导读：在分布式光伏发展如火如荼的时候，分布式光伏项目屋顶荷载问题，特别是易形成较大项目规模的钢结构彩钢瓦屋面的荷载问题，成为了项目开发中最为重要的一个痛点。在开具荷载证明之前， 如何对光伏发电屋顶承载力进行预判，以大致确定是否符合光伏项目的要求？
按时间分类：永久荷载(恒荷载)、可变荷载(活荷载)、偶然荷载(特殊载荷或偶然作用)。光伏电站系统属于新增恒荷载。
作用面大小分类：均布载荷、集中荷载、线性荷载。
作用方向分类：垂直荷载、水平荷载。
屋面结构自重：钢筋混凝土楼板自重、屋面钢梁檩条彩钢板的自重、屋面保温防水材料的自重、屋面原有构件及设备的自重(属于恒荷载)。
光伏电站系统荷载：光伏组件，支架、基础、电缆、汇流箱等(属于新增恒荷载)。
风、雨、雪荷载：因建设光伏电站，而导致的风、雨、雪荷载的增大。
施工荷载(后期运维荷载)：施工阶段，设备材料的吊装、运输、施工人员、施工设备等产生的作用影响，属于活荷载。
地震不属于荷载，地震是一种作用，关于地震作用的规定及验算，见GB50011-2010《建筑抗震设计规范》。
图纸的模拟计算：通过建筑物结构图纸，使用软件(如MTStool、理正结构工具箱等)对主要受力构件(如檩条、楼板等)初步核算。
现场勘察：实际建筑物与设计图纸对比，发现设计图以外新增荷载或因后期改扩建变更的荷载。
室外：屋面增建的设备间，电梯间，空调机或天线的设备基础、消防或通风管道等
室内：有无大面积漏水、梁板柱有无开裂、锈蚀及损毁、新增吊顶构件，屋面内部吊挂设备、屋面开洞、新增室内轨道吊车等。
如果想要获得可靠的荷载数据，应当经过现场勘察后，结合现场实际荷载情况，再进行结构建模等系统的核算。
钢筋混凝土屋面：新增光伏发系统的承载力校核验算通过率大于80%。结构方面比较适宜安装光伏发电系统。
侧重注意的问题：私自建造的建筑物、建设年代久远的老旧建筑，存在偷工减料的豆腐工程、私自改扩建情况影响了原建筑结构受力安全、与屋主沟通未来是否有屋面结构改扩建计划。
混凝土预制板屋面、预应力双T板屋面、马鞍板屋面，通过选择合适的安装形式，如适当降低安装倾角、避让敏感区域、阵列加装导流板、降低配重块高度和重量等，亦可正在安装光伏电站系统。
混凝土屋面光伏系统按单排组件最佳倾角进行安装、混凝土配重上考虑，约0.45KN/㎡。
金属屋面：新增光伏系统的承载力校核验算通过率小于50%。结构承载力不足情况较多，使用前需认真校核。
侧重注意的问题：是否为正规设计单位设计、能否获取原设计图纸、是否私自建造、是否建设期替换过钢材等级、私自改扩建情况影响了原建筑结构受力安全、与屋主沟通未来是否有屋面结构改扩建计划。
彩钢瓦屋面光伏光伏系统按组件顺屋面坡度平铺安装、支架檩条采用夹具夹在金属屋面瓦楞上考虑，约0.15KN/㎡。
经验方法一：
非正规设计院设计、非正规施工单位施工、无图纸或借图建造的厂房，基本都不可使用。因为其结构安全不可控、野蛮施工隐患多、材料以次充好。如Q235材料替换Q345材料使用。
经验方法二：
檩条跨度6米左右，檩条型号小于180，檩条核算易超限;
以上主要针对常见的C型或Z型檩条的门式钢架结构厂房进行预判，上述情况下通常存在增加光伏电站荷载后，应力比超限或挠度超限。
檩条跨度8米左右，檩条型号小于220，檩条核算易超限;
檩条跨度大于6米，檩条间的拉条仅为1道时，檩条核算易侧向失稳。
How to predict the roof bearing capacity of photovoltaic power generation? Does it meet the requirements of photovoltaic project?
Photovoltaic industry March 25, 2018
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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?
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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.
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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).
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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.
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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.
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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.
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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.
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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.
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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.
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