Are you a main contractor – or part of a preconstruction team – wondering how long it takes to install a prefabricated steel substructure?
If time is of the essence for your project, you may or may not be aware that digging and building in the ground can often take a long time.
The more traditional method of in situ concrete is extremely labour-intensive, and precast concrete can also be tricky as it often has to be transported on-site in sections.
So, how does prefabricated steel measure up to these methods? Well, the good news is that you could save a significant amount of time on-site.
As a subcontractor who specialises exclusively in prefabricated steel substructures, let me explain more below in regards to typical prefabricated steel installation times, and the factors that can affect them.
How long does it take to install a prefabricated steel substructure?
Without any doubt, prefabricated steel is the fastest way of constructing below-ground level.
For example, if the substructures are on your construction programme’s critical path, and were initially estimated using in situ concrete, changing the method to prefabricated steel could save you up to 70 – 80% on-site.
However, predicting precisely how long a prefabricated steel substructure can take to install is a bit of a tricky question, and can depend on a number of different factors.
To help explain, I’m going to try my best to answer this question by giving you a rough idea of the average timescales you can expect – along with the factors that can affect those timescales.
So firstly, here’s another example for you:
If you were considering installing a substructure which was, for instance, 8m long x 4m wide x 2m deep – in stable ground conditions (i.e. clay and a low water table), we would expect to excavate, install the substructure and pour the concrete in just six working days.
In comparison, we would expect the same job, only carried out with in situ concrete, to take around a total of 20-25 days (including the curing process).
What are the factors that can affect installation time?
As I mentioned above, there are various other factors that can affect the installation time of a prefabricated steel substructure. These are:
1. Ground conditions
A below ground specialist subcontractor should be able to assess the ground from a ground investigation survey. A thorough check of the ground investigation survey should allow them to assess the risk of leaving the sides of the excavation at 90 degrees.
This is something that’s usually measured from experience, and with input from a structural engineer. Sometimes it is suggested they complete their own trial dig on-site to confirm what was completed in the ground investigation matches up to the report.
This considerably reduces the risk of any earth collapsing. However, if there is the slightest change of collapsing, they may consider stepping the excavation and installation a permanent shuttering around the structure.
2. Whether the substructure is internal or external
Another factor that can impact on installation time is whether the prefabricated steel substructure is internal or external. Installing a large substructure externally in the winter will naturally add time onto the programme, due to the increased possibility of rain or snow.
Internally, there will be a roof over the works, which helps to reduce the impact weather will have on the installation programme.
3. The depth of the substructure
If the substructure is between one and two metres deep, it can be installed a lot quicker than a structure that is three metres deep or more.
The deeper a team digs, the higher the likelihood that they will need to install temporary works, which will extend their time on-site.
4. Access to the site
A prefabricated steel substructure can usually be manufactured to be five metres wide, and delivered to a site without having major logistical problems on the roads.
However, if your chosen subcontractor is installing the substructure in an existing building where there are limitations on getting the structure into the area, they may need to modularise the structure and fix it together on-site – adding further time onto the programme.
Advice from a specialist subcontractor
If you’re considering prefabricated steel as the best method for your below-ground substructure, we’d recommend contacting an architect, engineer or specialist subcontractor who can talk you through your options, and give you some free, impartial advice.
One of our clients swears by prefabricated steel, and now never goes with any other way of below-ground construction. They always use prefabricated steel, as the benefits and reduction in risk makes it a superior option for just about any project.
I hope you’ve found this blog helpful when looking at timescales and the factors that can affect the installation time of your prefabricated steel substructure.
On the whole, the prefabricated steel approach could save you around 70 – 80% of time spent on-site. However, there are a few factors above which can affect installation time.
Do you have any other questions about installing a prefabricated steel substructure for your project? Let me know in the comments’ section. I’d love to hear from you.