High Rise Building Demolition - Bottom Up Method

Kajima Corporation Buildings – Demolition Methodology

“There are so many quiet revolutions going on in tall buildings. Top-down construction is one such revolution, and here is another—bottom-up demolition.” Location TokyoCompletion Date Tower 1: 1968 Tower 2: 1972Demolition Date 2008Height Tower 1: 76 m (249 ft) Tower 2: 65m (213 ft)Stories Tower 1: 20 Tower 2: 17Primary Use Office

The demolition of older tall buildings is increasingly becoming an issue with the impact on the environment and re-use of materials. The new Kajima method offers a solution which addresses and improves upon typical demolition methods. This method will improve the sustainability of a building through its lifespan and final deconstruction. Aside from improving sustainability, this method also decreases the impact of demolition on its surroundings.

Figure 1. Demolition sequence: March 08		Figure 2. Demolition sequence: May 08		Figure 3. Demolition sequence: July 08

A high-rise construction boom in Japan during the 1960s and 1970s has resulted in a large amount of aging towers. Building owners have an interest in demolishing the old structures to replace them with more modern, safe, and work-friendly buildings, but there are several issues to address in this process.  The Kajima “Cut and Take Down Method” was developed to satisfy both safety and environmental concerns. In April 2007, Kajima started to develop this new demolition method to demolish its aging office headquarters buildings, which were 76 meters tall and 65 meters tall. Buildings are usually demolished by placing heavy equipment and workers on the top floor and then lowering the waste material down to ground level. The “Cut and Take Down Method” alternatively allows the workers to start at the base and work their way up. By starting at the bottom, gutting one floor, and then lowering the entire building on jacks one floor at a time, all work can be performed safely at ground level.

Figure 2: Demolition process underway

On the 85 by 60 meter site, the two towers were situated quite close to another office building and a residential building, emphasizing the need for a clean, quiet demolition process. To accomplish this, temporary columns are used around the structural column grid, the existing columns are replaced, and then hydraulic jacks are placed where the existing columns were and the building can be lowered to the next floor plate where the process is repeated.  The hydraulic jacks each had a capacity of 1,200 tons, and supported the structure through each cycle of lowering. A cycle would lower the whole building by 675 mm, which meant that five cycles were required for each floor (total of 3.375 meters). The total time to demolish a whole floor was six days: 2.5 days for lowering and the remaining time to demolish the rest of the structure.

Figure 3. Demolition process step 1: Cut the column. Cut length of 70 centimeters for a column and take off
Figure 4. Demolition process step 2: Extend the jack stroke. Extend length of 70 centimeters for jack stroke
Figure 5. Demolition process step 3: Take down all jacks. After doing step 1 & 2 for all columns, all jacks were taken down
Figure 6. Demolition process step 4: Take out beams and floor slab of the floor above

A “core wall and load transferring frame” system are utilized to temporarily reinforce the structure to prevent any lateral movements due to wind or earthquake forces. The core wall was 400–900 mm thick reinforced concrete and was placed in the center of the floor plates up to the third level to take any lateral forces of the superstructure. To ensure the transfer of lateral loads, the load transferring frame was installed in steel and connected to the existing structure. It was then tied into the core wall with a track-like system, which would lock in place in the event of an earthquake. The new method allows the dismantled building to keep the same level of seismic and wind resistance capability as its original design. It also reduces the amount of noise as compared with typical top-down approaches, because all the work is being completed at the ground level. Safety of workers is increased as well, due to the location of all the work being at ground level as opposed to the building top.

Figure 7. Removing columns after cutting

In considering the reduction of site waste being sent to landfills, this new method allows for a more efficient system of recycling and reusing. The orderliness of the process means that the materials from each floor may be sorted effectively so the maximum amount of material is sent to its rightful place instead of batches of material getting sent to the landfill without adequate sorting. The Kajima Towers were able to be sorted into 30 types of materials for recycling, as opposed to a typical 20 at other demolition sites. The recycling rate was over 90% for the interiors of the buildings, surpassing the average 55%.  Although this method was developed for a building with steel frame structure up to 20 stories high, it can be applied to larger-scale buildings as well. Furthermore, this process is especially useful in densely built areas where typical demolition may impact neighboring buildings. The demolition of the two Kajima Towers was completed in nine months for the 20- and 17-story buildings. Though the costs of this method may be 5–10% higher than traditional methods, the total time of demolition can be decreased by 15%, increasing the turnover rate of the site.

Figure 9. Core wall demolition