Q&A

STSK Consulting Ltd aims to help Engineers in their understanding of codes and solution to problems. In the Knowledge centre we provide information for every one to use and improve their technical knowledge and efficiency. In this page we aim to answer your technical questions that you may have, we also aim to compile questions that we have come across that you may find useful.

    • In the calculation of crack width, what cover do we need to consider if the cover is more than nominal?
In the calculations of crack width, cover to be used should be the nominal cover defined in BS 8500 minus the tolerance. See IAN 95/07  ”interaction with BS5400″ it states:

For the purposes of calculating crack widths, as part of the design process, in accordance with Table 1 of BS5400, the nominal cover (including any additions for long service life) derived from BS8500-1 should be utilised, however it is recommended that the fixing tolerance (CC) is deducted from the nominal cover in order to undertake reinforcement design based on the limiting crack widths.”

    • What is the min reinforced concrete pile embedment into the pilecap?
Pile cut-off level is normally required to be min 75mm above under-side of pile cap.
  • What is the horizontal load for pedestrian parapet that need to be considered?

 In accordance with Eurocode BS EN 1991-2 (2003) Clause 4.8 (1) Note 2:

“The forces transferred to the bridge deck by pedestrian parapets may be defined with their classification for the individual project or in the National Annex in accordance with EN 1317-6. A line force of 1,0 kN/m acting, as a variable load, horizontally or vertically on the top of the parapet is a recommended minimum value for footways or footbridges. For service side paths, the recommended minimum value is 0,8 kN/m. Exceptional and accidental cases are not covered by these recommended minimum values.”

UK National Annex to BS EN 1991-2 Clause NA2.3.2 states:
“The required class of pedestrian parapet for the particular situation should be chosen in accordance with EN 1317-6 and determined for the individual project. The characteristic value of forces transferred to the structure should be taken as the design loads given in EN 1317-6 for the relevant class of pedestrian parapet.

For the design of the supporting structure the minimum horizontal load should be taken as 1,6 kN/m, corresponding to Class E, for normal situations, and 3.0 kN/m 2 , corresponding to Class J, for exceptional situations where crowding can occur. The horizontal load should be applied at the top of the pedestrian parapet and should be considered to act simultaneously with the uniformly distributed vertical loads defined
in 5.3.2.1 of BS EN 1991-2.”

BD37/01 (or BS5400-2) Clause 7.1.2 states (Note this is superseded by the Eurocodes now):
“Effects due to horizontal loading on pedestrian parapets. In the design of the elements
of the structure supporting pedestrian parapets, the nominal load shall be taken as 1.4 kN/m length applied at the top of the parapet and acting horizontally.”

  • Is there a guidance on modelling springs in integral bridges?
The are few guidances available below are a summary:
BA42/96:   The Design of Integral Bridges, you can download this document from the original source by clicking here
Composite Highway Bridge Design from TATA Steel, you can download this document from the original source by clicking here
Steel Bridge Group: Guidance Notes on Best Practice in Steel Bridge Construction, this is a very good guidance for design of steel bridges. You can download this document from the original source by clicking here
ALP User Manual page 27 under Elastic-Plastic soil model, you can download this document from the original source by clicking here
  • In Prestress Beams (Y beams) I have noticed horizontal cracks towards the end of the beams, are these defective beams.
This type of cracks appear to be typical of bursting force. Towards the ends of the beams you will have the tendons, specially if it is an integral bridge where you have to deal with large hogging moments. Controlling these cracks are not easy if not impossible, the problem is that you need so much reinforcement to control cracking that there will not be insufficient space between the bars which will lead to other problems.
If the end are normally encased in a diaphragm in this case the durability will not be significantly affected. Some times the holes for transverse bars act as crack inducers. If the cracks are large one can repair this with resin injection, but if in the final state the cracks are to be encased in concrete by the end diaphragm or as part of an integral connection there is little point in the above remedial measure.
The prestress strands may have lost some anchorage over this area but the anchorage length will extend into the span to form a new transmission length, which may require a bit more consideration in case of integral bridges where it relies on the strands.
  • How can we use simple calculations to  calculate the embedment length of holding down bolts?
The simplest way is to treat the holding down bolts as reinforcement bar and calculate the anchorage length required for the forces on the HDB. This will result in a conservative design. You can look at the calculation process for anchorage length on http://www.stskconsulting.co.uk/wordpress/spreadsheets/ page.
  • What is the BS code for steel design-buildings? Is BS 5950 superseded by Euro codes?
The British Standard for design of steel building was BS5950 as stated. All British Standards were withdrawn in March 2010 and superseded by Eurocodes. The Eurocodes that Supersedes BS5950 are:BS EN 1993-1-1:2005, BS EN 1993-1-5:2006, BS EN 1993-1-10:2005, BS EN 1993-5:2007, BS EN 1993-6:2007, BS EN 1993-1-8:2005.This means that all British Standards will not be supported nor revised any longer
  • Are there any design charts for reinforced concrete column design to Eurocodes?
There are some charts available in the “Designers’ Guide to EN1992-1-1 and EN1992-1-2″ by R.S Narayanan & A. Beeby,  first Edition 2005, The publisher is Thomas Telford. The above include charts for Rectangular sections and Circular Sections in Chapter 5, Cl 5.2.5 page 68
  • What is the minimum length of bolt protrusion beyond the nut after tightening in accordance with the Eurocodes?
BS EN 1090-2:2008+A1:2011 Clause 8.2.2 states:
“The bolt length shall be chosen such that after tightening the following requirements are met for bolt end protrusion beyond the nut face and the thread length:
The length of protrusion shall be at least the length of one thread pitch measured from the outer face of the nut to the end of the bolt for preloaded and non preloaded assemblies .
If it is intended that a connection utilises the shear capacity of the unthreaded shank of bolts, then the dimensions of the bolts shall be specified to allow for the tolerances on the length of the unthreaded portion.
NOTE The length of the unthreaded bolt shaft of full cross section is shorter than the nominal unthreaded length (e.g. by up to 12mm for an M20 bolt).
For non-preloaded bolts, at least one full thread (in addition to the thread run out) shall remain clear between the bearing surface of the nut and the unthreaded part of the shank.
For preloaded bolts according to  EN 14399-3, EN 14399-7 and EN 14399-10, ” at least four full threads (in addition to the thread run out) shall remain clear between the bearing surface of the nut and the unthreaded part of the shank.
For preloaded bolts according to EN 14399-4 and EN 14399-8, clamp lengths shall be in accordance with those specified in Table A.1 of EN 14399-4:2005.”
  • Is there a maximum distance between reinforcement before they are considered lapped bars?
Because the purpose of a la p is to transfer a load from one bar to another, if the bars have a gap then the load path would include the concrete between the two lapped reinforcement bars. It is sensible to limit this gap, Eurocode 2 (EC2) Clause 8.7 specifies this requirement as 4 or 50mm max otherwise the lap needs to increase by the clear distance between the lapped bars.

 

2 comments on “Q&A
  1. MJ Ochola says:

    These are very useful spreadsheets. Keep us informed and include for bridge design like RC Deck, Piers, Abutments and steel-concrete deck

    Regards

    MJO

    • STSK Consulting says:

      OK thanks, I am working of few other spreadsheets, which I will upload as soon as they are complete. To get updates join us on twitter @stskconsulting

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