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Dear Martin,
In my opinion some limits should be given but in lieu of this I still use the previous code slenderness limits (180, 250 etc).
I suppose that means my preferred answer is B!!!!
Hope this helps
Regards,
A P
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Martin,
I would prefer guidance on limitation of strut slenderness to be reinstated in BS5950.
T A
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Dear Martin
I think that I have to be an "other" in response to your query. I am pleased to be able to say that I have recently progressed to free membership, after 50 years in the Structurals, and, although I am a trustee of the Benevolent Fund and remain interested in Institution affairs, I have cast aside any concerns about Codes, Eurocodes, design philosophies etc. In the matter of slenderness limits I have only to satisfy my own compression members.
I hope you will receive some helpful responses from other, more active, members.
Yours sincerely
B C
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Dear Martin
I support the reinstatement of BS5950 ie (b)
J E.
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Martin,
Thanks for your message.
This practice supports limiting slenderness and continues to use the maximum
slenderness rules in earlier versions of BS5950. I have to say, however,
that the issue does not often arise.
Regards
C K
C K A Ltd
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Martin
Further to your e-mail on the question of slender struts i support the
reinstatement of slenderness limits for compression members.
Regards
C L
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Martin
Personally I would feel happier if the original slenderness ratio limits were retained, possibly with a note to the effect they might be exceeded, subject to due consideration being given to all 2nd order effects, including …. (I am sure you can insert better than me!)
Regards Charles
C T
W H Partnership
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'b'
I agree!
Good luck with your quest
Regards
G E
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sorry I cannot help...........was a bridge engineer......now retired
G W
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Martin,
I am of the opinion that such an important issue requires some guidance
albeit basic. I would suggest that 'Option B' is the least we should expect
to be available as not all engineers, especially the younger less experienced
appreciate the consequences of inappropriate slender strut design.
I am not an advocate of taking the final decision from the engineer but
we all need some guidance in such matters.
Regards I J R
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Dear Martin
Strut Slenderness Limits
As a designer of steelwork in building construction, I would offer some comments.
1. The removal of the rigid limits given in BS 5950-1-1990 provides definite benefit for the design of efficient structures. An element with a slenderness of 251 may well be capable of adequately resisting the loads applied to it, and for instance in the design of roof plane bracing in single storey building subject to low wind load effects, economic advantage [safe advantage] can now be made of the removal of the limits.
2. As a design engineer I would not favour a return to prescribed limits. Prescribed limits would remove allowance for the engineer to exercise judgement and experience suggests, may result in needless discussions with Building Control engineers pointing out non-compliances with the code of practice, which would not be non-compliances with the Building Act.
3. I agree that there is an inherent danger with not having limits specified in the code, and I would welcome the code to recommend upper values, so long as the code acknowledges that such values may be exceeded. The source of the danger is not however the code of practice, but the level of knowledge and skill with the individuals and companies engaging in the design of steel structure. Should slender members be adopted by a designer, it is the designer’s responsibility to ensure that the member satisfies the requirements of the code of practice. It should not be the function of the code of practice to restrict all designers, on the basis that some ‘designers’ may not be appropriately experienced or qualified to ensure a safe design.
4. I suspect that the removal of the limits for the 2000 version of BS 5950 may be that there is no technical justification for requiring a designer to limit slenderness, and that the acceptable slenderness of a member should be left to the judgement and justification of the project steelwork design engineer.
In short, I would not welcome prescribed limits, and suggest that this would not go down well with fabricators engaged in the ‘cut-throat’ steel fabrication market. I would welcome (although I suspect neither you nor I require it) BS 5950-1-2000 to include guidance on the dangers of using slender members.
I see many other dangers to the construction of safe buildings, other that the potential for introducing members of inadequate slenderness. This matter seems to me to be merely a symptom of a larger problem relating to the fundamental understanding and ‘feel’ for the way structures work, education, and the reliance on computer based labour saving software tools (without which we could no longer do business).
I hope you find my comments of some use.
J D
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Dear Martin
In recent years I have been involved exclusively in insurance related matter. Regrettably, I havent been following the discussions on slenderness limits and I am unable to offer any constructive thoughts in this matter.
Sorry to disappoint but I wish you well.
Kind regards
K M
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b/ definitely
K F
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Dear Martin,
As a graduate of 5 years I was brought up using the original 5950 with slenderness limits.
As a fairly cautious engineer I still continue to use those values even though the code
does not require them.
I did briefly for a period think, well if the structure is strong enough then why limit yourself
to those values. I then argued that as well as producing a structure that is strong enough
the limits also produce one which looks right. An engineer can now design a strut that
is apparently strong enough but extremely slender but to joe-public a structure that looks safe is
probably just as important as one which is safe. I'll be voting a "b" then and will continue to
use those limits in any case.
Regards
Matt
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We (three engineers) vote for option b. even if it is only reinstated for guidance rather than a requirement.
N E
D L & Associates
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Dear Martin,
Thanks for your email on the lack of guidance for slenderness of compression members in the current BS.
I should introduce myself first. I have been on the retired list since end 1993, when I turned 65. I had been in the Cape Town Local Govt Building Survey checking structural submissions, after being retrenched at the collapse of the local steel industry in 1985. Prior to employment by the steel fabricator I had been with several consulting firms and had not specialised in any particular aspect of structures.
Here in South Africa we no longer rely on the BS codes so I have lost out on BS 5950 etc. The local steel code has many similarities with the Canadian code, and we have had some visiting Canadian specialists on silos and bracing. Our code does limit the slenderness ratio for compression members to 200 and to 300 for tension members. It also has limits for width/thickness ratios for elements in compression. However it has been said that codes of practice are given for those who have the knowledge to interpret them. There are many books that give much information for those concerned, even if some are regarded as being out of date!
I have been to your website. I have not opened all the comments files, but see that you have had a good response from your emails. I have had a look at your notes on your plane frame and 2D programmes. Since leaving the steel firm I have not had access to any analysis software so would be interested in acquiring these to amuse myself, perhaps also to comment on them.
Yours faithfully,
P S
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Dear Martin
Sorry it has taken me so long to reply.
I was brought up with BS449 and found BS5950 a bit of a chore. The most recent revisions have eluded me. I have used and still use the Constrado Blue book and more recently the BCSA red book on a day to day basis. I would find it difficult not to apply the slenderness ratio limits of 180 or 250 ( although I have seldom used the 350 limit).
It occurs to me that the increasing use of computers for the design of structural elements has enabled the least experienced Engineers to design the most complex structures without any real thought.
I think that, regardless of what the current, and future versions of the steelwork codes say. I shall continue to apply slenderness ratio limits.
Regards
P W
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Martin,
I have followed the debate with interest.
From many years in Industry, and now with an academics hat
on, I still keep my eye on a slenderness ratio of 180 for dead
plus live.
It does not become a "bad" idea overnight! Regards
P Y
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Dear fellow engineer,
Thanks for your efforts. Actually, it is about nine years that I
have virtually stopped engineering practice. I doubt if I can
contribute anything worthwhile. Nonetheless I admire your efforts
and wish you success. You can class me as UNSUBSCRIBE.
with best regards,
P J.P.
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Martin
I would prefer option B for clear guidance to all.
R P
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Martin,
I have just been to your web site and read some (not all) of the responses posted and there seems to be quite a groundswell of support for the re-introduction of the slenderness limits however, I noted with interest the postings at the end of page 6 with regards to the non-inclusion of slenderness limits in the National Annexe to EC3.
It would appear that there are many Engineers out there grimly hanging onto BS449 despite it having been declared “Obsolescent” by the BSI for some time and now deleted, along with CP3 Ch V Part 2, from the list of approved documents for Part A of the Building Regulations which comes into force on 1st December 2004.
Since the introduction of BS 449, I think back in 1957, with the slenderness limits, the design of structural steelwork has come a long way with regards to how the various section shapes perform under combinations of axial and bending forces at the ultimate limit state. It would appear that many Engineers are forgetting that there is also the serviceability limit state of deflection and that elastic shortening of struts is a deflection and whilst specific values are not given in Table 8, 2.5.2 does say “Other members may also need deflection limits.”
I would support BS 5950 as it stands but would suggest that there be some research into establishing a deflection limit for elastic shortening, or lengthening, of axially loaded members.
Regards,
S L
S L A Ltd.,
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I would be in favour of the reinstatement of slenderness limits (b) with advice also being included to assist the less experienced engineer in avoiding using sections that appear to have adequate capacity but would be in appropriate, i.e. thin walled sections that would be distorted by the galvanising process and particularly small outer diameter sections with thick wall thickness that may experience significant secondary stresses owing to fabrication and construction eccentricities.
regards
s j
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Martin,
I say B as I believe whippy high slender columns LOOK wrong.
Regards
S W
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Thank you for your E-mail of 8th November. I was amazed that BS 5950: 2000 omitted the maximum slenderness ratio requirements. My vote goes to (b) above. The reasons are well summarised by Adrian Mirfin in his letter to Verulam (The Structural Engineer 2.11.04 p 18).
Regards
J R
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Dear Martin,
Thanks for offering me the chance to express views on the Code about slender columns.
I agree that reinstatement of slenderness limits on column is important and necessary. It is not logical for having to check slenderness of RC columns in BS8110 but such checking in steel columns can be waived.
Regards,
TKH Y
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Dear Martin,
Writing from South Africa, our steel code {SABS 0162} specifies a max
slenderness limit of 200 for struts and 300 for ties with a waiver for ties
subject to consideration of flexibility, sag, vibration and slack etc.
Often, with current Architectural "structures" we have to bend the rules
a bit but at least our code rings the' alarm bells for us.
We would therefore vote for a b] as a recommendation only - not a regulation
-with a paragraph of explanation.
Well done for opening up this Forum. Hope this is the start of a
worldwide trend in Engineers talking to each other.
Perhaps we could have a "Dumb questions you were afraid
to ask Site"!!
a g
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Euro codes seem to be removing all guidance on good practice and relying more & more heavily on complex mathematical models. I believe this is a backward step. Modern procurement methods are squeezing design times and Euro codes are complicating the design process. Therefore the risk of mistakes is becoming greater.
I support the reinstatement of slenderness limits as a simple tool. However I also believe there should be opportunity for more complex procedures to be used at the designers discretion.
S W
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