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Structural Engineering Feasibility Study – Creating Stair Opening in a Hollow Core Slab, Vienne

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Summary: SARL Dobson Structures evaluated the feasibility of creating a stair opening in a hollow core concrete slab within a historic property. The structural survey confirmed the opening could be made without compromising the slab's integrity. Additionally, recommendations were provided to address the unfinished alcove opening with a safer, more durable solution, including lime-based mortar and improved steelwork.



SARL Dobson Structures was commissioned to assess the feasibility of creating a stair opening in a hollow core concrete slab within a historic property. The building, primarily constructed in stone, exhibited evidence of prior modifications, necessitating a thorough structural investigation.

During the initial site visit, we conducted a detailed structural survey to evaluate the building's current integrity. Observations revealed significant changes over the last four decades, including:

  • Alterations to the wall build-up on the first floor (roof removal and vertical extension),

  • Installation of hollow core precast planks, likely for rapid construction of the first floor, and

  • An unfinished alcove opening, lacking a proper lintel and incorrectly finished with cement-based mortar.

To address the client’s request, we verified the slab’s span direction and confirmed it adhered to standard construction practices. This analysis determined that, in principle, creating an opening for the staircase would not compromise the slab's load-bearing capacity.

Regarding the unfinished alcove, we identified the existing condition as unsuitable for long-term stability. The reliance on friction and shear resistance in the cement-based mortar posed risks, particularly given the property’s location in a low-to-moderate seismic zone. We recommended replacing the mortar with stone and lime-based mortar, followed by the integration of a refined steelwork solution. This solution, along with member sizing and detailed drawings, was provided to the client in our report.

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