A CRITICAL ANALYSIS OF SAO PAULO’S OCTAVIO FRIAS DE

OLIVEIRA ROAD BRIDGE

Edward C Wilkes1

1Undergraduate student University of Bath

Abstract: This is a detailed paper on the Octavio Frias De Oliveira bridge in Sao Paulo. It will initially cover

how the requirement for such a bridge came about and how the chosen design fulfilled these requirements. A

structural analysis will be carried out, including relevant design calculation checks to British Standards. The

paper will discuss the aesthetics, construction and other issues including future changes and improvements.

Keywords: cable-stayed, centrifugal, curved deck, Inclined towers, junction.

1 Introduction

The bridge Octavio Frias De Oliveira is a unique

reinforced concrete, cable-stayed highway bridge

consisting of two separate curved bridge decks with a

total span of 290m each. It is situated in the heart of

Sao Paulo, Brazil, and provides an important road

connection aimed at reducing congestion in the city.

1.1 Sao Paulo congestion

Since the beginning of the 20th Century, post world

war and depression in the US, Sao Paulo has

undergone an industrial boom. This has seen a

dramatic rise in the population and a subsequent rapid

expansion of the city. This has lead Sao Paulo to

become one of the most congested cities in the world,

having a fleet of over 6 million cars. As a result, the

city’s road network is undergoing significant

investment and reconstruction [1].

The bridge Octavio Frias de Oliveira is part of this

project, specifically it provides a connection between

the roads Marginal Pinheiros and Marinho Avenue.

Marginal Pinheiros is a main North-South traffic artery

for Sao Paulo that runs alongside the River Pinheiros,

originally part of a ring road for the city but long since

overgrown during the city’s expansion [5]. As shown

in figure 1 (red arrows) it is made up of 2, one-way, 4

lane carriageways on either side of the river. Marinho

Avenue is one of many east west routes into the city

centre (blue arrows in figure 1). It is the 13th cossing

over the River Pineiros, providing another important

connection between an east west route in to the city

and the Marginal Pinheiros.

1.2 Function and concept birth

The specific function of the bridge is to relieve

traffic at two other similar junctions to the north and

south of the bridge.

The bridge design therefore had specific

requirements to manage a certain volume of traffic. It

also would act as the junction between the

perpendicular roads itself by being curved in plan. This

allowed a smooth junction whilst achieving the

necessary spans over the river.

Both an entrance and exit slipway were required.

This meant the bridge had to provide 2 separate curved

bridge decks. The designers chose to provide this using

only one support tower, creating a twin cable stayed

structure with one mast; something never previously

done before. This allowed exploitation of this unique

structure as a landmark for the city.

The bridge Octavio Frias is able to receive up to

four thousand vehicles per hour in each lane. It is a

relief to the bridge of Morumbi, which at times of peak

gets up to seven thousand cars per hour. [2]

Figure 1 Road connections

Proceedings of Bridge Engineering 2 Conference 2009

April 2009, University of Bath, Bath, UK

2 Aesthetics

Bridge aesthetics will be analysed in accordance

with Fritz Leonhardts 10 rules for aesthetic analyses of

bridges. These 10 rules cover every aspect of bridge

aesthetics necessary for a successful design. Guidance

from Ref [8].

Figure 2 full bridge view and dramatic night shot

2.1 Fulfilment of function

This is an important area of bridge aesthetics for

producing a beautiful bridge. The main structural

element is the tower, this stands proud above the city at

a height of 138m. It can be seen to rise from ground

level to the top without interruption as a single

element, carrying the vertical loads from each of the

two bridge decks directly to the ground. This gives the

impression of strength and stability; the backbone to

the structural system. The cables at deck level are

clearly the main support for the deck, this is

accentuated by the shallow deck. However when your

eyes follow the cables up to the tower, it becomes

unclear as to which cables support what part of the

deck. This is due to the crossing over of the 144 cables.

This is a fundamental floor in the aesthetics of the

bridge; as soon as people are faced with the confusing

criss-cross of cables, the whole design looses its

beauty.

2.2 Proportions

The many cables however, have allowed the

bridge decks to be designed very shallow and sleek.

This is well proportioned against the strong primary

element, the tower. This draws your eyes to the tower

itself and its impressive shape, and away from the

messy net of cables. The cables begin to be viewed as a

single element that connects the stable tower to the

sleek deck; as such, the mess of cables becomes less of

an issue. The cross shape of the tower itself provides

areas of light and shadow underneath each side, which

help to accentuate its unique shape. However, to

prevent it appearing too bulky against the deck, a dark

line is apparent, splitting the tower in two, this makes it

appear as if there are two separate slimmer towers.

2.3 Order

Order is important in the lines and edges of a

bridge, repetition can be used to produce a crisp,

ordered design. The bridge deck is viewed as one

element, there are no horizontal lines or edges except

that of the mass of the deck itself. The bridge curves

with a satisfying constant curvature with equal spacing

of cable tie supports. The connections of the cables to

the deck are the only element that breaks up the soffit;

however these provide a reassuring functional effect

when viewed from beneath. The angle of each

connection is set into the concrete of the deck and

specifically angled to match the corresponding cable’s

angle. This ensures continuity of the line of action of

the cables when viewed from the side.

Although the shape of the bridge is so unique,

consisting of two curved decks, symmetry in the design

is still upheld. The two tracks are simple inverted

repetitions of each other even though they sit at

different levels.

2.4 Refinements

The tower is made up of two crossing, tapered

columns. The tapering is for structural efficiency,

however it also prevents the tower from looking top

heavy. The cable anchorages are expressed in the soffit

beneath the deck. These do not break the flow of the

slender deck however they act as a reminder to how the

deck is supported and highlights its reliance on the

primary element, the tower.

Figure 3 Refinements

2.5 Integration into environment

Cable stayed bridges work well in cityscapes.

Their towers can be tall and elegant, and the bridge

decks low and sleek. This bridge has achieved these,

however the bridge was meant to be a new, impressive

landmark for the city and through its unique design it

achieves this too. Its mast height is similar to that of

surrounding high rise office buildings so that it is not

too overwhelming in the area, although it gives so

much more to the city and to the landscape than any

convention structure or building.

2.6 Texture

Texture is an important feature on bridges. It is

often overlooked such as is the case with the bridge

Octavio. The finish on the bridge is a rough plain matt

finish. Each 3m stage of casting of the tower can

clearly be seen, and same goes with the deck. The soffit

from afar looks smooth, however upon closer

inspection, lines and defects in the surface from the

construction process are visible.

2.7 Colour

Colour is often used to create different effects on

bridges. The bridge Octavio Frias has a bright yellow

covering around the cables. This has been used with

previous cable-stayed bridges to contrast the blue sky.

It also gives the impression of diverging sun rays

breaking through clouds. The bright colour also helps

to blend the cables together and to reduce the negative

visual effect of them crossing.

Phillips have installed an advanced lighting system

consisting of LEDs into the bridge. The LED

ColorBlast projectors provided by Phillips allow the

dynamic interchange of colours. This allows the bridge

to be illuminated in almost any colour; possibly

reflecting special celebrations or events depending on

the time of year [3]. This further highlights how the

bridge can be looked upon as a local landmark as it can

be used to represent local and global occasions.

2.8 Character

The bridge Octavio Frias has huge amounts of

character. Its unique design is impressive; it causes

people to ask themselves how it works; how the

separate decks balance each other and how the loads

are shared through the tower, and whether in actual fact

it acts more like two separate bridges than one or if

each deck relies on the other for support.

2.9 Complexity

An amount of complexity within a bridge can be

visually interesting and exciting. The complexity due

to the crossing cables can provide this from certain

angles, however at others it can be chaotic as shown

below.

Figure 4 confusing array of cables

2.10 Nature

The incorporation of nature into structural design

of bridges and other structures can be a useful way to

make use, or remind people (through sculptural

appreciation) of the forms evolved over billions of

years by something other than man. There is some

mention of the influence of Leonardo da Vinci’s

Vitruvian Man on the design of the bridge highlighted

in Ref [4] as shown below. However there may be a

hint of architectural/sculptural post rationalization here.

Figure 5 Comparison to Vituvian man

3 Structural strategy

The bridge Octavio Frias de Oliveira is very

unique. It functions not only as a bridge to span the

river Pinheiros, but as the slip roads that form the

connection between the two perpendicular main roads.

Cable stayed bridges are best suited for medium-

span, low-level river crossings such as that required by

the bridge Octavio Frias de Oliveira. They largely only

transmit vertical loads through their foundations, which

is beneficial regarding the commonly poor ground

conditions adjacent to riverbanks. They are also elegant

and relatively cheap and simple compared to other

forms of bridge construction. For this particular

situation in Sao Paulo, a cable stayed bridge was

simply the only choice. Considering the requirement

for a bridge deck with such a tight curvature, most

bridge types are ruled out; such as suspension, stress

ribbon and cantilever. Many beam bridges in the same

area of Sao Paulo have been built with similar

curvatures, however with much smaller spans. An arch

bridge was not possible due to poor ground conditions.

Therefore a cable stayed bridge system had to be

created that could provide two separate curved traffic

carriageways from a single tower.

Two smaller, straight decked cable stayed bridges

were considered during the design process see Ref [4],

however this design was abandoned possibly because it

looked awkward, and because it did not provide a

smooth junction for traffic without requiring land space

adjacent to the river for the curved sliproads.

The solution was to form an X out of 2 towers,

each dedicated predominantly to each of the decks,

however gaining stability from a connection where

they cross. Each tower is inclined away from the

curved deck it is supporting. This ensures that forces in

the tower and the decks are mostly axial with minimal

bending. However due to eccentricities of the cable

resultant forces and the position of the deck (due to

curvature) out of plane bending is felt in the deck.

Sufficient longitudinal pre-stressed reinforcement is

provided throughout the deck to cope with these extra

tensile and compressive stresses as seen in figure 6

below. This reinforcement will also be responsible for

ensuring stiffness and stability of the deck under

centrifugal traffic loads on the curved carriageways.

Extra reinforcement is also provided in the tower to

cope with bending under uneven live loads.

Figure 6 longitudinal reinforcement (light green)

Cable stays (red and dark green) [4]

This inspired the deck section to be as in figure 7.

The two larger reinforced concrete sections at the

edges, span between the cable supports and also

produce a high second moment of area in the y-y plane

of the deck to cope with the lateral bending. The

thinner reinforced concrete slab predominantly spans

between the two edge beams to support the traffic

lanes, additionally it acts as a shear web for lateral

stiffness and in some parts compression due to

triangular arrangement of the cables.

Figure 7 Deck section through sagging region [4]

The cables support the deck in a semi fan

arrangement. They support each segment of the deck in

pairs. This pairing means that the support for the deck

is triangulated. This is a valuable advantage for cable

stayed bridges designed in this way; lateral stability of

the deck is dramatically increased, further allowing the

deck to be slimmer in depth.

The tower itself has built in triangulation in the

lower region due to the interconnected inclined towers.

This drastically improves lateral stability of the whole

bridge under uneven live loading such as centrifugal

traffic or extreme wind loads. This is important for

reducing moments on the foundations in the weak

strata beneath.

4 Calculations

The analysis of this bridge will be done in

accordance with BS 5400. Five load types are

considered; Dead, Superimposed dead, live traffic,

wind and temperature effects. These nominal loads will

be calculated, and the relevant partial factors applied.

They can then be applied in onerous and suitable

combinations to assess the bridge structurally by

comparing the effects against the element strengths.

4.1 Dead Loads

The volume of reinforced concrete in the deck has

been calculated as 10.5m3 per metre length, based on

deck sections from Ref [4]. Unit weight of reinforced

concrete = 24kN/m3. Therefore the dead load (DL) per

metre of deck = 10.5x24 = 252 kN/m. The dead load

can be factored using equation 1

DLfactored= DL γf1 γf3 (1)

Table 1 DL partial Factors for concrete for all load

combinations see Ref [7].

SLS ULS

γf1 1 1.15

γf3 1 1.1

ULS DLfactored = 252 x 1.15 x 1.1 = 318.7kN/m

SLS DLfactored = 252 x 1 x 1 = 252kN/m

4.2 Super-imposed dead loads (SIDL)

Super-imposed dead loading must be taken into

account when assessing the dead weight of the deck. It

is mainly made up from the steel barriers and asphalt

surface coating on the floor slab, plus some service

transmission lines, cables and lighting.

The weight of the barriers and services are

unknown, but can be assumed to add up to a UDL of

0.5kN/m2 covering the entire deck area. Density of

Stone Matrix Asphalt is 2300kg/m3, thickness of the

asphalt is 100mm, therefore weight/m2 = 23 x 0.1 =

2.3kN/m2, therefore total SIDL= 2.3 + 0.5 = 2.8kN/m

2

Deck width =10.5m, so UDL/m along deck = 10.5

x 2.3 = 24.15kN/m.

Table 3: partial factors for SIDL all combinations [7]

SLS ULS

γf1 1.2 1.75

γf3 1 1.1

ULS SI DLfactored = 24.15 x 1.75 x 1.1.= 46.5kN/m

SLS SI DLfactored = 24.15 x 1.2 x 1 = 31.9kN/m

4.3 Imposed Traffic loading

Each separate deck carries 2 marked lanes of

traffic plus a hard shoulder. This amounts to 10.5m of

carriageway width. In accordance with BS 5400 (Ref

[8]), this corresponds to 3 notional lanes, which is used

for derivation of the loads. Width of each notional lane

is therefore 10.5/3 = 3.5m.

HA loading is an imposed UDL acting over

notional lanes plus a knife edge load (KEL). Assuming

a loaded length of the entire span of the bridge (290m)

for assessing the HA loading, according to BS5400, the

Ha UDL per metre length of each notional lane can be

found from equation 2.

0.1

136W

L

= ×

(2)

L=loaded length=290m

Therefore HA UDL=20.8kN/m along one notional

lane. Dividing by the width of a notional lane gives the

UDL per metre squared: 20.8/3.5 = 5.94kN/m2

According to BS5400, a KEL of 120KN is

appropriate.

4.5 HB loading

HB loading, is based upon an abnormal truck load.

This load would rarely be exerted on the bridge,

however it may be the most severe load experienced by

the bridge in its life. The full 45 units will be applied,

this equates to 450kN per axle. When testing the deck,

the most severe effect may be caused by HB when the

axles are approximately at mid-span of two

consecutive deck spans between cable supports,

causing a maximum hogging moment over the central

support.

This requires a central axle spacing of 6m

corresponding to the deck span of 7.3m.

4.6 Wind loading

Specific calculation of wind pressure on structures

is a result of many different variables; wind tunnel

testing is certainly required for a true analysis of this

bridge due to the unique design. However it is beyond

the scope of this report. In accordance with BS5400,

the wind load can be derived based upon 120yr return

values. The maximum wind gust speed can be

calculated from equation 3.

Vc = v K1 S1 S1 (3)

v = mean hourly wind speed = 40m/s

K1 = wind coefficient from table

S1 = unnelling factor, can be taken as 1 for this

example

S2 = gust factor

vc = 40 x 1.43 x 1 x 1.07 = 61.2 m/s

Although tornadoes are not common in Sao Paulo,

they do happen, and must be taken into consideration

for extreme loading. This has been taken into account

by assuming a higher mean hourly wind speed. The

load exerted on the bridge must then be calculated

from equation 4.

Pt = q A1 Cd (4)

Where q = 0.613vc2 = 2296

A1 = solid horizontal projected area

Cd = drag coefficient as defined below

d = dl = 2.5m

For 1m length of deck, A1 = 2.5m

b/d ratio = 16/2.5 = 6.4

Therefore BS5400 states Cd = 1.25

Pt = 8609N/m = 8.61kN/m

Wind will also exert vertical loads on the bridge

deck. This also is important and must be calculated

from equation 5.

Pv = q A3 Cl (5)

A3 = plan area per metre deck = 16m2

Cl is defined below

For Cl, due to the curvature of the deck, it has a

certain super elevation built in to the design. This is

2.7% which is between 1 and 5 degrees. Therefore

BS5400 states Cl to be taken as 0.75.

Pv = 27550N/m = 27.6kN/m

Table 3 factors for wind for combination 2 [8]

SLS ULS

γf1 1 1.1

γf3 1 1.15 for a plastic analysis

SLS Pt factored = 8.61 x 1 x 1 = 8.61kN/m

SLS Pv factored = 27.6 x 1 x 1. = 27.6kN/m

ULS Pt factored = 8.61 x 1.1 x 1.15 = 10.9kN/m

ULS Pv factored = 27.6 x 1.1 x 1.15 = 34.9kN/m

4.7 Secondary live loads: Horizontal traffic loads

The bridge is unusual in that it has two curved

decks. Each of these decks can be treated separately for

their analysis. Horizontal centrifugal traffic loads will

occur as the traffic drive along the curved decks. For

an extreme case, BS5400 states that a horizontal load

of value given in equation 6 can be used, however this

is only a point load and is not suitable for analysing the

deck as a whole element under a UDL centrifugal load

from HA traffic.

30000

150cF

r=

+

(6)

r = the radius of the bend = 290m

Fc = 68.1kN

This is a single point load and is minimal

compared with the extreme horizontal wind loading.

4.9 Temperature effects

The bridge Octavio Frias has expansion joints at

the ends of the deck on side of the spans. Teflon

bearings are most likely provided over the support on

the tower. However these joints may become blocked

by debris at some point in the bridges life. This will

build up longitudinal stresses in the deck that may

contribute to failure of the section most likely by

buckling in compression where there is already high

compressive stresses, such as over the cable stay

supports. Assuming the coefficient of thermal

expansion (α) for reinforced concrete is 12µε/Co. Then

the stresses built up can be calculated directly from

equation 7. The bridge is in group 4 (concrete slab on

concrete beams)

Max. shade air temperature = 28 Ref [6]

Min. shade air temperature = -4 Ref [6]

Max. effective bridge temperature = 30 Ref [7]

Min. effective bridge temperature = -2 Ref [7]

( )T Eσ α= ∆ (7)

α= 12µε/Co

∆T=(30+2)Co

E=30GPa for concrete

σconcrete =12x10-6 x (30+2) x 30000 = 11.52N/mm

2

4.10 Braking and accelerating forces

Braking and accelerating forces can cause stresses

in the longitudinal direction of the bridge deck and

therefore must be considered in design. BS 5400 states

this can be taken as 8kN/m along a single notional lane

plus a 200kN force.

5 Load effects

5.1 Bending

To calculate the maximum bending moments

exerted in the deck, the deck is appropriately

considered as 2 continuous beams spanning between

the cable supports and a separate deck simply

supported between the beams. The beams are

considered to sit upon rigid cable supports; the cables

are assumed to have had the correct amount of

prestress put in them for the deck to act in this way.

This produces the first moment diagram in figure 10.

However the second moment diagram in figure 10

shows an exaggerated but more realistic approach

which takes into account the effect of the extension of

the cables on the moment diagram (i.e. the supports are

modelled as springs). Enough prestress will be put into

the cables to ensure this effect is kept to a minimum

when the deck is subject to imposed loadings plus any

future creep effects.

Figure 10 Deck moment diagrams

Maximum bending stresses are exerted in the deck

under load condition 2. The most onerous loading case

for vehicular imposed is taken as 2 notional lanes fully

laden with HA, and all other lanes with 1/3 HA, with

the KEL at central span. With maximum dead and

superimposed dead loads included. Wind load is

included.

Table 4 Partial factors for Live vehicle loading,

combination 2

SLS ULS

γf1 1 1.25

γf3 1 1.1

HAFactored ULS = 20.8 x 1.25 x 1.1 = 28.6kN/m

HAFactored SLS = 20.8 x 1 x 1 = 20.8kN/m

KELFactored ULS = 120 x 1.25 x 1.1 = 165kN

The span between each cable support is 7.3m,

assuming moments to develop as if each deck section

was fully fixed at both ends, the following free body

diagram can be drawn for the deck.

Maximum moments in the edge beams will occur in

hogging over the cable supports in the end span. This

moment can be found from equation 8.

Mhog =

2

8

wl (for UDL) +

3

16

Pl(KEL)

(8)

L=7.3m P=165kN w=29.6x2.33+46.5+318.7+3

4.9 =447kN/m

Mhog = 3203kNm. Assuming this is shared between

the two edge beams in the ratios 3:2 due to offset

loading, then Mhog =0.6x3203=1922kNm. The bending

stress exerted in the reinforced concrete section can be

calculated from equation 9.

My

Iσ =

(9)

M=1922kNm y=0.71m I=0.358m4

Calculated

σ = 3812kN/m2=3.81N/mm

2 (low stress)

5.2 Cable tension

The maximum force in any cable is experienced

under combination 2 loading in the end span where the

inclination of the cable is at its greatest. HB loading

will cause the most critical effects. HB loading will

cover 2 notional lanes with 1/3 HA on the final

notional lane. The vertical load (V) supported by a pair

of cables is the total loads over one span calculated

below. This is the sum of all DL, SIDL, HB, HA and

vertical wind loading. The HB vehicle is assumed to sit

with 2 axles at the point of support of the cables.

DL=318.7kN/m SIDL=46.5

kN/m

Wind=34.9kN/m

HA=0.333x29.6kN/m HB=450x2kN

V=3892kN.

The cables are at an angle of 37.8o to the

horizontal. Therefore the tension in the cable pair is

3892/sin37.8 = 6350kN. Assuming loads are carried in

the ratio 3:2 between the pair of cables due to the offset

HB load, then the tension in the most critical cable is

0.6x6350=3810kN.

The cables are assumed to be high yield steel.

They are pretensioned to relieve excessive sagging of

the deck under imposed loading. The required area of

steel for the cable can be calculated using equation 10

1.25

0.8 yield

PA

σ=

(10)

P=3.81x106kN

yieldσ = 760N/mm2

x 1.25 for pretension x 0.8 for 80% of yield

A=7833mm2, This corresponds to a cable diameter

of 98mm. The actual cables on the bridge are 100mm

diameter.

5.3 Deck compression

Due to the inclination of the supporting cables,

they exert a compressive force in the deck. This force

will be at a maximum near to the tower. It will exert a

compressive stress into the section in this area that may

cause failure when combined with bending in the deck.

The maximum effect will be under load combination 2

with full HA loading, DL, SIDL, and wind. The

vertical load supported by the cable is

V=(2.333x29.6+318.7+46.5+34.9)x7.3=3425kN

Therefore the average cable pair tension is

3425/sin58=4039kN . The compression in the deck at

the tower is given by summing the horizontal

components of all 18 pairs of cables on one side of one

bridge deck. C=18x4039cos58=38526kN. The

compressive stress from this axial force can be

calculated from equation 11.

P

Aσ =

(11)

σ = 38526/10.5 = 3670kN/m2 = 3.67N/mm

2

5.4 Lateral bending

Lateral bending is experienced in the deck under

wind loading and centrifugal vehicle loading.

Furthermore, due to the curvature of the deck there is

an eccentricity associated with horizontal components

of the cable tensions which produces out of plane

moments in the deck as well as the axial compression.

These forces exert out of plane bending stresses in the

deck section, the moment can be calculated from

equation 12.

2

8 4

t ccables

Pl F lM eF n= + +

(12)

Pt=10.9kN/m Fc=68.1 e=eccentricity=2m

n=number of cables=36 Fcables

=1070kN

L=140

m

M=106000kNm. The stress in the concrete from

this moment can be calculated from equation 6 above.

M=106000kNm y=8m I=370m4

σ concrete= 2292kN/m2=2.3N/mm

2 (low stress)

6 Serviceability

All bridges and structures will undergo some

amount of deflection under loading. Ultimately, the

amount of local deflection is related to the external

imposed loads applied. However the amount of

prestress in the cables that support the deck has a

dramatic effect on the initial global deflections and

long term creep deflections. BS5400 specifies that only

load combination 1 should be taken into account for

serviceability. A maximum of 25 units of HB loading

are to be considered if this causes the most onerous

effects. Assuming the cable supports are inflexible, the

highest deflection will occur in the end span due to the

end simply supported connection. For a UDL, the

maximum initial deflection can be calculated for a

fixed pinned system using equation 13.

4

185

wL

EIδ =

(13)

w=357kN/m

SLS

L=7.3m E=4x107

kN/m2

I=0.358m4

δ = 0.00038m = 0.38mm (insignificant)

7 Creep

Creep in concrete is a result of the continuing

setting of the concrete as it dries. It happens under the

effect of long term loads such as dead and super

imposed dead loads. The long term creep deflection

can be calculated for a loaded structural element of the

bridge. However, the small spans between the supports

of just 7.3m combined with the rigid beam elements

are unlikely to produce large long term defections.

Loss of prestress in the steel cables due to creep in the

steel is much more likely to produce significant long

term deflections over the length of the span. This can

have the effect of increasing the sagging moments in

the deck as shown in figure 10.

8 Natural Frequency

Vibrations in bridges can greatly influence their

design. It is important that the natural frequency of any

bridge does not fall within a certain range. This range

is between 5Hz and 75Hz. Above 75Hz can cause

physiological discomfort, below 5Hz and the bridge

could be excitable by cyclic wind or traffic loading,

and collapse could result. The natural frequency can be

below 5Hz, however some form of damping may be

necessary to limit the acceleration of the element. The

natural frequency of different elements of the bridge

can be calculated simply via the Rayleigh-Ritz

formula, equation 14.

( )2

2

0 4n n

EIF w l

mlβ = =

(14)

The values shown are natural frequencies for the

deck, both fixed-fixed and fixed-pinned configurations

are tested (assumed pinned at the end of the deck).

Values : E = 3x10^10N/m^2 I = 370m^4 m =

25200Kg/m l = 140m (span)

configuration (Bnl)^2

value

EI/ml^4 F0 value

Fixed fixed 22.37 1.147 23.96Hz

Fixed pinned 15.42 1.147 16.5Hz

5 < 23.96,16.5 < 75

As can be seen, both natural frequencies fall

within the permissible limits. However, this is only a

very simple preliminary analysis of the bridge using

basic formula. There may be many more complicated

vibration effects in this bridge such as coupling effects.

These can only be analysed using sophisticated

computer software, not within the scope of this paper.

9 Foundations and Geotechnics

Ground conditions and considerations often have a

dominant influence on the choice and design of bridges

and buildings alike. This is very much the case for the

bridge Octavio Frias. The location of the bridge is

adjacent to the Pinheiros river which is an affluent of

the Tiete River (which originally fuelled Sao Paulo’s

growth) which itself sits on a plateau in the Brazilian

highlands. The river Pinheiros has been extremely

polluted and as such has been canalised, now serving

little use to the city except small goods transportation.

However, adjacent strata to the river is still made up

largely from alluvial desposites built up during the

river Pinheiros’ life. It is on these deposites that the

bridge sits. These deposits are poor at carrying any

lateral loads or moments. It is common for suburban

mediam span river bridges to be cable stayed due the

nature of the way loads are carried and the common

poor soil conditions. Most cable stayed bridges such as

Octavio Frias de Oliveira work by keeping lateral loads

within the structure by balancing the deck either side of

the tower. Some fixity at the foundation of the tower is

still required for stability under uneven loading.

Other important factors that will influence the

foundation and structure are hidden services and train

lines. Running along side the river Pinheiros (10m

away) is the biggest electricity transmission line in the

country (345KV, shown in yellow in figure 11) [4], it

supplies one third of the city and could not be disturbed

under any circumstance. Also running along side the

river are two train lines, these are positioned

approximately 20m away from the river edge (shown

in blue in figure 11). Furthermore there are four 1m

diameter waste water delivery lines running

perpendicularly into the river itself (red in figure 11).

All of these would be extremely difficult and costly to

disturb. It was therefore appropriate to come up with a

design that used foundations that would avoid

disturbing these services. The X tower shape solved

most of these problems automatically.

Figure 11 Foundation layout, see Ref [4]

As can be seen in green in figure 11, the

foundations are spilt into 4 blocks. The two connected

masts that form the X shaped tower meet the ground

nicely either side of the water lines. Essentially the

bottom of each mast is then split into two; avoiding the

electricity transmission line. Each block is slim enough

to not protrude into the river, or get too close to the

train lines. The 12m lever arm between the support

foundations either side of the transmission line is just

enough to provide the necessary rotational fixity at the

base of the mast to carry uneven deck loads.

Each foundation block is similar. Each foundation

consists of a pile raft containing 28, 1.3m diameter

piles spread evenly over each raft in 3 rows at

approximately 2m spacing [4]. The depth of these piles

is unknown but is expected to be approximately 20-

30m. Furthermore there are 10, 0.4m diameter piles on

each block that are inclined outwards. These are

expected to be around 15m in length and provide extra

lateral stability adjacent to the river bank.

10 Construction

Figure 12 construction of tower and deck

The details of construction of the bridge are

derived mainly from photos during construction from

Ref [4].

It was paramount that none of the service lines that

run beneath the tower were disturbed, also the north

bound Marginal Pinheiros avenue could not be closed

down for construction as this would cause disastrous

effects on vehicles wishing to travel north-south

through the city. This left an available construction site

with a maximum width of just 20m between the river

Pinheiros and the north bound Marginal Pinheiros

Avenue. Although slim, this was plenty; elements

could be delivered to one end of the site and lifted in to

position by the cranes.

It was important to not disturb the train lines or the

Pinheiros Avenue. Due to the close proximity of traffic

and train lines, it was of great importance that there

would be no falling debris from the construction

works; a tempory cover was constructed to ensure

debris did not fall on to the train lines, netting covered

all scaffold and form work that was carried out over the

roads for the duration of construction.

The construction of the foundations were first to

be completed. All of the 112 1.3m diameter vertical

piles are assumed to be drilled, this was necessary due

to the large diameter of the piles and also to prevent

damage to the main water pipes whose construction

would not be able to stand the forces exerted during

driving. Casing would have been necessary during

drilling due to the geological conditions. The

foundations provided support for a slab to span

between them. This provided an essential working area

for the start of the tower construction. Before this

point, no heavy machinery could be placed here due to

the underground services.

The next stage was to found cranes that would

remain in the same position throughout the project. The

position of these cranes was of great importance; the

tower when complete would be 140m tall, the cranes

would gain lateral support through the tower they were

constructing; no free standing cranes could reach such

heights.

These cranes would be responsible for all concrete

pouring operations and lifting of elements for the tower

and the deck, they would not however have to reach

out along the 140m deck either side. Elements would

be lifted on the bridge deck itself and then transported

to the construction area at the end of the deck. A jib

length of 35m was therefore deemed sufficient.

The tower was constructed in 3m sections. Each

cast in place using removable formwork. The bases of

the legs (0 to 23m) were constructed first, straight off

the foundations using formwork supported off the

purpose built foundation slab. The span between the

legs that support the centre deck area were also

constructed in this way. The two legs of the tower

(23m – 81m) were constructed simultaneously. Before

the middle crossover or support was reached, the legs

had to withstand bending moments due to their self

weight and construction loads arising from their

inclination. These moments were transferred through

compression and tension in the upper and lower deck

supports respectively, rather than being transferred as

moments to the foundations. These forces however

increased as the towers increased in height, up to a

point where a support was required between the top of

the legs to hold them apart. This support also ensured

that bending stresses in the outside of the legs were

removed before casting the central crossover piece.

This support was provided by scaffold, built centrally

between the legs, sitting on trusses to transfer the loads

to the leg’s bases, see figure 12. This tempory scaffold

also provided the support for the formwork for the

central crossover piece itself.

Figure 13 Deck construction

As soon as 90m was reached in the tower, the first

cables could be added and so construction of the first

deck pieces could begin. The deck was constructed

using the suspended cantilever method, see figure 13.

This method of construction is very common for cable

stayed bridges; the ability to use this type of

construction makes cable stayed bridges an attractive

choice in the first place because the towers used for it

are part of the final structure. The basis of the

technique is that the deck is cast incrementally; a

section of the deck is cast, supported by cantilevered

trussed formwork, when set, the cable tie support is

added to this section and pre-stressed. This allows

support for the formwork to be moved forward and

cantilevered out for casting of the next section, without

creating extreme hogging moments in the deck. The

beauty of this method for many cable stayed bridges is

that this can be done symmetrically either side of the

tower, ensuring minimal bending moments are

transferred to the tower or foundations. Importantly it

also does not require tempory support from underneath

that would otherwise require the Marginal Pinheiros

Avenue to be closed during construction.

It was important to ensure that when the deck was

completed, that it would be where it was supposed to

be. This task was made more complicated due to the

curvature of the deck. The deck was designed with a

constant curvature with radius 290m. This simplified

matters because it meant the same formwork could be

used continuously throughout the deck as with a

straight deck bridge. Accurate lasers and visual

positioning stations were most likely used to ensure the

formwork was correctly positioned to make sure the

deck was cast along the desired path.

11 Durability

The cable ties that support the deck are covered in

a layer of HDPE. This is the primary barrier to shield

the cables from radiation and corrosion. This covering

is long lasting and should help the bridge live out its

supposed life expectancy. Should the cables need to be

replaced; redundancy designed into the structure can

allow one cable at a time to be removed.

De-icing salts used on reinforced bridges can

cause staining or spalling of the concrete. Due to the

climate in Brazil [6], this is almost never required, so

the bridge will not suffer from this.

The Stone Mastic Asphalt laid on the bridge deck,

is designed to have a long life. As such, it is very thick,

making up a large proportion of the deck dead load.

12 Vandalism

The bridge is situated in an area of Sao Paulo

called Brooklin. This area is Middle to Upper-class and

consists of mainly residential buildings. However

immediately surrounding Brooklin are other areas that

are not so safe. To access the bridge from the

pedestrian areas you must either cross the 4 lane

carriageway plus the 2 train lines, or walk along the

bridge itself of which there are no walkways available

to civilians. These points make it very hard to

vandalise the bridge in general; however if these

hurdles were traversed, vandalising the bridge may be

achievable. No vandalising by means of graffiti will

last long however; the bridge is now an important

landmark for Sao Paulo and its cleanliness is key.

13 Future changes

The bridge was built essentially as a junction as

well as a span over the river. It is unlikely going to

receive a dramatic increase of traffic above that which

it was designed for, unless there are significant

infrastructure improvements elsewhere along the routes

which influence the traffic it receives. The bridge is

part of such changes itself in an attempt to reduce

congestion in the city as described previously. There is

no provision or allowance for more lanes. However,

there is a lack of a pedestrian bridge here, the bridge

Octavia has not been designed with one. There is a

walkway for people, but for maintenance only. There is

scope for this to be made public in the future.

14 Suggested improvements

As suggested above, there is scope for a pedestrian

route across the bridge. This may have been a

worthwhile small investment to have designed this

feature into the bridge, even if its main function was to

allow tourists a closer look at the bridge, considering

this is supposed to be Sao Paulo’s new landmark.

Due to the complexity of the scheme, it may have

been not that much harder to have increased the deck

size slightly to leave scope for an extra lane. This may

have been an easier way to prevent future congestion

rather than more costly infrastructure alternatives.

There are weaknesses in the detail design of the

bridge. The connection between the tower and cables is

cast into position as one piece within the edge. This

makes replacing one of these pieces extremely

difficult.

15 References

[1] Britannica online encyclopedia. Sao Paulo. Anon.

[2] Bruno Loturco, 2008 .Revista Techne. A revista do

engenheiro civil.

[3] LEDs magazine. Anon. 2008. Phillips LEDs,

bridge Octavio Frias de Oliveira.

[4] Ponte Estaiada Octavio Frias de Oliveira

(Complexo Real Parque). Anon. Instituto de

Engenharia. Pages 3-30

[5] Brazilmax.com. Anon. 2008. São Paulo

Neighborhoods and Geography

[6] Universidade Metodesta de Sao Paulo. Anon.

Brazillian climate.

[7] British Standards 5400

[8] Ibell T. 2008. Bridge Engineering 1 Lecture notes