

“The question is, when will we learn to design and build so that our buildings are safe in earthquakes?, or expressing it in another way, when will the very structures, designed and constructed to provide shelter, no longer be agents of harm. These thoughts are not intended to criticise design and construction practices in Indonesia, but rather to acknowledge that the challenge of changing the way we do things; i.e., the way we design and build. Resistance to change seems to be a deeply embedded characteristic of the human condition. It is, however, tragic when what is being resisted has the potential for improved safety and human well-being.”

The rest of this article will be devoted to discussing two crucial lessons that must be learnt, and learnt humbly and quickly by design professionals and building owners.

Lesson 1: Many building owners and architects are of a mistaken opinion that it is sufficient to include engineers in the design process only after the architectural work is completed. This is a BAD approach that has serious consequences, especially in seismic design. In many cases, even if the structure is designable, it results in significant additional costs. For example, many seismic codes penalize unsymmetrical buildings by increasing the forces they are to be designed for; this can lead to astronomical increases in cost. As one researcher put it, “even the cleverest calculations and detailed design (structural and geotechnical – emphasis mine) cannot compensate for errors and defects in the conceptual seismic design of structural and non-structural elements.”

It is therefore important that close collaboration between the architect and the engineer start from the earliest possible stage. This ensures good building design, guarantees structural safety, reduces vulnerability, and limit costs. By doing so, both partners contribute with different, yet indispensable, expertise. The architect deals primarily with the aesthetic and functional design, while the engineer produces a safe, efficient and economical structure. In other words, it can be stated that a parallel design procedure is much better than a serial one, and is in the interest of the building owner. Building owners must therefore ensure that design professionals follow the parallel design process, in combination with the golden three “S” rule of simplicity, symmetry and separation.

Lesson 2: The next lesson has to do with the fact that strict adherence to the provisions of modern day seismic codes WORK. That is to say that there are available methods and practices that can be used to significantly limit the vulnerability of buildings to earthquakes. Simply put, the destruction of buildings during an earthquake can be effectively prevented by building in accordance with the recommendations of modern day seismic codes. Unfortunately, due to ignorance and indifference, this point is still not appreciated by some people in countries that have seismic codes.

An example of the benefit of adhering to seismic code provisions is the difference between the destruction that occurred in the recent Chile earthquake, and that which occurred in the Haiti earthquake. Chile is a country that takes earthquake-resistant design and emergency-preparedness seriously; Haiti on the other hand, similar to Ghana, had no clearly planned out earthquake-related mitigation measures. A point to note is that although Chile’s earthquake was considerably larger than Haiti’s, Haiti’s economy has faced a major reversal that would take decades, if not generations, to rebuild. The impact of Chile’s earthquake on its economy, although significant, cannot be said to be a major reversal.

It was noted in an earlier article of this series that the Council for Scientific and Industrial Research recently issued a press statement to the effect that a seismic code for the country is in its final stages of development. The author is not privy to the contents of this document, but would admonish those in charge of developing the code to ensure that it is based on the most recent available knowledge in the field. This is because earthquake engineering is a dynamic field that keeps changing based on lessons learnt from past earthquakes.

As stated earlier, British Codes like BS 8110 that are used for design in Ghana do not include seismic provisions. Interestingly, at the end of March this year, these codes are being withdrawn to be replaced by the Eurocode. The seismic provisions portion of the Eurocode, i.e., Eurocode 8, is considered to be one of the best modern day seismic codes. The author is of the view that the Eurocode is particularly relevant for Ghana, since it was developed taking into account different kinds of construction all over Europe, and would be a good starting point for developing a seismic code for the country. Its adoption, of course, with relevant changes as required by Ghana’s unique situation, would also not be a bad alternative.

The Eurocode unlike seismic codes for countries such as the US, Canada and New Zealand allows the use of masonry-infilled frames for the construction of new buildings in seismically active regions. This is a particularly important form of construction in many developing countries including Ghana, so adopting a code that bans this form of construction altogether would be a real problem.

Other seismic codes that could be helpful to the code developers are the Indian Code, the Nepalese Code and the Australian Code. The international standards organization also has the ISO 3010 code, however, this code just lays down a procedure for seismic design; it does not give firm values for the different variables involved.

Conclusions: In a developing country such as Ghana, the fight to create a society that is resilient to earthquakes is a tall order. It must be fought on all fronts: public policy, effective regulation and enforcement, mass public education, and the design and construction of earthquake-resistant structures. The latter has everything to do with professionals involved in the building and construction industry. This group of people are the ones who are supposed to be on the frontline of the battle. This group must therefore lead the charge in the fight against this canker by putting their own house in order; this will put them in a good position to help other groups put their act together.

Nii Kwashie Allotey, Ph.D., P.Eng., Email: nii50@inbox.com