Corruseal planned to build the new corrugated cardboard facility along similar lines to the facility it has in Cape Town. This Boksburg facility was planned to be a Phase 1 development with a view to adding to it at a later date.
This initial phase of the factory was built on a greenfield site and would cover an area of over 41 000m2 excluding the gatehouse. The factory required large minimally obstructed spaces to accommodate the production lines and to move materials. It was decided to have columns on a grid spacing of 25 x 13.5 metres throughout. The minimum clear height on the eaves of the production area was set at 9.0 metres. The clients brief included for 1.5 metre high roof monitors to incorporate translucent sheeting and smoke ventilation. Roof loading was required to support a future PV installation.
The project had a fast track construction program of some 6 months so the choice of a structural steel warehouse frame was the obvious choice. The detail of the roof configuration and type of columns was dictated by construction time pressures and practical constructability considerations.
A brief description of the structural framing
The main elements included 25 metre span trusses (or rafters) at 6.75 metre centres which were supported on girders spanning 13.5 metres. The internal footprint of the factory extended some 121 x 175 metres with no obstructing bracing in the production floor areas. All bracing was thus to be located in the perimeter walls. The lower portion of the perimeter walls were to have precast RC panels (varying between 1.5m and 2.1m high) with cladding above the precast walls to the eaves. Alternating translucent cladding strips were included in the vertical walls to suit the architects’ requirements.
The design of the 25 meter spanning elements compared lattice trusses versus cellular beam rafters. These elements also had to be fabricated with a 500 metre “top chord” radius to suit the roof profile. The trusses designed with a 1.5m depth (with continuity over the girder supports) proved to be a significantly more economical design. The trusses were designed with parallel chords and lacing. Sections selected were all various sizes of hot-rolled angles with gusset plates at node connections. The 500m radiused chord was easily achieved in this form.
Cold formed lipped channel purlins at 1.562m centres were required to support the sprung effect of the curved roof cladding. The truss bottom chord was braced with hot rolled angle knee braces bolted to the purlins.
The roof monitors stand 1.5 meters high x 6.75 metres wide (truss to truss). This sub-frame was constructed out of cold formed lipped channel sections (175 x 75 x 20 x 2.5) with knee bracing off the truss to control wind loading on the monitor.
The 13.5 metre spanning x 1.5 metre deep girders supporting every alternate truss were designed with hot-rolled channel sections on the top and bottom chords and hot rolled angles for the lacing. The selection of channel sections (with flat face horizontal) provided an efficient compression strut without requiring addition lateral bracing. The lacing was connected to the channels with welded gusset plates located on the channel centre line. The girders were designed to be continuous over the supports thus providing further economy of section weight.
Fabrication and erection
The main challenge on this project was the program.
In order to meet the required delivery dates the footprint of the roof structure was divided into a number of zones that matched the sequence that the structure was to be erected in and allowed for the envelope of the building to be closed in a phased manner. This ensured that all the steelwork in each zone was fabricated ready for delivery when required which allowed the installation to be completed and handed over for sheeting early in the program.
The erection process was also carefully looked at so as to pre-assemble as much of the steelwork onto the roof trusses at ground level before hoisting so as to minimise the installation of the smalls in the air which is always time consuming.
This method of construction thus allowed the follow-on contractors access to the enclosed structure at an early stage in the construction and enabled the savings on the program to be maximised.
The roof sheets were rolled directly onto the roof using a scaffold tower ramp and due to their length required the attendance of a large number of workmen to handle the sheets.
To control the effect of thermal expansion / contraction, the 175m roof cladding length was divided into thirds with the upstream sheet riding over the downstream sheet with a double purlin detail as advised by the cladding specialist sub-contractor.
The skylight roofs however have full length sheets 150m. long which was also decided by the cladding specialist sub-contractor.
How the project team worked together
This project was built with such speed and efficiency that it required a team of professionals, contractors and specialist subcontractors who had experience with similar projects. This experience is critical in order to plan and execute all the activities to merge towards the phased completion dates of the different component parts of the project. The 3D structural shop drawings were very professionally undertaken by an experienced and dedicated operator. This set the critical structural steel component of the project onto a winning footing.
How this project demonstrates the benefits of steel
The building of a roof structure of this size in the time that was allowed could have only been done in steel and shows that steel is the material of choice when it comes to factory and warehouse roofs. A curved roof of this size is really impressive when viewed from the outside and is a testament to what can be achieved with steelwork when suitable planning is employed.
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.
|Physical address of the project
|Cnr. Atlas & Commissioner Roads , Boksburg.|
|Google Maps link|
|Completion date of steelwork||September 2019|
|Completion date of full project||December 2019|
|Tonnage and steel profiles used||820 ton : Hot rolled columns , beams , angles , tubes , Cold rolled purlins & girts.|
|Project Team Role||Company|
|Nominator||TASS Engineering P/L|
|Client/ Developer||Corruseal Group|
|Structural Engineer||Kantey & Templer|
|Engineer||Kantey & Templer|
|Quantity Surveyor||Corruseal Group|
|Project Manager||Corruseal Group|
|Main Contractor||Abbeydale Construction|
|Steelwork Contractor||TASS Engineering P/L|
|Steel Erector||THLN Construction|
|Cladding Manufacturer||SAFAL Steel|
|Cladding Supplier||SAFINTRA South Africa (Pty) Ltd|
|Cladding Contractor||Tate & Nicholson|
|Paintwork Contractor||DRAM Industrial Painters|
|Photographer, Photo competition||Peter Hassall Photography|
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.
|CLADDING (If applicable)|
|Completion date of cladding||October 2019|
|Cladding profile/ type used||Roof : Saflok Zincal AZ150 / Sides : Widedek Colorplus AZ150|
|Cladding area coverage||Roof : 42,000m2 , Sides : 10,000m2|