“Connections design is a black art!” “I wouldn’t have a clue where to start!”

If, throughout my career, the age old “If I had a pound every time I heard you say that” was true I would be rich!

I have, as a result, decided to collate my experiences and pass these on to others in the hopes that I can dispel some of the myths surrounding this area of structural design.

Connection design really isn’t a black art, of course there are some different things that have to be considered during the design and calculations, but a lot of it comes down to common sense.

You don’t know where to start? I can appreciate a connections design project can be a bit daunting as there can be hundreds of connections involved. The key with this is to set up your project and workflow from the start and work smartly and efficiently! That is where this series of articles will be of use.

This series ‘Structural Steel Connections Design Made Easy’ is designed to help engineers who have little experience of a connections design project and may indeed help seasoned designers improve their efficiency. 

The multi part series will start from the point of being awarded the project, and move through setting up your project, best practices, explanation of connection types, and samples of connections design from first principles.

I hope these series will be of use and I welcome feed back from people as they read these articles. Hopefully I will learn something from others too!

Part 1: Setting up your project

Introduction.

I cannot stress enough that the efficient set up and workflow of your project can mean the difference between hitting your programme dates or negatively affecting the entire build programme with all the accompanying consequences. Connection design is usually the last link in the design process before steel is detailed by the draughtsmen and issued for fabrication. Quite often the case is the connections design will be completed in batches and released to the draughtsmen so that design and fabrication can run in parallel, but at a staggered pace, to decrease the time of steel to site. This will more than likely lead to a very tight programme schedule within which to complete the connections design. A key point to keep in mind is that if you are late with your designs it will result in the fabricator not being able to do their job. If the fabricator is standing around doing nothing then they will likely back charge the contractor for the costs incurred and guess what the contractor will do to recover these costs!!!

So, work smartly and efficiently, and get your workflow setup, ideally before even taking on a project like this. Monitor the progress carefully and try to predict any lateness in the delivery of work. If this is reported sooner rather than later, there may be a chance of making adjustments to the programme so that major dates are still maintained.

As stated previously, connections design projects can have hundreds of connections, some may even extend to thousands if it is a project of sufficient complexity. With all this information it becomes extremely important that your project has been set up in a way that promotes traceability. This is especially so within BIM compliant projects; any connection within the main building model has to have links to the calculations you have performed. 

It can be very easy to just set off designing connections without much thought on how they will all be organised and soon enough inevitable mistakes creep into the work, duplicate file names, calculations with no way of telling their location etc. This can be easily prevented with a robust file structure and naming nomenclature as is discussed later in this article.

So where do you start? 

At the beginning!

Collate information.

During the tender stage of the project you are bidding on, there is a good chance that not all information is present and you are making certain assumptions. A typical example is being given a  set of steel general arrangement drawings but no connection forces information. 

Before signing for the contract it is a good idea to make sure that all the assumptions you have made have been verified or clarified and that all requested information is present.

What should I expect?

Ensure that you have ALL current connection force information upfront and make sure it’s signed off for construction. This can be in a number of different formats. The easiest of which is having a set of plan and elevation drawings with all the worst case design forces and their acting directions. The benefit to this is that all information can be easy to see and work with. There may be some complex details which need further clarifications, but generally this is the industry expected level of information. 

The down side to drawings with worst case forces is that, as the connection designer, you don’t know if the forces are all acting concurrently or if they are part of a load combination where the corresponding loads in different directions are lower than those on the drawing you received. This is where engineering judgement plays a big part. Look at the connection and loads given. Are they likely to all act at once? How is the connection affected by including all the given loads? Quite often you will find that designing the connections to include all the given forces will be sufficient, but always take a moment to think about it. Sometimes loads can counteract each other so designing a connection to the maximum loads from different combinations can actually give a higher load capacity than if you were to use the loads for a specific combination. If in doubt always ask the person who gave you the loads to clarify! 

It is good practice to check over the load drawings and the steel G.A. Drawings for any inconsistencies. It is more often the case that the structural analysis model is separate from the design model leading to discrepancies. These need clarification before work should commence as there may be a change in the load information.

The other popular format for force information is to provide a spreadsheet output from the design software. This is a more complete set of information but be aware, the amount of data within the spreadsheet can be vast to say the least. It can also be difficult to determine which member the loads refer to. To help make this set of information most efficient to work with, a drawing should be with the information, which contains all the member reference marks as contained in the spreadsheet data. The spreadsheet should have been processed before given to you with appropriate filters so that you can easily find the relevant information. If it hasn’t got any filters then ask for a copy which has, otherwise you could be spending a long time sifting through data or preparing a spreadsheet for data interrogation.

ULS or SLS?

When you receive your load information it is important that you make a quick check to ensure that the forces provided are factored ULS forces. You will be surprised with the amount of times that you WILL receive unfactored SLS forces. It is not the responsibility of the connections designer to derive the load combinations and factor up the loads. This has already been done by the frame designer and should be provided by them.

Old School or Modern?

This next point should be already known from the tender stage assumption clarifications but it always pays to double check. In the UK it is important to confirm the connections are to be designed in accordance with Eurocodes or British Standards and that the forces you have been given correspond to the correct design code. Connections designed to one set of codes do not always work for the other set of codes.

Is it moving?

Check the forces provided are. Static/quasi-static loads and not dynamic i.e. requiring fatigue design checks. For example, in BS EN 1993-6-2007 under 2.1.3.3 Durability, all crane supporting structures need to be designed for fatigue amongst other environmental influences. Designing connections for fatigue is a completely different approach to normal static connection designs and will be the focus of a future article.

Keeping up to date.

One final point regarding the design forces provided, make sure you are given an issue register. Normally at the point of receiving the force information the frame design is supposed to be frozen. Quite often this is not the case and revisions are made all the time. New load information will need to be sent and if a register is not kept of these changes it will be easy for things to get missed, especially if the information is buried deep within your email system. If a register is not provided then it is good practice to create one and record the changes yourself and sending it out to the relevant parties each time a revision is made.

File structure.

There are many ways of file organisation and ways of presenting information. The method that will be discussed is based on experience and is not necessarily the best way. Each company will need to asses this based on their data management systems in place. 

Don’t be late for the register!

One of the first things that should be done before doing any design work is to create registers for your calculations and any marked up drawings. These registers are to record any new issues and revisions of your work. It ensures there is no confusion as to what is the most current information you have issued. It is also a good idea to set up a request for information log (RFI log) at this stage too. You will likely have an abundance of questions needing answers and it will be difficult to track them all if there is no record of what you have asked and what has been clarified.

Sounds like a plan!

Marked up drawings or ‘Marking plans’ showing the location of your connections are a great way of organising and presenting the large amount of calculations that will likely be generated in a project. Marking plans are like a map, they show the connection calculation number location for easy identification. A marking plan can be as simple as printing out a G.A. drawing and writing the calculation numbers on in pen, then scanning it to create an electronic document. This process can be more refined using software to create your own borders and number stamps etc.

Marking plans are most effective when they are setup for specific areas, these areas can include: 

• Floor/Roof plans.
• Elevations.
• Sections.
• Details. (Used for connections which are difficult to locate on standard plans)

These marking plans can then be subdivided per connection type to avoid information saturation. For example; having two marking plans for the first floor, one showing beam to beam and the other showing beam to column type connections.

If you don’t have any ID your not coming in!

For each calculation you do it must have a unique identification number, this is so that the calculation can be easily traceable. Further advice on naming conventions to be BIM compliant is given later in this article. The unique calculation numbers are then plotted on the corresponding marking plans for easy identification. 

When producing your calculations, you will quickly notice that one connection will be applicable to a number of locations, possibly over a number of levels. Try not to make connection calculations specific to a particular location and keep them general for re-usability otherwise you may be finding that you are duplicating connections reducing your working efficiency.

Depending on the size of the project, you could end up with a lot of calculations either paper based or electronic. It is important to get any paper based calculations digitised as quickly as possible to avoid any loss of information. If you are only using your computers operating system to organise files rather than a database file management system then it is a good idea to store the calculations in folders specific to the type of connection. This way it will be easier to perform any search functions and will provide consistency of data storage across projects.   

Connection Categories.

Break it down!

In an effort to become more organised with the workflow, it will help tremendously to break the large volume of connections down into group types. These groups will directly relate to the marking plans you will be creating and will produce a clear and intuitive method for navigating through the calculations and their locations. Without this level of organisation the marking plans as mentioned previously will quickly become saturated with information and it will become most difficult to locate the specific connections.

The groups are based on the types of connection throughout the project. From experience, the most common types of connections encountered are as follows:

• Base plates.
• Beam to beam. 
• Beam column.
• Bracing.
• Truss joints.
• Splices.
• Misc.

This is not an exhaustive list and is only a guide to some of the more common types. Of course you must assess what types of connections your project contains and create the necessary groups. For example you may have a lot of beam to concrete core type connections which will warrant a specific group.

Once you know how you are organising your connections and marking plans then the next step is to set up a standard naming convention.

Naming convention.

“What’s your name son”

This stage you will be setting up your naming convention for all your calculations in the project and will likely be the same convention you will use for the majority of your connection design projects.

It is rare to encounter a new project of significant scale which is not compliant with the Building Information Modelling framework (BIM) and, as such, there is a specific file naming convention to be adopted to be compliant with this approach and its related ISO standards. 

This article is not a complete guide to BIM and its working practices. There are plenty of articles on the subject, just use your favoured search engine to find them. This article will explain how to be compliant with the BIM framework naming convention for your connections project.

What’s in a name?

Generally according to BS EN 19650-2:2018 the standard BIM naming convention can take two forms depending on the state of the document. For example, if the calculations are a work in progress and not for review or comment but information purposes only then it can have the shortened 7 field name convention. If, however, the calculations are being issued for comment/review or they have been authorised and accepted then they require the nine field naming convention to show the suitability of the document and its revision. The nine fields of the naming convention are as follows:

Project Number – This is a unique project number and will normally be provided to you as a subcontractor.

Originator – Each company involved in the project will have a unique three letter identifier code, for example, MecaStruct LTD could be MST.

Volume/System – If the project is subdivided into zones or buildings then up to two characters can be used to identify the spatial sub-division. If the document applies to all areas then ZZ can be used or if it is not relevant to a specific area then XX can be used.

Level/Location – This field is used to specify the level or location and consists of two alpha numeric characters for example:

General Levels

00 – Base Level

GF – Ground Floor

01 – First Floor

02 – Second Floor

Basement Levels

B1 – 1 level below ground

B2 – 2 levels blow ground

Mezzanine Levels

M1 – Mezzanine above Level 1

M2 – Mezzanine above Level 2

Miscellaneous 

ZZ – Multiple Levels

EX – External

XX – no level/location applicable

Type – Type relates to the type of document you are naming. There are lots of different codes relating to all the kinds of documents/models/database etc you are likely to use on a project. The type codes you are likely to use on a connection design project are: 

DR – 2D drawings for the marking plans

CA – Calculations

Role – The role relates to what function you as a business are performing in the project. For example if you are the structural engineer then the code ‘S’ applies. If you are a subcontracted design engineer then you will likely use the code ‘X’ or ‘Y’

Number – This is the file or drawing number and is a four integer number using leadings trailing zeros. This is the part of the file name which can be used to differentiate the types of connection calculations you will produce. For example: the first number in the sequence of the four integers could relate to the type of connection, then the remaining three integers will be the sequential count for the connections as you produce them. E.g.

1XXX – Base plate connections

2XXX – Beam to column connections

3XXX – Beam to beam connections

4XXX – Etc.

Suitability – The status/suitability of the particular document or drawing you are releasing should be given a particular code here. There are a range of codes for the contractual status of the document whether its at preliminary or contractual stage. 

For preliminary stages there are a range of ‘S’ codes ranging from work in progress to suitable for review and comment. At this point if you are just wanting to release something as an indicative work in progress then the code S0 should be used. Once the document is at a stage where it can be reviewed for sign off then the code S3 or S4 can be used. After the document is authorised and signed off then A1, A2, A3 etc or CR for construction record can be used.

Revision – Revision is self explanatory and is used each time there is a new iteration of the document or change in document suitability. It is a numerical revision system using two integers using a leading zero. For preliminary non- contractual suitability codes then the numerical revision is prefixed with ‘P’ once the document changes to contractual suitability then the revision numbers are prefixed with ‘C’ 

As an example of a BIM compliant file name, the following is for a standard first floor marking plan prefixed 0001 and a beam to beam type connection prefixed with 3 for the numbering sequences.

Marking Plan = A2403-MST-ZZ-01-DR-X-0001-S3-P01

Calculation = A2403-MST-ZZ-ZZ-CA-X-3023-S3-P01 

Software.

“Computer says no”

This is a topic which has no clear answer. There are so many companies offering connection design software. Some packages are linked to the frame design software and some function as stand alone. The chances are if you use one of the leading brands of software for the structural frame design then there is connection design software within the same brand of products, typically, offering some kind of link to export the connection loads. Some software such as Autodesk Revit have basic connection design built in creating a direct BIM workflow with the main model.

Each connection design software has its advantages and disadvantages, but ultimately, will perform the design for you. You will soon learn through experience what works for the particular type of work you tend to do. To give an example, I found Tekla connection designer is more versatile for base connections but tends to give weld sizes on other connections which are far too conservative whereas Masterseries Masterkey steel connections was great for most types of connections but tends to be limited for base design. 

Something I spent more and more time with in recent years designing connections was IDEAS Statica steel connections. This software uses a component based finite element modelling approach which basically calculates the stresses through finite element analysis of shell elements in the plates and checks bolts, welds and plate stresses against BS EN 1993-1-8-2005 Design of Joints. It proved to be an invaluable tool when designing connections with any degree of complexity. A big advantage I found with it was the BIM links to other design software. For example, the drawing office could detail (with guidance) a particularly complex connection then export it into Statica to analyse.

A finite element analysis software such as Ansys or Abaqus can be used for connection design but I wouldn’t recommend it for anything other than the most complex connections. It is powerful software but the person using it has to be proficient with it to get meaningful results. It takes longer to set up a model and a good in-depth knowledge of material mechanics is required to get full benefit of plasticity in the joint.

The combination of software I used when designing connections was as follows and is meant as a  starting point for your research into which software will be right for you.

• Tekla Connection designer – an add-on to Tekla Structural Designer which I use for frame design.
• Master Series Masterkey steel connection design.
• IDEAS Statica

Workflow Setup

Now that you have everything set up to do connection designs, you need to create a workflow strategy which will likely involve other departments or companies.

“It’s all about the base”

One of the first things you will likely be asked for by the main contractor is the designs to ALL the base plates up front. This is because they will want to get all the holding down bolts/washers and cone boxes ordered for casting the foundations. They normally like to cast all the foundations with holding down bolts first before any steel arrives which has a number of benefits, such as there are less site access problems for heavy vehicles.

Synchronise Watches.

For projects of any appreciable size the project programme usually will have connection design and steel detailing running concurrently albeit staggered by a number of weeks to allow connection packages to be released to the drawing office for steel detailing.

“Set phasers to stun”

Buildings are normally erected in phases, therefore the steel detailing will correspond to these phases. For each phase in the erection sequence, steel normally arrives on site in a specific order. The detailers typically will split the steel model into groups called “trailer loads” and will number them sequentially to correspond to the delivery of trailers loaded with the fabricated steel to site. This means that it will be prudent to liaise with the main contractor and steel detailer/fabricator to acquire the erection phase plan and design the connections contained within the phases for issue. Something to take care over is these phases can run over multiple levels so don’t constrain your design workflow to be level by level otherwise you will end up with a situation where the drawing office is unable to proceed until you have done the connections they need. If the fabrication shop is held up because of this then it becomes very expensive, very quickly.

Summary.

What was all that again???

A summary of what has been written is as follows:

1. Collate all necessary design information (loads, design code, drawing registers etc.)
2. Set up your filing structure (Create marking plans, calc registers, RFI logs)
3. Send out any Initial RFI’s
4. Decide how you will split up your connection types
5. Set up your file naming convention (use BIM naming convention)
6. Ensure you have all relevant software and updates in place
7. Lease with main contractor and steel fabricator/detailer to determine the order in which connections are designed and issued.

Upcoming part 2 will be about common sense and practical approaches to connection design and feature an explanation of when best to use the different types of simple connections.