BRIDGE 1 – COLLISION PROTECTION BEAM – WEEK 2 OF
INSTALLATION
Last week almost all of the bolt holes had been
drilled into the abutment brickwork to a depth of approximately 400mm. These have now been extended to the required
650 mm depth. Those behind the Mabey supports will be done later.
The next operation was to pump the resin into the
holes (see above)...
...and then the first 6 bolts were installed at each end.
Once the resin had hardened the steel channel was packed vertically, leaving a
tapering gap behind it due to the leaning brickwork.
The Mabey props were then all removed, and the last 8
holes drilled. Then the resin and bolts were all installed in the remaining 28
holes and once hardened all bolts were fully tightened.
The gap between the back of the channel and the
leaning brickwork was found to be between 12mm at the top and app. 40 at the
bottom. This gap is to be filled by a rapid hardening liquid cement grout
poured in from the top.
Temporary timber shuttering was attached to the bottom
of the steel channel to prevent the liquid cement grout from running
out...
...as grout was poured in at the top.
The top of the grout was then
trowelled off,
leaving the work complete.
Once the grout has hardened the shuttering will be
stripped off and the entire north abutment support beam installation will be
completed.
Next Monday, once the shuttering has been removed, the
road closure and all fencing and equipment will be transferred to the south
abutment and the whole process repeated for the other beam.
8.9.2018 - JOHN
BALDERSTONE
Blogger's note: A holiday for Mrs. Blogger is now urgently due (he is joining her....) so there will be a two week break in the bridges blog.
Excitement builds - how far will the team get?
John, Thanks for the update. I can see that the abutment beam isn't going anywhere with 40 bolts deep in the brickwork, but I'm a bit surprised to see only 3 bolt holes which appear to be going to hold the actual collision protection beam in place on each side. Since this connection will carry a massive load in the event of a collision, I expected things to be a bit more substantial. But maybe I am missing something?
ReplyDeleteIf you review the third photo you will see that there are in fact 4 bolt holes for the beam to bolt onto, and as the person who commented below points out the beam is a sacrificial beam designed to stop the vehicle coming into contact with the bridge deck, without passing the force of the impact to the bridge structure itself. Think of it as a large stiff crumple zone
DeleteMaybe because they will be in compression in the event of a strike? Or even that they are designed to shear off to prevent more damage from energy transferred elsewhere in the structure?
ReplyDeleteThe CPB system was designed by Consultants Jacobs (Swindon office) to comply with all relevant codes. The 8 No. Gr. 8.8 bolts (4 each end) have a combined design shear vale of app 70 Tonnes. The failure load is very much higher. The system is designed to take the impact from a lorry travelling at 45MPH (this is a 30MPH zone) deflecting elastically by no more than 150mm, before returning to normal. This should ensure that the actual bridge steelwork is not even touched! The bolts in the brickwork have a smaller design load capacity (hence the larger size and the large number), and that has been downgraded further to take account of the age and condition of the brickwork.
ReplyDeleteThe beam in Hyde Lane, Cheltenham, shown in the first blog I posted, has been in position for many years and has been subjected to impacts, from what can be seen in the photo. The end fixings also look virtually identical to what we will be providing.
Thanks, John. I knew there would be an interesting answer! That's very clear now.
DeleteGreat and interesting blog john. Thank you for keeping us informed
ReplyDeleteJust been under the bridge. The contractors have done a really tidy job. You wouldn't know the beams were there (until you hit one - ouch!)
ReplyDelete