Non Destructive Testing of Existing Bridges

Transcription

1 DETAILS OF AGENDA ITEMS Review of Pilot Projects Proposed by Railway Board (a) Underwater Inspection NCR in collaboration with M/s Collins Engineers, USA, SR in collaboration with M/s Wilbur Smith Assoc., USA and CR in collaboration with M/s Ramboll, Denmark were allocated this pilot project. As per available information, only CR has completed it s project and submitted the report along with draft manual. Under water inspection is being done by almost all zonal Railways. CBE/CR shall give salient feature of report and a view shall be taken on adoption of draft manual submitted by M/s Ramboll. (b) Non Destructive Testing of Existing Bridges CR in collaboration with M/s. Ramboll, Denmark, NR in collaboration with M/s. Collins Engineers, USA and SR in collaboration with M/s. Wilbur Smith Assoc., USA were allocated this pilot project. As per available information, only CR has completed it s project and submitted the report along with draft manual. CBE/CR shall give salient feature of report and a view shall be taken on adoption of draft manual submitted by M/s Ramboll. (c) Acoustic Emission testing of Steel & Concrete Bridges NR in collaboration with M/s. TISEC, Canada and WR in collaboration with M/s. Dunegan Assoc., USA were allocated this pilot project. NR has completed it s project and submitted the report. CBE/NR shall give salient feature of report and also advice about it s usefulness specially in concrete bridges. A view to be taken in the seminar on it s usefulness and road ahead. (d) Fatigue Testing and Residual Life Assessment of Steel Bridges WR in collaboration with TTCI, USA and NWR in collaboration with Sharma Associates, USA were allocated this pilot project. NWR has completed it s pilot project and WR has made about 50% progress. CBE/NWR shall give salient feature of report and also advice about it s usefulness and steps required for its adoption specially for important bridges.

2 (e) Mapping of Unknown foundations and integrity testing of foundations NR in collaboration with M/s Olson Engg. has completed it s pilot project. Firm has demonstrated it to 20 railway officers. CBE/NR shall give salient feature of report and also advice about it s usefulness and authenticity. A view to be taken in the seminar on it s usefulness and road ahead. (f) Development of customized Bridge Management System SER in collaboration with PONTIS / DANBRO Ramboll /Camsys/FHWA was to develop BMS for IR. Status of project be given by CGE/SER (g) Instrumentation of Bridges Instrumentation of bridges was to be done by Railways associated with running of CC+8+2 and CC+6+2 loads. Visible progress made is by SER and SR. SER shall present it s results and other CBE s shall share their experience and give status of project. Also problems faced by Railways in running of CC+8+2 and CC+6+2 loads shall be discussed. (h) Development projects by RDSO RDSO is doing following projects, an update in form of presentation be given by ED/RDSO and CBE s should give their suggestions for it s speedy completion 1. Development of Analytical models and Codes for LWR on bridges. Procurement of Balance NDT equipment. 3. Development of Models and Testing methods for Residual life prediction for concrete bridges. 4. Development of Inspection, Testing Assessment & Rehabilitation methods and data base development of Masonry Arch Bridges in collaboration with UIC. CBE/ER, Sr. Prof/IRICEN and ED/RDSO have been nominated to be associated with project. This team to give update on project. 5. Application of Vibration Signature Technique and Development of Instrumented Rail based vehicle testing Labs for Bridge Health Monitoring, 6. Ambient vibration studies in situ of Bridges. 7. Bridge Scour Estimation, measurement and protection and use of various real time monitoring system like TDR.

3 2 8. Seismic isolation & Protection systems and development of guidelines/ codes for earth quake & laboratory facilities for testing of bridges and Development of Seismic retrofit measures. 9. Corrosion Protection Systems for steel and concrete structures. 10. High performance Concrete 11. Development of models for thermal stresses in concrete bridges and instrumentation. 12. Revision of fatigue provisions in IRS Steel Bridge codes. 13. Development of FRP bridge elements & temporary spans & staging. Track Bridge Interaction studies Proposed by ER No Pilot Project has been allotted to Eastern Railway. However, as a matter of safety, this railway had conducted under water inspection of eleven bridges. The results of the inspection along with a short film shall be presented by the undersigned during the seminar. For running of CC+8+2 and CC+6+2, this Railway has analyzed a large number of arch bridges with advance software like RING 1.5 and Modified MEXE Method. The comparative results shall be presented by the undersigned during the seminar. Bridges formed a critical component of infrastructure in Indian Railways. It is, therefore, essential that necessary checks are inbuilt in tender document itself which should ensure consistently good quality as a system. Compulsory use of batching plant and concrete pump in bridge works will help achieve this object to a very large extent. NHAI is a telling example of transformation of manual system of construction of road to totally mechanized system in small period of 5 to 10 years. The perceptible improvement in quality is there for everybody to see. Time has come now for Railways also to switch over to completely mechanized method of manufacture and placement of concrete. It is, therefore, proposed to include an additional para in eligibility criteria of bridge works for compulsory use of batching plant and concrete pump. 3 Proposed by NCR Approach Slab There is no comprehensive guidelines about provision of approach slab on new bridges. There are following cases for construction of bridges:- (a) Non ballasted deck bridge i. e. Steel Girder bridges. (b) Ballasted deck bridges i.e. PSC Girder/Slab etc

4 Some railways are providing approach slabs while this is not being provided in most of the cases. The issue requires deliberation and there should be same practice to be followed uniformly. In case approach slab is to be provided then RDSO should advise that how much reduction factor can be considered in the analysis of abutments and square return wall for live load surcharge and earth pressure. Rebuilding of Arch Bridges For rebuilding of Arch bridges, having longitudinal and transverse cracks, the common method being followed is provision of RCC Box inside the existing arch bridges. It is not clear if this should be treated as rebuilding of existing bridge or it should be treated as strengthening of arch bridge. The other aspect is that top of RCC box is normally kept at springing level of the arch. The gap between intrados of arch and top of RCC box is filled with Plain Cement Concrete. There is always a possibility of gap between intrados of arch and PCC. It results the existence of arching action in the existing arch and in case of poor structure it may sink/collapse leading to yielding of formation. Consequently track safety may be adversely affected. Clarification is required in this regard whether it is a standard arrangement for rebuilding of existing arch bridge. 4 Proposed by NWR Railway Board vide their letter No 2006/CE-I/Misc.(SC-2(RUBs) dated has desired to construct Limited Use Subways in lieu of unmanned / manned level crossings at critical locations. As per the Railway Board s above letter, the typical internal dimensions can be: height= 3.6m, road width= 4.0m and in no case the internal clear height be less than 2.5m. Height barrier shall be put at the approaches. Since this will be required to be provided at all Indian Railways, a standard type plan along with design details for various heights may be prepared by RDSO and circulated to all Railways.

5 Providing minimum dia of pipe / size of Box for bridges:- On date, it is not clear as to what shall be the minimum span for a Box / slab culvert and also what shall be the minimum dia for pipe culvert. It is also not very clear whether the irrigation drains are to be classified as a bridge or not. It would be desirable to have a uniform policy regarding provision of minimum size of pipe/ culvert. Supervision of Road Over Bridges fully constructed by sponsoring agencies:- There are different practices of supervising the Road Over Bridges (ROBs) which are being constructed on BOT basis fully by sponsoring agencies including railway portion. On some railways, these are being supervised by Construction Unit where as on other railways, these are being supervised by sectional AENs/ DENs or by officers of Bridge Line. It would be desirable to have a uniform policy for supervision of such ROBs, which are not being constructed by the Railways. Standard size of bridge drawings:- Presently different sizes of drawings are prepared for bridge in railways. There is no uniform practice regarding the size of bridge drawings. On some Railways even file size sketches are prepared for bridge drawings. As per Works Manual A 0 size is specified for GAD and detailed drawings for ROBs/ RUBs, important / major bridges. A 3 size is specified for site plan for ROBs/ RUBs and A 2 size is specified for temporary arrangements detailed drawings for bridge works but nothing is specified for minor bridges. It is proposed to have uniform policy regarding size of bridge drawings and this should find place in Bridge Manual. 5 Proposed by SER Steel Channel Sleepers for bridges located in curves Drawing No. RDSO/ B-1636 (Rev.2) is for Channel Sleepers on bridges located in straight. This does not cater for the channel sleepers on bridges located in curves. At present there is no supply of bridge timbers and therefore, channel sleepers are the only alternate sleepers available for girder bridge locations. Since there are some girder bridges located in curves (including some in transitions curve also), it is required that drawing is issued for channel sleepers for standard

6 spans of bridges located in curves also. Following aspects are required to be addressed in this regard: (i) Structural adequacy requirement of the sleeper to resist the increased lateral forces due to curving of track. (ii) Criteria or guidelines for fixing steel channel sleeper layout to match curved or transition position center line of track on the girders which constitute a series of straight chord lengths. In this context, RDSO, vide his letter No. CBS/SCS dt , has mentioned that standard drawings issued are fit for a curvature up to 1 only. RDSO has also advised Zonal Railways to design special type of sleepers (non-standard) for bridges situated over curvature above 1, based on the guideline given in Steel Bridge Code. In this connection, following items need to be discussed: i) The fact that standard Drawing( No. RDSO/B-1636 Rev.2) is fit for a curvature of 1, may be indicated in the drawing itself so that every Railway need not also the clarifications from RDSO individually. In Steel Bridge Code, no guideline exists for taking into account the curvilinear forces. Appendix-H of Steel Bridge Code gives the guidelines about distribution of Wheel Loads on Steel Troughing or Beams spanning transversely to the track, but this appendix does not take into account the forces due to curvature effect. Therefore, the details of design or checking, done by RDSO based upon which standard drawing is certified fit for 1 curvature, may please be supplied to Zonal railways so that design of channel sleeper beyond 1 curvature can be done by them. φ! "#$%% &%$'$ "#$%% &%$'$( #

7 (a) For Granular Soils Qu = Ap (0.5 D N + P D Nq ) + (i = 1 to n) K P Di tan Asi where, Ap = Cross sectional area of pile toe, in cm2 D = Stem diameter, in cm = Effective unit weight of soil at pile tip, in kg/cm 3 P D = Effective overburden pressure at pile toe, in kgf/cm 2 N q & N = Bearing Capacity factors (depending on at toe) = Angle of internal friction (i = 1 to n) = Summation for n layers in which pile is installed K = Coefficient of earth pressure P Di = Effective overburden pressure for i th layer, in kgf/cm 2 = Angle of wall friction between pile and soil, may be equal to = Surface area of pile stem in cm 2 in the i th layer A si (b) For Cohesive Soils Qu = Ap N c C p + C A s where, Ap = Cross sectional area of pile toe, in cm2 N c = Bearing Capacity factors (generally taken as 9) C p = Average cohesion at pile tip, in kgf/cm 2 = Reduction factor C = Average cohesion throughout the length of pile, in kgf/cm 2 A s = Surface area of pile shaft, in cm 2 From the above it is clear that the load carrying capacity is given separately for C soils and soils. But no formulae are given for C soils. In IRC : (Appendix 5), the Pile Load Carrying capacity formulae is for C soils. The formula given in IRC: is as following: Q u = R u + R f where, Q u = Ultimate Load Carrying Capacity of pile R u = Ultimate Base Resistance R f = Ultimate Shaft Resistance R u = A p (0.5 D N + P D Nq ) + Ap N c C p where, Ap = Cross sectional area of pile toe, in cm2 D = Stem diameter, in cm = Effective unit weight of soil at pile tip, in kg/cm 3 N q & N = Bearing Capacity factors (depending on at toe) N c = Bearing Capacity factors (generally taken as 9) C p = Average cohesion at pile tip (from unconsolidated undrained test)

8 P D = Effective overburden pressure at pile tip limited to 20 times diameter of pile for piles having length equal to more than 20 times diameter R f = (i = 1 to n) K P Di tan Asi + C A s where, K = Coefficient of earth pressure P Di = Effective overburden pressure in kg/cm2 along the embedment of pile for the i th layer, where i varies from 1 to n. = Angle of wall friction between pile and soil, may be equal to A si = Surface area of pile stem in cm 2 in i th layer, where i varies from 1 to n. = Reduction factor C = Average cohesion throughout the embedded length of pile, in kg/cm2 (from unconsolidated un-drained test) In this equation by putting value of C as zero and as zero, the formulae obtained are same as given in IS:2911 for soils and C soils separately. In the literature also, it is seen that the formula for pile load capacity is gives for C soils. The method of analysis & Design of Piles & Piles group shall be permitted as per acceptable methods described in the following publications: (i) Tomlinson- Pile Design & Construction Practice E.F & N SPON, Fourth Edition. (ii) Poulos & Davis Pile Foundation Analysis & Design - John Wiley & Sons, latest edition. In actual practice, in most of the cases the soils encountered are C- soils only and therefore it is required that the pile load carrying capacity is calculated for C- soils.