Automatic Addition of Self Mass Dead Load

[Nick Jackson]

Hi Again,

One feature I would dearly like to see would be the first line in the load section being dedicated to the dead load of the proposed member. I know that it can be added manually but as the program already has all the required information (section size, length, mass per m, density (timber) etc) it makes perfect sense for the program to add this load and not the user.

May I suggest a check box under Print BM & SF diagram in the loads tab. Default setting ON

In the design window, the load could be the first load under Load Name.

Kind regards

[Tony Bryer]

Re: Automatic Addition of Self Mass Dead Load

This has been suggested before. In the past I have not taken it further as the key issues are that when designing the program iterates through the section sizes so the o.w. keeps changing, and, secondly, that for steel beams the figure used should be for beam and casing, and we do not know the latter.

But thinking about it again, perhaps a way forward would be handle it the same way as we treat column base plate sizing: if you enter a figure that is larger than the minimum, the program does not touch it. If it is less it ups it to the minimum.

No promises, but I will give more time to consider this when I can.

[Tony Bryer]

Re: Automatic Addition of Self Mass Dead Load

Automatic calculation and addition of beam self weight will be added to SuperBeam 4.53, tentative release date mid April. For a preview see our web page http://www.superbeam.co.uk/sb453.htm

[Nick Jackson]

Re: Automatic Addition of Self Mass Dead Load

Hi Tony,

I have worked this a few times and have noticed a small quirk.

When you check the OW check box, the self weight is expressed as a UDL in the loads table.

Firstly, this entry is editable and I think as its machine derived it should be read only and greyed out.

Next, when you remove the check box, the self mass remains - it would be better if the software clears it to avoid having to manualy remove it.

Next, I think you should display the material density adopted by your calcs - perhaps this could be displayed alongside the value for E

Next, you could also display the self mass of the member, in kg (and kN) - could this go alongside the material dimensional properties Z and I. You could also display the total length (span + bearings). I request this as one customer ordered a beam from my calcs quoting the span without bearings and then blamed me for not pointing out that the bearings should have been added to the length. The self mass in kg is important as any item I specify over 20kg in weight has to go with a health warning about dangers of lifting etc. I realise that this is as daft as the warning 'this product may contain nuts' on a packet of peanuts, but there are idiots backed by lawyers who will sue any any oppertunity.

Finaly, I note that the self mass increases when you select the wet condition which is as it should be. However, if you uncheck the wet box, the self mass does not revert to the dry condition.

Apart from that - a very usable feature - thanks again.

Nick J

[Tony Bryer]

Re: Automatic Addition of Self Mass Dead Load

Thanks for the comments. The two ways of doing this were to add in completely separate o.w. fields which would have needed some major changes throughout the program or do it the way it has been implemented, i.e to automatically add an entry into the existing load table.

Yes, it is user editable but if you reduce the value to below the actual, then the rounded-up actual value will be put back in. If you increase it, say because you want to use the weight of a steel beam + encasement, then your figure is left alone.

The reason the load is not removed if you uncheck the box is that we don't know whether a load labelled as 'o.w.' is the one added by the program or one that the user entered since within the program it is just another load, albeit with a reserved name. You can remove it by unchecking the box and then changing the load type character from 'U' or 'R' to '-', then pressing Apply.

As to showing how the o.w. load (for timber beams) is derived, we could do this by taking out the rounding-up, but my immediate instinct is to prefer (say) a neat 0.15 in the load field rather than 0.115x0.270x420x9.81/1000 (=0.12). For flitch beams it's an even more complicated expression which might not fit in the field. In most cases the o.w. value makes no difference to the calculation but checking engineers (rightly) tend to get a little exercised when it is omitted.

FYI there is a wish list request for some form of material schedule on similar lines to the project summary which would list out the members, sizes, weights and physical lengths.

[Tony Bryer]

Re: Automatic Addition of Self Mass Dead Load

"Finaly, I note that the self mass increases when you select the wet condition which is as it should be"

I missed this first time round. The current implementation doesn't do this - I think you were probably seeing the rounding up at work. From a quick look in BS5268 and several textbooks I couldn't find a definitive adjustment to be made for wet conditions.

[Nick Jackson]

Re: Automatic Addition of Self Mass Dead Load

Hi Tony,

I am not aware of a BS5268 reference either. BS5268 notwithstanding, the density of the material will alter in the wet, or service class 3, condition. TRADA Green Oak in Construction, 1st edn, AIII.4 (page 163) states that all green oak construction should assume a density of 950kg/m3 for the wet or freshly cut state whereas the density of dry oak is between 680 to 720kg/m3, depending on which reference you select your data from.

In practice, I think the simplest solution for Superbeam would be to multiply the density figure for the dry state of any timber by 20% to get the wet state, depending on whether service class 3 checkbox is on or off.

Your users would still be able to edit the value if they wish, but given the natural variation in density, not to mention degree of intermediate dryness, 20% would, in my opinion, be good enough.

Kind regards

Nick J

[Tony Bryer]

Re: Automatic Addition of Self Mass Dead Load

Thanks for that - in the next release I will add a 20% or 25% uplift to the BS density when wet is selected.

[Tony Bryer]

Re: Automatic Addition of Self Mass Dead Load

You didn't need to delete the question - we all fail to see things until we find them, when it's then so obvious! One of the reasons we encourage people to post questions of wider relevance here is that the answers are available as a resource to everyone else.

To save everyone wondering, the question was "I'm new to Superbeam and I'm just trying the demo version. I've read your discussion re self weight of beams but I've searched for this feature on my version (4.55c) and can't find it anywhere. Could somebody tell me where it is?"

As said above, obvious once you know but perhaps a little cryptic for a new user. On the loads page of the beam edit dialog to the right of the span field and steel/timber check boxes is a box labelled 'Auto o.w.'. This triggers the incorporation of the self weight field. When this box is checked, the routine functions as follows:

1. The weight of the currently selected section is calculated
2. The program looks for a load name of 'o.w.'
3. If this load name is not present, it is added to the load table with a load value equal to the calculated self weight rounded up to the next 0.05kN/m
4. If this load is found, the current value is compared with the calculated self weight. If the current value is less it is replaced with the rounded up calculated value as above, otherwise it is left unchanged

Note that if an o.w. has been calculated and you then change the section for a lighter one, the o.w. value will not be changed by the program. To recalculate it, change the value in the load edit dialog to 0 and press 'Apply': the new value will then be inserted. Conversely if you want to use a higher value than the one shown (e.g. because the weight of the beam casing is material), then you can manually replace the automatically calculated value with one of your own and the program will leave it unchanged.