View Q&A

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?

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

potential for a snag looks to be minimal.

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.