US 20060037257 A1
A method for controlling the collapse of a building having multiple floors. The method comprises the step of providing at least one load-bearing strut between at least one set of adjacent floors and attached to the load-bearing structure of the building, the strut being constructed such that, under building collapse conditions, it absorbs enough of the energy released during collapse of the building to control the rate of collapse of the building to reduce damage thereto. A building collapse control system is also provided.
1. A method for controlling the collapse of a building having multiple floors, the method comprising the step of:
providing at least one load-bearing strut between at least one set of adjacent floors and attached to the load-bearing structure of the building, the strut being constructed such that, under building collapse conditions, it absorbs enough of the energy released during collapse of the building to control the rate of collapse of the building to reduce damage thereto.
2. A collapse control system, for a building having multiple floors, the system comprising at least one load-bearing strut located between at least one set of adjacent floors of the building, the strut being attached to the load bearing structure of the building, the strut being constructed such that, under collapse conditions, it absorbs enough of the energy released during collapse of the building to control the rate of collapse of the building to reduce damage thereto.
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This invention relates to prevention of the catastrophic/avalanche collapse of tall buildings.
There is an increasing need in the construction industry to modify tall buildings to such a level that they can withstand extreme damage without such damage leading to complete collapse of the building. In the construction industry, there is a widely held view that this is impossible to achieve in a cost effective and space efficient manner.
Where severe damage occurs to an intermediate level of a multiple storey building, the situation can arise whereby the damaged structure is unable to support the section of the building above the damaged area. As a consequence, this upper undamaged section of the building collapses onto the lower undamaged section of the building. The increased loading on this lower section is then too large to be maintained by the skeleton framework of the building and further collapse ensues. This chain of collapse can continue unchecked until the entire building is completely destroyed, effectively collapsing in a chain reaction.
The present invention seeks to prevent this form of collapse.
According to the present invention there is provided a method for controlling the collapse of a building having multiple floors, the method comprising the steps of:
According to the present invention there is further provided a collapse control system, for a building having multiple floors, the system comprising at least one load-bearing strut located between at least one set of adjacent floors of the building, the strut being attached to the load bearing structure of the building, the strut being constructed such that, under collapse conditions, it absorbs enough of the energy released during collapse of the building to control the rate of collapse of the building to reduce damage thereto.
The strut may comprise an outer housing, this housing may be telescopic such that it reduces in length under particular loading conditions. Alternatively the housing may be designed to buckle in a controlled manner or to form an inversion tube under load conditions.
The struts may be incorporated into the original structure of a building forming an integral part of the framework or they may be added retrospectively to an older building. They may be designed such that, upon collapse of the building, a survival space is maintained between adjacent floors of the building. This survival space may be, for example, approximately half of the height of the floor spacing of the original, undamaged building.
The struts are preferably hollow in configuration and include a further means for absorbing energy. The struts may include a crushable core material which may be formed from an open or a closed cell filler material. The structure of such a filler may be one of the group of foam, honeycomb, eggbox or a number of individual crushable elements may be used, such as buckling tubes. A homogeneous porous material may also provide a suitable crushable medium. Suitable materials may be metal (such as copper, aluminium, steel), polymer or ceramic (such as concrete), or a combination thereof.
The strut may further contain water which has a two-fold benefit, firstly to improve the thermal transfer properties of the housing material and secondly, the fire mitigation properties of the water can be utilised upon failure of the housing material. Valves may be incorporated in the strut housing to assist water distribution from the core of the struts. Alternatively, a water jacket could be incorporated into the strut to provide similar benefits.
Energy absorption means for the core of the strut may be provided by a mechanism which utilises a set of wires to be stretched or by manipulation of metal rods around a series of rollers within the strut.
The system may comprise plural struts, and in such a case stability of the collapse control system may be enhanced by interconnecting liquid filled regions of the struts such that multiple distributed struts are reduced in length at the same rate.
The housing may further comprise mechanical stops at regular intervals which support the static loading but fail under the increased dynamic loading associated with collapse. Internal column dividers may also be introduced to separate the core material into cells, this not only helps to prevent transmission of stress waves through the entire length of a strut but also eliminates the possibility of significant creep in the core material over the life of the building.
An example of the present invention will now be described with reference to the accompanying drawings, in which:
FIGS. 10 to 12 are schematic views of example components for employment in a system according to the present invention which employs active control;
It is an intention of the present invention that not only is the rate of collapse brought under control but that the extent of collapse be limited. In other words, after collapse of the damaged storeys, and potentially those immediately below the damaged sections as required to arrest the collapse phenomena, a survival space should be maintained on those levels where the energy absorbing struts 2 have been brought into play/activated. This survival space may, for example, be approximately head height or half of the original undamaged floor spacing distance. Such a clearance will allow any remaining personnel on the storey in question to escape being crushed by their local ceiling 4 (and floors above).
The telescopic mechanism 3 is shown in greater detail in
Energy absorption in the examples detailed so far is provided by compression of the crushable core 6. Additional energy can readily be absorbed by designing the housing 5 such that it fails predictably under particular loading conditions. Such modes of failure are illustrated in
Axial buckling of the housing 5 of the energy absorbing strut 2, rather than lateral buckling associated with the load-bearing strut 1, can be controlled by designing the struts 2 to the correct dimensions and introducing grooves or other geometrical changes into the strut housing 5 to initiate the buckling mechanism when a particular load is experienced. This buckling phenomena will then propagate along the length of the strut 2, wrinkling the housing 5, as a consequence significant levels of energy are absorbed.
Tube inversion, illustrated in
Energy absorbing struts 2 designed as in either of these examples could easily make use of the additional benefit of being filled with a crushable core 6, as in the telescopic example above, to further enhance the energy absorption properties of the device.
Suitable fillers may be formed from open cell structures or closed cell structures such as foam, honeycomb, egg box shaped layers or even porous materials. These fillers may be formed from metals, polymers or ceramics, the latter being formed, for example, by incorporation of soft foam beads into the wet concrete such that these form cavities in the set concrete which allow the material to be crushed, in this case the core will be pulverised, thus absorbing large amounts of energy.
Energy absorption may be performed through alternative means as illustrated in
Rather than using one of the above fillers, the strut housing 5, as shown in
A situation may arise where the damage to the building is local to only a few load bearing struts 1. This could, potentially, result in the upper storeys toppling to one side as asymmetric failure occurs. Such a scenario could be avoided where several of the energy absorbing struts 2 are evenly distributed over the plan form of the building and are hydraulically linked 13 to each other (see
Such an approach could be considered to be a passive system and is also shown generally in
As an alternative to the above compensation arrangements, active compensation may be provided, and examples of active control are shown in FIGS. 10 to 12. In this example, when one of the struts 2 fails a sensor first detects failure and a processor 31 sends an actuation signal to a strut on the opposite of the building to initiate a controlled collapse on that side. If plural struts are used and distributed-around the building then struts can be actuated at different times to control the collapse and prevent skew of that collapse.
In the example of
In the above arrangement the struts 2 are disposed in a generally vertical manner to control collapse in a downward direction. In the example system of
The examples described so far have generally been focussed on secondary devices mounted along side the main load bearing struts 1 of the building, however, the present invention may also be used as an integrated feature within new builds as described above in relation to
In this example under normal conditions, relative motion of the telescopic sections 3 is prevented by mechanical stops 15. These stops 15 are designed to sustain the static loading of the building but to shear under the increased dynamic loading associated with collapse of the building. The failure of these stops 15 reduces the length of the housing 5 such that the load is transmitted to the core material 6. Under this loading the core will be crushed, thus absorbing energy being released from the collapsing building. As described above, water 10 may be additionally filled into the hollow housing 5 to achieve improved thermal properties and introduce a level of fire mitigation.
In any of the above examples the energy absorption properties of the crushable core 6 may be improved by installing column dividers 16 such that the core is split into separate cells. This has the added benefit of preventing any significant amount of creep in the core filler material 6 over the life of the building.