Multi tier dependant drop down

Hi,

I am trying to create a spreadsheet which usues multiple drop downs. Each DD will need to provide differnnt options depending on the previous one selected. The photo below shows the columns and some of the data I need.

Table.jpg

I have also attached the main file if this helps.

I am trying to make it that depending on what I select in 'Element' will alter what available for selection in 'Sub-Element' which will alter what is available in 'Construction'.

Hopefully someone can help.

Thanks in advance, Jon.