Masonry Walls as Bracing for Double Storey Building Columns: Sufficiency and Considerations

Introduction

The work of columns in a building is primarily to transfer loads from the upper levels to the ground. When walls are constructed around columns before the columns are cast in place, these walls can initially bear a significant portion of the loads from the slabs and upper levels, eventually helping to form a vertical structure. In some cases, walls can take on the role of bracing for columns, but the sufficiency of this bracing must be carefully evaluated by structural engineers.

Masonry Walls as Bracing

Masonry walls do offer a form of bracing. However, the question of whether this bracing is sufficient to support the columns adequately requires a detailed structural analysis by an expert. The role of masonry walls as bracing supports the vertical columns and helps them to maintain their position, which is crucial for the structural integrity of the building.

RCC Frame with Masonry Infill

Lateral Restraint and Strut and Tie Method
Frame structures are typically not designed to treat infill masonry solely as a structural element. In such structures, load-bearing elements must be reinforced concrete (RCC) or structural steel. However, masonry infill significantly enhances the lateral stability of the frame structure. Through the application of the Strut and Tie method, masonry walls act as a strut, providing considerable support against shear failure and collapse.

Masonry Behavior

When lateral loads are applied to an RCC frame with masonry infill, a gap often forms between the RCC frame and the brick masonry at the off-diagonal corners (B-D). Meanwhile, the other diagonal corners (A-C) press against the brick masonry, inducing compression. This compressive force strengthens the masonry infill, making it behave as a strut. The failure modes of the brick infill can be either:

Compression, where bricks at the diagonal corners (A-C) are crushed. Shear, where diagonal cracks form along the masonry-mortar joints.

Building Code Considerations

According to TMS 402/602 Building Code Requirements and Specifications for Masonry Structures, masonry walls are generally considered to provide lateral bracing. However, the reliance on this bracing is not always advisable, especially in cases where walls have been removed during renovations, compromising the structural integrity of the building.

For structures where masonry walls act as a critical component of the bracing system, thorough structural analysis and design are essential to ensure the safety and stability of the building. Consulting with a structural engineer is crucial to address any concerns and to ensure that the building meets the necessary safety standards.

Conclusion
While masonry walls can provide necessary bracing for columns in a double storey building, the sufficiency of this bracing should be evaluated by a qualified structural engineer. Adequate lateral restraint and support are crucial for preventing structures from shear failure and collapse. Proper planning and design, including adherence to relevant building codes, are key to ensuring the safety and stability of buildings.