The MUCEM pushes back post-tensioning limits

Innovative isolation system for the MUCEM UHPFRC columns

The desire to make extensive use of UHPFRC, particularly in the columns, prompted an assessment by the French technical agency “Centre Scientifique et Technique du Bâtiment” in relation to seismic loading, and fire resistance specifications. No structural codes for UHPFRC existed at the time.

This assessment led to ball joints being added at the top and bottom of the columns to isolate them from seismic and wind loading; analysis of the response to fire was identified as the defining criteria for the design of prestressing for the columns.

The dual demands placed on the tree-like building columns required innovative solutions from Freyssinet experts – not only in terms of how to manage the sometimes-conflicting design criteria, but also in forming and assembling these elements.

An unprecedented level of precision for the MUCEM

Hence the floor girders of the building were first erected on temporary props, and the ring beam cast to provide a structure to support the precast column units during assembly. This required an unprecedented level of precision in the construction of the main beams.

Prestressing tendons run the full height of each column, and must connect each branch, creating a complex network of ducts and cables. The substantial joints that connect the columns to the floor beams were subsequently enclosed in precast UHPFRC shells

A phased assembly

Once again Freyssinet had to turn traditional procedure on its head to facilitate construction of a multi-span structure which had very slender flanges,making it impossible to deviate tendons over the supports.

Phased assembly was the answer, with the main isostatic span tensioned first; the shorter side spans were then put into continuity by tensioning tendons across the full bridge length.