Despite being completed in the early 1990s, the Marmara University Basibuyuk Training & Research Hospital in Istanbul remained unused for more than two decades. When plans were formulated for its occupation, retrofitting was necessary to meet the latest earthquake protection measures required in such an active seismic region

  • Name of the owner
    Marmara University Basibuyuk Training & Research Hospital
  • Name of the client
  • Delivery date of the project
    June 2014
  • Partners of the project
    Contractor: Freysas / Freyssinet Product Company
    Engineer: Prota

Multiple blocks

This process was made even more challenging by the fact that the hospital is a large complex, formed of a total of 16 different buildings that vary in height, size and stiffness. In fact the facility had already been retrofitted once since being constructed, but standards had subsequently changed and base isolation had become mandatory. The new codes also specified the operational limit states that the seismic protection system had to ensure the building could meet after an earthquake.

Distribution challenge

Analysis of the structure to define how and where the base isolators were to be distributed around the base of the buildings was carried out by the consulting engineer in collaboration with Freyssinet experts. But the demands of low stiffness and high damping that the system had to deliver, along with high horizontal displacement, had the potential to be contradictory.
It would have been impossible to obtain the desired outcome by using only lead rubber bearings for the seismic protection. These devices are generally designed either with high stiffness to offer high levels of damping, or low stiffness and low damping – it is not possible to get high and low in the same unit.

Key figures

Combined forces

For this project, the solution was to adjust the number and type of seismic protection units, rather than their characteristics, to achieve the required global stiffness of the inter-connected blocks. The devices proposed were split 50-50 between lead rubber bearings with high stiffness that dissipate a lot of energy, and sliding elastomeric bearings that accommodate the vertical load, but which enable the overall stiffness of the complex to be lowered.

The variation in heights and basement levels of the 16 buildings also posed a challenge for the design team, who had to propose a suitable level at which to install the devices. They must all be at the same level to operate effectively; and any lengths of columns below this level had to be strengthened with concrete jackets as they are directly impacted by full seismic forces.

  • 16
    Buildings in the complex
  • 687
    Devices installed

Avoiding torsion

Distribution and use of the protective devices varied depending on the characteristics of each building – the key aim was to ensure that the center of mass of each block corresponded to its center of stiffness, to prevent any potential damage from torsion.

Installation goal

One of the key factors that gave Freysas an edge in securing the work was the contractor’s solution to the execution of the work, which dispensed with the intrusive system of steel support frames that had been initially proposed.
The alternative proposed by Freysas was to employ a custom-designed system of clamps that were fixed to individual columns above and below the point where the isolation unit was to be installed. They were connected by high-strength prestressing bars and hydraulic jacks were employed to transfer the loads while the column was cut and the isolator element installed.
This much less disruptive procedure reduced the cost and physical impact of the retrofit, and enabled work to be completed on each column in just a couple of days. Multiple sets of the clamps were used, to enable work to be carried out on up to five columns at a time across the complex, in a carefully planned sequence.