Mirna Bridge
Encyclopedia
The Mirna Bridge is located between the Nova Vas
and Višnjan
interchanges of the A9 motorway in Istria
, Croatia
, spanning the Mirna River and the wide Mirna River valley. It is 1378 metres (4,521 ft) long and comprises two traffic lanes. The bridge has been open for traffic since June 2005. The bridge is one of the most significant structures on the motorway. The bridge was designed by Zlatko Šavor.
The A9 route between Umag and Kanfanar, where the Mirna Bridge is located, was upgraded to motorway standards in June 2011. However, the works did not include construction of a parallel structure across the Mirna River which would carry the additional carriageway. Expansion of the bridge to a full motorway is planned to start in 2013 and be completed by 2015.
The design of the bridge was initially in 66.5 metres (218.2 ft) spans, but the final layout was imposed by the particular soil conditions and the arrangement of the river bed and canals below the bridge. Since the soil supporting the bridge foundations has exceptionally low load carrying capacity, it was important to reduce weight of the structure as much as possible. Therefore the design employs two weight-reducing elements: longitudinal steel girders and piers with cap beams at varying heights. The latter reduces volume of concrete used for construction of the piers thereby reducing weight of the structure while giving the bridge a curved, concave deck.
The design of the pier foundations was further affected by the fact that the valley is a high quality agricultural area that had to be preserved as much as possible. The height of the reinforced concrete piers ranges from 13.45 metres (44.1 ft) to 40.03 metres (131.3 ft) and each of the piers is topped by a cap beam. The piers comprise an I-cross section with the webs aligned with the bridge axis. Peripheral piers (P1, P2, P20, P21) are executed on shallow foundations
, while the remaining piers are executed on driven piles. The superstructure consists of two longitudinal prefabricated girders of constant depth set 550 centimetres (216.5 in) apart made composite with the deck slab and cross-girders. Structurally, the superstructure is a 1354.86 metres (4,445.1 ft) long continuous girder across 22 spans, tracing a horizontal and a vertical curve. The cross section of the superstructure consists of two solid I-section steel girders of constant depth.
, the operator of the bridge and the A9 motorway where the bridge is located, and published by Hrvatske ceste
. Substantial variations between annual (AADT) and summer (ASDT) traffic volumes are attributed to the fact that the bridge carries much tourist traffic to the Istrian
Adriatic resorts. The traffic count is performed using analysis of motorway toll ticket sales.
Nova Vas
Nova Vas may refer to*Nova Vas, Brtonigla, village in the Brtonigla municipality in Croatia*Nova Vas, Kršan, village in the Kršan municipality in Croatia*Nova Vas, Poreč, settlement within the town of Poreč in Croatia...
and Višnjan
Višnjan
Višnjan is a village and municipality in Istria, Croatia. Višnjan is the site of Višnjan Observatory . The observatory is home of several long-running international summer programs for youth in astronomy, archeology, marine biology and other disciplines.-Geography:Višnjan is located 12 kilometers...
interchanges of the A9 motorway in Istria
Istria
Istria , formerly Histria , is the largest peninsula in the Adriatic Sea. The peninsula is located at the head of the Adriatic between the Gulf of Trieste and the Bay of Kvarner...
, Croatia
Croatia
Croatia , officially the Republic of Croatia , is a unitary democratic parliamentary republic in Europe at the crossroads of the Mitteleuropa, the Balkans, and the Mediterranean. Its capital and largest city is Zagreb. The country is divided into 20 counties and the city of Zagreb. Croatia covers ...
, spanning the Mirna River and the wide Mirna River valley. It is 1378 metres (4,521 ft) long and comprises two traffic lanes. The bridge has been open for traffic since June 2005. The bridge is one of the most significant structures on the motorway. The bridge was designed by Zlatko Šavor.
The A9 route between Umag and Kanfanar, where the Mirna Bridge is located, was upgraded to motorway standards in June 2011. However, the works did not include construction of a parallel structure across the Mirna River which would carry the additional carriageway. Expansion of the bridge to a full motorway is planned to start in 2013 and be completed by 2015.
Description
The deck structure stretches across 22 spans: 51.07 m (167.6 ft) + 15 x 66.5 m (218.2 ft) + 70.1 m (230 ft) + 2 x 50.01 m (164.1 ft) + 61.1 m (200.5 ft) + 42.6 m (139.8 ft) + 30.5 m (100.1 ft).The design of the bridge was initially in 66.5 metres (218.2 ft) spans, but the final layout was imposed by the particular soil conditions and the arrangement of the river bed and canals below the bridge. Since the soil supporting the bridge foundations has exceptionally low load carrying capacity, it was important to reduce weight of the structure as much as possible. Therefore the design employs two weight-reducing elements: longitudinal steel girders and piers with cap beams at varying heights. The latter reduces volume of concrete used for construction of the piers thereby reducing weight of the structure while giving the bridge a curved, concave deck.
The design of the pier foundations was further affected by the fact that the valley is a high quality agricultural area that had to be preserved as much as possible. The height of the reinforced concrete piers ranges from 13.45 metres (44.1 ft) to 40.03 metres (131.3 ft) and each of the piers is topped by a cap beam. The piers comprise an I-cross section with the webs aligned with the bridge axis. Peripheral piers (P1, P2, P20, P21) are executed on shallow foundations
Shallow foundation
A shallow foundation is a type of foundation which transfers building loads to the earth very near the surface, rather than to a subsurface layer or a range of depths as does a deep foundation...
, while the remaining piers are executed on driven piles. The superstructure consists of two longitudinal prefabricated girders of constant depth set 550 centimetres (216.5 in) apart made composite with the deck slab and cross-girders. Structurally, the superstructure is a 1354.86 metres (4,445.1 ft) long continuous girder across 22 spans, tracing a horizontal and a vertical curve. The cross section of the superstructure consists of two solid I-section steel girders of constant depth.
Traffic volume
Traffic is regularly counted and reported by BINA IstraBINA Istra
BINA Istra is a Croatian joint stock company founded in 1995 to facilitate construction and subsequent management of a Istrian Y motorway, consisting of the A8 motorway and the A9 motorway. On September 21, 1995, BINA Istra has been granted concession regarding management of the Istrian Y...
, the operator of the bridge and the A9 motorway where the bridge is located, and published by Hrvatske ceste
Hrvatske ceste
Hrvatske ceste is a Croatian state-owned company pursuant to provisions of the Croatian Public Roads Act , the county and local roads are managed by county authorities, while the motorways are managed by Croatian Motorways Ltd and other concessionaires.The company is currently administered by a...
. Substantial variations between annual (AADT) and summer (ASDT) traffic volumes are attributed to the fact that the bridge carries much tourist traffic to the Istrian
Istria
Istria , formerly Histria , is the largest peninsula in the Adriatic Sea. The peninsula is located at the head of the Adriatic between the Gulf of Trieste and the Bay of Kvarner...
Adriatic resorts. The traffic count is performed using analysis of motorway toll ticket sales.
| Mirna Bridge traffic volume | ||||
| Road | Counting site | AADT | ASDT | Notes |
| A9 | 2722 Mirna toll plaza | 4,659 | 10,821 | Between Nova Vas and Višnjan interchanges. |