Impact of new and old standards for mounting design

Arctic star solar PV network news: we here refers to of old specification is refers to structures Dutch contains specification GB50009-2012 and the steel design specification GB50017-2003,, this several specification is zhiqian domestic most bracket factory or PV structure design personnel design bracket by used of specification, and new specification is 12 years out of PV power station design specification GB50797-2012, inside has a chapter is specifically on bracket of design calculation do has specific provides. Here we’re talking about old and new specification refers to this couple, for convenience or in new and old specifications call instead.

A case study of Wuxi, location, site b, supports the highest elevation took for a +20.00m.

Old code: snow load 50 a maximum pressure of snow pressure

Basic wind pressure: wo=0.45kN/m^2,

Basic snow pressure: so=0.40kN/m^2,

Air pressure height coefficient: μ-z=1.23

Wind load shape factor: μ-s=1.4

Wind factor: Beta gz=1.0 (support systems and roofing are many points of contact, regardless of the resonance effect)

Wind load standard values: β μ μ zxwox SX WKB= gz=775Pa

Roof snow distribution coefficient: μ-o=1

Characteristic value of snow load: sK=sox u o=400Pa

Load combinations and a description:

Calculation of deflection:

COMB1=G+Wx+Sn

COMB2=G-Ws

Calculation of strength:

COMB3=1.2G+0.6*1.4Wx+1.4Sn

COMB4=1.2G+1.4Wx+0.7*1.4Sn

COMB5=1.0G-1.4Ws

G–dead load

Wx–wind loads (down)

Ws–wind loads (up)

Sn–snow loads

New: snow load 25 years maximum pressure snow pressure,

Basic wind pressure: 0.38kN/m^2

Basic snow pressure: 0.36kN/m^2

Specific formula as described in the GB50009-2012 specification for structural loads D.3.4

XR=X10+(X100-X10)(lnR/ln10-1)

R is the return period

Air pressure height coefficient: μ-z=1.23

Wind load shape factor: μ-s=1.3

Wind factor: Beta gz=1.0 (support systems and roofing are many points of contact, regardless of the resonance effect)

Wind load standard values: β μ μ zxwox SX WKB= gz=608Pa

Roof snow distribution coefficient: μ-o=1

Characteristic value of snow load: sK=sox u o=360Pa

Load combinations and a description:

Calculation of deflection:

COMB1=G+W+T

COMB2=G+S+T

Calculation of strength:

COMB3=1.2G+1.4W+0.6T

COMB4=1.2G+1.4Sn+0.6T

COMB5=1.2G+0.6*1.4W+T

COMB6=1.2G+0.6*1.4Sn+T

G–dead load

W–wind loads

Sn–snow loads

T–temperature loads

Value of by more than a few basic parameters, we can see that some of the differences between new and old standards. The following points:

1. the old edition of wind load shape coefficient is in accordance with the specific bracket angle value, while the newer versions of the specification clearly sets out the ground and the roof support wind load shape factor of 1.3.

2. the value of the wind pressure snow years, old norms are generally in accordance with 50 of maximum pressure value of the snow and new specification reduces the requirements, provisions shall be in accordance with a serious load of 25 numeric values (maximum pressure of 25 snow-how I wrote)

3. the method of calculating load combination effect has changed, legacy specifications General maximum snow load in taking together. New version of the spec was not clear, but the combinations given inside, accompanied by wind and snow loads are not, meaning that newer versions of the standard default does not consider the calculation of wind pressure snow pressure maximum effect on the bracket. (The explanation is that the wind is the biggest snow accumulation up, unable to inflict maximum snow, snow season of maximum load occurs is also different, personally think that makes sense)

4. Add a calculation when considering thermal load (for the temperature load, I did a special simulation analysis in most areas, very little effect on calculation of thermal load on the bracket, I personally think unless it is a in some extreme climate zone, or ignore the effects of temperature load could be considered, attached with or without temperature load to back bracket results)

Previously according to the value of the new and old standards of basic information and calculation software for load sizes, combinations of input to sap2000 constructed exactly the same model in inside the bracket, comparative analysis of the results obtained:

Legacy code value under the most unfavorable load combination beam of the support 3-3-axis bending moment

Legacy code value under the most unfavorable load combination beam of the support 2-2-axis bending moment

Beam bending strength calculation formula

=199×MPa

Bending strength of beam to meet the requirements

Beam shear resistant calculations shear force is too small and it is not here to work, (model results can also view)

Newer versions of the specification value under the most unfavorable load combination beam of the support 3-3-axis bending moment

Newer versions of the specification value under the most unfavorable load combination beam of the support 2-2-axis bending moment

Beam bending strength calculation formula

Bending strength of beam to meet the requirements

Still some deflection and comparison of stability here did not mention all posted.

New old specification Xia beam calculation results compared, new specification of calculation results more small, both ratio about for 0.69, this on means with we originally needs used section more big with steel volume more of bracket, if according to new specification to calculation design words, can selection small points of section, like here I of beam selected has C41x52x2.5 of c steel, completely can select small first, specifications of c steel, like C41x41x2.5, or C41x52x2.0. In an actual PV applications, just the stent’s steel consumption, will come down a lot, 20%-30% is less common, and specific savings depending on the actual project. Personal advice for the average roof bracket scaffolds can be designed according to new specifications, where individual extreme weather emergencies designed according to the old norms of conservative values.

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