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Project Description
This bridge over the Magdalena River near the town of Honda was completed in December 2019. The US$ 30 million structure is part of a series of major highway improvements to connect the Departments of Tolima and Cundinamarca.
The 407 m long cable-stayed bridge has a main span of 247 m and two back spans of 80 m each. The bridge is 16.3 m wide and carries two traffic lanes. The light-weight deck is composed of two cast-in-place post-tensioned concrete edge girders of 1.4 m in depth, which are lightened where stress levels allow it. In the transverse direction, the longitudinal girders are connected with concrete transverse beams 4.45 m apart which are also prestressed. The 96 total stay-cables are divided in two planes and are anchored on the deck every 9.9 m.
The towers, 60 m high above the deck level, are composed of two inclined concrete pylons connected with two transverse cross-beams, one below the deck and one above it. The pylons have a solid cross-section at the base and are hollow in the rest of their height, with a metal liner on the inner faces in the stay anchorage region. The towers are founded on 12.2 m diameter concrete caissons up to 38 m deep. The abutments consist of massive counterweights to which 6 stays are anchored; and through free POT bearings, they take the uplift force from the back stays. As the bridge is in a highly seismic region, it incorporates viscous shock absorbers, which can dissipate over 50% of the energy during a seismic event in the longitudinal direction.
Design/Construction Approach
The cable-stayed bridge design reduced the environmental impact on the river as the foundations are placed on land. The structure was designed according to AASHTO LFRD and the stay cables in accordance with the Post-Tensioning Institute (PTI) specifications.
The balanced cantilever method was used for the construction of the deck. Starting from each tower, each 4.45 m long segment and corresponding stays were installed one after another with a form traveller in a balanced way until reaching the counterweight, then the rest of the main span was built. The post-tensioned light-weight design adopted for the deck proved simple and efficient, enabling a segment construction cycle of five days. The towers were cast in 4.5 m tall increments using climbing formwork and brackets.
A major challenge was ensuring a correct placement of the deck, to achieve the desired profile and a perfect match between the last segments. Many variables played a role in this, among which: tension in the cables, weight and stiffness of the segments, temperature, etc. For this purpose, Pedelta also provided geometric control and technical assistance during construction.
