I am afraid as a Project Manager

I am afraid as a Project Manager this is not my field of expertise. However instinct tells me guidance should be included in the standards for such a critical design element. (B)

Regards,

A C
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As a graduate engineer with very little design experience I would say b) as at this stage in my learning I feel guidelines in this area are critical. Newly qualified engineers do not always have the necessary knowledge or even confidence to make an experienced or accurate judgement on this issue.

Dear Martin
Since I am a graduate my opinion doesn't really count that much but I
would like to state that I totally agree that there is a foul in results
when using the formula of axial deformations considering axial stiffness
alone to calculate Dl in slender elements. Buckling will cause additional
bending stresses and deformations & it's a matter of bending stiffness
as well. Crushing Euler load on elements under compression, based on
slenderness, doesn't take into account secondary effects like
P-D. (Perry- Robertson literature would help)

Dear Martin,
I would be interested in learning how you calculated the magnitude of Dv.
We all know how to calculate the Euler's buckling load and to provide in
turn an adequately safe strut section, but to calculate the transverse
deflection for any (other) value of (axial load) is something I've never
done.
Could you enlighten me on this?
By the way, we in India are not really affected by changes in BS, since we
have our own codes to be followed. Our code (IS:800-1984) specifies the same
limitations as the ones mentioned in the old BS code (& omitted in the new
version.)
Nevertheless I would support you in your option (b).

With Regards,
D. G. B
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The slenderness limits are in my opinion "good practice". They are similar to designing structures of correct proportions, an experienced engineer immediatly knows if something looks right or wrong because, or aided by, it's relative proportions. To that end it is not necessary for BS5950 to limit sections on arbitary slenderness levels but merely offer guidance, by the SCI for example, on correct proportioning.

Sorry I'm not a Structural Engineer. It's 25 years since I designed a
column! However I do remember about these ratios in compression members and
my practical knowledge of overloading things leads me to consider that
buckling is an issue that should be addressed and that control of
slenderness makes sense.

I can't see any reason why slenderness limits cannot be re-instated, as at present the code seems to be lacking in direction regards this area.

___________________________________________________________________________________________________________________

Dear Sir,

In reply to your e-mail I tend to use the old slenderness limits in the
absence of any other guidance.
I would therefore select (b) from your options.

Regards,

G S

Martin
In Australia we also have suffered the same fate
as slenderness limits have been deleted from
recent steel codes. This is not good in my opinion
as many younger Engineers have no concept of
what a reasonable limit should be. Vibration and
robustness is often a deciding factor and this has
been lost in the current AS 4100.

Best Wishes

J N. MIStructE.

I believe that there should be guidance in the BS re slenderness of struts, thus I guess I my answer is option b, however I would prefer is the BS gave guidance, ie not mandatory, rather than a requirement for the slenderness limits.

The closer you try to get to "up to full standard" the more likely you are to
run into conflict with DIN codes. The only choice is either to publish
something "lesser", and let the member nations "fill in the gaps" or spend the
nex hundred years trying to fight it out between BS, DIN, AFNOR etc.

G F

Martin D
I consider slenderness limits should be retained in the code to assist the
designer in achieving safe designs . Unfortunately too many codes are
creating 'grey' areas which is not helpful to anyone, particularly in busy
design offices where simplicity is often crucial.
Therefore I agree with option b)

Martin R

Guidance limits are extremely useful when you have only one-off designs and little time to prove otherwise.

The final result we should all be trying to achieve is a safe robust structure that is not too prone to abuse.

Sorry Martin, I work in Programme Management. The only slender struts I know about are propping up my desk. I suppose I'm a (c) Don't understand the question.

RB

The prior limits were nonsense. If you look at real structures from Pylons to Aircraft through railway station canopies, all of which work fine, all of them have slenderness limits well greater than 1/180 or 1/150.

There is a practical limit of handling etc which is in the order of L/600, when the steel would buckle up under its own weight ( try a 254 102 22, ryy=2; you can pick this up if it is 12 m long, but not 15 m long.)

We have a self imposed limit of l/r 350 for bracing tubes, because up to that length they pick up and handle well, and do not curve too much in use.

I'd be quite happy to see that any member which could in service carry any strut load should be limited to l/r<350.

I am no Luddite, and I fully expect the human race to progress with the understanding of the sciences, but the removal of the slenderness limits for compression members from BS5950 is in my opinion a risky step, especially where designs are being prepared by inexperienced engineers. I am sure that the current BS's are becoming more, and more documents for means of issuing the conclusions of research scientist/engineers and are not there as aids for the working engineer who is under extreme pressure to keep design costs down.

For example the slenderness guidance ensures that horizontal roof bracing is kept to sensible sizes to avoid unsightly deflections and possible secondary bending stress due to Pdelta effects. Also slender bracing members can be more affected by induced vibrations from certain normal operations within the building. The old BCSA handbook gave certain span/depth criteria for roof bracing elements to avoid the above.

When a client looks at a structural element of his/her building and notices slender members, or defected members there is a normal human response for unease, and possible questioning of the design, albeit that the design is probably OK!

Firstly, I believe that it would be very sensible to re-introduce slenderness limits for the design of steel struts, but whilst retaining the facility to design struts outside these limits providing that a more rigorous analysis were used. My reason for this is that, like it or not, struts are sometimes designed by both inexperienced structural engineers and also others who are not structural engineers and who probably should not be designing structures but are going to do so anyway! The introduction of slenderness limits would provide a safeguard against a disaster caused by little knowledge. Alternatively, it could be argued that a few good well publicised disasters might actually discourage people from dabbling when they shouldn't!

Interestingly, BS5950 Pt 1 does address second order effects in Appendix C by introducing a second order moment which is proportional to the stress in the strut. This does not, however, address bending stresses due to self weight (relevant to very slender inclined and horizontal struts) and I do not think that such effects are included in design tables produced by BCSA/SCI (The Blue Book). Second order and self weight effects can be critical in very slender struts. BS5950 does not state at what slenderness such effects need to be considered and such guidance would be welcome.

In practice, really slender struts do not "look right" and for this reason are not frequently used. However, their use can arise and for this reason we should have a BS that addresses the problem in a sensible and pragmatic way and does not leave the door open to possible error.

Problem with Strut Deformation

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