By James Scarisbrick, Tom Watkinson & James Yip

Introduction Taipei 101 is a 509.2m tall skyscraper situated in the northern region of Taiwan, in the city of Taipei Formally world’s tallest building Constructed between 1999 and 2004 at a cost of $1.8 billion 101 stories overground, as well as 5 underground

Taipei Basin The Taipei basin is located at the Northern corner of the island of Taiwan Occupies an area of 243 sq km and altitude of less than 20m The basin has 3 major water sources flowing through it: ◦ The Keelung River ◦ The Hsintien River ◦ The Taihan River The geological structure inside the basin consists of Quaternary layers above the Tertiary base rock

Geology of Taipei Basin The stratigraphic formations of the Quaternary layers are: 1.Sungshan Formation 2.Chingmei Formation ◦ Hsinchuang Formation 3. Wuku Formation 4.Banchiao Formation The Taipei basin is formed by: ◦ Alluvial deposits ◦ Quaternary unconsolidated material ◦ Tertiary base rock Quaternary layers

Tertiary Base rock The basins base consists of: ◦ Tertiary sedimentary rock ◦ Volcanic rock Lithologically and stratigraphically similar to the folded and faulted strata

Taiwan situated on boundary between Philippine Sea plate and Eurasian plate. Philippine Sea plate moving northwestward at 7cm/year, and subducting beneath the Eurasian plate at northern Taiwan. Problems – Seismic activity

Four key faultlines around basin: Taipei fault Kangjiao fault Shanchiao fault Hsinchuang fault Shanchiao and Hsinchuang major faultlines Circles show location and magnitude of recorded earthquakes Hidden fault also suspected – investigations showed it was large 10m thick fault, only 200m from site Building a superstructure problematic Problems – Local fault lines

Many tremors and earthquakes over the years Many buildings have collapsed or been severely damaged Notably the Chi-Chi earthquake in 1999 and the Hualian earthquake which struck during construction in 2002 Problems - Earthquakes

Changing sea levels have filled basin with lots of layers of unstable silt and clay High groundwater table Potential risk of liquefaction during earthquakes Solid bedrock not found until up to 60m below the surface, therefore creating stability issues for the skyscraper Problems - Stability

Engineering solutions 5m thick concrete mat foundation Veritable forest of m diameter concrete piles into quarternary layer of rock Embedded with added high-strength concrete over 30m into the bedrock 36 extra-high strength steel and concrete columns protrude ◦ 12 corner and bracing columns ending at floor 26 ◦ 16 full height columns that form the core ◦ 8 full height, 3m x 2.4m "mega-columns" distributed around the perimeter

Columns are reinforced with moment-jointed beams at each floor Two storey high outrigger steel trusses tie the core columns to the perimeter’s 8 mega-columns at every eighth floor 700T tuned mass damper between 88 th and 92 nd floor The engineers noted that this final structure is expected to survive once- in-2,500 year seismic events, i. e. - events which produce accelerations up to 0.5g at ground level Engineering solutions

General solutions Rigid foundations with flexible superstructure or; Flexible foundations with rigid structure Isolation of the base – passive structural vibration control Elevated building foundation on high damping rubber bearings A steel plate shear wall - steel infill plates bounded by a column-beam system

Frequency of “felt” earthquakes has increased since completion of Taipei 101 Concerns that the stress on the earth from the 700,000 tonne skyscraper may have reawakened dormant fault-lines Not enough data to make firm conclusions though Also argued 700,000 tonnes of earth was excavated for the foundations therefore net effect of stress is zero Possible cause?