taiwan-quake-why-buildings-stand-tall-on-shaky-ground

Buildings tilted precariously, shattered windows, crumbling stairs… images from Wednesday’s early morning 7.4 magnitude earthquake in Taiwan were disturbing.

 

One thing that stood out, however, was that despite reports of about a 100 buildings collapsing, the rest stood firm, including the island’s tallest skyscraper, Taipei 101, a symbol of pride for the Taiwanese.

 

Quakes are routine in Taiwan, which is located along the so-called ‘Pacific Ring of Fire’ around the Pacific Ocean. Quakes are also the reason why the island exists as it was pushed out of the sea by the collision of two tectonic plates. It is criss-crossed with 51 known fault lines and many more not discovered as yet.

 

Apart from around 2,000 minor intensity quakes, seven quakes of magnitude 7 hit the island in the last 50 years. The 7.1 quake of 1999 – which left 2,400 dead – was counted as the worst in Taiwan’s memory… that is until the tremblor of April 3 struck.

 

Of the tragic deaths this time, nine lives were lost due to falling rocks and landslides. One died in a building collapse in Hualien.

Over the years the government has frequently implemented and revised building rules, making changes after observing quake damage and research. Old and illegal structures built years ago have simply been destroyed in earthquakes.

 

The imprisonment of five persons involved in the construction of a 17-storey building which collapsed in the Tainan earthquake of 2016 sent out a stern message to builders and developers of zero tolerance to substandard work.

 

Always prepared

Earthquake preparedness has also been critically important. The Taiwanese know what they have to do after a quake warning – quake drills have been made mandatory in educational institutes and offices since 1999.

 

Early quake warnings reach citizens through cellphone and TV alerts around 2 to 7 seconds before a quake as sensors all around the island pick up the first vibrations of a tremor and fast responders immediately spring into action. Damage is assessed via close-circuit TV and locations identified for relief work.

 

When it comes to regulations, Taiwan first implemented its seismic force requirements (SFR) for buildings, which was based on the format of the US Uniform Building code, in 1974. New changes factoring in various building occupancy categories were incorporated into SFR in 1982.

 

The Ministry of Interior added the Seismic Design of Structure chapter in building technical regulations in 1997, setting out  Specifications of Seismic Design for Buildings, to be followed at the designing stage of the building.  

 

From introduction to earthquake engineering to the exact specifications of earthquake resistant engineering design, this handbook collected information on design regulations of buildings for engineers to follow.

 

By 1999 most buildings had been retrofitted with steel frames added to the exteriors and extra pillars put in for good measure.

Revisions were done in 2006 and 2011 before the latest Seismic Design Specifications and Commentary of Buildings by the Construction and Planning Agency of the Ministry of the Interior (CPAMI) was implemented on October 1, 2022.

 

The four important revisions in the new regulations include increased safety near fault zones, making weak ground floors quake-resistant, refining data related to soil liquefaction (when saturated soil loses its strength and stiffness after intense shaking, say in an earthquake, which can cause buildings to collapse) as well as design to counter liquefaction; improved design quality and effectiveness of seismic isolation and damping elements.

 

Fault zone safety: In case of a quake due to fault movement the adjacent faults have considerable ground displacement with intense shaking, which can cause serious damage to buildings. Active faults and the impact of quakes on areas close to these faults were studied and analysed. Safety regulations in these zones were changed accordingly to ensure that the structures withstood the “near-fault effect.”

 

Ground floor collapse: Ground floors are weak usually because most tall buildings have open spaces there for public use with fewer structural walls and supports compared to upper floors. Thorough assessment and structural reinforcements in such weak floors are recommended in the new rules.

 

Work is allowed in a phased manner in structures requiring mandatory changes before these are completely overhauled or rebuilt. Owners of buildings are provided safety evaluation assistance and help in selecting methods to prevent ground floor weakness.

 

Soil liquefaction: Soil liquefaction in an earthquake can cause subsidence, which can make a building tilt or collapse. Data from 600 such cases from Taiwan and abroad was collected and analysis and calculation of localised liquefaction resistance of soil was done in different areas of the island.

 

Then, a new soil liquefaction assessment method was developed and included in the new regulations for localities to follow. Design engineers can also use the data to identify liquefaction risks in construction plans and come up with liquefaction-resistant designs.

 

Seismic isolation and dampers: Safety regulations involving use of seismic isolation and dampers were put in place in 2006. By 2009 around 80 buildings had adopted the technology and by 2022 more than 1,000 buildings had opted for the safety measures.

 

A structure built directly on the ground is damaged when it moves with the motion of the earthquake. Isolating it from the ground with flexible bearings or pads known as base isolators prevents damage as the force of the quake is absorbed by the base, lessening its impact on the structure.

 

A damper, usually a lead-based device that looks like your car’s shock absorber, absorbs energy when a structure moves.  

“Damper Baby,” a 660-metric-tonne steel sphere with 41 steel layers, which is suspended between floors 87 and 92 of Taipei 101, helps reduce the building’s movement in a quake or storm.

 

The pagoda-inspired building has been in the news ever since video footage of the recent Taiwan quake showed it swaying ever so slightly when other structures around it shook and swayed.

 

That’s the magic of science and technology in the modern world.