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Farm Bridge System

Simple, low cost, robust farm bridges are required on almost every farm where there is a watercourse, channel, or creek. Here is the story of an innovative approach that produces a first rate solution.


Background

Dairy farm consolidation was gathering momentum in the early 1990's. As with much of the agricultural sector around Australia, the drive for larger economic units had become unstoppable, the consequence being that the small dairy farm was no longer "viable". Aggregation of small farms was a reality.

But there was an emerging problem. The smaller farm units were served by a network of irrigation channels that divided the properties. Drains had also been constructed throughout the channel network to convey seepage water and saline groundwater. 

The problem? How to get access across the channels and drains.


The First Call

Living in northern Victoria at the time, one day in May 1992 I was contacted by a dairy farmer to design a small bridge across an irrigation water supply channel. The farmer needed easier access between paddocks for his herd. I designed a conventional steel beam and timber deck bridge of sufficient width to allow a small tractor to pass over it.

Several months later, another dairy farmer called me for a solution to connect two properties that were bisected by a drainage channel. Because the farmer was expanding his dairy farm, and he wanted to be able to move stock and feed from one property to the next, the bridge had to be designed to support relatively high loads for a farm - in this case T44 design vehicle load. 

T44 is equivalent to 44 tonnes gross mass, represented in the sketch below by a prime mover (with a single front axle) and 96 kN/axle for tandem axles. 

                     

The other design issue at this site was the span. The bridge needed to traverse the open drain, and it had to support a range of loads.


A New Look At An Emerging Problem

At that time I realised that more dairy farmers would be confronted with a similar access problem. They would want a simple bridge system with high load carrying capacity, durability, ease of construction, and relatively low cost.

My research led me to an advertisement in a construction magazine about prestressed concrete floor slabs used in multi-storey buildings.

(Remember, this was in the days before the Internet and the World Wide Web in Australia).

After various inquiries of the manufacturer about the potential for using these floor slabs in a bridge situation, the solution was clear. 

Prestressed Hollow-core Concrete Slabs


The Design

Adapting these floor slabs for bridge purposes was relatively simple. The design produced a very strong and durable result, and the procedure consisted of:

  • initial site soil assessment
  • reinforced concrete pad footings
  • the hollow core slabs
  • anchorage to the footings
  • a topping slab to integrate each of the individual hollow core slabs
  • side rails or fencing
  • erosion control of the supporting embankments

The photo below shows the placement of the pre-stressed hollow core units of a typical bridge.


Bridge span 11 metres, width 3.6 metres


Many small bridges have been constructed of different widths and spans to suit the needs of the farmer. 

Widths are from 2.4m to 6.0m
Spans are from 8m to 13m

Go to FARM BRIDGE EXAMPLES and see photographs of many applications. 

Maximum length of the concrete slabs is 14 metres, so the maximum span that can be achieved is 13 metres.


Want Further Information?

Although these simple bridges have been designed for farms, they could also be suitable for creek crossings, local roads, walking trails, bike trails, and National Parks.

In the past several years I have received many inquiries from people and organisations seeking an appropriate access to, or on, their properties. Almost all the inquiries are about cost.

I have responded personally to each and every inquiry. To make better use of your and my time, here is now what to do.


Is your inquiry about a bridge to take heavy loads?

  • If your bridge site is in Victoria, go to Hollow Core Concrete and mention that you were directed to them by me, Des Menz.
  • If your bridge site is in Queensland or northern New South Wales, go to Precast Concrete and mention that you were directed to them by me, Des Menz.
  • If your bridge site is elsewhere in NSW, try either of the above sources.
  • If your bridge site is in South Australia, try Hollow Core Concrete.
  • If your bridge site is in Western Australia, there are several possible options. Search “hollow core concrete” and make your own inquiries. 

NOTE 
A limitation to making this bridge an economic proposition is distance from the factory. The concrete slabs in the bridge system described are manufactured in Queensland, Victoria, and Western Australia, and they used to be manufactured in New South Wales. If you are interested in this system, then your property would need to be within a few hours travel by truck from the factory, otherwise freight costs will be significant.


Is your inquiry about a bridge to take light loads, such as a car, farm ute, and tractor?

If your needs are for a lower cost and lesser load carrying capacity bridge then the Easy Fit might be your answer.

The Easy Fit is a D-I-Y solution, or it can be simply assembled by a contractor.


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