“The reason we’re using Trimble is to find a better way to do something we’ve always done before. “ says Rosa Kirwan (JEG intern on the NCH Project)
The sheer scale of this project has forced the JEG team to ‘think outside the box’ and draw in new ideas and methods that they may not have used before in this country or industry.
Some of the numbers displayed in the chart below give an idea of the enormity of the task that the team face over the course of this job.
However……the same scale can also have a big positive effect on efficiency, as any improvements implemented can multiply up quite substantially and provide schedule certainty in this complex environment.
Due to the size of the hospital (160,000m²) and the high density of services in the building the team estimated there was over 400,000 individual anchor points to be set out for the Mechanical and Sprinkler systems. Setting out in the hospital is further complicated as there are a mixture of straight and curved gridlines due to the shape of the building.
Using traditional methods (tape measure, dimensioned drawing) you would hope to set out between 20 -30 points per hour, which equates to approximately 440 man weeks plus the time it takes to create over 120 dimensioned drawings. Setting out this way over a large area is very inaccurate and as the team are dealing with fine margins for coordination they had to do something different.
One of the team had seen the Trimble system used before on a project in Australia and suggested this may be a solution worth investigating.
Contact was made with the vendor, demonstrations carried out on site and the team felt this could be a winning solution.
Setting out using Trimble offers a much higher precision positioning of support points for all M&E installations and ensures that all elements of design and build come together in a construction project. On the NCH we are using the Trimble Robotic Total Station (RTS) 873 to identify and verify mechanical support points which are to be installed on ceiling and floor slabs.
Trimble Robotic Total Station (RTS) 873 and tablet computer
For coordination and clash elimination on site the JEG BIM team were already modelling in the threaded rod supports. By using a BIM plug in, the Trimble system is able to extract the exact point (X,Y,Z co-ordinate) where the rod intersects with the structure, thus creating a 3-dimensional node. These nodes can be filtered and labelled depending on which service they are supporting.
Once an area/zone is fully coordinated the service nodes can be dropped from the model to a .CSV file. This file is then loaded into the Trimble tablet computer and then you are ready to head out into the field.
Onsite the Trimble Total Station is setup the same as any other surveying station, triangulated off 3 known points. From there the preloaded points can be selected by service and marked out. Once a point has been set out, it’s marked off on the tablet and saved. Therefore, if you weren’t able to complete an area in one visit or there was something blocking access, it’s easy to see what still has to be set out.
The Trimble system means we can set out between 60-80 points per hour to an accuracy of 3mm, which equates to approx. 160-man weeks for the project scope.
Team members operating the total station and red, yellow & black colour coded set out
Setting out points are colour coded by service and discipline when marked on the concrete slab for ease of identification by installation teams.
One of the major issues the team had to overcome on the NCH project is how they could get to install their first fix anchors and drop rods ahead of the construction sequence, but still not interfere with other contractors productivity.
Under normal circumstances, due to the density of services in a building like this we are unable to install our first fix until the civil contractor has completed one side of the internal partitions. This would mean we would not get access to the majority of the Hospital until mid to late 2020 based on the construction schedule. However, by using the Trimble system and incorporating an idea that was featured in the LEAN Times No. 72 back in February 2019 the team are able to set out and install C-clips before the partitioning is installed.
This means we can start setting out and installing C-clips as soon as we have access to an area and other trades can progress unhindered as well.
Once the civil contractor has finished one side of his partitions in this area we can then start hanging up the pre-fabricated supports directly onto the C-clips.
This system means a lot of schedule time is saved as activities can now happen concurrently instead of waiting for one discipline to complete before another can commence.
Next month we will have more innovations from our JEG NCH team to share with you, so…….watch this space!
JEG team members setting out in the NCH
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