TOKYO SKY TREE

abstractA report after paying a site visit to the world’s highest steel structure, “Sky Tree”, modeled after Hohryuji, an earthquake resistant Japanese pagoda. Included, are Sky Tree’s basic features, a brief structural comparison between Sky Tree and more than a century old timber pagoda,…. unleashing the structural secret of Japanese pagodas, having the ability to resist earthquake and Sky Tree’s chronological account of development.

Hohryuji an IntroductionIn the land of the rising sun where typhoons swept frequently and the land is shaken by earthquake, stands the tower of Hohryuji, a typical traditional Japanese five-story timber pagoda, that existed for more than 1300 years and still remained standing today. There still exist over 300 timber pagodas in Japan today and are considered one of the typical Japanese beauty. The long existence of these pagodas in strong seismic regions is still a big question. This special earthquake resistance ability of the five-story timber pagodas in Japan remain a mystery up to now. This paper unleash this secret.

Basic FeaturesHighest steel structured tower in the world: 634m.Mainly used as a digital broadcasting facility by 6 commercial stations including NHK. It has two observatories at heights 350 and 450m.Located in Oshiage, Sumida Ward, TokyoDesigned by KK Nikken SekkeiConstructed by KK ObayashiModeled after the earthquake resistant Japanese Pagoda

Structural Comparison

SKY TREE PAGODA

Rigid Seismic isolation by friction bearing to columns

Central RC pillar wrapped by steel structure shaft

Central timber pillar that serves as a snubber

Welded truss pipe structural frames

Columns and beams are not firmly connected

“Katana” configuration Tapered configuration

Commentary 1

Basically, the Japanese pagoda is a flexible structure using seismic isolation by friction bearing. This is a non-linear dynamic analysis of a sliding structure, where the shear balances at the sliding interface. Friction bearing reduce the shear forces at the bearing, so the columns hardly to be damaged during an earthquake. Sky Tree, however is a rigid structure. The main structure uses steel frames with double the standard strength for the key elements.

Commentary 2

The snubber constrains each floor level of the pagoda from swinging too far at any direction, (shimbashira.) Sky Tree copied this idea, however it uses the latest oil-dumping technology for restraining seismic and wind forces. The central RC pillar of Sky Tree is connected by oil dampers on several stages from the wrapping shaft, a 12 celled steel structure which serves as passage for facilities as elevators, pipes and cables.

Commentary 3

The pagoda’s structural connection between columns and beams are not firm, so each level can vibrate in a flexible manner during an earthquake. This concept was not applied in Sky Tree. Welded truss pipe structural frames was adopted. The size of structural pipe used is 2 meters in diameter having 10 cm thickness. In one welding occasion 4 welders were deployed.

Commentary 4

Katana is the traditional Japanese Samurai lethal sword. It has a warping configuration due to the sudden cooling during molding. This tapered configuration is common to all towers in the world. What is unique with Sky Tree is that tapering was done at a triangular base. All other existing towers in the world are tapered at a square base.

Commentary 5

Just imagine a rigid structure with all forces, including wind and seismic loads are absorbed by its foundation. Sky Tree adopts the knuckled wall pile technology to meet all loads. This type of pile is one of a kind. See Appendix A for most commonly used piles. The knuckled wall pile has never been used throughout the worlds construction history.

April 12 2010SKY TREE Elevation when

me and MES company colleagues paid a site visit.

Appendix A1

Appendix A2

Appendix A3

HohryujiVS

Sky Tree

Site PicturesElevation 349 meters

April 12, 2010

END

Thank you for your Attention

ByNoel Buca

Layout and Civil Engineering Dept.Plant and Environment HQ