Parts of the building or entire building collapses.
Potential structural strengthening projects
Fit and fix plywood shear-wall/s up through the building.
Existing or new timber wall framing is fitted and fixed between the existing flooring and floor framing of the floor above. Plywood sheets are fitted and fixed to one or both sides of the wall framing. Hold-down ties may be required at each end of the shear-wall to resist overturning of the shear-wall in its own plane. The hold-down may be fitted up the full height of the wall and fixed down into the foundations of the shear-wall.
Form or strengthen a floor or roof structure (diaphragm).
a) Overlay existing flooring with plywood to form floor structure (diaphragm):
Existing flooring is overlaid with plywood that is screwed down to the existing flooring and floor framing. To provide adequate load transfer between sheets of plywood, a light-gauge galvanized steel strip is laid under the plywood joint with the centerline of the steel strip on the joint line. The screws on the perimeter of each plywood sheet pass down through the plywood and steel strip, into the flooring and floor framing.
b) Make floor structure (diaphragm) continuous by fixing through bottom plate of partitions:
Where the plywood of the floor structure (diaphragm) abuts a wall, a light-gauge galvanized steel angle is folded and fitted into the angle formed by the floor and the wall. The plywood sheet perimeter edge-fixing screws pass down through the plywood and the horizontal leg of the angle, and into the flooring below. Prior to fitting the wall linings, the vertical leg of the angle is fixed into the wall bottom plate with screws.
c) Where the supporting shear wall in the space below is not aligned with a wall in the floor above, new timber framing (blocking) is fitted and fixed between the top plate of the wall below and the flooring on which the plywood structure (diaphragm) is fitted. A light-gauge galvanized steel strip is placed under the plywood over the centre line of the wall top plate below. The plywood is fixed down through the steel strip and the flooring, into the blocking below with screws.
d) Fit flat-strap bracing in ceiling space to make structure (diaphragm):
To provide enhanced bracing capacity within the restricted space under a pitched-roof structure, proprietary galvanized steel strips bracing can be installed. Depending on the capacity required, multiple strips are fixed with screws to timber framing (blocking) that is pre-fitted and fixed into the roof or ceiling framing. The steel strip bracing is provided pre-punched for the screws, and packaged into a coil pack for easy of delivery into the roof space.
Fix masonry facade or wall to floor or roof structure (diaphragm).
The masonry is tied back onto supporting floor and roof structures (diaphragms). Steel dowels are grouted into the brickwork and fixed to blocking fitted between the joist members. The blocking is in turn fixed to the adjacent joists. Plywood perimeter strips and additional nailing down into the joist are provided to carry the face loading from the masonry wall into the structure (diaphragm) so that the seismic inertia load can be transferred to walls parallel to the loading.
Possible first steps with a structural engineer
They assess the structural capacity of the masonry building and provide specifications for the required strengthening work.
Updated on 15th December 2016