Praeter Engineering have been involved in one of the biggest construction projects in Scotland; the St James Quarter project, works involved retaining the existing John Lewis Partnership (JLP) building whilst allowing the counstruction to proceed under the live fully occupied building. There were 9 columns supporting the southern side of the JLP building which were successfully “jacked” up onto temporary trestles, the existing concrete columns cut through below a supporting gripper plate and removed. The existing columns were supported on steelwork grippers by post tensioning a number of macalloy bars through and around the column in order to grip onto the column.
The loads in the trestles varied from 100T up to 450T, additional beams spanning between the trestles supported the new construction joint of the existing slabs. Praeter Engineering used a combination of hydraulic cylinders and flat jacks to support the existing superstructure in combination with load cells and a 24hr live monitoring system. The existing (live) structure was monitored 24/7 with a combination of load cells, displacement sensors, ATS and daily surveys. After the dig down was completed new steelwork columns were constructed and the load from the existing columns jacked down onto the new columns.
Praeter Engineering have also completed the de-stressing of the temporary ground anchors within the retaining structure around the project. As soon as each of the concrete floor plates were constructed this would support the retaining structure in the permanent case allowing for the removal of the temporary Dywidag prestressed ground anchors to be de-stressed. Praeter fabricated jack components to allow for easy removal of the load from the ground anchors.