ESR2: Reduction of uncertainty in assessing concrete strength of existing structures

In 2013, the 8-storey Savar building in Dhaka-Bangladesh disasterous collapsed resulting in a deathtoll of more than 1100. This resulted in the deadliest garment-factory accident in history, as well as the deadliest accidental structural failure in modern human history. Following the collapse, the “Accord on Fire and Building Safety in Bangladesh” was established to maintain minimum safety standards in the Bangladesh textile industry. Nearly 1600 factories were covered by the Accord, representing around one third of the Bangladeshi textile industry.

As part of the Accord, Arup was commissioned to carry out structural inspection on the factory buildings. The structural assessment of existing buildings require the availability of information regarding the general arrangement of the structural elements with all the dimensions and the cross-section dimensions of all these elements. In addition, information about the loads applied to different parts of the building need to be assessed. Finally, the properties of the materials used in the structure has to be assessed. Among all the information required to carry out the structural assessment, the material properties proved to be the most difficult to assess. Accurate measurement of reinforcement inside the reinforced concrete members can be made with specialised equipment. At the time of constructing many of the textile factories in Bangladesh, concrete was hand mixed on site and due to the lack of natural gravel, normally using broken brick as a substitute, quality control was not tight and there are a lack of records on concrete test results from the construction time.

All these factors resulted in a large strength variation of concrete strength, which needs to be accurately assessed on the basis of the existing structure. Currently, the methods available for the non-destructive assessment of concrete strength are not able to provide the degree of accuracy required to accurately and safely assess the already loaded buildings.

This situation is resulting in a high degree of uncertainty in the structural assessment. TRUSS will develop new reliable methods and techniques to assess the strength of stressed concrete in existing buildings. The results are to be directly applicable into the building structural assessment and for that they need to reliable.

In the 1st phase, Arup and UCD will establish the statistical correlation between tested and measured concrete strength of existing structures based on existing methods and techniques. In the next phase, new methods and techniques will be suggested and studied in details to assess their applicability, factors influencing results and variation of results. At the end of this phase, the methods and techniques will be refined to improve their reliability and accuracy.

In the 3rd phase, the newly suggested methods and techniques will be used on actual structures and compared with previous results obtained from the currently existing methods.

The objective is quantifying the uncertainty in concrete strength assessment of existing buildings. A statistical correlation between tested and measured concrete strength of existing structures will be made based on existing methods and techniques. New methods will be suggested and compared to results on actual structures using currently existing methods.
New methods and techniques for assessing concrete strength in existing structures more accurately and reliably than the current methods.
This project involves a secondment of some months to University College Dublin (UCD) (supervised by Dr. McNally). The ESR will use the material and structural laboratory facilities in UCD to carry out analytical and experimental work on the new methods and techniques.
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