Historic Building at Risk

Due to its location in a high-seismic zone, Bucharest City Hall faced considerable earthquake threats. Originally built in two phases (between 1906 and 1912 with additional stories added in the late 1940s), the structure consists of masonry walls up to 3.6 feet thick, reinforced concrete slabs, and a U-shaped layout measuring approximately 292 by 213 feet, reaching a height of nearly 85 feet. As a historical structure vulnerable to seismic activity, it required advanced protection measures to mitigate earthquake risks.

A History of Seismic Activity

Over the decades, the building endured four major earthquakes ranging from 6.7 to 7.4 on the Richter scale, leading to concerns about structural integrity and the risk of collapse. A conventional seismic retrofitting design proposed in the late 1990s was later replaced with a seismic base isolation system, ensuring compliance with updated seismic codes and reinforcing seismic protection for historical structures.

Custom-Engineered Seismic Protection

To enhance safety, the project involved the design and installation of 262 isolators and 36 dampers, meticulously engineered to accommodate the substantial displacement requirements of the region (up to 4.9 feet). This specialized system significantly improves seismic protection for historical structures by decoupling the building from ground motion, allowing it to withstand powerful earthquakes.

Large-Scale Testing for Seismic Devices

Two types of lead rubber bearings, each approximately 3.3 feet in diameter and 1.6 feet in height, were developed to support loads of up to 560,000 pound-force foot (lbf-ft). Given their size, no European facility was equipped to test them, requiring shipment to the United States for rigorous validation. This level of testing is critical when designing seismic protection systems for historical structures.

Reinforcement Measures

To enhance structural stability, the main contractor reinforced the raft foundation with micropiles and constructed reinforced concrete beams beneath key walls. Once the isolators and dampers were placed in designated locations, loads were transferred onto them using flat jacks. These remained in place to ensure performance, an essential process for seismic protection in historical structures.