Construction World December 2021

SPECIALIST CONTRACTORS OR SUPPLIERS

Consul t ing Eng ineeres

Civi l Eng ineering Contractors

Special ist Contractors or Suppl iers

T he newly completed Ashton Arch in the Western Cape i s South Af rica’s fi rst concrete t ied-arch bridge constructed us ing a transverse launching method. The bridge replaced an exi st ing mul t i -arch bridge, which no longer ful fi l led i ts funct ional requi rements such as ser vice l i fe, width and hydraul ic capaci ty. The new t ied- arch bridge compri ses a cable-supported concrete deck which spans 110 metres between supports wi th arching ribs ri s ing 22 metres above the asphal t road sur face. AECOM were the appointed structural engineers , whi le the bui ld was contracted to H&I Construct ion. State-of-the-art bridge analys i s sof tware packages were used for the construct ion stage analys i s , in-ser vice analys i s , and des ign, a joint ef fort by AECOM’s SA and UK Long-span complex bridge teams . The management team of H&I Construct ion worked in close relat ionship wi th AECOM to develop met iculously detai led method statements , wel l in advance of each act ivi ty, to ensure compl iance and agreement before construct ion commenced. The New Ashton Arch forms part of a broader construct ion project conducted under the auspices of Western Cape Provincial Government ’s Department of Transport and Publ ic Works . Thi s involved the reconstruct ion of parts of Trunk Road 31 Sect ions 2 and 3, between Ashton and Montagu in the Western Cape which includes the hi storic Cogmanskloof pass . The greater Ashton-Montagu region, and Cogmanskloof Pass in part icular, has experienced substant ial flood damage on several occas ions over the years . Thi s resul ted in mul t iple road closures and s igni ficant operat ional di srupt ions , wi th adverse impacts on the local economy. The largest of these recent floods occurred in March 2003, wi th severe block and overtopping at the new Ashton Arch locat ion as shown below. A key cons iderat ion of the bridge was to minimi se flow restrict ion and improve the avai lable f ree board wi thin the restrict ions of adjacent propert ies and road al ignment levels . Through an economic NEW ASHTON ARCH

analys i s , the technical opt ions for the river cross ing and construct ion strategy were evaluated wi th due cons iderat ion of the impact of construct ion strategy on road user costs . The selected final des ign of the bridge cons i sts of a s ingle span (110 m) concrete t ied arch solut ion wi th a deck suspended by stay cables which accommodates four traf fic lanes and two pedestrian walkways . Thi s

40 20 th Best Project Awards 2021