The winter period is crucial from the point of view of safety of large facilities, due to heavy snow. In 2006 it was snow on the roof that was one of the direct causes of the largest construction disaster in Poland – the collapse of the roof at the Katowice International Fair.
Piotr Możwiło an expert in monitoring of static load in Prospect advises on how to ensure the safety of the buildings during the winter.
The issue of the requirement to remove the excess of snow from the roof, and the obligation to maintain the property in proper condition is determined by the Official Gazette of 1994 No. 89 item. 414 Act of 7 July 1994 – Construction Law, and more art. 91a. The owner or manager of the facility is required to ensure its safe use, inter alia, in the event of strong winds or heavy snowfall.
Newly built facilities, as early as in the design and construction state, have a developed a plan for both the clearing and continuous monitoring of static loads created on the basis of the allowable strength of the building. Under these assumptions we determine the maximum permissible weight of the snow, which can be located on each square meter of the roof. In Poland, there are four snow zones that define the acceptable amount of snow on one square meter. The estimated weight of the first zone is 71 kg per m² the second about 91 kg per m², in the third zone it is 112 kg per m². The fourth zone allows greater loads.
That’s right. In some regions during the winter due to the intensification of atmospheric precipitations one should pay particular attention to the roof structure. These are areas of Southern Lesser Poland, Subcarpathian region and the southern part of Lower Silesia. In the case of zones, over a width of up to 5 km from the border zones of snow, one can adopt the load from any adjacent zone.
In the case of self-determination of the weight or thickness of the snow cover or to comply with the a calculations mentioned above, it is recommended that the decision to initiate activities related to snow removal is taken before reaching or exceeding the permissible standards. It gives time to complete snow removal services at all parts of the roof. Unfortunately, most administrators or managers decide on snow removal only by measuring the thickness of the snow cover. The thickness is not the sole determinant which should determine the commencement of procedures to remove the layers of snow. Bulk density depends on the time for which snow cover has been on the roof, as well as on the humidity and temperature of substrate and air,. Thus, the determination of the thickness of the cover relative to the weight can be estimated only as follows:
|*Characteristic thickness of the snow cover in zone IV is in the range of 0.37 m at the border zone to about 2.5 m in the upper parts of the mountains.|
gk -characteristic thickness of the snow cover
kN/m3 – kilonewtons per cubic meter
To determine the characteristic snow load on the ground Gk assumed the average bulk density of weight of snow = 2.45 kN/m3 everywhere in the country. This value should be taken to determine the snow load in individual cases.
The problem arises precisely in the case of older facilities, for which the plan of roof snow removal and static measurement has not been developed or does not specify allowable weight that can spread on the roof. In this case, The Polish Standard Loads in static calculations PN-80/B-02010 should be the determinant. It allows a maximum weight of snow at 1 m of roof surface in each zone. Despite the fact that the acceptable thickness and loads that may spread on the roofs in the various snow areas is determined, it should be taken only as pictorial information and a decision should be based primarily on the structure strength of particular facility.
According to the Regulation of the Minister of Labour and Social Policy of 26 September 1997, working at height means to work on a surface which is at least 1.0 m above the floor or ground and requires special permission and medical examinations. Thus, when the work is done on the surface of 1 m above, and there are no permanent elements on the roof which secure from the fall or it is not enclosed on all sides by full walls (up to at least 1.5 m), we have to hire a person or company who has the required permissions to work at heights and medical examination, confirming the ability of these people to work.
Prospect is company implementing construction and corrosion protection with use of professional climbing equipment all over Poland. Prospect specializes in removing snow and continuous measurement of static loads on roofs, roofing repair, annual and five-year technical inspections; anti-corrosion protection of steel and concrete, repair of steel and reinforced concrete structures, installation and dismantling of steel structures, technical expertise of chimneys, towers and GSM masts, mounting and sale of birds protection systems, as well as painting halls, factories, flyovers, silos, warning painting of GSM towers and chimneys, and fire-proof paint. The employees of Prospect hold required by Polish law medical examination and training giving them the entitlement to work at heights, as well as a number of other certificates necessary for professional delivery of climbing services. The company has also an equipment base, allowing them to work in the toughest conditions.
Tel.: +48 (22) 400 06 58
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