Miquel Rosales, AIA, is President of
Rosales and Partners of Boston, MA. With more than 20 years of lead design experience worldwide, Rosales is recognized
internationally as an expert on bridge aesthetics and design. Below he shares his
thoughts and ideas about the creation of Greenville's Liberty Bridge:
1. Is the cantilevered cable stay design unique to Greenville or had it been accomplished
before?
The design of the Liberty Bridge which consists of curved deck with a single suspension
cable attached on the outer zone of the curvature is unique to the USA. There are
similar bridges built in Germany and Spain but not with the same exact geometric
characteristics. The Liberty Bridge is considered one of the best pedestrian bridges
worldwide and has received numerous international and national design awards.
2. What had to be considered to design the bridge with such a long sweeping curve?
With this type of bridge it is important to conduct extensive calculations and analysis
to ensure the optimization of the structure and the balance of the forces. We were
also very interested in creating a viewing platform to the falls and park and that
is why we proposed to locate the cables away from the view of the falls. Of course
local soil conditions and topography also played an important role. We wanted the
bridge to seamlessly fit into the landscape.
3. The finished product is incredible, but through the creator's eyes would you
do anything different relative to the look of the bridge?
I think the bridge works well with the overall park design and its different levels
and access points. It is a very transparent and elegant bridge. Probably the steel
tower (s) cross section diameter could be a bit smaller but in general I am very
satisfied with the end result. I hope the City of Greenville will keep maintaining
the bridge on a regular basis so that it always looks great.
4. Was the lighting a forethought or afterthought in the design process?
The lighting of the bridge is integral to the experience of crossing the bridge
at night and it was always part of the design from the initial stages. The soft
blue light transforms the appearance of the walking concrete surface making it appear
much softer and delicate.
5. How long did the design process take - from conception to detailed construction
documents?
It probably took around 3 years which is not unusual for a landmark pedestrian bridge.
We are in the process of completing a footbridge in Fort Worth, Texas and it has
taken almost 5 years. Bids were just received a month ago and construction is set
to start soon. When a bridge is unique in nature it always takes longer to complete
the construction drawings and sometimes it also takes more time to find additional
funding for construction. However, at the end, clients and communities feel that
it was worth it to wait if results are similar to the ones achieved with the Liberty
Bridge.
6. Just how many people can safely fit on the bridge at once?
I would say over 1,300 people can safely fit on the bridge at once without any problem.
We used high levels of safety standards well beyond the actual physical live load
capacity that the bridge can accommodate.
7. The design lends itself to vibration/swaying but it seems to do very little of
either. How did you accomplish this?
The bridge utilizes a stiff steel truss underneath the deck that helps stabilize
the structure during use. In addition, the forces are balanced between the cable
above the deck and the three ring cables located under the deck that connect to
the steel truss. The bridge actually moves but it is not uncomfortable. It actually
sways more when there are less people using it.
8. Did you have to consider wind and seismic extremes in your design?
Yes, all possible live and dead loads need to be considered. For example, small
vehicles can also use the bridge. We had a very successful collaboration during
the final design with structural engineers Schlaich Bergermann and Partner, which
resulted into an outstanding bridge.
9. How did you choose the materials - form, function, aesthetic? If all of the above,
which ones weighed heavier than others?
For such a bridge it was important to use mostly steel since the members would be
smaller, more slender and easier to connect/weld. There was an extensive study of
the characteristics and performance of the cables in order to find the best configuration
and details. The bridge balances well both aesthetics and functional considerations.
10. What were you trying to evoke from your design?
I wanted to create a bridge that will combine both nature and technology into a
synthesis of both that would enhance the overall area. I think we achieved this
goal and I am very glad that so many people like the bridge and use it regularly.