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  1. captain_slow

    AS3600_2018 - clause 6.2.4.2 for seismic modelling

    Just chiming in to say that I am seeing a lot of design to mu = 1 and Sp = 0.77 for mid-rise structures in Melbourne. Designers generally adopt cracked sections of around 0.35-0.4 Ig. It seems that the non-ductile assumption along with section cracking produces designs that look very similar to...
  2. captain_slow

    AS3600 elastic analysis with secondary bending moments

    Moment magnification is how consideration of buckling effects is stitched into AS3600. I am not an expert on non-linear material models but I would say that it's important to consider buckling effects when designing slender columns. Otherwise you end up just doing concrete section design (as...
  3. captain_slow

    Biaxial Bending in Column for Response Spectrum case

    @OP, You want to capture all combinations of load actions in your analysis and design. I am not sure what the "U1" and "U2" refer to but I can certainly help with point b). You can take envelope actions - that is take the maximum moments in both major and minor axis and apply them...
  4. captain_slow

    Footing design combinations for overturning & bearing stress to Australia Standard

    I was going to mention AS4678 too; it is clearly a limit state code and appendix J is an extremely useful appendix (albeit with some outdated references). Having said that this code still assesses soil capacity for bearing as "allowable" (please do correct me if I am wrong).
  5. captain_slow

    Footing design combinations for overturning & bearing stress to Australia Standard

    @human909, I have seen piling contractors throw geotechnical reports "in the bin" and adopt their own set of soil parameters "based on prior experience". At some point our field got so good at putting failsafe systems in place that we moved on from adjusting our understanding to fit reality...
  6. captain_slow

    deflection of space frame in span under gravity by hand calculation

    @OP, Decent analysis of space frames is a fairly advanced task that requires some sort of finite element modelling for an accurate answer. Your best bet is to hire a structural engineer with 3D FEA software capability. If you are only interested in deflection estimates (as opposed to signed...
  7. captain_slow

    Footing design combinations for overturning & bearing stress to Australia Standard

    @OP, I am a little late as the discussion seems to have reached a reasonable conclusion. I will however say that in my experience (Melbourne, Australia) application of ULS combinations to allowable pressures obtained from geotechnical reports is common practice. @human909, Sincere thanks for...
  8. captain_slow

    Learning Programming for Structural Engineering

    @Celt83, OK I think I know what we are talking here then. Yes I agree that there is a heap of closed-form solutions out there that can be used to solve a lot of this stuff. I am sure we all have our spreadsheets with several implementations of these things. I am talking more from the angle of...
  9. captain_slow

    Bolt edge distance

    @ OP, I concur with Agent666. On another note, I would say that more edge distance is almost always better as fabricators seem to rarely get it perfectly right and bolt holes often end up getting butchered on site due to mis-fit; sometimes the engineer is never even told about such butchering...
  10. captain_slow

    Learning Programming for Structural Engineering

    @ Celt83, Let's double down and make sure we are not talking about different things. Say you have a UDL load on a beam. How would you say the process of resolving it using FEA goes? What I am saying is that step 1 is to discretise the UDL load into a series of point loads applied at beam...
  11. captain_slow

    Learning Programming for Structural Engineering

    @Celt83, Finite element modelling is not the same as coming up with a closed-form piece-wise solution, there are too many moving pieces to just say it's the same thing. Small number of nodes introduces error through inadequate discretisation of uniform loads, not through "lower accuracy" of...
  12. captain_slow

    Roof Collapse in Perth, Australia

    Glazed roofs are spooky and I always find myself triple-checking thickness of glazing panes, it's exactly the kind of thing that can get bumped up in thickness by a couple of millimetres (for thermal efficiency or something) and end up having an enormous effect on the structure.
  13. captain_slow

    Most cost efficient column layout in RC buildings

    Many ways of looking at it but ultimately the cheapest concrete structure is probably one with a symmetric arrangement of shear walls and some sort of a 2-way flat plate on columns type of thing. Remember that unless you have actual line supports for the one-way slab (such as continuous walls)...
  14. captain_slow

    Roof Collapse in Perth, Australia

    Always unnerving to see a building failure like this, it's a chilling reminder of stakes at hand and the kind of responsibility that we all bear in construction industry. Public will think that the engineer is at fault and engineers will think that the builders/contractors are at fault - it's...
  15. captain_slow

    Learning Programming for Structural Engineering

    @OP, For a beam element FEA solver you have to work with generic formulas for beam deflections under generic loads. This is a complex topic, however I reckon I can give you the generic stiffness matrix: Generally speaking you have to do the following: 1. Discretise your load. 2. Discretise...
  16. captain_slow

    Learning Programming for Structural Engineering

    @Complete_columns, Mostly agree with everything you say - especially the "edge cases". Engineers have a weakness for falling into "just get it to work on paper" type of situations, which is a complex professional issue deserving its own thread. I just want to say that I really like your...
  17. captain_slow

    Learning Programming for Structural Engineering

    @IDS, I am the first person to admit that choice of programming language depends on the type of problem at hand. VBA has its ups and downs with the ups being Excel integration and how commonplace it is (certainly more commonplace in structural consulting than any other language) and the downs...
  18. captain_slow

    Learning Programming for Structural Engineering

    @OP, If you are a non-programmer and would like to learn programming AND you do not have any particular application/project in mind I would 100% recommend starting with Python. Python is a minimalistic language and so it is possibly the easiest environment to learn basic principles of...
  19. captain_slow

    How do you model PT slab in your full structure model?

    @OP, This question has been on my mind lately and here are some thoughts. I see that @MrHershey has weighed in with some code-related feedback regarding lateral loads. I will chip in and give some opinion on the state of vertical loads... - addition of PT tendons does not really alter...
  20. captain_slow

    ‘Slabless’ concrete stairs

    @MIStruct_IRE, Straightened length s a bit of simplification that gets the message across, however rotation at each stepped joint and the consequent opening up of steps will add a lot of movement that is not strictly speaking flexural in nature. That's to say if the stepped joints don't simply...

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