Guidance for the Selection, Use, and Maintenance of Cable Barrier Systems (2012)

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45 Six types of NCHRP Report 350-accepted cable barrier systems are currently available for use on U.S. highways, as follows: • Weak-Steel Post Cable (3-Strand) Guardrail (low-tension) • Brifen Wire Rope Safety Fence (high-tension) • Gibraltar Cable Barrier System (high-tension) • Nucor Steel Marion Cable Barrier System (high-tension) • Safence Cable Barrier System by Gregory Industries Inc. (high-tension) • Trinity CASS Cable Barrier System (high-tension) Several full-scale crash tests have been conducted to evaluate these systems and, based on these tests, Acceptance Letters have been issued by FHWA. Table 4.1 lists the different systems and the corresponding FHWA Acceptance Letters. A more detailed list of these systems is presented in Appendix B of the contractors’ final report. Each of these systems is available in a variety of configurations with variations in the number of cables, cable heights, post spacings, post sizes, post embedments, test levels, etc. The following sections give a general description of the different available systems. 4.1 Weak-Steel Post Cable (Three-Strand) Guardrail Prior to the recent advances in cable barrier technology, the most common design was the generic cable guardrail, also known as a low-tension system. A low-tension cable system, based on the Washington State design, has been tested in accordance with the NCHRP Report 350 TL3 recommendation at the Texas Transportation Institute [50]. The tested system consisted of three 19 mm (0.75 in) 3 × 7-steel-strand galvanized wire rope cables having a minimum tensile strength of 110 kN (25 kips). The cables were supported at the appropriate heights above ground by S75 × 8 rolled steel posts, 1,778 mm (70 in.) in length, using hook bolts. The hook bolts open up to permit the cable to release from the post when a force ranging from 2,240 N (500 lb) to 4,450 N (1,000 lb) is applied normal to the longitudinal axis of the post. The posts were spaced 4.9 m (16.0 ft) apart. Steel soil plates, 203 mm × 610 mm × 6 mm (8 in. × 24 in. × ¼ in.) in size, were connected (welded) to the posts at a height of 100 mm (4 in.) from the lower end. The posts, with the welded soil plates, were embedded 851 mm (33.5 in.) in soil. The cable ends were connected to the ground by cable anchors attached to large concrete blocks. The concrete blocks were about 1450 mm × 1150 mm × 990 mm (57 in. × 45 in. × 39 in.) in size. The cables were pretensioned using turn-buckles attached to spring compensator end-assemblies. The spring compensators had a spring rate of 2,000 ± 222 N/mm (450 ± 4.5 lb/in.). The tension in the cables is set based on the atmospheric temperature (about 4,450 N [1,000 lb] at 18°C [65°F]). C h a p t e r 4 Descriptions of Available Cable Barriers

46 Guidance for the Selection, Use, and Maintenance of Cable Barrier Systems Generic cable barrier systems are available in different configurations. Three different posts are used with these systems: S75 × 8 steel I-beam (Acceptance Letter B64—SGRO1-a), flanged steel U-channel (Acceptance Letter B64—SGRO1-b), and weakened rounded timber post (Acceptance Letter B64 sup–SGRO1-c). Additionally, different cable setups are used. For roadside applications, all cables are placed on the same side of the post, the side closer to the road. When the barrier is placed in the median, two cables are placed on one side of the post and the other cable is placed on the opposite side. The heights of the cables relative to ground level also varied for different generic cable barrier installations. The most common cable heights are similar to the tested configuration. The lowest cable in this design is set at 533 mm (21 in.) from the ground with the other two consecutive spaces at 114 mm (4.5 in.) above (see Figure 4.1a). In other cable barrier designs, the heights for the three cables are set at 533 mm (21 in.), 686 mm (27 in.), and 838 (33 in.) from ground level (see Figure 4.1b). New York State recently introduced a four-cable barrier design (Acceptance Letter B-161). The heights of the four cables in this design are set at 254 mm (10 in.), 406 mm (16 in.), 559 (22 in.), and 712 mm (28 in.), as shown in Figure 4.1c. 4.2 Brifen Wire Rope Safety Fence The Brifen Wire Rope Safety Fence (WRSF) system is available in different configurations. The distinctive characteristics of the system are the Z-shaped post and the interweaving of the cables between adjacent posts. Three- and four-cable configurations are available. For Manufacturer/Product Name Acceptance Letter No. NCHRP 350 Test Level Generic Weak-Post Cable Guardrail B-64, B-64 Sup, B-161 TL3 Brifen Wire Rope Safety Fence B 82 B82 A, B, B1, C, C1,D TL3, TL4 Gibraltar Cable Barrier System B-137 B137 A, A1, B, C TL3, TL4 Nucor Steel Marion Cable Barrier System B-96, B96A, B167 TL3, TL4 Safence Cable Barrier System by Gregory Industries Inc. B-88, B-88A-E TL3, TL4 Trinity CASS Cable Barrier System B-119,A,B B-141,A,B,C,D,E,F B-157 TL3, TL4 Table 4.1. Currently available cable barrier systems. (c) four cables, 6” spacing(b) three cables, 6” spacing(a) three cables, 4.5” spacing Figure 4.1. Sample cable heights for generic cable barriers.

Descriptions of available Cable Barriers 47 both configurations, the top cable is placed in a slot at the center of the post. The other two or three cables are woven around the posts. Different cable height configurations have been tested and accepted as TL3 and TL4 roadside barriers. The first system tested was a TL3 four- cable design as shown in Figure 4.2a (Acceptance Letter B-82). In this design, the top cable is placed at a height of 720 mm (28.4 in.) from ground level. The bottom cable is placed at a height of 510 mm (20 in.). The middle two cables are placed at a height of 675 mm (26.57 in.). A three- cable design is also available and has been tested for TL3 condition, as shown in Figure 4.2b (Acceptance Letter B-82C). The heights of the three cables for this system are 460 mm (18 in.), 600 mm (23.5 in.), and 720 mm (28.4 in.). A third design, a TL4 system with four cables, has also been tested and accepted by FHWA (Acceptance Letter B-82B). The heights of the cables for this design, as shown in Figure 4.2c, are at 480 mm (18.9 in.), 630 mm (24.8 in.), 780 mm (30.7 in.), and 930 mm (36.6 in.). The Brifen WRSF designs are high-tension systems. The cables are tensioned based on the ambient temperature. This tension varies from 14.0 kN (3.1 kips) at 30°C (86°F) to 36.0 kN (8.1 kips) at 10°C (50°F). The posts are typically placed inside a tubular steel socket embedded in a 305 mm (12 in.) diameter × 760 mm (30 in.) deep concrete footings. Driven posts or posts set in driven steel sleeves are also acceptable with the Brifen systems. Typical post spacing of the Brifen system is 3.2 m (10.5 ft). Post spacing of 2.4 m (7.87 ft) and 6.4 m (21 ft) were also tested in accordance with NCHRP Report 350. 4.3 Gibraltar Cable Barrier System The Gibraltar high-tension cable barrier system is available in different configurations. The distinctive characteristic of the system is that the cables are attached to the post using a single 30 mm (7⁄16 in.) diameter steel hair pin. The system consists of three or four 19 mm (0.75 in.) 3 × 7-steel-strand galvanized wire rope cables. Prestretched and non-prestretched cables can be used with the system. The cables are connected to C-channel posts that are 83 × 63.5 × 3.8 mm (3.25 × 2.5 × 0.15 in.) in cross section. The posts are placed such that adjacent posts are on opposite sides of the cables. The posts are typically connected to the ground through steel sockets that are embedded in reinforced concrete cylinders. Other con- nections, such as driven posts, have been accepted by FHWA. Varied post spacing can be (a) TL3 – four cable (b) TL3 – three cable (c) TL4 – four cable Figure 4.2. Cable height configurations for Brifen WRSF systems.

48 Guidance for the Selection, Use, and Maintenance of Cable Barrier Systems used with the Gibraltar cable barrier system. Spacing from 3 m (10 ft) to 9 m (30 ft) can be used with the system. The Gibraltar cable barrier system has been tested in accordance with NCHRP Report 350 and is accepted for TL3 and TL4 conditions. The main difference between the TL3 and TL4 systems is cable spacing and length of the posts. For the TL3 three-cable system, the cable heights are set at 508 mm (20 in.), 635 mm (25 in.), and 762 mm (30 in.) from ground level, as shown in Figure 4.3a (Acceptance Letter B137). For the TL4 three-cable system, the heights are 508 mm (20 in.), 762 mm (30 in.), and 990 mm (39 in.), respectively, as shown in Figure 4.3b (Acceptance Letter B137a). A third system with four cables has also been accepted at TL4 condition (Acceptance Letter B137b). The heights of the cables from ground level are 508 mm (20 in.), 635 mm (25 in.), 762 mm (30 in.), and 990 mm (39 in.), as shown in Figure 4.3c. 4.4 Nucor Steel Marion Cable Barrier System Two Nucor high-tension cable barrier systems are accepted for use on the National Highway System: a three-cable TL3 system (Figure 4.4a—Acceptance Letters B96 and B96A) and a four- cable TL4 system (Figure 4.4.4b—Acceptance Letter B167). Both systems use 19 mm (0.75 in.) 3 × 7-steel-strand wire rope cables. Prestretched as well as non-prestretched cables can be used (a) TL3 – three cable (b) TL4 – three cable (c) TL4 – four cable Figure 4.3. Cable height configurations for Gibraltar cable barrier systems.

Descriptions of available Cable Barriers 49 with these systems. The cables in both systems are attached to 6 kg/m (4 lb/ft) U-channel steel posts. Locking hook bolts, 6.4 mm (.25 in.) in diameter, are used to connect the cables to the posts. For the TL3 design, the three cables are placed at heights of 545 mm (21.5 in.), 650 mm (25.6 in.), and 750 mm (29.5 in.), as shown in Figure 4.4a. The top and bottom cables in this design are placed on one side of the post while the middle cable is placed on the opposite side. The TL3 design was tested with three different post spacings: 2 m (6.5 ft), 3.8 m (12.5 ft), and 5.1 m (16.7 ft). All tests met the NCHRP Report 350 criteria with variation in barrier deflections. Two different post embedment types were used in the TL3 tests: Direct driven posts with a trapezoidal soil plate, and a socket steel sleeve set in a 300 mm (12 in.) diameter concrete cylinder are available. For the TL4 design, the bottom cable is placed at 380 mm (15 in.), the top two cables are placed at 890 mm (35 in.), and the remaining cable is placed at 640 mm (25.2 in.) from ground level as shown in Figure 4.4b. Two of the four cables are placed on one side of the post and the other two are placed on the opposite side. Each post is fixed to the ground by means of a plastic socket that is embedded in a 300 mm (12 in.) diameter concrete foundation. The spacing between the posts is 6.1 m (20 ft). 4.5 Safence Cable Barrier System Safence high-tension cable barrier systems have been tested under TL3 and TL4 conditions. The cables in these systems consist of 19 mm (0.75 in.) 3 × 7-steel-strand prestretched wire rope cables. Systems with three different types of line post have been tested. These post types include an elliptically shaped steel post, an I-shaped post (41 mm flange width and 80 mm web width), and a C-shaped post (95 mm × 30 mm). All three posts have a thickness of 4 mm. The elliptical posts were used in the original TL3 Safence design (Acceptance Letter B88). This system had four cables that are placed at heights of 480 mm (18.9 in.), 630 mm (24.8 in.), 780 mm (30.7 in.), and 930 mm (36.6 in.) from ground level, as shown in Figure 4.5a. All four cables in this system are placed on the same side of the post and attached using twisted hooks. (a) TL3 – three cable (b) TL4 – four cable Figure 4.4. Cable height configurations for Nucor cable barrier systems.

50 Guidance for the Selection, Use, and Maintenance of Cable Barrier Systems This system is intended for non-median applications (roadside application only). The posts in this design are spaced at 2.5 m (8.2 ft) and embedded 1.11 m (3.6 ft) in soil. The I-shaped post was used in the second TL3 Safence cable barrier design (Acceptance Letter B88-a). In this design, the four cables are placed at heights of 480 mm (18.9 in.), 560 mm (22 in.), 640 mm (25.2 in.), and 720 mm (28.3 in.) from ground level, as shown in Figure 4.5b. All four cables are inserted in a slot at the center of the post and separated by plastic spacers. This design can be used for both median and roadside applications. A similar design, using C-shaped posts instead of the I-shaped post, has been accepted by FHWA (Acceptance Letter B88c). The posts, in both designs, can be driven directly into the ground or embedded in 200 mm (8 in.) diameter by 600 mm (24 in.) deep concrete footings. Additionally, post spacings of 2 m (6.5 ft) or 3 m (9.8 ft) can be used with this TL3 design. Two Safence designs have been accepted by FHWA at the TL4 level (Acceptance Letter B88d and B88e). Both designs are similar except for the number of cables. The first design uses three cables placed at heights of 480 mm (18.9 in.), 640 mm (25.2 in.), and 720 mm (28.3 in.) from ground level, as shown in Figure 4.5c. The second design has an additional cable at 560 mm (22 in.) height, as shown in Figure 4.5d. The TL4 designs are similar to the second TL3 design. The posts, however are made stronger, ATSM A50 steel is used instead of the A36 steel used in TL3 designs. Each post was also stiffened at the ground line by adding a steel plate inside the C-post. Additionally, a steel hook was added to the top of each post to delay the release of the cables from the posts during the impact. 4.6 Trinity CASS Cable Barrier System The Trinity CASS high-tension cable barrier systems have been tested under TL3 and TL4 conditions and are available in different configurations. The cables in these systems consist of 19 mm (0.75 in.) 3 × 7-steel-strand prestretched or non-prestretched steel wire ropes. Three and four cable systems are available. The cables are placed in a slot at the center of the post and (a) 1st TL3 design four cables (b) 2nd TL3 design four cables (c) 1st TL4 design three cables (d) 2nd TL4 design four cables Figure 4.5. Cable height configurations for Safence cable barrier systems.

Descriptions of available Cable Barriers 51 separated by plastic spacers. The posts can be anchored to the ground using steel sockets that are cast into concrete cylinders, steel tubes driven in soil, or posts directly driven in the soil. Different post spacings, ranging from 2 m (6.5 ft) to 10 m (32.5 ft), can be used with the CASS systems. The original CASS design uses cold-formed C-shaped posts and has been accepted at TL3 condition (Acceptance Letter B-119). The cable heights relative to ground level in this design are 530 mm (21 in.), 640 mm (25.2 in.), and 750 mm (29.5 in.), as shown in Figure 4.6a. The sec- ond CASS TL3 design uses hot rolled posts (Acceptance Letter B-141). The posts in this design are weakened by drilling two 17.5 mm (11⁄16 in.) diameter holes through each flange at ground level. The cables were kept at the same heights as the original design, as shown in Figure 4.6b. A TL4 design, using the same weakened S4 × 7.7 posts, has been tested and accepted by FHWA (Acceptance Letter B-141). This design uses three cables placed at heights of 530 mm (21 in.), 750 mm (29.5 in.), and 968 mm (38 in.) from ground, as shown in Figure 4.6c. A second CASS TL4 design that uses four cables instead of three, has been accepted by FHWA (Acceptance Letter B-157). The cables, in this design are set at heights of 530 mm (21 in.), 750 mm (29.5 in.), 640 mm (25.2 in.), and 968 mm (38 in.). 4.7 Other Designs A new generic high-tension cable barrier system is in development at the MwRSF and is cur- rently being tested in accordance with MASH. The tests are selected such that the system would be placed anywhere along the lateral direction of 4H:1V or shallower sloped medians. The system uses four 19 mm (0.75 in.) steel wire ropes (Figure 4.7). The cable heights are at 343, 610, 876, and 1,143 mm (13.5, 24, 34.5, and 45 in.). The four cables are attached to S3 × 5.7 steel posts via specially designed keyway brackets. The brackets are designed to fracture at a certain load level and allow the cables to separate from the posts. The brackets are connected to the posts using 8 mm (5⁄16 in.) diameter bolts, washers, and nuts (two per cable). The posts, (a) 1st TL3 design C-Post - three cables (b) 2nd TL3 design I-Post - three cables (c) 1st TL4 design I-Post - three cables (d) 2nd TL4 design I-Post - four cables Figure 4.6. Cable height configurations for Trinity CASS cable barrier systems.

52 Guidance for the Selection, Use, and Maintenance of Cable Barrier Systems in the tests, are imbedded 1.0 m (3.3 ft) in the ground. The installation length in the tests was 183 m (600 ft), which is the minimum length required under MASH. Even using this length, load cells placed at the end anchors showed a 136 kN (30 kips) increase in cable tension force due to an impact with the 2270 P vehicle. This leads to the conclusion that higher deflection would be observed for longer installations. Four full-scale crash tests have been conducted on this system, and three additional tests are planned in the near future. The tests vary in vehicle type (1100C, 1500A, and 2270P), barrier loca- tion (near side, far side, placement relative to the median), and soil strength (weak and strong soil). A matrix of tests for barrier systems that would be placed anywhere in 4H:1V sloped median will be finalized based on observations from the tests conducted on this system. Figure 4.7. MwRSF generic high-tension cable barrier system.