Wind pressure analysis on roof

Hi Derek,

there are efforts being made to make SWX a better design tool for "mechanical buildings and mechanical equipment integration into buildings". In the 2011 release the addition of a "grid" is being implemented to support that particular referencing scheme typically used in the design and detailing of buildings. Obviously, the addition of certain "features" like walls, which may appear as lines in a drawing or slabs in a 3D assembly but when looked at in detail and are composed of various "parts" like framing, drywall, insulation etc are not going to be done for 2011- I don't even know if they are planning them but it would seem like a logical thing to do if you want to make some head way in that space. Also the drawing package would need to support the particulars of a typical building drawing scheme like all the wall details one one page, the door details on another  - we wouldn't want the civil guys to get out of the habit of flipping all over drawing sets to get a handle on some detail like say an indoor water feature. While you could do this sort of drawing now it would fall in the full pain in the you know where area - at least at my skill level. I would surmise that their strategy on this front is something like, well let's see if we can lure the civil guys to some tool connected with us (Draftsight), which in addition to getting us connected with the right users in a positive manner - giving the thing away - it also has the potential of inflicting damage on our main competitors major cash generator in this area. By the time we get some traction going in that area the need (demand really) for 3D in that space may well have emerged and by that time we hopefully will have added enough horsepower to (SWX or even CATIA) be a contender in the BIM space. Construction is the worlds largest industry and the way it is currently practiced leaves a lot of room for improvement compared to the mechanical tools (sensibly adopted to the practice of buildings/civil structures which isn't done yet), in my humble opinion. I agree it is a different kettle of fish and work needs to be done. However, the advantages of 3D, assuming the complexity problem can be managed (not a bad assumption in my view, given enough time), are quite compelling. It will drive significant changes to the supply chain as the opportunity to charge for coordination error driven change will fall quite a bit. Thus the cost of building will drop accordingly. Obviously other advantages emerge as well such as leveraging 3D data in analysis and to some extent manufacturing.

Well enough of that. As far as wind modeling of structures with Flow sim goes - as a first approximation it is probably a pretty decent tool. I have done a hockey rink flow simulation the goal of which was to identify low velocity areas where snow would accumulate which in turn would be used to assess snow loading distributions. Essentially is a uniform load distribution a sensible assumption? Does non-uniformity lead to any sort of issues? You can design a structure to take a fairly substantial load which is evenly distributed but will have serious issues if the load is along way from uniform even at reduced magnitude. Same would apply for pressures. In my experience which I have to admit is pretty limited when it comes to building codes, is that the codes through out some loading like 40 PSF or the 100 years storm numbers, which may or may not be anything close to reality. Which is why engineers in this area, when things get expensive (like building a large tower), might do some flow modeling to gain insight in specific areas, but when it comes to validation they are going to head into a boundary layer wind tunnel and run some measurements. The 40 PSF number or a Fow simulation result is probably good enough for a solar panel array, a house, a factory, a billboard....whatever. You can see how well this works, and it isn't just a load specification problem, it can be a construction problem as well, when roofs blow off in storms, trailer parks get trashed etc. But it isn't very often a big building goes down - they may lose some glass panels but even that isn't all that common.

Got to go.