أرضيات الايبوكسي Metallic Epoxy

Architects and design offices, often tend to perform the details of corner joints for Façades based on Aesthetic purposes and “to some extent” the performance impact, I said “to some extent” because they will not be able to cover the critical areas detail like Façade Specialists, in light of that, the specialist have to take responsibility of all critical areas on his shoulder, he must clarify the impacts of each proposal, to guarantee the best performance for building envelope, and façade fenestration.

One of the critical areas in the Façade packages is “The corner joint,” which simply means the intersection between two Elevations. whether at a 90-degree angle, or otherwise.

For Corner joints, we have two options to perform the detail and address the area:
The “Single Corner Mullion” or the “Double Mullion System”.

Here’s what to consider when choosing between them:

Single Corner Mullion:
. It may be purely aesthetic, but it is a structurally risky area due to its limitation in accommodating lateral loads (Wind and Seismic).

. High stiffness but less flexibility to accommodate lateral displacement differences between two perpendicular façade units.

. When seismic loads or thermal movement occur, stresses are likely to accumulate at the same point, increasing the risk of cracking, silicone failure, or even bending/ denting of the section itself.

. Difficulty achieving the required high "Drift Accommodation" in high seismic areas.

Double Mullion System:
. Each Elevation will move relatively independently, increasing the ability to absorb interstory drift.

. Easier control of water leakage and thermal movement.

. Better behavior in seismic events. That’s Why some Building Codes like AAMA 501.6 (Seismic Testing of Curtain Wall Systems) and AAMA 501.4 (Curtain Wall Seismic Performance) recommend the Double Mullion system in seismic areas or require some special conditions to accept the Single Corner Mullion and testing the behavior of corners in lateral pressure and earthquakes.

The Comparison between the two options has different aspects, each of which is a subject. But in general, each way has its pros. and cons., Also, we have to know that some building codes may force you to choose the option. e.g., the ASCE-7 code requires Curtain wall systems to withstand interstory drift, sometimes up to 2% – 2.5% of the floor height in high seismic areas. And this makes the Single Corner Mullion in a difficult situation to accommodate this large drift without silicon failure or sector denting.

In contrast, some codes allow the use of a single corner mullion but require greater tolerance for movement (AAMA 501.4 and ASTM E330), and using high flexible silicone materials (AAMA 808.2-92 and ASTM C1184), also perform seismic mock-up tests (AAMA 501.6 and ASTM E2126) To ensure the system's ability to handle displacements caused by earthquakes and strong winds.

At the end. I recommend keeping the following considerations in mind while you are performing the Corner joint design:
. The building corners are the most exposed points to wind pressure coefficients (GCp), often 1.4 – 1.6 times higher than the pressure on a flat surface façade.
.  A single corner mullion will be subjected to bi-axial bending (two-way bending) instead of one-way bending, increasing stresses.

By addressing these key points and aligning your design with relevant codes, you can select the optimal corner joint detail for your project.

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Written by Jehad Alkhandaq.