Footbridges are built to improve road safety for pedestrians and motorists. First and foremost they must be functional and low maintenance structures. There is, however, the question for designers of whether they can be more than that. “Footbridges of unique character can fit into any environment and add a pleasing quality to such”, states John Anderson, SMEC’s Functional General Manager for Structures, based in Cape Town. “They can be hardy and robust and still become visible markers that good design can improve the public space”.

SMEC was involved in the design development of three concrete footbridges across varying landscapes within South Africa. Their designs relate to their surroundings and also to the fact that they must survive the harsh realities of theft, vandalism and life with limited preventive and routine maintenance.

A common thread through each bridge design is the use of bespoke in situ concrete forms rather than standard precast concrete sections. In each case the bridges were staged and formed with shutters.

The Pacaltsdorp Pedestrian Bridge situated in George in the Western Cape, serves its purpose by connecting people from a low cost housing development to work opportunities in the nearby town. The bridge is a 65 m long continuous four span, self-anchored arch supported stress ribbon bridge with a maximum span of 21.2 m. It has semi-integral abutments and a slender 220mm thick concrete stress ribbon deck that spans up to 12.6 m between the crests of the arch sections.

“The project was not about urban regeneration or creating recreational routes it was about getting people walking to work off the highway”, explains Anderson. “It was evident that the design process must find the pedestrian’s preferred route and then serve that route to draw people onto it.

We looked at solutions that might minimise the height pedestrians must climb and descend. We also considered issues of safety and security for the pedestrian and the motorist. It can therefore be argued that every footbridge is unique because the people that use it are unique; purely in where they have come from and where they are going to. If designers ignore this basic starting point there is a high chance that the intended end-users will respond by ignoring their footbridge”, he notes.

The bridge superstructure was simply built in situ in layers. This process was labour intensive and provided work for a significant number of skilled carpenters and artisans. In the South African context, structures that minimise materials and maximise labour input help uplift poorer communities.

The questions raised in the design of the Pacaltsdorp Bridge are recurrent in the South African context where many people live in informal settlements and have to walk to job opportunities, schools and amenities.

Another such instance was the Ergo Road Pedestrian Bridge on the N17 highway in southern Johannesburg. For the residents of an adjacent informal community, with work opportunities and schooling on the other side of the freeway, the bridge was an urgent necessity. The challenges at Ergo Road were the flat terrain and convincing the community to use the bridge and to avoid the temptation to quickly run across the highway. The concept for the bridge therefore had to first and foremost serve the pedestrians’ needs and to follow their desired route.

Once again the use of a continuous cast in-situ structure allowed a bespoke structure that could be tailored to the specific needs of the site. In this instance there was a strong need to reduce the depth of the deck below the walking surface to reduce the grade separation and therefore the length of the required ramps up onto the bridge.

A close neighbour of the Ergo Bridge on the N17 is the Regents Park Bridge. Again, the design of this bridge was driven by the basic need to provide an attractive and direct route for pedestrians. The site was especially dangerous for pedestrians, and in the end a crossing with a 58m long main span was conceived to enable the future highway widening.

The extra challenge in this instance was these attributes had to be integrated with the need for a long span crossing. After reviewing a myriad of options the use of a simple self-anchored suspension bridge with an in situ concrete deck slab cast on staging proved to be the most economical option.

“These projects have proved that limited construction budgets are not a real constraint for designers”, concludes Anderson. “The limits are set by the designer’s input and investment into the project. The process of letting the function and context of the site lead the design process will usually produce an attractive structure that sits comfortably in its location”.