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BRIDGE CONSTRUCTION METHODS &APPLICATION CASE 1)

By:Herry Vaza 2)

Idwan Suhendra3

)

ABSTRACTSelection of construction methods for a bridge structural design highly

depends on understanding of structure system and structure behavior as well asunderstanding of materials used and availability of equipment to perform the jobsfrom that it will produce low cost structure. In the case of a complex bridge structure,selected working methods prior structure analysis make static calculation moresimple. For those, the engineer should capable to select appropriate working method

in designing a structure in order to get great benefit to the project realization that is,producing an effective and efficient bridge structure.

Today, Indonesia as other countries has adopted advanced structure andtechnology indicated by application of prestress structure, cable supported structure,slim and light structure and more challenging of an architectural demand. Hi-techconstruction which is normally indicated as complex and unique design and of acourse require latest design skill with precise engineering analysis in the designstage as well as in construction process. An optimum working method for bridgeconstruction requires accurate engineering calculation and has a sound designbackground and skilled resources. This will strongly affect to the structure safety andworking environment. The structure safety will be top priority other than architecturaldemand, cost saving and limited time schedule.

A sound of technical understanding will be developed from experience toperform real design of construction engineering. Lesson from Indonesian experiencein construction of a complex bridge such as Martadipura steel truss arch bridge willbe discussed in this paper. The bridge in term of length is categorized as specialbridge with an appropriate construction method and adequate skills will produceworking safely and cost saving.

1) Presented in Indonesia-Korean Conference, Bandung July 2007.2

) Directorate of Technical Affair, DGH, Public Works3) PT Hutama Karya.

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1. INTRODUCTION

Indonesia is a tropical country consists of many islands and has many great and

small rivers. More than 88.000 bridges or equivalent about 1.000 km in length,

permanent and temporary bridges including railway crossing are recorded. From

those amount more than 29.000 bridges located in the main road network system

which supporting the economics directly i.e. at the national and provincial roads link.

Those are equivalent to 450 km in length and the rest exist on the district, rural, and

urban roads.

To accelerate the road infrastructure development program especially the

bridge construction, the governments policy is directed toward superstructure

standardization, by providing component stock of bridge standard span as well as

technical construction standard drawing that can be constructed in the field. The

purposes of standardization of bridge superstructure mean to guarantee of quality of

construction product which fulfilling the requirement as specified to ease construction

works. This standardization reason is not a surprised matter, because in the reality

from the existing 88.000 bridges mostly crossing the small rivers.

From all of the existing bridges on the national and provincial road links, the

amount of bridges that crossing the rivers with width more than 100 meters is less

than 2%. Although, rivers with big channel is not so much compare to others,

Indonesia has also adopted advanced bridge structural and technology as indicated

by application of prestress structure, cable supported structure, slim and light

structure and the more challenging architectural demand for crossing big rivers as

well as for urban infrastructure.

2. STEEL TRUSS ARCH BRIDGE

Selection of bridge type highly depends on river condition, construction cost,soil conditions, and purpose and function of the bridge. Suspension bridge will be

effective for span more than 500 meter and cable-stayed bridge will be effective for

300-800 meter span. While arch bridge will be effective for 100-250 meter span with

exception to Lupu Bridge in China span 550 meter which is become the world record

for the arch type and open to traffic in 2006.

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Martadipura Bridge in Kotabangun, East Kalimantan is the third bridge crossing

Mahakam River after Mahakam I Bridge in Samarinda and Kartanegara Bridge in

Tenggarong. The bridge is the second bridge in that type in Indonesia after Rumbai

Bridge in Riau and the longest span ever built with main span 200 meter, Fig 1.

There are several factors to be considered in construction of the long span

bridge such as selection of an appropriate method to produce safe construction and

in the same time involved optimum cost and minimum accident. The aforementioned

factors are a big challenge and exist in the Indonesia development era, because as

we know Indonesian experienced and skill engineer especially in the construction

segment have different behavior from those for a normal structure. For special

bridge, design and construction document should be an issued and as reference forprocurement strategy as well as for bridge construction.

Figure 1. Martadipura Bridge

Load transfer mechanism for steel truss arch bridge in principle is that those all

loads which are normally distributed over bridge deck is transfer through hanger and

continued to rigid truss, and then forwarded to substructure in form of vertical force

which is equivalent to live and dead loads, while for horizontal force the magnitude

depends on arch crown-span ratio. Furthermore, in the construction stage, the most

dominant loads occur during erection are mainly from dead load, live load (erection

equipment/traveler) and wind/temperature load, which depends on where bridge

located.

Figure 2. Main Span - Steel Truss

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3. CONSTRUCTION OF STEEL ARCH BRIDGE

Every bridge has different characteristics even it comes from same type.

Specific construction method should be considered for each design to create

effective and efficient product. In the lack of preparing construction method resultscost significantly increase due to miss-understanding forces exist during construction

or to prevent from exceeding structure capacity and even in some cases, the

structure cannot be erected. In this condition, contractor is not fully aware of working

method which is normally attached in the contract document.

Normally, contractor should consider a simple method as possible within

available resources in addition to abovementioned construction sequence which

available in contract document in order to obtain optimal products.

Understanding of structure behavior, type and characteristics of the material as

well as equipments will be benefit, and if necessary perform re-analysis in preparing

construction step (construction engineering) in order to have better understanding of

the structure according to work steps to obtain optimum result. The following tips

should be considered when determining a working method:

River profile, current direction and velocity

Support structure as an integral part of the construction method

Equipments

In-land waterways

Construction engineering analysis

Design Concept up to Construction Stage

Familiar with design drawing prior preparing construction drawing is most critical

parts for the contractor and will dictate the end products.

Design drawing is made by engineer in design stage. The drawing made by

engineer normally in the form of complete structure (final stage). In case of steel truss

arch bridge is normally forwarded to steel manufacture workshop. In the workshop,

engineering drawing is detailed for every single component and marked for bolts

position and length require as necessary accurately based on existing drawing.

Special software such as BOCAD or XSteel normally is used in preparing soft-

drawing to minimize an error. All produced drawings are reflected the engineeringdrawing which is in final form.

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Furthermore, approved soft drawings are forwarded to be manufacture within

the workshop and every single component is made precisely according to the

approved drawings. Complete components than proceed for trial assembly in

workshop to ensure every single component and bolts hole is fitted each others.

Rectification is made before components are transported to bridge site.

In the bridge site, all bridge components are erected according to marks and

sequencely erected which is available in manual guideline prepare by steel

manufacture. An alternative procedure is possible, if the appointed contractor has a

different sequence. An alternative procedure should have approved by engineering

prior implementation.

For selected method of construction, when erected main structure, the steel

truss arch should proof that the gravitation is neglected and therefore the contractor

should capable with their method to achieve the elevation as shown in the soft

drawing otherwise remain components could not be fitted in the position as the main

structure is not erected as the schedule.

After all steel truss components are in position and in accurate elevation than

continuing with erection of hanger and deck system (tie-beam) excluded concrete

deck. In this stage, elevation of steel truss will deflect from original as the weights of

tie-beam apply and adjustment should carry-out to bring steel truss up to the original

position. Contractor should capable to perform all adjustments require up to this

stage by any means.

Pouring the concrete deck is following step and will induce bridge to deflect

much and will make the support to further longer as elasticity of the bridge. The

magnitude of movement can be predicted from analysis, however the tightening of

the structure connections is great influence to this movements and this normally is

not consider in analysis. Minimize numbers of bolts used in structure could help

better in prediction of this movements. Adjustment in this stage is not worth as the

dead load become higher. The deck deflection under dead load should be controlled

so available bridge camber is within bridge design criteria.

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Construction Engineering

After proposed method of construction is selected and discussed with the

engineer than the contractor performs analysis and engineering calculation to

prepare engineering construction drawing and procedure. For this project contractoruses stayed cable and pylon as the tools for erection the arch system. In analysis the

critical part to be determined including dimension of stayed cables, pylon stability as

well as the temporary support and auxiliary. The following analysis exists in preparing

construction engineering drawing and procedures.

Figure 3. A Construction Method Concept Proposed by Designer

In construction design, we should understand assumptions adopted by the

designer when designing the bridge structure and performs analysis. When bridge

behavior under serviceability limit state have been familiar than construction scenario

and alternative construction method can be further explored. From the best

alternative than evaluation on forces exist in every stage of working method against

allowable can be checked, Figure 4 and Figure 5.

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Figure 4. Construction Engineering Analysis Carry-out by Contractor

The following ultimate limit state should also be considered and total load

should define during design to avoid overloading during construction:

Structure weight at all the stages

Traveler load and formwork

Equipments load on the deck

Temporary live load

Figure 5. Complete Structure Checking by Contractor

It can be seen that moment, tension, and deformation on the cable under

ultimate limit state loading are significantly different from those at serviceability limit

state, and even more. Therefore, detailed and accurate calculation will produce

successful construction, low accident and cost in considerable within timeframe.

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Construction Method

In case of the Martadipura steel truss arch bridge, the alternatives should be set

forward before establishing the working method. To enable selection of an

appropriate method such alternatives include as shown in Figure 6 below.

Figure 6. Construction Method Design

This alternative is selected to replace the weakness of previous alternatives.

The cable stayed pylon formerly are founded on the river, now is moved to pile-cap

of main pier and consider bearing capacity of pile against additional load from the

pylon. While backstayed is anchored at the previous pier because based on the

analysis, the pier can resist lateral force as horizontal projection of stayed cable

forces.

Pylons located at main pier at the outer side of the truss. This position has an

advantage for truss stability against lateral wind load in addition to maintain arch

bridge alignment. Furthermore, the stayed cable connects to the truss which are

located at outer side of the truss to allow mass-crane manuver freely when moving to

the next segment.

4. CONSTRUCTION PROCEDURE

Preparation

Prior to arch assembly, make sure all accessories such as metal bearing and

support triangle have been mounted. While truss mounted simultaneously should be

linked first as per beam number. Arch truss mounting can be conducted by fastening

vertical beam onto temporary triangle. At this time, all position should have been

defined based on measurement.

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Pylon Erection

Pylon erection is conducted using crawler crane of 45 ton capacity. For simply,

pylon erection is conducted simultaneously between left and right side. Pylon

verticality should be always controlled during erection so that inclination at the top ofupper pylon is not more than 5 cm.

Arch Truss Erection

First segment is erected following vertical beam assembly at the support by

using crawler crane on the pontoon and then continued by second and third

segments by using mass crane (manual crane). During operation, truss

lowering/displace as resulted of self weight should have been measured to anticipate

significant displacement of the next segments.

Strand Mounting

Stayed #1

Backstayed strand can be mounted after pylon erection or simultaneously with

mounting of strand stayed #1. To prevent Tip Tower Displacement (TTD)

beyond tower elasticity limit due to truss load, precamber can be provided by

giving prestress at the backstayed. Stayed #1 is mounted at lifting point of the

truss and than prestressing conducted until truss elevation is achieved as

schedule and then continued by mounting of the next segments.

Figure 7. Construction Stage Stayed Cable #1

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Stayed #2

Stayed #2 is mounted after erected 8 (eight) segments to prevent significant

displace of the truss. The displacement control is conducted at the end or tip

truss. If the displacement is not controlled and match to the elevation requiredthan prestretching cable is made and repeated until match to the schedule.

Figure 8. Construction Stage Stayed Cable #2

Stayed #3

Stayed #3 is mounted after erected 12 (twelve) segments. Prestretching may be

required at the previous stayed (stayed #2) to adjust the elevation. Stayed #3

acts as lifting up truss to achieve the elevation.

Stayed #4

Stayed #4 is mounted after 17 (seventeen) segments erected. During mounting

of stayed #4, all the previous stayed should have been checked to prevent

overstress at stayed #3 and stayed #4. Elevation should also be checked to

adjust any stayed point is not match to the schedule. At all time, the main piers

are monitored in the position as for truss elevation and any discepency of the

pier position should be adjusted against the schedule.

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Figure 9. Construction Stage Stayed Cable #4

Final Erection

During erected of the last segment, measurement is conducted between main

pier P7 against the opposite pier P6 in order to estimate the remaining gap. If

necessary beams length are adjusted. For final segment erection, mounted bottom

chord first and than follow with diagonal beam, vertical and finally closed with top

chord.

Hanger Assembly

At this stage, all arch truss bolts has been tightened to 100%, and all cable

stayed at supports P6 and P7 remain in the position.

Possible displacement is solely caused by pile elasticity and displacement is

expected to be very small and not affect tie-beam assembly. After that, all hanger

bolts are tightened to 100%.

Tie-Beam Assembly

During tie-beam assembly, P6 and P7 should be avoided from horizontal

displacement and only elastic movement due to the pile elasticity is allowed. Tie-

beam is then assembly symmetrically from the center to P6 and P7. Since cross-

girders have not been assembly at this stage, outer and inner tie plates are fastened

to connect between tie-beams 70% tight. The cross-girder assembly should be

adjusted with jointing of the tie-beam as it should be adjusted with proposed

elevation of the tie-beam.

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Figure 10. Several Photos: Erection Steel Truss Arch Bridge

5. CLOSING

In preparing the construction method for specific bridges, working method

should have been defined in the design stage for minimized risk of failure and to

make optimal structure as well as to create simply static analysis.

Nowadays, It becomes common in procurement of a bridge structure; the owner

tends to open a bid in the form of Engineering Procurement and Construction (EPC).

In such cases, the engineer has fully understanding of the design, material and

equipments involved to produce cost effective structure within timeframe. When this

system is adopted than we only need how to ensure the safety and constructability of

proposed structure. To answer to this question, an independent consultant should be

engaged to justify and making proof to the proposed design.