'edfan':
Structurally, no, there isn't. BUT! To put it simply; You ain't got much twixt you and the boogey man! I.E.; There isn't much in the way of security there! - EVEN against heavy WEATHER! All the 'high-tech' there is cannot protect you from harm (of virtually any nature) quite like a good, solid door!
MARK YOU: If a determined 'baddy' WANTS TO GET IN - he WILL! The best you can hope for is to slow him/her/it down as much as possible!
Torsion-box = great idea! - But use heavier materials!
Not everything is improved by '...leaner and meaner...'!
There is no way in hell you're going to get a 90min. fire delay with a LIGHTWEIGHT torsion-box design even with insulation internally! This would require steel realistically - and, in my opinion, this is too ugly to EVEN contemplate!
I sincerely hope this helps...
Warmly, Griz
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"Is there any reason a torsion box couldn't work? Wouldn't that allow "us to use thinner, cheaper material while maintaining sturdiness? You "basically use the perimeter to install locks and hinges. Otherwise, is "there a technical need for a solid wood door? (I don't question the "aesthetic value of solid wood.) If we capped it with the usual "weatherstripping material, would that do the job? " "Is there an outstanding book or plan around that would produce a "really sturdy front door without using the usual solid material?