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Precast Manufacturing of Stadium Bleachers for University of Botswana Stadium Project

During October 2010, China Jiangsu placed an order with Rocla for the manufacture of 335 stadium bleacher products to be used at the University of Botswana’s new stadium project. China Jiangsu had been awarded the contract for construction of the complete stadium, but constraints in terms of the physical space available on site had a significant negative impact on the viability of in-situ casting of the stadium’s seating. Arup, the consultants on the project, therefore specified that the bleachers should be precast.

Stadium BleacherExperience from many requests for specialized precast members over the last decade has made it clear to Rocla that the South African construction industry is often hesitant to consider precast construction elements as a viable alternative to in-situ. It appears as though clients, consultants and contractors alike are not willing to risk having a large portion of work outsourced as this would reduce their ability to manage the overall project risk. This fear is mostly a function of inexperience in the successful utilization of precast as a means of fast tracking a project and improving the quality of products.

 

Due to a lack of general acceptance in the industry, and therefore also inexperience on behalf of the client, (consultant, contractor or the entity paying for a project), to foresee all the possible problems in the process, the precast manufacturer generally takes huge risks in completing the manufacture and supply of the precast members.

The best way for a precast manufacturer to negotiate its way around these risks is by participating in the planning of projects from as soon as the inception phase. Unfortunately this is not always possible as the decision to consider precast very often arises only once a project is already ‘running late’. In such cases many hasty decisions are often made in terms of weighing up quality against cost and the time available. These hasty decisions can and do result in miscommunication, additional expenses generally incurred by the pre-caster and discontent from the client.

Stadium BleacherWith the University of Botswana’s stadium project the availability of physical space implied that the decision towards precast was taken much earlier in the project timeline. In this case Rocla was therefore able to participate in the discussion and design process between Arup and China Jiangsu and thereby reduce the risks associated with technical aspects, handling, transportation, delivery deadlines and the eventual placement of the product by the client.

The constraints that were placed on manufacturing of the products, which distinguished the project in terms of difficulty, were the following:
The bleachers of a stadium form the most visible part of the structure as people actually sit on these members and are thus able to touch and inspect them at close range. The first and foremost specification of the precast members was therefore that the finish should be of immaculate quality. This implied that products were to be cast upside down in order to obtain an off-shutter finish to all visible surfaces. By implication the products therefore had to be manufactured in such a way as to allow for turning of the finished product without compromising safety or the appearance of visible surfaces. This called for discussion between the precast manufacturer, the consultant and the contractor. Eventually the products were turned in the precast yard and delivered to site in the correct orientation so as to minimise the risk that the site’s relatively uncontrolled environment would pose. No lost time injuries were experienced.
Secondly, the design called for 85 variations of the product, which implied that the mould design had to allow for adjustability. Moreover, the availability of physical space on site necessitated the orderly delivery of products so as to allow placement to follow suit. The moulds were therefore designed to accommodate frequent upward and downward dimensional changes.
Rocla opted to have the products manufactured at its Roodepoort factory in order that the manufacturing process could be monitored closely. The result of this strategic decision was that products had to be transported 380km to be delivered in Gaborone.
Final delivery of the bleacher products occurred towards the end of July 2011 with a total delivered mass of product of 945 tons. Today, the stadium is complete and in use. Products were delivered within the agreed upon time frame and the quality thereof was and still is superb.

Manufacturing of Specialised Counterweight Products at Limpopo Power Stations

In June of 2010 Murray & Roberts Projects approached Rocla to investigate the manufacture of three sets of 16 customised crane counterweighs. These were required for cranes operating at both the Medupi and Kusile projects.

counterweightThe Medupi Power station’s two main contracts had been awarded to Hitachi of Japan and Alstom (renamed ACTOM in 2009). The boiler contract was awarded to Hitachi Power and to the joint venture partner Hitachi Power Europe. Construction work and pressure part manufacture was awarded to Hitachi Power partnered with Murray and Roberts and DB Thermal.

Hitachi Power had specified the exclusive use of Wolff Cranes on site for this construction contract. Wolff Cranes, a German manufacturer, had implied that the cranes and all their equipment (i.e. the counterweights) would have to be imported from Germany. As shipping cost is a direct relation to mass, it therefore made sense to try and manufacture these counterweights locally, whilst ensuring adherence to the strict requirements laid down by Wolff Cranes. These cranes had an approximate unit cost of 1mil euro so attention to every detail was critical. The manufacturing process would have to conform to strict mass and dimensional tolerance requirements in accordance with Wolfff Cranes’ German manufacturing standards.

counterweightAfter negotiations and assurances from Rocla, Murray & Roberts opted to partner with us for the manufacture of these counterweights, content that we were up to the task. The risk to us was relatively high as products would weigh between five and eight tons each, so scrapping of products could thus prove to be exceptionally costly, especially as sign off of the products would imply flying a German Engineer to the manufacturing facility for inspection.

Critical aspects that had to be considered with the project :

The fact that Wolfff Cranes is based in Germany implied that numerous translational issues had to be resolved. The first of these had been to confirm that German specifications correlate with that of South Africa. This would be critical towards the final sign off of products.

We all eventually agreed upon specifications that included a dimensional degree of accuracy 1 and an allowable tolerance of ±2% in terms of mass. As the tolerance on mass is never really a consideration with standard precast elements, Rocla had to re-evaluate its processes to ensure that this tolerance could be met. The manufacturing process was therefore monitored through trails and a strict quality process was implemented from inception through to completion. The project team performed numerous tests on the proposed concrete mix design throughout to ensure that the desired density was consistently obtained. The mass of the finished products was then tested by a third party before final approval of the counterweights by Wolfff Crane’s installation engineers.

Another issue that emerged during the planning stages of the project was that German aggregates were found to have lower typical unit masses when compared to that of Southern Africa. This implied that a special mix design, which utilises the relatively low specific density of granite, had to be used in order to better obtain the size and mass requirements set out in the specifications.

In modelling the products, it became apparent that Wolfff Cranes made use of voids, cast into the concrete, to accurately obtain the required counterweight masses. This was due to fluctuation of volume to mass ratios of the various products. Whilst some of the products fell within the allowable tolerance with regards to mass, others, using the same concrete, were found to fail in this regard. This anomaly was overcome by casting voids into some of the products’ centres of gravity, assessing the final product mass and then filling these voids with different quantities of concrete and/or polystyrene, as required, in order to achieve final mass within tolerance.

Wolfff Cranes’ specification also required that all of the counterweight blocks be manufactured with cast-in galvanised lifting hooks and handling elements. These were all manufactured in house and sent out for galvanising.

Manufacturing of the products eventually started towards the end of October 2010, and continued until the end of March 2011. In this time Rocla manufactured a total of 48 products for this project with a combined mass of 370 tons. Wolfff Cranes eventually approved the products at the first inspection and Rocla was able to deliver on time and within specification.

By manufacturing the products at our plant, we not only created job opportunities for local residents, but also demonstrated that we have the capability to manufacture custom products to stringent international standards.

Concrete Shutter Project: Ingula Pumped Storage Scheme

Towards the middle of 2011 Rocla was approached by CMI-JV to manufacture precast concrete shutters for the main underground works of the Ingula Pumped Storage Scheme near Ladysmith. These concrete shutters would be used to form the outer permanent skin for construction of columns and beams in an underground pump station eliminating the requirement for any formwork. The scheme will eventually be used to generate hydroelectricity during peak demand periods of the day. Excess power on the grid generated by conventional coal and nuclear plants at night, will be used to pump water to the upper reservoir, ready for the following day peak requirements.

Concrete ShutterJoint venture partners of CMC, Impregilo group and PGMavundla were awarded the project on a design and construct basis and would therefore perform the task of both consultant and main contractor on the job.

Complexities on the project included the following:
Both CMC and Impregilo are Italian based companies. Communication and ease of reference to standard specification was somewhat difficult.
The total project will comprise a total of 552 units made up of 38 variations of three product cross sectional shapes. Moulds therefore had to be modular in order to accommodate these various shapes.
The specified allowable tolerances on products were very tight to allow for the correct positioning of rebar on site. This, coupled with the fact that the wall thicknesses of the shutters were designed at only 70mm with the longest unit spanning in excess of 11.0m, would require a very high standard of workmanship with the manufacturing of moulds.
Also in fitting with the above requirements, Rocla had to fine tune and maintain a very specific concrete mix design to allow for the required finish as well as successful handling of these very large elements. Details on the products included inverse cut-outs, positioning holes, male and female joints throughout and blind lifting holes.
The project is estimated at a total mass of approximately 1,200 tons and will be completed by mid 2012.

Precast Concrete Mine Liners for Botswana

During November of 2011 Redpath Mining approached Kwena Rocla in Botswana, part of the Rocla group, for the manufacture and delivery of highly specialized, bespoke precast concrete tunnel liner products for a project at Maun Mine in Northern Botswana.

Mine LinerRedpath (South Africa) Pty Ltd, the contractor, had obtained sample moulds and patent rights for the products from an Irish precast company. Due to the costs associated with importing of these moulds, a strategic decision was made to appoint Rocla to also manufacture the moulds locally, to the licensor’s design and strict specifications.

The final decision was for the products to be manufactured at Rocla’s Botswana facility, with the mould manufacture assigned to Rocla’s Roodepoort facility to project manage. This included work both in-house and at external sub-contractors :
Rocla had to ensure that mould drawings presented to the various internal and external mould manufacturers would render functional and financially viable moulds. Budgetary constraints forced us to consider various different options for the manufacturing of these moulds, thus stretching the imagination of Rocla’s technical team. Eventually, the decision was made to manufacture moulds made of concrete to the specification of the Irish company rather than taking Rocla’s typical route of steel moulds. Rocla’s in-house facility, capable of manufacturing these moulds, proved to be invaluable.
This new concept of actually manufacturing concrete moulds required a significant internal project management effort. The project therefore required a significant amount of versatility within Rocla.
This tunnel liner project definitely set a new benchmark in terms of complexity for bespoke products within Rocla. The amount of technical and administrative issues that had to be addressed in a short amount of time surpassed that of any previous project and it therefore taught the technical team a number of invaluable lessons.
The patented Irish shaft lining system consists of eleven segments that make up a full ring after assembly with each full ring having a length of 610mm. In order to complete the full length this shaft, Rocla must manufacture a total of 9300 segments with a total mass of 3,813 tons.

The actual contract period was initially 18 months, but Kwena Rocla was asked to produce all the units within a period of 8 months. The customer intends to install a further 8 shafts for the required infrastructure over the next 10 years.

The success of this project demonstrates our capability of producing specialist and customized precast concrete solutions. Rocla’s high level of technical expertise and experience with local materials and conditions made it ideally suited to the successful manufacture of these items.

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