Photo taken on Nov 14, 2015 shows the overhaul site of Sanyuanqiao cloverleaf junction in Beijing, capital of China. A pivotal cloverleaf junction in a downtown Beijing commercial zone was closed for overhaul this weekend, amid hopes of reinforcing the 30-year-old structure without paralyzing traffic flows. [Photo/Xinhua]

BEIJING - A pivotal cloverleaf junction in a downtown Beijing commercial zone was closed for overhaul this weekend, amid hopes of reinforcing the 30-year-old structure without paralyzing traffic flows.

The most challenging part of the overhaul, the replacement of the 1,300-tonne bridge structure, began at 11 pm Friday on Sanyuanqiao cloverleaf junction on the northeastern part of Beijing's Third Ring Road.

Road workers were instructed to dismantle the old bridge and replace it with a prefabricated new steel structure.

The process was initially planned to last for 24 hours, but the central beams of the old bridge were in a much worse condition than expected, causing extra dismantling work.

Beijing Municipal Commission of Transport has extended the traffic ban to 30 hours from the initial 24 hours.

Traffic to the bridge zone will resume after 5 am Sunday, the commission said in a circular posted at its website and sent to millions of mobile subscribers in Beijing Saturday morning.

Replacement of the bridge structure costs 39 million yuan ($6.1 million), according to the commission.

The Sanyuanqiao cloverleaf junction is a major congestion point on a tollway to the airport. It also links two pivotal highways: the Third Ring Road and the highway linking downtown Beijing with the outlying Shunyi District.

Sanyuanqiao is one of the most familiar place names for foreigners in Beijing, as it is close to a cluster of foreign missions and international companies in eastern Beijing.

Built in 1984, the bridge is in a poor shape and needs reinforcement for safety reasons.