Frew

Frew Benefits

  1. Accurate simulation of problems with a wide range of capabilities for retaining walls
  2. Integrated partial factor analysis including EC7
  3. Quick method of analysis and extensive output capabilities

About This Software

The ideal tool for embedded retaining wall analysis

Frew enables engineers to define and solve even the most complex embedded retaining wall design problems quickly. Easy to set up and use, Frew is relied upon by leading engineering firms around the world.

Fast analysis with high quality and flexible output

Input

Frew has been developed with a model wizard to enable the user to set up the problem quickly and Frew automatically generates nodes for the user based on level inputs. Advanced input features are also available such as the batch testing feature which allow the user to compare the performance to the retaining wall at different toe levels.

With this software, engineers can calculate the required wall embedment length using a choice of methods. Frew offers quick problem setup and revision with a unique stage ‘memory’ feature. 

Analysis

Frew checks the stability of cantilever and propped retaining walls using the Limit Equilibrium analysis methodology. Using Soil Structure Interaction, Frew predicts the displacement, shear forces, and bending moments of the wall. With this software, engineers can calculate the required wall embedment length using a choice of methods. Frew offers quick problem setup and revision with a unique stage ‘memory’ feature. It enables users to model sheet pile corrosion by varying the stiffness down the wall.

More advanced analysis options have been developed for Frew. For example, the user can carry out integral bridge analysis or model wall relaxation.

Output

Frew and predicts the displacement, shear forces, and bending moments of the wall. The program also calculates the earth and water pressures on each side at each construction stage. Suitable for sheet pile, secant, contiguous or diaphragm walls, it supports the latest building standards.

It also provides fast analysis with high quality and flexible output, including results that can be exported to Excel for post-processing.

Frew Screenshot

Quick Overview

Frew enables engineers to define and solve even the most complex embedded retaining wall problem quickly.

Features

Incorporated Stability Checks

Frew allows the user to run limit equilibrium analyses on each construction stage within the program. This allows the user to determine the wall toe depth more easily. This feature considers the fixed or free earth mechanism. The analysis considers groundwater levels, groundwater flow, surcharges and multiple prop positions.

Oasys_Frew_Stability_Check

The output shows the calculated toe level for each stage and the lowest calculated toe level can be used to automatically generate nodes.

Frew - toe depth summary

Alternatively, if the user would like to specify the toe level, this feature could be bypassed.

Frew_node_generation_data

Analysis Methods

  1. "Safe" flexibility method - the soil is represented as an elastic solid with the soil stiffness matrices being developed from pre-stored stiffness matrices calculated using the "Safe" finite element program. This method is ideally limited to a soil with linearly increasing stiffness with depth, but empirical modifications are used for other cases.
  2. Mindlin method - the soil is represented as an elastic solid with the soil stiffness based on the integrated form of the Mindlin Equations. This method can model a wall of limited length in plan but is ideally limited to a soil with constant stiffness with depth but again empirical modifications are used for other cases.
  3. Subgrade reaction method - the soil is represented as a series of non interactive springs. This method is considered to be unrealistic in most circumstances.
  • problem geometry including dig depths, distances to remote boundaries
  • wall profile bending stiffness and creep
  • soil stratification, strength, density and stiffness
  • struts (or anchors) including prestress, stiffness, inclination and a lever arm (to represent rotational fixity).
  • surcharges including depth and extent
  • groundwater levels and pore pressures each side of wall.

Frew is a program to analyse the soil structure interaction problem of a flexible retaining wall, for example a sheet pile or diaphragm wall.

The wall is represented as a line of nodal points and three stiffness matrices relating nodal forces to displacements are developed. One represents the wall in bending and the others represent the soil on each side of the wall.

Frew_subgrade_reaction_model

The soil behaviour is modelled using one of three methods:

Frew_loaded_boundary_vs._rough_ridge_boundaries

The program analyses the behaviour for each stage of the construction sequence. At each stage it calculates the force imbalance at each node imposed by that stage and calculates displacement and soil stresses using the stiffness matrices. If the soil stresses are outside the active or passive limiting pressures correction forces are applied and the problem solved iteratively until the stresses are acceptable. Allowance can be made for arching within the soil body when calculating the active and passive limiting pressures.

The following input parameters are included in the analysis:

The program gives results for earth pressures, shear forces and bending moments in the wall, strut forces and displacements. These are presented in tabular form and can be plotted diagrammatically. In addition the number of iterations, the displacement error between successive interactions and the maximum earth pressure error are output.

A video giving an overview of the analysis methodology and advanced analysis options can be viewed here:

Advanced Analysis Options - Undrained to Drained Modeling

  1. initialise stresses with drained materials
  2. Switch to undrained soils
  3. Model sequence
  4. Apply estimated undrained pore pressure profile to undrained materials (no movement)
  5. Switch to drained parameters (no movement)
  6. Switch to long term pore pressures

Frew will now calculate the undrained pore pressure based on the Mohr Coulomb or Modified Cam Clay models. The user can do this by assigning a drained material to the undrained material in the Property Table (see below) and the program uses this as a basis for its pore pressure calculation.

Frew_property_table

This enables the user to bypass the manual sequence (outlined below) that was required for the modeling of drained to undrained soils and vice versa.

Typical Modelling Sequence:

Advanced Analysis Options - Wall relaxation and creep

Frew enables the user to specify the wall relaxation which can be used to model creep.

Frew - specify wall relaxation

Creep is modeled by applying the relaxation and change in Youngs Modulus.

Frew - Creep modelled

Advanced Analysis Options - Modelling Axi-Symmetric Problems

Frew provides facilities for analysis of a plain strain excavation (e.g. an infinitely long trench) by enabling the user to apply a rigid boundary at the centerline of the problem.

Frew - Modelling Axi-Symmetric Problems

Modeling of Props and Anchors

Struts may be inserted (or removed) at any node at any stage in the analysis. More than one strut may be defined at a particular node, and not all struts need to act simultaneously.

Modeling an applied moment or moment restraint

An applied moment or a moment restraint at a node can be modelled by using a strut with an inclination of 90 degrees and a non-zero lever arm together with an applied pre-stress force or a stiffness respectively.

Frew - Modelling Props & Anchors

Modeling of Props and Anchors

Stressing an anchor may be modeled by specifying a strut with a pre-stress force equal to the stressing force and a zero stiffness. The stiffness of zero would maintain a constant force at the point of application throughout the analysis.

In subsequent stages after the anchor is 'locked off' it is usually convenient to remove this strut and insert a strut that models both the pre-stress and stiffness of the anchor

Inclined anchors are modeled by specifying an inclination to the horizontal and if they are not applied at the vertical axis of the wall a lever arm can be specified to allow for this.

Easy Inputs - Model Wizard and Graphical Input

The New Model Wizard is accessed by selecting the 'File | New'(Ctrl+N) option from the main menu, or by clicking the 'New' button on the Frew toolbar. The New Model Wizard is designed to ensure that some basic settings and global data can be easily entered.

Frew - Model Wizard

Frew - Model Wizard 2

Clicking "Finish" completes the wizard and creates Stage 0 with the input data.

The graphical input view will open to allow entry of node levels (if these are being created manually). If automatic node generation was selected, the graphical input view will show a single soil zone extending the full depth of the problem.

More soil zones can be added as required to set up the initial ground profile for Stage 0.

Strut and surcharge data is added separately, and additional stages created

A video showing how the wizard and graphical input can be used to create a file is available here:

Easy Inputs - Automatic Node Generation

Frew now generates the nodes automatically based on inputted levels (of stratigraphy, struts etc.). This option also allows the user to input the toe level of the wall or use the toe level calculated from the stability check.

The whole process, including the setting up of the problem, the stability analysis and the automatic node generation is demonstrated in this tutorial video:

Frew - Node generation

Easy Inputs - Batch Analysis for Multiple Toe Levels

Frew allows the user to specify a number of toe levels.

Frew -Node Generation

By doing this, they can create a number of files with wall toe depths at different levels. Consequently, the outputs and performance of the walls at different toe depths can be compared.

A demonstration showing how to set this up and create the multiple files is available in this video tutorial:

Partial Factors

Frew allows the user to specify partial factors, which can be applied to material properties or surcharge input parameters.

Frew - partial factors

A pre-defined list of code compliant partial factors are also available:

Frew - code compliant partial factors

Graphical and Tabular Outputs

The graphical and tabular outputs in Frew have been developed for use by Eningeers in design and as images in reports.

The tabular outputs can be printed by stage or exported to excel for further analysis.

The graphical output enables the user to zoom and scale. Specific outputs can be chosen (e.g. displacements or bending moments) and the envelope of results can be viewed.

Frew - Graphical Output

A demonstration of the graphical and tabular outputs is available in this tutorial video:

Verification with Site Data and FE

Frew has been used for a number of years and there are numerous examples of where Frew results have been compared to 2D FE and empirical results.

Various illustrations of this can be found in literature:

Ciria C580 (Appendix A10)
Rocoe, H. (2003), Retaining Wall Movements, CTRL Contract 430 - Ashford Tunnels, BGA International Conferenve on Foundations

An example of where Frew has been compared to site data can be found in the following case study: http://www.oasys-software.com/casestudies?id=56/

A further example of where Frew has been used to obtain data for 3D FE analysis and its results compared can be found in the following case study: http://www.oasys-software.com/casestudies?id=63

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Locked to an individual machine but transferrable by the user to another machine.

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Shared Licences can be activated on any number of machines, however you can only concurrently use the number of licences that you have purchased.

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