International Symposium on Industrial Chimneys and Cooling Towers, Prague, Oct 8-11, 2014 Construction Techniques of The 3 rd Bosphorus Bridge in Istanbul, Turkey M. Orçun TOKUÇ 1 and Tamer TUNCA 2 1 Engineer at ENDEM INSAAT, Istanbul, Turkey 2 General Manager at ENDEM INSAAT, Istanbul, Turkey Keywords: Suspension Bridge, Cable-Stayed, Slipforming, Pylons ABSTRACT: This paper presents the construction of the 3 rd Bosphorus Bridge to be built in Istanbul, Turkey. The 3 rd Bosphorus Bridge has a unique construction that is regarded as the bridge of the firsts. It is going to be the widest suspension bridge in the world with a width of 59 meters and the longest spanning one that has 8 lanes of motorway and 2 lanes of railway on it, with a main span of 1408 meters. Another first of the bridge is that it is the suspension bridge with the highest bridge pylons of the world, with a height of 322 meters. A hybrid system that consists of two different construction techniques which are cable-stayed and suspension bridge is used for the 3 rd Bosphorus Bridge. The construction of the bridge includes three main parts. Side spans including anchorage and approach block, main span and pylons. Anchorage and approach blocks are built up by conventional methods. Pylons, triangular in cross section and with 1.50 m wall thickness, are raised up by slipforming up to elevation +208.00 and then continue with climbing form up to elevation +322.00. A special formwork was produced by Bygging International, the Swiss company, and used in the construction of pylons. 1 INTRODUCTION The 3 rd Bridge is built on the Bosphorus, Istanbul within the Northern Marmara Motorway Project. The rail system is going to be integrated with the Marmaray and the Istanbul Subway to link Atatürk Airport, Sabiha Gökçen Airport, and the 3 rd Airport which will be constructed. The Northern Marmara Motorway and the 3rd Bosphorus Bridge is executed with Build- Operate Transfer model with an investment value of 2 billion dollars. The overall length of the bridge is 2164 m which includes a 1408 m main span and two 352m side spans. The bridge construction comprises a two towers twin cable stayed and suspension, post-tensioned concrete box decks. The width of concrete deck is 59 m. A shaped towers are 322m height. Each tower is supported by open caisson foundation with a 22.4 outside diameter and the thickness of caisson is 1.2 m. The main materials used in the construction of the bridge are
concrete, reinforcement steel, structural steel and cable. The amount of materials is 230000 m 3, 50000 tons, 57000 tons, 28000 tons, respectively. The concrete class is used in the construction of anchorage block and approach concrete is C50 and C40 is used for other parts of the bridge. The class of reinforcement steel is S500b and of steel structure is S355. The post-tension cables class Y1806S7. Fig.1 presents the longitudinal section of the bridge. 2 SIDE SPAN Figure 1: Longitudinal section of the bridge. Side span includes mainly three parts. These are anchorage, approach blocks and side deck. The total length of side span is 378 m. The length of approach concrete is 94 m and the length of decks 284 m. A cantilever segment which extends beyond the towers is 24 m long. To begin with, anchorage is the part of the bridge that is located at end of the side span and support for the main suspension cables fixed at the top of the pylons. The depth of anchorage hole is 34.5 m from the ground level of the anchorage. Suspension cables are scattered on the anchorage block in two groups. These cable groups pass through a splay chamber and they are all bounded under 20 m of this room as presented in Fig.2. Figure 2: Section of the anchorage block The concrete of anchorage block is divided by 25 segments and each segment is poured intermittently. The first of 9 segments are constructed together with a steel anchor frame manufactured in ENDEM s workshop. Fig.3 presents a view of bottom segment of the anchorage block. The amount of concrete which is used in the construction of anchorage is 23619 m 3.
Figure 3: A view of bottom segment of the anchorage block Ground approach block is constructed in three parts and each part is 28.5 m long as shown in the Fig.4. The sheaths of cable-stays are anchored at each 14.40 m along the ground approach. Five double rows of the post-tensioned cables at each 14.40 in the transverse direction are installed. Total amount of the concrete which is used for ground approach is calculated as 2080 m 3 for one side. The amount of reinforcement steel used in ground approach block is 2080 tons for each side of the bridge. Figure 4: The section of ground approach block Conventional formworks which have dimensions 2m x 2m are used for ground approach and two lanes for these formworks are built passing through the concrete block. Fig.5 presents views of ground approach block and sheaths of stays. Figure 5: Views of ground approach block and sheaths of stays.
As for the side deck, the construction sequence is composed 6 segments along the longitudinal direction as sketched in Fig.6. The total length of side deck is 248 m. Special scaffolding and formworks were manufactured by K-TECO, the Korean company. The width of the deck is 59 m and the height from the very bottom point is 5.5 m. The deck s type is concrete box girder and constructed by means of cast in-situ concrete. It has 10 segments along the transverse direction. Post-tensioned cables are installed in all these segments both in transverse and longitudinal direction. The amount of post-tensioned cables used in the construction is 2752 tons. The amount of concrete is 20000 m 3 and of reinforcement steel is 3700 tons. There are some gaps within the decks to dismantle formwork and to jack posttensioning cables. Figure 6: Segments of the side deck along the longitudinal direction Two pumps which have 56 m boom length are allocated for the concrete of deck. One of the two pumps is the main pump and the other is used as spare one to prevent cold joints that can be formed if any delay occurs during pumping of the concrete. A mobile pump which has 26m long boom is used for the parts of decks where the main pump cannot reach easily. Figure 7: Views of the side deck Fig.7 presents some late views of the side deck during construction by the end of February in 2014. Eventually, piers are constructed under side decks. Four types of piers are constructed on each side of the bridge. Climbing form is used to construct the piers. Friction pendulum bearings between the decks and piers are used to dissipate seismic energy in both vertical and horizontal direction as seen in the Fig.8. The amount of concrete is 6084 m 3 and of reinforcement steel is 900 tons for the construction of piers.
3 PYLONS Figure 8: Views of piers and bearings. Pylons, triangular in cross section and with 1.50 m wall thickness, are raised up by slipforming up to elevation +208.00 and then continue with climbing form up to elevation +322.00. A special formwork was produced by Bygging International, the Swiss company, and used in the construction of pylons. Slipform is composed of three decks. These are top, middle and hanging decks. The top deck services for pouring of concrete. The threaded vertical bars also erected at the top deck. The middle deck is generally is used for manufacturing such as putting the horizontal reinforcement, embedment, carrying out vibrating of concrete etc. Hanging decks are located in both sides of the pylons. Curing of concrete is carried out by hanging decks. The height of shutter is 1.00 m and the concrete is placed in layers of approximately 200 mm. Fig.9 presents the assembly of slipforming. Top Deck Yokes Middle Deck Hanging Deck Figure 9: Assembly of slipforming Hydraulic Adjustment Mechanism (HAM) part is used to decrease wall thickness and dimensions evenly around all parts of the shutter. A spindle that connects inner and outer yoke legs is utilized to decrease wall thickness. The spindle can be manually operated by adjusting the difference of thickness along the height of pylon. A guide mast located within the shell of pylons is used to form an inclined shape. This part rises up with slipforming simultaneously as well. Typical movement of HAM is presented as in Fig.10.
Guide Mast Figure 10: Movement of HAM along the section of pylons and guide mast. There is a pipeline which is mounted along the height of pylons to pump the concrete from the ground to the top of pylons. The concrete is distributed by using a distributor at the top deck of slipforming. The concrete flows into shutter by means of corrugated pipes that attached a hopper as shown in Fig11. Figure 11: Movement of HAM along the section of pylons and guide mast. The mean uprising height of slipforming is calculated as 2.04 m/per day. Excepting temporary stop during the construction, two shifts in a day, 24 hours, are scheduled for the construction of pylons. The number of man for two shifts working on slipform is 63. The construction of pylon between elevations +13.00 and +208.00 is completed within 155 calendar days. Total amount of the concrete which is used for pylons is calculated as 67270
m 3 for one side. The amount of reinforcement steel used in pylons is 14164 tons for each side of the bridge. There are 5 temporary struts that will be built between two pylons. The main goal of temporary struts is to restraint deflection in the transverse direction. This deflection stems from self weight of towers and service load during the period of construction. This deflection also leads to additional moment due to geometric eccentricity. Temporary struts are made of steel as shown in the Fig.12. Figure 12: The construction of temporary struts Cross beam is located between two legs of towers and connected with post-tensioned cables.1 st temporary strut is constructed at elevation +96.00 m and the formwork of crossbeam is built on the strut. Steel beams are erected transversely between two components of 1 st temporary strut. Before erection of the strut, scaffolding modules for the crossbeam are assembled. During the construction, 1 st temporary strut will carry axial forces due to dead load, wind load, difference of temperature and shrinkage of concrete. The maximum axial force value which strut reaches is 14000 kn in accordance with engineer (T-Engineering) data. Therefore, a pre-loading process is carried out for the strut is by using hydraulic jacks. The strut should be released after the first layer of cross beam is built in an effort to transmit axial loads exclusively to crossbeam. Figure 13: Views of scaffolding cross beams and 1 st temporary strut
After releasing of the strut 1 st and 2 nd post-tensioning process is commenced.the concrete of cross beam is poured in four segments. The conventional formworks are used to cast the walls of crossbeam. The amount of concrete and reinforcement steel used for crossbeam 2260 m 3, 710 tons, respectively.. 4 MAIN SPAN Figure 14: Views of crossbeam. The length of main span is 1408m and unlike side span, 1360 of 1408 m main span will be built as a steel construction. Steel deck will be erected in parts which each is 4 meters long. Main span consists of three separated segments which are transition, cable stiffened and suspended deck. The length of three segments is 588m, 536m and 288 m respectively. The section is of steel deck is shown as Fig.15. 5 CONCLUSION Figure 15: Cross section of the steel deck. The 3 rd bridge has some significant skills that can be seen at first glance. It will be the widest suspension bridge in the world when it is completed. Another skill of the bridge is that it is the suspension bridge with the highest bridge pylons of the world, with a height of 322 meters. A hybrid system that consists of two different construction techniques is an advantage for the bridge. Large scale suspension and cable stayed bridge has many complex details Even though more studies needs to be done more for these type of construction, they still find a wide application. REFERENCES www.3kopru.com Method statements of The 3 rd Bosphorus Bridge members, ENDEM Construction Industry and Trade Co, Inc., 2013, Istanbul,Turkey