Click for next page ( 19

The National Academies of Sciences, Engineering, and Medicine
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 18
18 The design of see-through rails reaches a point where a key question must be posed: "How much investment for aesthetic purposes is appropriate for a railing that should attract little attention?" (It is supposed that the scene beyond is the reason for seeing past the railing.) There will be a point of diminish- ing returns in fashioning a see-through rail, given the con- textual issues of how they are seen. It may be possible to achieve acceptable visual access with small openings in the rail. Answering this question should be a major goal of the visual preference studies. An aspect not demonstrated in the graphic studies but clearly apparent in existing examples of concrete barriers is the issue of the shape and location of the view window. Concrete barri- ers such as the Texas T411 have vertical openings between deep posts. A contrast to this is the concrete post-and-beam (P&B) type of rail (e.g., Kansas Corral), which has a horizon- tal opening. The depth of the T411 openings makes it impos- sible to see through the rail unless the viewer is nearly perpen- dicular to the rail. Until then, on approach to the rail, the surface appears as a solid, although textured, barrier. The rail offers lit- tle in the way of functional visual access. The horizontal open- Figure 10. Dimensions of typical bridge railings ing of the P&B rail, however, affords a wide, continuous view (in millimeters). window that is easily discernable on approach to the rail. Even though the concrete beam provides a significant visual screen, the viewers' eyes can easily connect the upper and lower uniform surface. The T411 was modified to perform in accor- scenes into an understandable image. dance with NCHRP Report 350 TL-3 by providing a flat, smooth, vertical traffic face for a height of 457 mm along the lower portion of the barrier and forming the openings above APPLICATIONS that height. In the case of steel see-through rails, the most limiting fac- A key question in aesthetic design is "how much visual tors are (1) the allowable deformation of the horizontal ele- impact will the barrier modification have and why?" The ment and (2) the exposure of the vertical supports to an impact- degree of visual impact will depend heavily on the visual ing vehicle. The question becomes "how far back can the prominence of the barrier relative to the background. How supports be placed and still achieve the requisite support for does this relationship affect the design of rails? To investigate the horizontal elements?" The vertical opening distance or this question, the researchers developed a series of barrier clear space between rail elements must be considered, as well examples. These were used in a graphical study to explore the as the size of the horizontal elements that define the contact relationship between barrier and background. area of the rail. An easy way to help ensure proper impact per- Four images of each study alternative are presented in four formance is to reduce the clear opening between the horizon- settings. The first is the barrier alone, the second is with a rural tal elements to a point that an impacting vehicle cannot reach background, the third is with an urban background, and the the vertical support. At some point we approach an increas- fourth is with both a rural and urban background. The back- ingly uniform surface, one for which concrete is a more suit- ground imagery is stylized to represent a visually complex able material. urban backdrop and a simpler, flatter, rural scene. Since this study was to determine the effects of contrasting shapes, the graphics are prepared in shades of gray. The graphics show a true-to-scale (with the road) image of a 914-mm-tall, single- slope wall. The shoulder is 1.8 m wide and the travel lane is 3.7 m wide. The joints shown in the barrier are spaced 7.6 m. Alternative A--Untreated and Recessed Panels Alternative A1 is an untreated single-slope barrier (Fig- ure 12). Figure 11. Plan view of Texas T411 bridge rail cross Alternative A2 has recessed panels of contrasting color section (in millimeters). (Figure 13).

OCR for page 18
19 Figure 12. Alternative A1--single-slope barrier. Figure 13. Alternative A2--recessed panels. The contrast between these two rails without the back- ground is significant. The untreated barrier reinforces the line of the roadway, while the segments of the panel design reduce This study explores how much surface contrast is neces- this effect dramatically. In the rural set, A1 mimics the lin- sary to achieve the effects noted in Alternative A. A com- earity of the background, while A2 appears more static by parison of the two barriers without background clearly indi- comparison. In the urban set, A1 stands in strong contrast to cates the dashed line reduces the apparent length of the rail. the numerous lines behind it, but A2 starts to blend with the The effects found in the two backgrounds in Alternative A background. In the combined rural/urban set, each rail appears are the same as well. This suggests that it may be possible to more visually balanced with the background. achieve a significant visual effect while limiting the segment- imparting elements to the top portion of the rail. Alternative B--Recessed Line Alternative B1 is a single, recessed line about 102 mm Alternative C--Arches wide with a 13-mm-wide line above (Figure 14). Alternative B2 is a recessed line alternately broken into Alternative C1 is a 7.6-m arch pattern (Figure 16). 7.6-m and 15.2-m segments (Figure 15). Alternative C2 is a 15.2-m arch pattern (Figure 17).

OCR for page 18
20 Figure 14. Alternative B1--recessed lines. Figure 15. Alternative B2--segmented line. This study was used to compare the effect of lengthening a continuous pattern, in this case an architectural pattern. The prominent edge and caused the rail to be more distinct against curves of the arches seem to be in character to the rounded all backgrounds. Copings, shown in Figure 18, may provide forms of the rural background. The shorter version feels an economical technique to improving the look of a barrier more "architectural" than does the long arch alternative. The without affecting impact properties of the structure. Alter- longer pattern appears to be in higher contrast to the back- native D provides some coping options. Two (D1 and D2) are ground than the shorter version due to the reduced numbers very simple; three (D3, D4, and D5) are more complex, with of lines on the surface. However, each may tend to blend too more edges. much with the urban background. Alternative D1 is a coping without any additional surface treatment (Figure 19). Alternative D2 is a coping with an added protruding sur- Alternative D--Copings face spaced at 15.2 m and with the same surface color as the barrier (see Figure 20). Alternative B incorporated a design that added a contrast- Alternative D3 is a contrasting color added to the protrud- ing detail near the top of the barrier. This created a more ing surface (Figure 21).

OCR for page 18
21 Figure 17. Alternative C2--15.2-m arch. Figure 16. Alternative C1--7.6-m arch. more pronounced in the urban example. Barriers that allow a Alternative D4 is a protruding surface lengthened and lot of the background to be seen may run the risk of losing a matching the barrier color (Figure 22). necessary degree of visual prominence. The visual prominence Alternative D5 is a contrasting color added to the protrud- of these types of barriers may be increased through the use of ing surface (Figure 23). strong colors. The effect of adding a spaced, protruding surface is the same as was found in alternatives A, B, and C. Alternative E--Open Metal Rail The rail shown in Figure 24 relies on collapsible steel pan- els that on impact would form a smooth, steel barrier. The see- through character of this design tends to blend the barrier with the background in both rural and urban settings. The effect is Figure 18. Alternative D--copings.

OCR for page 18
22 Figure 19. Alternative D1--coping only. Figure 20. Alternative D2--coping with protruding surface. Alternative F--Open Tube Rail the face has been converted to a curved recess. The effect will This rail, shown in Figure 25, exhibits the same character- add depth to the face by imparting subtle shading to the bar- istics as Alternative E. It is similar in concept to the widely rier face and may have some "directive" capabilities regard- used Wyoming Rail that features square tubing. The issue with ing impacting vehicles. This is a visually prominent barrier, railings that allow a lot of visibility through their structure is but the small amount of open space beneath the beam makes the question of "what is being seen?" The goal of any see- it appear less massive. Even though there is little view shed through barrier is to give visual prominence to the background available through the openings, it is enough to complete the scene. This suggests that the aesthetic character of these rail lower portion of the view above the rail. Despite their small types is of less importance than that of solid barriers since we size, the openings also reduce some of the linear emphasis of are intentionally making it less visible. If this is the case, the the rail. form of the rail may be less important than its finish. Discontinuous Element Concepts Alternative G--Concrete Post and Beam Introducing discontinuous elements into the face of a bar- This alternative is a modified version of a typical concrete rier treats the barrier as a static unit over distance and time. post-and-beam design. In this alternative, shown in Figure 26, A feature of some designs is that simple aesthetic elements