Structural Letter Report: Cracking Along Steel Fream Column
This structural inspection letter report was prepared and commissioned under the instructions of our client,
Sonia Marquez. We have been requested by our client to provide a structural assessment on the cracking developed at the steel frame column between the original property line and the extension at Andover Road, Twickenham. A single, non-disruptive site visit inspection was conducted on the Monday 5th February 2020. The weather condition at the time of the inspection was clear.
This report is intended primarily for information and is to be read in conjunction with any other specialist reports and investigations. In accordance with our standard practice we must point out that this report is based upon our inspection of
the premises and any other information made available to us, both written and oral, which we have assumed to be correct. Structural Engineering Services will not accept liability to any third party for any loss, consequential or otherwise, for whole or parts of the conclusion and recommendations provided in this report.
Brief Description of The Existing Property
The property is a two-storey semi-detached property build approximately around the 1930’s with a singlestorey rear extension added around 2006. The property appears to have been formed in solid brickwork façade with presumably a traditional cut roof. Steel frame has been installed to support the rear elevation opening.
The local geological map has been highlighted in the figure indicated below. The superficial deposit is Kempton
Park Gravel Member which is a combination of sand and gravel. The bedrock is London Clay Formation.
We carried out a non-intrusive general site inspection of the property, recording our observations and stating our conclusions in this letter report.
With regards to the interior of the property:
- Relatively small horizontal crack have developed at the steel frame column in the flank wall between the original property and the extension. The cracks are visible on both sides of the boxing out of the steel frame however, the cracks seems to be larger on the extension side of the property. The cracks are vertical and follow the boxing out of the steel to top of ceiling level. The crack seems to become slightly smaller at the top of the frame boxing. The room above was not inspected but we do not expect the cracks to have developed at first level however, this will need to be checked.
- The left hand side of the steel frame does not show any signs of cracking except small hairline crack extending from top of the steel frame to ceiling level, refer to image 5. The steel frame does not exhibit any signs of excessive deflections.
With regards to the exterior of the property:
- Small vertical hairline crack is visible on the external face of the property following the mortar line at the interface between the original and the extension of the property. The hairline cracking in the mortar seems to disappear above the base of wall. Crack width approximately 2mm
Cracks described above are likely to have developed due to differential settlement between the relatively shallow original footings to the main property and the new foundations to the extension. Since the cracking is predominantly on the flank wall side of the steel frame column it is possible that localised differential settlement is occurring at that location. No excessive deflections have been observed in the steel frame and ground conditions are such that we can within reason rule out heave or damage to foundations due to tree roots. Furthermore, the cracking locations and pattern seems to be inconsistent with excessive ground movement. However, further investigation can be performed to inspect the interface between the original and extension foundations in order to identify any damage or movement.
- This type of cracking is classified by Digest 251 ‘Assessment of damage in low-rise buildings’ as ‘cracks easily filled’ in category 2 of damage. The cracking on the internal face can be masked with suitable lining. External repointing of brickwork will be required to ensure weather tightness. It should be noted that the cracks may reappear in the future due to continuous differential settlement