Abstract of Special Research Report (SRR-No.20)
National Institute of Occupational Safety and Health, Japan
Study on Safety Countermeasure of Cranes Against Earthquake
|Yutaka MAEDA and Yoshio KITSUNAI|
: The Southern Hyogo-prefecture earthquake hit around the Kobe City in the early morning of 17th January 1995, and caused a great deal of damage to many cranes. Through on-the-spot investigation and questionnaire, main feature of damage to cranes by this earthquake was found that (1) tower cranes and jib cranes suffered more damage compared with overhead travelling cranes and bridge cranes including container cranes. (2) main damage of overhead travelling cranes was falling down or derailment from the runway girder due to large deformation of building, and container cranes and unloaders were damaged due to movement of foundation associated with soil liquefaction, and (3) tower cranes fixed to buildings with stays were more severely damaged than ones standing by themselves, and the stays seemed to pay the important part of damping or amplification of seismic vibration.
Survey of Damage of Cranes in the Southern Hyogo-prefecture Earthquake
|Yoshio KITSUNAI and Yutaka MAEDA|
: On the early morning of 17th January 1995, a very severe earthquake hit around the southern portion of the Hyogo prefecture, particularly the city of Kobe. The earthquake caused catastrophic disaster, with more than 6,400 people dead, about 300,000 injured due to collapse of more than 100,000 buildings resulting from severe shaking and fire. All types of cranes such as container cranes in Kobe harbor, unloaders, jib-cranes in shipbuilding yards, tower cranes in building lots, overhead travelling cranes in manufacturing works, etc. were broken or failed significantly.
The Vibration Characteristics of the Tower Crane Used in the Construction Site
|Seiji TAKANASHI, Akira TSUBOTA and Kimio KIKUCHI|
: As for the tower crane, earthquake resistance has been taken into consideration and design has been done in the same way as for other structures. However, the dynamic behavior has been hardly examined so far. Therefore, in this study, a free vibration test was carried out to examine the dynamic characteristics such as natural frequencies, damping factors and the mode shapes of the tower crane. The experiment was conducted on a tower crane used in the construction site. The experiment was done two cases. The first was for the tower crane without stays standing by itself with a tower mast of 24m length. And the second was for the tower crane with a tower mast of 75m length, with stays installed in 2 steps in the height direction. For the latter case, the test was repeated for different plays of stays. A jack was set in a stay, as the mechanism to adjust length. If the initial stress was added to the jack, there was no play in the stay. If not so play was left in the stay.
Vibration Test on Model of Construction Tower Crane
|Katsutoshi OHDO and Takanobu SUZUKI|
: The Hanshin Awaji earthquake caused much damage to construction tower cranes, and some cranes collapsed or fell to the ground. Fortunately, the earthquake occurred in the early morning, so fatal accidents by the collapsed cranes had not been happened. However, if the earthquake had occurred in the daytime, it was assumed that not only the construction workers but also many pedestrians or car drivers around the sites would had been killed or injured.
Buckling Strength of Stay of Construction Tower Crane
|Katsutoshi OHDO and Etsuji YOSHIHISA|
: The Hanshin Awaji earthquake caused much damage to construction tower cranes, and many stays that connected the tower cranes to buildings under construction were broken. As a result, some cranes collapsed or fell on the ground. In spite of this situation, the buckling strength of the stays has not yet been made clear, and even experiments on the buckling strength of the stays has hardly been performed. To prevent the collapse accidents of tower cranes due to the earthquake, the design method of the stay needs to be established.
: This specific research started with the occasion of the Southern Hyogo-prefecture earthquake in 1995, which caused a great deal of damage to many cranes. The dynamic effect of earthquake on jib cranes and tower cranes is not prescribed in the standard for proof against earthquake of crane.