Project Name: Helicoidal Bridge
Location: Risaralda, Colombia
Company: Gregorio Renteria Ingenieros SA (GRISA)
Engineer: Gregorioa Renteria Antorveza
Types of analysis used: Construction stage analysis, moving load analysis, post-tensioned analysis, dynamic nonlinear analysis, seismic isolators
Program used: midas Civil
Length: 395m
Diameter: 180m
Year of inauguration: 2010
The Helicoidal Bridge is part of a road that has a total of 3.5 kilometers, of which 125 meters are tunnel and 395 meters of the bridge. The bridge is 395.30 m long with a diameter of 180 m. All mounted-on friction pendulum seismic isolators allow the displacement of the superstructure in the event of an earthquake or due to changes in temperature.
As a solution to the instability of the slopes and the difference in height, an alignment was designed including a geometric helical figure, like the spiral of a spring.
The bridge has 7 spans at 50m and 2 terminal overhangs at 28m. It has 2 abutments and 8 hollow circular piers with two have a section of 3.20 m in external diameter and for the tallest pier on each slope and 2.30 m in diameter for the remaining piers. The height of the piers varies between 4.82 m and 25.59 m.
The post-tensioned concrete box girder has a 10 m wide deck and a constant section height of 2.20m. It has a 7% gradient and 8% superelevation. The elevation of 38 meters makes it possible to take to the ridge of the mountain to travel practically to the back of the hill.
Unstable soil, composed of volcanic ash and residual materials.
Impossibility of expanding the existing road.
Minimum intervention of the terrain, to guarantee the stability of the road alignment.
This structure was selected from several alternatives due to the safety it represents since it did not require a major intervention on the ground, which does not present great stability due to geographical conditions.
In addition, the work does not register high environmental impacts and represents greater long-term stability.
The construction methodology chosen for this project is that of balanced cantilever segmental construction, which is carried out through form travelers, installed on the surface of the slab of the support beams.
To execute it, a form traveler formwork system is mounted with a crane that allows the first segment to be poured, which after setting is tensioned. To install the second traveler, the first must move on to the already poured segment. The construction of the voussoirs is made symmetrically on the column; the length of the cantilever depends on the design specifications. In this project, four travelers were used to speed up the splicing of the cantilevers.
This project was of high risk, which was assumed by the builders and designers since to achieve that the cantilevers of this bridge built in successive segments with such high gradient, superelevation, and radius of curvature they had room for error of less than 3 cm of added displacements X, Y, and Z. It was possible thanks to compliance with strict construction and quality control protocols.
Before putting the bridge into operation, the road had traffic records of up to 7 thousand vehicles per day, mostly heavy vehicles, with average operating speeds of less than 20 kilometers per hour. Therefore, any problem on the road generates significant traffic jams.
The proposal that has been built makes it possible to improve the level of service and increase road capacity, with a dual carriageway with two lanes in each direction, as opposed to what was thought of two two-way carriageways each.
Additionally, 'inverted pendulum' type seismic isolators were used, a state-of-the-art technology that creates a structural discontinuity, between segments and support, using a mechanism in which two concave surfaces meet. This allows the bridge to 'float' on the seismic isolators in the event of a seismic movement. In other words, the energy of an earthquake is not transmitted to the superstructure and it is freed from this requirement.