Engineering Verifications

The developments in the Computer Aided Design programs leading to more complex envelopes and continuous improvement architectural cladding materials, combined with increased tendency towards hightech façades made façade engineering an important discipline in the construction industry. We have foreseen this demand in the late 90s and established an Engineering Department which will only concentrate on technical and engineering of all issues of building physics science incorporated to façades. This investment led today a very highly qualified and experienced team of specialist engineers with Ph.D and master’s degrees who are able to work with all international (AAMA, BS, EN) as well local (SNIP,GHOST,NF,DIN) norms, codes and standards.

The function of the department is to give engineering consultancy services to the R&D Department which develops new systems, prototyping services to the custom design and product development team, to calculate all engineering issues during the project design phase, to guide the testing laboratory and to give periodical training to all technical departments. The department is equipped with the world’s newest technological equipment and the latest state of the art computer simulation models incorporating the most sophisticated methods from finite elements (FE) up to Computational Fluid Dynamics (CFD) methods, transient as well as steady state analysis, three dimensional as well as two dimensional modeling. All building physics issues; from Virtual Wind Load analysis to Static and Dynamic Structural Calculations of the system and its components, from Heat Flow Analysis to Condensation Analysis. Ventilation Pressure Analysis, Acoustical and Fire Simulations are as well in the scope of the department.

 

Wind induced pressure is a major design consideration for determining the structural analysis of the façade design. Wind loading codes of practice are limited to simple building geometries and offer little or no guidance on the aerodynamic effects of the complex façade geometries. When confronted with complex geometries or intricate façades where the building norms do not specify the wind load requirements the classical approach is to make wind tunnel simulations on scaled models (about 1: 200) of the entire building, as well as the neighbor buildings. The results are substantial extrapolations of pressure distribution which cannot give an accurate representation of pressure integration over façade. Also the scales used give rise to modeling limitations, where complex façade geometries cannot be represented.

For each project our engineering department analyses the national and international codes, the wind tunnel results if any and then designs a Virtual Wind Tunnel Model using CFD (Computational Fluid Dynamics) to predict more precisely if there is any inconveniency between the classical analog simulation and the digital simulation model. CFD analysis can be very useful to tackle with some of the limitations of wind tunnel testing since an accurate CFD model is not limited by scale. Detailed pressures over the façade and generally the mean pressures are much better predicted in CFD simulations, especially for intricate external façade elements such as shading devices and for externally ventilated double skin façades, where the codes of practice and the norms have very little guidance.

Wind induced pressure is a major design consideration for determining the structural analysis of the façade design. Wind loading codes of practice are limited to simple building geometries and offer little or no guidance on the aerodynamic effects of the complex façade geometries. When confronted with complex geometries or intricate façades where the building norms do not specify the wind load requirements the classical approach is to make wind tunnel simulations on scaled models (about 1: 200) of the entire building, as well as the neighbor buildings. The results are substantial extrapolations of pressure distribution which cannot give an accurate representation of pressure integration over façade. Also the scales used give rise to modeling limitations, where complex façade geometries cannot be represented.

For each project our engineering department analyses the national and international codes, the wind tunnel results if any and then designs a Virtual Wind Tunnel Model using CFD (Computational Fluid Dynamics) to predict more precisely if there is any inconveniency between the classical analog simulation and the digital simulation model. CFD analysis can be very useful to tackle with some of the limitations of wind tunnel testing since an accurate CFD model is not limited by scale. Detailed pressures over the façade and generally the mean pressures are much better predicted in CFD simulations, especially for intricate external façade elements such as shading devices and for externally ventilated double skin façades, where the codes of practice and the norms have very little guidance.

  • Static Modeling
  • Frame Integrity
  • Stress Analysis
  • Deflection Analysis
  • Anchor Analysis
  • Seismic Modeling
  • Impact Modeling
  • Fatigue (Cyclic )
    Simulation

An important element of the façade is glass, not only because it gives the façade its character but on the other hand due to its miraculous and intricate attributes, glass deserves most attention and engineering approach among any of the façade elements. It’s fragility besides its strength, thermal properties as well as light aspects; its behavior under thermal stress made glass selection a specialized discipline of engineering. Curtain Wall history is full of glass failures than any other type of failure. Thanks to the developments in the computer software programs all these issues can be modeled, all risks can be predicted and unwanted results are avoided. The most used modeling techniques are based on (FE) finite elements analysis, where the deflections of the glass and the stress on any part of the glass are predicted. We also use (CFD)

“Computational Flow Dynamic “models which yield more accurate results in relevant load combinations, and complicated glass carrying structures. Another important issue for glass selection is calculating the thermal stress accumulated in the spandrel glasses, verifying if adequate ventilation is provided in the space behind the spandrel glass. We use CFD models as well as specially designed local programs such as “Vitrage Decision“of French CEBTP. Engineering Department also helps to select the glass combination taking into account the thermal requirements versus the photometric properties, taking into account the radiation as well as the convection and conduction issues. This becomes very important in Double Skin Façades especially in forced ventilation systems. Although it is taken as granted, Acoustics Engineering is one of the most demanding disciplines in selection of the glass.

This study is to be realized with an holistic approach incorporating all elements of the façade, so a façade engineer experienced in acoustics consulted by an acoustics engineer is indispensable for success. Selection of the internal seals, installing sound reducing infill and playing with the combination and position of the glass and pvb layers is the secret of Acoustics Engineering. Our team has the chance to witness a lot of test made in our laboratory as well as on site, and to test their theoretical models with the real measurements, and hence guide our design department at the very beginning of the custom design systems.

The drop securing function of glass is a basic criterion for selection. Impact Tests according to the European Standard DIN, EN 12600 must be carried out to achieve this requirement. This test passes, when no large pieces of broken glass fall to ground. This test can be implemented at laboratory as well as on computer virtually.

The pendulum impact is a dynamical load simulation. The impact of the pendulum body which is modeled with a mass of 50 kg and its twin tires (according to DIN, EN 12600) is approached to the pane in little time steps. The arising contact in interaction with the pane, the variable tire foot print area and the continuously changing force during this process which acts on the pendulum as well as on the glass pane, is solved by the time step method. The drop height as well as the position of the impact can be chosen freely. The last but not the least issue about glass selection is fire safety glasses. We use complicated fire simulation software to predict the maximum temperatures that will be reached on the glass as well as the frames holding the glass. This is a preliminary study which can point out potential errors or which will give an insight to the designer in the design phase in order to avoid unnecessary expensive tests in fire chambers.

The creative use of advanced analytical tools and techniques allow the engineering department to achieve buildings that respond well to their climatic conditions. Thermal analysis applications include:

  • Convection and radiation, using advanced computational methods.
  • General heat transfer calculations, thermal bridges.
  • Moisture and condensation analyses, estimation of surface temperatures.
  • Calculation of U-Values for building construction parts.

To predict the performance of a double skin façade is not a trivial exercise.

Performance assessment of double skin systems introduces thermodynamics and fluid mechanics. The temperatures and airflows result from many simultaneous thermal, optical, and fluid flow processes, which interact and are highly dynamic. These processes depend on geometric, thermo physical, optical, and aerodynamic properties of the various components of the double skin façade structure and of the building itself. The temperature inside the offices, the ambient temperature, wind speed, wind direction, transmitted, and absorbed solar radiation and angles of incidence (each of which are highly transient) govern the main driving forces. Airflow modeling methods might be employed to assist the design of natural or hybrid ventilation systems in the decision making process. The considered airflow modeling method is "Computational Fluid Dynamics" (CFD).

The ordinary but basic condensation analysis is an essential of the work whether two dimensional and three dimensional or whether steady state and transient. In steady state condition, thermal analysis of the façade system or the interface of façades and buildings is made in two or three dimensions and in time independent form. While making surface condensation and heat transfer analysis, climate conditions of different countries are taken into consideration.

In transient method, thermal analysis of the façade system or the interface of façades and buildings is made in two or three dimensions and in time dependent form. Heat transfer and surface condensation analysis of system details are carried out in relation to daily monthly tt yearly internal and external temperature changes and in relation to the general climatic conditions of the countries in question.

Overall curtain wall thermal performance is a function of the glazing infill panel, the frame, construction behind opaque (spandrel) areas, anywhere perimeter details. Thermal performance of frame is calculated according to EN 10077-2 even with the test, and then the overall performance is calculated.