Full damage reports were not immediately available after a 7.4-magnitude earthquake struck off Taiwan’s east coast on April 3, but its National Fire Agency reported that 28 buildings collapsed, mostly in Hualien County, the area closest to the epicenter of the earthquake, with the death of at least nine. people and almost 1,000 injured. Most of the deaths were caused by landslides, which trapped 152 people in tunnels and mountainous areas, the agency said.
It was the worst earthquake to be felt in Taiwan in nearly 25 years.
In the city of Hualien, one person died in the partial collapse of the mid-rise Uran building, with about 10 occupied floors. Local officials said eight others were rescued from the leaning building. They also said several roads and bridges were closed due to damage or for inspection. Train service was temporarily suspended.
“I am deeply grateful for the messages of support we have received from around the world and to our first responders for their life-saving work,” Taiwan President Tsai Ing-wen wrote on social media.
Nearly 100 miles north of the capital, Taipei City, Mayor Chiang Wan-an said on social media that the most serious local damage was to beams and columns on the first floor of an apartment building historic, called South Airport House. Residents of 49 units were temporarily moved to nearby hotels.
Taipei 101
The country’s tallest building, the 1,667-foot Taipei 101, appeared to perform well in the earthquake. As ENR reported during its construction nearly twenty years ago, the office tower was designed to withstand seismic forces beyond local code minimums at the time. Dennis Poon, managing director of New York City structural engineer Thornton Tomasetti, which worked on the design of Taipei 101, says the structure was redundant.
To provide the greatest lever arm against overturning, the structure concentrates the main loads on two vertical megacolumns, usually 3 x 2.4 m, separated by 22.5 m along each face, almost touching the perimeter wall inclined at its base. The main floor beams connect each megacolumn through moment connections to a central corner column along the same grid line, forming a toe board. The 22.5 square meter core consists of 16 box columns in four lines, which are generally fully braced between floors. Composite floors are usually 13.5 cm thick.
On the equipment floors every eighth level, outriggers connect the megacolumns and the core. Outriggers are generally formed by vertical bracing of main floor joists above and below the equipment floors. Further crossings between main perimeter columns at these levels form belt trusses around the tower. Two smaller outriggers connect the central core columns to inclined H-shaped uprights on the face of each module.
The Taipei 101 has a tuned mass damper system of 660 metric tons to help with wind loads and reduce sway. The damper isn’t designed to help with seismic forces, but Guelph, Ont.-based Motioneering Inc., which designed the system, needed to determine how it would perform during earthquakes, says Jamieson Robinson, vice president of operations and director of the company and its project manager at Taipei 101.
The 6 m diameter steel ball of the passive damper system has its movement limited to approximately 1 m in any direction by a pin connected by a steel ring to the dampers on floor 87, which can dissipate energy during seismic events and prevent the ball from swinging dangerously.
“The tuned mass damper basically just goes along for the ride when the building is shaken by an earthquake,” says Robinson.
The tower even endured an earthquake during its construction that damaged two cranes used in the project, and has weathered more direct earthquakes and typhoons in Taipei since its completion.
“At the time, the building was doing very well,” says Poon.
Earthquake and aftershocks
Map by staff/TNS/NewscomThe earthquake struck at 7:58 a.m. local time and was followed by dozens of aftershocks, including one with a magnitude of 6.5, according to the Seismological Center of the Central Taiwan Weather Administration.
Taiwan is located near the Pacific Rim’s “Ring of Fire,” known for its frequent earthquakes and volcanic eruptions, according to the U.S. Geological Survey. In the last 50 years, six other earthquakes of magnitude 7 or greater have occurred within 250 km of this one. The largest was the magnitude 7.7 Chi-Chi earthquake in September 1999.
The Chi-Chi earthquake killed more than 2,000 people and damaged or destroyed more than 57,000 buildings. Many of the collapsed buildings had an average age of less than a decade, but were found to have deficiencies unlike skyscrapers, which were subject to further government design review.
After that earthquake, Taiwan officials organized a reconstruction commission for recovery. They also passed legislation that increased construction supervision and quality control. The country has continued efforts to be better prepared for earthquakes in the years since, including launching programs to assess the integrity of older buildings. Last fall, Taipei Mayor Chiang Wan-an announced an urban renewal plan focused on older buildings that are not sufficiently earthquake-resistant.
