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Berger, Waimberg, Stucchi 3rd fib International Congress - 2010

DESIGN AND EXECUTIVE CONTROL OF THREE CURVED BOX GIRDER

BRIDGES IN S.PAULO

Daniel Berger, EGT Engenharia, São Paulo, BR

Marcelo Waimberg, EGT Engenharia, São Paulo, BR

Fernando Rebouças. Stucchi, EGT Engenharia, São Paulo, BR, (EPUSP)

ABSTRACT:

The present paper deals with three Curved Box Girder Bridges, built in

prestressed concrete, erected by the cantilever method, that compose the

Road Interchange in the crossing of the Anhanguera Highway with the

Marginal Tietê Avenue.

The most important is branch 900, with two intermediate spans of 125m, two

lateral spans of 90m and radius of curvature of 235m. Another bridge of the

Complex, branch 200, has a side span built in single cantilever from a side

support anchored in the rock.

Beyond the description of geometry, the structure and the construction phases

of these bridges, the paper intends to present the systematic of the deck level

control, the load control on the temporary columns and stress control in some

chosen sections of the girders.

.

Key words: Curved Box Girder Bridge, Cantilever Method, Construction phases.

Berger, Waimberg, Stucchi 3rd fib International Congress -2010

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ANHANGUERA COMPLEX INTERCHANGE

The Anhanguera complex consists of a set of constructions to improve the traffic at the

arrival of Anhanguera Highway to São Paulo.

It is located between the current bridge Atílio Fontana and the km 19 of Anhanguera, in

Osasco.

It will have new Viaducts, Bridges, u-turns, additional tracks, footbridges and other

improvements.

The project will facilitate the crossing of the river Tietê and access to the region of Lapa,

Vila Leopoldina (Ceagesp) as well as neighborhoods such as the Mutinga quarter, thus

improving the heavy traffic of over 100 thousand vehicles per day in Anhanguera and

Marginal Tietê. The figure below shows the Anhanguera Complex and the branch 900, 500

and 200.

Fig. 1 The Anhanguera Interchange

The paper will focus on the Anhanguera Interchange bridges (branches 900, 500 and 200)

with emphasis on the structural solution, the constructive aspects and monitoring.


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BRANCH 900

DESIGN SOLUTION

The branch 900 bridge is the one with the largest span, 125m long. It has two 100m side

spans and two 125m central spans. Its curvature radius is 235m which results in major torsion

efforts. The figure below shows the branch 900.

Fig. 2 Branch 900

The bridge cross section is a one-cell box girder with variable height of 5.8m at internal piers

and 2.95m at mid-span. The width of the deck is 11.80m. The bridge was built in a double-

balanced 61m cantilever. The figures below shows the cross section at mid-spam and piers.

Fig. 3 Cross Section

Due to the large curvature of the bridge it would be impracticable to have two bearing

devices on columns P1, P2 and P3 to restrict the torsional rotation. The huge transverse

moments would generate important tension on the internal bearing devices. It´s important to


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remember that during the constructive phase, still in cantilever, external temporary columns

would be under tension. Upon the cutting those columns there will be tension on the external

bearing devices and during the creep effect tending to the continuous beam, there will be

tension on the internal side. The figure below shows the curvature and the position of the

piers P1, P2 and P3.

Fig. 4 Curvature of the bridge

To eliminate tension on internal and external bearing devices, the support has been defined

with a single bearing instead of two. In addition, in order to reduce torsion on the deck, this

device was placed eccentrically on the top of piers P2 and P3, at the internal side of the

curve. The bearing positions are showed below.

Fig. 5 Bearing devices

MODEL CALCULATION

The structure was calculated with a 3D frame model, including “offsets” between beams and

columns, variable sections and soil-structure interaction.

The effect of the eccentric bearing was studied to confirm the viability of the solution.


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Below you can see efforts of bending moments on the box girder with double support (fig.6),

single-centered (fig.7) and eccentric support (fig.8) to compare the cases.

The efforts of the three cases of bearing devices are calculated by load combination: Dead

load (to) + Live load (45 ton truck + 0,5tf/m2)

Fig. 6 Bending moments in the model with double support.

Fig. 7 Bending moments in the model with single-centered support.

Fig. 8 Bending moments in the model with single-centered support on P1 and eccentric on P2

and P3.

It is evident the convenience of the adopted solution.

A specific study of the support diaphragm was developed in a hybrid model with bars in

general and Finite Element shells in the region of the diaphragm.

The diaphragms were dimensioned using strut and tie models. Confirming calculations,

stresses obtained in the FEM were compared with strut and tie results. The comparison

showed that applied models were appropriate. The figure of FEM model is showed below

and the diaphragm geometry with prestressing tendon is showed in fig.10.


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Fig. 9 Model with finite elements shells connected with the original frame elements model.

Fig. 10 Diaphragm geometry with prestressing tendon.

Diaphragm on P2 – Principal stresses (tf/m2) – Live Load+Dead Load+Prestressing (without

the diaphragm tendon) in the figure below


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Fig. 11 Result FEM without diaphragm tendon

Diaphragm on P2 – Principal stresses (tf/m2) – Live Load+Dead Load+Prestressing (with the

diaphragm tendon) in the figure below

Fig. 12 Result FEM with diaphragm tendon

It can be observed that for service loads prestressing was sufficient to eliminate or reduce

tension stresses to values below the concrete tensile strength.

In the Ultimate Limit State, where the theory of reinforced concrete requires consideration of

a strut and tie model, the suspension reinforcement required is much greater than those

prestressing tendons1.


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BRANCH 200

The branch 200 bridge is the one with the largest curvature, with a radius of 120m. Its spans

are 54m and 90m long. This branch starts at the existing bridge, called Atílio Fontana. Due to

interference with the bridge, a one-half span was built in single cantilever and the others in

double cantilever.

Single cantilever was erected in the 90m side span, rigidly fixing this pier to the rock.

On the left of the figures below branch 200 under branches 500 and 900. On the right the

cantilever of branch 200 during construction.

Fig. 13 Branch 200 (single cantilever)

Fixing in rock was made possible by means of 28 100tf φ67mm anchorings for tension and

12 φ1.6m caissons for compression arising from efforts in this pier (N = 980tf, M =

19,869tfm). The figure below shows the foundation of the single cantilever.

Fig. 14 Extreme pier of the 90m span.


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The cross section of the bridge is a one cell box girder with variable height of 4.85m at the

central pier and 2.3m in the middle of the span. The width of the deck is 11.80 m.

CONSTRUCTION METHOD FOR BALANCED CANTILEVER

The constructive method of balanced cantilever was first designed by Emílio Baumgart. The

idea is to erect cast-in-place segments outwards from the piers, connecting them to the

previously built structure.

During erection of double cantilever, asymmetric loads tend to unbalance the structure. To

ensure stability, temporary columns may be used, as for the bridges mentioned here, or

cantilever can be rigidly fixed at piers.

For double cantilevers of branches 900, 500 and 200 provisional monitored columns were

adopted. For branch 200 simple cantilever the superstructure was fixed to the pier, which was

anchored in rock.

Constructive sequence:

1) Erection of bridge columns and temporary columns

2) First segment cast on falsework support

3) Assembly of form traveler

4) Balanced cantilever (formwork, reinforcement, concrete, prestressing and advancing of form

travelers in a one week cycle)

5) Cast of falsework supported girder segment

6) Conclusion of balanced segments

7) Moving form traveler for closure casting

8) Casting of closures and prestressing of positive tendons

9) Temporary columns demolition

10) Execution of pavement and casting of New Jersey barriers.


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Fig. 15 Constructive Sequence

BRIDGE MONITORING:

Bridge monitoring allows to follow and ensure quality throughout the course of the Bridge

construction.

The results of each phase are compared with design values to check their consistency or

anomalies in the process.

In case of defects, they can be repaired immediately without affects job performance.

Monitoring System provides safer constructive process, since it allows knowing how are the

main elements of the Work in each construction phase.

The Monitoring System consists of three elements listed below:

A) Monitoring of balanced cantilever levels.

B) Monitoring of temporary columns strain

C) Monitoring of balanced segments strain.


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Monitoring of balanced cantilever levels:

At each construction stage (after casting a segment, prestressing it or advancing the form

traveler) measurement of levels are conduct. These levels were always compared with the

theoretical values and if necessary the model was back-analyzed according to data.

Those levels were always measured early in the morning in order to minimize the effects of

temperature variation in the concrete.

The figure below shows the points to take the measurement of levels. All the segments had a

certain point to each measurement level.

Fig.16 Points to take the level for each segment.

The location of the next segment was always made in relation to the previous one through a

construction camber, with relative elevations, never absolute values. That camber represents

the misalignment of the new segment considering the previous one and the figure below

shows this misalignment.


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Fig. 17 Construction camber

For computing the construction camber it was used the scheme suggested by Mativat². With

estimated vertical displacements, the bridge profile can be obtained as if segments were cast

in alignment. With camber adjustments, a new profile results at the specified position. The

figure below shows this position during the construction.

Fig. 18 Geometric place of cantilever extremes – construction camber.

Fig. 19 Theoretical profile for Branch 900 on pier P3 during construction phase.


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Monitoring of temporary columns strain:

The decision of monitoring these columns was made especially to bring safer condition to the

step of cutting, since they are elements of vital importance during the construction phase.

We chose measuring strain and indirectly estimating the forces acting on those columns for a

much more economical usage of strain-gauges instead of load cells. The strain-gauges were

put in bars and showed on figure 21. The bars with the strain-gauges were put in the piers and

show on figure 20.

Fig.20 Strain-gauge on the bars

Fig.21 Strain-gauge on the Piers

Columns’ strains were read and compared with the back-analyzed theoretical design values.

Since measured and computed strains were consistent and close, we can conclude that the

theoretical forces in temporary columns must also be close to actual values. The figures

below shows the comparison with the specific deformation of theoretical and measured

strains in one pier of branch 900 temporary columns.


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Fig. 22 Theoretical and measured strains in one pier of branch 900 temporary columns.

Monitoring of strains of segments:

Strains were measured in critical sections of the segments. They were measured at the four

corners of the cross section as stated below. The strain-gauge were put on the bars and

showed on the figure 20.

Fig. 23 Positioning of the strain-gauges

Those strain measurements were compared with the theoretical values in some of the

construction phases in order to control the process.

The Monitoring System has led to a safer construction process, as it made possible to follow

the main elements of the Work in each construction phase.


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CONCLUSIONS

Branches 200, 500 and 900 were already constructed. The constructive method and

Monitoring System enabled to meet the expected execution deadline. The final level were

well closed to the project level.

With the Monitoring of temporary columns and segments and the control of the levels

allowed to verify whether the constructive phase was in good condition like the expected.

REFERENCES

1. Leonhardt, Frtiz and Monnig, Eduardo, “ Construções de Concreto”, V.3, 1979

2. Mathivat, Jacques, “ The Cantilever Construction of Presstressed Concrete Bridge”,

1983.

stucchi executive control of precamber

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