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For folks who aren’t architects (like me), we don’t give much thought to building design. We blissfully carry out our lives in and around structures.

I’ve had the privilege recently to try to understand how a building takes shape during the design process. I’ve discovered that there seem to be 2 methods at either ends the same spectrum. Top-down and bottom-up.

Each has an profound affect on not only the designs an architect produces but also how they run their business, engage with clients and consultants.

<h2>Top down</h2>

This approach is often driven by a strong personality (usually a director) with a creative vision. That creative vision is influenced predominantly by that individual’s style and personal tastes. Clients select these architects because there is often something in the design that resonates with the client.

In top down architecture, aesthetics reign supreme over most other design factors. With top down there is often a piece of the architects personality in the design. So any factor that threatens that design is often taken personally.

The advantage to top down is that clients know what they’re getting. There is often an obvious design language that shines through no matter what the context of the project. Clients are drawn to it and will select an architect because of it.

The disadvantage is that the architects desire can become a risk factor for the client too. If they’re too stubborn to challenge their own design language for the good of the project, clients can feel like they’re not getting the outcome they want.

Top down architecture is a challenging balance between client needs and aesthetic form. It often assumes that you can’t have both - it's either/or.

<figure><a class="colorbox colorbox-insert-image" href="https://res.cloudinary.com/dz9xllyip/image/fetch/q_auto:good/https://s3-ap-southeast-2.amazonaws.com/www.urban.com.au/s3fs-public/pictures/article-images/68a94254b4bcd524b38e5eaba1d4ca2e.jpg" rel="gallery-all" title="568 Collins Street. Image © Ryan Seychell"><img alt="" class="image-article-full-width-580px" height="870" src="/sites/urban.melbourne/files/styles/article_full_width_580px/public/pictures/article-images/68a94254b4bcd524b38e5eaba1d4ca2e.jpg?itok=MMYiw_FD" title="568 Collins Street. Image © Ryan Seychell" width="580"></a>

<figcaption>568 Collins Street. Image © Ryan Seychell</figcaption></figure><h2>Bottom up</h2>

This seems to be an emerging practice, particularly in Melbourne. Bottom up doesn’t start with any defined design language. The design starts with client needs first and foremost as well as site context.

It's a far more fluid process where both artistic and scientific inputs are related to the design during various iterations. Aesthetics are still important, but they’re more responsive than oppressive. This can result in some really creative designs that clients love.

The type of client that selects this approach is a little more adventurous. Yet they still want to drive the design process - they want a piece of their personality in the design - not just the architect. They want to use the design as a way to improve project outcomes.

Bottom up assumes that you can have striking form and meet the needs of clients. It is a both/and approach compared to top down. Architects that master the bottom up approach become known not for design language or style, but for project outcomes.

Bottom up also requires architects to really push boundaries of construction methods, planning regulations and engineering assumptions. These things are not for the feint hearted.

<h2>Which is best?</h2>

I think it's about personal preference really. I tend to sway towards bottom up, mainly because I believe in this approach to other areas in business (like The Responsive Organisation movement). Of course there is also another way to look at this - that is top down and bottom up are really a spectrum. Different firms would sit at different places on this spectrum and perhaps change depending on the market conditions.

In any case, I find the complexity behind the process fascinating. It makes me look at and experience buildings entirely differently, observing them and wondering - how did they arrive at that design outcome?

This post originally appeared on <a href="http://www.gwts.com.au/blog/entry/top-down-vs-bottom-up-architecture">Global Wind Technology Services' blog</a>. Lead image credit: <a href="http://oh-yes-melbourne.tumblr.com/">oh.yes.melbourne</a>.
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cskipsey

Top down versus bottom up architecture

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By Dr Seifu Bekele, Principal Wind Engineer, Global Wind Technology Services.

The increasing height of tall buildings, accompanied with the use of light materials, means that modern day buildings are becoming more sensitive to wind. These flexible buildings may be subjected to excessive levels of vibration under the action of wind. Excessive levels of vibration adversely affect serviceability and occupants’ comfort in a building. In response to this challenge, to achieve design objectives, there are number of motion control methods suggested and implemented by building designers.

The wind structure interaction is mainly characterized by the along wind and across wind responses. The across wind dynamical responses are initiated by vortex shedding. When wind blows perpendicular to the face of the building, vortices are shed alternately from opposite sides of the building. When a vortex is formed in one side of the building, the wind speed is increased on the other side (which correspond to low pressure). These fluctuating vortices induce fluctuating forces perpendicular to the wind direction. This fluctuating load is responsible for most of the dynamical responses of buildings. Alternating vortices from five different building shapes are shown in Figure 1.

<figure><img alt="" height="400" src="/sites/urbanmelbourne.info/files/pictures/article-images/building_shape_and_wind_forces_visualisation.jpg" width="372"><figcaption>Figure 1 Vortices generated behind a building</figcaption></figure>The vortex shedding induced lift forces can lead to prohibitively large across wind motions and their mitigation becomes a principal design concern. The following are some of the suggested methods to reduce the dynamic response created by vortex shedding-induced forces.

<h2>Building Layouts</h2>

Research into vortex induced excitation show that the peak response corresponds to a critical reduced velocity of 10 and above. This reduced velocity is a function of wind speed at roof height (VH), building frequency (f) and building dimension of the small side (L) and is determined by the following equation: By increasing the building dimension, thereby reducing the aspect ratio of the two sides, it is possible to reduce the vortex induced responses.

<h2>Aerodynamic Modification</h2>

The organized shedding vortices can be reduced by changing building’s cross-sectional shape. Some of these treatments are chamfered corners, building openings, tapering, and drop of corners. By using these techniques, considerable reductions of dynamic loads are reported. The tallest building, Burj khalifa utilized this aerodynamic treatment to reduce dynamic wind response effectively.

<h2>Building Properties</h2>

The resonant structural responses of buildings are directly related to building mass, frequency and damping. The damping directly from the building has a limited variability according the type of building (ie. prestressed concrete or steel) and is difficult to predict. However, the building mass and stiffness can be varied to reduce the dynamic response due to vortex shedding. If the building frequency is kept constant and the mass increased, then the predicted building accelerations can be reduced. Similarly, higher frequency also leads to a reduction in the predicted acceleration, as well as predicted dynamic loads.

<h2>Misalignment of Excitation and Response Directions</h2>

This is based on the idea that vortex shedding induced forces are important only for the wind directions which are approximately normal to the face of a building. Thus, organising the structural system so that its principal axes of stiffness are along the building diagonal is suggested. This leads the generalized forces for these diagonal modes of vibration to become a mixture of drag and lift forces that are more random or broad band in comparison with pure vortex shedding lift forces that results in a narrow band. This arrangement reported by Isyumov resulted in a substantial reduction in the dynamic responses.

<h2>Dampers</h2>

Recently, using auxiliary dampers to reduce the dynamic responses is becoming more acceptable. Tuned mass, viscous and tuned liquid dampers are commonly used types. The type of damper depends on the available space, budget and level of dynamical reduction desired. Tuned liquid sloshing dampers are becoming more popular due it their ability to be incorporated into the building water reserve. The tuned liquid damper devices achieve a reduction of the dynamic responses by sloshing in water tanks and dissipate energy. Wind tunnel test for 220m residential building resulted with top floor acceleration above the recommended criteria. This high acceleration can be reduced using liquid dampers.

Auxiliary dampers are also used to reduce dynamic loads due to seismic loads. Reducing wind and seismic loads means that less material is required in the construction of the building. Thus, sustainable building design which optimises the structural efficiency uses auxiliary dampers.

Wind tunnel study for structural loads and human comfort study has been in use for decades. The cost of building construction can be reduced substantially by predicting the wind load tailored to the individual building rather than using a general guideline, which leads to conservative load estimations and higher cost or increased risk. The disasters caused by strong winds are minimised due to an increased understanding of wind characteristics, modeling techniques, dedicated wind tunnel studies and the years of experience gained in the field. Advances in the measurement techniques and analysis in wind tunnel testing, as well as in building materials, has opened a door to the construction of taller and more complex buildings and reduce building motion.

To cope with the demand of the present day super high-rise towers in terms of vertical transportation, motion control and sustainable design, researchers and practitioners contribute to the advancement of the knowledge in building construction. The wind tunnel usage, computational fluid dynamics and the related analysis methods are also expected to continue growing to fulfill the future demand.

This article first appeared on the <a href="http://www.gwts.com.au/blog/entry/building-motion-control">Global Wind Technology Services Blog</a>.

Lead image credit: <a href="https://www.propertyobserver.com.au/https://www.flickr.com/photos/mugley/2179712241">flickr</a>.
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How motion is controlled in tall buildings

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It's as Melbourne as the MCG, meat pies and cold days in summer. It's wind whipping through <a href="http://www.theage.com.au/victoria/lack-of-soul-has-docklands-tenant-ready-to-leave-20110927-1kvgz">Docklands</a>.

When there is even a breath of wind about, Docklands is like one of those cool machines that <a href="http://www.indoorskydiveaustralia.com.au/">simulates sky diving</a>. OK, maybe that is a little over the top, but you get what I mean. I understand that it was a windy place prior to development, but I do not think that is an excuse.

The people of Melbourne deserve better and what is worse <a href="http://www.places.vic.gov.au/our-projects/fishermans-bend">Fishermans Bend</a> could potentially end up in the same situation. Fishermans Bend is not wholly owned and managed by one vendor (like Docklands was/is); as developments take form in Melbourne's newest enclave the wind effects are modelled only on the current proposals, not the precinct as a whole.

Meaning it is quite likely that by the time new developments are designed, they could create wind problems for established developments. If you are a retailer, it is possible you will get the worst end of the stick in this situation; people may just stop visiting your establishment and sadly you will have no leg to stand on in terms of recourse.

There are two elements that I believe need to be addressed here:

<ol>
<li>How do we model and masterplan in a way that holistically addresses the microclimate of a precinct?</li>
	<li>How do we provide developers and authorities with an objective platform to accurately assess wind comfort?</li>
</ol>
The first factor is not an easy one to solve; my thought was to study masterplan scenarios to find out the best way to deal with excessive wind concerns. The result being to provide guidelines for building mass and orientation per site.

But there are problems with this when it comes to expectations that land owners have on the return or value of their asset. Put simply, it requires land owners and developers to work collaboratively together for the good of the precinct. This is possible, but knowing how adversarial property development can be, it is not immediately probable. It could, however, be done if it is undertaken early enough so land owners are not given any expectations prior to specific rezoning.

As for the second issue, I believe there is some ambiguity when it comes to wind criteria for comfort. For the safety criteria it is easy to agree between developer, architect and planning authority; it is either safe for humans or not. But when it comes to comfort, consensus among project stakeholders becomes difficult because there is a much higher level of subjectivity.

How many times a year will it be too windy? Will it only be windy on those icy days in winter, in which case no one wants to be outside sipping a latte anyway. How do you know people will not be comfortable? Can't they just wear a coat? All these types of discussions take place and what results is only a few design concessions are made to relieve wind issues.

It is the ambiguity in the criteria that is the root cause. Having said that, the criteria, developed back in the 70's is a brilliant piece of work. Pioneering for its day! But we know more about wind and its effects now and have much more data to draw from. The old criteria can be built upon to create a new criteria that addresses development, not just in Docklands, Fishermans Bend or Melbourne, but all over Australia.

So where does this leave us? To develop a new criteria needs research as the want and need exists in understanding more detail about the human response to wind. Temperature has an effect on comfort as does the season. For example , in winter we just accept that it is going to be uncomfortable outside so wind as much less of an effect. When it is chilly, even a breath of wind can make it unbearable.

A new criteria could be developed to take these things into consideration. I am interested in what everyone thinks about the wind and higher density living, especially those that live in and around the Melbourne CBD.

Craig Skipsey is a consultant at Global Wind Technology Services: an Urban.com.au Industry Hub member.

Lead image courtesy Chris Mitchell (Flickr).
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Craig Skipsey

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