Considerations on the conversion, rehabilitation and final-ly demolition of high-rise buildings have been subsumed under this heading.
4.7.1 Conversions
Conversions are constantly being made to any high-rise building with thousands of square metres of useful floor space. Redecoration and modernization are the common-est conversions, in addition to those necessitated by changes in operational procedures and use of the build-ing.
More stringent or additional requirements in respect of fire protection, installations or computer systems can also make conversions necessary.
On the one hand, conversions and changes of use are fa-cilitated by the separation of shell (= supporting structure), installations and interior finishing commonly applied in the construction of modern high-rise buildings; at the same time, however, it is precisely this separation that im-poses limits on what is economically acceptable. Even if technically feasible, conversions involving changes to the existing structural system, i.e. to the supporting structures, will usually be rendered impossible on account of the costs involved. For this reason, conversions will almost al-ways only affect the interior finishing and the installations.
The range of possible conversions extends from simply relocating interior wall elements or fitting complete new false ceilings or laying new floor coverings to “gutting”
the building completely. In such a case, all or part of the
building is restored to the condition of a shell and then refinished with corresponding installations and interior finishing in line with its new use.
However, if these conversions result in considerably higher loads for the building, these loads will have to be discharged via extended foundations in extreme cases.
Particular attention will have to be paid to settlement in this context. The problem can be minimized by providing additional piles, for example. From a technical point of view, however, this will prove fairly difficult as the working height of the drills is usually limited by the height of the various levels in the underground car parking.
The fact that conversions are often undertaken while oper-ation continues without interruption in those parts of the building and on those floors not affected by the work not only makes the work more difficult, but also increases the risk for the insurer. The nuisance due to noise and un-pleasant odours or temporary failure of the sanitary instal-lations, heating or ventilation are relatively harmless phe-nomena. The dust inevitably generated by such conver-sions, on the other hand, can have serious consequences if high standards of purity and hygiene must be met by those areas still in operation, such as computer systems or doctors’ offices.
As in the case of “normal” building work, the use of such flammable substances as adhesive and bituminous mater-ials or naked lights, for instance for soldering and welding, will be unavoidable when carrying out conversions. Ex-tremely stringent requirements must therefore be imposed on the fire-protection measures due to the incomparably greater risk potential. In particular cases, the fire brigade will have to be ready on site to take immediate action if an emergency arises.
Another problem associated with conversions is that the normally strict controls with regard to access and author-ization are often suspended for the conversions: workers, suppliers and the vehicles transporting materials and equipment need “open doors”. This naturally also in-creases the risk of unauthorized persons exploiting the situation and simply marching into the building.
Conclusion: all conversions, no matter how slight, must be thoroughly planned in advance and organized in detail with due consideration given to all eventualities.
4.7.2 Rehabilitation
Rehabilitation is an extreme form of conversion. The two commonest reasons making rehabilitation measures ne-cessary are
– physiologically harmful materials, such as materials containing asbestos or materials with excessive formal-dehyde concentrations, or
– potentially dangerous structures.
All the aspects already mentioned in the previous section also apply here in particular. In addition, there is the prob-lem of disposing of the physiologically harmful materials.
Correct disposal of contaminated materials and sub-stances not only poses a technical challenge, but is also one of the most difficult jobs for third-party liability
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ers on account of the possible environmental impact and health hazard.
In the majority of cases, it will be impossible to continue normal operation of the building while the rehabilitation work is in progress. For this reason, such rehabilitation will usually also be associated with conversion and a completely new interior finish.
An alternative method was employed when Winterton House in London was rehabilitated in the 1960s. All false ceilings and facade linings were removed first. The new brick facade was then built up on its own foundations around the steel supporting structure. The facade was secured to the supporting structure by means of steel brackets for reinforcement. An active construction was required to compensate the differences in thermal expan-sion of the facade and supporting structure. In this case, the roof structure links the inner skeleton with the outer wall via hydraulic presses. These presses are in continu-ous duty and maintain a constant compressive strain on the upper edge of the masonry. The building’s outer and inner columns were reanchored in the roof structure, thus reducing the load in the columns. Ceilings in line with today’s state of the art were then installed.
4.7.3 Demolition
Demolition remains the method of last resort when even changes in use, conversion and rehabilitation can no long-er meet the more stringent requirements imposed on a building.
It is no longer standard practice today and in many coun-tries even illegal simply to demolish a building – often with the help of unskilled labourers. Experienced special-ists are needed not only in order to meet environmental regulations requiring that all materials and parts accumu-lated in the course of the demolition work be carefully sorted, but also to judge how the complex supporting structures will react during the demolition. Within only a few years, the demolition of a building has ceased to be a low-tech job and become a highly specialized technical task.
Specialists often take over when the building has finally been gutted, i.e. when all interior finishings and installa-tions have been removed and duly disposed of (recycling) and when there are no further physiologically harmful materials in the remaining supporting structure. Either the building is then dismantled carefully and with as little noise and dust as possible, the reinforced concrete literally being “nibbled away” by special machines, or – if the cir-cumstances permit – explosives experts apply their pre-cisely primed charges to the predetermined points after analysing the drawings and inspecting the remaining building. As spectacular explosions of high-rise buildings have proved, experienced experts can make a building collapse in such a way that the surrounding structures remain undamaged. Less carefully planned explosions, on the other hand, have caused serious damage to the surrounding areas.
80 BLASTING OF A HIGH-RISE OFFICE BUILDING