ParaMatic was commissioned by a contractor on behalf of CapeNature to measure the site then conceptualise and detail the new steel stairway to Stilgat at the De Hoop Nature Reserve in the Western Cape. ParaMatic used a 3D scanner to capture the site and modelled and detailed the new stairway in Tekla Structures.

The De Hoop Whale Trail is a world-famous long-distance hiking trail in the De Hoop Nature Reserve administered by CapeNature. The 54 km trail has overnight stops along the trail and runs through mountain and coastal regions. Part of the trail runs along a coastal ridge with a detour down a steep valley to a renowned swimming cove and picnic spot at Stilgat. The hiking path runs approximately 100 m from the sea and is subject to daily exposure to sea air, mist and wind borne salt spray. The original timber and wire rope ladders on the mountainside have long since decayed from rot and corrosion and the climb from the mountain path to the sea is perilous. With an increasing trend in the average age of hikers, the client realized that the route either had to be closed or made safe. Cable or chain ladders were considered too risky for the profile of the hikers and a stairway was approved for the path to Stilgat.



The brief

The owner proposed and approved a stairway but stipulated that the stairway had to be aesthetically unobtrusive, sympathetic with the area, modular and lightweight and make a minimal use of cement works. Maximum off site manufacture was required.

No survey data on the site was available.

The remoteness of the site makes regular maintenance impractical. The site is far from the Reserve main offices on a rough road and is in a pristine, undamaged coastal zone. On-site contractors are hard to manage on such a large site as De Hoop and the owner wanted site activities to be as short as possible and with the smallest possible labour force. The project was also on a tight deadline so as not to affect the 2020 Summer hiking calendar.

Morning mist, wind spray and heavy early morning condensation are regular environmental considerations. Softwood rots quickly and is wholly unsuited to the climate. Uncoated steel corrodes within days.

Wherever possible, the staircase had to follow the mountainside to allow it to blend in with the undergrowth and avoid breaking the silhouette of the cliff.

The stairway had to allow for perennial river flow in the stream bed and not block the stream in full flow. Access to a lookout point was discussed.

Road access close to the site is only possible using a small four-wheel drive vehicle, with a rough climb from the unloading point to the installation site. All components therefore had to be suited to portage over rough terrain without endangering the installation contractor’s staff.

Site welding had to be eliminated or minimized. Drilling using battery packs would be acceptable, so anchor foundations into existing rock was considered the preferred route for fixing wherever possible.

Heavily burdened hikers must be able to descend the stairs without slipping on wet surfaces.

The area does experience intermittent fires, but is remote and considered inaccessible to fire fighters with other priorities during a fire. It was not practical to route the stairway away from flammable vegetation. The structure must be essentially fire proof and if a component is fire damaged, the design should allow for replacement without welding. Fire damage should not compromise the immediate stability of the structure.

The cost of a stainless steel structure was beyond the budget of the project. A structural, duplex hot dip galvanized solution was considered the most likely functional and economic solution.

Why steel?

The owner proposed and approved a stairway but stipulated that the stairway had to be aesthetically unobtrusive, sympathetic with the area, modular and lightweight and make a minimal use of cement works. Maximum off site manufacture was required.

No survey data on the site was available.

The remoteness of the site makes regular maintenance impractical. The site is far from the Reserve main offices on a rough road and is in a pristine, undamaged coastal zone. On-site contractors are hard to manage on such a large site as De Hoop and the owner wanted site activities to be as short as possible and with the smallest possible labour force. The project was also on a tight deadline so as not to affect the 2020 Summer hiking calendar.

Morning mist, wind spray and heavy early morning condensation are regular environmental considerations. Softwood rots quickly and is wholly unsuited to the climate. Uncoated steel corrodes within days.

Wherever possible, the staircase had to follow the mountainside to allow it to blend in with the undergrowth and avoid breaking the silhouette of the cliff.

The stairway had to allow for perennial river flow in the stream bed and not block the stream in full flow. Access to a lookout point was discussed.

Road access close to the site is only possible using a small four-wheel drive vehicle, with a rough climb from the unloading point to the installation site. All components therefore had to be suited to portage over rough terrain without endangering the installation contractor’s staff.

Site welding had to be eliminated or minimized. Drilling using battery packs would be acceptable, so anchor foundations into existing rock was considered the preferred route for fixing wherever possible.

Heavily burdened hikers must be able to descend the stairs without slipping on wet surfaces.

The area does experience intermittent fires, but is remote and considered inaccessible to fire fighters with other priorities during a fire. It was not practical to route the stairway away from flammable vegetation. The structure must be essentially fire proof and if a component is fire damaged, the design should allow for replacement without welding. Fire damage should not compromise the immediate stability of the structure.

The cost of a stainless steel structure was beyond the budget of the project. A structural, duplex hot dip galvanized solution was considered the most likely functional and economic solution.

Structural framing

Steel is the material most suited to manufacture of varying lengths and geometries. Standard hot rolled sections were used for the stair stringers and platforms. All elements were limited in mass to ensure they could be hand carried onto site for bolted assembly.

The client provided a typical section for the handrail detail which had to be modified to suit hot dip galvanising after welding.

The client agreed that standard stair treads had an industrial appearance and that non slip grating types treads could be painful in a fall. The final stair tread concept was a carcass of a thin plate with bolted-on machined timber stair inserts, selected for their anti-slip properties. Treads are replaceable, using counter sunk bolts. A damaged insert would not affect the short term usability of the stairway. Hardwood or recycled plastic treads were specified as these do not require treatment or maintenance.

Site Survey: No information on the site was available. ParaMatic used a Leica BLK360 to scan the site and obtain a point cloud. Before the scan, we identified and marked the most probably route using barrier tape and pegs and scanned this path. The Leica is small and portable and is easy to place in awkward positions. A typical scan takes 2-3 minutes and approximately 40 scans were made. The pointcloud and panoramic photographic detail allowed us to identify practically every surface and feature of the rock faces and digitise the routing for the stairway. No physical measurements were taken. Individual scans are composited to make up a single point cloud model of the site. All the decisions regarding final stair dimensions were made in the drawing office

Before installation, we returned to site with foundation drilling templates and marked the positions of each of the stair components for drilling of the holding down bolts. Using exposed rock surfaces wherever possible.

Cost and Speed: The owner’s budget for detailing was even lower than that of a standard structural steel frame supplied at standard fabrication rates. Detailing in Tekla allowed the model to be developed over the point cloud, eliminating the iterative testing which slows projects and delays detailing. Tekla Stuctures is especially powerful for detailing of special details and configurations and facilitated rerouting after the model was reviewed. Tekla produces consolidated bills of material which allowed us to quickly check that we were within our mass budget and provided detailed cutting lists and component drawing to ensure that the manufacturer was able to purchase accurate materials and bolts requirements and deliver precisely the detailers intent.

 After two days of scanning, we were able to produce the model and detail drawings within 10 days of drawing time

Installation:

What is most impressive about this project from a technical perspective?

The owner had originally anticipated that the finished material would be delivered by helicopter, owing to the remoteness of the site. By detailing accurate, finished sub-assemblies in small, portable, site bolted frames, the owner was able to eliminate helicopter transport and more importantly inspect prior to delivery and confirm that components met the required dimensions, reducing site corrections to a minimum.

ParaMatic were able to deliver on the promise of a purpose designed stairway with a limited budget quickly and effectively by importing a point cloud into the model. Traditionally, a point cloud is data heavy and is used to generate a model which is then used for further detailing. Tekla Structures systems architecture allows for modelling and viewing in realtime without delays and machine crashes.

How does this project demonstrate the benefits of steel as a material?

Steel is a perfect building element for elaborate builds – the ready availability of structural sections and the ability to bend and weld stock plate from the same material for a cost effective yet unique and hardy product. Joining and coating processes are simple and well understood and relatively simple. Further, steel allows for relatively simple site alterations and welding without significant quality compromise.

What is special/ unusual/ innovative/ aesthetic about the steelwork in this project?

Absolutely no measurements were taken on site and the modeller was totally reliant on the output of the scanner.

Usual practice is to visit site with a clipboard, camera and a tape measure. The nature of the site makes this impossible. Steep, loose slopes break up lines of sight and the only practical site solution without a scanner would have been to build modular frames and cut and weld them on site to suit the topography. While surveying has a role, the data returned by the surveyor has no “look and feel” and does not provide for determining better alternatives in the second round of design.

Using prefabricated frames changes the nature of the project, eliminating the need for boilermakers and welders to be given safe working plaftorms and converts the project into a simple erection sequence carried out by competent steel erectors.

It is unusual for handrails to be fully detailed and manufactured prior to delivery to site. Scannign made this possible.

How did the project team work together (e.g. contractor involved early, challenges/ ease of communication etc.)

The ParaMatic team visited the site with the Project Originator and Champion, employed by the Owner, and the project Engineer. On a cold, windy and wet day we marked out the best route with barrier tape and discussed alternatives. After the routing was finalised and agreed and paced out we scanned the route from cliff top to beach level. On returning to the offices, we prepared a first model which was forwarded to the client for comment and approval. Overlaying the model on the point cloud allowed all parties to visualise the routing and issue approval to continue. Without the scan of the site, we would have to rely on tape measure and photographs, normally problematic on a complex site. The scanner allowed us to plan around vegetation and decide when vegetation could be easily removed for later regrowth, again taking decisions up front which would have been referred to the field engineer during the construction.

Project motivation editorials are provided by the project nominator. If any technical details, company names or product names are incorrect, please notify the SAISC so that the error can be corrected.

PROJECT OVERVIEW
Physical address of the project Street Address Town Province De Hoop Nature Reserve, Bredasdorp, Western Cape
Google Maps link  
STRUCTURAL STEELWORK
Completion date of steelwork 31/03/2020
Completion date of full project 15/04/2020
Tonnage and steel profiles used 5.8 tons of Channels, Tubes and Platework
   

If you were a part of this project, and your company details are incorrect or missing – please notify the SAISC so that the error can be corrected.