Celebrating Brandwacht pedestrian bridge

Celebrating the Brandwacht pedestrian bridge

Providing safe passage for the surrounding community, Mossel Bay Municipality’s Brandwacht pedestrian bridge serves as a prime example of how structural engineering design can blend with aesthetic elements to enhance mobility experiences. First and foremost, though, it was an essential intervention to minimise pedestrian fatalities.

At least five people – including four children – have died trying to cross the R328 at Brandwacht, and countless others have been injured in vehicle collisions.

For a long time, the road was a dangerous one that residents had to face daily, walking from their homes on the other side of the R328 to reach retail outlets, the local primary school and a church.

Vehicles travel at high speed along this route, often ignoring the speed limit. Furthermore, because of the alignment of the road and the fact that people would cross at grade, forward visibility and stopping sight distance were poor, creating a lifethreatening hazard.

For Mossel Bay Municipality, the situation was untenable, and an urgent solution needed to be found. Subsequently, in April 2018, Royal HaskoningDHV was appointed for the design, procurement and construction supervision of the bridge after assisting Mossel Bay to secure Municipality Infrastructure Grant funding.

The goal was to create a structure with simple, elegant lines insofar as the construction methods would permit. Articulation of the bridge deck was therefore eliminated to save money and time, and avoid unnecessary adornment.

Elevation of the bridge showing how well it fits into the environment and enhances the perceived quality of the surrounds

Engaging the community

Importantly, before construction commenced, community leaders, as well as the primary school principal, were consulted to determine the best position for the bridge.

The opportunity to create jobs and new skills was also maximised via community participation goal targets. Local SMME subcontractors and labour were hired to collaborate on the project, while comprehensive training was provided in areas that included gabion construction, formwork, steel fixing, pouring of concrete, and working at heights.

Design considerations

The decks of pedestrian bridges are often very light and vulnerable to collision forces. So, to overcome this complication and go

A pedestrian perspective. The overhead cage is open to the sky at the entrances but closed at the point where the bridge crosses the road to maximise safety

KEY FACTS ABOUT THE BRIDGE

above the required 6 m vertical clearance, the deck was built monolithically with the piers. The rationale behind this is that if a collision force were to strike the deck, the piers would also help keep it from collapsing. This approach also made it possible to eliminate two bearings per pier support, which decreases the need for future maintenance.

From a construction efficiency perspective, the formwork for the bridge deck was pre-assembled off-site. This maximised the opportunity to plan the actual erection and assembly, and minimised disruption to traffic.

Shapely soffits and wave elements

The design incorporates a security screen and cage. Smooth curves were added to give the impression that the cage gets bigger as pedestrians get closer to the middle, which is usually where people feel the most constrained.

Since the cage was a prominent feature of the bridge, it was designed with an emphasis on aesthetics. The horizontal members are shaped like waves and painted blue to represent the ocean nearby. Additionally, the cage enclosure is made of a transparent material to ensure that the steel elements stand out and remain the focal point.

The cage has been left open at the top of the jack spans and closed over the main span traversing the road below. This also creates the impression of openness, rather than a hemmed-in feeling, while crossing the bridge.

Other noteworthy aesthetic elements include the curved deck soffit, providing smooth lines across the trunk road below, while radiused corners soften visible deck edges.

PROJECT TEAM

Client: Mossel Bay Municipality Consulting engineer: Royal HaskoningDHV Contractor: EMPA Structures

• The reinforced concrete bridge structure comprises a three-span, continuous, varying-depth T-beam • The bridge crosses the R328 with a 16.6 m central span and 12.59 m jack spans A pedestrian perspective. The overhead • It is perpendicular to the road with a deck cage is open to the sky at the entrances depth of 1 m at the columns, while the but closed at the point where the bridge midspan and abutments have a deck crosses the road to maximise safety depth of 0.65 m • The deck has a minimum vertical clearance to the soffit of 6 m • The horizontal clearance is 3 m from the shoulder to the concrete piers on the R328 • The deck width between kerbs is 2 m • Polycrete handrails were installed to a minimum height of 1 m • The western landing consists of a 1:8 ramp and staircase access to provide accessibility from the northern and southern approaches

Community bridge safety

Completed in October 2021, the pedestrian bridge has made a lasting difference to the Brandwacht community, and especially the local children who pass through this portal every day to reach their primary school. It’s a classic lesson in road safety, and an outstanding example of best-in-class social infrastructure in practice.

ABOVE View of the cage highlighting the blue structural element that represents a sea wave

LEFT Residents on their way back home from the shops