Assessment of Troja footbridge dynamic response

Troja footbridge was a slender suspension footbridge with internal system of suspension and prestressing cables. The footbridge was at the time of construction (1984) an innovative structural design. It had 3 spans 85,5+96+67,5 m with total length of 249 m and width 3,8 m. It collapsed in winter 2017 after mere 33 years of service. 

To make an expert testimony after the collapse, multiple teams investigated the debris and make analytical models, which were often very complex, in order to find clue and lesson for the future. One of these models was created in software SCIA Engineer and it was used for precise dynamic analysis of the footbridge. The expert testimony content and conclusions are, however, confidential. In order to achieve maximal precision, cross section was modelled by slab elements with cables and prestressing tendons. Additionally, different types of concrete were used in the model of the deck. To achieve maximal precision, model was extended to cover also the steel parts of the railing. The model contained 1779 slab elements and 7624 beam elements (out of which 5850 were parts of railing).

Given the complex, yet periodical shape, the structural model was created parametrically in Excel and imported in SCIA Engineer via Table Input. By Table Input all beam and slab elements, loading, supports and main cables were imputed. Prestressing tendons were created manually in the SCIA Engineer. Model was compared with dynamic measurements taken on the bridge in 1984 (when construction was finished) and the results were perfect fit.

Parametric approach was chosen for the model creation and in my opinion was the only viable approach, given the number of members in the model.

Reference: Created exclusively for Faculty of Civil Engineering, CTU in Prague, 6/2018, www.fsv.cvut.cz