Seismic Response of Tower Crane Supported by Pile Foundation in Soft Clay

Kazuya+ITOH++Fumitaka+ARAI++Naoaki+SUEMASA++Satoshi+TAMATE++Toshiyuki+KATADA

Abstract：Earthquake resistance of temporary structures is inferior to that of permanent structuresA tower crane supported by a pile foundation，which is one of the temporary structures，is often used when constructing high-rise buildingsThe tower crane installed in a high position may be vibrated largely by strong seismic ground motion because of its slender structureDynamic response characteristics of the structure with a pile foundation are greatly influenced by the surrounding ground and the foundation type as wellIn current Japanese design mode，however，the seismic load is only to be defined as 20% of the weight of a crane，neither dynamic unstability of the structure nor influence of the surrounding ground type is sufficiently consideredIn this paper，a series of centrifugal shaking table tests was performed to investigate the seismic characteristics of the tower crane supported by a pile foundation in soft clayTwo different weight conditions were set for the crane jib to accurately simulate practical situationsFrom the test results，the dynamic behaviours of the tower crane and the influenced factors were discussedIn addition，it was concluded that the weight conditions for the crane jib give significant influence on the level of pile damage and might lead to different failure patterns of the tower crane

Keywords：seismic interaction，centrifuge modelling，tower crane，pile foundation，shaking table test

CLC Number：TU473Document Code：AArticle ID：1000-0666（2017）01-0035-10

Introduction

A tower crane supported by a pile foundation is installed on the outside of a structure during construction when it cannot be installed in the insideThe pile foundations have been designed based on the standard of the building constructor because there are no design guidelines on pile foundations of the tower craneHowever，even a temporary structure such as a tower crane can cause large damage if it over-turns due to an earthquakeTherefore，it is necessary to clarify the earthquake resistance of the tower crane and determine the design standards of a pile foundationThe dynamic response characteristics of tall structures are influenced by the vibration characteristics of the related factors such as structure，a pile foundation and a surface groundFurthermore，the rigidity of the ground surrounding the pile foundation may deteriorate during the seismic ground motion and eventually the structure may become unstableTherefore，when determining the structural stabilities，the interaction between the ground and the structural system has to be taken account，especially in case of soft clay ground which is weak against vibrationGenerally，the earthquake-resistance of a tower frame structure used during construction works is smaller than that of the permanent structure because it is only temporarily used and its structure is likely to be designed without considering seismic vibration to minimize construction costsHowever if the temporary tower crane is struck by an earthquake，there is a strong possibility that the resulting damage may affect not only the construction site but also the surrounding houses and passersbyIn fact，there was a serious accident during the Chi-Chi earthquake in Taiwan where a climbing jib crane fell to the surface ground from a height of 260 m and five people diedIn this case，the climbing jib crane，installed on the top of a skyscraper under construction，was thought to be damaged by the unexpected strong vibration due to the large earthquakeAccording to the design code of the crane，an earthquake load is assumed to be 20% of vertical loadHowever，in the case of a strong earthquake，the assumed maximum earthquake load on a tower crane may be exceeded because of its unstable slender structureTherefore，it is essential to analyze the dynamic characteristics of the tower cranes to prevent any damageThe effect of loading conditions on the response characteristics have been analyzed through the previous centrifuge testing of tower craneIn this paper，to develop an understanding of its dynamic behaviors，a model tower crane supported by a pile foundation in soft clay was investigated by using dynamic centrifugal shaking table tests