How to predict the roof bearing capacity of photovoltaic power generation? Does it meet the requirements of photovoltaic project?
Photovoltaic industry March 25, 2018
Guide: when the development of distributed PV is in full swing, the load on the roof of distributed PV project, especially the load on the steel structure color steel tile roof which is easy to form a large project scale, has become the most important
pain point in the project development. Before issuing the load certificate, how to predict the bearing capacity of photovoltaic power generation roof to roughly determine whether it meets the requirements of photovoltaic project?
1. Classification of roof load of photovoltaic power generation
Classification by time: permanent load (dead load), variable load (live load), accidental load (special load or accidental action). Photovoltaic power station system is a new dead load.
Classification of action surface size: uniformly distributed load, concentrated load and linear load.
Classification of action direction: vertical load and horizontal load.
2. Loads involved in roof distributed photovoltaic project
Self weight of roof structure: self weight of reinforced concrete floor slab, self weight of roof steel beam purlin color steel plate, self weight of roof thermal insulation and waterproof materials, self weight of original roof components and
equipment (belonging to dead load).
System load of photovoltaic power station: photovoltaic module, support, foundation, cable, combiner box, etc. (belonging to new dead load).
Wind, rain and snow load: the increase of wind, rain and snow load caused by the construction of photovoltaic power station.
Construction load (later operation and maintenance load): in the construction stage, the effects of equipment and materials hoisting, transportation, construction personnel and construction equipment belong to live load.
Earthquake is not a load, but an action. See gb50011-2010 code for seismic design of buildings for the provisions and checking calculation of earthquake action.
3. Load prediction
Simulation calculation of drawings: through the building structure drawings, use software (such as mtsool, Lizheng structure toolbox, etc.) to preliminarily calculate the main stressed components (such as purlins, floors, etc.).
Field investigation: comparing the actual buildings with the design drawings, it is found that the load added outside the design drawings or changed due to later reconstruction and expansion.
Outdoor: additional equipment room on the roof, elevator room, equipment foundation of air conditioner or antenna, fire fighting or ventilation duct, etc
Indoor: whether there is large-area water leakage, whether the beams, plates and columns are cracked, rusted and damaged, new ceiling components, roof internal hanging equipment, roof opening, new indoor rail crane, etc.
If you want to obtain reliable load data, you should conduct systematic accounting such as structural modeling after field investigation and combined with the actual load on site.
4. Prediction of concrete roof load
Reinforced concrete roof: the passing rate of checking and checking the bearing capacity of the newly added photovoltaic system is greater than 80%. In terms of structure, it is more suitable to install photovoltaic power generation system.
Key issues to pay attention to: privately built buildings, old buildings with a long history of construction, tofu projects that cut corners on work and materials, private reconstruction and expansion affect the stress safety of the original building
structure, and communicate with the owner whether there is a roof structure reconstruction and expansion plan in the future.
For the concrete precast slab roof, prestressed double-T slab roof and saddle slab roof, the photovoltaic power station system can also be installed by selecting appropriate installation forms, such as appropriately reducing the installation inclination,
avoiding sensitive areas, installing deflectors in the array, reducing the height and weight of counterweight blocks, etc.
The concrete roof photovoltaic system shall be installed according to the best inclination angle of single row modules and considered on the concrete counterweight, about 0.45kn/m2.
5. Prediction of metal roof load
Metal roof: the passing rate of checking and checking the bearing capacity of the new photovoltaic system is less than 50%. There are many cases of insufficient bearing capacity of the structure, which shall be carefully checked before use.
Key issues to pay attention to: whether it is designed by a formal design unit, whether it can obtain the original design drawings, whether it is built privately, whether the steel grade has been replaced during the construction period, whether
the private reconstruction and expansion affects the stress safety of the original building structure, and communicate with the owner whether there is a roof structure reconstruction and expansion plan in the future.
The photovoltaic system of color steel tile roof shall be installed according to the flat laying of components along the roof slope, and the support purlin shall be clamped on the metal roof corrugated with clamps, about 0.15kn/m2.
6. Fast prediction method of metal roof load
Experience method 1:
Plants designed by informal design institutes, constructed by informal construction units, without drawings or built by borrowing drawings are basically not allowed to be used. Because of its uncontrollable structural safety, many hidden dangers
of barbaric construction and shoddy materials. If Q235 material is used instead of Q345 material.
Experience method 2:
The purlin span is about 6m, the purlin model is less than 180, and the purlin is easy to exceed the limit;
The purlin span is about 8m, the purlin model is less than 220, and the purlin is easy to exceed the limit;
When the purlin span is more than 6m and there is only one brace between purlins, the purlin is prone to lateral instability.
The above is mainly for the common portal steel frame plant with C-type or Z-type purlin. In the above cases, the stress ratio or deflection exceeds the limit after increasing the load of photovoltaic power station.