internal forces when steam bending wood

Jun 2019
Hi all, first of all is this the most appropriate forum of the many options to pose some questions relating to the forces created when wood steam bent .

I understand the practical aspects but I cant get the relevant maths to tally,

a few facts first ..

when bending the wood the outside surface is totally restricted from expanding by the green strap with end blocks . so as the wood bend the inside surface is compressed. the force to compress the wood is a constant . a value i have practically tested. the strap has a tension gauge at G. so i know the tension force being exerted within the restraining strap.
It seems logical that the force in the strap should be equal to the compression constant x area,
However the the force within the strap is far less than this figure , only about 3- 40 % . can anyone explain where the force is coming from to compress quite a volume of timber . ( without he strap the timber would break across the outer surface as it is relatively weak in tension.)