Approval of non standard Railway girders
In this video we will understand the authority competent to approve non standard railway girders. Also recently railway board has issued very detailed instructions for adoption of non standard open web girders. We will see those provisions in detail as well.
Now coming back to provisions for approval. Railway board had long back issued clear instructions through its letter dated 11.08.2014 which are still unchanged. As per this letter all the non standard railway girder drawings are supposed to be approved by CAO Con or PCE of zonal railway. However they should be used only in cases when they are unavoidable. CAO or PCE should record the specific reason and justification for using such drawings.
Apart from above instructions railway board has recently issued one very important instruction in this regard vide its letter dated 18.10.2024. This letter speaks about planning of non standard open web girder spans.
The most important and operative para of this letter is para number 3. Para no. 3 mandates that prior approval of railway board shall be taken through PCE with complete justification, while adopting non standard open web girders.
Detailed instructions are further elaborated in Annexure-I of this letter. It stipulates that as far as possible RDSO standard span should be adopted. If there are site constraints in adopting them suitable measures like extending the pier cap may be adopted. In case new bridge is to be located close to existing bridge, staggering of pier arrangement may be considered. Anticipated scour should be dealt properly.
If non-standard spans are adopted care shall be taken, while designing, to follow available RDSO standard drawings of nearest OWG span with minimum required changes made to meet the essential design requirements. Complete procedure of detailed design, however shall be followed as per DBN that is design basis note approved by RDSO. It means in each case of non standard OWG, DBN shall be approved by RDSO. As per extant instructions, finally design of all non-standard spans of OWG shall be approved by Zonal Railways.
It further stipulates that Design Basis Notes (DBN) of Non-standard spans of OWG in all bridges shall be approved by RDSO. Critical values of various design parameters such as loading, fatigue category, partial factor of safety, type and specifications of HSFG bolts etc. shall be specified in DBR/DBN. Connection design at every node shall be examined carefully with respect to member capacity and number of rivets/HSFG bolts required/ provided. RDSO shall also specify the check points of vital design stages so as to ensure that design process is followed correctly by DDC & PC. Here DDC means detail design consultant and PC means proof consultant.
The stages of fabrication process to be inspected by DDC & PC and QAP shall be part of DBN. It means that DDC and PC will remain involved in fabrication stage as well to ensure that fabrication is being done as per design requirements. However their clear role shall be mentioned in QAP made for steel fabrication.
Designs may either be done by in-house Design Cell of CAO Con or through outsourcing the work to competent Detail Design Consultants (DDC) duly proof checked by Proof Consultants (PC). In the later case also, the design cell shall be involved to verify that the design is being done as per the approved DBN and all vital design stages are completely satisfactorily.
The engagement of DDC and PC and quality of fabrication shall be regulated and monitored as under:
a. Only competent DDC and PC of repute, having professionally trained designers, shall be awarded the consultancy works. DDC and PC shall be engaged from the very beginning of the project and they shall remain associated with the construction of bridge till commissioning or defect liability period. During construction stage, same DDC and PC will provide necessary advice or design modification as and when warranted.
b. While engaging Proof Consultants, any conflict of interest with DDC or Contractor shall be avoided. IIT or NIT may be associated for technical guidance & opinion only in exceptional cases. It means proof checking by IIT or NIT is to be adopted in exceptional cases where special technical opinion is required and not as a norm.
c. Same DDC and PC shall be involved in the design of foundation, substructure, super structure, launching & erection schemes, temporary works, formwork etc. to safeguard against any mismatch in designs, proper estimation of various loads or damage during the final erection on sub-structure. It means same designers shall remain engaged from foundation till final launching and erection.
d. Professional Liability clause of sufficient duration shall be added in the contract of DDC and PC. The responsibility of these Consultants in case of any failure shall be clearly laid down in tender conditions.
All About Bridges