Eight-storey concrete frame block with bowing brickwork and brick slips movement

Five circa 1950/60s eight-storey blocks of concrete frame construction with cavity brickwork infill walls, with bowing brickwork and brick slips movement, due to concrete frame shortening – repaired by some rebuilding brickwork and brick slips, mech

case study 5731bcc53d2c00.87769077 - Eight-storey concrete frame block with bowing brickwork and brick slips movement

The subject development comprised of five circa 1950/60s eight-storey blocks of flats of concrete frame construction with cavity brickwork infill walls below windows and full height to flank elevations.

Problem

The infill cavity brickwork walls were constructed with an external skin of LBC type bricks, 75mm to 95mm cavity, and a hollow clay pot internal skin.

The infill walls were constructed from each concrete floor beam to the underside of the floor beam above with approximately 65mm support to the external brickwork.

This left 40mm protruding to accommodate six/seven courses of 35mm brick slip bedded onto the floor beam, forming the appearance of continuous brickwork. The bricks have weathered well, with little sign of spalling, though some damaged bricks were noted.

The manufactured brick slips were 35mm thick with a bedding groove to the rear.

The brick slips were bedded down onto the last brick course of the infill wall and onto the face of the concrete beam, with sand and cement mortar up to the first course of the brick wall above (no horizontal soft joints were found).

A cast-in wire butterfly tie was uncovered that had not been bent out and bedded into the mortar as intended. Previous repairs, bulging leaning movement, and hollow and missing brick slips were all noted.

case 25 a - Eight-storey concrete frame block with bowing brickwork and brick slips movement

Hollow clay blocks formed the internal skin of the cavity walls constructed in-between the concrete floor/beams and columns.

The wall ties were found to be galvanised vertical twist, generally adequately bedded, clear of building debris, installed to a good pattern and of adequate density.

No head restraints were located with the last row of ties six/seven courses down from the head of the wall. No significant corrosion to the existing ties was noted.

case 25 b - Eight-storey concrete frame block with bowing brickwork and brick slips movement

Discussion

We found that the buildings had generally performed well, including the buildings’ brickwork infill walls, with the exception of the brick slips and the head of the infill walls.

Since the buildings had been completed, the concrete used in their construction had shrunk, the concrete frame had shortened and the bricks’ first irreversible expansion had taken place.

Where brickwork and concrete frame abut these opposing stresses were putting the brickwork in compression, locking in the brickwork to the continuous brick slips to the flank walls.

This effect was further augmented by thermal expansion, especially to the south-facing walls.

Where the walls were not adequately tied the compression force had been released laterally, causing bulging and leaning of the brick slips and the head of the wall down to the first row of effective ties.

Most of the brick slips had become detached from the concrete beam, probably due not only to the compression force described above but to differing movements and poor fixing details. Modern-day standards require a mechanical fixing to each brick slip.

Solution

AWT completed a remedial scheme providing a viable repair by rebuilding sections of the brickwork and brick slips, introducing a pattern of mechanical fixings to the brick slips and angled head restraints along with a number of horizontal soft joints.

Action Wall Ties (AWT) are specialists in masonry reinforcement and repair, providing professional solutions to a wide variety of structural problems. Contact us on 01227 721 255, or email us.

 

 

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