Joints

Purpose

Defining joints allows to:

generate automatically rigid bodies associated with tubular intersections,
create entities that can be subjected to code checks computations.

A joint is composed of one or more tubular intersections and the tubes which form the tubular intersection are chords and braces:

the chords have the same diameter and thickness and are aligned,
the braces have a diameter less than or equal to the chords diameter.

If the joint has a single intersection we say that the joint has a single end node, otherwise the joint has two end nodes.

The figures below show different types of joints (the chords are in blue and the braces in violet):

one tubular intersection, one (end) node:

Two chords and one brace	One chord and two braces

three tubular intersections, three nodes, two end nodes, four chords and five braces:

A joint has a minimum of three tubes as shown in the first two figures above.

In DeepLines, a chord or a brace is defined by a segment of a line: this segment belongs to a section whose one of the extremities is close to the intersection point of the tubular intersection.

Joints can be defined manually by the user or generated automatically.

Defining joints manually

Creating the root node of joints

Joints are distributed in groups of joints. To prevent joints groups from mixing with objects groups of the model, the group of joints is a children node of a root node in the tree model. Consequently, to create a group of joints you have to create first the root node of joints Joints root:

Creating a group of joints

Once the Joints root is created, you can create a joints group by using the contextual menu of the Joints root:

Creating joints

To create joints in a joints group select the item Edit... in the contextual menu of the joints group:

The following panel is opened (it is shown below not empty: 40 joints have been defined previously):

To define a joint, open a row in the table with the upper arrow at left of the Rows number edit box: a blank row is opened (the 41st row in the figure above). You have to give the definition of the joint:

choose a joint name,
enter the definitions of the chords and braces: each chord or brace is defined by a segment of a line, so give the line and segments names,
if your joint has more chords than the number of opened chords columns indicated in the Chords number edit box (2 in the figure above), increase this number to open more chords columns. If necessary, do the same thing for braces.

When clicking on the OK button, the created joints appear on the tree of the joints group:

If you want to see or modify the definition of a particular joint, use the item Edit... of the contextual menu of that joint: the same panel as the joints group is opened, but the row of the joint is shown framed in black.

From an Excel sheet, a copy/paste can be done to fill joints data in the table.

Tip

If the table is empty, you can copy/paste from Excel without opening rows in table. If not, you have to open as many rows as necessary with the Rows number edit box.

Warning

Before copy/paste, make sure that the column numbers of chords and braces in the table are the same as those in the Excel sheet. If not, you have to open as many chords or braces columns as necessary with the Chords number and Braces number edit boxes.

Joints are shown in the 3D view only in the wireframe mode. A joint is represented by a red circle around the intersection node and the chords are shown in blue while the braces appear in violet:

All model components	Only joints

Generating joints automatically

The contextual menu of a joints group has the item Generate joints... which opens the following panel:

First select lines or groups which contain lines from which the tubular intersections will be searched.

Note

It is recommended to gather previously the lines used to define the joints in a group object. The rigid bodies will be created in the same group (see below).

Warning

At each intersection point, the lines must have a section defined otherwise the lines will not be detected during the generation: there must be a section extremity at the same level as the intersection point otherwise the line will be excluded from the search for lines participating in the tubular intersection.

Moreover, the segments properties (outside diameter and thickness) have to be defined because they are used to discriminate tubes into chords or braces.

The following parameters are used to build the joints:

Maximal distance allowed between nodes belonging to the same intersection: this parameter is used to locate extremities nodes of the lines sections which are close enough to participate at the same intersection. If the distance between nodes is less than or equal to the value of this parameter, the nodes are considered to belong to the same tubular intersection.
Among the tubes belonging to the same intersection, the chords of the joint are the tubes which are aligned and which have the same diameter and thickness.

More precisely:
- Two tubes are considered to be aligned if the scalar product of their normalized vectors checks the formula: \(\frac{180}{\pi}\arccos\left(\left|\vec{v_1}\cdot\vec{v_2}\right|\right) \le \text{tol}_{\text{ang}}\) where \(\text{tol}_{\text{ang}}\) is the parameter Maximal angular tolerance allowed for chords alignment in degree.
- Two tubes are considered to have the same diameter if their diameters \(D_1\) and \(D_2\) check the formula: \(100\times\max\left(\frac{\left|D_2 - D_1\right|}{D_1}, \frac{\left|D_2 - D_1\right|}{D_2}\right) \le \text{tol}_{\text{diam}}\) where \(\text{tol}_{\text{diam}}\) is the parameter Maximal ratio of diameters allowed between chords in percentage.
- The criterion on diameters applies to thicknesses mutatis mutandis and the same parameter is used.

The diagnostics of this functionality are displayed in the frame at the bottom of the panel and are also written in the LOG_History.txt file.

Joints appear in the tree model below the joints group node and the table of the joints group is filled as you can see if you open it.

Generating rigid bodies automatically

Once a joint has been created or generated, the rigid bodies associated to the tubular intersections can be generated. There are as many rigid bodies as tubular intersections belonging to the joint.

Rigid bodies must have been created before the launch of analysis by the solver. They are also used to determine the end sizes of the braces for the calculation of code check.

The reference point of the rigid body is the intersection point of the tubular intersection on the chords line. The fairleads of the rigid bodies are defined for chords and braces:

If the chords belong to the same line, only one fairlead is created for all the chords otherwise each chord has an associated fairlead. The fairleads associated to the chords are all at the relative position (0, 0, 0) from the reference point of the rigid body.
The relative positions of the fairleads associated to the braces are determined from the end sizes of the braces. The end size of the brace at the extremity close to the chords line, is the distance between this extremity and the chords line, taking into account the diameter of the chords. More precisely, the end size is \(E_s=\frac{\text{R}}{\sin(\theta)}\) where \(\theta\) is the angle between the chord and the brace and R the chord radius. The relative position of a fairlead associated to a brace is \(E_s\vec{v}\), where \(\vec{v}\) is the normalized vector of the brace.

When a fairlead is created, a connection between the fairlead and the node of the line section concerned is created.

Remark: in the particular case where two lines intersect in the shape of an X, a section will automatically be created for the line which will be taken as a brace to be able to connect the extremities of the section with the fairleads of the rigid body, see the Particular case of an intersection in X-shape section below.

You can generate the rigid bodies during the automatic generation of joints by checking the Generate rigid bodies check box. Or you can generate them interactively after the joints have been defined or generated by clicking the Generate button in the zone Generation of rigid bodies. In the last case, you can select all the joints or a fixed number of joints by selecting rows in the table.

Once the rigid bodies have been generated, they appear in the tree and in the joints table. For example, in the part of the joints table shown below, the rigid bodies appear in the columns RB_1 and RB_2, and the column RB_2 is filled only for joints having two tubular intersections (see section below).

If all lines participating in the definition of a joint are in the same group in the tree model, the rigid bodies are placed in this same group, otherwise they are placed directly below the root of the model.

Particular case of an intersection in X-shape

Consider two lines that intersect in the shape of an X. In the figure below titled "Initial configuration", one of the lines has sections (A,X) and (X,B) while the other has sections (C,X) and (X,D). Each of these four sections has a segment characterized by a diameter and a thickness. If the two segments of the same line have equal diameters and thicknesses and these diameters and thicknesses are greater than the diameters and thicknesses of the segments of the other line, these two segments will form the chords of the joint. In the figure, these are the segments of sections (A,X) and (X,B) which will define the chords.

The generation of the rigid body associated with this tubular intersection will create a rigid body having X as a reference point and two fairleads at points E and F: see the figure "After generating rigid body". After connection with the rigid body, the extremities of the sections become E and F. To ensure the continuity of the line, a section (E,F) will be created which will have a segment having a fake property: its property values will be very small. This fake section will participate in the calculation of an analysis by the solver, however it will not participate in the definition of the joint nor in the calculation of code checks. It is shown in violet in the figure on the right.

Initial configuration	After generating rigid body

It is possible to avoid creating this fake section, by splitting the line of the braces into two lines at the intersection point.

In the case of automatic generation of joints, if the diameters and thicknesses of the segments participating in the definition of the joint are all equal, the chords will be taken on the line which is not split. Note that in the case where the intersection in X only consists of two lines, it is not possible to predict which of the two lines will constitute the chord line.

Merging tubular intersections

For structural code checks computations, close tubular intersections can be merged into a single joint which has, consequently, two end nodes.

You can merge tubular intersections by clicking on the Merge button in the Merge close intersections section of the panel of a joints group. Select joints which are candidates to the merge and choose a value for the Maximum distance allowed between intersections points parameter: all the intersections whose reference points have a distance less than or equal to the parameter value will be merged into a single joint.

The merge of intersections can be activated during the automatic generation of joints by checking the Merge close intersections check box.

Note that the merge of intersections can be performed before or after the automatic generation of the rigid bodies.

For a same joint, there will be as many rigid bodies created as there are merged intersections. In the joints table shown in previous section, the four last joints are built from the merge of two tubular intersections, that's why two rigid bodies appear in their definitions.

Joints which have several nodes are represented by as many circles as there are intersection nodes, these circles being linked by two lines. In the figure below, the four joints at the base of the jacket come from the merge of two tubular intersections.

Warning

Only joints separated by a single line section containing a single segment can be merged.

Code check criteria

Before launching code checks computations, you can check that the defined joints meet the following criteria:

the chords have the same diameter and thickness and are aligned,
the braces have a diameter less than or equal to the chords diameter.

For that, click on the Check button in the Code check criteria section of the panel of a joints group. Tolerances for chords diameters ratio and alignment can be chosen by the user as already explained in section: Generating joints automatically.

Note that if the joints were generated automatically, by construction, these criteria are necessarily verified (if the values of the angular and diameters ratio parameters chosen for the check are the same as those used during generation).

The values of the two tolerances used for the check are saved and will be used by the calculation of code checks.

Creating joints from an Excel sheet

Joints can be defined from an Excel sheet which must have the name: Joint.

There are two ways to load in the model the Excel sheet of joints:

define your entire model from Excel sheets and load the Excel file as described in section DeepLines model in Excel format.
from an existing model, load only the Excel sheet of joints from the contextual menu of the Joints root:

Note that in this last case, you can load the totality of the definition of joints and joints groups or modify locally the definition of a joint or a group of joints.

The following link gives you an example showing how to define joints explicitly (first group) or automatically (second group): example of an Excel sheet for joints.

Creating joints from a TDL file

Joints can be defined as a *JOINT section of a file in the TDL format. Refer to section Importing lines data from external file to see information about this format.

The joints are created when the TDL file is loading from the item menu Create from mesh :

The section *JOINTS of a TDL file can have an arbitrary number of lines of the following syntax:

IDJo JoType NNo NoID1 [NoID2] NCh ChID1 [... ChID_NCh] NBr BrID1 [... BrID_NBr]


IDJo	ID of the joint
JoType	Type of the joint which is always 0 (for a Circular Hollow Section joint)
NNo	Number of end nodes at the extremities of the chords line: can take only the value 1 or 2
NoID1	First end node ID which belongs to the first chord and a brace
[NoID2]	Eventually, the last end node ID which belongs to the last chord and a brace only if the number of nodes is NNo=2
NCh	Number of chord beams (must be at least equal to 1)
ChID1	ID of the first chord beam
[...ChID_NCh]	Eventually, subsequent IDs of the chord beams (up to NCh)
NBr	Number of brace beams (must be at least equal to 1)
BrID1	ID of the first brace beam
[...BrID_NBr]	Eventually, subsequent IDs of the brace beams (up to NBr)

All the nodes, chords and braces IDs must be integers.

Each node ID must reference a connection ID (see section *CONNECTION) and must be referenced in the list of nodes (see section *NODE). The coordinates of this node correspond to the coordinates of the meeting point of all chords and braces not taking account their eccentricities. For a joint, each chord or brace ID must be referenced in the list of the rigid beams (see section *RIGID) or the flexible beams (see section *FLEXIBLE).

Using joints in a structural code check study

You have first to create a New Code Check study on Steel Tubes:

The joints you are defined in the model, appear in the Selection tab of the code check study panel as described in section Code check study: