If the Load Path Isn't Straight, the Load Must Then Turn

𝘉𝘶𝘪𝘭𝘥𝘪𝘯𝘨𝘴 𝘚𝘰𝘮𝘦𝘵𝘪𝘮𝘦𝘴 𝘙𝘦𝘧𝘶𝘴𝘦 𝘵𝘰 𝘣𝘦 𝘖𝘳𝘥𝘪𝘯𝘢𝘳𝘺

Sometimes a building does not only need to be functional.

An owner wants a spacious and grand lobby for his hotel. Those weird vertical pillars are not allowed here as they obstruct the view. But this strict requirement does not apply to the room floors above.

A premium condominium owner prefers an all-rounded living experience: a facility floor with a gym, swimming pool and rock-climbing zone. Above this floor are two tower blocks hosting the residents, while below it is a car park with as little obstruction as possible.

These are typical situations that introduce irregularities into a structure.

𝘞𝘩𝘢𝘵 𝘵𝘩𝘦 𝘖𝘸𝘯𝘦𝘳 𝘋𝘳𝘦𝘢𝘮𝘴, 𝘛𝘩𝘦 𝘌𝘯𝘨𝘪𝘯𝘦𝘦𝘳 𝘉𝘶𝘪𝘭𝘥𝘴

A pathway must be provided for every load to travel to the foundation.

When the owner wishes for the non-existence of a column in the hotel lobby, the engineer cannot simply grant the wish. Instead, the engineer provides a transfer element that redirects the load from the floating column to walls or columns that continue towards the foundation. A transfer can take the form of a beam or slab.

A table is a good illustration of a structure. Two stacked tables are then a simple example of an irregular structure with a transfer. The top of the bottom table acts like a transfer slab: it receives the load from the table above and redirects it to its own legs.

Now imagine the same principle in a high-rise building. The transfer element must complete this load delivery to the supports below while carrying the accumulated loads from the structure and occupancy above.

 

𝘛𝘳𝘢𝘯𝘴𝘧𝘦𝘳 𝘪𝘴 𝘔𝘰𝘳𝘦 𝘵𝘩𝘢𝘯 𝘢 𝘉𝘪𝘨 𝘚𝘵𝘳𝘶𝘤𝘵𝘶𝘳𝘦

As you can imagine, significant concentrated actions, including shear and bending, can develop within the transfer element. Providing sufficient strength is therefore merely a basic requirement for a sound design.

Concentrated loads and large transfer elements also demand that engineers deal with deflection, creep, cracking and differential movement. These can affect façades, partitions, waterproofing and finishes even when structural strength remains adequate.

During construction: dense reinforcement, tricky anchorage, tight tolerances, temporary propping and work sequencing each introduce additional difficulty for the builders.

 

𝘓𝘰𝘰𝘬 𝘖𝘶𝘵 𝘧𝘰𝘳 𝘵𝘩𝘦 𝘞𝘦𝘢𝘬𝘦𝘴𝘵 𝘓𝘪𝘯𝘬 𝘪𝘯 𝘵𝘩𝘦 𝘌𝘯𝘵𝘪𝘳𝘦 𝘊𝘩𝘢𝘪𝘯

Irregularities do not only affect the gravity load path.

Consider a tower sitting on an open podium. The upper floors may be fully supported by shear walls, while the podium has fewer vertical elements and larger open spaces. Underneath, the car park needs wider bays and clear paths for vehicles.

The lateral stiffness of the building may therefore change abruptly, with a significant reduction around the podium or car park levels.

Under lateral loading, deformation can concentrate around this softer level rather than being distributed more evenly over the building height. This is the basic concern behind a soft-storey condition.

 

𝘐𝘯𝘵𝘦𝘨𝘳𝘢𝘵𝘦 𝘒𝘯𝘰𝘸𝘭𝘦𝘥𝘨𝘦 𝘪𝘯𝘵𝘰 𝘠𝘰𝘶𝘳 𝘗𝘳𝘰𝘧𝘦𝘴𝘴𝘪𝘰𝘯𝘢𝘭 𝘞𝘰𝘳𝘬𝘧𝘭𝘰𝘸

Our Engineer's Cheat Sheet – Irregular Framing & Transfer Levels compresses the key transfer concepts, framing risks and review checks into a one-page reference for use when time is limited.