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  1. bugbus

    Paradoxical strut-and-tie tests (less = more)

    I came across this paper recently which has me quite puzzled. In summary, 3 types of deep-ish beams (L/D = 4.4) were tested to failure. The first, a simply-supported rectangular beam ("Reference"); the second with an inner void formed to match the assumed strut-and-tie arrangement ("Void"); and...
  2. bugbus

    Interesting ponding/deflection problem

    There was a previous thread about water ponding on slabs that got me thinking about an interesting problem. I have not had any luck solving this theoretically, so for now it remains just a thought experiment. Imagine a massless plate with elastic modulus E and thickness t that is simply...
  3. bugbus

    Calculating characteristic strengths based on test data

    Currently I'm working on a spreadsheet to calculate characteristic strength values based on test data (mainly concrete cylinder strength, but in theory could apply for anything). The gist of it is as follows: Calculate sample mean (x̄) Calculate sample standard deviation (s) Based on number of...
  4. bugbus

    Buckling capacity of twisted plate strut

    I saw one of these brackets holding up a kitchen benchtop and it got me thinking about how the buckling capacity of this twisted strut would compare to the equivalent untwisted version? I suppose it basically boils down to something similar to below (ignoring the twist itself): Does anyone...
  5. bugbus

    High strength reinforcement - AS 3600 vs AS 5100.5

    Here is a quick comparison of AS 3600 and AS 5100.5 regarding provision for high strength (> 500 MPa) reinforcement: AS 3600 (including up to Amendment 2 as of 2021) Scope allows for reinforcement up to 800 MPa, with a limit of 600 MPa to be assumed for ultimate limit states unless noted...
  6. bugbus

    Plate washers for oversize/slotted holes

    I have a few questions about plate washers that AS4100/AS5100.6 require for oversize or slotted holes. I want to make sure I have this right. Taking the case of an M20 bolt as an example, it is clear from the code that anything other than a standard 22 diameter hole would count as oversize or...
  7. bugbus

    Steel 'strut-and-tie' design

    I have a situation where we are using a grillage of steel beams to temporarily support and jack up another structure. There are separate jacking points and packers along the cross beams; when the jack is at the end of its stroke length, the load will be transferred to the packers and the jacks...
  8. bugbus

    Bolt capacity in hand-tightened condition

    Are there any situations in which hand-tightened bolts (less than snug tight, basically loose) can be relied on for structural capacity? I am checking a steel-composite structure which is intended to be continuous for the future live loading. The beams are initially to be installed in a...
  9. bugbus

    General rant - early career burnout

    Lately I have been pretty disheartened with my job. I'm a structural engineer with around 6-7 years of experience, and now am finding myself with an ever-increasing amount of responsibility and juggling an ever-growing workload. Work/life balance is a thing of the past. Weekend work is basically...
  10. bugbus

    Friction coefficient between sandstone and plastic

    I'm looking for a (conservative) friction coefficient between sandstone (ground to a flat, smoothish surface) and a plastic packer (could be HDPE, nylon, or similar). The packer will temporarily support a precast concrete element on a sandstone base before a grout layer is cast beneath it. I...
  11. bugbus

    A few questions on stress concentrations, yielding, strains, etc.

    I am trying to learn more about FEA using nonlinear materials to assess the capacity of steel structures, components, brackets, etc. I understand that when using linear-elastic analysis around sharp notches, re-entrant corners, and the like, there will always be a stress concentration that...
  12. bugbus

    PFC steel grade from 1995?

    I am dealing with an existing steel structure that was designed in 1995. I have the original drawings but there are no steel grades specified anywhere. The section that I'm looking at is a 300PFC. I'm not sure if this is 250 or 300 Grade, and it is the difference between this structure...
  13. bugbus

    Most 'efficient' truss type for a pedestrian bridge

    Hey folks, I originally considered putting this topic in the Bridges forum, but I figured there's probably just as much experience with trusses in the main Structural forum. Recently I have been working on some concept designs for steel truss pedestrian bridges with spans in the order of...
  14. bugbus

    Hidden & neat-looking splice connections for SSHS

    I'm working on a pedestrian bridge concept design, which will be a truss comprising square SSHS sections. The truss will need to be transported in at least a few pieces, and spliced together on site. I recently saw the following example, but I'm not sure what is really going on internally. My...
  15. bugbus

    Why does heating reinforcement penalise the allowable stress, while welding does not?

    I understand that many codes penalise heating of reinforcement over 450ºC (~850F) by reducing the allowable stress to around half of the original yield strength, e.g. from 500 MPa to 250 MPa. But why is it that welding does not have the same rule when it exposes the steel to temperatures of...
  16. bugbus

    Seismic isolation using conventional laminated elastomeric bearings

    I want to get a few different opinions on the following questions relating to the seismic response of bridges supported on laminated elastomeric bearings. For a bit of context, new bridges built in Australia usually comprise prestressed concrete girders with a cast-in-place deck, and supported...
  17. bugbus

    How to deal with technical incompetence?

    I will start by saying that no one, including myself, is immune from making blunders or being totally clueless on certain technical topics. It’s only human and it’s totally forgivable. After all, this is the benefit of working in a team with a wide range of experience. Unfortunately, as with...
  18. bugbus

    Penetration through existing brick wall

    Client wants to cut a large penetration, approx. 800 mm wide x 300 mm high (32" x 12"), through the footing of a brick wall, in order to feed through several conduits into a building. The footing is around 400 mm wide (16"), appears to be 4 wythes thick, and supports a brick cavity wall on top...
  19. bugbus

    Incrementally launched bridge with both horizontal and vertical curvature

    I am reading the book Incrementally Launched Bridges by Göhler and Pearson (2000), trying to better understand the limitations of incrementally launched bridges. Regarding the geometry of the bridge, I understand that the best shape of the bridge is one that follows a screw line (i.e. constant...
  20. bugbus

    Falling tree load case

    We are occasionally asked to design bridges in forested areas where there is a possibility for a tree or large branch to fall onto the bridge (e.g. nature walks, golf courses, etc.). It is not a load case that is spelled out in any of the bridge design codes (as far as I'm aware). For bridges...

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