Timber bridges: where beauty and utility coincide

The Fremantle Traffic Bridge, photographed in 2022

I was on my bike yesterday, cycling down to Fremantle, and stopped for a breather under the old Traffic Bridge over the Swan River.

Built in 1939, almost entirely of jarrah piles and “rough-hewn” jarrah timbers, the bridge is 219 m long with 22 six-metre spans. It is one of the last great timber bridges in Western Australia, and may well be the last, as its demolition and replacement with a more modern structure was recently announced.

I nearly always stop under the bridge when I am cycling along my favourite route around the river. It provides a shady and restful spot on a summer day, but also gives me an opportunity to admire the lovely work of the old bridge carpenters, especially the broad-axemen, and the well-recognised structure of piles, stays, stringers, corbels, walings, decking and railings.

Compared with most people (I suppose), I am familiar with the arcane terminology describing the components of a timber bridge. This is because when I was at Forestry School many years ago, we studied timber engineering. One of the most interesting parts of the course was learning how to design timber bridges of various size and capacity, the largest of which needed to be capable of carrying (at least) a bulldozer on a low loader, or a log truck carrying massive hardwood logs. Our textbook was called The Australian Timber Engineering Design Handbook (I still have my copy, sixty years-on); it is a mine of information about the strength and durability of Australian timbers, and contains pages of complicated tables and nomographs. These we used to calculate the load-bearing capacity of different bridge timbers, dimensions and designs.

As it turned out, I never actually used all this stuff to design and construct an actual bridge, but I remember the satisfaction of doing the calculations and coming up with a design (on paper) for a wonderful timber bridge. In my imagination it would span some swiftly-flowing river and looked something like The Bridge Over the River Kwai, and would be capable of carrying a locomotive and a rake of enormous karri logs.

Reflecting on this, I suddenly remembered a story of my father’s which concerned someone who did become professionally immersed in the art and science of building timber bridges.

When Dad was a young man he had a particular friend, a contemporary at university in the 1920s, who graduated in civil engineering at the same time Dad graduated in Agricultural Science. After his graduation, his friend was appointed to the position of Junior Engineer with the government’s Main Roads Department, and was posted to Bunbury. A few months later, he told Dad this story:

I had only been on the job for a week or two when The Boss, the Regional Engineer, called me in and gave me my first big assignment: to design a timber bridge over [he named the creek] on a relatively important rural road. He specified the length and width of the bridge and the potential load the bridge would carry. I was proud to be given this task and set about putting into practice all the theory I had learned in my engineering studies at university: the type of timber to be used, the dimensions of each component, the load-bearing capacity, modulus of rupture, and so on. I consulted the timber engineering tables and the MRD manuals and guidelines, did the calculations.... and finally came up with a beautiful design. It met all the specifications to a T.

Proudly I took it in to show the Boss.

The Regional Engineer mulled over the design, double-checked the calculations and assumptions, reworked them, and double-checked the double-checks, and then sat back and smiled. “You’ve got it exactly right, son” he said “Well done .... but just to make sure, I think we’ll double everything”.

Dad’s friend said this was his first glimpse into the real world of civil engineering as practiced by a grizzled old public servant who knew how to cover his backside, as opposed to the theoretical world in academia.

When I began my forestry career n the early 1960s, Western Australian foresters were still building roads, especially in the karri country where many of the more remote State forests were still completely inaccessible. Any road in this high-rainfall country inevitably required bridges and culverts. Mostly we did the job “on the cheap” because budgets were tight. The department could not afford to buy steel girders or concrete pipes, so river and creek crossings always involved building timber culverts and bridges, and making use of material available, and free, on the site.

Compared to the work of the Main Roads Department the so-called “forestry bridges” were of a fairly simple design, usually comprising a pair of bedlogs sunk into the river bank at each end, and two, or sometimes three log joists (called stringers) across the span. A broadaxe was used to square the stringers on one side (this became the top of the stringer) and they were “spotted” at each end so that they could be neatly seated onto the bedlogs. Once the basic structure was in place, heavy timber decking purchased from a local sawmill was spiked into the stringers. Thee spikes were called ‘Cooks Nails’. A brace and bit was used to drill the hole, and then the spike was driven home with a sledge hammer. Apart from providing a smooth surface, the decking also performed the important function of spreading the load in case a stringer failed. If they could be obtained for nothing as off-cuts from the local sawmill, running planks would be nailed across the decking, from one end of the bridge to the other.

Traditional forestry bridges never had safety rails, not in my experience anyway, but the final act after construction was completed was to plant a pair of guide posts at both ends of the bridge. Sometimes these were even painted white.

The Forester’s Manual (every field officer’s bible) contained a section on bridge construction and a blueprint for a standard bridge. I didn’t ever see this blueprint being consulted in the field. Perhaps by my day the technology and methodology was so well known that every forest officer could do it by memory.

During the 1950s a variation on the traditional forestry bridge was invented by forester Phil Shedley. This was called the All-Stringer Bridge, which had five or six stringers, squared on three sides, pinned side-by-side with long iron rods driven through pre-bored holes. There was no decking. The two great advantages of the All-stringer bridge was that the timber was available free, close to the bridge site, and there was no need to spend precious funds on the purchase of timber decking from a local sawmill.

Miraculously, the first-ever All-stringer Bridge, built by Phil Shedley over the upper reaches of the Weld River in 1953, still survives … although it is no longer used:

The first All-stringer Bridge (photograph by Ray Flanagan)

One of the last All-stringer bridges was constructed across the Frankland River at Caldyanup in the late 1970s. This was what was known as a “low-level crossing” deliberately designed to be submerged by winter floods, but so well locked into the rocky abutments, and so well spiked together, that it survived.

An all-stringer bridge across the Frankland River at Caldyanup.

(Photo courtesy of John Sclater)

All-stringer bridges were cheap and relatively easy to build (spiking the logs together was the hard part), but because they were usually built of marri, they did not last well, and today there are almost none still in existence.

Jarrah or wandoo timber was always specified for forestry bridges. Karri was too prone to infestation with termites, while marri was deemed too likely to catch fire and burn away; no doubt the reason for the steady disappearance of All-stringer bridges over the years.

But irrespective of the type of timber used, forestry bridges were always built on the old Main Roads Department principle of “double-everything”. In other words, they were massively over-designed. But this was not always the case with some of the earlier constructions, built during horse-and-cart days when the builders did not anticipate the size and weight of future traffic.

There is a good story illustrating this. It concerns ‘Black Dave’ Hughan, who for many years was the Bush Boss in the Millar’s timber operations in the karri country. Black Dave was an experienced bushman, and a man of few words. His logging crew was shifting to a new felling area one day, and the shortest route was across an ancient forestry bridge over the steep gully of a winter creek. The creek was dry at the time but the driver of the massive D7 logging dozer didn’t like the look of the old bridge and refused to drive his machine across. Black Dave had driven bulldozers in PNG during the war, as a member of the Army’s Forestry Company, constructing airfields, roads and bridges while being bombed by the Japanese. He knew no fear.

“I’ll test it” he said, jumped onto the dozer and started off across the bridge. Half-way over the entire structure collapsed. After the dust and racket subsided, Black Dave emerged, dusting himself down as he clambered back up to the road.

“That tested the bastard” was all he said.

Corporal Dave Hughan, at the helm of a logging tractor in PNG during the War (picture courtesy of Jack Bradshaw)

Sadly, the end of the timber bridge in Western Australia is nigh. The Main Roads Department now use steel and concrete, and “forestry bridges” (the term itself is an anachronism) in the southern forests are more likely to be pulled out and replaced by concrete culvert pipes than to be repaired or newly constructed. Opposition to timber cutting by environmentalists has made it almost impossible to source the timber, and the closure of the timber industry and decline in forest management has resulted in the decimation of skilled timber and forestry workers.

This is a shame from several points of view. The timber bridge is part of the heritage of Western Australian engineering. In the case of the great wooden bridges built of jarrah by Main Roads and Public Works departments, bridge design and construction was both a science and an art. It involved calculation of loads, knowledge of the strength and durability of timber and of the laws of architecture. Even the beautiful draftsmanship of the bridge blueprints could be admired as artwork in their own right. When it came to construction, specialised skills were required, and although the work was basically done by “bush carpenters” working with axe, broadaxe, block and tackle, crowbar, brace and bit, mawl and adze, the outcome was nearly always a thing of beauty, with every baulk and strut fitted to perfection. The timber bridge was a symbol of the old-fashioned workmanship of timber workers who took an immense, but quiet pride in their work.

What could be prettier than the Gilgering Bridge over the Avon River, built entirely by hand and of jarrah timber and hand-forged iron bolts, here seen just after completion in 1897:

The Gilgering Bridge over the Avon River

I cannot leave the subject of timber bridges without touching on the wonderful railway bridges built on the logging railways in the jarrah and karri forests over the years, especially before World War II. These were not designed or constructed by professional engineers, but were the work of the bush workers and navvy gangs who built the narrow gauge bush railways that carried steam locomotives pulling rakes of massive logs. In the years before the war (before tractors and chainsaws became available) all of this work was done “by hand”. There were no machines … simply horse or bullock teams, block and tackle, spirit level and boning rods, the axe, the adze, the broadaxe and the brace and bit. Apart from their resourcefulness, bush carpentry skills and physical strength, the men who built these wonderful bridges had considerable courage – it was often dangerous as well as difficult work.

I often think about the famous old logging railway along the Donnelly River west of Manjimup, built in the 1930s. In one section of the line there were 12 trestle bridges in nine km of line. Regrettably today only the remnants survive, but we are lucky that photographs were sometimes taken of these remarkable achievements.

A trestle bridge over the Warren River on the Quinninup-Jardee line

(Photo by Jack Bradshaw)

The navvies who built these bridges had skills of the highest order. In some cases, the trestle bridges were actually curved to accommodate curves in the railway line as it wound its way along the bank of a river, but they were constructed in perfect harmony and alignment with the railway formation. They may have looked flimsy, but they could carry hundreds of tons of locomotive and logs, and were robust enough to withstand winter floods. Their only real enemy was forest fire, and it was fire, in the end, that ended the life of most of them.

While I regard the end of the era of timber bridges as a tragedy, I will conclude with a glimpse into a real tragedy. It makes a good epitaph for this story.

There is a forestry bridge over the Dombakup Brook on the old road from the Brockman homestead to their cattle lease on the coast. The bridge is just above a deep pool in the brook. It is a spot to avoid on a misty winter evening when the late sun is slanting through the karri trees and the wind is in the river oaks. The pool is haunted.

Down the road a mile or two, where today the pines and blue gums tower over the bracken in former farm paddocks, were once the most remote of the Group Settlement blocks, coming out west of Northcliffe. Settled in the 1920s, under the most unfavourable conditions, the first settlers suffered great privations. Not being able to make ends meet, one young settler left home to try to make money in the Goldfields, leaving behind his wife and two children. He promised to be back in a year.

The year came and went and he did not return. So, in despair, the young woman walked to the pool in the Dombakup Brook and drowned herself and her children. Two days later, the young man returned. He had been delayed by bad weather and boggy roads.

It is said that the ghosts of the young woman and her children can still occasionally be seen in the mist that swirls around the pool on a winter evening, and the winds in the sheoaks speak of sorrows and regrets.

I know that pool and that bridge. Although the original bridge was replaced by a fine new one in the 1960s, the scene and the atmosphere is unchanged. I was there and watched the new bridge being built by the incomparable forestry overseer Ted Loud and his gang of forest workmen. It was Ted who told me that story.