Precast Stress RibbonPedestrian Bridgesin Czechoslovakia

Jiri StraskyChief Design EngineerDopravni stavbyDesign and Construction EngineersBrno, Czechoslovakia

P edestrian bridges (or footbridges asthey are called in many parts of the

world) have been used by man sinceantiquity to cross rivers, deep gorgesand narrow mountain passes. One com-monly used method has been to suspenda walkway from a fiber rope catenaryspan — somewhat similar to a primitivesuspension bridge.

The stress ribbon concept borrows thesuspension bridge principle but devel-ops it further by using high strength ma-terials and modern engineering technol-ogy — especially precasting and pre-stressing methods.

In a prestressed concrete stress ribbonbridge high strength steel cables arepassed through a series of precast con-crete components, the deck assemblyof which can be tensioned from stiffabutments. Whereas in a suspensionbridge the main load carrying compo-nent is the cable with the deck acting asa stiffening element, in a stress ribbon

bridge both the cable and the deck canbe independently tensioned, thus add-ing considerable rigidity to the struc-ture.

It should be mentioned that in con-trast to highway bridges, pedestrianbridges carry relatively light loads.However, the effects (deflection, vol-ume changes and other displacements)due to temperature differentials can bequite significant.

Recently, nine precast stress ribbonpedestrian bridges were designed inCzechoslovakia. Seven of these bridgeshave now been built and are in full op-erational use. The structures are aesthet-ically beautiful and have become wellrecognized landmarks enjoyed by allsegments of the population.

The superstructure of the pedestrianbridge is formed by a prestressed bandwhich is attached to rigid end abut-ments. The deck is made up of precastconcrete segments which are suspended

52

Describes the design features, constructionprocedure and economic considerations involved inbuilding several stress ribbon pedestrian bridges inCzechoslovakia using precast concretecomponents.

on high strength steel bearing cablesand then shifted along the cables to thespecified position. Prestress is inducedin the deck after the joints between thesegments have been concreted in place.This compression gives the structuresufficient rigidity to withstand the deadand live loads.

The pedestrian bridges vary from oneto four spans. The longest span length is472 ft (144 m) and the maximum lengthof the structures is 1329 ft (405 m). A

summary of the major characteristics ofthe bridges designed by the EnterpriseDopravni stavby is given in Table 1.Figs. I through 7 present a panoramicview of the stress ribbon bridges builtthrough 1985.

DESIGN FEATURESThe key design features of the pedes-

trian bridges are summarized in thissection. All the bridges have a uniform

Fig. 1. Pedestrian bridge in Brno-Bystrc.

PCI JOURNAL/May-June 1987 53

Fig. 3. Pedestrian bridge at Kromeriz.

cross section as shown in Fig. 8. Thedecks are assembled from precast seg-ments 12 ft wide, 10 ft long and 1 ft thick(3.80 x 3.00 x 0.30 m). The clear widthbetween the railings is 10 ft (3.00 m). Aspart of the design, the segments havetwo openings of 5 in. (12 cm) diameterfor laying trunk and electric cables.

The longitudinal arrangement (seeFig. 9) is determined by the givenstructural system and the selected hori-

zontal force. With a dead load (g) of 19.9kips per ft (27 kN/m), the maximumhorizontal force HQ may equal 5394 kips(24 MN). The superstructure betweensingle supports has the shape of a cat-enary which differs only slightly from asecond degree parabola. The pedestrianbridges were designed for a live load (p)of9.68 kips per sq ft (4.00 kN/m").

The precast segments were manufac-tured with high strength concrete hav-

54

Fig. 4. Pedestrian bridge in Prague-Troja.

Fig. 5. Pedestrian bridge in Prague-Troja.

ing a specified cube strength of about7000 psi (50 MPa). The sections of thesegments are of two types: waffle sec-tions (see Fig. 10) which form the majorpart of the span and solid sections whichare located at the supports.

During erection the segments arehung on bearing cables which are heldin a pair of troughs. After erection thesegments are prestressed by the secondgroup of cables placed in the ducts

within the deck.The bearing cables and prestressing

cables are formed by six 0.612 in. (15.5mm) diameter strands which are an-chored in pairs. The specified strengthof the cables is 261 ksi (1800 MPa).

The bearing cables are arranged intwo ways, depending upon their numberand magnitude of the horizontal force.When 2 x 6 cables are used, the cablesare placed in each trough in one row.

PC! JOURNALMay-June 1987 55

Table 1. Major characteristics of stress ribbon pedestrian bridges in Czechoslovakia.

Pedestrianbridge

Figurenumber

Numberof spans

Maximumspan

length, l,,ft (m)

Sag ofmaximum

span,fft (m)

Length ofstructure

ft (m)Year oferection

Brno-Bystrc 1 1 206.69 (63.00) 3.94 (1.20) 226.38 (69.00) 1979Brnn-Komin 2 1 255.91 (78.(X)) 4.43 (1.35) 275.59 (84.00) 1985Kromeriz 3 1 206.69 (63.00) 3.94 (1.20) 248.03 (75.60) 1983Radonice - 1 206.69 (63.00) 3.94 (1.20) 242.78 (74.00) 1984Prerov 19 2 221.46 (67.50) 4,69 (1.43) 334.65 (102.00) 1983Zatec - 2 247.70 (75.50) 5.25 (1.60) 406.82 (124.00) DesignPrague-Troja 4,5,21 3 314.96 (96.00) 5.54 (1.69) 856.96 (261.20) 1984Nymburk 6,7 3 334.65 (102.00) 6.50 (1.98) 758.53 (231.20) 1985Velke Brezno - 4 472.00 (144.00) 9.52 (2.90) 1329.40 (405.20) Design

Fig. 6. Pedestrian bridge at Nymburk.

However, when 2 x 12 cables are used,the cables are placed in two rows.

During erection the segments arecarried only by one-half of the cablesplaced in the lower row. After erectionthe cables placed in the upper row arepulled through and tensioned. Theamount of cable tensioning determinesthe final configuration of the structure.

The bearing cables are protected byconcrete with a specified cube strengthof about 5800 psi (40 MPa) which is pre-stressed. The minimum cover of the ca-

bles is 2.17 in. (5.5 cm).The prestressing cables are placed in

the segments in ducts formed by con-crete. However, in the joints, saddlesand anchorage blocks the ducts areformed by steel tubes.

The end segments of all the stress rib-bon pedestrian bridges are placed dur-ing erection on elastomeric bearing padssituated on abutments (see Fig. 13). Thisallows the deck to move up and down,respectively, as the temperature fallsand rises. At the end abutments there

56

Fig. 7. Pedestrian bridge at Nyrnburk.

are anchorage blocks which connect thesuperstructure with prestressing.

It is important to be aware that verylarge horizontal forces [as high as H =6745 kips (30 MN)] will need to betransmitted from the end abutments intothe foundation. This load transfer can hedone by:

(a) Flexurally rigid bored piles.(b) Raking compression and tension

piles.(c) A combination of wall diaphragms

and micropiles,

(d) Soil and rock anchors.The decision as to which is the most

suitable foundation to use will dependlargely upon the geological conditions atthe site and the available mechanicalequipment.

The shape of intermediate supports ofstress ribbon bridges with more thanone span is shown in Fig. 11. Thestructural design of the supports re-sulted from the chosen method of erec-tion. In contrast to a continuous stressribbon bridge built in Freiburg, Ger-

PCI JOURNALIMay-June 1987 57

Fig. 8. Typical architectural configuration of pedestrian bridge: (a) cross section;(b) elevation. Note: 1 cm = 0.3937 in.

many, 19 in which the concrete band issupported by pendulum piers with ta-pered tables, the pedestrian bridges de-scribed herein use a concrete saddle.The saddles are cast after erecting allthe segments in the formwork which ishung on adjacent segments. Instead ofpendulum piers having a concrete hingeat the footing, the saddles are frameconnected with pendulum piers havingreinforcing steel.

In the intermediate supports thebearing cables pass over steel saddlesformed by two, 7.9 in. (20 cm) diam-eter, circular cylinders which are sup-ported by steel footings connected withscrews to the monolithic piers. Since thestress of bearing cables gradually in-creases during their tensioning, at thetime of erection of segments and castingthe joints, troughs and saddles, theirelongation also increases.

Similar to curved ducts of prestressedconcrete structures, friction is generatedin the steel saddles. The result is that itshorizontal component loads the pierswith a bending moment. Since the con-crete hinge is designed at the footing,the stability of the piers must be en-

sured. Therefore, the intermediate sup-ports were reinforced with temporarysteel struts (see Fig. 17). *"

The above structural design makes itpossible to remove the dependence ofthe construction of the concrete saddleson the sag of bearing cables which va-ries in the course of their constructionaccording to temperature and loading.The increased stress is taken by the re-inforcing steel.

The pavement is formed by epoxyconcrete 0.4 in. (1 cm) thick which at thesame time waterproofs the deck. Therailing is either made of ropes or thinwalled vertical posts. The pedestrianbridges are illuminated at night eitherby lamps located in the handrails or byreflectors placed on poles outside thestructure.

CONSTRUCTIONPROCEDURE

The precast segments are manufac-tured in a steel mold in a one-day man-ufacturing cycle. Concrete is compactedby surface vibrators. In order to reducethe effects of creep and shrinkage of

58

0

0

Fig. 10. Typical precast segment on bearing cables.

Fig. 11. Pedestrian bridge showing intermediate support,

concrete, the segments are cast from 6 to12 months before the erection of the su-perstructure.

Fig. 12 shows schematically the con-struction sequence of a two-span pe-destrian bridge. Bridges with more thantwo spans are constructed in a similarway. When foundations, anchorageblocks and intermediate supports areconstructed, the assembly of the super-structure is started. This assembly is di-vided into five stages as follows:

(a) First, the end segments are placedon elastomeric bearing pads on theabutments (see Fig. 13). In the troughs

of these precast members are steelmembers which determine the positionof the bearing cables. Then, steel strutsare placed on the intermediate supportswhich secures the stability of the piers(see Fig. 12a).

(b) The bearing cables are drawn by awinch. The strands are wound off fromthe coils and at the side abutment areslowed down by a cable brake whichalso ensures the same length of allstrands in the cable. Each cable is alsoattached to an auxiliary rope which en-ables the back drawing of the haulingrope (see Fig. 12b). After drawing, each

0 'I-

0

Of

0

0

0

Fig. 12. Erection procedure of pedestrian bridge.

V

PCI JOURNALIMay-June 1987 61

Fig. 13. Erection of the end segment.

cable is tensioned to the prescribedstress, In structures where the cables areplaced in one row, all bearing cables aredrawn. However, in structures wherethe cables are placed in two rows, onlythose cables which are placed in thelower row are drawn.

(c) The segments are erected in singlespans by means of a crane truck (seeFigs. 14 and 15). The member assem-bled is first placed under the bearingcables and is lifted as far as the cablestouching the bottom of the troughs.Then, hangers are placed in position,secured by screws and the segment isfixed to the hauling rope. The auxiliarycable is attached to the hauling cable tomake its back drawing possible. Then,the segment is directly shifted along thebearing cables into the determined po-sition by a winch (see Fig. 16), Here,

steel tubes are placed which will formcable ducts in joints. The segment isthen drawn to a member assembled ear-lier. This process is repeated until allthe members are assembled (see Figs.12c1 and 12c2).

(d) When all the segments are assem-bled, in structures with two rows ofbearing cables, the cables in the upperrow are pulled through and tensioned.In this manner the design shape of thestructure is obtained. Then, the false-work of monolithic saddles is hung onthe neighboring segments (see Fig, 17),prestressing cables are pulled throughand the reinforcement of the troughsand saddles is concreted at the sametime. In order to reduce the effects dueto creep, shrinkage, temperature and ac-cidental movement of pedestrians, thedeck is partially prestressed as early as

62

F = ig. 14. Erection of a segment of the first span.

possible. When sufficient strength isreached, all the cables are tensioned to apredetermined value.

(e) After grouting the cables, the rail-ings are erected and the pavement iscast. Then, the load test is carried out(see Fig. 12e).

STATIC ANALYSISThe static action of the pedestrian

bridge is determined by the construc-tion method and structural arrangementof its members. The analysis was carriedcut for two different stages as follows:

(a) Erection stage (see Fig. 1$a).(b) Service stage (see Fig. 1$b).It should be noted that the shape and

the state of stress of the structure at theend of the erection stage determine the

stress pattern which develops in thestructure during its service life.

(a) Erection StageDuring erection the precast segments

are hung on the bearing cables whichare now loaded by:

— Their own self weight.— The weight of the segments.— The weight of the concrete closure

.joints.— The weight of the troughs and sad-

dles.— The effects caused by temperature

changes.As a result, the cable acts as a per-

fectly flexible unit. Since the cables arenot connected to the supports with thesteel saddles, they can be shifted alongthem according to the imposed load.

PCI JOURNAUMay-June 1987 fi3

Fig. 15. Erection of a segment of the second span.

Hence, the cables act as a continuousunit which crosses fixed supports.

Now, at a change in load, friction isdeveloped in the steel saddles, the mag-nitude of which may reach as much as 10percent of the cable tension force. Thebehavior of the bearing cable is also af-fected by the change of its elongation inthe anchorage blocks and by possibledisplacement of the end supports.Therefore, the analysis at the erectionstage has taken into consideration all ofthe above factors.

In the design computations, due ac-count must be taken of the required finalshape of the structure after erection hasbeen completed. The various operationssuch as concreting the joints, the troughsand the saddles were planned in such away that the effective friction forces atthe saddles were almost negligible. As aresult, the anchorage stress of the bear-ing cable was determined with such ac-curacy that the final erected shape waswithin 1 in. (2.54 cm) of the designshape.

(b) Service StageAfter concreting the joints, troughs

and saddles, the structure distributes allthe other loads, i.e., the prestress effect,the weight of the pavement and railings,the live load, the deformation of sup-ports, the temperature changes and theeffects due to concrete creep andshrinkage because the thin concreteband is stressed not only by the normalforce but also by the shear force andbending moment.

Since the structure is very slender,local shear and bending stresses de-velop only under point load and at thesupports. Because these stresses are rel-atively small, they do not affect the be-havior of the entire structure. Thismakes it possible to analyze the stnic-ture in two closely related steps.

In Step 1, the stress ribbon is analyzedas a perfectly flexible cable which ishinge connected to the supports. Thehinges are assumed to occur at the thirdpoints of the length of the concrete sad-dles where their rigidity is already sub-

64

Fig. 16. Shifting of a segment.

PRESTRESSING EFFECT

TEMPERATURE FALL LIVE LOAD

ADDITIONAL DEAD LOAD LIVE LOAD

TEMPERATURE RISE LIVE LOAD

CREEP AND SHRINKAGE TEMPERATURE FALL LIVE LOADof CONCRETE t

LIVE LOADLONG-TERM DISPLACEMENT

OF SUPPORTS TEMPERATURE RISE LIVE LOAD

Flow chart showing analytical sequence of stress ribbon pedestrian bridge.

stantially high. To facilitate the analysis,standard computer programs for a con-tinuous cable are used. From these pro-grams the unknown horizontal force (H)and the deformations of the supports ofsingle spans can be determined.

In Step 2, shear and bending stressesin single spans are evaluated using theanalytical method given in Ref. 2 forcable stayed bridges. The stresses in theconcrete saddles and piers are obtainedby analyzing the intermediate supportfor loading as if the reaction is acting atthe supports of single spans. At the endsupports it is assumed that the eccentrichinge connection is developed only

under very heavy load.The analysis of stress ribbon pedes-

trian bridges is carried out according tothe flow chart shown above.

The design assumptions and qualityof workmanship were checked by mea-suring the deformations of the super-structure at the time of prestressing andduring the loading tests. Only a few ofthe key results in a typical structure aregiven here. Since the shape of a stressribbon structure is extremely sensitiveto temperature change, the temperatureprofile was carefully recorded at alltimes,

The strength capacity of the pedes-

PCI JOURNAL.IMay -June 1987 65

Fig. 17. Falsework of the saddle.

trian bridge at Prerov was tested usingthree, fully loaded vehicles (see Fig. 19),weighing 10.5, 18.9 and 21.9 tons (11.6,20.8, and 24.1 t) with the axle loadreaching as high as 8.7 tons (9.6 t). Inthis test both the total bearing capacityof the structure and the bearing capacityduring localized bending wereevaluated. Fig. 21 shows the measuredand calculated deformations of thestructure for two vehicle positions.

The results of the load tests on the (cur-rently) longest pedestrian bridge built inPrague-Troja for the first load are shownin Table 2. It should be noted that in thisload test, only the deformations at thernidspans and horizontal displacementswere measured.

The pedestrian bridge was first loadtested using 38 heavy -trucks weighingfrom 2.8 to 8.4 tons (3.1 to 9.3 t). Thetrucks were placed on the entire spanlength of the structure as shown in Fig.20. Then, the vehicles were placed oneach span. As can be seen, the compati-bility of the results is very good.

Table 2. Deflections at midspans ofpedestrian bridge in Prague-Troja.

Span 1 Span 2 Span 3in. (cm) in. (cm) in. (cm)

2.24 7.87 1.57Calculation(5.70) (20.00) (4.00)

Measurement 2,20 7.32 1.57(5.60) (18.60) (4.00)

DYNAMIC ANALYSISStress ribbon structures are very sen-

sitive to dynamic loads because of theirlow bending stiffness, low vibrationdamping and low natural frequencies.For this reason, it was necessary to ana-lyze their dynamic response both theo-retically and in the field,

The pedestrian bridges were mod-elled as systems of cables connected atthe tops of pendulum piers. Structureswith only one span were solved as anisolated cable with nonflexible sup-

66

C.-0

C

z

CDrn

C)4

Fig. 19. Load test using three heavy vehicles — Pedestrian bridge at Prerov.

ports. In solving forced vibration, theharmonic force passing through thebridge was substituted by a harmonicforce acting at midspan. The frequencyof the harmonic force was assumedequal to the frequency which is mostcommonly caused by pedestrians,namelyf = 2 Hz.

The stress ribbon structures in Brno-Bystrc, Brno-Komin, Prerov andPrague-Troja were subjected to dynamictests. In the course of the load tests theagreement of excited natural frequen-cies with theoretical values was investi-gated. The structures were excitedeither by a human force, or by a pulserocket engine, or by a mechanical rota-

tion exciter. For illustration, Fig. 22shows the theoretical and excited modesof vibration of the pedestrian bridge inPrague-Troja.

In addition, the damping of vibrationwas investigated. For example, in thecase of the Prague-Troja pedestrianbridge, it was demonstrated that in theregion of dynamic displacement of themidspan of the second span, thelogarithmic decrement of damping vvaried from 0.008 to 0.012.

From the results of the dynamic tests,which are described in greater detail inlief. 3, the following conclusions can bemade:

I. Stress ribbon pedestrian bridges

Load 1 load 2

HO 10000 kN 2Hi 12845 kN Hz' 12585kN767.5 285 +

675 285

a 105 189 fkNl

fl rz-6.4-202

C4

81012 I

189 DcNIx [ml219fT n Ill

-20

45

10120 6 12 18 24 30 35 42 48 54 60 66 72 78 84 2O

x(mL----------caLCutQ1on

meaSurTr

Fig. 21. Load test of pedestrian bridge at Prerov: (a) scheme of structure; (b) deformationdue to load 1; (c) deformation due to load 2. Note: 1 cm 0.3937 in.; 1 m = 3.2802 ft;1 kN 0.2248 kip.

PCI JOURNAL/May-June 1987 69

_fKi =t3MHz ---Wcr :t.65OHz

^_ea. 96.m 1 Aso 1

cdaulation _ measurement

Fig. 22. Theoretical and exciter-induced modes — Pedestrian bridge at Prague-Troja.

cannot be overstressed either by exces-sive vibration caused by people or byacts of vandalism.

2. The speed of motion caused bypeople should not exceed the recom-mended limit of 0.95 in. per second (24mm/sec) that is recognized as a limit ofunpleasant feeling (bouncing effect).

ECONOMICCONSIDERATIONS

The cost of building stress ribbon pe-destrian bridges depends on the spanlength, the cable sag, the total length ofthe structure, and especially on the geo-graphic site and existing geological con-ditions. The general availability of localmaterials, skilled labor and mechanicalequipment might be other factors toconsider.

All of the bridges designed by Enter-prise Dopravni stavby have been builtacross rivers, in places where it was notpermissible to erect piers in the riverbed. Also, for architectural reasons,cable stayed structures were excludedin the planning stage. Since centeringswith temporary supports in the river bedwould be prohibitively expensive, the

cost of stress ribbon structures was com-pared with cast-in-place cantilever seg-mental structures.

A comparison of the costs for theabove two structural systems showedthat the prices were about the same forsingle span structures. In this case, theprestressed band was chosen becausethe components could be assembledquickly and easily and the architecturalform was aesthetically pleasing.

The economic advantage of stress rib-bon bridges is manifested in multispanstructures. For the same span and sag,the horizontal force of multispan struc-tures is the same as for single spanstructures. Also, the cost of the founda-tion is the same. Therefore, the cost of apedestrian bridge per square foot (perm2) decreases as the number of spans in-creases. For illustrative purposes, twotypes of structures are compared. Thesewere designed to span the Vltava Riverin Prague.

The structure, built in 1984 (see Figs.4, 5, 20 and Table 1), is formed by a pre-stressed concrete band of three spans[280.5, 314.9 and 221.5 ft (85.5, 96.0 and67.5 m) ] making up a total span of 816.9ft (249 m).

The pedestrian bridge follows the

70

Table 3. Consumption of materials for pedestrian bridge inPrague-Troja.

Stressribbon Cantilever

Part of bridge Materials

Concrete

structure structure

cu ft 9182 22,955(m s) (260) (6,50)

Prestressing steelSuperstructure tons 66.9 53.1

(metric tons) (68.0) (54.0)

Reinforcing steeltons 40.4 58.1(metric tons) (41.0) (59.0)

Concretecu ft 13,773 7240(m 3) (390) (205)

SubstructureReinforcing steel

tons 26.1 31.5(metric tons) (26.5) (32.0)

Wall diaphragmssq ft 8396 3444

Foundation (m2) (780) (320)

Micropilesquantity (No.) 36 —

contour of the ground on both banks ofthe river. It rises from the abutments tothe intermediate supports and at themidspan bridges the river. The largehorizontal force [6016 kips (27 MN)[is transferred into the foundation by acombination of wall diaphragms and mi-cropiles.

The compared structure was formedby a continuous beam of four spans[83.7, 193.6, 314.9 and 218.2 ft (25.5,59.0, 96.0 and 66.5 m)1. The span lengthof the structure was the same, i.e., 816.9ft (249 m).

The superstructure of the I cross sec-tion had a depth varying from 13,12 to3.94 ft (4.0 to 1.2 m). The bank spanswere concreted in place on centeringand the central span was built by the

Table 4. Cost of pedestrian bridge inPrague-Troja (in million crowns).'

Stressribbon Cantilever

Part of bridge structure structure

Superstructure 2.236 6.605Substructure 0.920 0.995Foundation 4.661 1.020Total 7.817 8.620

Because of the different monetary systemsused in Czechoslovakia and the United States,it is not possible to give a meaningful conver-sion rate front Czech crowns to U.S. dollars.

cantilever method. The bridge wasfounded on wall diaphragms.

Tables 3 and 4 present the quantities

PCI JOURNAL/May-June 1987 71

of materials and the costs of both thecompared structures. It is apparent fromthe tables that even with the high priceof the foundation, the total cost of thestress ribbon bridge is lower than thecost of the cast-in-place cantileverstructure.

CONCLUSIONSThrough 1985, the National Enter-

prise Dopravni stavby has constructedabout 3000 linear ft (900 m) of precaststress ribbon bridges. Currently, othersuch bridges are in the design and plan-ning stages.

In retrospect, it can be stated confi-dently that stress bridges are:

— Easy to assemble and quick to erect— Functional— Aesthetically beautiful— Economical— Enjoyed by the peopleThe above advantages far outweigh

the cost of transmitting a large horizon-tal force. In the author's bridge depart-ment, designs have been developedwhich further extend the capabilities,range of application and economy of

stress ribbon bridges. It is his belief thatsuch structures will find wide applica-tion in the future.

ACKNOWLEDGMENTThe design system of the pedestrian

bridges described in this paper weredeveloped by the National EnterpriseDopravni stavby in Brno, Czecho-slovakia, The dynamic analyses and testswere carried out by Dr. Pirner fromTazus (the Institute for Testing ofStructures) in Prague.

The design of these pedestrianbridges was awarded the first prize inthe Czechoslovakian competition foryoung engineers and architects.

The structural design, static and dy-namic analyses of the above bridges aredescribed in detail in Ref. 3. If anyreader is interested in securing thispublication, please contact the author:

Dr. Jiri StraskyDopravni stavby, n.p.Design and Construction EngineersBohunicka 5065927 BrnoCzechoslovakia

r * w

NOTE: Discussion of this paper is invited. Please submityour comments to PCI Headquarters by February 1, 1988.

72

REFERENCES

1. Batsch, W., and Nehse, M., "Spannband-briicken als Fuj3gangersteg in Freiburg imBreisgau," Beton-und Stahlbetonbau, No.4, 1972, pp. 49-52.

2. Kollbrunner, C. F., and Hajdin, N., "Con-tribution to the Analysis of Cable-StayedBridges," Institute for Engineering Re-search, Verlag Schulthess AG, Zurich,Switzerland, 1980.

3. Strasky, J., and Pirner, M., DS-L Stress-Ribbon Footbridges, Dopravni stavby,

Brno, Czechoslovakia, 1986.4. Tang, M. C., "Stress Ribbon Bridge in

Freiburg, Germany, Features PrestressedConcrete Deck Slab," Civil Engineer-ing-ASCE, May 1976, pp. 75-76.

5. Tilly, G. P., Cullington, D. W., andEyre, R., "Dynamic Behavior of Foot-bridges," IABSE Surveys S-26184.

6. Walther, R., "Stressed Ribbon Bridges,"International Civil Engineering Monthly,V. II, No. 1, 1971172, pp. 1-7.

PCI JOURNALMay-June 1987 73