Shear and moment capacity of the Ruytenschildt Bridge
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In August 2014, the Ruytenschildt Bridge, a reinforced concrete solid slab bridge, in Friesland, the Netherlands was tested until failure. One of the goals of the experiment is to analyze the failure mode of the slab bridge under a tandem of 4 wheel loads and to compare the capacity of the full bridge structure to the predicted results, to have an idea of the residual strength of existing bridges. The methods used are experi-mental (testing of the bridge to failure in two of its five spans) and analytical. The analytical work involved predicting the bending moment capacity, the shear capacity and the punching capacity of the bridge. In both spans, the bridge failed in flexure. The total capacity during the experiment was significantly higher than pre-dicted. The results indicate that the traditional rating procedures for shear are very conservative when applied to slab bridges that benefit from transverse load redistribution.
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Shear and moment capacity of the Ruytenschildt Bridge
- 1. Challenge the future Delft University of Technology Shear and Moment Capacity of the Ruytenschildt Bridge Eva Lantsoght, Cor van der Veen, Ane de Boer, Karen Flores
- 2. 2 Overview • Introduction to case • Prediction of capacity • Test results • Discussion • Summary & Conclusions Slab shear experiments, TU Delft
- 3. 3 Proof loading Case Ruytenschildt Bridge • Proof loading to assess capacity of existing bridge • ASR affected bridges • Insufficient information • Study cracks and deformations for applied loads • Crack formation: acoustic emissions measurements • Control load process • Ruytenschildt Bridge: testing to failure in 2 spans
- 4. 4 Proofloading Ruytenschildt Bridge Existing bridge Partial demolition and building new bridge
- 5. 5 Cross-sections Ruytenschildt Bridge • Testing in span 1 and span 2 • close to end support • close to mid support • Critical position for shear
- 6. 6 Predicted bending moment capacity Flexural capacity Span 1 Span 2, support Span 2, span Mcr (kNm) 1816 1690 1592 My (kNm) 3925 5662 3717 Mu (kNm) 4964 7064 4705 Corresponding tandem load Pcr (kN) 880 1278 1460 Py (kN) 2368 7720 3532 Pu (kN) 3102 9940 4496 Moment at cracking, yielding, and ultimate + corresponding tandem load
- 7. 7 Predicted shear capacity Span Span 1 Span 2 Shear capacity Ptot (kN) Ptot,slab (kN) Ptot (kN) Ptot,slab (kN) bstr 3760 7606 4020 8132 bpara 3236 6546 3432 6943 bskew 4804 9718 5328 10779 • Effective width for skewed viaducts? • Slab factor of 2.023 from slab shear experiments
- 9. 9 Test results proofloading Span 1 • Maximum load 3049 kN • Maximum available load for span 1 • Flexural cracks • No failure • Order additional load for test 2!
- 10. 10 Test results proofloading Span 2 • Maximum load 3991 kN • Large flexural cracks • Flexural failure • yielding of reinforcement • Settlement of bridge pier with 1.5cm • Elastic recovery to 8mm 0 500 1000 1500 2000 2500 3000 3500 4000 4500 0 2000 4000 6000 8000 10000 Load(kN) Time(s)
- 11. 11 Discussion • Loads larger than estimated capacities prior to test • uncertainties about material properties • Flexure as governing failure mode • Shear: further research on skewed slabs is necessary
- 12. 12 Conclusions • Ruytenschildt Bridge • Testing to failure in 2 spans • Measurements • Shear and moment capacity determined • moment capacity: need for material parameters • shear capacity: effective width for skewed slabs? • Observed failure mode: flexure
Editor's Notes
- Thank you for the introduction mr/ms. chairman. Today, I will give a presentation on the shear and moment capacity of the Ruytenschildt Bridge. The authors of this paper are Dr. Lantsoght from Delft University of Technology and Universidad San Francisco de Quito, Dr. van der Veen from Delft University of Technology, Dr. Ane de Boer from the Dutch Ministry of Infrastructure and the Environment, and I am Karen Flores, former student at Universidad San Francisco de Quito, and I will present this work on behalf of the authors.
- Let’s start with an overview of today’s presentation. First, I’ll introduce the case, then we’ll look at the predictions of the capacity. Then, we’ll see the test result, and discuss these, and finally we’ll round off with a summary and conclusions.
- In the Netherlands, a large research project on proof loading is in progress. Proof loading can be used as a last measure to see if a bridge is able to carry a given loading without signs of nonlinearity or onset of damage. The types of bridges for which typical assessments based on calculations are sometimes not conclusive, and for which proof loading can be interesting are, for example, bridge with damage caused by material degradation, such as alkali-silica reaction, or bridges for which we don’t have enough information, such as bridges without plans. During a proof load test, we study the formation and growth of cracks as well as the deflections under the applied loads. Crack formation is followed with acoustic emissions measurements. Since these measurements need three cycles of loading to the same load level, they control the load process in the field. The Ruytenschildt Bridge was a special case. This bridge was schedule for demolition, so instead of carrying out a proof loading test, we were able to load the bridge until failure. It’s a five-span reinforced concrete slab bridge, and we could test to failure in two spans.
- Here you can see the replacement scheme of the bridge. On the left side, you can see the existing bridge, and the dashed region was going to be demolished first, while traffic could stay on the remaining part of the old bridge. Then, the dashed part is replaced with the new bridge (as you can see on the right), traffic is sent over the new part, and then the other part would be demolished and replaced, and the bridge would be opened to two lanes of traffic and a bike path again. To split up the bridge in two parts, a saw cut was made, splitting the bridge up into two independent parts. We tested the 7,365m wide part that was going to be demolished first.
- So the bridge was a five span bridge, and we tested in spans 1 and 2, close to the end support (sup 1-2 in the drawing) and close to the mid support (sup 2-3 in the drawing). For both spans, we used the critical position for shear at 2,5d from the face of the support to place the loading tandem.
- Here you can see the results of the predicted bending moment capacity. In this table you can see the moment at cracking, yielding and ultimate for the sagging moment in spans 1 and 2 and for the hogging moment of span 2 over support 2. In the next part of the table, you can find the corresponding tandem load to be placed on the loading tandem to reach these moments. What I need to tell you here is that these values are based on the material properties that were determined after the test, and that the first cores that were drilled from the bridge indicated a lower compressive strength for the concrete, so we actually expected lower maximum loads.
- Here you can see the predicted shear capacities. When we determine the shear capacity of a slab under a concentrated load, we need to determine the effective width over which this load can act. In the Netherlands, research on straight slabs showed that the best method is to take a load spreading from the far side of the load, per axle, and use a 45 degree load spreading to the face of the support, as shown in part a of the sketch here. However, for skewed slabs, we don’t experimental evidence on how to deal with this, so it could be that we should analyze the slabs the same way as for a straight slab (part a of the picture, bstr in the table), it could be that we use 45o with regard to the axis of the axle (part b of the picture, bskew in the table), or it could be as shown in part c of the figure, where the angle is the same as for the case of a straight slab (bpara in the table). Another effect that we know from testing slabs in shear in the lab is that the Eurocode shear prediction on average is too conservative. The average tested to predicted ratio for slabs under concentrated loads close to supports failing in shear is 2,023. However, this value is again determined for straight slabs. For skewed slabs, we know that the stress concentrations are larger at the obtuse corner. Perhaps this means that the increase for skewed slabs is not as large as for straight slabs and that in skewed slabs less tranverse redistribution can take place. What you see in this table are the maximum values of the load on the loading tandem to get a shear failure. Given the uncertainties about the calculation for skewed slabs, we can give a range of values in between which we expect the shear failure to lie.
- Now I’m going to show you a video of the experiment.
- Here are the results of testing the first span. You can see the loading scheme for the last loading cycles, the cycles until failure. Prior to this, we carried out a large number of cycles which correspond to the load levels in a proof loading test. Since the material properties that were determined before the test had resulted in lower values, the maximum amount of load that was available for the test was 300 ton. We reached a maximum load of 3049 kN, and we could observe flexural distress, but failure was not achieved. For the second test, we ordered 100 tons more of counterweights.
- Here are the results of the second span. Now we could achieve failure, at 3991 kN, when we had large flexural cracks, indicating yielding of the reinforcement. Moreover, we had a settlement of the pier at support 2: at the maximum load this settlement was 1,5 cm, and after elastic recovery and unloading it was still 8 mm.
- What we’ve learned from these tests is the following. First, as I mentioned before, there were some uncertainties about the material properties, so that the loads necessary to reach failure were larger than estimated prior to the test. In span 2, where we achieved failure, we saw that flexure was the governing failure mode. An interesting observation here as well is that we saw that for shear, we need further research on skewed slabs to identify the effective width for shear on skewed slabs, and that we need experiments to identify the transverse load redistribution capacity of skewed slabs.
- So now we come the conclusions of this presentation. We learned about the two tests on the Ruytenschildt Bridge, and the measurements we used. We focused on the shear and moment capacity of the bridge. For the moment capacity, we saw the need to have extensive material research prior to the test, since the results of a limited number of concrete cores gave a too low value of the compressive strenght. For the shear capacity, we saw the difficulty in estimating the shear capacity of skewed slabs. Finally, we saw that in span 1, there was flexural distress but we did not reach a failure, and that in span 2, we achieved a flexural failure of the slab, combined with settlement of the substructure.
- This concludes my presentation for today, and I’d like to thank you for your kind attention. If you have questions, I’d ask you to contact Dr. Lantsoght, who was the main researcher of this project. You can find her contact information on this slide.