State of Play 2018/wk23

{state of play posts are a snapshot of activities started and/or completed by the point in time indicated. Thus not what was done in a week, but what was done between the current post and the last “state of play” post.}

WordPress themes and Website Modifications

Learning theme development (css/php) got put aside whilst worked on some fee paying jobs, which is good {need more billable work}. Have looked at some other existing themes, but none fully meet my needs. They either have unsuitable layout or colour schemes. Thus left writing a child theme, or full theme. At present child themes and starter themes don’t really appear to be time savers: as need to learn all the undocumented styles used in the theme to be modified. The fastest approach seems to be to ignore existing css styles and create new styles for desired objectives. At moment sticking with sketchpad theme, as it does have more extensive support of wordpress features than most other  themes have: just have a few issues with some text being too small, and its use of images which hinder changes to colour scheme and more importantly it isn’t responsive to screen size.

Revised Pricing of Certificates for Carports and Verandahs

Maintaining the effort level pricing concept, but using the base block prices as unit prices to calculate fee for more involved systems. Basically original pricing of certificates was:

  1. Flat free standing canopy: $110
  2. Freestanding Canopy with 3D structure: $550
  3. Other free standing canopy: $220
  4. Assessing canopy attached to other structure: $220

Thus fees under old system for attached flat canopy would have been $110+$220 = $330, and that for attached gable roof canopy $220+$220=$440.  In the early days,my view was that assessing attachment to the house should have a minimum fee of $1000 to discourage such want: just as it is a hassle to install all the strengthening requirements, it is a hassle to design and assess all such requirements. However having adopted the use of AS1684.2 to estimate existing tie-downs in house, and otherwise having standardised strengthening requirements, the assessment of the existing was simplified.  Due to such simplification, I had been erroneously discounting the $220 for assessing the attachment. Erroneous because that is not what the additional fee was solely about.

A freestanding canopy is typically symmetrical. So wind coming from one direction across the canopy has the same effect as that coming from the opposite direction. So typically with directions identified as theta=0,90,180,270, for free standing only need to consider theta=0,90, as the other two directions are the same. When a set of columns on one side of the canopy is removed the effect of the wind now changes, and now at a minimum need to consider directions theta=0,90,180. Additionally with a gable canopy where the two rafters were previously experiencing the same effects, with columns removed from one side and thus now having different supports to each side, now have different effects in each rafter. Thus have additional members and supports to assess. Thus whilst the two rafters may have the same specification, they require different evidence-of-suitability to verify that such specification is suitable for each rafter. Adjacent structures whether attached or not also affect wind loading on the canopy. That is the airflow over the house onto the canopy changes the pressures experienced by the canopy and also the pressures experience by the house. As attached  canopies are not fully covered by the wind loading code and, adjacent buildings and fences can create enclosure, the determination of pressure coefficients can get complicated and uncertain. Such uncertainty gives rise to higher risk in design and decision making.

Flat canopies were initially taken as simpler than gable canopies. Collar-tied roof trusses in timber canopies are more complex structural form than the simple beams in a flat canopy: but for quick assessment they can be considered as simple beams. Similarly cold-formed steel canopies with gable roof can be quickly checked assuming simple beams. On the other hand flat canopies can have a variety of structural forms with fewer or greater number of beams than a gable canopy. The simplest flat canopy is steel roof sheeting spanning between two fascia beams: manufacturers typically have span tables for such canopies, and not something I typically need to check. More typically have to check flat canopies involving multiple beams with a variety of spans. Flat canopies also have same problems as gable canopies in terms of determining wind pressures coefficients. Additionally determining design wind speed can be a simple exercise or an involved exercise.

Consequently I decided to scrap the reduced fee for flat canopies, and also scrap the fee for assessing attachment to existing structures. The fee of $220 for attachment to existing structures may still apply if only assessing the existing structures suitability for an attached verandah.

The new pricing structure as of (3/6/2018) is as follows:

  1. Free standing 3D structure (eg. pyramid or hexagonal footprint): $550
  2. For each enveloping rectangle with unique structural form (hips are considered as separate rectangles): $220
  3. For each interface between adjacent rectangles: $110
  4. If fee exceeds $880, then won’t supply certificate will document and supply the calculations

For a flat canopy attached to house the new fee doesn’t change it is now $220+$110=$330, it is just built up from different unit prices. The same fee also applies to an attached gable canopy.

A free standing Gable Canopy with L-Shaped Plan: 3 rectangles (leg 1 + junction + leg 2) 3$220=$660 or if the two legs have the same span then 2$220=$440, if latter attached along two sides to house then have 2 interfaces, but they are equal therefore only 1 billed ($110) so gives $550. If legs have unequal spans and attached to house along two sides, then fee $880: no certificate issued, will supply calculations.

Note that a certificate is a summary of the results of calculations. For simple structures the summary in the certificate takes less effort than writing the calculations out in full. For more involved structures, writing the certificate requires more effort, and summarising the results becomes more cumbersome. More importantly writing the calculations out becomes important for keeping track of what I am doing. {eg. for the simple I can punch numbers through calculator without writing anything down.}

So for typical gable canopy major increase in price, bringing it closer to the minimum fee of $660 a certificate is likely to cost elsewhere.  The new fees should better reflect the effort involved in detailed wind load assessment, and minimising wind loading requirements. {eg. councils may advise wind class N3, we can typically reduce this to N2 as assignment of N3 is typically not done with full assessment of the wind loading environment. Similarly can typically reduce roof pressure coefficients when the blocked under condition in appropriately imposed by council.}

Post on Determining Wind Load Pressure Coefficients

Got stalled writing example of determining pressure coefficients, when hit the hipped roof requirements. The issue I had was that when the pressure coefficients for hipped roofs were first dumped into AS1170.2:2002, my views were:

  1. Not necessary
  2. Not Acceptable to put such judgement in the code, should do the additional wind loading research to verify the coefficients or otherwise properly reference published research
  3. Flawed

Except the other day when looking at the code, the diagrams seemed ok! So what was my issue with the requirements for hipped roofs being flawed? The result I need to write another post on wind loading of hips before completing the original post.

Technical Library and Wind Loading Functions

Been creating a test workbook for revised wind loading functions. Attempting to combine canopy and enclosed building coefficients into a single subroutine. Modified some of existing routines breaking various design workbooks due to increased number of parameters or change of data type. In particular I have changed some of the boolean variables into integer codes: from a spreadsheet typically call the functions with 0, and 1, and in the main these will retain their original meaning as far as selecting the appropriate options. Also added sentinel values for conditions outside the scope of the code: these sentinels I will slowly replace with my judgements and interpretations.

Wind Loading to AS4055

Started to create new wind loading workbook to AS4055, its presentation is being modified to a vertical format, once modified will convert to google sheets, which would then make it usable on android phone. With time I will reinforce the idea that whilst AS4055 is limited to housing, the wind classification system defined within is not so limited: the wind (speed) classification system is for manufactured structural products (MSP).

Creating Workbook for Structural Design

Whilst writing article on determining pressure coefficients decided will also write a series of posts on creating workbooks for structural design.

Legislation

Made a note that legislation was an issue cannot remember what that was to be about though. May have something to do with professional cults running around getting legislation to grant them a monopoly. Not sure why engineers Australia keeps referring to Queensland’s RPEQ’s: all that such legislation does is make the approved persons into members of a silly form and rubber stamp brigade. I can see why Victoria may be heading down that path, they already have a silly form brigade for building approval {RBP(engineer)}.

I retain my view engineering takes place at the frontiers of science and technology: its not an occupation, you cannot be trained to be an engineer. You can be trained in applied science and existing technology. To become an engineer requires opportunity and inherent ingenuity to push the frontier. The people currently claiming to be engineers are barely conversant with the proper scientific assessment of the established technologies.  So legislation to grant such incompetents monopoly is not acceptable.

Legislation should regulate what is to be done, not who is to do it. However, transforming opinion into laws, where science should be applied is not acceptable. The legalisation of the BCA/NCC and Australian standards is getting out of control.

Technical Advocate

The primary activity of the so called architects and engineers, is the role of Technical Advocate. In this role a person is able to defend and justify a design decision, rather than simply document and specify wants and whims.

So whilst all persons are typically able to document and describe their wants, they are not necessarily able to defend those wants with respect to suitability of purpose: most especially suitability for purposes they didn’t even consider. For example the primary purpose of a car is to get from “A” to “B”, it is not a fundamental requirement that a car have crash resistance: it is however a semi legislated requirement. It is thus a purpose which wouldn’t necessarily consider if focused on the real purpose. Similar impositions go for buildings. The primary purpose of a building is to provide adequate shelter from the weather: it is not a purpose of a building to be energy efficient, but such is imposed. Some of these impositions can be modified, if understand the origin and intents of the code clauses: unfortunately a lot of so called engineers take the easy route and blindly comply.

A technical advocate assists you to comply with codes, by determining needs first, assessing suitability of proposal against needs, and then checking against the wants and whims of legislators. That is the technical advocate separates the science from the subjective judgements and then questions the subjective.  If having a hard time with your architect, engineer and council (or other regulator) chances are they don’t have adequate understanding of where the science ends and the judgement begins. Get new architect and engineer, and bypass the council with private certification.

Virtual Technical Assistant

Been revisiting the potential use of fiverr as an alternative to an escrow service. Its fees are high, but it is also a market place: and with some suitable logistics tools should be able to build a virtual team.

Canopy Workbooks

I have created several workbooks for design of simple monoslope flat canopies. At present they are mainly simple sketches for use with spann tables and the likes. A couple I have added calculations to, as I mainly use cold-formed c-sections, I initially setup to check c-section members.

However, getting more RHS canopies so considered setting up to use AS4100, but that not so easy. Whilst I have VBA functions, they require pointing to lots of section properties, which I have to get into the workbook for each of the structural members. Doing so gets cumbersome.

Wrapper Functions AS4100 Steel Design

Wrote wrapper functions for checking bending resistance to AS4100, the functions are now similar to AS4600 functions and make use of DAO to get section properties from MS Access rather than using workbook lookup functions.

The only problem now is that the inputs to AS4600 and AS4100 are not the same. So now into process of writing further wrapper functions to swap between AS4100 and AS4600, to which will eventually add timber (AS1720) and aluminium (AS1664). Then for example will be able to write one workbook for say canopy of platform design and easily check structural sections for different materials.

Section Properties

Added some extra sections to section properties workbook, which then required updating the MS Access database. Something of an inconvenience. Originally QPro was able to read Paradox database files directly, but Excel and Access don’t have the same connectivity. On converting to Office 97, I did originally have MS Excel workbook linked to MS Access, so changed the database and then simply refreshed the spreadsheet. The office grew and then had incompatible versions of Excel and Access, which caused Excel to crash when attempting to link to database from incompatible version: so ended up with two sets of files. Then broke the link, as typically faster to modify the worksheet to get a job done than revise the database.

The benefit of the database however is direct referencing of the fields, and being easily able to see the data using different forms best suited to the task at hand. Forms are easier to create in MS Access and directly link to tables and fields, than using VBA and Excel. Nonetheless considering making use of Excel/VBA to get revised information into MS Access: especially given that most users don’t have MS Access.

Section properties also being revisited with respect to post on: building a structural design workbook. The issue here is getting the section properties for the structural members into a workbook, and not wasting memory with all section properties.

Revised workbook for sections built-up from plate elements.  The workbook has several different worksheets for standard shapes (boxes, T-Sections, channels, I-Sections), mostly each sheet uses XY-Chart to draw the section, and then the sheet contains calculations for centroid, Ixx, Iyy, Zxx, Zyy. For the boxes added rx, ry, Sxx,Syy, Iw, J, with estimates of phi.Ms and phi.Nt. The calculated resistances are estimates because doesn’t do all the conditional  checks, just does the basic calculations (phi.fy.Ze, phi.fy.A), however once have all the properties can manually copy to the sections database and then use AS4100 spreadsheet to make more formal check. I revised because have project using non-standard RHS for which don’t have any published section properties: just a catalogue of sizes material grade used and self-weights.

It suggests could do with writing Excel/VBA routines to automatically add properties from my built-up sections workbook to the sections library.

One of the other benefits of VBA and MS Access is applying a consistent set of rules to each section property record. For example a VBA function can calculate phi.Ms for every section in the sections database, and such functions can be used in queries. A query can be used to find all sections with phi.Ms >= 20 kNm as an example. Where phi.Ms is comparable across materials, whilst Ixx and Zxx are not. The sections table already contains the design code suitable for each section, just made little use of it thus far: but once got wrapper functions for AS4100/AS4600 can start using.


Revisions:

  1. [03/06/2018]: Original – not completed
  2. [10/06/2018]: Completed