CROSS Safety Report
Failure to grout steel frame bases
A reporter describes a problem that arose during the construction stage of a project when a steel frame supporting pipe and cable racks was loaded before the frame baseplates were grouted.
Key Learning Outcomes
For civil and structural design engineers:
- Clearly specify on drawings how bases are to be made including holding down and grouting requirements
- The various BCSA Codes of Practice for the erection of steelwork help designers to design and detail structures so they are easier to erect
For principal contractors, contractors and steelwork subcontractors:
- Grouting of bases should be carefully considered and planned as part of steelwork erection
- The BCSA Code of Practice for Erection of Low Rise Buildings details good practice in steelwork erection including use of risk assessment and method statements (RAMS)
- Adequate quality assurance and competent supervision helps to ensure steelwork is installed in accordance with the design
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The Full Report below has been submitted to CROSS and describes the reporter’s experience. The text has been edited for clarity and to ensure anonymity and confidentiality by removing any identifiable details. If you would like to know more about our secure reporting process or submit a report yourself, please visit the reporting to CROSS-UK page.
A reporter describes a problem that arose during the construction stage of a project. A steel frame to support pipe and cable racks was designed to be erected and have baseplates grouted before it was loaded with services. The gap between the substructure and underside of the baseplates was specified to be filled with non-shrinkable cementitious grout. However, the frame baseplates, which were fixed with cast-in bolts, were not grouted before the erected steel frame was loaded with services.
The reporter goes on to say that the cast-in bolts were not designed to take compression or lateral loads and could have buckled, bent or been damaged during construction. The erection sequence for the steel frame did not comply with the approved drawing which showed the grouting should have taken place before loading of the frame.
The reporter concluded that, in this case, the contractor’s method statement should have provided for safe construction and ensured the structural integrity of the permanent works.
Expert Panel Comments
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Expert Panels comment on the reports we receive. They use their experience to help you understand what can be learned from the reports. If you would like to know more, please visit the CROSS-UK Expert Panels page.
Failure to adequately fix a structure to the substructure can occur for many reasons including the base being poorly detailed, cast-in fillers not being removed, the grout not being suitable or, as in this case, the grouting process not being undertaken. Bolt failure, baseplate failure and excessive lateral deflections of superstructures under loads could result from such errors.
Fixing, levelling and grouting bases
The design of the structure may require a particular method to be adopted when fixing, levelling and grouting bases – where this is the case the designer should specify it. Generally, however, column bases are adjusted for level using steel shims or folding wedges, no larger than necessary, positioned centrally under the base plate. Steel wedges may be symmetrically positioned around the perimeter of the base plate close to corners and the holding down bolts loosely tighten prior to the setting out being checked and the base grouted. The wedges can help avoid instability and overstressing of the holding down components during erection of steelwork which, it must be remembered, is a temporary stage. Designers must consider how steelwork could be erected when designing and detailing the bases, including, for example, considering required grout thickness and specification and the need, or otherwise, for grout inspection holes in larger baseplates.
In cases where there is a design interface between the designer of the substructure and the steelwork, there is the opportunity for risk to thrive; a concern that CROSS has identified often. Where design is fragmented, the responsibilities of each designer should be clearly defined with one designer taking the lead to ensure all interfaces are considered. CROSS-US report 992 - Steel column erection anchoring connection failure injured worker, published in 2021, describes how a construction worker was injured during the erection of a steel column due to shortcomings in erection procedures and inadequacies in a column base connection. Clarity of responsibility for column base design was also considered critical.
Where design is fragmented, the responsibilities of each designer should be clearly defined
In the case reported here, it appears the design clearly indicated the need to grout bases prior to loading the steelwork. As suggested by the reporter, the contractor’s control systems should have had a series of hold points to ensure that each stage was completed before moving on to the next. It appears there may have been a basic lack of control on site. Competent supervision and good RAMS together with effective quality control on site would normally guard against such errors occurring. CROSS-UK report 1038 - Column stability during erection, published in 2021, noted the importance of RAMS for steelwork erection referencing the BCSA Code of Practice for Erection of Low Rise Buildings. This Code could be considered essential reading for all involved in the provision of steelwork frames, and particularly for designers and any supervisory site personnel where steelwork erection takes place.
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