Engineering Consultancy
Overview

Engineering analysis is a tool to allow the solution of engineering design problems; computer-aided engineering analysis allows the solution of increasingly complex engineering design problems. Engineers at CREA Consultants have experience in solving engineering design problems, this experience then allows us to efficiently scope our analysis. This therefore means that CREA's core business is engineering consultancy; it is the case that most of the design projects we undertake require advanced engineering analysis.

The core competence for CREA's engineering consultancy is the study of structures and components subjected to extreme, hazard and generally unusual loading. The skill is in being able to characterise the load and then to define and build a mathematical model to reasonably represent the physics of interest. In assessing the response to extreme and hazard loads it is often necessary for the design assessment to be carried out as "beyond design code assessments, that is allowing the responses to exceed the code allowables. We are content to examine those problems that are outside the normal "comfort zone", or where specialist knowledge is required that may not be a part of the client's core competence.

We will always turn down projects where we know we cannot meet the client's requirements, unless the client specifically requests we continue.

The CREA Design Services

CREA offers its advanced design consultancy in several ways:

  • As a design service

    This is the standard form of design consultancy where CREA produces a finished design to the clients brief. We will prepare all calculations and if necessary drawings, and where necessary we will contract in additional support. (We will usually contract in design detailing expertise and draughting as this is more cost effective.) Geotechnical services are provided by a partner consultancy.

  • As an add-on to the Client's own design

    It is often the case that a design team requires a specific experience to be able to complete a design, and this experience is not part of the core business. Where it is within our core expertise, CREA can provide the necessary experience for the duration of the project on a consultancy basis. The advantage being that once the project is complete so is the CREA involvement and the cost of the specialist knowledge does not have to be borne without suitable project work to cover the cost. The secondary advantage is that as a consultancy CREA is able to continue to provide any necessary support on an ongoing basis. Two examples of why this may be necessary:

    • Design "usually" leads construction or manufacture, and it is not unknown for the design to need review and update as a consequence of factors that only come to light during the fabrication. A consultant will be fully able to take on such late project tasks as and when required, this saves the cost of retaining specialist staff between design and manufacture.

    • Many industries, particularly the safety related industries require submission of work to regulators and other approving bodies. This process is carried out after design. A consultant will be able to provide support answering approval queries and comments long after the design and fabrication is complete.


    These are just two examples of why employing a consultant is cost effective, there are many more such as the consultant providing and funding their own professional development.

  • As an advice service

    This is simply the provision of an external view with respect to a project, feeding potential design considerations into the client's design team and acting as a part of a brain storming process. CREA does not necessarily have to carry out the design work, sometimes an external opinion is useful

  • As an expert reviewer of work

    Many opportunities exist for needing external expert or peer review of work, the following identifies some such areas:

    • Quality Assurance

      Rigorous QA review of work should be based upon the reviewer being reasonably detached from the design team. This is normally achieved by the QA team crossing over from other projects. As this is not always possible CREA can carry out reviews to enable clients to demonstrate rigorous and independent QA checking. This is useful in safety related industries, particularly civil nuclear.

    • General Project Reviews

      If a client has a situation where they are extending their capability a high level overview of work carried out can often save potential problems or embracement at a later date. CREA is content to provide a high level overview of designs and work procedures to assist in capability development

    • Peer Review

      Peer review is a requirement in many industries, mainly the safety related industries. CREA has experience working with the UK MoD naval regulators and as such can provide various peer review services including Independent Technical Assessment (ITA). The service can also be provided as a "dry run" type process where QA assessments can be performed to ITA standards. This helps prepare teams for the rigours of regulatory and other approvals.


Scope of Design Capability
Structures and Components

CREA's experience covers a wide range of structural forms from both civil engineering and mechanical engineering fields. The following are some examples:

  • Nuclear Power Generation/Nuclear Reprocessing:

    • Seismic, temperature and environmental loading of structures, including reinforced concrete containment structures, steel buildings, towers, chimneys and pipe bridges.

    • Seismic Soil-Structure Interaction (SSI) and Structure-Soil Structure Interaction (SSSI) analysis of facilities.

    • Seismic and operational loading of mechanical handling plant, cranes, charge machines, etc.

    • Seismic, temperature, vibration and operational loading of vessels and pipe work.

    • Analysis techniques include: linear and non-linear static; linear and equivalent linear modal response; linear, equivalent linear and non-linear time-history (transient); steady state and transient thermal analysis with and without non-linear properties; coupled field thermal and structural.

  • Offshore Oil and Gas:
  • Onshore Petrochemical:
  • General Industry/Commercial:

    Towers and Masts
  • Forensic/Troubleshooting:

Loading Regimes

CREA offers an engineering consultancy service for the design of structures and components subjected to extreme environmental, hazard or unusual loads (extreme loads):

  • Environmental Loading
    • Wind 
      • Long return period loading 
      • Vortex Shedding
    • Wave
    • Seismic
    • Temperature Extremes
  • Hazard Loading
    • Fire
    • Explosion/Blast
    • Impact
  • Dynamic Loading/Response
    • Vibration
    • Impact
  • Thermal
    • Steady State
    • Thermal Transient

Static Loads on Structures

Analysing structures and components subjected to static loading is clearly the most common form of engineering analysis. Static loads take many forms and include static representations of dynamic loads. One of the most common dynamic loads applied as a static load is wind loading. However, static loading does not mean an unconditionally simple analysis, particularly if there are non-linearities present.

CREA's capability with static loading is wide ranging and includes:

  • Simple load application;
  • Non-linear static loads, that is static loading that is non-linear with one of the analysis parameters such as time, structural response frequency, temperature, etc;
  • Non-linear material response;
  • Non-linear structural response such as large displacement (P-Delta and stress stiffening effects);
  • Contact, where areas of the structure separate or make contact due to the loading; and
  • Any combination of the above (and others)

Dynamic Loads on Structures

Many structures and components are subjected to dynamic loading, however, as the responses can be complex these loads are often characterised as static loads. The dynamic responses are then catered for by means of additional response factors or reduced design allowables. There is often a significant advantage to be gained from performing a dynamic analysis as depending upon the analysis type the actual (or near actual) response is assessed and the need for additional design factors is removed. Indeed, pseudo-static loading approaches work by assuming that the dynamic response develops and amplifies. A full dynamic analysis can often identify attenuation or no amplification.

CREA's engineers have thirty years of experience in examining dynamic loads on structures. Our general approach is to work up the chain of complexity in dynamic analysis as this has two advantages: building complexity builds validation of the final result; and if a reasonable or comfortable solution is found using the initial approaches the analysis can be stopped leading to a more cost effective solution.

CREA's has experience in most forms of dynamic analysis such as:

  • Steady state;
  • Random vibration; and
  • Shock.

Methods of solving dynamic problems include:

  • Hand assessment (using texts such as Biggs and Blevins);
  • Mode frequency and modal response analysis;
  • Harmonic (steady state); and
  • Time-history or transient analysis.

The combination of skills and analysis capability allow us to approach many dynamic loading scenarios including:

  • Seismic;
  • Wind;
  • Wave;
  • Vibration;
  • Blast/Explosion; and
  • Impact.
Temperature and Thermal Load

Thermal and temperature loading of structures covers many loading scenarios, from simple daily atmospheric temperature variations, to process temperatures, through to fire. CREA has the capability and experience to analyse these and many other thermal processes. Our analysis can be carried out as a steady state loading, or a transient load. The material properties can be linear or non-linear, along with linear or non-linear heat loss and heat gain. Using ANSYS it is possible to directly map the thermally induced temperature and heat profiles directly to a structural model to efficiently study the physical effects of the thermal loading.

One particular area of expertise within CREA is the analysis of offshore production facilities subjected to fire loading to allow optimisation of passive (and a lesser effect active) fire protection. The technology can also be used to predict a time to potential global collapse, this then allows the safety case to take account of the stability of the structure when assessing escape times.

Some examples of CREA's thermal analyses:

  • Fire loading to offshore oil and gas production facilities for fire protection optimisation;
  • Fire loading to pressure vessels and other process equipment to demonstrate survivability, this includes an assessment of heating of internal contents and pressure rises;
  • Fire onto a chemical reactor (non-nuclear) to predict survival;
  • Temperature distribution in a disc brake during a failure condition; and
  • The assessment of the heating of a fire appliance aluminium boom whilst fire fighting.
Extreme and Hazard Load Resistance

When considering response to these types of loading the application of standard design codes of practice is either modified or not applicable. CREA's engineers have over 30 years experience in designing to these conditions in many industries, particularly safety related industries. In designing to resist extreme loading it is often possible to design to mitigate effects. For instance, structures can be designed to "ride" earthquakes, or resist fire and explosion.

Another common approach, more normally applied to fire resistance, is to allow a structure to collapse, but to control the collapse. The process is for the safety case to define a reasonable safe evacuation time, then for the fire protection to provide stability for the evacuation period. This technique allows a cost effective protection system to be designed.

The techniques necessary to design for extreme loads also lend themselves to trouble-shooting designs where there has been a failure to perform to specification, where a specification has changed significantly, or where there has been an actual failure in operation.

Structure/Component Load Capacity

The assessment of load capacity, be this for operational loading or the ability to sustain over-load is a common engineering requirement. The need can arise where new loads are to be applied to a structure, or where an existing structure has to meet new regulatory requirements.

Another common use of the examination of load capacity is for the purposes of post incident investigation where it is necessary to find the potential cause of failure, i.e. forensic investigation of loading and response. Equally, the examination may be due to a product's failure to meet specification where it is necessary to change safe working loads or to identify design modification.

CREA employs all of the methods described on this page to carry out forensic examination of structures, this is typically a combination of analysis and inspection of the actual structure or component.

Multi-Physics

The term "Multi-Physics" is relatively new, and has been coined to describe the interaction between say fluid flow and structural response. It is of particular importance where the flow of say water through a system loads the structure and causes structural deflections. If the deflection is significant enough to alter the flow regime, then a feedback of structural deformation to the fluid analysis is necessary (or desirable). Engineers have dealt with multi-physics for decades: wind on structures; airflow over aircraft; boats moving through water; aero-elastic response of towers, masts and wings; response of structures to blast, fire, etc. However we now have some classification of multi-physics, and the bulk of the past analysis has been of the loosely (or weakly) coupled variety. This is where the loading from one physical environment, fluid flow for instance, is calculated separately from the structural response. There is no formal automatic feedback loop from one to the other, although sensitivity studies may be performed.

The top end of the multi-physics environment is where all physics affecting a structure are calculated in the same tightly integrated package and the interaction of the various physical environments is assessed simultaneously.

CREA's current capability is of the uncoupled and loosely coupled variety. The areas of expertise are identified throughout this page.

Beyond the Code Allowables

There are many situations where it is necessary to design structures or components to perform beyond the requirements of design codes and design standards. The most common of these is the assessment of structures to extreme or hazard loads, where the probability of occurrence of the loading can be very low, such as 10-4 per annum. These are the kind of loads applied to safety related structures such as nuclear facilities and offshore production facilities. In these design cases the load factors are often reduced to 1.0, and the limiting design stress becomes the onset of yield, or even allowing partial yield of cross sections.

This kind of approach is usually found where the "As Low As Reasonably Practicable" (ALARP) principle is being applied to risk of failure. There is now a trend for operational safety cases to be required to obtain regulatory approval to operate plant and systems that pose a danger to the general public and workers alike. These safety cases now often require the demonstration that designs satisfy the ALARP principle. The ALARP principle is the demonstration that the risk of severe injury or death is As Low As Reasonably Practicable. This requires that the designers demonstrate that the design has used "state of the art methods", and that all reasonably foreseeable loads have been considered. Reasonably foreseeable loading can often mean looking at loads with a probability of occurrence of 10-4p.a., compared to the normal design consideration of 0.02p.a. or 10-2 (more commonly referred to as 1:50 year and 1:100 year events).

CREA's experience in this level of design and analysis has been developed in our work to support safety cases in the nuclear, defence and oils and gas sectors. We are able to demonstrate structural resistance for beyond design code responses with reference to the code being used as a basis. A structure is not unsafe because it fails to satisfy a design code, beyond design code design is used to eat into the inherent conservatism of codes.

Finite Element Analysis as a Design Tool
General Design

Finite Element Analysis is well suited to the analysis of structures and components with the results being passed to the design process. An often overlooked capability is to allow the FE solution to perform design calculations. CREA uses the well developed and powerful macro programming language within ANSYS to perform design calculations within the solution. This removes the need to perform general and in many cases detailed design assessments on the analysis results each time an analysis is run. The outcome is an efficient means of screening the outcome of parametric and sensitivity analyses. The result is a very much reduced design time and allows effective examination of design options.

Design Optimisation

A very powerful extension of allowing the FE solution to perform design calculation is to run design optimisation. Design optimisation will typically be used to make efficient use of material, reduce weight, cost or stress. The process can also be used to automatically scan a design for design parameters, or it can be used to tune or detune structures subjected to a particular loading regime.

CREA uses the ANSYS design optimisation facility in conjunction with the macro language to optimise design.


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2011 CREA Consultants Ltd, High Peak, UK
Last Updated 25 Apr 2011