The installation of photovoltaic systems on the roofs of Brazilian buildings has grown dramatically due to all the benefits that solar energy provides.
Among them, savings on energy bills, predictability of expenses, environmental issues, enhancement of the company's image and guaranteed return on investment, among other advantages.
However, buildings are often not prepared to receive the additional load from solar s, as their roofs and structures were not designed or built properly.
Contextualizing the problem
Building structures must withstand the following loads:
- Own weight;
- Weight of the tiles;
- Utilities (loads added by electrical conductors, cable trays, water and refrigeration pipes, etc.);
- Overload (load added by people and equipment that will work momentarily on the roof, items hanging from structures – such as banners);
- Additional loads (photovoltaic s);
- Wind action.
Contrary to popular belief, the actions of the winds must also be considered. In fact, in most cases wind is the most significant load that the structure will have to .
The norm ABNT NBR 6123 – Forces due to wind in buildings determines the considerations that must be made due to the forces exerted by winds on buildings.
More details about standards and issues that must be evaluated can be found in the article Prior assessment of roofs before installing photovoltaic systems.
The remedy to ensure that installation does not become a nightmare for the owner and the installing company is to have the structure analyzed by a competent specialist.
This analysis must accompany a report with the respective ART stating whether or not the structure is ready to receive the installation of photovoltaic systems.
Structural reinforcements
In several cases it is necessary to make reinforcements so that the structure can the installation of photovoltaic systems.
This occurs mainly in warehouses and sheds where, for cost reasons, structures are often designed and built within the limit permitted by standards or even outside the recommendations of technical standards.
When there is a need for reinforcement, the responsible professional must provide a calculation report and an executive project showing the assembly details, in addition to obviously providing the respective ART.
In general, the costs of structural reinforcements do not exceed 5% of the investment in the photovoltaic system, extending the operating time. payback (return time on investment) in a maximum of two or three months. The deadline for carrying out the reinforcement is also not long, and can be carried out in a few weeks. In this way, carrying out structural reinforcement, when necessary, does not make the photovoltaic project unfeasible. Let's look at some examples of reinforcements most commonly used to install s.
Installation of pillars
In some cases it is necessary to install pillars to better distribute the diagonal forces of the building. Attention must be paid to the positioning of the pillars, as most of the time the best position from the point of view of mechanical efforts does not meet the needs of the flow of people, machines and cars. You should look for an option that meets all your needs.
Reinforcement in roof purlins and shears
Purlins are the structural elements to which roof tiles are attached. The shears, in turn, are the structures ed on the pillars and on which the purlins are mounted.
Generally, the purlins are the ones that directly receive the loads from the s, regardless of the installation method used (studs, flat-rail ou speed rail).
In these cases, when necessary, reinforcement consists of fixing a tube or beam in parallel along the entire length of the purlin. Fixation can be done using screws or welding.
The choice of method depends on the viability of the installation, considering the execution time and the environment where it will be carried out (environment with flammable materials, high flow of people, etc.). In structures with a ceiling, it may be necessary to remove the tiles to carry out the work.
Alternative to reinforcement
In some cases it is possible to install the s without reinforcing them. To do this, you need to work on a layout of the arrangement that distributes the s in more robust points, which the additional load – a structural calculation must, however, be carried out to the weight limit that can be applied to the elements.
An example is seen below, where structural analysis showed that the purlins would not withstand the additional stresses due to the installation of the s.
To avoid reinforcement in the purlins, it was decided to position the s aligned with the scissors, within a maximum occupancy margin of 1,5 m on each side.
