Ring Beam update
My last post got us to the point of reaching the excavation depth of the Ring Beam. THis post will go into a little more detail.
Due to the amount of reinforcement of the piles, the construction sequence of the Ring Beam had to be modified. As you can see from the sequence below, the reinforcement in the piles needed to be cut.
However in order to decide how much-needed to be cut a quick calculation was required to see what bond length was required in order to hold the Ring Beam up.
Once the reinforcement requirements for the Ring Beam were calculated, the decision to cut the reinforcement could be made. However although the calculations demonstrated that all the reinforcement was not necessary, the decision was still made that all the reinforcement bars had to be coupled back together, once the SCL had been completed. I am in the process of trying to find out why this decision was made.
The next issue is trying to obtain the 200mm SCL required in the cavity below the piles, where the Ring Beam will sit. There has been several modifications, but it now seems that with design #4 (as seen below) we are managing to get the correct SCL profile.
Trials are taking place as I write, we will see if this construction method works
Holdfast Training Services Trial Blog 
Well praise be to the God of curious things….
Here are the curios……..well for me at least!
The first sketch appears to show the cage reinforcement extending beneath the toe of the bored pile – how’s that then?
The bar cut pattern suggests that the centre front and rear bars are to be retained; yet the section shows the centre left and right retained
The calculation is strange – why would you wish to ‘hold up’ the ring beam?
The ring beam acts to retain the toe of the wall laterally so you need a shear key – I think that this explains the need for replacing the reinforcement. I would have thought that there would have been a need for anchorage – oh well !
The calculation is required because the next phase is too excavate below the ring beam. As such it will be suspended, only temporarily, until the SCL is in place.
Hmm, If you’re suspending the beam and it is the pull out bond strength that worries why would you couple back all bars straight as before at great expense of couplers and labour instead of a small number of bent bars? Is the capacilty of the coupler an issue? Like this blog lots!
The governing factor is not the bond length required to suspend the ring beam in the short term. It is the reinforcement required to provided shear reinforcement between the piles and the ring beam in the long term. Hence the bond length calc results were ignored and we were instructed to keep all the reinforcement.
Thanks Mike. Makes a certain amount of sense now. Plus, you managed to discus the lenth of piles and a ring beam without resorting to double entendres and much smirking!
Cheers Richard. Reference your last comment about the capacity of the couplers. I just checked them out on the Internet and the bolts are suppose to shear off once the correct capacity is reached. I went down to check if the bolts on the couplers were sheared off. Guess what they weren’t and it was 10 mins before the concrete pour. They have had to cancel the pour, rip out the shuttering and tighten all the bolts up till they shear. You have made me about ad popular as a pork chop in a synagogue. However it has cost them a fraction of the price of ripping out the ring beam and starting again. I will explain with photos in more detail when I get a chance.