Aesthetic Concrete Barrier Design (2006)

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The guidelines presented herein were developed for use by engineers and designers applying aesthetic surface treatments to safety shape, single-slope, and vertical-face concrete barri- ers. In addition, guidelines for stone masonry guardwalls are presented. The guidelines were developed for specific barrier shapes, and careful attention to applying the appropriate guid- ance to the correct barrier shape should be exercised. The development of the guidelines for each barrier type was supported by performing full-scale crash tests and in some instances using computer simulation. These guidelines, when appropriately applied, satisfy the performance evaluation cri- teria for NCHRP Report 350: Recommended Procedures for the Safety Performance Evaluation of Highway Features Test Level 3 (i.e., 100 km/h [62 mph]).(1) These guidelines do not address the structural design of any type of barrier. GUIDELINES FOR SAFETY SHAPE BARRIERS Guidelines for safety shape concrete barriers presented herein were developed by Texas Transportation Institute under NCHRP Project 22-19. These guidelines apply to the New Jer- sey and the F-shape concrete barriers and were developed for Test Level 3 (TL-3) of NCHRP Report 350. The guidelines also apply to service levels higher and lower than TL-3. For service levels lower than TL-3, the presented guidelines may be conservative. The guidelines for aesthetic surface treatment of the safety shape barriers are defined as a set of relationships between different surface asperity parameters. All generalized surface asperities (i.e., perpendicular, rounded, or angled surface interruptions) are defined in terms of the depth d and angle θ, as shown in Figure A-1. The perpendicular asperity is a subset of the angled asper- ity with θ = 90 degrees. The rounded asperity can be approx- imated as an angled surface asperity by selecting an effective angle θ. Figure A-1 uses a tangent to the rounded surface at half the depth d to define an effective angle θ. Guidelines for the safety shape barriers were developed for 90-, 45-, and 30-degree asperity angles. Use of these guide- lines is restricted to the specified angles, and interpolation between relationships for use with other asperity angles is not recommended. These guidelines define the surface asperity as the portion of the barrier that is recessed into the barrier surface. In other words, an asperity is to be considered a depression in the sur- face of the barrier. Thus, the width of the asperity, W, has been defined as the distance between the outer edges of the asperity, as shown in Figure A-2. Additionally, the asperities A-1 are only introduced into the very uppermost flat portion of the barrier face (above the barrier break point). The developed guidelines are independent of the asperity spacing (Ws), which is the distance between two adjacent asperities, as shown in Figure A-2. The design guidelines are presented in Figure A-3 (in metric units) and Figure A-4 (in English units). Asperity depth, d, has been plotted as a function of asperity width, W, for asperity angles of 90, 45, and 30 degrees. For each of these curves, “acceptable” and “not recommended” regions have been indicated. All aesthetic surface treatments done to safety shape barriers should lie in the “acceptable” region. In Figure A-3, lines representing the “geometric boundary” for the 45- and 30-degree asperities are also shown. These lines simply imply that for the specified asperity angle, an asperity configuration to the left of the line is geometrically not possible. In addition to meeting the requirements specified in Fig- ure A-3, care must be taken to ensure that no patterns of sur- face asperity have repeating upward sloping edges. Such pat- terns are likely to cause vehicle instability and high roll angles on impact, possibly resulting in vehicle rollover. Examples of Using the Aesthetic Design Guidelines for Safety Shape Barriers Two sample design exercises are presented to demonstrate the use of the aesthetic design guidelines in applying aes- thetic surface treatments to concrete safety shape barriers. Example 1 An aesthetic surface treatment shown in Figure A-5 is evaluated and modified using the aesthetic design guidelines in this example. The initial design consists of repetitive asperities cast into the barrier top. The width of the asperities is 300 mm, and a gap of 100 mm exists between adjacent asperities. The asperities are 19 mm deep, and the edges of the asperities are cast at an angle of 45 degrees. Using the design guidelines in Figure A-3, it can be seen that, for the 45-degree asperities, asperity width (W) of 300 mm and asperity depth (d) of 19 mm exists in the “not recom- mended” region. Therefore, modifications to the initial design are necessary. Figure A-6(a) shows a modified design in which the asper- ity width was increased to 350 mm while the depth remained the same. This modified configuration now exists in the “acceptable” region of the aesthetic design guidelines. In Figure A-6(b), the width of the asperities was kept the same APPENDIX GUIDELINES FOR AESTHETIC BARRIER DESIGN

A-2 Figure A-1. Generalized types of surface asperities for safety shape barriers. Figure A-2. Surface asperity geometry variables for safety shape barriers. Figure A-3. Final design guidelines for aesthetic surface treatment of safety shape concrete barrier (metric). (i.e., 300 mm), but the depth of the asperities was reduced to 13 mm. This modification also results in a configuration that exists in the “acceptable” region of the design guidelines. Example 2 In this example, the initial design shown in Figure A-7 con- sists of two types of asperity. The first type of asperity is 350 mm wide and 25 mm deep and has 45-degree asperity edges. The second type of asperity is 100 mm wide and 25 mm deep and has 90-degree asperity edges. Gaps between adjacent asperities are 100 mm wide. Using the design guidelines in Figure A-3, it can be seen that, for the 45-degree asperities, asperity width (W) of 350 mm and asperity depth (d ) of 25 mm exists in the “not recom- mended” region. Similarly, the 90-degree asperities that are 100 mm wide and 25 mm deep also exist in the “not recom- mended” region of the design guidelines.

A-3 Figure A-4. Final design guidelines for aesthetic surface treatment of safety shape concrete barrier (English). Figure A-5. Initial aesthetic barrier design. Figure A-8 shows a modification to the original design. The width of the 45-degree asperities was increased to 400 mm, while the depth was kept the same (25 mm). In addition, the width of the 90-degree asperities was reduced to 30 mm, while the depth was kept the same (25 mm). Making this mod- ification shifts the asperity configurations for both angles to the “acceptable” regions in the final design guidelines. If a width of 30 mm for the 90-degree asperities appears too small, the designer may consider changing the asperity angle to 45 degrees and increasing the asperity width. As an example, Figure A-9 shows one such modification in which the original 90-degree asperities have been replaced by the 45-degree asperities that are 200 mm wide and 7 mm deep. This modification also shifts the asperity configuration to the “acceptable” region in the design guidelines. GUIDELINES FOR SINGLE-SLOPE AND VERTICAL-FACE BARRIERS Guidelines for single-slope and vertical-face barriers were developed by Caltrans(2) and approved by the FHWA in acceptance letter B-110. These guidelines permit the fol-

A-4 (a) (b) Figure A-6. Suggested modifications to the initial design using the aesthetic design guidelines. Figure A-7. Initial aesthetic barrier design. lowing types of surface treatments to single-slope and vertical-face barriers: • Sandblasted textures with a maximum relief of 9.5 mm. • Images or geometric patterns cut into the face of the bar- rier 25 mm or less and having 45-degree or flatter cham- fered or beveled edges to minimize vehicular sheet metal or wheel snagging. • Textures or patterns of any shape and length inset into the face of the barrier up to 13 mm deep and 25 mm wide. (Geometric insets with an upstream edge and an angle of up to 90 degrees should be less than 13 mm.) • Any pattern or texture with gradual undulations that have a maximum relief of 20 mm over a distance of 300 mm.

A-5 Figure A-8. Suggested modifications to the initial design using the aesthetic design guidelines. Figure A-9. Suggested modifications to the initial design using the aesthetic design guidelines. • Gaps, slots, grooves, or joints of any depth with a max- imum width of 20 mm and a maximum surface differ- ential across these features of 5 mm. • No patterns with a repeating upward sloping edge or ridge. • Any pattern or texture with a maximum relief of 64 mm, if such a pattern begins 610 mm or more above the base of the barrier and if all leading edges are rounded or sloped to minimize any vehicle snagging potential. (No part of this pattern or texture should protrude below the plane of the lower, untextured portion of the barrier.) GUIDELINES FOR STONE MASONRY GUARDWALLS Guidelines for stone masonry guardwalls were developed by the FHWA.(3) Native area stones are applied as a veneer to enhance the appearance of concrete barriers in this type of aesthetic treatment. Following are the guidelines for applying this treatment. • Construct the guardwall true and uniform along its length, with no stone projecting more than 38 mm beyond the neat line. • Rake the joints and beds to a depth of 50 mm on the front and top sides and to 38 mm on the back. • Make mortar beds and joints according to Table A-1.(3) • Use a one-piece capstone for the full width of the guard- wall for at least 25% of the total length. Use a two-piece capstone with the joint within 100 mm of the guardwall center for the remaining length. • Place all stones, including the capstones, randomly to avoid a pattern. • Lay stones to reflect the width of the expansion joints. • Do not leave a gap or a mortar edge at the expansion joint. • Use various sizes of stones to coin or key the corners of the guardwall. Stones that create protrusions greater than those described are not considered crashworthy. Based on aesthetics and stone Class Rubble Class B Class A Dimensioned Beds (inches) Joints (inches) 0.50 - 2.50 0.50 - 2.00 0.50 - 2.00 0.38 - 1.00 0.50 - 2.50 0.50 - 2.00 0.50 - 1.50 0.75 - 1.00 TABLE A-1 Masonry bed and joint thicknesses

availability, a smoother stone face may be used, such as Class A or B masonry. REFERENCES 1. Ross, H. E., Jr., Sicking, D. L., Zimmer, R. A., and Michie, J. D., NCHRP Report 350: Recommended Procedures for the Safety Performance Evaluation of Highway Features, Transportation A-6 Research Board, National Research Council, Washington, D.C., 1993. 2. White, M., Jewell, J., and Peter, R. “Crash Testing of Vari- ous Textured Barriers.” Contract No. F2001TL17, Califor- nia Department of Transportation, Sacramento, CA (2002), 126 pp. 3. “Standard Specifications for Construction of Roads and Bridges on Federal Highway Projects: FP-96.” Federal High- way Administration, Washington, DC (1996).