Staged Construction Analysis

With LUSAS Bridge, unlike some software, only one model file need be created and this can contain all of the information required to carry out an analysis of every stage of construction. The effects of geometric and material nonlinearity, and time-dependent material effects such as creep and shrinkage can all be included within the one analysis run.

Overview

Modelling of a staged construction process in LUSAS Bridge requires a complete model to be built with all geometric and material properties, supports and loadings assigned. The birth and death facility is then used to activate and deactivate groups of elements and associated attributes in order to mimic each stage of construction.

The complete staged construction analysis process for a model is controlled in the loadcase panel of the LUSAS Treeview. Detail of the loadcase Treeview for the cable stayed bridge model (shown below) is shown opposite.

Staged construction with LUSAS

• Model full staged construction with beams, shells and solid elements (some software only permits beams to be used)
• Full activation and deactivation of elements is supported
• Model any support condition and add or remove supports as required during the construction sequence
• Sliding bearings may be modelled using nonlinear contact (slidelines)
• Support and loading facilities including temporary/traveller loads
• Apply loads anywhere onto any model
• Change loading/stress/strain over time and lock- in stresses, if applicable, between stages
• Prescribed displacements or jacking loads may be used as spans are completed
• Time-dependent material properties include stress related concrete creep and shrinkage to CEB-FIP Model Code 1990, (and others) and includes creep recovery
• Custom time-dependent curves for particular material properties and codes
• Use single or multi-tendon wizards to define and assign tendon properties and time-stages to features of a model.
• Steel relaxation, time effect on elastic modulus, tendon post-tensioning losses from creep, shrinkage, and superimposed loads
• Cumulative effects can be reported separately for each loadcase, such as post-tensioning effects, or for the effects of just creep and shrinkage
• Incremental effects can also be specified allowing you to view and assess the net changes to the structure since the previous stage.

Typical staged construction methods supported

• Staged placement of beams and slab for continuous structures (PCC beams or steel beams)
• Cast insitu span-by-span construction of continuous beams
• Precast segmental span-by-span erection
• Cast insitu balanced cantilever construction
• Precast segmental balanced cantilever construction
• Progressive erection of precast segmental decks
• Incremental launching
• Balanced placement for cable-stayed bridges

Stationary / travelling formwork 

Span-by-span 

The erection of all segments for a span in a set, which is then aligned, jointed, and ultimately, usually, longitudinally post-tensioned together to make a complete span. 

In LUSAS, this can be modelled as a line beam model with optional fleshing of the deck cross-section to show results contours. 

The animation below shows the construction sequence for the twin rib span-by-span example shown (substructure not included). The analysis can incorporate post-tensioning  between stages, and creep effects as construction continues, as required.

Progressive placement 

A one-directional placement process where bridge segments are placed in sequence, extending out over supports as an ever increasing cantilever, until the next support is reached.

Progressive placement with jacking-up of supports

A one-directional placement process where bridge segments are placed in sequence, extending out over supports as an ever increasing cantilever, until the next support is reached and then jacked-up into position.

Balanced cantilever

The building of a bridge superstructure from both sides of a pier in a scales-like fashion. 

Using LUSAS, creep / shrinkage analysis can incorporate an age attribute (for precast elements) and checks on robustness can also be made as, for example, where a segment may be inadvertantly dropped by crane and where dynamic effects (impulse) are important. 2nd order (P-delta) effects could also be included.

Incremental launching  Incremental launching involves the casting of a continous chain of bridge segments on-site adjacent to the actual location of the bridge and then pushing the growing superstructure out over temporary and permanent supports at the bridge's location. A good example of a bridge built using this method of construction is the Blackwater Viaduct in the Republic of Ireland. Using LUSAS, incremental launching can be carried out for both in-line deck launching, or for a curved deck launch. Modelling of incremental launching can be done in two ways, either by pushing the model over a series of fixed supports or by activating and moving a series of supports backwards under a model that is incrementally being added to. Examples of both methods are shown below.

Photo: Benaim

Click to play each movie (in new window)

Staged Construction Analysis : Example of use

The Original I95 Mississippi River Bridge was designed to be a record-breaking, cable-stayed structure linking the States of Illinois and Missouri in the USA, helping to relieve traffic on existing bridges across the river.  Designed by Modjeski & Masters for its clients Missouri and Illinois Departments of Transportation, staged construction facilities in LUSAS Bridge were used to model an 800 day construction period, followed by a 10000 day period to allow for creep over that length of time.

This 

Post-tensioning

Certain types of staged construction analysis may also require post-tensioning. See the post-tensioning product information page for more details.