Industrial Buildings

A safer and better working environment for industrial buildings

The advantage for study found a number of drivers for change; cost, sustainability; fire resistance and security.

Any alternative to steel portal frames would have to not only be of comparative cost but also offer better programme times and be an architecturally attractive option for designers and structurally have the ability to be easily used with non-concrete components. In addition, the structural solution should have widely available components and resources from competitive specialists.

Taking all of the above into consideration, the best alternative solution to steel portal frames is a concrete load-bearing wall with a lightweight roof. This is a very straightforward design and construction approach that can be easily adapted.  The load-bearing walls can be either propped or cantilevered. For the propped wall, the stability comes initially from push-pull props. When the roof is complete the props are removed as the roof then provides the propping force and takes the horizontal loads back to the flank walls. For the cantilevered option, the walls cantilever from the base and do not need any propping or reliance on the on the roof for stability. However, these walls do need to be thicker than propped walls.

Both wall options offer the same range of benefits that are of particular value for this market:

• They are structurally multi-functional in that they carry the vertical load and provide all the longitudinal bracing
• They provide, without additional cost, thermal efficiency, fire resistance and security
• They do not have intrusive columns that can account for up to 5% of space in portal frame sheds
• They can be used with many types of roof structures
• They can be produced off-site or on-site with all the chosen finishes fixed in place prior to erection thus improving quality, site safety and construction speed
• They offer high levels of air-tightness, notoriously difficult with steel portal frames due to the multitude of metal joints
• When cast on site using locally-produced ready-mix concrete they reduce the CO2 emissions associated with transportation
• They use reinforcing steel which is made from 100% recycled material.

STEEL OR CONCRETE?
The increased steel price there has already brought a noticeable increase in the use of concrete columns in warehouses.
The cost of concrete columns is about half the cost of steel columns. Many consultants still design  warehouses in the traditional way, in steel, mainly because that is what they are familiar with.

CLIENTS’ WAREHOUSE REQUIREMENTS
 The requirements of warehousing for clients has become more specific i.e. security, fire resistance, insulation, appearance and durability(in coastal conditions).
The clients that we are targeting are the likes of Nestle, Clicks and Hirsch group.

PRECAST
In order to effectively compete for market share against steel, it is necessary to consider  precast concrete elements, formed and constructed on site and on the ground.
Concrete would have the advantage over steel in that the concrete elements (walls, columns, beams, trusses and slabs) can be constructed in situ on site or precast on the ground and lifted into their final position on site, as opposed to steel that has to be prefabricated in a workshop then transported to site and erected into position.
When forming a precast concrete element on the ground, the ground slab forms the majority of the formwork. The vertical formwork height would be the thickness of the section of the element. Consider a concrete column 20 m high  constructed in situ as opposed to forming and constructing it on the ground and the lifting it into position with a crane.    
Concrete can compete favourably against steel with all elements in warehouses, except the roof sheeting (unless security is a critical issue)

The foundations for concrete will be heavier than for a normal portal frame solution. However, the loading on the ground will be a line load from the walls rather than point loads from columns. This would simplify the foundations. For cantilever walls the foundations will most likely have to be piled as would the propped wall option if the ground capacity is low or the shed walls are high.

The cladding can be whatever is required. A major benefit of using concrete walls is that if a masonry or concrete finish is required then this could be incorporated into the manufacture of the inner skin. Both skins can be lifted into position in one operation thereby saving construction time.

The construction of the roof is also simplified with concrete walls as, unlike with steel portal frames, the roof beams are simply supported on the walls. The spacing of the roof beams could be optimised as they would not be reliant on the portal frame spacing. Roofs may be light or heavyweight. A heavyweight roof would provide extra thermal insulation and mass.

With all their benefits, it is surprising that the use of concrete walls for industrial sheds is not widespread in South Africa as it is throughout Continental Europe. One of the main reasons for this may simply be inertia. The continued rise in steel prices and the development of a viable concrete option will do much to address this. The Cement & Concrete Institute plans to work with the concrete industry partners such as Tilt up Charles Van Eck, the concrete contractors group, and product manufacturers to facilitate the availability of a real alternative to the tin shed.