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INTRODUCTION
Holistic Model
Factors affecting the life of metal components and their relation to the modules of the holistic model. These parameters will affect the modules in the holistic model that deal with pollutant (salt) deposition and removal (natural cleaning or washing). The microclimatic conditions of the component can also be influenced by maintenance and cleaning (conditions of use), especially if the component is in the area of dirt accumulation.
All these factors (exposure and conditions of use) determine the microclimate experienced by the building component. How the microclimate affects the building component will depend on the material of the component e.g. galvanized steel, Colorbond, zincalum, aluminum, etc. The ultimate outcome of how the microclimate affects the material and local characteristics is the corrosion rate that extends the life of the component.
In an earlier phase of the project, the final report detailed changes to the holistic model to adapt it for use with gutters. The program was used to create a database for Queensland schools used in the project software.
HOLISTIC MODEL MODULES
Salinity Retention
State of surface of building component
Damage to Components
Paint application to galvanized steel and zinc is not modeled because paint application is done after components are installed and quality control on such paints is poor. Colorbond is a Bluescope steel product and has proven outstanding performance in most locations in Australia. A typical illustrative grade of Colorbond is zincalum AZ 150 (150 gm-2) coated steel sheet (low carbon steel) coated on both sides with a 5 µm epoxy primer containing chromate.
Colorbond was introduced as a material in the holistic model for the previous phase of the gutter-based project. In this phase of the project, this model has been refined and validated with a series of measurements.
MODEL MODIFICATIONS FOR SPECIFIC BUILDING COMPONENTS 5
Roof Sheeting
The roof type determines whether the surface remains in condition 3 for hours when it rains. Condition of the roof: The condition of the roof covering is cleaned or not, which determines whether rule R1 or R2 (see downspouts) will be applied in the calculation of the mass loss of condition 3. The deposition of salt takes place on the roof of the building around the edges and other positions of the roof surface.
For roof slabs, the rule for condition 3 classification is similar to downpipes except in this case the extension of condition 3 by an additional N hours only applies when the roof is a very flat roof and the rain >X mm. It is believed that leaf litter that builds up on roofing can affect the pH of rainwater and thus the corrosivity of the water. Tests were carried out to determine if this was the case and if extra factors should be included in the mass loss calculations.
The results show that pH changes do not need to be taken into account in mass loss calculations. Similar to drain pipes, if there is an edge, the calculated mass loss Ms2a for condition 2 and Ms3a for condition 3 is multiplied by the edge mass loss accelerator factor.
Roof Fasteners
Roof mounting/roof plate compatibility: There are 2 cases to consider when it comes to the compatibility between the roof mounting and the roof plate: compatible or not compatible. If the roof attachment and roof covering are not compatible, an acceleration factor is applied in the State 2 and State 3 mass loss calculations (see downspouts). Material type: There are 3 material types that are eligible, namely stainless steel, thermally coated and galvanized.
For each material considered, there are 16 different possible scenarios that will be considered and are listed in Table 12. NOTE: The last section (III) where the stem is embedded in the beam, was previously programmed and will be used to provide the information for the database. The deposition of salt is on the roof of the building around the edges and other positions on the roof surface.
An additional building envelope factor is required in the calculation of salt deposition for the middle part of the roof truss (II). This means that if the rain event occurs before 6 am and after 6 pm, i.e. overnight, then the surface continues to remain in state 3 until after the first 3 hours without rain from 6 am to 6 pm :00. If the rain event is during the day between 6am and 6pm, then the roof will only dry in the next 3 hour period without rain.
If it rains in time interval t, then state that in time interval t it is wet and time interval ( )t+1. The temperature and relative humidity in the roof space only apply when considering the middle section of the roof fastener (II). The area of solar radiation is determined by the latitude of the location of interest and is as given in Table 14.
RHext - external relative humidity for that 3-hour period δ - a constant dependent on time of day and season. The factor to promote condensation is to be brought in at a given frequency at dawn, for example 8 times a month.
Ridge Capping and Flashing
The drainage conditions at ridge caps and flashings are always drained and therefore there are no extended wet hours in case of rain. Material Compatibility Factor: As with the roof attachment, ridge capping and flashing have a compatibility factor. The compatibility factor lies between the material of the ridge cover and the roof and the roof.
Window Frames
Steel Supports
Subfloor Members
Ventilation factor: For sub-floor members there is a ventilation factor which is dependent on the ventilation rates. The ventilation condition, in turn, affects the time a surface remains wet after wetting from a salt wetting period that is a state 2 condition. A ventilation factor is a constant associated with each level of ventilation as shown in Table 19.
Exposure: Subgrade located inside the building is assumed to be fully shielded and not exposed, so base elements are considered as shielded exposure only. Material type: There are 3 types of materials for floor elements which are considered galvanized, zinc and bare steel. For each material considered, there are 6 different possible scenarios that would be considered and are listed in Table 20.
For subfloor elements, the salt deposit is the face of the building, without regard to the face position. The figure below shows the data entry screen for entering the area factor, the factors for the different ventilation levels and also the formula for calculating the salt deposition rate for subfloor elements. The implementation of the state 2 classification rule for subfloor elements is similar to state 3 classification in other components.
Extending the surface to state 2 by an additional N hours only applies if the surface is classified as state 2 using the condition RHs >ε and the drainage state is not drained. The number of additional hours a surface remains wet will depend on the level of ventilation.
Testing of Models
This is a downspout with a square cross section and an insert at the top of the downspout to connect it to the gutter. This insert allows the downspout to be adjusted to different distances from the wall, where the main part of the downspout and gutter is attached. Looking at the outside of the Zincalume square section downspout (Figure A7), you can see that the only red rust (RR) on the outside is where the downspout has been corroded from the inside out.
Figure A8, Top section insert showing no corrosion on the upper surfaces of the insert or the main body of the downpipe. Figure A9, Top section insert showing no corrosion on the upper surfaces of the insert or the main body of the downpipe. The round galvanized pipe, Figure A12, shows that the greatest coating loss inside the pipe is in the areas where water flows over it, and the most coating loss on the outside of the downpipe is at a joint and on what was a horizontal lee (unwashed) surface.
The yellow line is the precipitation readings from a weather station located within 250 meters of the downspout, the readings have been multiplied by 10 so that they are clear on the graph (a reading of 40 is actually 4 mm). Precipitation measurements are taken every 15 minutes and a rain depth of 0.2 mm is required for the meter to display. This means that light drizzle may not be registered, but may flow from the roof down the downspout. It would be expected that within the closed area of the downspout the RH would have been closer to 100% than recorded.
The pH was measured on the first day and then after 1, 4, 12 and 22 days (Note: . the water was readjusted to obtain the mass determined in step 3 before each pH measurement). LAG1 sample: A very large liquid amber tree hangs over the house and contributes almost 99% of the litter. CG sample: Sincalume gutters that are 5.5 years old, tile roof of the same age and the house is located in Clayton.
Most of the metal content in the leaf litter solutions was in the very low range.
APPENDIX A
APPENDIX B
