No Slide · PDF fileFirst International Seminar on the Design & ... – Segmental precast & erected to form individual spans ... • Increases selfweight,

First International Seminar on the Design &

Construction of PENANG SECOND BRIDGE

15-16 November 2011

Superstructure Design of Approach Bridge

RB International Formerly Benaim (Malaysia)

In Association with RB Perunding Sdn Bhd

By: Mr. Afshin Forouzani / Mr. David Collings

The Legend Hotel Kuala Lumpur

• Project Description: Alignment, Design Features, Statistics, etc.

• Options Considered for Deck

• Deck Articulation & Form

• Options Considered for Prestressing

Introduction

Project Alignment

Work Packages

• Tot. Deck Area: ≈ 461,000 m2

• Tot. Length: ≈ 16 km

• Typ. Span: 55 m

• Number of Piers: 289

• Carriageway Width: 14.5 m

• Number Segments: 8,092 No.

• Design & Construction Programme: 45 months (March 2013)

• Segment Weight: 120 tons max.

Package 2: Design Features & Statistics

Options Considered - Deck

• Beam & Slab Deck:

– Cheaper in terms of superstructure costs but:

• Will require many more piers in water and similar number of piles per

pier. More pilecaps & more operations

• Will require substantial in situ concreting works (deck slab & beam

connection) → slower in terms of programme

• Will require around 4500 beams to be erected

• Will require around 9000 bearings with their associated maintenance

problems

• Will require many erection gantries and / or falsework

• Aesthetically inferior

Beam & Slab Deck

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Beam & Slab Deck

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Typical ‘T’ Beam Design

• .

Options Considered - Deck

• Steel Beams / Box Girder:

– Ruled out due to cost of steelwork & substantial maintenance

requirements

• Concrete Box Girder:

– Economical Deck

– Optimum use of substructure

– Fast to construct if precast & erected using a gantry

– Aesthetically pleasing & environmentally friendly with minimum

requirement for in situ work

– Has been used on many similar projects in the past in Malaysia &

worldwide (e.g. KL: STAR LRT, SPRINT Highway , New Pantai

Expressway, Pasir Panjang Semi-Expressway Singapore, etc.)

Concrete Box Girder

• .

Span Arrangement

• Reference made to a study in 2003 recommending spans of

around 40-60m & highlighting marginal difference in 40-60m

span range (2-3%)

• Factors taken into account:

– Number of piers in water

– Construction programme implications of using more piers

– Safety and convenience of small boats traffic navigating below deck

– Ease of segment precasting, handling (weight) and erection

– Use of flat soffit for ease of precasting & better aesthetics

– Environmental impact of number of piers in water

• Conclusion: 55m span is chosen as optimum & practical

Cost Comparisons for various spans

• Span Length Study (2003)

Possible Forms of Construction

• Span by span the only feasible option given the total length of

bridge:

– Whole beam precast in a long line mould

– Whole beam precast in segments stitched together in a long line

mould (e.g. Tagus 2nd Crossing)

– Segmental precast & erected to form individual spans

• Balanced cantilever:

– In situ: too slow & too much work over water

– Precast: less work over water but still too slow as deck erection is

much slower (around 1-1.5 weeks per span)

Typical Balanced Cantilever Construction

• .

Typical Balanced Cantilever Construction

• .

Whole Span Precasting

• Whole span precasting:

– Likely to be much faster in terms of beam erection per work front (1

span per day is easily achievable) → huge advantage.

– Elegant for a project of this size

– Fewer operations in terms of load out & beam erection.

– Fewer operations during erection & simpler logistics

– Slightly more efficient in terms of materials (5-10%) compared to

segmental construction

– Requires heavy cranage (1200T) at precast yard & foundations

– Requires a heavy & expensive marine crane for beam erection

– Has risk of single floating crane mechanical breakdown &

associated delays

Typical Whole Span Erection Using Launcher

• .

Whole Span Precasting

• Whole span precasting:

– Requires a higher level of technology & it has never been done in

Malaysia

– Highly specialists operations during erection without residual value

in terms of transfer of technology & local participation

– More expensive due to heavy cranage requirements for precasting &

erection

– Crane will require more water depth → more dredging

– Higher risk due to having 1 substantial marine crane (breakdowns,

etc.)

Whole Span Precasting

• Whole beam precast in segments stitched together in a long line

mould:

– Very similar to whole span casting except that it allows casting of

deck in segments first

– Is more versatile for decks with curved alignment

– Utilises more standard segment moulds

– Requires a few long line stitching bed only & not a whole span

mould

– Faster in terms of beam production per long line mould / bed

Example of Whole Span Beam Precasting

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Example of Whole Span Beam Segmental

Precasting

• .

Example of Whole Span Beam Erection

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Example of Whole Span Beam Erection

• .

Span by Span Segmental

• Can be erected very fast using a modest gantry supported off the

substructure

• Requires less sophisticated construction methodology & it has

been done in Malaysia before.

• Maximises local participation

• Will be less costly due to cheaper precasting & erection by

avoiding:

– Heavy overhead gantry cranes in precast yard

– Heavy foundations for gantry crane rails & casting bed

– Expensive floating crane for erection

Whole Span Segmental

• Gantry cranes & Moulds will have value after project ends as

they can be used for future projects → future asset

• It is relatively easy to achieve curved alignment

• Launching Gantry does not require any water depth → not critical

to dredging. Only require minimal dredging for segment transport

barges

• Less susceptible to delays as a result of failure and / or break

down of gantry crane as there will be 4 work fronts

Deck Articulation & Form

• Twin box girder used to keep segment weight down for maximum

economy

• Use of expansion joints minimised to reduce maintenance costs

& associated delays in replacing joints

• Initially typical 15-Span modules (825m) considered economical

& near optimum from the deck point of view

• Number of bearings minimised through the use of monolithic

connection between deck & columns over central 4 piers

• However due to seismic requirements (“no collapse” for 2500

year return period earthquake) deck articulation revised:

– 6-Span module (330m long)

– Elastomeric High Damping Rubber Bearings were adopted

Initial Deck Articulation: 15-Span Module

• .

Final Deck Articulation & Bearing layout on typical 6

span module

Deck-Bearing-Pier Interface

Deck-Bearing-Pier Interface

•Interaction & Coordination

•Seismic Risk

•Analysis & design

Alignment

Longitudinal Section

Granite bedrock

Soft mud

Risk

•Ship impact,

construction barges,

short term

•Seismic criteria 1:475

increases to 1:2500 Risk

Time

Ship impact Ship impact

Seismic

Risk

•Ship impact,

construction barges,

short term

•Seismic criteria

1:475 increases to

1:2500

Risk

Time

Ship impact Ship impact

Seismic

Seismic performance levels

475 year

return

(Serviceability)

2500 year

return

(Ultimate)

Bridge deck,

piers, piles

Minimal

Damage

No Collapse

Bearings Minimal

Damage

No Collapse

Joints Repairable

damage

No Collapse

Earthquake locations near Malaysia

Penang

Subduction Zone

Seismic Study

•Seismic assessment study by

University Teknologi Malaysia for

CCCC Highway Consultants

•Local site effect analysis report by IEM,

CEA

Time history Analysis

Seismic Study

•Seismic assessment study by University

Teknologi Malaysia for CCCC Highway

Consultants

•Local site effect analysis report by

Institute of Engineering Mechanics,

China Earthquake Administration

Effects of soft soil – higher accelerations

Design accelerations

1:475 year PGA 0.055g

at bedrock

1:2500 year PGA 0.110g

at bedrock

Design issues

Deck isolation by rubber bearings reduces forces at

pile cap level.

Previous use of rubber bearings

Bearing elastomer requirement for P2X with and

without preset

Asymmetric seismic effects

330m

Asymmetric seismic effects

Asymmetric seismic effects at joints

Use of dowels to limit movement

Stainless steel dowels

Options Considered for Prestressing

• Fully Internal:

– Relatively efficient in terms of prestressing due to high eccentricity of

cables

– Less economical in terms of deck concrete as use of ducts in webs:

• Penalises web performance and adds to web thickness & weight

• Increases selfweight, prestress & reinforcement quantities as a result

– Precasting is more complicated due to

• Interference of prestressing tendons with reinforcement

• Requirements for concrete blister anchor blocks

Options Considered for Prestressing

• Mix of Internal & External Prestress

– Most optimum in terms of:

• Prestress design (around 10%)

• Selfweight

• Reinforcement

– Still requires glue (slows down gantry erection cycle by a day) →

increase in erection programme number of gantries

– Precasting slightly more complicated due to

• Interference (clash!) of prestressing tendons with reinforcement

• Requirements for concrete blister anchor blocks

Options Considered for Prestressing

• Fully Externally Prestressed

– Considered “State of Art Technology”

– Although not so optimum in terms of prestress design (around 10%)

– Dry Joints

– HDPE ducts are:

• Very durable as they are thick, continuous & impervious, with better

overall quality

• Inspectable

• Replaceable

– Lends itself to tropical climates in which freeze/thaw cycles do not

exist, and de-icing salts are not used

– Segment erection is very fast using dry joints (1.5-2 spans a week

per gantry are possible)

Typical External Prestressing Ducts

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Typical External Prestressing Ducts

• .

Options Considered for Prestressing

– Leads to simple segments:

• Without internal blisters

• Fast to precast

• However concessionaire required the use of epoxy in segment

joints for additional safety

• Finally a mixture of internal & external prestressing was used

• Segments were still kept relatively simple:

– no blisters except at deviators

– relatively straight internal tendons

Typical Spans – Segment Arrangement

• .

Method of Deck Erection

• Using overhead launching gantry

• Segments delivered below on barges

• Segments to be assembled using temporary prestress (glued

joint)

• 1st stage internal & external tendons stressed, sufficient to carry

selfweight & some construction loads

• Span placed on temporary supports

• Gantry advances without the need for any in situ concreting

works

• Further 2nd stage continuity prestressing is applied to resist

superdead, live and other loads

Typical Arrangement of Prestressing

• .

Whole Span Segmental Deck Erection

• .

Typical Deck Erection

• .

Typical Sequence of Span Erection

• .

• ≈ 2700 No. Segments cast so far

• 4 No. Launching Gantries mobilised

• Segment Launching started early 2011

• ≈ 140 Spans Erected so far

Progress as of December 2010

Segment Load-Out Jetty

Segment Load-Out Jetty

Arial Photo of Precast Yard

Segments Cast

Segments Cast

Arial Photo of Gantries Erected

Arial Photo of 1st Span Being Erected

Full Span Erected

More Spans Erected

CONCLUSIONS

• Partnering principles used between the Owner, Contractor,

Designers & Checker led to a fast track design

• Construction methods & techniques considered by the Designer

right from the start of the project

• Base Isolation techniques were used to reduce seismic loads on

substructure

• Innovative Use of High Damping Rubber Bearings & use of locally

produced rubber

www.rbiconsult.com

THANK YOU FOR LISTENING!

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