Scaffolding checks EN 12811-1 (esasd.13)

 

esasd.13

The innovative technologies like Parametric Modelling, Template Analysis and TrueAnalysis, together with advanced analysis options covering different types of non-linearity enable the engineer to perform real Computer-Aided-Engineering in the field of scaffolding design.

Highlights
Full integration in the main graphical user interface
Integrates complete modelling, analysis and drawings
Detailed modelling of all scaffolding parts
Semi-automatic determination of buckling lengths
Specific checks according to EN 12810 and EN 12811

Modelling

SCIA Scaffolding offers different approaches for modelling of different types of scaffold. The user chooses what best meets their current needs.

Scaffolding types

Steel as well as aluminium materials are available for input and analysis.

Tube & Coupler scaffold consists of tubes connected by couplers. Their main advantage is their versatility. SCIA Scaffolding models this using the coupler types given in Annex C to EN 12811-1.

Modular systems are defined as systems in which the transoms and standards are separate components. The standards provide facilities at pre- defined (modular) intervals for the connection of the other scaffold components. One of the main advantages is a short erection time.

Frame systems are a special type of modular systems in which standards and transoms are already welded together as fixed frames.

Modelling methods

Direct Scaffold Modelling

All standard modelling and manipulation (copy, move, mirror, etc.) functions and all available tools (UCS, activity, layers, etc.) of the generic SCIA Engineer environment are used for setting up an analysis and structural (or CAD) model of the scaffold.

In the case a 2D or 3D CAD model of the scaffold is available, this is directly imported as an analysis model. Even an architectural model is imported, which allows the user to model the scaffold next to the existing building.

In addition, any pre-prepared User Blocks, i.e. standardised or parametric blocks of geometry defined by the user (e.g. commonly used frame systems), are read into the model of the analysed scaffold.

Scaffolding Templates

Engineers who deal with the design of scaffolds regularly will definitely welcome the possibility to prepare tailor-made templates for all types of scaffolds they have to handle. The advantage of using templates is that all common data (e.g. materials, cross-sections, stiffnesses, combinations, basic geometry, etc.) will be defined just once – on creation of the template, which allows for a very fast input.

Analysis

The analysis of the scaffold includes proper defi- nition of loads and combinations, calculation and design in compliance with the scaffolding-related code.

Loading

According to EN 12811-1 a scaffold should be designed for two specific conditions:

  • In Service: characterized by a high working load and only a minor wind loading.
  • Out of Service: characterized by an extreme wind loading and a small percentage of the working load.

Two SCIA Engineer unique features are used here with great advantage: Template Analysis and Load Generators. Templates save a lot of effort as they may have predefined all required load cases and combinations. Load Generators enable the user to define the loading plane and the program automatically distributes the loading on all members within that plane. This is for example used for generation of wind loading on the scaffold.

Calculation

The analysis includes standard linear elastic analysis, as well as advanced second order analysis which includes both global (P-Δ) and local (P-δ) effects. SCIA Engineer uses a stability analysis to determine the buckling shapes of the scaffold, which in turn are used as imperfections for the full second order analysis.

Other calculation features are used for handling of various specifics of scaffold structures: non-linear functions for coupler stiffness, friction supports for base jacks, pressure-only supports for abutments, gap elements for margins between the pen and hole, etc.

Design: limit states

In the ultimate limit state, the scaffold members are checked according to the capacity check defined in EN 12811-1. SCIA Scaffolding also per- forms a coupler check as defined in EN 12811-1. In addition to the specific scaffolding checks, full design and check of the structure according to EN 1993-1-1 is also available for those scaffolds which do not meet the EN 12811 prerequisites.

Moreover, users can evaluate deformations of the scaffold and even perform a check on the relative deformations. This is particularly important for ledgers that support floor boards.

Scaffolding components

SCIA Scaffolding allows for an accurate modelling of different scaffolding components including their appropriate specifics.

Diagonals are typically attached with an eccentricity due to the geometry of the attachment between the standards and the diagonals. In addition to the eccentricity, a special behaviour of diagonals in modular systems is that they mostly have a small gap along their length, caused by a slight margin between the pen and hole. If specific test results for the diagonals of modular systems are available, the stiffness derived from the tests is accounted for using a translation spring.

SCIA Scaffolding integrates an extensive library of couplers which contains the different types given in Annex C to EN 12811-1 including their stiffness. The user can also add their own couplers in this open library.

Scaffolding structures typically have two types of floor systems: metal boards or wooden planks.

The metal floor boards are accounted for in the stiffness of the analysis model. If wooden planks are used, however, the stiffness of the planks cannot be accounted for since the planks are put loose on the transoms. In this case, the planks are modelled as an extra load.

Base jacks at the bottom of the scaffold feature specific behaviour. In most cases, the base jacks are not fixed to the ground. Moreover, the horizontal resistance is purely dependent on friction. This is modelled using friction supports.

Also the connection between the ties and the façade as specified in EN 12810-2 is effectively modelled.

Drawings

A separate module [see esadt.01 - Steel overview drawings] is an extra and very effective tool for the automatic generation of 2D and 3D overview drawings of the structure. The generated images can be edited, combined with other drawings and inserted in a paper space gallery. All drawings remain connected to the original model, which means that they are automatically regenerated after any modification of the model.

Code checks

Input of initial deformation of structures for scaffolding users, together with member check (DIN 4420 part 1) and connection or scaffold coupler checks for scaffolding structures according to EN 12811-1

Extensions to EN Steel Code Check according to the Scaffolding code EN 12811-1

The Eurocode steel code check has been extended for the design of scaffolding projects. Additions have been made for:

  • Checking tube members (art. 10.3.3.2; interaction equation and DIN 4420 part 1)
  • Checking base jacks according to Eurocode (Checking the ultimate moment (Mu) depending on the axial force in the selected standard)
  • Checking non-linear hinges in connecting nodes between standards with horizontals, standards with diagonals and beams with beams. The non-linear hinges are selected from a (pre- defined) user library list in SCIA Engineer
  • Checking resistance values against the design forces (Annex C of EN12811-1) and the combination of actions (art. 10.3.3.5; equation 10 and 11) for couplers from a user library. This library provides the following user-selectable items:
  • Right-angle coupler
  • Sleeve coupler
  • Swivel coupler
  • Parallel coupler

Determination of system and buckling lengths for columns beyond a node with a flexible hinge

In typical scaffolding projects, columns in a frame are considered continuous; however in this case, the connection between the columns is typically a flexible hinge. This means the system length should go on beyond the flexible spring. However, in former SCIA Engineer versions the system length is automatically stopped at the node if a hinge, either free or flexible, is found.

In SCIA Engineer the determination of system lengths (and buckling lengths) beyond a node with a flexible hinge is different from the standard solution where the system and buckling lengths are determined by the flexible hinge and will be cut at the level with the hinged node. When the scaf- folding functionality is selected this determination ignores the node with the flexible hinge and the system length will automatically go beyond this node and will therefore not consider it as a divider for the buckling lengths.

24/03/2016