Design Guidelines for Test Level 3 through Test Level 5 Roadside Barrier Systems Placed on Mechanically Stabilized Earth Retaining Walls (2022)

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294 10 AASHTO LRFD FORMAT DESIGN GUIDELINES SECTION 1 DESIGN GUIDELINES 1.1 SCOPE This section provides guidelines to design two MSE wall components: the BMS and the MSE wall reinforcement. The guidelines are applicable to test levels TL-3 through TL-5 criteria as defined in Section 13 of AASHTO LRFD Bridge Design Specifications, and for inextensible MSE wall reinforcement (e.g., strips, bar mats) Depending on the design, two points of rotation are possible as shown in Figure 1.1- 1. The point of rotation should be determined based on the interaction between the barrier coping and the top of the wall panel. With reference to Figure 1.1-1, the point of rotation should be taken as Point A if the top of the wall panel is isolated from contact with the coping by the presence of an air gap or a sufficiently compressible material. The point of rotation should be taken as Point B if there is direct bearing between the bottom of the coping and the top of the wall panel or level-up concrete and if that material will not crush during impact. Leveling Pad Rotation Point A Overburden Soil Moment Slab Traffic Barrier C.G. Panels Finished Grade Rotation Point B Critical Section Figure 1.1-1 BMS system for design guideline.

295 1.2 DEFINITIONS Rotation Point A—The rotation point of a BMS system if the top of the wall panel is isolated from contact with the coping by the presence of an air gap or a sufficiently compressible material as shown in Figure 1.1-1. Rotation Point B—The rotation point of a BMS system if there is direct bearing between the bottom of the coping and the top of the wall panel or level-up concrete as shown in Figure 1.1- 1. 1.3 NOTATION TL3 = refers to test level 3, as defined in AASHTO MASH TL4-1 = refers to test level 4, as defined in AASHTO MASH, with a barrier height of 36 in. TL4-2 = refers to test level 4, as defined in AASHTO MASH, with a barrier height greater than 36 in. TL5-1 = refers to test level 5, as defined in AASHTO MASH, with a barrier height of 42 in. TL5-2 = refers to test level 5, as defined in AASHTO MASH, with a barrier height greater than 42 in. H = height of the barrier measured from the finished grade (in.) ha = moment arm taken as the vertical distance between the point of impact of the dynamic force and the point of rotation A (ft) hb = moment arm taken as the vertical distance between the point of impact of the dynamic force and the point of rotation B (ft) h1 = tributary height of the soil, where the loads are resisted by the first layer of the soil reinforcements (ft) h2 = tributary height of the soil, where the loads are resisted by the second layer of the soil reinforcements (ft) hc = moment arm taken as the vertical distance between the point of impact of the dynamic force and the middle of the weakest section of the coping (ft) Ld = dynamic load (kips) Ft = impact load in the lateral direction, perpendicular to the barrier (kips) FL = impact load in the longitudinal direction, along the barrier (kips) Fv = impact load in the vertical direction on the barrier (kips) LL = horizontal distance over which the impact load is distributed (ft) Lv = vertical distance over which the impact load in distributed (ft) Ls = static load equivalent to the dynamic impact force (kips) lA = horizontal distance from the CG of the BMS system to the point of rotation A (ft). lB = horizontal distance from the CG of the BMS system to the point of rotation B (ft). M = static moment resistance to overturning of the BMS system (kips-ft) Fs = static resistance to sliding of the BMS system (kips) P = static resistance to pullout of the reinforcement (kips)

296 pdp-1 = dynamic pressure for pullout of the first layer of soil reinforcement (psf) pdy-1 = dynamic pressure for yielding of the first layer of soil reinforcement (psf) pdp-2 = dynamic pressure for pullout of the second layer of soil reinforcement (psf) pdy-2 = dynamic pressure for yielding of the second layer of soil reinforcement (psf) Qdp-1 = dynamic line load for pullout of the first layer of soil reinforcement (lb./ft) Qdy-1 = dynamic line load for yielding of the first layer of soil reinforcement (lb./ft) Qdp-2 = dynamic line load for pullout of the second layer of soil reinforcement (lb./ft) Qdy-2 = dynamic line load for yielding of the second layer of soil reinforcement (lb./ft) R = yield resistance of one unit of reinforcement (kips) W = weight of the monolithic section of barrier and moment slab per unit length plus any material laying on top of the moment slab (kips/ft) Wmin = minimum width of the moment slab measured from the roadside face of the panels (ft) γ = load factors ɸ = resistance factors ɸr = friction angle of the soil – moment slab interface (degrees, °) ɸs = friction angle of the soil (degrees, °) σv = vertical normal stress in the soil (ksf)

297 1.4 GUIDELINES FOR THE BARRIER 1.4.1 General The barrier, the coping, and the moment slab should be safe against structural failure. Any section along the coping and moment slab should not fail in bending or shear when the barrier is subjected to the design impact load. The barrier should not fail structurally during the impact. Two modes of stability failure are possible in addition to structural failure of the barrier system. They are failure by sliding and failure by overturning of the BMS system. The equivalent static load defined in this section should be used for sizing the moment slab, and should be checked against the sliding resistance and overturning resistance of the barrier. The design for the structural capacity of the barrier, the coping, and the moment slab should make use of the impact load defined in Table 1.4.4-1 and follow the relevant procedure recommended by AASHTO LRFD Bridge Design Specification. The minimum width of the moment slabs should be as follows: 4.0 ft for TL-3, 4.5 ft for TL- 4-1 and TL-4-2, 7 ft for TL-5-1 and 12 ft for TL- 5-2. The length of moment slabs should be greater than 20 ft with steel shear dowels across the joints of adjacent moment slabs to transfer the load. Dimensions outside these ranges can be used provided it is shown that sufficiently rigid body behavior is achieved. The use of shear dowel bars is considered a construction standard. The bars are used to connect the joints between the moment slab sections. A gap is provided between the inside face of the coping and the back traffic face of the wall panel to prevent contact between the coping and the wall panel. C1.4.1 Much of the current knowledge and experience with MSE structures and traffic barriers has been captured in Section 11 and Section 13 AASHTO LRFD Bridge Design Specifications. These recommendations are aimed at designing a BMS system that would generate 1 in, 1.5 in, and 1.75 in of maximum dynamic movement at the top of the barrier for TL-3, TL-4, and TL-5, respectively, and 1 in permanent movement or less at the coping section for all test levels. These displacements are considered acceptable as they would likely require little or no repair after a design impact event. Such displacements should not affect the future impact performance of the barrier system. The dowels used in the TL-3, TL- 5 and TL-5 full-scale testing were as follows: Two # 9 steel bars were used for TL-3 and TL-4 test level joints. For the TL-5 test level, three #11 steel bars were used. In all cases, the bars were embedded 18 in into each adjacent moment slab section. The widths of the gaps in the full- scale crash tests TL-3, TL-4 and TL-5 were as follows: 0.75 in. (19 mm) for TL- 3, TL-4-1 and TL-4-2, and 1.5 in. (38.1 mm) for the TL-5-1 and the TL-5-2.

298 1.4.2 Sliding of the Barrier The factored static resistance (ɸP) to sliding of the BMS system along its base should satisfy the following condition (Figure 1.4.2-1): ɸ P ≥ γ Ls (1.4.2-1) where: Ls = equivalent static load (kips) (Table 1.4.2-1) ɸ = resistance factor = 1 (AASHTO LRFD Bridge Design Specifications 10.5.5.3.3) γ = load factor = 1.0 [extreme event] P = static resistance (kips) C1.4.2 If the soil–moment slab interface is rough (e.g., cast in place), ɸr is equal to the friction angle of the soil ɸs. If the soil– moment slab interface is smooth (e.g., precast), ɸr should be reduced accordingly 2tan tan 3r s φ φ= . The static force P is calculated as: P = W tan ɸ r (1.4.2-2) where: W = weight of the monolithic section per unit length of barrier and moment slab between joints plus any material laying on top of the moment slab (kips) ɸ r = friction angle of the soil–moment slab interface(degrees, °) Table 1.4.2-1 Equivalent static loads for moment slab design Test Designation TL-3 TL-4 TL-4 TL-5 TL-5 -1- -2- -1- -2- Rail Height, H (in) 32 36 >36 42 >42 Ls (kips) 23 28 28 80 132 He (in) 24 25 30 34 43 Wmin (ft) 4 4.5 4.5 7 12

299 1.4.3 Overturning of the Barrier The factored static moment resistance (ɸM) of the BMS system to overturning should satisfy the following condition (Figure 1.4.4-1): ɸM ≥ γLs (hA or hB) (1.4.3-1) where: Ls = equivalent static load (kips) (Table 1.4.2-1) ɸ = resistance factor = 1 (AASHTO LRFD Bridge Design Specifications 10.5.5.3.3) γ = load factor = 1.0 [extreme event] ha = moment arm taken as the vertical distance from the point of impact due to the dynamic force to the point of rotation A (ft) hb = moment arm taken as the vertical distance from the point of impact due to the dynamic force to the point of rotation B (ft) M = static moment resistance (kip-ft) C1.4.3 The moment contribution due to any coupling between adjacent moment slabs, due to shear strength of the overburden soil, or due to friction which may exist between the backside of the moment slab and the surrounding soil should be neglected. Point of rotation B is used for precast barriers directly placed on level-up concrete. Point of rotation A is used if there is a gap between the barrier and the top of the panel wall or a thickness of compressible material on top of the panel wall. M should be calculated as: M = W (lA or lB) (1.4.3-2) where: W = weight of the monolithic section per unit length of barrier and moment slab plus any material laying on top of the moment slab (kips) lA = horizontal distance from the CG of the weight W to the point of rotation A (ft) lB = horizontal distance from the CG of the weight W to the point of rotation B (ft)

300 1.4.4 Design of the Coping The critical section of the coping must be designed to resist the applicable impact load condition for the appropriate test level as defined in Table 1.4.4-1 (Figure 1.4.4-1). This should include moment and shear resistance and should be calculated according to AASHTO LRFD guidelines. Figure 1.4.4-1 presents an example of a critical section in a BMS system. Depending on the geometry of the section, the location of the critical section may differ from what is shown in the figure. Rotation Point B Rotation Point A Overburden Soil Moment Slab Traffic Barrier C.G. Panels Finished GradeCritical Section Figure 1.4.4-1 Coping and possible critical section. Table 1.4.4-1 Dynamic loads for barrier design Design Forces and Designations TL-3 TL-4 TL-4 TL-5 TL-5 -1- -2- -1- -2- Rail Height, H (in) 32 36 >36 42 >42 Ft Transverse (kips) 70 70 80 160 260 FL Longitudinal (kips) 18 22 28 75 75 Fv Vertical (kips) 4.5 38 33 160 80 LL (ft) 4 4 5 10 10 Lv (in) 18 18 18 40 40 He (in) 24 25 30 34 43(1) (1) For barriers taller than 54 in, use He=52 in

301 1.5 GUIDELINES FOR THE SOIL REINFORCEMENT 1.5.1 General The reinforcement guidelines aim to ensure that the reinforcement does not pullout or yield during the selected design impact event. C1.5.1 In this section, the recommendations for the load in the reinforcement due to the impact are based on a pressure diagram approach back calculated by using the design loads in excess of static earth pressure loads recorded in full-scale crash tests or FE impact simulations. The design load for pull out is different from the design load for yielding. The reason is that the design load for pullout is an equivalent static load while the design load for yielding is a measured dynamic load. The recommendations in this section were provided based on measurements from crash- tested and/ or simulated BMS MSE wall systems. The MSE wall was reinforced with galvanized steel strips with ribs perpendicular to their long axis with 1.97 in width x 0.16 in thickness. The strip length was 10 ft for TL-3, TL-4-1, TL-4-2, and TL-5-1, and 16 ft for TL- 5-2. The density for all the strips was

302 1.5.2 Pullout of the Soil Reinforcement The factored ultimate static resistance (ɸP) to pullout of the reinforcement should satisfy the following condition: ɸP ≥ γs p s At+ γd pdp At (1.5.2-1) where, ɸ = resistance factor = 1 γs = load factor for static load = 1.0 ps = static earth pressure (psf) At = the tributary area of the reinforcement unit (ft2) (based on h1 or h2 in Figure 1.5.2-1) pdp = dynamic pressure for pullout of the reinforcement (psf) (Table 1.5.2-1 and Figure 1.5.2-1) γd = load factor for dynamic load = 1.0 Table 1.5.2-1 Pressure for reinforcement pullout Test Designati on First Layer Second Lay pdp-1 (psf)1 pdp-2 (psf)1 TL-3 370 165 TL-4-1 370 270 TL-4-2 370 270 TL-5-1 725 400 TL-5-2 1240 680 See Figure 1.5.2-1 C1.5.2 The reinforcement resistance P should be calculated by the equation shown in AASHTO 11.10.6.3.2-1. The full length of reinforcement shall be considered effective in the calculation of P. Galvanized steel strips with ribs perpendicular to their long axis and of length 10 ft were used as MSE wall reinforcement in all full-scale crash tests. The strips dimensions were approximately 1.97 in x 0.16 in. Two rows of strips were used in each panel, with three strips installed per row. In the three crash tests carried out, half-panel sections and full-panel sections were used. The full-panel sections used were approximately 5.6 ft wide and 4.9 ft high.

303 Traffic Barrier C.G. h h Moment Slab Soil Top Layer of Reinforcement Second Layer of Reinforcement p dp-1 p dp-2 p s 1 2 Figure 1.5.2-1 Pressure distribution pdp for reinforcement pullout.

304 1.5.3 Yielding of the Soil Reinforcement The factored resistance (ɸR) to yielding of the reinforcement should satisfy the following condition: ɸR ≥ γs ps At + γd pdy At (1.5.3-1) where, ɸ = resistance factor = 1 γs = load factor for static load = 1.0 ps = static earth pressure (psf) At = the tributary area of the reinforcement unit (ft2) (based on h1 or h2 as shown in Figure 1.5.3-1) pdy = dynamic pressure distribution for yielding of the reinforcement (psf) (Table 1.5.3-1) based on h1 or h2 as shown in Figure 1.5.3- 1) γd = load factor for dynamic load = 1.0 Table 1.5.3-1 Pressure pdy for reinforcement yielding Test Designati on First Layer Second Layer pdy-1 (psf)1 pdy-2 (psf)1 TL-3 1415 300 TL-4-1 1755 300 TL-4-2 1755 300 TL-5-1 3250 485 TL-5-2 4440 675 See Figure 1.5.3-1 C1.5.3 In this section, the recommendations for the dynamic load in the reinforcement due to the impact are based on a pressure diagram back calculated by using the maximum recorded loads in full-scale crash tests or FE impact simulations minus the static earth pressure loads. C1.5.3-1 The factored resistance ɸR to yielding of the reinforcement is specified in Article 11.10.6.4 of AASHTO LRFD. The cross section of the reinforcement should be reduced to account for metal losses due to corrosion in accordance with AASHTO LRFD 11.10.6.4.2. The connections between the reinforcement and the wall panels should be designed to satisfy the dynamic yield forces.

305 Traffic Barrier C.G. h h Moment Slab Soil Top Layer of Reinforcement Second Layer of Reinforcement p dy-1 p dy-2 p s 1 2 Figure 1.5.3-1 Pressure diagram pdy for reinforcement yielding.