Orchard House – RC Column Strengthening using CFRP

Beta Scope

Orchard House project comprised the vertical extension of the inner city building to add two additional storeys. Our scope of works included:

• Detailed visual inspection.
• Desk study to review previous surveys.
• Evaluation of capacity of existing columns considering shape of some bull-nosed columns.
• Design of columns strengthening using Carbon fiber reinforced polymers (CFRP).
• Preparing method statement.
• Inspection of repair works.

Background

Beta Design Consultants were commissioned by the client, Jehu Group, to assess the current capacity of column sections and design required strengthening to accommodate future loading. This existing building was built in the 1960s and is proposed to have two further stories added to it. The existing columns require repairing and strengthening. Structural strengthening using Carbon Fibre Reinforced Polymers was the ideal option as the required increase in capacity was achievable with CFRP. The method offered remarkable advantages in terms of project programme and cost compared with other options such as strengthening with steel sections or concrete jacketing (concrete encasement).

Beta Approach

Column Strengthening Approach
We evaluated the capacity of existing sections and compared them with future loading to identify columns that require strengthening. Many conservative assumptions were made previously due to the absence of test results so the structural assessment was updated to consider the latest test results and remove any incorrect assumptions. The capacity of the existing columns was based on the survey results provided, no of rebar diameters and concrete compressive strength. The design was verified for each case and findings were presented for each column.

CFRP design calculations were prepared according to the Concrete Society TR55. The calculations are quite involved so BDC developed a Mathcad sheet to implement for each column loading. To ensure that the design calculations were accurate, BDC carried out an independent internal verification to ensure the Mathcad sheet was giving the expected results. Each column was re-evaluated internally by a different structural engineer working in a different team to offer the client assurance that the design quality satisfied stringent control measures.

Beta DC produced a proposed method statement for the repairs and strengthening that considered the condition of the existing columns and the proposed materials. The works were completed by Beton Bauen, a specialist concrete repair and strengthening contractor who are members of the CRA.