Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
4C H A P T E R 2 In 2008, ETAG 27 became effective in the EU. The guide- line includes material conformity guidelines and identifica- tion tests, which are not summarized here because they apply to specific European standards. The following discussion of ETAG 27 is summarized from EOTA (2008) and Peila and Ronco (2009). The summary describes the test that is being recommended for acceptance by transportation agencies in the United States. The test site must consist of a structure capable of accelerating a concrete block to the test speed and delivering the concrete block into the fence with the necessary precision. The slope downhill of the fence, referred to as the reference slope, must be within 20 degrees of parallel to the block trajectory in the last 1 m before the impact of the block with the fence (Figure 2-1). The trajectory of the block may be vertical or inclined (Figure 2-2 and Figure 2-3, respectively) and inscribed in a vertical plane orthogonal to the line con- necting the post bases. The test fence is required to consist of three functional modules or panels with four posts. The manufacturer is allowed to decide the installation geometry and post spac- ing. The height of the fence cannot be reduced from that of the tested height and cannot be raised more than 0.5 m (1.6 ft) for fences with a tested height of less than 4 m (13 ft) or 1 m (3 ft) for fences with a tested height of greater than or equal to 4 m (13 ft). Modification of the post spacing and the inclination of the main ropes from those tested are allowed within a tolerance specified by the manufacturer. The manufacturer is responsible for evaluating the forces acting on the structure to demonstrate the fitness for use of any modified fence. An installation manual is required as part of the certifica- tion process and it is required that the manufacturer follow the manual when installing the fence at the test site. The block used for testing can be unreinforced or reinforced concrete in a polyhedral shape (Figure 2-4). The density of the block is required to be between 2,500 and 3,000 kg/m3 (156 and 187 lb/ft3). The maximum size of the block is required to be 3 times smaller than the nominal height of the fence. The mass and size of the block is measured before each test. The average velocity of the block within the last 1 m from the fence must be greater than or equal to 25 m/s (82 ft/s) for all tests. The impact energy is calculated as the translational kinetic energy of the block at impact. The test procedure consists of two service energy level (SEL) tests and one maximum energy level (MEL) test. The MEL test is chosen by the manufacturer before the test and is required to be greater than or equal to three times the SEL test. There are nine classifications for MEL ranging from 100 to greater than 4,500 kJ (37 to greater than 1,660 ft-tons) (Table 2-1). The test and fence characteristics recorded before each test include the following: ⢠Mass of the test block ⢠Nominal height of the fence ⢠Photographs of the position and construction of the fence ⢠Geometric parameters of the fence ⢠Mechanical and physical characteristics of fence components The test and fence characteristics recorded during each test include the following: ⢠Block speed evaluated in the last 1 m before impact with the fence ⢠Block trajectory ⢠Maximum elongation of the fence ⢠Photographic records to give a complete record of the fence behavior including deformation, deflections, brak- ing time, and proof that no ground contact occurred before the maximum elongation is reached ⢠Foundation peak forces and time-force diagrams European ETAG 27 Testing Standards
5 Figure 2-1. Section view of the relationship between the block trajectory and reference slope in ETAG 27. Source: Photo courtesy of Yeh and Associates, Nomenclature adapted from EOTA 2008. hN Blo ck Tra ject ory Notes α=0° ⤠α ⤠90° β=αâ20° ⤠β ⤠α+20° hn=Nominal Height Figure 2-2. Test facility in Italy set up according to the ETAG 27 guideline for a vertical drop test. Source: Photograph courtesy of B. Arndt. Figure 2-3. Styrian Erzberg test facility in Eisenerz, Austria, set up according to the ETAG 27 guideline for an inclined test. Source: Photograph courtesy of B. Arndt. Figure 2-4. Shape and geometry of ETAG 27 test blocks made of unreinforced or reinforced concrete. Source: Photograph courtesy of B. Arndt. The test and fence characteristics recorded after each test include the following: ⢠Residual height of the fence ⢠Description and photographic records of damage to the fence Block speed measurements are taken using at least one high- speed video camera with areas of special interest covered by additional cameras as necessary. Measurement of forces on anchorage and ropes is adapted to the specific fence with at least 3 measurements on the main ropes of the center fence panel.
6The SEL tests are conducted with two launches of a block at the same kinetic energy as specified by the energy level clas- sification. The objective of the tests is to evaluate the abil- ity of the fence system to intercept and contain successive impacts within specified performance criteria. The first SEL test is required to impact the center of the fence system. The fencing passes the test if ⢠The block is stopped by the fence. ⢠No ruptures occur in the connection components and the opening of the panel mesh is less than two times larger than the initial size of the mesh openings. ⢠The residual height of the fence after the test (without removing the block) is greater than or equal to 70 percent of the nominal height of the fence. ⢠The block does not touch the ground before the fence reaches the maximum elongation during the test. The block is then removed from the fence and no main- tenance is allowed. The second SEL test is also required to impact the center of the fence. The fencing passes the test if ⢠The block is stopped by the fence. ⢠The block does not touch the ground before the fence reaches the maximum elongation during the test. Energy level classification 0 1 2 3 4 5 6 7 8 SEL (kJ) â* 85 170 330 500 660 1,000 1,500 >1,500 MEL ⥠(kJ) 100 250 500 1,000 1,500 2,000 3,000 4,500 >4,500 *Note: No test performed at SEL for energy level classification 0. Source: Adapted from EOTA 2008. Table 2-1. ETAG 27 energy level classifications. Table 2-2. ETAG 27 residual height categories for MEL test. Category Residual Height A ⥠50% of nominal height B Between 30 and 50% of nominal height C ⤠30% of nominal height Source: Adapted from EOTA 2008. The MEL test is conducted with one launch of the test block into the test fence at the energy specified. The objective of the test is to characterize the maximum energy capacity of the fence system. The manufacturer of the fence is allowed to decide whether the MEL test is conducted using the same fence as used for the SEL tests after being repaired or on a new fence. The test block is launched into the center of the new or repaired fence and the fencing passes the test if ⢠The block is stopped by the fence. ⢠The block does not touch the ground before the fence reaches the maximum elongation during the test. The classification of the residual height of the fence mea- sured after the MEL tests is outlined in Table 2-2.
