Project Type
Project Team Zoom Interview Case Study
Project Summary Case Study
Steel Profiles Used
  • Date of Steelwork Completion
  • Tonnage
  • Tubes and Pipes
    Structural Tubes & Hollow Sections – Round
Metal Cladding and Roofing Overview
  • Date of Cladding Completion
  • Material Used
    Colorplus® AZ 150, Grade G550 (Safal Steel)
  • Other Materials Used
    The required climatic conditions within the completed building envelope dictated the roofing system to be used comprising a two layer sandwich configuration of 0,47 Widedek ceiling sheets , a 135mm Starlite Insulation blanket and 0,53 SAFLOK external weather sheeting.
  • Cladding Profile
    Saflok 700 - Concealed Fix (Safintra South Africa)
  • Cladding Tonnage
  • Cladding Area Coverage (m2)
Project Overview

The Mpumalanga International Fresh Produce Market is perfectly located within the luscious Lowveld as
catalyst to stimulate growth in the agricultural sector, create a significant number of job opportunities,
create scope for the establishment of downstream business and act as an important tool to fight food
The design of this modern facility addresses the needs of the modern food industry and is designed to
operate more effectively and efficiently than existing, traditional fresh produce markets. The entire
project consists of 17 buildings; each playing an integral part of the market operations. In order to achieve
the design requirements, improvements were made to the physical infrastructure layout, the building
structures and in turn affecting the operations and management of this ‘market of the future’.

True to the saying: “Form follows function”, the design of the main market building has been designed to accommodate the most flexible market operations according to the current requirements, but also for possible future alterations and expansion to these operations.

Three dimensional tri-angular tubular arch trusses spanning 220m in length with two rows of support columns spaced at 68m in between, grants the operator the required flexibility to position cold rooms, racking and set out the most productive operational equipment layouts. The side end supports for these trusses in the form of supporting concrete portal frames were integrated in the design of the building to accommodate mechanical equipment and forms the support structure for the insulated panel envelope of the building that houses insulated sectional doors that open
onto the side platforms. Translucent modular sheeting to the southern sides of these concrete portal gables allow for natural light to enter the building without excessive heat transmission. The roof sheeting consists of a sandwich panel of 135mm insulated material with sheeting to the top and bottom to maximize temperature control within the building.

The market layout was designed to accommodate for future expansion by extruding the roof design to the back. Current grid line numbering runs numeric from the top to bottom to ease and consolidate future design extensions with the current design. Sail material roofing at the back of the building connects lightly with the back end gable that will also allow flexibility for future expansion.

If you are an SAISC Member, and your company was involved with this project, please notify Reubenett Andrews (011) 726 6111.

Project Details
From the very outset it was realised that to manufacture a roof of this size with the Main Structural members being 3,6m toblerone trusses of welded construction and then deliver them to Nelspruit was going to be an extremely expensive transport exercise and would not make economic sense and thus the decision to make the entire structure piece small was taken very early during the tender preparation phase. The idea of manufacturing 33 number similar toblerone trusses each being 70m long and 3,6m in size made up of piece small components required some innovative thinking with respect to how one would make suitable jigs to ensure that all the components would fit together correctly when it came to assembling them on site. A huge amount of time was dedicated to this challenge during the detailing process and the design and detailing of the jigs was integral to that process.
The required climatic conditions within the completed building envelope dictated the roofing system to be used comprising a two layer sandwich configuration of 0,47 Widedek ceiling sheets , a 135mm Starlite Insulation blanket and 0,53 SAFLOK external weather sheeting. The roof is split into three equal segments for sheeting separated by gutters with the 68m long SAFLOK roof sheets being rolled on site and pushed up a scaffold ramp onto the roof. The area of the roof is approximately 30,000m2 with a side cladding area of 6,200m2. The sides of the building are clad with 0,47 Widedek sheets with a 50mm layer of Lambdaboard for insulation. The Widedek ceiling sheets were installed in various lengths lapped over the purlins since they do not form part of the weather envelope. Doubler plates were introduced at all the toblerone truss connections to strengthen the walls of the truss chords against buckling but more importantly , from a fabrication point of view , it simplified the jigging of the chord members by enabling the connections to be fully fabricated in simplified jigs separate from the chords then added to the chords in a single line jig setup. Since the roof profile had such a large radius it was also decided , and agreed , to fabricate the trusses with segmented chords and the splice locations were carefully chosen to limit the number of different connection configurations in the truss segments. The roof consists of 11 trusses in its length , 3 truss spans over its width and 7 truss segments in each span which amounts to 231 truss segments all told. As such it was extremely important to ensure quite early in the fabrication process that when assembled the full trusses would provide the correct dimensional profile to accurately fit into the roof on site. Similarly the configuration of the support column / girder / truss intersection was incredibly complicated and the trial assembly of this section of the roof at the workshop was seen as being critical to the success of the Project. Assembly of the toblerone trusses on the site necessitated the provision of a number of assembly frames which had to be set out , lined and levelled to ensure the accurate assembly of each truss before hoisting. A major concern throughout the installation phase of the Project was that the holding down bolts at the two concrete abutments of the roof would talk to each other such that 210 meters of roof truss would fit snugly between the steel buttress frames once they were mounted on them. Even though accurate surveys were provided by the Main Contractor and we had allowed some tolerance in the buttress frames base plate holes it was not a given that with such a long length of steelwork we would end up with a perfect fit. As it turned out the building works were fit for purpose and the Main Contractor could be commended for a job well done. The trial assembly at the workshops proved invaluable to the installation on site. At 70 meters long tandem lifting was the order of the day.
The main challenge on this Project was the shear size of the roof structure and it’s structural framing system requiring a major consideration of how to transport it to the site 330 km’s away from the fabrication shop. This was overcome by detailing it as piece small allowing the transport loads to be maximised which then added further challenges as to how to fabricate it like a meccano set while ensuring all the pieces went together seamlessly. These challenges were overcome by careful consideration of the jigging systems that would be used for the fabrication of the components and then trial assembling the major structural components and interfaces between them.
Benefits of Steel in this Application

Structural Steel is the only construction material that could have been used to achieve such large scale open spaces under roof that were integral to the Architects vision for this development.
8 No internal columns for a 30,000m2 roof coverage is unprecedented.

With its high strength to weight characteristics and the ability to assemble such light weight elements of steel in a structural configuration that would enable such large span structures to be designed, makes it the ideal material.

The use of tubular sections further enhances the visual appeal of the roof structure let alone them being the most structurally competent sections.


Project team - "We envisaged a MECCANO set and made it work in this magnificent roof structure"