I'm working on our FTB to rigid barrier thrie beam splice drawings and I need to ask you a few questions about the design. I've attached PDF's of our preliminary drawings:
(See attached file: 0715s08 2.pdf)(See attached file: 0715s08 1.pdf)
When you get time, please take a look at these drawings and the following questions:
1. What size and type of bolts are used to attach the thrie beam terminal connectors to the barriers? In our drawing 8 of 9 above we've shown a through bolted connection using five 7/8" dia. HS bolts (ASTM A449 Type 1) with hex nuts and washers under the nuts and heads. This is what we use for permanent attachments of thrie beam to our concrete traffic railings. In the attached photo you sent me, it looks like some kind of big lag screw (3/4" dia.?) was used for the test installation:
(See attached file: DSCN2687.JPG)
Can you give me any specs or the name of a manufacturer for these lag screws/bolts? Do these screws/bolts require the use of an expansion sleeve? If we wanted to use through bolting only, do you see any problems other than fit up of the bolts and the terminal connectors on the two opposite sides of the barriers?
2. Proper lateral positioning of the FTB relative to the end of the permanent barrier is proving to be a challenge with all the different shape barriers and end transitions we currently use or have used in the past - 32" F shape (shoulder and median), 42" F shape, 32" Jersey shape (shoulder
and median), 32" and 42" vertical face, corral shape, 8' F shape / soundbarrier, etc. On drawing 8 of 9 above we show two combinations: 1) FTB to permanent median barrier and 2) FTB to an old FDOT style shoulder barrier transition.
Depending on the shape and overall thickness of the permanent barrier and lateral positioning of the FTB, potential snag points could be created. We're still looking at all our possible combinations of approach and trailing end configurations. One combination with a possible snag point is shown on the upper right corner of drawing 8 of 9. If the direction of
adjacent traffic is right to left on this plan view, the exposed lower end of the FTB could be a snag point. To reduce this potential I'm thinking of filling the cross hatched area with miscellaneous asphalt. If the direction of adjacent traffic is left to right on the plan view, the
potential for a snag looks to be minimal.
Another problem seen in this same plan view is bending and fit up of the thrie beam guardrail on the back side of the barrier. I'm thinking of using offset blocks on the back side of the FTB between the FTB and the terminal connector so the thrie beam doesn't have to be bent as shown. A second offset block may be needed at the end of the FTB to engage the middle portion of the thrie beam.
When you get time, please take a look at these issues and let me know what you think.
I got a chance to go through your PCB transition questions this morning. I have written my responses and comments below in red.
1. What size and type of bolts are used to attach the thrie beam terminal
connectors to the barriers? In our drawing 8 of 9 above we've shown a
through bolted connection using five 7/8" dia. HS bolts (ASTM A449 Type 1)
with hex nuts and washers under the nuts and heads. This is what we use
for permanent attachments of thrie beam to our concrete traffic railings.
In the attached photo you sent me, it looks like some kind of big lag screw
(3/4" dia.?) was used for the test installation:
Can you give me any specs or the name of a manufacturer for these lag
screws/bolts? Do these screws/bolts require the use of an expansion
sleeve? If we wanted to use through bolting only, do you see any problems
other than fit up of the bolts and the terminal connectors on the two
opposite sides of the barriers?
The bolts used in the full-scale test were 3/4" dia. by 6" long Powers Fasteners Wedge Bolt Anchors. We have been using these anchors quite a bit lately and have been happy with them. We use them to attach the SAFER barrier to the concrete walls of the race tracks. I have attached the specs for this anchor. It does not use a sleeve. On important note on these anchors is that we used the anchors with a minimum 8" spacing between anchors. The performance of the anchors can degrade under smaller spacings. As such, you may need to change the anchor layout shown on you drawing to use the three outer holes in the end shoe and the two inner holes. This is shown in the picture you emailed me. This layout gives the 8" spacing.
As far as through-bolting the end shoe, that is fine as well. You may encounter issues hitting rebar as you mentioned.
2. Proper lateral positioning of the FTB relative to the end of the
permanent barrier is proving to be a challenge with all the different shape
barriers and end transitions we currently use or have used in the past -
32" F shape (shoulder and median), 42" F shape, 32" Jersey shape (shoulder
and median), 32" and 42" vertical face, corral shape, 8' F shape /
soundbarrier, etc. On drawing 8 of 9 above we show two combinations: 1)
FTB to permanent median barrier and 2) FTB to an old FDOT style shoulder
barrier transition.
Depending on the shape and overall thickness of the permanent barrier and
lateral positioning of the FTB, potential snag points could be created.
We're still looking at all our possible combinations of approach and
trailing end configurations. One combination with a possible snag point is
shown on the upper right corner of drawing 8 of 9. If the direction of
adjacent traffic is right to left on this plan view, the exposed lower end
of the FTB could be a snag point. To reduce this potential I'm thinking of
filling the cross hatched area with miscellaneous asphalt. If the
direction of adjacent traffic is left to right on the plan view, the
Charles, as you mentioned, the snag risk at this location is not significant unless the potential for two way traffic and reverse hits is present. However, we would recommend that the potential be reduced in this situation. Ron and I discussed you suggestion to use asphalt to fill in the hatched area. We believed that this should reduce snag, but we have a couple of concerns. First, it would be important to use the fill asphalt to make a smooth and complete fill of the hatched area. The fill should completely cover the area and any gaps would be undesirable. Second, we are a little concerned about the ability of the asphalt to prevent rim and wheel of an impacting vehicle from gouging or digging into the asphalt and creating a snag hazard or exposing a corner of the barrier. A better method may be to make a simple form and place a concrete fill in the hatched area. This will be more resistant to gouging during the impact and provide better reduction of snag potential.
Another problem seen in this same plan view is bending and fit up of the
thrie beam guardrail on the back side of the barrier. I'm thinking of
using offset blocks on the back side of the FTB between the FTB and the
terminal connector so the thrie beam doesn't have to be bent as shown. A
second offset block may be needed at the end of the FTB to engage the
middle portion of the thrie beam.
You can use offset blocks to eliminate the need for the bending the thrie beam in this situation, but there are some things to consider. First, you will want to offset the beam from the barrier at two locations at a minimum and more would be preferable. You would want to block the area near the joint between the barriers as well as the of the end shoe connection at minimum. It should also be noted that the use of the blockouts may introduce bending loads into the bolts or anchors used in the end connection with the blockout. Thus you may want to check and possibly increase the capacity of these anchors. I would not recommend using the Wedge Bolt anchors in this installation due to lack of bolt embedment and the potential for bending loads. Instead I would require the through-bolt option here.
When you get time, please take a look at these issues and let me know what
you think.
I have a couple of other comments about your CAD with the four types of installations. On the top installation, the median installation, there may be some issues with reverse hits on the non-staked side of the transition barriers downstream of the permanent barrier. I think we have discussed before that impacts with the stakes on the back side of the barrier are very likely to result in increased rotation of the barrier sections and thus increased potential for vehicle instability. As such, we are not very excited about the use of the transition in the median area. However, we realize that you may have no better options at this time. Until we have investigated this issue more thoroughly, the best recommendation I can give is that we are concerned about reverse hits in this installation due to the potential increase in barrier rotation and resulting increase in vehicle instability. Another thing to keep in mind with the median installation is slopes. Do you know what kind of slopes you will be installing the barriers on??
My last comment concerns the fourth installation detail at the bottom of the page. This trailing end transition should be fine for installations only dealing with one way traffic, but on narrow highways with two way traffic, the potential for reverse hits on this installation is significant. In that case we would recommend you install the approach transition here.
Here is a sketch that shows our old F and NJ shape traffic railing transition, an FTB and a Thrie Beam Splice:
(See attached file: Old Transition.pdf)
This section of traffic railing is supported by the wing wall that is part of the end bent. The bridge would be at the far left side of the sketch.
The old W beam guardrail end shoe would have bolted up to the 2'-6" long "End Post" section. We plan to fill in the recess at the bottom of this section with concrete to reduce the snag potential for traffic moving left to right. For traffic moving right to left, we plan to leave the recess open. The Offset Blocks at the back of the FTB are there to keep the Thrie Beam straight (unbent).
The "Varies" dimension is drawn at 1'-0" but could be any length from 0' to many feet. Our problem shows up at the left end of the "Varies" dimension where the Thrie Beam Terminal Connector straddles the deck expansion joint.
We can't bolt across this joint with the Terminal Connector as thermal movements of the bridge would likely tear the connection apart. Thus we're thinking of using a 25' stick of thrie beam to get the left Terminal Connector (as seen in the sketch) up on the bridge beyond this problem area. The right Terminal Connector would be attached to the FTB at the same location as is currently shown.
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