Mullion and Transom Design for Curtain Walling Systems
The Four-Step Structural Calculation of Curtain Wall Framing — From Load Collection to Profile Selection, and Why Stiffness Governs
Course Description
Every glass facade is carried by a slender aluminium skeleton that nobody sees from the outside: the mullions running from floor to floor and the transoms spanning between them. This comprehensive technical CPD course works through their structural calculation in four steps, in a fixed order: collect the loads, build the structural model, find the forces, the reactions, and the deflection, then choose the section and check its strength.
You'll learn how the design wind pressure becomes a line load on a mullion and how glass weight becomes point loads on a transom at the setting blocks; how the bracket arrangement defines the structural model, why the spigot does not make a mullion continuous, and why the movement joint and the glass joint must never be confused. The course then turns the calculation around: the deflection limit — span over 200 with an absolute cap for framing under wind, span over 500 or 3 millimetres for a transom under glass weight — is set equal to the allowable value and solved for the second moment of area the profile must provide.
Presented by Eugene Korch (facade engineer and IAST Programme Director), the course answers the question that surprises engineers arriving from steel and concrete: why a curtain wall mullion is almost never sized by strength. The answer comes in three layers — the geometry of long spans, the material properties of aluminium with a third of steel's stiffness, and the economics that shape every manufacturer's profile range — and the strength check that remains is about thin walls buckling locally, not metal yielding.
Combining the four-step sequence with a complete worked mullion and worked transom — every number shown on screen — and a review of the errors seen on real projects, this course is designed to give you a framing calculation you can carry out, check, and defend, and reactions the bracket designer can trust.
Included in Facade Intelligence Professional Membership (FI PRO)
Learning Outcomes
By the end of this course, you will be able to:
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Distinguish the serviceability loads that govern deflection from the factored loads that govern strength, and translate between allowable stress and limit state formats
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Run the four-step calculation in its fixed order: loads, model, forces and deflection, section and strength
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Convert the design wind pressure into a line load on a mullion using the bay width, and the glass weight into point loads on a transom at the setting blocks
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Build the correct structural model from the bracket arrangement: simple span, continuous mullion, hung or seated sections
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Explain why the spigot transfers wind but carries no bending, and keep the movement joint and the glass joint apart
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Apply the two workhorse formulas: the mid-span moment of a uniformly loaded simple beam and its deflection
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Understand the second moment of area as pure geometry, and why manufacturers publish their catalogues sorted by it
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Apply the deflection limits: span over 200 with the absolute cap for framing under wind, span over 500 or 3 millimetres for a transom under glass
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Turn the calculation around: solve the deflection limit for the required second moment of area and pick the shallowest adequate profile
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Explain, in three layers, why stiffness governs curtain wall framing at storey height — geometry, material, and economics
What's Covered
Introduction
The hidden skeleton: mullions and transoms behind every glass façade.
The surprise for engineers from steel and concrete: sized by stiffness, not strength.
Scope: aluminium stick curtain wall framing, extending to unitised mullions.
The Calculation in Four Steps
The fixed order: collect the loads, build the model, find forces and deflection, choose the section.
The two workhorse formulas of the uniformly loaded simple beam.
The second moment of area: pure geometry, and the number the whole lecture leans on.
The hierarchy: glass to transom to mullion to bracket.
Collecting the Loads
Wind as the dominant action: pressure, suction, and the corner zones.
The line load on a mullion: design pressure times bay width.
Dead load: glass weight, framing weight, and the quick estimate from thickness.
Barrier loads where the wall doubles as a barrier.
Serviceability versus strength: different loads for different checks, and the allowable stress question.
Building the Structural Model
The mullion as a simple beam between floor-level brackets.
Single spans and continuous mullions: what continuity buys and costs.
Why the spigot does not make the mullion continuous.
Hung and seated mullions, and why the axial force rarely matters.
The transom bending in two directions at once.
Forces, Reactions, and Deflection
The mid-span moment and where it grows fastest.
The movement joint and the glass joint: two different joints in one mullion line.
Support reactions: the exact input the bracket design needs.
The deflection formula turned around: solving for the required second moment of area.
The deflection limits and the physical reasons behind them.
Choosing the Section, and Why Stiffness Governs
Picking the shallowest adequate profile from the manufacturer's range.
Layer one: geometry — deflection demand grows faster with span than strength demand.
Layer two: material — aluminium at a third of steel's stiffness.
Layer three: economics — why no manufacturer makes a profile where strength governs at storey height.
The strength check that remains: local buckling of thin walls.
Where strength can govern after all.
The Worked Example
A complete worked mullion: from bay width and storey height to the selected profile.
A worked transom: wind out of plane and glass weight in plane, together.
Reading the answer: which check governed and how much room is left.
Summary and Checklist
The four steps in their fixed order.
The principles that carry the subject.
The common mistakes and where they come from.
Where the results go: reactions to the bracket design, loads onward to the glass.
Course Schedule
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Course Overview
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Course Objectives
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How to Navigate the Learning Materials
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Introduction Video
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Lecture
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Post-Lecture Reading List
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Knowledge Check
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Certificate: Download & Share
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About this course
- £120.00
- Practice test questions
- CPD Certificate: 2 hrs
- Interactive 3D models
Your Instructors
Programme Director, IAST Eugene Korch
Eugene is a façade engineer and educator with extensive experience in building envelope design and technical specification. Through the Institute for Architectural Science and Technology (IAST) and Facade Intelligence, he delivers CPD training to architects and construction professionals across the UK. His teaching approach emphasizes practical application and accessibility, making complex technical subjects understandable for design professionals.
Who Should Enrol
This course is designed for:
Architects needing to understand what sizes the visible grid of a curtain wall and why profiles are as deep as they are.
Architectural Technologists working with curtain wall details and profile selection.
Envelope Designers coordinating framing depths, bay widths, and glass sizes early in design.
Façade Specialist Contractors requiring a working knowledge of the framing calculation behind their systems.
Junior Façade Engineers learning the mullion and transom calculation from load collection to profile selection.
Building Envelope Consultants advising clients on curtain wall engineering and system capability.
Structural Engineers needing to understand how façade framing is modelled and where its reactions land.
Project Managers overseeing projects where framing depth affects floor area, cost, and appearance.
Cost Consultants understanding how spans, bay widths, and deflection limits drive profile cost.
Design Managers coordinating façade and structural packages.
Course Details
Format: Self-paced online course with video lectures.
Duration: Approximately 2 hours.
CPD Points:2 hours structured CPD / 2 Learning Units.
Access: 12 months from enrolment.
Certificate: CPD certificate issued upon completion.
Prerequisites: A working grasp of basic structural mechanics (bending, shear, deflection, stress). Pairs naturally with Wind in Action and the bracket design courses, which use this course’s reactions.
What Makes This Course Different
The whole calculation in four steps, in the fixed order real projects follow — nothing skipped, every formula explained.
The calculation turned around: solving the deflection limit for the required second moment of area, the way profiles are actually chosen.
The stiffness question answered properly, in three layers — geometry, material, and economics — not asserted as a rule of thumb.
The strength check treated for what it is in thin-walled aluminium: local buckling, not yielding.
A complete worked mullion and transom with every intermediate value on screen, and the common mistakes reviewed against real projects.
Join the Facade Intelligence Professional Membership (FI PRO)
Membership fees start from £320 per year
Gain access to all upcoming seminars and a wide range of the most sought-after short courses.
Corporate discounts are available for teams of 10 or more.
For a bespoke quote, please contact our team at [email protected].
