Laser scanning, digital set out ensure clash-free steel support
With Aldi set to open late this year at the Indooroopilly Shopping Centre, CSD Group Australia was engaged to do pre-construction works for the supermarket’s new location – on level one of the shopping centre, above a carpark.
The project involved reinforcing the floor of the new Aldi store with additional steel support.
CSD Group performed a laser scan and digital site set out prior to detailing the steel supports that will be installed to the ceiling of the current carpark, beneath the store’s location.
The 3D laser scan and digital site set out by our total station unit (ICR) were done simultaneously and took just one day – six hours and three hours, respectively. CSD also undertook the laying out of all concrete fixings, and site fitting plates, using our inhouse ICR unit.
Laser scanning, point clouds and detailing
At the office, the 3D scans were processed and stitched together using the Faro SCENE software to show picture-quality point clouds of the carpark. The concrete columns, pen marks showing post tension (PT) cables and conduit locations in the ceiling of the carpark and rebar in the concrete columns also needed to be picked up in the scan.
All these enabled more accurate steel detailing by ensuring that rebars, PT cables and service conduits were avoided. It also made detailing steel according to existing site conditions easier.
Once complete, the point cloud was imported into Tekla to begin steel modelling. Without doing a laser scan, steel detailers would normally simply refer to the drawings received from client.
In this project, the plan had uniform, evenly spaced brackets and beams. But upon cross checking on the point cloud, the following were determined:
Steelwork had to be redesigned to be installed to attach to the ceiling vs the intention to install to the concrete columns, due to rotation and out of square existing concrete columns. The redesign resulted in cost savings, easier installation and faster fabrication while maintaining structural integrity.
All steel was to be fixed to the underside of slab with masonry anchors at 1m centres. We managed to avoid all PT cables as marks (scanned by others) were all picked up. Beams were fixed to existing concrete columns with first fix bracket t-plates, each with six (6) Hilti fixings. All rebar marks were picked up by the scan, so all 16 brackets were modelled individually to miss the rebar. Each bracket ended up being different.
Columns were not square to each other and were on a rotation. This would not be picked up with a tape site measure. The ceiling is sloping, so the steel is not all at the same level. It was adjusted to make grout between top fix plates and ceiling to a minimum.
The new steel model was re-imported to the point cloud in correct position. Using virtual reality (VR), a “walk through” of the carpark was also done while in the office. The VR enabled us to do a more enhanced clash check between new and existing structures. The following was observed:
Following the original plan, the steel beams in some parts will result in very low headroom that will be below the minimum 1950cm floor to ceiling/beam heights for this carpark. The beam cranks connecting into existing concrete columns had to be redesigned to be smaller in depth. This would not have been picked up until after steel installation if no point cloud was used.
More accurate steel drawings
Laser scanning makes pre-construction work more efficient and accurate. With laser scanning, our steel drawings for the Aldi project already incorporated details of existing structures and marks.
Without laser scanning, some of these minute details would likely be overlooked and would be observed during site installation.
Digital lay outs – the biggest cost saver
Taking measurements digitally is more accurate and less laborious than manually using a tape measure. For the Aldi project, CSD Group undertook digital layout for core drillings in columns and masonry anchors drillings in ceiling.
CSD Group utilised its ICR unit on site taking points to geo locate the site. The reason for this was that after modelling was complete the ICR unit was taken back to site to lay out all site drilled holes into existing structures (concrete and steel). These holes would have taken over a week for a team of site workers to manually mark out with a tape measure and laser levels, with elements for human error. Using the ICR unit approximately 350 site drillings were accurately marked out by CSD technicians in hours, by one person, with all human error taken out of the equation.
To summarise, laser scanning and digital set out and layout benefited the Aldi project on the following points:
More accurate steel drawings
Minimal to zero chances of steel rework and clashes with PT cables, conduits, rebar, pipes
More accurate measurements
Less time spent on site
Extensive 3D site survey that can be uploaded, viewed and referred to offsite anytime, anywhere, minimising the need to return on site
Point clouds may be utilised for other purposes by the project manager
Faster turnaround time
Cost savings, especially on digital layout