Accommodating Movements in Facades

The connection between a building's facade and its primary structure is like a duo dance, posing some tricky challenges! The facade, the stylish outfit of a building is directly linked to the building's movements. So, when the structure decides to groove and shake, the facade can't help but follow along. Unless addressed early in the design process, the consequences can be a real showstopper!

The movements experienced by buildings are primarily due to live loads such as users, wind, and seismic activity in addition to temperature and moisture fluctuations. The components respond differently to these forces for several reasons such as:

Thermal Response: Different materials used in construction have distinct thermal properties, and hence when exposed to temperature fluctuations, these materials expand or contract at different rates. As a result, the components of the building may undergo varied movements, potentially causing challenges in maintaining structural stability.

Material Characteristics: The choice of materials can influence the behavior of facade to external forces. For example, metals, concrete and plastics exhibit different degrees of flexibility, contributing to variations in how different building components, such as facades, beams, and columns, respond to applied loads.

Construction Techniques: Advancements in construction techniques have introduced innovative methods and materials that allow for greater architectural freedom and efficiency. However, these modern techniques may also introduce additional complexities in managing structural movements. For example, lightweight construction materials might offer cost and design benefits but could result in higher deflections under load.

Architectural Elements: The design of architectural elements within a building can significantly influence its response to movements. Features such as cantilevered facades, large-span roofs, or intricate geometries can introduce unique challenges. These design choices may result in uneven distribution of loads, increased deflections, or localized stress concentrations.?

Effective mitigation of the issues associated with movements in facades requires consideration of key factors in design, construction, and maintenance.

Coordination with structural team - For almost all types of facades, the dead load of the system and associated supports along with the different applied loads are carried by the primary structure of the building.

Failure to provide sufficient allowance for in-service movements in the connections between fa?ade and structure will result in load being transferred through elements of the building envelope, which they are not designed to carry. This may result in leaks, cracks in brittle elements, failure of connections, buckling of mullions and breakage of glass.

To avoid these problems, it is important for the structural designers to engage with the fa?ade contractor’s designers to understand the requirements and limitations of the facade bracketry. Structural elements should be chosen such that the movements which the cladding has to accommodate are reasonable and unusual movement requirements are not imposed on the cladding.

It is also important for the structural engineer to provide his movements report to the fa?ade designer, enabling the fa?ade team to cross verify the fixation capacity.?

Customization and Adaptation: Facade systems need to be customized to suit the specific requirements of the project.

Stick curtain wall systems: Stick curtain wall systems, while flexible and customizable, have limitations to accommodating significant building movements. The individual mullions and transoms are connected using mechanical fasteners, which may not allow for large amounts of movements. If excessive movements are induced on the system, it can lead to joint failure, resulting in leaks, cracks, or compromised system performance.

Unitized curtain wall systems although limited in its flexibility and customization, is advantageous in accommodating building movements. The prefabricated units can be designed to accommodate greater range of movement while maintaining the integrity and performance of the system.

External Connections: It is a common practice these days that the building fa?ade is integrated with external shading devices. These elements ensure a greater indoor comfort levels as they block sunlight and reduce the amount of solar gain.

While the external shades are great for the energy efficiency of the building, it is important to carefully design the connections of these elements to the main structure. Mostly of the time, the connections are penetrated through the fa?ade joints, to be fixed back to the main structure.

The facade elements and shading devices may experience different rates of movement and if the connections through the facade joints do not allow for independent movement of the shades and the facade, it can lead to compromised weatherproofing creating potential points of entry for air and moisture.

Lack of movement in the connections, can also lead to localized stress points, potentially causing cracking, deformation, or failure of the facade elements.

The connections through the facade joints can also create thermal bridging, undermining the energy efficiency of the building resulting in increased heating or cooling loads.

Hence careful design considerations are required when installing external shading devices.

Employing flexible connections or joint systems that allow for relative movement between the shading devices and the facade elements will help mitigate movement issues at fa?ade joints. Using thermal breaks around the connections will allow for efficient thermal performance of the system.

?A coordinated approach enhances the overall performance and safety of the building and minimizes potential structural issues that may arise from movements. Instead of working in isolation, a coordinated effort among facade engineers, architects, and structural engineers is essential to effectively address facade movements, paving the way for successful and resilient architectural projects.