Steel connections serve to connect two or more structural elements made of steel. We use a design process to analyse and calculate the strength and stability of such connections so as to ensure the strength and stability of the structure itself.
Steel connection design can be a massive challenge, especially when calculations are made by hand. In these cases, the work processes can become especially tedious and even tiresome if the necessary checks haven’t been properly carried out to comply with all code requirements.
On that end, most experts agree that typical details, especially of standard structures, are efficient enough that it makes the design process and detailing of structures and steel connections pretty straightforward. In other cases, some engineers tend to overcomplicate things and end up with a complex and intricate connection with somewhat compromised durability.
This article will focus on the basics of steel connection design and the characteristics of the trade and will talk about some of the best software solutions which can help make things a lot easier.
What is Steel Connection Design?
Generally speaking, steel connections can be classified into three different subcategories. All of these classifications can help in the design process as they can help narrow down solution choices based on practical reasons.
Simply put, you can classify connections by the following characteristics:
- Connecting Methods: Nowadays, bolts and welds are the most prevalent connecting mediums. Bolts offer economical installation solutions, while welds are simple. We’ll talk about them more below.
- Internal forces that steel connections should transmit: Design should also be based on the internal forces of the structure, or more specifically, the connection itself should be able to transmit. As such, connections can be shear, axial, and moment connections, defined by the load they are to carry.
- The joining members: This classification is based on the connecting structural members, which can actually be a primary consideration when designing steel connections. These can be beam-to-column, beam-to-beam, splice connections and base plate connections.
About Welded and Bolted Connections
Modern projects will mainly use bolts and welds to connect steel structural members. In earlier years, rivets were the main connecting medium, but welds and bolts have replaced them for various reasons.
They have more or less replaced rivets entirely as they were a solid alternative to lower installation costs, and they were also easier to install and maintain. There are two main bolt types commonly used in steel construction designs, and these are preloaded and non-preloaded bolts, which are all divided into classes (or grades) based on their strength, with classes 8.8 and 10.9 being the most prevalent. There are certain situations which need to be taken into consideration, such as the fact that they can loosen under vibratory loads, which can compromise overall structural strength. In such cases, special bolt assemblies should be used to prevent this phenomenon. Of course, making periodic inspections of the main connections is vital to ensuring that the nuts are properly tightened.
These connections also have a rather simple design and only require little material and a few parts. One of the problems that may arise is that welds tend to shrink, and this needs to be taken into consideration during the design phase, especially in the case of more massive welds. Additionally, inspecting the welds can be a challenge, and because of this, maintenance may be more difficult and expensive. Still, different weld types will also have different qualities, so taking a closer look at them is essential before opting for one in the design process. Welding is mostly carried out in fabrication shops under controlled conditions rather than onsite since the weld quality can be compromised due to external factors.
The Finite Element Analysis, or FEA, serves to obtain internal forces and deformations that are used for analysing the strength and stability of the structure as well as its connections, and as such it has become a cornerstone of structural engineering and steel connection design.
The FEA method helps engineers determine how different materials and connecting components respond to load.
Design Software for Steel Connections
For the most part, experts recommend using a full-scope software solution that can design non-regular connections as well. While Limcon, Ram, and PROKON are all solid go-to options in connection design, they are only able to work with connections that are already predefined in their libraries. In these cases, engineers need to create additional models in FEA tools to assess stress limits, which is a time-consuming process. This, however, may make things a bit more complex due to complications in modelling the welds, material non-linearities, non-linear contacts between the connecting members etc.
Because of this, our design projects are primarily carried out using IDEA StatiCA, which is a premium steel connection design software that can verify almost any geometry connection type and can design anything from simple to fairly intricate and complex projects with ease.
The solution gives engineers the freedom to design a wide variety of connection topologies, either starting from scratch or with the help of pre-made templates.
Furthermore, IDEA StatiCa can easily perform a wide variety of design checks, like stress checks, stiffness analysis, overall utilization verification, and buckling analysis.
Additionally, engineers have the option of importing geometry and joint loadings from other global analyst tools, automatically importing the required joint data and applying them to any design project.
Lastly, the team behind the software also provides massive documentation on their platform to help those engineers who are aiming to learn more. The team also regularly organizes webinars where they show real-world examples of the works designed by the software.
The Dos and Don’ts of Steel Connection Design
As said before, standard structures with tried and tested elements are often straightforward to design and create. Oftentimes, however, engineers seem to overcomplicate otherwise simple connections, which may lead to unnecessary headaches, missing deadlines, and added costs.
So, here are some of the best practices that engineers should adhere to before/during, and even after the design process:
- Respond to RFIs as fast as you can. Delays can slow down the entire detailing process.
- Indicate any codes for the connection design.
- Be communicative with the connection engineer and listen to their experience and suggestions.
- Put the actual design reactions on framing plans and stay away from using the uniform design load criteria.
- Try to avoid having different depth beams share the same moment connection because this can create larger forces on a column as bottom flange plates are at different elevations.
- Avoid mixing 8.8 and 10.9 bolts, as it can lead to installation errors.
- If you need two separate bolt diameters on the same project, ensure to make them at least two diameters apart to avoid installation mistakes in the field.
- Weld sizes shouldn’t be larger than 8mm. When larger options are required, check whether you can use longer and smaller alternatives.
- During the design process, review web yielding, web buckling, and local flange bending of wide flange columns in moment connections. This will be less expensive than implementing the necessary reinforcements later on.
There’s More to Steel Connection Designs
These are only some of the basics that engineers need to consider when designing different steel connections. To be honest, listing out the best practices and all considerations would take a lot more time and would make this article much longer. As such, if you have any questions or concerns, you can always reach out to us to learn more.