Wednesday, 29 April 2020

Take a more detailed look into the model definition of Pangolin with us

1. Geometry definition

Geometry in Pangolin can be described by lines or circular arcs and polygons made up of the former two.
The relevant components are the simplest ones, acting as converters from the native Grasshopper geometry types, with the possibility of specifying a Consteel Layer.

2. Section definition

The geometry definition of the sections is more refined since Consteel uses detailed section models composed of solid representation for analysis and thin-walled representation for standard design checks. There are two options to create sections in Pangolin: use a predefined section from the section bank or create custom sections by predefined parametric macros.

Predefined sections from section bank

7000+ different profiles can be defined from the section bank (hot-rolled, cold-fromedetc.). This workflow contains two steps:
1. Getting the section preview from the bank.
2. Getting the actual section from the preview. (The reason for this is the performance, as in Pangolin sections are real objects, loading all the 7000+ sections from our bank would take minutes even on a powerful pc.)
The section bank component provides various filtering options, to help select the section. After the desired section preview is selected, you can create a real section from it along with a material, and check the cross-section surface in Rhino.

Custom sections based on predefined macros:

This workflow consists of placing a section macro component, selecting a base macro, and defining the macro parameters.
One of the most important unique features of Consteel is its advanced analysis and design calculations for members with cold-formed sections having various stiffeners. Correspondingly Pangolin makes it possible to create custom cold-formed sections, with custom stiffeners parametrically:
As you can see, the components help in building complex sections with available default values providing a wide range of parameters to be customized.

3. Structural member definition

Defining beams is as easy as pulling the reference edges and the beam section into the Beam component:
In the example above we also defined a haunch on the beam ends, another unique feature of Consteel, which will be taken accurately into account during analysis and design. 
To make modelling easier, Pangolin also provides several useful implicit data conversions, like in the picture above: at the start, we have the IPE 300 beams, and just connecting them into a Grasshopper Plane parameter, the beams get converted to their local coordinate systems. This plane can be directly connected with the Z purlins section direction parameter to correctly lay them upon the main beams.

4. Structural details

Let us stop at the purlins for a moment! Pangolin also provides a detailed linking of structural objects through Consteel’s link elements which can be rather important in order to consider accurately the lateral restraint effect on the beam provided by the purlins.
The definition of link elements includes setting the interface position, the direction, and the stiffness attributes of the connection.
Defining supports for the model is also helped by automatic conversions, where you can directly ask a beam’s endpoint, and place the support there, instead of manipulating with indexes through a complex definition.
Pangolin also provides the possibility to define edge and plate supports.

5. Load definition

Pangolin’s load definition includes load cases, grouped into load groups with specific types like permanent, variable, snow, etc... and custom load combinations. Once the model is sent to Consteel, you can also use its automatic standard-based load combination generator with the groups and cases defined in Grasshopper.
As for the loads themselves, currently, you can define nodal loads, uniform and variable line loads, and uniform and variable plate loads. Additionally, to help place loads on bar members, Pangolin provides a load transfer surface component, which distributes the surface load on (optionally filtered) beams overlapping it.

Variable surface load definition with two points:

6. Using the model for calculations

The model can be calculated by Consteel or Steelspace. Communicating the model with either is done through Pangolin’s Connection component.
This component can accept all Consteel objects and will save a .smadsteel file, and/or send them to Consteel running in the meantime. You can automate either one by defining true for the corresponding parameters.
Additionally, the component will make sure to send everything needed to make the objects valid. Meaning you only have to pull in the beam objects, loads, and supports. The underlying lines, sections, materials, haunches, load cases, support models, and others will be automatically collected by Pangolin for you.

Wednesday, 22 April 2020

Cloud in the structural world

In the last couple of years the term „cloud computing” could be seen almost everywhere. Although it might seem that it’s a new technology, the concept has been around since the 1960s and it’s evolving still. 
But what is the cloud? And why should you care? Let’s take a closer look!

 There are three broad concepts that define the cloud:

  • delivering a service, such as computing or storage, as a utility
  • multiple people sharing the same computer resource
  • access via networking

If you are not sure what do these concepts mean, think about your daily activity on the internet.

It’s everywhere

If you are unfamiliar with modern-day cloud services, let me tell you, you are using some sort of cloud service most of the time while you are on the internet. I’m sure you’ve used one of the Google services like Docs, Sheets or Drive. What do these services provide for you? Google Drive, for example, delivers a storage service, where you and other users share resources, the storage space in this case. And you can access it via a network called the internet. With Sheets and Docs, you can have Word and Excel-like functionalities in your browser, which are kind of computing services, where the computing resource is shared amongst users. 
If you apply this train of thought on other services, you realize that in fact, every Google service is a cloud service from Gmail to Maps. But not just Google, these services are everywhere, just think of Spotify, Netflix, YouTube, the list goes on.

Where is everywhere?

“But where is it the cloud exactly?” you might ask. Although it seems it is all virtual, the cloud requires hardware as part of the infrastructure. A cloud solution is made up of a variety of physical hardware such as servers, backup devices, load balancers that are usually located at multiple geographical locations.
The virtual part of the infrastructure means that they separate resources from the physical hardware. This technology called virtualization. A software sits on top of the physical hardware and abstracts the machine's resources, such as memory, computing power and storage. Once these virtual resources are allocated into centralized pools, they are considered clouds.

The benefits

One of the most compelling benefits of putting a service in the cloud, that it frees the end-users’ machine from doing the hard work. When you access one of these services, the heavy lifting is done by the above-mentioned infrastructure. And it is designed to be able to do this kind of work. With the centralized virtual resource pool, the infrastructure can be scaled, meaning more memory, storage or computing power can be added and adjusted automatically, to different needs.

  If you go further with this idea, it is somewhat obvious that if the cloud handles all the resource-heavy tasks, then you don’t need a particularly powerful machine on the client-side. This conclusion opens the possibility to use the services from almost any device, from mobile to tablet. It is a huge boost to accessibility.
Another great aspect of cloud services is that sharing documents between users is way easier since everybody is on the same infrastructure. With the centralized data, sharing a file does not mean transferring a file, but granting access to a document that you own.
Also, the data are specifically safe on these systems. The databases and storages are designed to be fail-safe with many backup devices.

Our vision

Once we looked around in the industry, we realized that the possibilities that the cloud has, are not exploited. It is safe to say that structural analysis and design software are a bit behind the world. As we always engaged in innovation, an idea started to take shape, that structural design experience could be so much more if we take advantage of the opportunities of the cloud. As we started to explore the possibilities the present state of cloud computing we realized that the future is now.
Therefore, we created Steelspace, a new platform for structural engineers to make knowledge sharing and collaboration easier. 

I hope this summary made things clearer, and next time you use a classic structural software I hope you have the same thought in your head as we do: how much more could it be?

Friday, 17 April 2020

Buckling resistance of members: imperfection or reduction factor? - Part 2

The imperfection amplitudes

The Eurocode EN 1993-1-1 offers basically two methods for the buckling verification of members:

(1) based on buckling reduction factors (buckling curves) and
(2) based on equivalent geometrical imperfections.

In the first part of this article we reviewed the utilization difference and showed the relationship between the two methods. It was concluded that the method of chapters 6.3.1 (reduction factor) and 5.3.2 (11) (buckling mode based equivalent imperfection) are consistent at the load level equal to the buckling resistance of the member, so when the member utilization is 100%. The basic result of the procedure in 5.3.2 (11) is the amplitude (largest deflection value) of the equivalent geometrical imperfection. However, the Eurocode gives another simpler alternative for the calculation of this amplitude for compressed members in section 5.3.2(3) b) in Table 5.1, where the amplitude of an initial bow is defined as a portion of the member length for each buckling curves (Fig. 1.). We use the first column (“elastic analysis”) including smaller amplitude values.

Figure 1. Initial bow amplitudes

It is an obvious expectation that these two standard procedures should yield at least similar results for the same problem. However, this is by far not the case in general.

In order to show the significance of the imperfection amplitudes this part is dealing with these two calculation methods, the variation of their values and the effect on the buckling utilization.

Let’s see again the simple example of Part 1: a simply supported, compressed column with a Class 2 cross-section (plastic resistance calculation allowed). The column is 6 meters high and has an IPE300 cross-section made of S235 steel. The two methods are implemented into Consteel and on Figure 2. it can be seen, that the two values for the amplitude of the geometrical imperfection is very different – e0 = 24 mm by the 5.3.2(3) b) Table 5.1 (L/250) and e0 = 13,4 mm by the 5.3.2 (11) (same as in Part 1).

Figure 2. Two alternative amplitudes for the same problem

This difference is not a single, unique case but the two methods give systematically different values. These differences are illustrated in Figure 3. for that column as the function of the member length ‘L’.
Figure 3. Two alternative amplitudes as the function of the member length

As it is clear the values based on the method of initial bow by the 5.3.2(3) b) Table 5.1 are always considerably higher than the buckling mode based imperfection amplitude values of 5.3.2 (11). In order to see the influence of this difference on the buckling utilization of the member let’s see the following figure, where the utilization are illustrated for 3 different member length with the following calculations:

(1) Green: utilization calculated by the buckling reduction factors using 6.3.1
(2) Blue: utilization calculated by the buckling mode based equivalent geometrical imperfection using 5.3.2 (11)
(3) Orange: utilization calculated by the initial bow based equivalent geometrical imperfection using 5.3.2(3) b) Table 5.1
 Figure 4. The different utilization of the same member with different standard calculations

As it was discussed in Part 1 the reduction factor method (2) and the buckling mode based imperfection method (2) gives the same utilization (100%) when the buckling resistance is reached. The initial bow method (3) however gives a very conservative result in all the cases, its utilization curve goes always well above the “true” utilization values of the buckling mode based imperfection method (2) because of the systematically higher amplitudes. This difference is larger for more slender members, where the second order effects are more significant, and also higher around the buckling resistance of the member. Accordingly, at the compression force related to the correct buckling resistance (the 100% utilization point) this method gives very high utilization:

§  for member length L = 6,0 m: 160%
§  for member length L = 4,5 m: 154%
§  for member length L = 3,0 m: 138%

As a summary it can be stated that the amplitude of the equivalent geometrical imperfections (using either methods for the shape) influences significantly the final buckling utilization (and accuracy) of the member. Generally it is true, that the most simple and widely used method based on the initial bow shape defined in section 5.3.2(3) b) Table 5.1 gives very conservative (much too safe) utilization for the member buckling problem.

Wednesday, 8 April 2020

Shear field theoretical background and comparison against shell model

This article aims to cover the theoretical background of the shear field stiffness determination methods implemented in Consteel. Modeling with the shear field stiffness based method will also be compared with shell modeling of trapezoidal deckings in Consteel.

Monday, 6 April 2020

Get to know Pangolin

Introducing Pangolin, the new ConSteel integration with Grasshopper

In quick summary: 

  • What is it? - Pangolin will be a plugin to integrate structural modelling and analysis into your parametric Grasshopper definitions
  • When? - Pangolin will be released together with ConSteel 14
  • Where? - As a download from or the Yak package manager of Rhino

Basic workflow:

1. Create your Grasshopper definition of the structure’s geometry

2. Define the complete structural model based on the geometry with Pangolin’s component

3. Preview the generated structural model real-time right in Rhino

4. Send the generated structural model to ConSteel (or SteelSpace, or just save a ConSteel import file for later use)

5. Analyse the model utilizing the full power of ConSteel’s unique analysis and design calculations

6. Change the Grasshopper model’s input parameters as needed, go to step 4. and check the parametric model again in a matter of seconds.

Main modelling features provided by Pangolin:

  1. Geometry: Lines, arcs, polygons
  2. Structural members: Beams, plates, supports, rigid bodies, diaphragms, link elements
  3. Sections: from ConSteel section bank, or created by section macros, including cold-formed sections with stiffener definition support
  4. Custom structural attributes: release stiffness model, support model, material properties
  5. Loads: Nodal, line, surface loads
  6. Load configuration: load combinations, load groups, load cases, load transfer surfaces 
  7. Organization: Layers, and structural groups
  8. I.O. : Load from file, load from ConSteel, save to file or ConSteel
  9. Integrated parameters for unambiguous definitions, avoiding the use of nebulous generic parameters:

In the following posts we will inspect Pangolin’s features more closely, including the following main use cases:

  1. Using Pangolin in a top-down Grasshopper model first approach
  2. Using Pangolin to automate complex or repetitive modelling tasks while still using mainly ConSteel’s modelling tools (eg. programmatically placing plate loads on a predefined surface)