Software version:       ConSteel 17 Build 3303

Keywords:                  Modeling; Analysis; Design; Lattice girder; Getting started;

Model examples

Design objective, choice of design standard

This design guide is intended for novice ConSteel 17 users and provides a step-by-step guide for designing a simply supported lattice girder. The geometry of the lattice girder to be designed is known from the architectural conceptual design, (Figure 1). According to the concept, the lattice girder chords are made of hot-rolled sections of HEA120, while the lattice bars  are made of cold-formed SHS80x4 sections. The design of the connections is not included in this guide.

It is well known that structural design is always carried out according to a certain standard or its version. The selection of the standard can be made from the Design Standard menu when creating a new model in the Project Center, or it can be modified later in the Standards tab [S1] selection panel (Figure 2).

The desired design standard can be selected from the list on the left of the panel. In this case, we select the EN Recommended option [S2]. The parameters applied by the selected standard can be accessed by selecting the corresponding row of the middle table [S3] of contents in the right-hand table [S4]. In Figure 2, the combination factors corresponding to Table 1.1 of the EC0 standard have been selected, whose parameters are shown in the right-hand table.

Setting the  grid raster editor

First, let’s set the size of the raster according to the span of the structure by using the corresponding button [1] of the tool group on the left, which will bring up the Grid and Coordinate System adjustment panel (Figure 3).

For example, for the 19.6m long support, the Size window can be set to 20000 millimeters [2]. To update the setting, press Enter. With the above setting, the raster will be 20m wide in X and Y directions, the raster line density will be 1000mm, and the step spacing will be 250mm. It is convenient to add the grid support model in the X-Z global coordinate plane, so the raster editor will be rotated to the X-Z plane. To do this, select the XZ plane option [3].

Loading initial cross-sections

One fundamental characteristic of general structural analysis programs is that they can only work with specifically defined cross-sections. Therefore, the first step is to choose the initial cross-sections for the task, according to the conceptual design. This may seem contradictory to the simple manual methods taught in basic statics courses, where the specific dimensions of the cross-section were often irrelevant information (e.g. calculation of internal forces). When using computer programs, however, we need to provide specific cross-sections even if their dimensions do not affect the static quantities to be calculated (e.g. in the present case, the normal forces of a truss beam). Nevertheless, we should aim to select cross-sections that match the geometrical size of the structure. In this case, the preliminary design served this purpose.

Initially, the section library for the current model is empty, so we first need to select the appropriate cross-sections. To do this, go to the Structure Members tab [4] and select the Section Administration option [5] on the left side of the horizontally positioned tool group, then select the “From Library…” button [6] in the panel that appears (Figure 4).

Figure 5 shows the loading of the HEA120 section, compliant with the European standard, which will be assigned to the chords. We select the region of the cross-section standard (European) and then its type (H profiles). From the list that appears, we can select the type of section (HEA) [7] and then the height of the section (120) [8]. By pressing the Load button [9], the program learns the cross-section, and from then on it knows everything about the cross-section and can work with it. Repeat the procedure as many times as you need different sections. Finally, the window is closed by pressing the Close button [10].

In our case, also a CF-SHS 80×4 closed section (from Library/Hollow sections – cold formed/CF-SHS/CF-SHS 80×4) was loaded for the bracing members (Figure 6).

Later on, you can obtain all the information about the cross-section using the Section module. To do this, select the cross-section in the table by clicking on the corresponding row and then click on Properties… to display all the properties of the cross-section, such as type data; cross-section characteristics, etc. The program works with two cross-section mechanical models in a dual manner. The GSS (General Solid Section) model [11] is used for static calculations and the EPS (Elastic Plate Segment) model [12] for standard design operations (Figure 7). The cross-sectional properties (surface area, moments of inertia, etc.) can be displayed by pressing the button [13].

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Did you know that you can use Consteel to design a pre-engineered Metal Building with all its unique characteristics, including web-tapered welded members, the interaction of primary and secondary structural elements, flange braces, shear and rotational stabilization effect provided by wall and roof sheeting? 

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This overview delves into Consteel’s solution, offering an alternative approach to calculating effective cross-sectional properties and reshaping conventional methodologies in structural analysis and design.

Determine the strength utilization of a double symmetric welded I cross-section with 384×4 web and 300×8 flanges, if the internal forces on the cross-section are N_Ed=500kN compressive force and M_y,Ed=100kNm bending moment. The material grade of the cross section is S235.

Calculation of cross-sectional properties

First, take the cross-section data (symmetric welded I-section), from which the Consteel software generates the EPS (and GSS) (see Online Manual/10.1.1 The EPS model) cross-section model (Fig. 1).

If the cross-section is class 4, the effective model is determined by the assumed normal stress distribution. According to EC3-1-1, the EPS model of a class 4 cross-section can be defined in two ways :

– method A: based on pure stress conditions,

– method B: based on complex stress condition.

In order to compare the results, the cross-section properties will be calculated by method A at first and then by method B.

Cross-sectional properties by method A

• pure compression N_Ed  (Fig. 2): 

A_eff=4720mm²   

• pure bending M_y,Ed  (Fig. 3): 

W_eff,y,min=864080mm³

e_z=14.5mm 

Cross-sectional properties by method B

GATE

The latest version, Consteel 17 is officially out! In 2023, our main focus for Consteel development is improving usability. New features prioritize efficient model manipulation, easy modification, and clear information presentation across Consteel, Descript, and our cloud-based platform, Steelspace. In this comprehensive video, we walk you through a step-by-step workflow guide, demonstrating how to leverage Consteel 17 to its full potential.

If you would like to delve deeper into the new features, check out our detailed blog post for an in-depth exploration of Consteel 17’s capabilities.

In Consteel, the calculation of cross sectional interaction resistance for Class 3 and 4 sections is executed with the modified Formula 6.2 of EN 1993-1-1 with the consideration of warping and altering signs of component resistances. Let’s see how…

Application of EN 1993-1-1 formula 6.2

For calculation of the resistance of a cross section subjected to combination of internal forces and bending moments, EN 1993-1-1 allows the usage -as a conservative approximation- a linear summation of the utilization ratios for each stress resultant, specified in formula 6.2.  

$$\frac{N_{Ed}}{N_{Rd}}+\frac{M_{y,Ed}}{M_{y,Rd}}+\frac{M_{z,Ed}}{M_{z,Rd}}\leq 1$$

As Consteel uses the 7DOF finite element and so it is capable of calulcating bimoment, an extended form of the formula is used for interaction resistance calculation to consider the additional effect.

$$\frac{N_{Ed}}{N_{Rd}}+\frac{M_{y,Ed}}{M_{y,Rd}}+\frac{M_{z,Ed}}{M_{z,Rd}}+\frac{B_{Ed}}{B_{Rd}}\leq 1$$

Formula 6.2 ignores the fact that not every component results the highest stress at the same critical point of the cross-section.

In order to moderate this conservatism of the formula, Consteel applies a modified method for class 3 and 4 sections. Instead of calculating the maximal ratio for every force component using the minimal section moduli (W), Consteel finds the most critical point of the cross-section first (based on the sum of different normal stress components) and calculates the component ratios using the W values determined for this critical point. Summation is done with considering the sign of the stresses caused by the components corresponding to the sign of the dominant stress in the critical point.

(For class 1 and 2 sections, the complex plastic stress distribution cannot be determined by the software. The Formula 6.2 is used with the extension of bimoments to calculate interaction resistance, but no modification with altering signs is applied)

Example

Let’s see an example for better explanation.

GATE

Did you know that you could use Consteel to build 3D models with smart link elements which automatically adapt the model when profiles are changed?

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Did you know that you could use Consteel to determine the optimum number of shear connectors for composite beams?

Download the example model and try it!

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Did you know that you could use Consteel to perform local and distortional buckling checks for cold-formed members?

Download the example model and try it!

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Did you know that you could use Consteel to calculate effective cross-section properties for Class 4 sections?

Download the example model and try it!

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If you haven’t tried Consteel yet, request a trial for free!

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When applying design rules in load combination filter, the most frequently used utilization type is Steel – Dominant results. What results are exactly considered by this option and what do corresponding limitations mean?

Introduction

There are four ways to apply load combination filter: based on limit states and load cases, manually, and by rules. Unlike the other three methods, filter by rules is only possible based on analysis and/or design results.

The most effective way to reduce the number of load combinations is definitely the use of design rules.

With design rules, load combinations can be selected based on utility ratios. Utilizations are available from several design checks, including dominant results and detailed verifications for steel elements, such as general elastic cross-section check, pure resistances, interactions, and global stability.

The meaning of the dominant check

The dominant check is not always the check which gives the maximal ratio but the one with the maximum RELEVANT ratio. Typical example: if plastic interaction formulas are valid, those results will be dominant over general elastic cross-section check results, although the latter are higher.

Steel – Dominant results

Steel – Dominant results option contains the utility ratio of the dominant check at every finite element node, in all load combinations. Meaning that there are as many utilization values as the number of load combinations calculated, in every FE node.

It is also important to understand the difference between the utilizations of Maximum of dominant results and Steel -Dominant results. Maximum of dominant results option contains the dominant utility ratio of the dominant load combination at every node, like an envelope of Steel-Dominant results. Meaning there is only one utilization value in every FE node. Also, it is the same as the dominant result table on Global checks tab.

When a rule is applied, the utilizations of the chosen utilization type are compared against the limitation. The load combinations which give the results that correspond to the limitation, are selected by the rule. Every FE node of the selected model portion is examined.

Limitations in case of Steel – Dominant results

• Maximum: to select the combinations which cause the maximum utilization at any node. It can be the same as Maximum of dominant results, except if there are combinations where the utilization is the same and it is maximal. In this case, here all the combinations are selected, while with Maximum of dominant results, there is always one maximum.
• More than % of maximum: to select the combinations as in ’Maximum’ plus those which cause utilization that is more than the given percentage of the maximum. E.g. at a certain point max utility ratio is 80%, Limitation= More than 90% of maximum. This rule will select all the load combinations which cause utility ratios between 0,9*80=72% and 80%.
• More than: to select the combinations which cause utilization more than the defined value at any point.

Let’s see an example of a simple 2D frame for better explanation. Right-side beam is in the portion for which three design rules were applied. Five points are selected for representation but of course all the nodes of the portion are examined against the rules’ limitations.

The utilizations of the five dedicated FE node in all 11 load combinations are shown on the below diagram. (To find all of these utilizations in the attached model, global checks must be calculated for the load combinations one-by-one.)

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