Practices for High-Tension Cable Barriers (2016)

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25 Some agencies refer to the manufacturers’ specifications and certifications for all hardware items, whereas others identify each component separately and list the appropriate ASTM or other standard to which the item must comply. Manufacturer’s Representative Most agency specifications or special provisions require that a representative with thorough knowledge of the system being installed be identified for the project and be acceptable to the project engineer. Many specifications require that this person be on site before beginning work and for all major phases of the installation. Some require the representative to be present for the final tensioning and certify to the project engineer that all work has been completed in accordance with the manufac- turer’s specifications and installation manuals. Consultation and Training Many state agency specifications require the manufacturer to provide training to the contractor’s installation crew. Michigan requires that each member of the workforce be issued a certifi- cate indicating completion of such training. Michigan Depart- ment of Transportation (DOT) also has a special provision requiring several training sessions, both in the classroom and on site, for emergency medical services personnel, tow truck operators, and state construction and maintenance workers. Plans and Shop Drawings The requirements for plans and shop drawings are relatively similar for most state agencies and require detailed dimensions and locations for all barrier runs and end anchorages. These drawings typically show post lengths, spacing, and heights above ground, as well as individual cable heights and all con- nection details, splice locations, and miscellaneous hardware. It is important that the shop drawings also include an end terminal anchor design based on existing soil conditions. Some agencies require that all design calculations be included and that the final foundation design be signed and sealed by a professional engi- neer licensed in that agency’s state. Florida and Michigan spec- ify the methods to be used to calculate the theoretical anchor deflection and overturning potential with assigned factors of safety. Florida sets the design load based on cable temperature of 0°F, whereas Michigan uses -25°F. The primary objective of this synthesis report was to iden- tify the range of appropriate topics for inclusion in specifica- tions and special provisions relating to the selection, design, installation, and maintenance of high-tension cable barrier (HTCB) systems. To gather data for this effort, a literature review was conducted and a survey form sent electronically to all 50 state transportation agencies, and a 100% response rate was obtained. In addition, information was obtained from each of the manufacturers of the five systems currently deemed eligible for federal reimbursement by FHWA. The informa- tion thus obtained has been reviewed and summarized for this report. CONCLUSIONS As noted in chapter four, existing state specifications and special provisions for HTCB vary in content and detail from a few pages to more than 30 pages, whereas some agencies rely entirely on the specifications and installation guidelines provided by the manufacturer of each proprietary system. Because the Michigan guidelines were the most comprehen- sive, each of the following headings corresponds to those in that state’s Special Provision. The commentary under each heading is intended to serve as a guideline for any agency desiring to create or modify its own specification or special provision for HTCB. Description Most state specifications reviewed simply require that the HTCB be installed as shown on the plans and according to the manufacturer’s specifications or as directed by the project engineer. Some agencies also include the required character- istics of the barrier; for example, either a three or four cable design and the NCHRP Report 350 or AASHTO Manual for Assessing Safety Hardware (MASH) test level. Other state agencies include these system characteristics under the Materials heading. Materials Because all of the HTCB systems are proprietary, the materials, including cables, posts, connection hardware, and end anchors, must meet the manufacturers’ specifications for the system that was tested and for which an FHWA eligibility letter was issued. chapter five CONCLUSIONS

26 Geotechnical Information Most DOTs now recognize the importance of designing end anchor foundations and line post footings for on-site soil condi- tions. Many state agencies provide limited soil data to the con- tractor, usually with a caveat that it may not be representative of all soil conditions on the project. It remains the contractor’s responsibility, in conjunction with the manufacturer, to deter- mine if additional soil borings are needed to design the termi- nal anchorage blocks or post footings. Because of its extreme weather conditions, Michigan requires that post footings be 15 in. in diameter and be set 48 in. in the ground. At least one manufacturer includes three “standard” terminal anchor designs in its installation manual based on soil conditions rang- ing from a strong soil to one that is completely saturated. General HTCB System Design Most state agencies do not have a separate section for design per se, but refer to the Plans, Manufacturers’ Guidelines, and Shop Drawings prepared for the project. Michigan DOT includes its design criteria for foundation designs in this section. Concrete Foundation Construction Michigan is the only state that includes detailed specifications for foundation and footing concrete in its special provisions. HTCB Construction and Installation Most agency specifications require that the HTCB be installed according to the plans and the shop drawings developed by the manufacturer for each project. They also detail the proce- dure for the initial tensioning upon completion of the project and the timing for re-checking and adjusting the tension as needed within a specified time period. One agency, at this point, requires a certification from the manufacturer stating that the installation was installed in accordance with the design and the manufacturer’s recommendations. Cable Terminal Foundation Monitoring Michigan appears to be the only state that requires that each anchor foundation be monitored for movement by installing three reference markers on each terminal anchor and two control markers nearby. All surveying work must be done by a surveyor licensed in Michigan. Anchor movement of more than 1 in. over the first 12 months following final cable ten- sioning and resulting in any tension loss in the system must be addressed at no cost to the department. Measurement and Payment Most agencies pay for the length of barrier installed, exclusive of end anchorages, at the bid price per linear foot. Anchorages are each bid as a unit price. Washington State, however, has a single bid price per linear foot for the HTCB installation from end to end, including transition sections, cable-to-guardrail connections, foundations, end anchors, and all associated hardware. Florida pays for the HTCB per linear foot, exclu- sive of the end anchors, but divides the end anchor payment into two categories—the first being a unit price payment for the end terminal assembly including the end terminal posts and associated hardware, and the second being a price based on the cubic yards of concrete needed for the end anchorage block, including reinforcing steel, labor, and equipment need for its installation. Several state agencies also require the contractor to fur- nish a spare parts package to the DOT upon completion of a project. These packages generally consist of all the materials needed to repair a specified amount of damage; for example, 500 ft of HTCB or a specific length of cable and number of posts, sockets, connection or attachment hardware, and end anchor components. (Note: Replacement parts stockpiled by the contractor to repair or replace safety hardware damaged before project acceptance are eligible for federal funding and any such parts not needed during construction may be retained by the contracting agency for future repairs. In addi- tion, federal-aid highway funds (except Interstate funds) may be used to repair damaged safety features that meet current standards when hit and to upgrade substandard installations after a crash. In the latter case, where state agencies collect the cost of replacement from the responsible party, federal- aid participation is limited to the betterment costs.) At least one new and calibrated tension meter is generally specified as well. The spare parts package can be paid as a lump sum item or a unit price item for each component supplied. On-Going Research Under its Regional Pooled Fund Program, the Midwest Roadside Safety Facility (MwRSF) at the University of Nebraska–Lincoln initiated development of a generic four- cable, high-tension median barrier. The goal of this effort is to produce a nonproprietary design that can be placed on a 1V:4H slope and prevent penetration by most passenger vehicles. The safety improvements included wider cable spacing, increased cable heights, modified post cross sec- tions, and optimized cable-to-post attachments. This proj- ect is expected to continue through 2015 and possibly beyond. Further information on this effort may be found on the MwRSF website at http://mwrsf.unl.edu/reportresult .php?reportId=18&search-textbox=cable. RESEARCH SUGGESTIONS Because HTCB has now been in use in the United States for more than a decade, many of the earlier concerns have been addressed to some extent. The two major issues were terminal anchor and post foundation failures and barrier penetrations

27 primarily resulting from the lateral placement of the cable on median slopes. The foundation problems appear to have been addressed. Most agencies require foundation designs to be based on an analysis of common soil conditions on each project. NCHRP Report 711 provided specific guidelines on optimum barrier placement on slopes to minimize vehicle underrides and/or overrides. NCHRP Report 711 also identified topics to be consid- ered for further study. The first of these addressed the need for detailed in-service performance evaluations for the various HTCB systems currently installed. Although each of the pro- prietary systems performed similarly in controlled crash tests, there may be differences in crash performance and subsequent repair efforts in the field. If so, the information gathered in evaluation reports could be very useful to each state agency as additional HTCB projects are developed. The following items are suggested for inclusion in any such evaluation efforts: • Manufacturer; • Number of cables and height of each; • Run length between anchors; • Lateral distances from edge of shoulder and/or from ditch bottom; • Slope from edge of shoulder to barrier; • Impact conditions; that is, impact speed and angle and vehicle type; • Long-term performance of materials (corrosion); • Reusability of hardware; and • Maintenance concerns. The second topic suggested for additional study was devel- opment of a revised testing matrix and evaluation criteria that would allow the performance of a specific cable barrier design on slopes to be considered in the selection process. Another issue that could be addressed is the effect that impact loading might have on the end anchor foundation designs. The states that require site-specific designs and the manufacturers appear to use the forces exerted on the anchors by static cable tensioning alone to design the foun- dations against movement, uplift, and overturning.