CONCRETE/STEEL vs STEEL-ONLY WEIGHBRIDGES

Which is better, a combination of concrete and steel or steel-only weighbridges? What follows is a discussion that highlights the pros and cons of both.

Introduction

Steel-only weighbridges are gaining a larger and larger foothold in Australia. But are they superior to the traditional concrete and steel weighbridges? As separate construction materials, both concrete and steel are remarkable, which is why they are extensively used in our society. Concrete is excellent in compression (a squeezing force) but weak in tension (a bending force). Steel, on the other hand is both excellent in compression and tension.

To improve the tensile (bending) strength of concrete, steel reinforcement is placed inside concrete slabs (prior to pouring). The two materials form an excellent bond and act as one, thus making the concrete slab both excellent in compression and excellent in tension.

While this brief introduction appears to favour steel, bare in mind that steel is stronger kilogram for kilogram. But steel-only weighbridges do not use the same mass as that of concrete and steel weighbridges. So the question is not, "Is steel superior to concrete?", because in may cases it is. The question should be, "Does a steel-only weighbridge use a sufficient amount of steel to make it superior?"

Both types of weighbridges have advantages and disadvantages, and these are expanded upon below.

Steel-Only Weighbridges


Advantages
+ Long-Lasting Surfaces (Provided the Surfaces are Treated) Galvanised or well painted steel is very hard-wearing. Kilogram for kilogram, steel is stronger than concrete. Even when the surface coating is damaged, steel forms a skin a rust which prevents further corrosion.
+ Fast and Easier to Install Steel decks are usually fabricated in smaller modules and these modules are joined together to form the complete deck. The modules are easy to manipulate with a crane and easy to transport.
+ Easier to Relocate Light and small modules are easy to manipulate with a crane and easy to transport. The concrete foundation is obsolete, however.
+ Generally Less Expensive Option Steel-only decks are generally less expensive but this obviously depends on the amount of steel used. More steel makes a deck stronger but requires more fabrication labour to weld steel pieces together.

Disadvantages
- Quantity of Steel used Must Be Questioned Because the top of steel decks are covered in floor plate, it is difficult to ascertain just how much structural steel is used to fabricate the steel-only deck. A general indication is the price of the deck. The lower the price, the less steel that is used.
- Lighter Structure Means More Severe Movements on the Loadcells A steel deck is a lot lighter than a reinforced concrete deck. The deck therefore moves more vigorously as vehicles enter and exit the weighbridge which causes more severe rocking movements and may compromise the longevity of other weighing components.
- Steel Expands More with Heat Both concrete/steel and steel-only weighbridges expand with the heat from the sun. Steel-only weighbridges expand more which means a larger buffer gap is required allowing loadcells a greater range of rocking movement. Loadcells, especially end loadcells, are also forced on to greater angles with the expansion, introducing greater off-centre loading.

There has been a trend throughout Australian weighbridge manufacturers to cut costs by reducing the amount of steel used in both steel-only and concrete and steel weighbridges. This obviously weakens the overall strength of the weighbridge and reduces its working life. QWM has resisted this trend due to the fact that we have built our reputation on supplying heavy-duty, quality weighbridges.

Another consideration not often thought of is the source of the steel used to fabricate the steel-only weighbridge. The majority of steel-only weighbridge decks are imported from Asia and are fabricated with Asian structural steel, which is inferior to Australian structural steel. These Asian imports will also have future ramifications on our economy and work force as less Australian steel is purchased. QWM does provide the option of steel-only decks to our customers but supplies Australian-made steel decks using Australian structural steel only.

The key point with steel-only decks is, "How much steel is used to fabricate them?" Weighbridge designs should include an overload factor of 30% above that which is intended from day-to-day operations. With minimal steel in some steel-only designs, especially with Asian imports, the expected life span of these decks must surely be less than those expected for concrete and steel weighbridge decks. This coupled with expected reduced loadcell life spans due to expected additional movements and stresses suggests that steel-only weighbridges are a medium-term structure, not long-term as some suggest.

Beware the pricing. The cheaper the price, the inferior the product. If fabricated well and with a solid, proven design, a steel-only deck will not necessarily be cheaper than a concrete and steel weighbridge.

Concrete and Steel Weighbridges


Advantages
+ Long-Lasting Surfaces (Provided the Concrete is Prepared Correctly) Provided the concrete is prepared correctly (vibrated and cured and steel reinforcement is positioned correctly) concrete is a very durable product with hard-wearing surfaces.
+ Heavier Structure Resists Severe Deck Movements The mass of the deck is significantly more than a steel-only weighbridge and this mass resists movement as a vehicle enters or exits the weighbridge. This minimises rocking of the loadcells.
+ Less Expansion with Heat While the concrete and steel weighbridge does use steel main beams and cross pieces and therefore will expand with heat, this movement is far less than a steel-only weighbridge. This minimises loadcell off-centre loading.
+ More Confidence in the Structural Integrity While concrete and steel weighbridges are not immune to structural failure, past experience confirms that concrete and steel weighbridges are a longer-lasting product

Disadvantages
- Longer Installation Process Both steel-only and concrete and steel weighbridges require a concrete foundation. Concrete requires atleast two weeks to cure to a suitable strength to allow the deck construction on it. Concrete and steel decks then require a second curing period whereas steel-only weighbridges do not.
- More Difficult to Relocate Concrete and steel weighbridge decks are very heavy and typically larger than small, steel-only modules. Relocation is therefore slower and more costlier.
- Generally More Expensive With the trend towards minimal steel in steel-only weighbridges, concrete and steel weighbridges are generally more expensive. If a steel-only deck is designed with sufficient steel, however, there should not be a large difference in pricing between the two types.

QWM has been installing and servicing weighbridges for 50 years. The majority of our installations over that time have been concrete and steel deck weighbridges, although we have designed and installed a number of steel-only weighbridges for customers that stipulated this product (perhaps for weighbridges that will regularly be relocated). It should be noted that these steel-only designs would not resemble today's low-profile, modular steel-only weighbridge decks. Many of these past designs were built solidly, in line with our reputation for installing long-lasting, well-engineered designs. In those 50 years, we have seen how our weighbridge designs stand up to the test of time and how others' designs fare aswell. QWM believes that concrete and steel weighbridge deck designs fare best over time. Steel-only decks, even when fabricated well, would seem to degrade quicker through weather and every-day use than concrete and steel decks. This suggests that concrete and steel weighbridges are truly a long-term structure.

What is Best, Concrete and Steel or Steel-Only?

While QWM has built its reputation on supplying solid and heavy-duty weighbridge designs, we also must compete in an ever-changing weighbridge manufacturing market. As we always have, we offer both concrete and steel weighbridges and steel-only weighbridges. In line with the trend towards lighter, modular steel-only weighbridges, we offer an Australian designed and built steel-only weighbridge deck, fabricated with Australian-only structural steel and also imported, low cost designs suitable only for specific markets.

Our view is that the lighter, steel-only weighbridge decks (together with their expected loadcell replacement schedule) represent a medium-term asset, which could be ideal for sites that do not have a long-term life-expectancy or that do not expect heavy weighbridge traffic. A concrete and steel weighbridge represents a long-term asset which is ideal for permanent installations or heavy traffic sites.