May 24 2007
London based Pyramid Builders have developed an idea for increasing the lateral load resistance of large blockwork walls and carried out full scale tests at CERAM.
In a preliminary phase of the work four walls each 8.1m long and 5.1m high in 140mm thick concrete blockwork have been built and tested under lateral load. Each wall was built in 7N/mm2 concrete blocks and a designation (iii) mortar. They were built off an Aquaguard dpc and were tied to steel columns at each end with 175mm Ancon frame ties. At the head of the wall HRV head restraints were fixed to a steel channel soffit at 900mm centres. Movement joints were included between the blockwork, the steel columns and the soffit.
Two of the walls contained wind posts, in one a 100mm square steel box section was tied to the blockwork with Ancon ties in each course. 3.5mm bed joint reinforcement (BRC) was used in each of the bottom nine courses and then every other course. In the second a 100mm x 60mm wind post was built into the blockwork and similarly anchored. Bed joint reinforcement was used in every course with a second 2m long section extending 1m either side of the wind post.
Two of the walls contained bond beams at the 9th and 15th layer each containing two 16mm dia. reinforcing bars. These walls contained bed joint reinforcement in each course.
The walls were tested to destruction after curing for 28 days. Lateral load was applied using air bags over the whole area of the wall and reacted by a plywood faced steel framework. Deflections were monitored at the face of the wall.
All of the walls tested had similar ultimate failure loads.
The one with the integral wind post cracked at 3.6kN/m2 prior to failure at 5.2kN/m2. The other walls did not crack before failure or in the case of wall 2 did at close to the failure load.
All of the walls resisted loads well above what might be expected in practice and well above that for a wall without either bond beam or wind posts. The construction of the walls containing the bond beams was simpler than those containing the wind post and their effect has been to enable the wall to span effectively in two directions and resist considerable loads.