Altok Kurşun, Civil Engineer, MSc.,
Gülsan Holding Executive Board Member
The Kömürhan Bridge is a modern masterpiece that provides the new passage of the D300 Highway, which connects Malatya and Elazığ provinces, through the Karakaya Dam Lake, which is located on the Fırat River which also separates the two cities. The main span of the bridge is 380 meters. Most of this span is orthotropic steel in cross-section. The total length of the bridge is 660 meters, with a 180-meter anchorage block on the Malatya side and a 100-meter post-tensioned concrete approach bridge that provides the connection to the tunnel on the Elazig side.
The width of the structure is 25 meters in the main span and it carries 2x2 traffic lanes. 100-meter approach bridge with post-tensioned box type cross-section reaches to 30,6 meters width while it is connected to the tunnel. At the post-tensioned concrete superstructures, lateral prestressing was also used.
In the bridge, 2x21 cables are arranged in a single plane in the middle of the deck. The deck is fixed-in the pylon. The cables consist of low relaxation Ø 15.7mm wire ropes with 7 strands of high strength (1860 / 1670MPa).
The shortest of the cables is 106 meters and the longest one is 390 meters. The number of ropes in the chosen cables is minimum 50 and maximum 100. With a total height of 168.5 meters, the pylon is in the shape of an inverted letter Y, and consists of a reinforced concrete box section. Steel cores are also formed in the areas where the cables are anchored in the pylon. The pylon was placed on the ground through 46,5x16,0x7,0 meters headstall sitting on 2 reinforced concrete caissons of 15 meters in diameter and 22.5 meters in depth which are arranged under beam level.
WE HAVE A COMPATIBLE WORK WITH DOĞUŞ İNŞAAT
Civil Engineer and Gülsan Executive Board Member Mr. Altok Kurşun, who is one of the firstly recalled experts in Turkey when the “bridge” is subject, informed us about Kömürhan Bridge and its construction process. Mr. Kurşun stated that:
In normal circumstances, such bridges are constructed with two pylons. Due to its single pylon, Kömürhan Bridge is the fourth bridge in the world with a single pylon. The reason why it has a single pylon is that a passenger ought to enter the tunnel on the Elazig side as soon after it passes over the Fırat River. Middle span is very important at bridges with stretched inclined suspension. It is required to have remarkably larger spans at both sides in order to balance the loads on pylons when the mid-span is loaded. On the Malatya side of the Kömürhan Bridge, there is a 180 meter counter weight block corresponding to the anchors of the suspension bridges.
Because when you load the middle span of the bridge, you try to tilt the pylon towards the middle. To balance this, a balance structure is required at the back. We could not erect a pylon at the Elazig side, since there is a tunnel right after the middle opening. For this reason, we have a 100 meter approach viaduct at the exit between the bridge and the tunnel. When the tunnels are of two tubes, there must be a certain distance between them. For this reason, although width of cross-section is same along with the bridge of Kömürhan, it becomes larger while it is approaching to the tunnel. The width of the approach viaduct also increases from 25 meters to 30 meters. Thus, a single-pylon structure with a middle span of 380 meters emerges. Naturally, the torsional rigidity of the structure becomes very important, when the bridge has a single pylon.
Serious problems may occur during the construction phase, if the necessary precautions are not taken in advance. To prevent this, the pylon is rigidly attached to the superstructure. In addition, cables in Kömürhan Bridge are in the middle of the cross section and in a single row. All of these make Kömürhan Bridge a special structure. As the ground structure, there are two caissons with a diameter of 15 meters and a depth of 22.5 meters under the pylon.
To open these caissons, firstly the surrounding ground was stiffened with injections. We have a 46.5x16.0x7.0 meter headstall on the caissons and a 168.5 meter pylon attached to the superstructure.
It was a very harmonious work with Doğuş Construction, our JV partner, because the parties know and trust each other. In the project, two tube tunnels were built, each of which is 2400 meters long in addition to the bridge. There was a very large landslide zone, and a special solution for that area was applied, and a bridge intersection was built.