3.2 Temperature Match Curing ( TMC ) and Heat Calculation Curing Plan
With tower wall concrete thickness exceeding 1m , each tower lift was monitored , via thermocouples cast-in to the north face , to ensure that the maximum peak ( 75 o C ) and differential (< 28 o C ) internal hydration temperature requirements were not exceeded for individual concrete pours . 8 number 100mm cubes were taken from the last concrete barge delivery , placed in the water bath on the jumpform and the water bath connected to the cast-in thermocouples via wires projecting vertically through the construction joint . The TMC concrete cube test results provide evidence that in-situ strength of concrete pours reached the minimum requirements for both the removal of shutters ( 6.0N / mm 2 ) and / or the jumping of the formwork ( 10.0N / mm 2 ) in accordance with the designer ’ s heat calculations , for summer and winter , that set requirements for early striking of the shutters to minimise risk of excessive cooling shock resulting in early thermal cracking .
The points of the segment pour centrelines , bridge and tower axes reference lines , curves and their centre points and local jumpform triangulation survey checks were marked using the 4 Global Navigation Satellite System ( GNSS ) on the internal and external jumpform working platforms and by Totalstations within the inner and outer jumpform platforms . Pairs of monitoring prisms were installed on the external tower face in every 5th segment and surveyed from the adjacent tower . As-built surveys from the previous segment pour were undertaken on the day after pouring concrete , processed and used for any required shutter adjustments for the proceeding lift . Allowable plan positional tolerances of + 25mm ( corners ), + 10mm ( centrelines ) and + 10mm level ( centrelines ) were recorded for every segment .
3.3 Structural Health Monitoing System sensors
The surface area of the towers is approximately 26,000m 2 and whilst every part of the structure is accessible at touching distance , the towers had various sensors installed to monitor the structure . These sensors comprise of :
- Cast in : strain gauges ( static ), corrosion sensors , temperature ( concrete ),
- Post-fixed : strain gauges ( dynamic ), tiltmeters , accelerometers , temperature ( air ), GPS , anemometer .
Figure 12 : North tower – temporary formwork is lifted off
1 / 2017