David Sanderson, Trimble’s analysis and design product manager, explains what Staged Construction Analysis is and its impact on structural engineering practices
Ultimately, it comes down to accuracy. As buildings grow taller and more complex, the need for increasingly precise and insightful structural analysis grows alongside them. While the principles behind Staged Construction Analysis (SCA) are not new, its integration into structural engineering software now enables designers to replicate real-world effects on the structure and construction process in stages.
Understanding SCA
SCA is an analysis procedure that recognises the changing state of the structure over time. At each stage of construction, any or all of the following may change:
- The extent of the physical members included in the model.
- The material properties (particularly for time-dependent materials like concrete).
- The types and scale of applied loads.
SCA blends the strengths of traditional subframe analysis with modern 3D analysis, identifying that loads, stiffness and member behaviour don’t appear all at once but evolve with each new pour, connection or floor.
It enables engineers to add in detail to simulate how a structure can take shape and perform at different build stages, calculating accordingly. This can lead to significant design efficiencies, reduced conservatism and a better reflection of how the building will actually behave, both through construction and beyond.
This analysis process is typically more relevant for taller, concrete-based structures, where effects like creep, shrinkage and stiffness variation can influence the structure’s final state. It gives structural designers the tools to investigate how construction speed, load and timing assumptions influence design outcomes.
Why use SCA?
More efficient design envelope that eliminates extremes
Before SCA, engineers would use a combination of traditional 3D analysis and what’s known as chasedown analysis – a method designed to emulate the traditional subframe analysis by chasing reactions down through the structure. The result is a considered envelope of possible results, often unnecessarily conservative and leading to overdesign.
However, SCA can produce results at both ends of the spectrum but also gives engineers the option to eliminate unnecessary extremes. Taking a simplified example, in a three-storey structure with a significant transfer beam, a traditional 3D model might show large bending moments driven by assumed global displacements. Meanwhile, a chasedown analysis might produce a lower (but arguably more realistic) hogging moment at a critical support.
SCA allows for variable inputs such as construction speed and load percentages at each stage, so engineers can run scenarios that reflect the real conditions of the build.
In one example, the same beam might show a bending moment of 295 kNm under traditional analysis, 411 kNm under chasedown and something in between (eg 310-332 kNm) using SCA. That middle ground may offer a more economical yet still robust design.
By understanding the load paths and stress distributions at each construction stage, engineers can identify areas where materials can be used more efficiently while reflecting a more realistic construction programme. This potentially reduces the need for temporary supports or modifications as construction progresses, leading to cost savings and a more sustainable use of resources.
It’s important to note that if different ways are selected, be sure to understand the implications of the criteria chosen.
Simpler wind and seismic drift checks save design time
Tall buildings bring another challenge in the form of conflicting stiffness demands between second-order analysis and lateral drift checks. In traditional workflows, some engineers often duplicate models. One is set up for strength design and one for drift, with different stiffness modifiers applied to each. This is time-consuming and opens up room for potential error, especially as the design evolves.
SCA helps resolve this. While it doesn’t produce isolated loadcase results (since it builds up loading through stages), engineers can continue to use an unstaged 3D model just for drift checking, applying appropriate stiffness modifiers for that task. Meanwhile, the SCA model handles the strength design. This removes the need to maintain two separate design models and simplifies coordination.
How SCA helps reduce second-order effects
In tall buildings, second-order effects – like sway and bending – can amplify internal forces and make a structure appear to need more strength than it actually does. Traditional analysis methods often assume fixed stiffness throughout the structure’s life, exaggerating these effects and leading to overdesign. But that stiffness isn’t constant during construction.
By using SCA, engineers can reflect how a structure changes during construction. For example, it accounts for the fact that not all parts of the building are in place or fully hardened at the same time. They can better understand and optimise these effects in the final state of the building.
The result is not only a safer and more efficient structure but also potentially significant material savings, which, of course, can translate to reduced cost and lower environmental impact.
Implementing SCA to simplify workflows
While SCA offers greater accuracy and insight into how a building behaves during and after construction, managing the complexity manually can be time-consuming.
Tools like Tekla Structural Designer simplify this by integrating SCA directly into the core analysis and design workflow, making it an accessible and valuable strategy for modern structural engineering projects. Engineers can define construction stages, apply time-dependent loading and analyse the structure’s response all within a single model environment.
This simplified approach eliminates the need for maintaining separate analysis models, reduces the risk of error and supports better-informed design decisions earlier in the design process, with detailed reports aiding in documentation and decision-making processes.
SCA is not about replacing structural engineers’ knowledge; it’s about enhancing it.
Learn more about Staged Construction Analysis by watching Trimble webinars
*Please note that this is a commercial profile.
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