Temporary Works: Temporary Structures
Temporary Works
Temporary works can introduce difficulties into any building process.
Apart from the fact that this most sensitive section of structural works is much too often left between the Consultants and Contractors chairs, various site conditions often result in costs increases and additional construction risks.
Additional costs aside, a frequent and unwanted consequence of these factors is an undesirable impact on finished layouts, full impact of which is usually only recognized once structural works are completed!
A frequent problem in London, and this applies to any city in any country really, is a situation where setting out of permanent replacement structures is constrained by traditional temporary structures systems of needles and props. This method commonly dictates that permanent structures provide a reduced headroom or that temporary works infringe on otherwise spaces not initially involved in construction process.
We specialize in resolving a very specific problem where limitation of access impose a resulting reduction in available headroom or indeed dictate abortive expenditure related to temporary works.
Problems
Traditional temporary works methods provide for construction of vertical props at each side of the subject wall which support horizontal needle beams. Needles are then inserted into the subject wall above the proposed permanent replacement structure.
Problems arise if no access is available to the areas above and below the location of proposed permanent replacement structure. This is often the case in Victorian conversions, or indeed in blocks of flats where in order to achieve desirable headroom the traditional needles would have to be applied inside the properties belonging to the neighbours above and below the subject property. This is obviously not practical or indeed possible and inevitably the headroom achieved with traditional methods is significantly reduced due to necessity to accommodate the thicknesses of temporary supports in addition to the thickness of permanent supports, within the confines of one property only.
Further problems arise if the access for construction purposes is available only to one side of the subject wall. Traditional prop-and-needle arrangements cannot accommodate this situation.
Some More Problems
Traditional prop-and-needle systems always undergo a noticeable deformation as the loadings are applied onto them. These deformations can be sizeable.
Prop-and-needle systems block both sides of the subject wall and this demands that the props are spaced further apart (to allow for introduction of permanent structures), which results in longer needles. In addition to this, permanent structures also deflect, and the total deformation of supported structures (eg. a wall) is equal to a sum of deformations of the temporary and permanent structures. The result is a noticeable deformation of such supported walls which presents itself as cracking through those walls.
In case where relatively heavier loads have to be supported (eg. walls at lower levels of a say three or four storey building) it is often required that a separate foundation is constructed under the each line of the props. This is an abortive cost as such foundations are constructed solely for the temporary support operations which typically last no more than a few days.