Mastering Complex Precast Stairs: A Deep Dive

We’re glad to present an interview with Kalpana Subandh, Project Manager at StruEngineers India, with over 20 years of detailing (draughting) precast elements & structure with special expertise in precast stairs detailing, including those having complex geometries.

We’re sure her insights would be valuable for understanding the complexities and innovations in the field.

Let's dive into the conversation to learn more about this fascinating aspect of the precast construction industry.

Host: Hi Kalpana, thank you for joining us today. We're excited to learn more about the fascinating world of precast stairs and more so, the ones having complex shaped & geometries. Could you start by giving us a brief overview of why precast stairs are becoming so popular in the construction industry?

Kalpana: Hi, thank you for inviting me for the discussion. Precast stairs have revolutionized the construction industry due to their efficiency, durability, and aesthetic flexibility. Nearly every building features stairs, and using precast concrete allows us to ensure uniform quality, strength and durability while significantly reducing construction time and costs. This is especially beneficial for large-scale projects where the repetitive nature of stair flights can be efficiently managed through precast solutions.

Host: Yes, most of us are aware of the advantages of having precast stairs in construction projects. While straight-flight precast stairs are quite common, we also see many precast stairs in various shapes and complex geometries. Can you explain why there is a need for precast stairs with such intricate designs?

Kalpana: Yes. Complex geometries in precast stairs are utilized for several reasons.

·      First, there's the aesthetic appeal - unique and intricate designs can enhance the visual appeal of a building, creating a distinctive architectural signature.

·      Then, there are the functional requirements - complex shapes can optimize space usage, especially in irregular layouts.

·      Additionally, certain geometries can better distribute loads, reducing the need for additional supports and optimizing material usage.

Host: Interesting. Could you give us some examples of common complex geometries in precast stairs?

Kalpana: Sure. Some common complex geometries include spiral stairs, which wind around a central column and save space while providing a visually striking element. Winder stairs have triangular steps that allow the stairs to change direction, making efficient use of limited space. Split stairs, or bifurcated stairs, create grand entrances and facilitate smooth flow in large buildings. And cantilevered stairs appear to float without visible supports, providing a modern, minimalist look.

Source: www.researchgate.net

Source: www.researchgate.net

Host: Let’s discuss curved or winder precast stairs - what unique design challenges do these stairs present?

Kalpana: One needs to remember that a flight of stairs is a single precast element – even the curved ones. If we were to take the example of winder precast stairs the challenges that present themselves are:

·      Torsional Stress - due to the angled transitions at the winder steps, causing stress at turning points.

·      Axial Load - distributed across the stair flight, with higher stress concentrations at the landings and points where the winder steps change direction.

·      Horizontal Thrust Forces - at the winder transition points. There are horizontal thrust forces acting outward, especially where the direction of movement changes, requiring strong connections at these points.

·      Bending Moments - occur at the winder steps where the cantilever effect is more pronounced due to the change in direction and the irregular shape of the steps.

·      Shear Forces - are concentrated at the transition between straight and winder sections, as well as at the points where the steps meet the supporting structure, to prevent lateral movement.

·      Dynamic Loads: Foot traffic introduces dynamic loads, particularly at the winder steps where changes in direction increase impact and stress, necessitating reinforcement.

·      Seismic Forces: In seismic zones, winder stairs require strong connections to resist lateral forces, particularly at the winder section, which may be more vulnerable to seismic activity due to the change in direction.

Copyright: www.struengineers.com

Copyright: www.struengineers.com

Copyright: www.struengineers.com

Host: That’s quite complex as compared to straight flights of precast stairs!

What are the most crucial points to consider while detailing precast stairs, especially those with complex geometries? What inputs need to be clear, and what are the challenges that might arise?

Kalpana: In my previous answer, I talked about some additional forces that act on the stairs due the complex geometry itself. Therefore, both design and detailing of precast stairs with complex geometries is a meticulous job and involves several crucial considerations.

·      Accurate Measurements: We’ve to ensure that all dimensions are precise to avoid any issues during manufacturing and installation.

• Clear Specifications: Detailed specifications for materials, reinforcement, and connections to ensure structural integrity.
• Load Calculations & distribution: Properly calculating all loads, including dead loads, live loads, and any additional forces such as seismic or wind loads and ensuring the load is evenly distributed so that the structure can handle the various stresses and forces.
• Reinforcement Details: Precise detailing of reinforcement to handle complex stress distributions, torsional forces, and bending moments.
• Connection Points: Ensuring all connection points are clearly defined and designed to handle the anticipated forces.
• Coordination with Other Trades: Coordinating with other trades to ensure there are no conflicts with plumbing, electrical, or HVAC systems.
• Site Constraints: Considering site-specific challenges and ensuring the design fits within the available space without compromising functionality.

Host: Excellent insights. Now, tell us how do you and your team address these challenges and manage to work with such high levels of precision and accuracy at an amazing speed?

Kalpana: We use advanced tools and software to meet these challenges. One of the key tools we use is our own proprietary software, StruSoft IMPACT. It enhances our efficiency and accuracy by facilitating:

• Automatic Shop Drawings: StruSoft IMPACT generates precise shop drawings automatically, which saves a tremendous amount of time and ensures all details are accurate.
• Automatic Material Take-offs and Bar Bending Schedules

This combination of automation and advanced functionality allows us to handle complex geometries and challenging projects efficiently.

Host: That's impressive! It was nice knowing about your expertise in precast stairs design & detailing and thank you for sharing how you leverage technology to overcome these challenges and achieve such remarkable results, Kalpana.

Kalpana: Thank you. It's been a pleasure discussing these topics with you.

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Want to learn more about precast stairs and how they can elevate your next construction project? Connect with the team at StruEngineers India to discuss your specific needs and explore innovative solutions.

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