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. I have made comments below in red.

Thanks

Bob Bielenberg, MSME, EIT

Research Associate Engineer

Midwest Roadside Safety Facility

130 Whittier Building

2200 Vine St.

Lincoln NE, 68583-0853

402-472-9064

rbielenberg2@unl.edu

 I just looked at your recent research report Development of a Retrofit, Low-Deflection, Temporary Concrete Barrier System., It is very good on this important topic.

Couple questions,

One, Is the defection distance critical when the barrier is used to separate traffic during construction.

The deflection distance is not as critical, but should be considered when separating traffic. Previous research at MwRSF investigated the TCB deflection limits for less critical TCB installations [http://mwrsf.unl.edu/researchhub/files/Report243/TRP-03-113-03%20(revised).pdf]. This research argued that when temporary concrete barriers are used on the edge of a bridge, the risk of the entire line of barriers falling off the deck requires that deflection limits be selected to preclude such behavior in almost all impact scenarios.  Hence, it was recommended that at the edge of a bridge deck, design deflection limits should be selected to contain more than 95 percent of all crashes, basically the TL-3 impact conditions.  In all other barrier applications, the consequences of a barrier exceeding the design deflection criteria are not severe. In these situations, a more modest deflection limit criterion based on an 85th percentile impact severity was deemed more appropriate.

In chapter 15 of report TRP-03-295-14, we did an analysis of deflections for the low-deflection TCB at the 85^th percentile impact. Based on these results, the computer simulations indicated that dynamic deflections for the low-deflection TCB system would range between 18.2 in. (462 mm) and 23.6 in. (599 mm) at the 85th percentile impact condition. In order to be conservative, it is recommended that installations in non-critical locations use an estimated dynamic deflection value of 24 in. (610 mm) until further full-scale crash testing at reduced IS values or in-service evaluation of system damage for lower severity impacts indicate that lower deflection estimates are more appropriate. This deflection value would correspond to a working with of 46.5 in. (1181 mm). For critical installations adjacent to drop-off or bridge deck edges, the full-scale crash tested system deflection should be applied.

Two, Is it reasonable to use one of the concepts considered but not tested such as the composite with the thrie beam attached.

I would not recommend using one of the untested concepts at this time. It is feasible that one or more of the untested concepts may work, but without more analysis and testing we cannot be confident in their safety performance. In the case of the thrie beam stiffening you noted, that design has not been fully developed in terms of attachment details to the barrier sections and the amount of deflection reduction in undefined.