G'day Dennis,
To get the best advice/help, need some more info. Some detail photos of the pier would help as well.
When you say above that the pier is "square steel 100mm channelling", do you mean it's 100PFC (which is a channel shape like this:
http://sable.net.au/product/channel-steel/100-pfc/ ) or is it 100SHS (square hollow section like this:
http://www.steelweb.info/100x100x6.htm )