In the European Union 40% of the total final energy is consumed in residential and tertiary buildings. That is reason behind several European Directives established with the aim that the Member States develop long-term strategiesencouraging the renovation of residential and commercial buildings applying specific energy efficiency criteria. In order to define efficient strategies they have to be established in a holistic way; beyond individual buildings and thinking in wider terms of districts and cities. For this reason, several research projects are nowadays exploring the best way to perform retrofitting activities with those results in mind.
Nonetheless, the definition of a retrofitting strategy for any neighbourhood or any city is a trivial issue. There are many factors that must be analysed before proceeding with such intervention. Although the objectives to be achieved are often clear (reduction of energy consumption, reduction of greenhouse gas emissions, including renewable energies, etc.), the method to achieve those objectives is variable and different measures can be applied to the same scenario with varying degrees of success. The analysis of the most effective measures in cost-benefit terms requires of a considerable amount of information about the considered area and carrying out a series of complex calculations that allow to obtain indicators associated with the several possible interventions that may take place.
So it is at this point that the use of ICT (Information and Communication Technologies) adds value: performing calculations through simulation tools (including energy, costs and environmental aspects among others) the analysis of the different scenarios is more accurate and also tedious manual processes prone to failures are automated. However, although different simulation tools are available in the market a single specific tool that fully automates retrofitting interventions just does not exist nowadays.
In this regard, CARTIF is currently working on several projects aimed at creating such tools for designing retrofitting projects in cities such as the new project Nature4Cities or OptEEmAL, started in 2015. Both projects are funded by the European Commission under the Horizon 2020 R&D programme.
Nature4Cities aim is the development of a tool to support design of energy retrofitting projects in urban environments by applying Nature Based Solutions (NBS). This type of solutions has already been covered by my colleagues in a previous post.
On the other hand, OptEEmAL project focuses on developing a design platform for energy retrofitting projects at district level. Working with input data provided by the user (BIM, CityGML and other type of data) the OptEEmAL platform automatically generates and evaluates possible retrofitting scenarios based on implementing a set of measures for energy conservation.
Such measures are contained in a catalogue according to a data model based on standards (such as IFC). The solutions included in this catalogue are both passive (envelope improvements, change of windows) and active (concerning energy generation systems, renewable energies or control strategies) and are applied both at building and district level. These measures may be generic solutions with default values or specific solutions provided by commercial entities.
In order to evaluate the various potential scenarios, a set of performance indicators are analysed and then categorised into different categories: energy, comfort, environmental, economic, social and urban. Once the optimisation has taken place, the OptEEmAL platform shows to the user the solution with better results in terms of indicators. As a result of the process OptEEmAL provides the user with very detailed information on the retrofitting project.
CARTIFwill continue working in this area of knowledge with our strong commitment to support energy efficiency and ultimately improve the cities and places where we live.
In recent years, being the instrumental techniques cheaper and cheaper and the computational algorithms more accesible (even open source) several researchers and consultancy companies are developing new 3D abilities. Laser scanning or photogrammetry techniques are applied to mechanical or structural systems in order to collect some geometric specifications, which may be not available for different reasons.
Although direct engineering process will usually have the technical reports and drawings of the product prior to its building or manufacturing, it is usual that the old factories or buildings are not documented or, if they are, it is quite common that the drawings do not match to project. And even so, the time may have caused differences in the material behavior (chemical attacks, damage, settlements of supports or other common structural pathologies).
Footbridge stadium Balearic (Mallorca, Spain)
Often the collected data are focused on geometric dimensions and surface characteristics such as roughness and color. One of the most obvious applications is the three-dimensional reconstruction of architectonic buildings, either for rehabilitation or development of augmented drawings (BIM) or for historical or industrial heritage.
Being very useful the geometric data collected, in structural engineering it is necessary to add more information about the characteristics of different building materials, the joints between them and their possible interaction with the supports and the ground.
Fortunately, other enabling technologies to extract some additional information are also becoming more widely available. In this post we will see how using simple acceleration records and identification algorithms together with computational model updating techniques can complete the geometric information so that all technical specifications, necessary to estimate the dynamic behavior of the structure under study, can be obtained. These procedures do not require destructive testing and, even though these tests were viable, they did not provide the required information despite their higher cost.
First it should be noted that the geometric data collectedusing 3D techniques, irrespective of dimensional accuracy, refer to a particular state of load on the structure (at least due to the gravitational action) and corresponds to a particular ambient temperature. Both conditions can affect in a significant way when dealing with slender structures such as bridges and pylons. Furthermore these constructs generally experience unavoidable deformations due to environmental actions that can also affect dimensional accuracy of the 3D model.
Second it is interesting to note that in structural engineering and building is usual to use commercial components (proper cross-sections, formworks, pipes, lamps, …) of known discrete dimensions. This enables the possibility of carrying out adaptive scaling for improving the dimensional accuracy or for local refinement. So, it is not necessary comprehensive dimensional records and low cost systems (both instrumental as compact cameras and computer software) can be good enougth.
Considering the above and assuming certain skills for computational modeling, it is posible to create a preliminary model of the structure. On this model, using the finite element method, it is easy to estimate the incremental deformation due to certain loads or thermal actions and through appropriate correlations begin to estimate certain internal parameters (effective density, stiffness, damage, etc.). However, the methodology is especially important when the above information is combined with modal data.
To do this, first thing is to have the experimental eigenmodes (identified through operational modal analysis by post-processing acceleration records under environmental loading) and then select certain parameters of the computational model to be modified. Now it is the turn to adjust the value of these parameters (through optimization routines and depending on the sensitivity of each parameter and its range of reasonable values) to match with the experimental modes to the numerical ones (calculated via FEM). This process should take into account not only the most representative mode shapes but also their modal frequencies and damping.
Once proper values for these parameters are determined, the computer model can be used not only to generate the corresponding technical documentation of the as-built structure but also to estimate their vulnerability to accidental loads, or to evaluate the life-span or to estimate the performance of conservation jobs, among other applications. Those tasks are known as “structural re-engineering”, whose advantages can be matter for other post.
