SETTING OUT BUILDINGS
For buildings with normal strip foundations the corners of the external walls are established by pegs located directly from the survey control or by measurement from the site grid. As these pegs would be disturbed in the initial excavations their positions are transferred by total station on to profile boards set well clear
of the area of disturbance. Prior to this their positions must be checked by measuring the diagonals.
The profile boards must be set horizontal with their top edge at some predetermined level such as damp proof course (DPC) or finished floor level (FFL).Wall widths, foundation widths, etc., can be set out along the board with the aid of a steel tape and their positions defined by saw-cuts. They are arranged around the
building as shown in Figure . Strings stretched between the appropriate marks clearly define the line of construction.
In the case of buildings constructed with steel or concrete columns, a structural grid must be established to an accuracy of about ±2 to 3 mm or the prefabricated beams and steelwork will not fit together without some distortion. The position of the concrete floor slab may be established in a manner already described. Thereafter the structural grid is physically established by Hilti nails or small steel plates set into the concrete. Due to the accuracy required a 1 theodolite and standardized steel tape corrected for temperature and tension may be preferable to a total station.
Once the bases for the steel columns have been established, the axes defining the centre of each column should be marked on and, using a template orientated to these axes, the positions of the holding-down bolts defined . A height mark should be established, using a level, at a set distance (say, 75 mm) below the underside of the base-plate, and this should be constant throughout the structure. It is important that the base-plate starts from a horizontal base to ensure verticality of the column.
Holding down bolt positions