Click for next page ( 73


The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement



Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.

OCR for page 72
A-1 APPENDIX GUIDELINES FOR AESTHETIC BARRIER DESIGN The guidelines presented herein were developed for use by are only introduced into the very uppermost flat portion of engineers and designers applying aesthetic surface treatments the barrier face (above the barrier break point). to safety shape, single-slope, and vertical-face concrete barri- The developed guidelines are independent of the asperity ers. In addition, guidelines for stone masonry guardwalls are spacing (Ws), which is the distance between two adjacent presented. The guidelines were developed for specific barrier asperities, as shown in Figure A-2. shapes, and careful attention to applying the appropriate guid- The design guidelines are presented in Figure A-3 (in ance to the correct barrier shape should be exercised. metric units) and Figure A-4 (in English units). Asperity The development of the guidelines for each barrier type was depth, d, has been plotted as a function of asperity width, W, supported by performing full-scale crash tests and in some for asperity angles of 90, 45, and 30 degrees. For each of instances using computer simulation. These guidelines, when these curves, "acceptable" and "not recommended" regions appropriately applied, satisfy the performance evaluation cri- have been indicated. All aesthetic surface treatments done to teria for NCHRP Report 350: Recommended Procedures for safety shape barriers should lie in the "acceptable" region. the Safety Performance Evaluation of Highway Features Test In Figure A-3, lines representing the "geometric boundary" Level 3 (i.e., 100 km/h [62 mph]).(1) These guidelines do not for the 45- and 30-degree asperities are also shown. These address the structural design of any type of barrier. lines simply imply that for the specified asperity angle, an asperity configuration to the left of the line is geometrically not possible. GUIDELINES FOR SAFETY SHAPE BARRIERS In addition to meeting the requirements specified in Fig- ure A-3, care must be taken to ensure that no patterns of sur- Guidelines for safety shape concrete barriers presented face asperity have repeating upward sloping edges. Such pat- herein were developed by Texas Transportation Institute under terns are likely to cause vehicle instability and high roll angles NCHRP Project 22-19. These guidelines apply to the New Jer- on impact, possibly resulting in vehicle rollover. sey and the F-shape concrete barriers and were developed for Test Level 3 (TL-3) of NCHRP Report 350. The guidelines Examples of Using the Aesthetic Design also apply to service levels higher and lower than TL-3. For Guidelines for Safety Shape Barriers service levels lower than TL-3, the presented guidelines may be conservative. Two sample design exercises are presented to demonstrate The guidelines for aesthetic surface treatment of the safety the use of the aesthetic design guidelines in applying aes- shape barriers are defined as a set of relationships between thetic surface treatments to concrete safety shape barriers. different surface asperity parameters. All generalized surface asperities (i.e., perpendicular, rounded, or angled surface Example 1 interruptions) are defined in terms of the depth d and angle , as shown in Figure A-1. An aesthetic surface treatment shown in Figure A-5 is The perpendicular asperity is a subset of the angled asper- evaluated and modified using the aesthetic design guidelines ity with = 90 degrees. The rounded asperity can be approx- in this example. The initial design consists of repetitive imated as an angled surface asperity by selecting an effective asperities cast into the barrier top. The width of the asperities angle . Figure A-1 uses a tangent to the rounded surface at is 300 mm, and a gap of 100 mm exists between adjacent half the depth d to define an effective angle . asperities. The asperities are 19 mm deep, and the edges of Guidelines for the safety shape barriers were developed for the asperities are cast at an angle of 45 degrees. 90-, 45-, and 30-degree asperity angles. Use of these guide- Using the design guidelines in Figure A-3, it can be seen that, lines is restricted to the specified angles, and interpolation for the 45-degree asperities, asperity width (W) of 300 mm between relationships for use with other asperity angles is not and asperity depth (d) of 19 mm exists in the "not recom- recommended. mended" region. Therefore, modifications to the initial design These guidelines define the surface asperity as the portion are necessary. of the barrier that is recessed into the barrier surface. In other Figure A-6(a) shows a modified design in which the asper- words, an asperity is to be considered a depression in the sur- ity width was increased to 350 mm while the depth remained face of the barrier. Thus, the width of the asperity, W, has the same. This modified configuration now exists in the been defined as the distance between the outer edges of the "acceptable" region of the aesthetic design guidelines. In asperity, as shown in Figure A-2. Additionally, the asperities Figure A-6(b), the width of the asperities was kept the same

OCR for page 72
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. (i.e., 300 mm), but the depth of the asperities was reduced to edges. The second type of asperity is 100 mm wide and 13 mm. This modification also results in a configuration that 25 mm deep and has 90-degree asperity edges. Gaps between exists in the "acceptable" region of the design guidelines. adjacent asperities are 100 mm wide. Using the design guidelines in Figure A-3, it can be seen Example 2 that, for the 45-degree asperities, asperity width (W) of 350 mm and asperity depth (d ) of 25 mm exists in the "not recom- In this example, the initial design shown in Figure A-7 con- mended" region. Similarly, the 90-degree asperities that are sists of two types of asperity. The first type of asperity is 100 mm wide and 25 mm deep also exist in the "not recom- 350 mm wide and 25 mm deep and has 45-degree asperity mended" region of the design guidelines. Figure A-3. Final design guidelines for aesthetic surface treatment of safety shape concrete barrier (metric).

OCR for page 72
A-3 Figure A-4. Final design guidelines for aesthetic surface treatment of safety shape concrete barrier (English). Figure A-8 shows a modification to the original design. The the original 90-degree asperities have been replaced by the width of the 45-degree asperities was increased to 400 mm, 45-degree asperities that are 200 mm wide and 7 mm deep. while the depth was kept the same (25 mm). In addition, This modification also shifts the asperity configuration to the the width of the 90-degree asperities was reduced to 30 mm, "acceptable" region in the design guidelines. while the depth was kept the same (25 mm). Making this mod- ification shifts the asperity configurations for both angles to the GUIDELINES FOR SINGLE-SLOPE AND "acceptable" regions in the final design guidelines. VERTICAL-FACE BARRIERS If a width of 30 mm for the 90-degree asperities appears too small, the designer may consider changing the asperity Guidelines for single-slope and vertical-face barriers angle to 45 degrees and increasing the asperity width. As an were developed by Caltrans(2) and approved by the FHWA example, Figure A-9 shows one such modification in which in acceptance letter B-110. These guidelines permit the fol- Figure A-5. Initial aesthetic barrier design.

OCR for page 72
A-4 (a) (b) Figure A-6. Suggested modifications to the initial design using the aesthetic design guidelines. lowing types of surface treatments to single-slope and Textures or patterns of any shape and length inset vertical-face barriers: into the face of the barrier up to 13 mm deep and 25 mm wide. (Geometric insets with an upstream edge Sandblasted textures with a maximum relief of 9.5 mm. and an angle of up to 90 degrees should be less than Images or geometric patterns cut into the face of the bar- 13 mm.) rier 25 mm or less and having 45-degree or flatter cham- Any pattern or texture with gradual undulations that fered or beveled edges to minimize vehicular sheet have a maximum relief of 20 mm over a distance of metal or wheel snagging. 300 mm. Figure A-7. Initial aesthetic barrier design.

OCR for page 72
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- Make mortar beds and joints according to Table A-1.(3) imum width of 20 mm and a maximum surface differ- Use a one-piece capstone for the full width of the guard- ential across these features of 5 mm. wall for at least 25% of the total length. Use a two-piece No patterns with a repeating upward sloping edge or ridge. capstone with the joint within 100 mm of the guardwall Any pattern or texture with a maximum relief of 64 mm, center for the remaining length. if such a pattern begins 610 mm or more above the base Place all stones, including the capstones, randomly to of the barrier and if all leading edges are rounded or avoid a pattern. sloped to minimize any vehicle snagging potential. (No Lay stones to reflect the width of the expansion joints. part of this pattern or texture should protrude below the Do not leave a gap or a mortar edge at the expansion joint. plane of the lower, untextured portion of the barrier.) Use various sizes of stones to coin or key the corners of the guardwall. GUIDELINES FOR STONE Stones that create protrusions greater than those described MASONRY GUARDWALLS are not considered crashworthy. Based on aesthetics and stone 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 TABLE A-1 Masonry bed and joint thicknesses aesthetic treatment. Following are the guidelines for applying this treatment. Class Beds (inches) Joints (inches) Rubble 0.50 - 2.50 0.50 - 2.50 Construct the guardwall true and uniform along its length, with no stone projecting more than 38 mm beyond the Class B 0.50 - 2.00 0.50 - 2.00 neat line. Class A 0.50 - 2.00 0.50 - 1.50 Rake the joints and beds to a depth of 50 mm on the front and top sides and to 38 mm on the back. Dimensioned 0.38 - 1.00 0.75 - 1.00

OCR for page 72
A-6 availability, a smoother stone face may be used, such as Class Research Board, National Research Council, Washington, D.C., A or B masonry. 1993. 2. White, M., Jewell, J., and Peter, R. "Crash Testing of Vari- ous Textured Barriers." Contract No. F2001TL17, Califor- REFERENCES nia Department of Transportation, Sacramento, CA (2002), 126 pp. 1. Ross, H. E., Jr., Sicking, D. L., Zimmer, R. A., and Michie, J. D., 3. "Standard Specifications for Construction of Roads and NCHRP Report 350: Recommended Procedures for the Safety Bridges on Federal Highway Projects: FP-96." Federal High- Performance Evaluation of Highway Features, Transportation way Administration, Washington, DC (1996).