Lawrence Schäffler looks back on how the looming threat of WWII kick-started the development of the NZ Air Force’s infrastructure and how a shortage of reinforcing and structural steel demanded unusual designs during the construction of concrete runways and hangars at the Whenuapai and Ohakea air bases.
PLANS FOR CONCRETE runways and hangars at Whenuapai and Ohakea began in the late 1930s when the government decided to build new bases for heavy bombers. These aircraft would carry out pre-emptive strikes on enemy warships lurking too close to our shores.
At Whenuapai, for example, the grass runway lay on a 35 metre deep bog and wasn’t ideal for light planes – particularly in wet conditions – let alone bombers. Laying steel-reinforced runways, though, wasn’t an option. Reinforcing steel was in short supply and importing it from Britain was not only prohibitively expensive, it would also take some 15 to 20 months to arrive.
Despite these hurdles, the job was given to the then Public Works Department (PWD), and one of its civil engineers was the young Bob Norman. He later (1964) became a founding member of the NZ Prestressed Concrete Institute, and later still, its president.
“The only solution was a runway that didn’t use steel. Instead, PWD developed a design for a pattern of interlocking, hexagonal concrete blocks (3.5 metres across the flats) using tongue-and-groove joints.”
The hexagon block design was used at both bases. Ohakea received two runways – both 1500 metres long and 45 metres wide. Each comprised some 60,000 hexagons. Engineers’ notes (sourced from the NZ Air Force Museum) show that these runways consumed around 82,000 cubic yards of concrete.
Some 20,000 tonnes of cement was used, provided by Wilsons (Portland), Milburn (Otago) and Golden (Nelson), with smaller quantities from Australia and the US. Greywacke gravel from the nearby Rangitikei River was used for aggregate.
Each hexagonal block held 2.25 cubic yards. Forms were removed four to eight hours after pouring (depending on air temperature). Pouring proceeded continuously over 24 hours, with three shifts being worked. The best day’s output was 1313 cubic yards.
Three runways were built at Whenuapai. One is no longer in use, but remarkably, the other two are. Runway 03/21 (2031 metres long and 45 metres wide) was resealed with asphalt in the 1990s. Runway 08/26 (1581 metres long and 45 metres wide) retains its original hexagonal concrete.
Whenuapai was opened to civilian aircraft after the war and in 1947 National Airways Corporation (Air New Zealand’s predecessor) began a regular passenger and freight carrying service from the base. This continued until 1965, when the new international airport at Mangere became operational.
Pre-WWII – in Europe and the US – hangars were typically built with structural steel but as with the runways, says Bob, the difficulty in accessing steel in New Zealand demanded a novel design for the new hangars.
Ohakea received its new hangars first – Whenuapai’s followed a few years later. A report in the Evening Post newspaper (11 January, 1938) outlined the scale of the Ohakea project – as well as the problems it faced:
“The twin hangars for which tenders are being called will be the largest in the Southern Hemisphere. Each hangar will have a ground area of 220 feet in width and 190 feet in depth, with a door opening 25 feet high, closed by sliding doors. The roof design is unusual, for in place of one or other of the forms of standard construction adopted in the Royal Air Force stations in Great Britain, the roof span members will be 10 great arches of reinforced concrete, the feet of which will sweep down far outside the walls proper.
“The design has been adopted to meet the difficulty in obtaining heavy structural steel at the present time, for the sections required for so great a span are not rolled in Australia, and England would not have been able to fulfil the order for over a year, and as the contract period is of 15 months from the commencement of work the simultaneous programme of expansion would have been seriously delayed. Even were the delays acceptable, the cost of such sections would be considerably greater than the reinforced concrete arches decided upon.”
The PWD’s chief design engineer – Charles William Turner – designed the hangars. A canny Welshman born in 1901, Turner immigrated to New Zealand in 1925 and landed a job with the PWD in Wellington. He became involved in seismic design following the 1931 Hawke’s Bay earthquake and this work formed the basis for the country’s first earthquake design code.
Turner used the identical monolithic design for the four hangars (two at each base). As described by Geoffrey Thornton in Cast in Concrete (a history of concrete in New Zealand), they comprised “huge arched roofs with a total span of 82.9 metres and … 0.6 metre deep ribs with a 100mm thick slab. The ribs were anchored outside the hangar proper.”
Ohakea’s hangars (18 metres high) were completed in 1939 at a cost of £76,750 each. In the late 1980s they received a corrugated iron cladding, and some of the arched buttresses on the sides of the hangars were enclosed. These alterations have extended the life of the hangars – and they remain in use today.
In 1990 the hangars were recognised by the Institute of Professional Engineers of NZ (IPENZ) as one of New Zealand’s most significant engineering achievements. They were among the world’s first large, stressed-concrete arch buildings. IPENZ organised the awards to celebrate the country’s sesquicentenary.
Despite the ingenuity, innovation and sheer bloody-mindedness displayed by those concrete pioneers, the history of the Ohakea and Whenuapai runways and hangars carries an unfortunate footnote: the bombers never arrived.
When WWII broke out, the Wellingtons remained in Britain (where they were needed far more urgently) – though they were deployed as the New Zealand Squadron.