A common requirement in property development is to reuse all or part of the existing structural frame, floors or façade of the building. Where there is a lack of information on the existing building, for example through lack of drawings or knowledge of the construction materials’ properties, an investigation is required to provide sufficient information to the engineer.
RC Framed Buildings
In reinforced concrete framed buildings, Moorhead Richardson can determine the strength of concrete and reinforcement.
Concrete strength is best determined by extracting concrete core samples, which are tested in the laboratory to establish compressive strength. To gain a wide spread of results, while reducing the extent of sampling, there are complementary non-destructive testing (NDT) techniques, such as:
Ultrasonic Pulse Velocity (UPV) testing (using a ‘Pundit’),
which can provide an estimate of concrete quality based on the velocity of a signal through a concrete element.
Rebound hammer testing (Schmidt Hammer), which can estimate concrete quality based on surface hardness.
The reinforcement distribution in the concrete frame and floors is determined using a cover meter and radar scanner (or Ferroscan) to map out the position of embedded reinforcement bars. Some localised exposure of the reinforcement is normally undertaken to confirm bar size, type and condition.
A sample of the exposed rebar can be taken to determine its tensile strength in the laboratory.
In addition to strength testing, concrete core samples can be tested in the laboratory to determine cement content, sulphate content and alkali content, or subjected to petrographic examination to estimate water:cement ratio, cement type, aggregate type and a number of other characteristics.
Reinforcement Scanning Surveys (Ferroscan)
Using Ground Penetrating Radar technology (GPR), embedded reinforcement details can be obtained non-destructively.
A grid is placed on to the concrete surface and scans undertaken in the X & Y directions. Once processed, the data can provide a 3D view of the scanned area.
It is often desirable to reuse the building’s foundations, even if most of the superstructure is to be demolished. Moorhead Richardson is able to undertake an investigation of the existing foundations by scanning and intrusive investigation, such as deep coring, of the ground or basement slab to determine the thickness, locations of pads, reinforcement layout etc.
Steel Framed Buildings
In steel framed buildings, Moorhead Richardson can determine section sizes and connection details for the engineer. This often requires the careful removal of the encasing concrete to expose the structural details.
Moorhead Richardson is experienced in limiting to a minimum the amount of intrusive work while still gaining the required information. In test locations, a sample of the structural steel can be taken, which will be physically tested in the laboratory to determine its tensile strength and chemically analysed to estimate its type. Together, the results are used to estimate the steel grade. Measured structural details can be compared to historic and modern standard section sizes to provide the engineer with the details of the structural element used.
A common development strategy is the removal of structural elements within the building, such as floors and frame components, whilst retaining the façade. Moorhead Richardson has experience in such façade retention investigations, where there is the need to determine how the building façade is connected to and supported by the structural frame.
Resistance to Fire
Reinforced concrete elements resist the impact of fire through protection provided by the concrete cover to the reinforcement. British Standards specify minimum depths of cover for different structural elements. As part of a fire assessment, Moorhead Richardson can undertake a survey of a building to determine the depth of concrete cover across representative elements.
Warehouse Slab Investigations
In factories and warehouses, the building occupants often need to install racking and shelving, and check that mechanical handling equipment, such as forklift trucks, can operate safely on the ground bearing floor slab.
Moorhead Richardson is experienced in these types of investigation and, by arranging the attendance of a ground investigation company, can establish the strength of the concrete slab and the supporting ground conditions beneath. Using guidance notes, it is possible to assess the load carrying capacity of the floor and its suitability to support specific racking loads and vehicle wheel loads.
In some cases, it is not possible to prove the load carrying capacity of a suspended floor or structural element through calculation, or the theoretical calculations show the element to fail marginally.
In these circumstances, Moorhead Richardson can undertake a load test of the element. This entails gradual loading under controlled conditions with water in a tank or metal weights. As the element is loaded and unloaded in cycles, dial gauges placed beneath are monitored. At the end of the loading cycles, it is possible to ascertain the load supported and the percentage recovery of the element. Beneath the loaded areas, catch-scaffolds are placed to ensure a safe distribution of the load should sudden failure occur.
Following the completion of siteworks, all retrieved samples are tested in a UKAS accredited laboratory, where applicable. On receipt of the test results, Moorhead Richardson will prepare a report. The report may be purely factual, if requested by the client, to allow the client’s engineers to make their own interpretation of the investigation findings. More usually, Moorhead Richardson will provide an interpretative report that assesses the investigation findings in relation to current British Standards, codes of practice and industry guidance.