Every connection is analyzed and properly fitted. Not a plate or bolt goes unturned. Safety is embedded in our culture. In addition to having dedicated Safety professionals on nearly all of our projects, all of our field Superintendents are OSHA trained. We know that higher levels of supervision ensure better safety and more efficient teamwork. Not a single aspect of it has ever been sacrificed for production. In fact, our Superintendents are mandated to manage each project with productivity and safety as balanced considerations.
We excel at detailed planning and coordination between our client, our shops, our field teams, our subcontractors and other trades. With expertise in a variety of fabrication types, our team can offer expert assistance with any aspect of your steelwork project. The family-run business operates out of Lancashire close to all major motorways and can be hired to work directly with clients, or as subcontractors, across the UK. In addition to structural steel fabrication, Bolton Steel Structures can also offer aluminium and sheet metal components. To find out more, get in touch with us for a free, no-obligation quote.
Formed in , Bolton Steel Structures Ltd has fabricated and erected numerous structural steel fabrications around the globe.
Structural Fabrication & Erection Work
Originally run by a father and son duo, Bolton Steel Structural has a firm place in the local and national business community. The primary structural interface affecting steel erection is how the frame is to be connected to its supports. UK practice is generally to use holding down bolts that are cast-in-place with some scope for lateral adjustment. Cast-in-place bolts have the advantage that they can contribute to the stability to the steel superstructure immediately — subject to suitable packing and wedging.
The problem with casting in bolts without adjustment is principally one for the foundation contractor and not the steel erector. Using post-drilled fixings requires that the equilibrium of the structure be temporarily secured using, say, guys.
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This is rarely economic for primary members of the frame but is often used for secondary members such as wind posts for glazing. These can be offered up after the main frame is securely aligned and held in position using the main frame whilst their base fixings are drilled. The same considerations apply where the steel frame has to be fixed to a concrete core or a masonry wall.
Ideally, an adjustable steel attachment plate should be cast into the wall, then surveyed and adjusted such that the subsequent process involves merely as steel-to-steel erection. In composite construction , the metal deck may need to be assessed for its ability to stabilise the steel members to which it attaches in the temporary condition before the concrete is placed and cured. The "wet concrete" stage is often when the decking is "working hard" to provide support for the dead load which is quite high.
Attention needs to be given to ensure that the asymmetric loading conditions that can arise are carefully controlled. Finally, primary frame members such as portal rafters may rely on secondary elements such as purlins, ties and knee braces for their stability — even under self-weight only. Occasionally these secondary elements may be timber. In all such cases it is necessary that the erectors have a clear understanding about how many secondary members need to be in place and how securely they need to be connected before the crane lifting the primary frame member is released.
The most frequent source of difficulty during erection is associated with the fit-up between the erected steelwork and components that require tight tolerances. As mentioned previously, the NSSS tolerances are determined by what is economic within the process capability of the industry and what is necessary for reasons of structural stability. To determine what particular adjustments or clearances might be needed at a support interface between the steel frame and a close-fitting component, an estimate is needed of the variability of the support position offered by the erected steel frame.
A separate estimate of variability will be needed based on the details of the supported component and its associated dimensional tolerances. Typically it will be concluded that the supporting cleats need to incorporate adjustability at the attachment interface point.
In some cases there may be architectural or engineering reasons why the range of adjustment might need to be limited. There might be aesthetic restrictions or, in extreme cases, the additional eccentricity of loading could be critical. Perhaps the gaskets between components can only accommodate a limited amount of adjustment. For heavy cladding panels and masonry walls, the contribution of deflection under load is often a significant issue.
Pre-cambering can be used to compensate for predicted deflection under dead load, but estimates of deflection are not generally exact. The danger might then be to plan the necessary restrictions as described above but to ignore any uncertainty in the estimate of deflection. Assuming the deflection calculation to be fully accurate could then lead to the discovery of this contribution to overall variability only after erection on site, with consequent disruption whilst the solution was sorted out.
Site connections should generally be bolted, as it is faster, less susceptible to poor weather conditions, and has less onerous access and inspection requirements than site welding. Structural bolting practice for buildings in the UK is based predominantly on property class 4. The recommended option of M20 8.
Property class 4. There may be situations, for example a column splice subjected to large load reversals in a braced bay, where the designer considers that joint slip is unacceptable.
Erection of steel structures
In these cases property Class 8. Preloaded bolts are also predominantly used on bridgeworks. Common practice is to specify fully threaded bolts, meaning one bolt size can be universally used for a large number of connections. The use of M20, 8. Although there are potential minor extra manufacturing costs due to an increase in the average bolt length and a need for more threading, significant overall savings are possible when standard, fully threaded bolts are used:. Site welding is not normally preferred if a suitable bolted connection is possible.
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When site welding is adopted, provision must be made for protection against inclement weather, and good access is needed for both welding and inspection. Providing such protection and access may have programme implications, as well as the direct costs involved. The extent of routine supplementary non-destructive testing NDT for site welding is generally the same as factory welding. Temporary works is more usually associated with the erection of bridges , but the following points may also apply to steel buildings. There are three categories of temporary works, all of which need to be justified and provided or procured in a timely and economic manner:.
Many of these minor items can be detailed, in consultation with the permanent works designer, so that they need not be removed after use, which will avoid the risk of damage and the requirement for remedial works and additional inspection. Where lifting lugs, for example, cannot be detailed to clear deck reinforcement they can be removed using approved cutting procedures, say 25mm above the flange.
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The final objective of the erection process is to handover the frame to following trades in an acceptable condition. The key criterion here is the positional accuracy of the erected frame, and this depends on an understanding of how the erected position of a steel frame is controlled. A steel framed structure is a very large assembly of a large number of relatively slender and flexible components. Overall accuracies of approximately 1 part in are sought for plumb and line of the completed structure, using components that may individually be manufactured with greater variability than 1 part in In addition, deformations such as the flexure of the structure under self-weight of steel affect its actual position.
A clear understanding is needed of both the concepts involved and the methods used for control of the erected position of a steel frame. Within an inspection and test plan, tests undertaken at handover of an erected steel structure could be considered to be final acceptance tests.
To be meaningful, all tests require the following to be specified:. Firstly, a dimensional survey is the usual method of testing, but its accuracy is limited by the accuracy of the surveying equipment. Dimensions are only measured to at best 2 mm and often 5 mm, using optical instruments. This limited accuracy means that it may not be possible to achieve, or demonstrate, compliance of the frame.
Secondly, the location and frequency of checking might well represent less than a quarter of all main frame connection points. Thirdly, the normal procedure for alignment of columns by plumbing-up see earlier is not a final acceptance test as such. Demonstration of compliance using a full three-dimensional survey of the complete structure as a final acceptance test is not practical, because of difficulty, time and expense.
Neither is it necessary if the purpose is to ensure the stability of the frame. When tolerances are satisfied over a representative part of the frame, deviations in the rest of the frame can be assumed to be acceptable based on a visual inspection alone. Tolerances specified in the NSSS for erected steelwork assume that the frame position is checked under the self weight of the steel members alone.
Due consideration must also be given to the fact that the frame position will vary according to wind loading, so checks should be made in calm weather conditions.