IFC. What is it, what for and what is its relationship with BIM?

Industry Foundation Classes

IFC (Industry Foundation Classes) is a standard data format which objective is the exchange of information between files that have been made by different authors; something like a PDF applied to BIM. It is an open, neutral format, not controlled by software producers, born to facilitate interoperability between various operators.

It is the main tool for the realization of the Open BIM, which represents a universal method for collaboration in the design and construction of buildings based on open standards and workflows.

Current BIM systems can create proprietary representations of construction components. IFC adds a common language to transfer that information between different BIM applications, while maintaining the meaning of different pieces of information in the transfer. This reduces the need to remodel the project in each different application. It also adds transparency to the process.

In the BIM methodology, professionals can use software from different companies, but the IFC format can link them together when exchanging valid information, regardless of the base software used.

What are the advantages of the IFC:

The main advantage offered by the IFC format is the possibility of collaboration between several figures involved in the construction process allowing the exchange of information through a standard format, in addition to easily linking alphanumeric information (properties, classification, quantities …)

It also speeds up the work, all the information of the constructive object is defined only once, providing consistency to the shared information of the project. It unifies the language of the different elements of the project, enabling the detection of possible errors or clash detection.

This leads to a higher quality, a decrease in design errors, a reduction in costs and time savings with consistency of data and information throughout the execution and maintenance process.

This format has been created by the BuildingSMART organization, formerly known as the International Alliance for Interoperability (IAI). BuildingSMART is an international organization that aims to improve the exchange of information between software applications used in the construction industry.

Currently,work in being done to formalize the IFC in other projects, such as linear engineering projects.

What is the relationship between IFC files and tenders?

With the arrival of the mandatory BIM requirements in certain tender processes in the public sector, the IFC format becomes more important, since the tender documents specify deliverables with the standardized IFC.

In summary, administrations will request the drawings in pdf and the IFC of the BIM model.

CLASH DETECTION

Errors that are normally detected on site can now be discovered and anticipated in the office through the BIM model, with the “Clash Detection” or “Interference Detection” tool:

What is an interference? An interference occurs when different elements intersect in the same space.

We highlight 3 types of Interference Detection:

  1.  Hard Clash or Hard Interference: that happens when two objects cross each other.
  2. Soft Clash or Soft Interference: that happens when objects invade geometric tolerances of other objects.
  3. 4D / Workflow Clash or Workflow Interference: which resolves crashes and programming anomalies, as well as delivery interferences.

Advantages of Clash Detection or Interference Detection:

  • It helps us to identify, inspect and notify Interferences quickly and efficiently in a project model between multiple disciplines: architectural, structural or MEP (Mechanical, Electrical and Plumbing).
  • Benefits cost control, accelerating the construction process and having a perfect design for the construction phase between architects, engineers and contractors.
  • It also provides a collaborative approach and helps finalize design changes in a very interactive way for the user. All these benefits have made clash detection and BIM coordination, one of the fundamental characteristics in virtual construction technology.

In conclusion, the detection of clashes will undoubtedly reduce construction time, minimize errors and provide a great understanding of the functionalities of the design before construction.

Today, most of the world’s leading construction, engineering and architecture companies rely on the capabilities of BIM platforms for design coordination, conflict detection and resolution, as well as programming. 3D modelling and the Common Data Environment (CDE) within BIM helps them greatly to reduce design errors.

When planning is done in advance, it reduces costs and modifications at later stages. The biggest advantage of the projects implemented by BIM is that it allows to take informed decisions in the early stages and saves engineers, MEP contractors and stakeholders a lot of issues at the end of the project.

Our company SDEA, uses Bentley Systems BIM technology for our designs, and a key tool that facilitates the good result of them, is the “Clash Detection” or “Interference Detection” tool. This tool detects conflicts, either between our models and point clouds, or between different models, elements, etc.

Together with ProjectWise, another collaborative working tool and managed environment from Bentley Systems, workflows are simplified and communication between the different parties involved in a Project is improved, which translates into a reduction in time and costs within the Project.

Example of Clash Detection applied in one of our designs for installation of electrical disconnectors in railway electrification network.

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Clash detection

THERMAL PROCESSES ARE ALREADY CONTROLLED THROUGH ADVANCES IN SIMULATION CFD

Temperature inside the Equipment in a sterilization process simulation

The implementation of new technologies in the industry is continuously increasing. The transition from the classical model of industry to the Factory of the Future and Industry 4.0 is an increasingly tangible reality. Furthermore, in Galicia, where the food and canning sector is at the forefront, it is necessary to search for and implement these new technologies in order to guarantee industrial competitiveness in the face of commercial pressure from third parties.

The EMTyS project (Thermal Multiprocessing Equipment and CFD/DES Simulation) was born from this idea. The objective of this project is to create a small equipment that can carry out the most common thermal processes in the food sector, such as sterilization, cooking, defrosting, etc.; and to complement it with computer tools and new technologies, such as Computational Fluid Dynamics (CFD), Discrete Event Simulation (DES) and Virtual Reality. In this way, the aim is to model these processes by computer and optimize them before taking them to an operating industrial plant, thus achieving a significant impact on the saving of raw materials and energy consumed.

The EMTyS project, financed through the Conecta Peme 2018 programme of the Galician Agency for Innovation (GAIN) and co-financed by the European Union through the European Regional Development Fund (FEDER), is carried out through the participation of several companies: TACORE, CITEGA, SDEA_Engineering Solutions and SOLTEC INGENIEROS, and with ANFACO-CECOPESCA as the technological centre.

Within this ambitious project, the work of SDEA_Engineering Solutions consists of the creation of a computer application that allows several iterations of different simulations of thermal processes used in the food sector using Computational Fluid Dynamics techniques.

This branch of engineering makes possible to create a 3D model of the Multiprocess Equipment with the product inside and to simulate a great variety of thermal processes using a computer by making use of a GUI (Graphic User Interface) that is easy to use. Thus, it will be possible to analyze the evolution that the products will have over time without having to waste raw material for it. Thanks to this, companies will be able to test their processing “recipes” on the computer in a simple way before testing them on the product.

Combining this with comprehensive monitoring in the simulations, areas within the equipment itself with low thermal output, or process recipes with insufficient energy optimization can be examined. This real-time monitoring in the simulations at any point of the Equipment is totally unfeasible in a real process, so this application becomes an ideal assistant for any manufacturer or process designer who wants to achieve the highest quality in their products without having to give up optimal energy efficiency in their plant.

Real time temperature and pressure evolution graphs during a simulation

ADVANCED CALCULATION METHODS IN THE PRECAST INDUSTRY ARE BECOMING INCREASINGLY NECESSARY.

GRC Facade Panel

Complex architectural elements are becoming increasingly common, and it is therefore necessary to use appropriate tools to support the challenges of the industry. An example of this is façades made in GRC.

The challenges related to enclosures and façades, with increasingly demanding requirements in structure, energy and aesthetic criteria have made certain methods guided by regulations [EUROCODE, ASHRAE…] somewhat obsolete. Advanced calculation methods are unavoidable in the construction industry.

SDEA_Engineering Solutions, with extensive experience in complex system calculations, has been involved in projects related to the GFRC [GlassFiber Reinforced Concrete] industry and its application to façades, providing design support using finite element models. Particular features of GFRC including anisotropic behaviourtypicalof materials in the concrete family and failure models, which were successfully used to shorten the design process and the construction of test prototypes.

GRC Panel

The SDEA_Engineering Solutions team has also participated in other areas related to construction, including calculations ranging from dimensioning structures with exceptional loads such as seismic and dynamic wind response to HVAC and acoustic comfort.

FSI STEEL STACK STRUCTURAL FEA ANALYSIS

Steel stack wind contours

Chimney miniature

When designing steel stack structures, several rules from standards as “ASME STS-1” or “ASCE 7” have to be taken into consideration to assure security during its useful life. This is particularly important for those located in areas subjected to heavy environmental loads, such as high activity seismic zone 4, due to the slender nature of this kind of structures thus low resonant primary modes prone to be easily excited by seismic or wind actions. In this article a brief outline about the designing process and considerations is provided based on the experience in FEA use gathered by the SDEA engineering team along different projects.

The main goal to achieve for the structure is to keep its design stresses under certain load combinations below a maximum allowable value. That is a common design strategy through many sectors; the difference here is the forces acting over the structure are somehow easy to misunderstand.

The first step is to determine the load combinations that the structure is going to be subjected to. Standards as “ASCE 7” or national regulations define the basic group of combinations to be considered during the assessment of the design, for example:

Load Combinations

The whole set of load combinations should be taken from the standards, from project’s characteristics or from customer’s requirements.

Once the load combinations are defined and the most relevant loads are identified, it’s time to calculate each of these values separately by using a finite element analysis (FEA) method over a detailed 3D model. Next, a summary of three of the most common loads shared for the most part of the projects is presented:

The first one is the dead load, and can be defined as the weight of all material incorporated into the structure, including its fixed permanent equipment such as ladders, platforms, etc. A constant when calculating stresses for different loads is that the worst situation is the one to be considered. Thus, in this case unlike the following ones, effects that reduce the total mass such as corrosion have not to be taken into consideration to not underestimate the stresses induced by the dead load expected in a real situation. A static structural FEA model can be used to precisely calculate the stresses induced by this load on every section of the stack.

The second common load is the wind load, or better said, are the wind loads. Wind load can be divided in two different loads: static and dynamic. The first one represents the action of the constant part of the wind pressure and is calculated using a static FEA model where a height dependant pressure load is applied to upwind and leeward surfaces. This pressure is obtained using standard’s equations, and usually depends on factors as the local wind speed, the geometry of the structure and the height of the point where the pressure is being applied.

The other wind load is the dynamic one, and it has to be considered due to the lightweight and flexible nature of steel stacks. It is defined as the load produced by the oscillations generated by the wind-structure interaction. “ASME STS-1” standard contains a set of rules to calculate the dynamic wind response. A more complex CFD fluid structure interaction model should be used in this case to assess the structure-vortex interaction in order to then evaluate the stresses produced. More details about the dynamic wind can be seen in this article.

Static wind profile

Last but not least, we have the earthquake load, defined as the horizontal and vertical loads related to the response of the structure to seismic motions, and are calculated using the response spectrum method. In terms of the FEA model, a coupled modal analysis plus response spectrum model is required. The pseudo-spectral acceleration (Sa) used as input for the seismic response spectrum is calculated according to the following equation:

Spectral acceleration

Where g is the gravity acceleration. R and U are factors that depend on the structure itself, being R the seismic force reduction factor that depends on the geometric characteristics of the structure and U the use factor, which defines the category of the building depending on its function and importance. The ground environment is defined by the factors Z and S. The seismic zone factor Z depends on the magnitude of the seismic forces presented on the region where the stack structure is going to be standing, and the ground factor S is a value used to define the geological conditions of the terrain.

U.S. Seismic Zones Map

The last factor C is the seismic amplification factor. It is the non-constant value that provides Sa with the frequency dependant behaviour. An example of a real pseudo-spectral acceleration is showed in the next graph:

Seismic pseudo spectral acceleration

Both the dynamic and earthquake loads have a paramount importance when designing steel stack structures due to its slender and flexible nature. Frequency excitations close to the structure’s natural mode of vibration can lead it to failure because of the appearance of resonance phenomenon. To mitigate this effect, cost-effective solutions as tuned liquid dampers (TLD, as explained in this article) are widely used.

Once every relevant load is calculated and combined according to appropriate normative, the maximum allowed values have to be obtained to assess the design, with the idea of improving it in case of not meeting the requirements, or optimizing it reduce the project expenses! These value’s calculation methodology is described in standards such as “ASME STS-1”, and are directly related to the structure’s parameters such as diameter, plate thickness, material properties, etc. Various values have to be obtained depending on the project conditions, being the most common maximum allowable values for longitudinal compression and the longitudinal compression and bending combination.

FLUID INDUCED VIBRATION

CFD contours for back wind

Preventing structural failure due to fluid induced vibration is a common challenge in the design of structures or assemblies exposed to fluid flow. Aero-elasticity theory describes the non-linear interaction between fluid-flow-induced forces and the inertial and damping characteristics of the solid structure. Depending on the nature and frequency of the flow-induced fluid forces a structure may undergo different types of flow induced vibration.

When fluid flows around a bluff body, coherent flow structures develop in the wake of the body which may become detached from the body and shed into its wake creating pressure fluctuations. If the vortex shedding frequency is close to the natural frequency of the structure, a lock-in effect occurs where the vortex shedding frequency synchronises with the natural frequency of the structure.

As a result of lock-in, resonant vortex-induced vibration (VIV) may occur, characterised by large amplitude oscillations which may lead to significant structural damage. Vortex-induced vibration is a major challenge in a range of industries such as; aerospace, oil & gas, power generation, manufacturing and civil infrastructure (such as high rise buildings, long span bridges, etc).

CFD Fluid induced vibration cone flowmeter SDEA

Another common type of flow induced vibration encountered in engineering systems is acoustic resonance vibration resulting from a non-linear interaction between the structure and high frequency pressure oscillations within the acoustic range. This type of FIV range is discussed in Part II of this Flow Induced Vibration series, the current blog entry will be primarily concerned with VIV. Two mitigation strategies may be taken to reduce the risk of damage due to VIV, the engineer can either:

  • Try to modify the flow, creating smaller scale structures whose energy is more rapidly dissipated by the viscosity effect or.
  • Modify the structure’s stiffness in order to move the natural modes of the structure to a higher frequency range and avoid resonance.

In many cases, the challenge arises from a failure of the design process to properly identify and assess any FIV sources and the structural or mechanical components that are at risk of developing FIV problems during installation or service. Computer Aided Engineering (CAE) techniques such as CFD and FEA offer a valuable tool for the fast and reliable assessment of FIV risk as well as an evaluation of potential mitigation strategies quite early on in the design process. This can lead to a reduction in development costs and an increase in the reliability of design.

How to address the problem: CFD and FEA assessment There are different alternatives to evaluate the likelihood of fluid induced vibration lock-in phenomena.

The classic approach uses non dimensional characteristics of the flow represented by invariants like Strouhal’s number. When this method is adopted different flow quantities involving geometric dimensions, velocity and material properties of the fluid are calculated to get a rough estimation for the main frequency excitation of the fluid, and that is directly compared with the natural mode frequencies of the structure. Normally a criteria based on a safety factor is assumed to get a safe design, some of our projects use a target requirement of 25% margin between the shredded fluid frequency and the natural harmonics of the structure. The main drawback of this simplified method is the non-conservative approach of assuming just a single forcing frequency and ignoring the wider frequency composition of the fluid forces. This is illustrated in the frequency plot in the Figure 2 below where the CFD predicted force signal is shown to have a much wider frequency composition than that indicated by a simple Strouhal number calculation.

With advances in CFD such as more accurate hybrid RANS-LES turbulence models and an increase in the available computing power, CFD has emerged as a reliable tool for the accurate simulation of turbulent flows and the associated fluid forces. Transient pressure pattern obtained from the CFD is obtain and using Fourier Analysis, these fluid force signals are decomposed into their spectral representation. Modal analysis using FEA may then be used to determine the natural frequencies of the structure and establish the likelihood of VIV occuring. In addition, FEA based harmonic response analysis may be used to evaluate the amplitude and stresses associated with the structural response. A detailed understanding of the structural response allows for the accurate assessment of structural fatigue life.

CFD FIV cone flowmeter SDEA

With advances in CFD such as more accurate hybrid RANS-LES turbulence models and an increase in the available computing power, CFD has emerged as a reliable tool for the accurate simulation of turbulent flows and the associated fluid forces. Transient pressure pattern obtained from the CFD is obtain and using Fourier Analysis, these fluid force signals are decomposed into their spectral representation. Modal analysis using FEA may then be used to determine the natural frequencies of the structure and establish the likelihood of VIV occuring. In addition, FEA based harmonic response analysis may be used to evaluate the amplitude and stresses associated with the structural response. A detailed understanding of the structural response allows for the accurate assessment of structural fatigue life.

SDEA’s specialist CFD and FEA services allow our clients to integrate ASME based assessments of fatigue life due to FIV into their design processes.

Industry test case: A cone Flow meter A Cone flow meter is a differential pressure flow measurement device widely used in Oil & Gas industry to obtain reliable flow rates for multiphase flows. The cone in the flow meter is subjected to high amplitude alternating turbulent forces that can potentially trigger vortex induced vibration of the cone under normal operating conditions, leading to component failure. A CFD model was used to simulate the most energetic turbulent length scales in the wake of the cone using advanced hybrid RANS-LES models and obtain the transient fluid forces acting on the flow meter structures. A FFT of the force time-series is used to obtain the spectral signature of the fluid forces. FEA based modal analysis is then used to compute the main vibrating modes of the structure as shown in Figure 3 below.

CFD fluid induced vibration SDEA FIV

The first bending mode of the structure – at 48 Hz – is shown to matches one of the high energy frequencies of the fluid force occurring at approximately 40 Hz. There is therefore a high likelihood of lock-in phenomena occurring and leading to resonant VIV unless the design is modified.

A new design configuration was developed, incorporating two additional support legs. This resulted in an increase in the frequency of the natural vibration mode and a reduction in the associated stresses levels.

Figure above shows the final design with stress contours for the first bending mode obtained from an FEA based harmonic response analysis. If you would like to know more about our team’s capabilities FIV and fatigue analysis or to discuss how we can help with your challenges in this area, please do get in touch. If you want to see an animation on FIV please visit our youtube channel and take a look to this video.