14 Understanding Staged Construction

hewson consulting engineers civil, structural and bridge engineering

Third International Bridge Seminar

Understanding Staged Construction

Integration of staged construction and time

dependent effects into the design of bridges

Andrew Hodgkinson

hewson consulting engineers civil, structural and bridge engineering

hewson consulting engineers

civil, structural and bridge engineering

A brief history

Staged construction is not new



A brief history

Engineers have been using staged construction to build bridges for centuries



Staged Construction

Engineers must assess the significance of staged construction on the final forces and deflections in the structure.

Time dependant effects of creep and shrinkage must be taken into account through idealised models e.g. CEB-FIP78, CEB-FIP90, ACI etc.

Checks of adequacy of the structure during construction may also be required.

Determination of precambers to ensure correct final structure geometry is often needed.

Can be utilised to alter and optimise force distribution in structures



Bridge Construction Methods

The most common bridge construction methods include:

Composite beam and slab (precast or steel beams)

Full Cantilever Method (FCM) integral or bearings

Span by span insitu or precast

Incrementally launched

or a combination of these methods

Greatly influences the final force and stress distribution

throughout the deck



Bridge Construction Methods Composite Methods



Bridge Construction Methods FCM Method



Bridge Construction Methods Full span or Span+1/4 method



Bridge Construction Methods Incremental launching



Analysis Methods

Methods have developed over time

Engineers have been used to developing a series of analysis models for the significant construction stages and combining the

results.

Creep redistribution idealised using hand calculated upper/lower bound creep (f) factors.

Prestressing usually idealised as manually calculated equivalent loads

Many bridge designers have developed spreadsheets in an attempt to make the analysis more efficient.

Nothing wrong with these methods as they have served us well over

many years but there are now alternatives



Analysis Methods

In-situ stitches

balanced

cantilever

Cantilever

Dead load

BMD



Analysis Methods

As-built BMD

Instantaneous

BMD



Analysis Methods

Final

BMD

Over time the bending moment distribution creeps from the as-built

condition towards the instantaneous condition. Masbuilt

Minstant

f eMMMM 1.)( asbuiltinstantasbuiltfinal



Integrated Analysis Method

Results require no post-processing to combine separate analyses

Calculation of creep/shrinkage automatically based on actual construction time-line

Combination with in-service static and dynamic loadings on structure can be undertaken within the analysis

Iterations to achieve economic design are quick to implement.

A greater level of accuracy is achievable.

Precambers readily determined

A method by which all construction stages, all loading

(including prestress) and time dependant effects (where

applicable) are integrated into a single analysis



Example 1 Composite Precast Beam and Slab

N6 Galway to Ballinasloe PPP Scheme ST26



Example 2 Insitu PT voided, top-down

M3 Clonee to North of Kells PPP Scheme S20



Example 3 Curved FCM Bridge on bearings

Johor Ramps



Example 3 Curved FCM Bridge on bearings

Johor Ramp A



Example 4 165m FCM Bridge integral piers

Coastal Highway from Johor Bahru to Nusajaya Bridge 2



Example 4 165m FCM Bridge integral piers Coastal Highway from Johor Bahru to Nusajaya Bridge 2



Example 5 Concrete Cable Stayed Bridge

Bonny River Cable Stayed Bridge, Nigeria

overall length 930m with 350m main span

single plane of stays

diamond pylons



Example 5 Concrete Cable Stayed Bridge

Bonny River Cable Stayed Bridge, Nigeria



Example 6 Concrete/Steel Cable Stayed Bridge

New Wear Bridge, Sunderland



Example 6 Concrete/Steel Cable Stayed Bridge New Wear Bridge, Sunderland



Concluding thoughts

Integrated analysis can save time (and money) where staged construction is important

Accurate analysis of structure deflections and required precambers

Efficient analysis provides opportunities for design refinement

Careful implementation needed to ensure that active elements, boundary conditions and loads accurately represent each construction stage

Not to be treated as a black box careful checking of results is needed.



A final word of warning

Documents

14 Understanding Staged Construction