AESTHETIC CONSIDERATIONS FOR URBAN PEDESTRIAN

BRIDGE DESIGN

By Shijin Yangl and Dongzhou Huang,Z Member, ASCE

ABSTRACT: Many urban pedestrian bridges have been built in the world. However, their aesthetic aspect hasoften been neglected. As the loadings of an urban pedestrian bridge is comparatively small and its width isrelatively narrow, the modeling of the bridge is more flexible than other types of bridges. In this paper, thefactors affecting the formation of urban pedestrian bridges are analyzed. These factors include the surroundings,positions of viewers, and types of bridge structures. Additionally, some basic considerations and regulationsconcerning the aesthetic shaping of urban pedestrian bridges and plane and space compositions are developed.These regulations can help engineers better understand the aesthetic aspect of urban pedestrian bridge design.Finally, the aesthetic analysis of several existing bridges based on the presented regulations is given.

Plan View

, '

--rf-'n--IlI---'-­__L.U. -W--.

: 1 0)

INTRODUCTION

With the rapid development of motorization, there is a greatdemand for the separation of pedestrians and vehicles in cities.During the last several decades, a large number of pedestrianbridges have been constructed to replace crosswalks on thestreets in many countries. Unfortunately, the aesthetic aspectof these designs has often been neglected. Few significant con­tributions have been made in the advancement of pedestrianbridge aesthetics, in contrast to the great number of contri­butions on those of buildings and other types of bridges (Leon­hardt 1984; Bridge 1981; Gage and Vandeberg 1975; Com­mittee 1991). Since the live load of a pedestrian bridge iscomparatively small and its roadway width is relatively nar­row, there is more freedom for bridge designers to choosepleasing shapes for their bridges. Moreover, the spaces on ornear pedestrian bridges, which tend to be spectacular places,attract more people than other types of bridges. Consequently,pedestrian bridges require at least as much consideration ofaesthetics as that for other types of bridges.

FACTORS AFFECTING THE MODELING OFPEDESTRIAN BRIDGES

There are many factors that should be considered in mod­eling pedestrian bridges. Functional, environmental, visual,and structural conditions are the main factors. Loading types;traffic volumes and speeds; the width of each part; and theclearances of spans are included in the functional condition.Topographic characteristics and surrounding environment arecovered by the environmental condition. Topographic charac­teristics imply the locations of dividing strips and green belts,widths of traffic lane and walkway, locations of undergroundpipes, and so forth. The surrounding environment mainly in­volves the characteristics of nearby surroundings, public fa­cilities, and green belts. Visual conditions include the conceptthat pedestrian bridge modeling should meet the requirementsof people's visual sense and provide good visual sense effectsfor various visual points. The structural condition incorporatesthe idea that pedestrian bridge modeling is related to its struc­tural system and material.

'Sr. Engr., Dept. of Bridge Engrg., Tongji Univ., Shanghai, 200092,China.

'Res. Prof., Dept. of Civ. and Envir. Engrg., Florida InternationalUniv., Miami, FL 33199; Sr. Structural Engr., Florida Dept. of Transp.,Bartow, FL 33830.

Note. Discussion open until August I, 1997. To extend the closingdate one month, a written request must be filed with the ASCE Managerof Journals. The manuscript for this paper was submitted for review andpossible publication on March 20, 1995. This paper is part of the JOUTFUlI

ofArchitectural Engineering, Vol. 3, No.1, March, 1997. ©ASCE, ISSN1076-0431/97/0001-0003-0008/$4.00 + $.50 per page. Paper No.10341.

MODELING OF PEDESTRIAN BRIDGES

According to basic engineering design procedures, pedes­trian bridge modeling is analyzed from the three aspects ofplan, elevation, and space design.

Plan Types

The lines of pedestrian flow control the plan of a pedestrianbridge. The embryonic form of a pedestrian bridge plan shouldcorrespond to the natural pedestrian flow. Fig. 1 shows themost common plan types of pedestrian bridges formed ac­cording to crossing types and the line of pedestrian flow. Plantypes of pedestrian bridges can often be divided into the singleline type, closed type, and radial type. The single line typeincludes the U type [Fig. l(e)], broken line type [Fig. l(d, 0],straight line type [Fig. l(c, j)], and S type [Fig. 1(1)]. Theclosed type covers square types [Fig. l(g)], ring type [Fig.l(i)], and diamond type [Fig. l(k)]. The radial type is a plantype of pedestrian bridge that begins from the center and ex­tends outward in a radial direction, such as the T type [Fig.l(a)], Y type [Fig. l(b)], and X type [Fig. l(h)].

Choosing a plan type for a pedestrian bridge is related to aseries of factors, such as the traffic, bridge objective, andbuilding environment. Among those factors, the relationshipof the pedestrian bridge with its environment is the most im­portant one in pedestrian bridge modeling.

Characteristics of Plan Shapes

During the plan design, we should keep an eye on the char­acteristics of the plan line type. Plane directivity of the singleline type for a pedestrian bridge is strong with a sense of

:m~ :i-rt :0::0-::'::""(a) (b) I (c) (d) ,

-0', - ~~-~-- --0:: - --.''--- -w -- - -- --J(e) , '(t) I : (g) ; \h) : (I)

:i ~\~...... ...-' ,,'"..-. ,,- -_. I --

,O~ - -00--.. \ I ,

FIG. 1. Plan Embryonic Form

JOURNAL OF ARCHITECTURAL ENGINEERING / MARCH 1997/3

J. Archit. Eng. 1997.3:3-8.

Dow

nloa

ded

from

asc

elib

rary

.org

by

Uni

vers

ita S

tudi

Di P

isa/

Sba

on 0

4/26

/13.

Cop

yrig

ht A

SCE

. For

per

sona

l use

onl

y; a

ll ri

ghts

res

erve

d.

Harmonious Plan Shapes with Surroundings

A space enclosed by buildings around a road crossing isreferred to as the crossing space. The shapes of the buildingsaround the crossing give the crossing space various character­istics as well as people within them different psychologicalsenses. Based on people's psychological sense, the crossingspace is divided into the closed and the open (generally ac­cording to the ratio of the visual distance to the height of thebuilding).

straightness and strength. The curve type displays a rhythmicalmotion feature of the whole body with a sense of secludednatural extension. The closed type is of an integrative centri­petal space shape emphasizing the beauty of symmetry andsequence. A pedestrian bridge of the closed curve type drawsspecial attraction for being pleasing, plentiful, and plump. Theradial type composed of both a central part and flange partspresents a symmetrical, neat, and directional sense. A bridgecomposed of a horizontal line and a vertical line shows a senseof balance and stabilization [see Fig. 2(a)]. When the radialtype is combined with oblique lines, the plane line type is fullof vitality, giving a symbolic visual center [see Fig. 2(b)].

(b)

The pedestrian bridge (see Fig. 3) on the intersection of NanJing Road and Xi Zang Road in Shanghai is a case in pointfor its harmony with crossing shape. The walkway at thiscrossing is narrow and the commercial buildings are dense.The crossing space surrounded by the curved boundaries ofthe buildings displays a completed shape. The bridge with aplane shape of an elliptical ring coincides with the crossingoutline so that the plane curve of the bridge is in harmonywith the curve of the buildings (see Fig. 3). In addition, allstairways are extended into the insides of the buildings. Thespaces in the stairways furthermore serve as a site for adver­tisements. All these display an inner organic link of the sur­rounding buildings with the bridge.

For the open crossing space shown in Fig. 4, the surround­ing buildings are scattered without a visual center. The bridgeplane in the radial type has an extending shape showing per­meability with the extension toward the environmental space.In this situation the pedestrian bridge becomes the visual cen­ter in the crossing space. Therefore, the bridge and its envi­ronment tum out to be the organic whole.

Fig. 5 shows an open crossing space in which the surround­ing buildings are integral and identical displaying a stablespace shape. The closed square plane of the pedestrian bridgereveals a sense of stability. It connects all the surroundingbuildings and makes them become a whole unit. When thesurrounding buildings of a crossing do not provide an integralshape, thus creating a more complicated space characteristic,the best way to resolve the plane composition of a pedestrianbridge is to hold the main characteristics of the environment,to try to achieve an identity with the environmental shape, and

FIG. 2. Plan Shape of Radiation 'TYpe

FIG. 3. Nanling-Xizang Bridge In Shanghai

FIG. 4. Open Crossing Space with Radiation Type

4/ JOURNAL OF ARCHITECTURAL ENGINEERING / MARCH 1997

FIG. 5. Open Space with Closed Square Type

FIG. 6. Open Space With K Type

J. Archit. Eng. 1997.3:3-8.

Dow

nloa

ded

from

asc

elib

rary

.org

by

Uni

vers

ita S

tudi

Di P

isa/

Sba

on 0

4/26

/13.

Cop

yrig

ht A

SCE

. For

per

sona

l use

onl

y; a

ll ri

ghts

res

erve

d.

to lay stress on meeting the function condition (see Fig. 6).The shape of the crossing shown in Fig. 6 is a compositeconsisting of K and T types. The multiroad crossing is linkedas a whole unit by the pedestrian bridge with a S-curve shape.

Arrangement of Elevation

On the premise of meeting the functional condition, the el­evation of a pedestrian bridge and its surrounding environmentshould be composed as an organic whole on many levels ingood order. Mostly, people view a pedestrian bridge at a dis­tance. The visual effect of a bridge mainly depends on theelevation arrangement of the pedestrian bridge. As bridge de­signers know well how to meet the functional condition, hereinthe emphasis will lie in the analysis of the elevation arrange­ment using the principal of the visual angle (Shang 1980;Leonhardt 1984).

Visual Angle

There are many visual points to view a pedestrian bridge.In the 19th century, Meltes (Leonhardt 1984) in Germanyachieved various optimum vertical visual angles to view build­ings by the laboratory method: 45° is the optimum angle forviewing the details; 27° is the central visual angle range notonly good for viewing the whole, but also good for seeing thedetails; 18° makes people feel the clear target with its sur­rounding sceneries as the background. Hence, scene range canbe divided into four types: short distance, middle short-dis­tance, middle long-distance, and long distance (see Fig. 7).

Visual Effect and Elevation Arrangement of Main VisualPoints

When a pedestrian bridge is located at a straight street or+ type crossing, the picture viewed from the long-distancevisual range is composed of the bridge and the buildings onthe both sides extending toward the central point. The bridge

1-1_a-tl_b:""""'II--C-+, d ~

h ~:-::::-=--1-8-0.....--------60=-s=--

t:!=~ 2h -4 3h..j l=Oh==---- _

a -. Short-distance; b -- Middle Short-distancec -- Middle Long-distance; d -- Long-distance

FIG. 7. Visual Angle

FIG. 8. Bridge with Street Mark

is located at the important level with the action of the visualcenter. In this situation, the surrounding space should be thebasis for establishing the individual character of a pedestrianbridge and determining the elevation. As shown in Fig. 8, inorder to integrate the bridge with the surrounding environment,a tower is set up on the pedestrian bridge. When a pedestrianbridge is located at other types of crossings the long-distancevisual picture is composed of the bridge (foreground), and thesurrounding buildings (background). The pedestrian bridgeand its environment influence each other. So the sense of feel­ing to the. background and the application of the contrast orthe coordinating methods play an important role in dealingwith the elevation of a pedestrian bridge. If the back buildingsare important and show a balanced shape, the coordinationmethod should be used to arrange the elevation. If the backbuildings are in a dynamic and unstable state, the contrastmethod should be used to coordinate the whole picture so asto make the pedestrian bridge and its background balance.

The middle-distance visual picture possesses a differentspace characteristic. It shows the space relationship between apedestrian bridge and its surroundings as well as some effectsof their details. The modeling of a pedestrian bridge greatlydepends on the visual effect of the middle-distance visualsense, so does its elevation arrangement. In the short-distancevisual picture, as the pedestrian bridge occupies most of thepicture, it gives a feeling of oppression to the visual sense.The bridge and its surroundings become counteractive witheach other, which gives people a non-coordinating feeling.Therefore, the selection of the shape, color, and material ofthe pedestrian bridge are very important factors because theyaffect visual sense. The design of its details should give acheerful and cordial qualitative feeling. In addition, during themodeling of a pedestrian bridge based on the short-distancevisual picture, it should be noticed that the buildings that maybe less aesthetically pleasing should be obstructed or put inthe secondary position in the view. Generally, the elevationarrangement of a pedestrian bridge is always made by consid­ering the visual effect in the middle-distance scene first, thenthe long-distance visual effect. Finally, the elevation arrange­ment can be properly modified according to the effects of theshort-distance visual point and visual point under the bridge.

Arrangement of Elevation and Outline

The top line of a pedestrian bridge floor system is definedas the outside outline of the elevation of the bridge composedof the bridge floor parts, railing, and the outer shape of lightingfacilities. The outside outline generally implies the bridgespan. The boundary of the span under the bridge is named asthe inside outline composed of the lower edge of the super­structure, bridge piers, ramps, and road surface. Space en­closed by the inside outline occupies the important position inthe elevation arrangement.

When people view a pedestrian bridge, its outlines attracttheir attention deeply. The outlines are especially obvious on afoggy day, in the morning, in the evening, or in the contrastinglight. To make the elevation of pedestrian bridge span a vividscene, the inside and outside outlines of the bridge should becoordinated. As the formation of the pedestrian bridge tendsto be succinct and tenuous, suitable designing of the outlineis necessary to yield the whole beauty of the bridge. In addi-

FIG. 9. Xlnsheng Bridge (Japan)

JOURNAL OF ARCHITECTURAL ENGINEERING / MARCH 1997/5

J. Archit. Eng. 1997.3:3-8.

Dow

nloa

ded

from

asc

elib

rary

.org

by

Uni

vers

ita S

tudi

Di P

isa/

Sba

on 0

4/26

/13.

Cop

yrig

ht A

SCE

. For

per

sona

l use

onl

y; a

ll ri

ghts

res

erve

d.

FIG. 10. Basket Arch Bridge In Talyuan

FIG. 11. Campus Bridge In Shanghai

FIG. 12. Cable-Stayed Bridge of Glass Steel

tion, the perspective effect in motion should also be consid­ered. The Xin Sheng pedestrian bridge of Japan (see Fig. 9),which is a single rib arch bridge bottom road, is located in anatural park. To achieve the changing picture of the elevation,the hanger robs are arranged at an oblique angle 80° with thebeam axle (Fig. 9).

The span-depth ratio of a pedestrian bridge gives people aunique impression of the bridge. Though the elevation of thebeam bottom is mainly based on the traffic function, the spanlength can be chosen in different ways. When the roadwaywidth is narrow and the space is closed, the suitable span­depth ratio should be taken to achieve the elevation's aestheticperception of the bridge. When the roadway width is wide andthe space is open, multispan bridge should be considered, inaddition to the consideration of the span-depth ratio.

The shape of bridge piers directly influences the whole el-

6/ JOURNAL OF ARCHITECTURAL ENGINEERING / MARCH 1997

evation. The bridge pier can be built in various ways, but itsoutline should be distinctive. The elevation of a bridge piershould be integrated with the main girder. At the same time,it should be considered the integration of the pier and lift part,to decrease the trivial feeling and increase the modeling effectof the inner outline. Ramps, the first stage in the traffic systemof pedestrian bridges, plays an important role in the functionof environmental link and in the combination of topographicconditions. However, it can only be treated as subordinationin the design of the whole elevation.

Space Modeling

For the space modeling of a pedestrian bridge, more con­sideration should be given to the comprehensive visual effectfrom various angles and many visual points. especially fromthe motion view. The space shape of a pedestrian bridge inmotion should meet the balance principle (Shang 1980), whichis the organic combination of the elevation and plane. It is anideal method by using a model to study the effect of the spacemodeling of a pedestrian bridge. There are a lot of pedestrianbridges that adopt the space modeling type, showing goodloading capacity and beautiful shape. As shown in Figs. 10and 11, the pedestrian arch bridges of basket type are in aspace shape. Fig. 12, the glass steel pedestrian cable-stayedbridge, and Fig. 13, the pedestrian shell bridge in a sea startype with stairs the full extent of the whole bridge, are alsogood examples of the space modeling.

V-type pier and box sections are the ideal components forspace modeling. Arches and cable towers are especially flex-

FIG. 13. Shell Bridge of Sea Star

FIG. 14. Gonghexin-Zhonghun Bridge in Shanghai

J. Archit. Eng. 1997.3:3-8.

Dow

nloa

ded

from

asc

elib

rary

.org

by

Uni

vers

ita S

tudi

Di P

isa/

Sba

on 0

4/26

/13.

Cop

yrig

ht A

SCE

. For

per

sona

l use

onl

y; a

ll ri

ghts

res

erve

d.

ible in the modeling of a pedestrian bridge. In addition, theintegration of a pedestrian bridge and its surrounding shouldbe considered in space modeling. If a pedestrian bridge con­nects two buildings, the emphasis should be put on the effectof the inner visual point and a closed type of pedestrian bridgecan be used (Fig. 14). This kind of pedestrian bridge servesas a corridor that connects buildings in function and type.

EXAMPLES

Fig. 15 shows the pedestrian bridge of Xian Lie Road inGuang Zhou City. It is located in an open section of a road,surrounded by some high-rise buildings and the green pedes­trian way. The bridge has a span length of 45 m and is a rigidframed structure with a depth of beam of 60 cm at mid-span.According to the different needs of the motor lanes and walk­ways, the elevation is formed by three different sections. Thebridge has slant legs serving as the stairways that not onlyenrich the elevation arrangement, but also decrease the heightof the bridge so as to attract more people to go up the bridge.The modeling characteristic is that the bridge becomes theopen-space visual center.

The Lian Gen Pedestrian Bridge (Fig. 16) is located at amultiroad crossing. The central part of the pedestrian bridgeis in a radial shape. The wing parts are linked with some sin­gle-line types of the bridge in different directions, forming thespace pedestrian traffic system with multilevel grades. Threeradial wings are formed by three concave curves in differentdirections. The core part has a big round hole and a centrallighting. Thus, the bridge appears uniform and balanced. Thiskind of the plane composition lightens the dead load of thecentral part of the span and disperses the pedestrian flow. The

FIG. 15. Xlanlle Road Bridge In Guangzhou

FIG. 16. Llangen Pedestrian Bridge (Japan)

FIG. 17. Basket Pedestrian Bridge (Japan)

decorative plates of the bridge are light blue, the main beamis dark blue, and the bridge pier is light gray. The whole bridgelooks tenuous, graceful, and harmonious with the environment.The bridge floors of three wings have different colors of pave­ment that guide the different directions of the traffic. Besides,the ring-type benches are installed around the central hole ofthe bridge floor.

Fig. 17 shows a pedestrian arch bridge of basket type thatis located in an open space in Japan. Two arch ribs connect atone end of the bridge and gradually apart to the other bend.Then, the arch feet are separably set at both sides of the bridge.The elevation composed of arch ribs, hangers, and bridge floorforms a hollow net that has an "isolated" role in the archi­tecture and adds the levels. The gentle and beautiful arch ribbecomes the strong contrast with the tenuous and straighthangers, which shows the characteristics of stiffness as wellas gentleness. The different treatment of the high and low archfeet adds the change of the outline under the span. The sideview of the branched arch ribs is an inverted Y shape. Theinverted V-type space has a good framing role. The top viewof the arch rib is also an inverted Y shape that achieves theplane change of the bridge. As the elevation of the bridge isorganically combined with the plane, the space structural mod­eling gives people different scenery from different visualpoints.

CONCLUSIONS

I. Since the loading of a pedestrian bridge is small and thebridge's width is narrow, the modeling of urban pedes­trian bridges is more flexible than other types of bridges.Urban pedestrian bridges should be outstanding architec­tural works. The modeling of a pedestrian bridge is notmerely to meet traffic functions, but also to make itsshape join the urban environment as much as possible.Therefore, the environmental condition is one of mainfactors in the modeling of a pedestrian bridge.

2. The plane composition of a pedestrian bridge should beb~ed on the function condition. It should meet the prin­Ciple of plane composition, possess the plane shapebeauty, and be harmonious with the road crossing.

3. In the elevation design of a pedestrian bridge, attentionshould be paid to the visual effect of different visualpoints, the treatment of the levels of the model, and out­side/inside outlines, in order to achieve overall beauty ofthe whole bridge.

4. In the. sp~ce modeling of a pedestrian bridge, the organic~ombma~lOn of the plane with the elevation of the bridgeIS most. Important. Planning of an urban traffic systemshould mclude the pedestrian and nonmotorized trafficsystems.

JOURNAL OF ARCHITECTURAL ENGINEERING / MARCH 1997/7

J. Archit. Eng. 1997.3:3-8.

Dow

nloa

ded

from

asc

elib

rary

.org

by

Uni

vers

ita S

tudi

Di P

isa/

Sba

on 0

4/26

/13.

Cop

yrig

ht A

SCE

. For

per

sona

l use

onl

y; a

ll ri

ghts

res

erve

d.

ACKNOWLEDGMENT

The writers wish to gratefully acknowledge the reviewers for theirvaluable suggestions.

APPENDIX. REFERENCES

Bridge beauty-landscape of highway bridge. (l98\). Japan Hwy. Soc.,Tokyo, Japan.

8/ JOURNAL OF ARCHITECTURAL ENGINEERING / MARCH 1997

Committee on General Structures. (1991). Bridge aesthetics around theworld, Subcom. on Bridge Engrg., Trans. Res. Board, Washington,D.C.

Gage, M., and Vandenberg, M. (1975). Hard landscape in concrete. Lon­don, The Architectural Press, London, England.

Leonhardt, F. (1984). Bridge aesthetics and design. MIT Press, Boston,Mass.

Shang, B. H. (1980). Bridge aesthetics. Senbei Publish Society, Senbei,China.

J. Archit. Eng. 1997.3:3-8.

Dow

nloa

ded

from

asc

elib

rary

.org

by

Uni

vers

ita S

tudi

Di P

isa/

Sba

on 0

4/26

/13.

Cop

yrig

ht A

SCE

. For

per

sona

l use

onl

y; a

ll ri

ghts

res

erve

d.