Study on Selection Schemes of Blasted Columns of Buildings
to Improve Efficiency and to Secure Safety during Demolition
Kenta Higashi1 and Daigoro Isobe2
12

Graduate School, University of Tsukuba
Ibaraki 305-8573, Japans1620917@s.tsukuba.ac.jp

Division of Engineering Mechanics and Energy, University of Tsukuba
Ibaraki 305-8573, Japan
isobe@kz.tsukuba.ac.jp

Strong demand for demolition of buildings increases due to the aging of buildings which werebuilt during the period of high economic growth and the redevelopment of cities. At present,demolition using heavy equipment is mainly conducted in Japan; however, the demolition
work will be prolonged and the cost will increase if the scale of the building becomes larger.
A blast demolition technique is often used in Europe and the United States to solve theconcerns of demolition using heavy equipment. The blast demolition techniques can avoid
dangerous work at a higher place and can be completed at a relatively low cost in a shortperiod. However, as demolition planning are mainly conducted based on proprietary
technology of some vendors, the technique requires high levels of knowledge and experiencein such occasion when selecting blasted columns. Furthermore, Japanese buildings aredesigned more strongly than in Europe and in the US, so the rules cannot be simply adapted.
To ensure reliable and safe demolition, it is necessary to establish a quantitative selection
scheme of blasted columns based upon criteria of dynamics.
In this study, a blast demolition planning tool of buildings based upon a parameter called the(a) 0.9 s (before (b) 1.0 s (1st blast) (c) 5.0 s (after thethe 1st blast)
1st blast)(d) 9.0 s(e) 30.0 s (final form)

Fig. 1 An example of blast demolition analysis (10-story, 7×3 span model, random selection of
blasted columns)(a) 0.9 s (before (b) 3.9 s (before the (c) 6.0 s (after thethe 1st blast)
2nd blast)
2nd blast)(d) 6.9 s(e) 30.0 s (final form)

Fig. 2 An example of blast demolition analysis (10-story, 7×3 span model, selection of blasted
columns with the largest variance of the key element index values at third floor)

key element index [1], is developed. The index indicates the contribution of a column to thestrength of the building and can be numerically evaluated; the higher the index value, thehigher the contribution to the overall strength of the building. An Adaptively Shifted
Integration (ASI) - Gauss code [2] is applied to blast demolition analyses of ten-story steel
framed building models with different span numbers. Various selection schemes of blasted
columns using the index were evaluated by comparing the efficiencies and levels of safety
during demolition; namely, by comparing the relation between the number of blasted columns
and the heights of remains after the demolition, and by the scattered distance of members afterdemolition. First, the blasted columns were selected randomly to derive a simple relation
between the number of blasted columns and the heights of remains of buildings. The results
indicated that there are similar tendencies in the relation regardless of the number of spans.
However, some results deviated from the tendencies. In those cases, safety could not besecured because the buildings collapsed in the lateral direction (Fig. 1). Next, some selection
schemes of blasted columns based upon the key element index values were applied to securesafety during demolition. The variances of key element index values were considered, inparticular, to make a large difference in the distribution of the index values in each layer ofthe building. A difference in efficiencies of demolition appeared between each selection
scheme. The efficiency deteriorated in most of the selection schemes as the number of spansincreased. However, the efficiency maintained the same level when the columns with thelargest variance of the key element index values at the first floor were selected as the blastedcolumns. As shown in Fig. 2, most of the cases using the variance of index values showed acollapse motion in vertical direction, and the scattered distances of structural members weresignificantly suppressed.

References[1] D. Isobe: An Analysis Code and a Planning Tool Based on a Key Element Index forControlled Explosive Demolition, International Journal of High-Rise Building, Vol. 3, No. 4,
pp. 243-254, 2014.
[2] K.M. Lynn and D. Isobe: Finite Element Code for Impact Collapse Problems of Framed
Structures, International Journal for Numerical Methods in Engineering, Vol. 69, No. 12, pp.
2538-2563, 2007.