Tunnels and Structures

Problem Statement I have been trying out different structural FE software to evaluate their automatic reinforcement design functions. For an underground structure, multi-layer reinforcement design in SLS is a must. Surprisingly, most of the STR FE tools cannot handle multi-layer reinforcement very well. Typical problems are: Software does not have the capability to add the second or third layer at deeper positions automatically - instead it usually places them at the same depth as the first layer. FEM-Design does a great job at SLS design - but unfortunately, all additional reinforcement is placed on the first layer. Software can check multi-layer reinforcement, but it can only check one arrangement - it cannot do an automatic design. Software can do multi-layer design, but only for ULS, it can check SLS for the reinforcement defined by ULS. I can guess that this is pretty useful for above-ground structures, but for underground structures, SLS usually governs our reinforcement design. Best Practice at the Moment There are a LOT of STR FE tools and I am not claiming that I am aware of the capabilities of all of the ones out there. (Please reach out if you know more - so I can try them out or I can update the post with new information.) But at least, I have tried SOFiSTiK, FEM-Design, Robot, Lusas, RFEM6. I know that SOFiSTiK can do multi-layer design, but not without simplifications. User is asked to define the multi-layer reinforcement arrangement by LAY method. This requires a fixed diameter and minimum-maximum area of reinforcement for each layer. Using these inputs, SOFiSTiK can produce continuous As maps, required reinforcement area, for SLS. That’s great! But how does it achieve this really? In short: ...

It started with ITA (International Tunnelling Association) WG 11’s catalogue of immersed tunnels. The third one (and also the fourth) in the list is from Copenhagen. Actually, the culvert is located in the most photographed region of the country - under Nyhavn. In this excellent catalogue prepared by Nestor Rasmussen (DK) and Walter Grantz (USA), the S.3 tunnel has been described as shown below. Then, search is started. With the help of people from Reddit, we found the location of the tunnel in the HOFOR database. The possible location is under Nyhavn’s connection to the sea - which shown with blue dashed line. In one of the documents, it says “Den dykkede ledning i Nyhavn blev nu også lagt. Den gik fra Kvæsthusgade til Havnegade.” which translates to “The submerged pipe in Nyhavn was now also laid. It ran from Kvæsthusgade to Havnegade.” Afterwards, I contacted the Københavns Museum, and Jakob Ingemann Parby, Senior Researcher and Museum Inspector, has reached out to me to provide more resources. In one of the resources online, Københavns Energi A/S’s (previous name of HOFOR) book called “Fra stinkende rendestene til computerstyrede kloakker” (in English “From smelly gutters to computerized sewers”) had more information on the topic. This beautiful image shows the lowered steel pipes: Let’s zoom in a little bit. I think they used barrel as ballast to sink the pipes. Pipe may look like very flexible, but it’s not actually, the design of the pipe is with bent corners as shown in the image. Actually, we even have a construction drawing. We can see the backfilling and longitudinal profile of the pipe. They had gate valves to periodically flush the pipes that accumulate dirt and sediments. Another construction stage photo is coming from Københavns Museum archive - Jakob Ingemann Parby. You can see the cranes and same shape: ...

Introduction Last month, we had an interesting and long discussion over the email with the creator of PCTempflow, a widely used software for fire analysis, and others like PCSheetPileWall and Framework: Gerrit Wolsink . Over the course of the many emails, we have agreed that there is something wrong (or incompatible) in the Eurocodes. This brief article is our joint effort on clarifying our views on this problem. If you have any input, please feel free to reach out. ...

Before Introduction This is the paper we have written with my dear wife Pinar Akdogan Demir, based on our experience from Istanbul tunnels. I was already considering uploading the paper here, but when I saw that my paper was not inside the proceedings USB due to a mistake (which also was almost preventing me from presenting - because they simply forgot us), it was a must. So, here it is. As always, get in touch if you have any comments. ...

Estimating damage level on the existing buildings due to tunnelling is a tricky business which depend on many factors and cannot be over-simplified. But one of the simplifications that has been used commonly is equivalent beam method. Equivalent beam method allows us to simplify the rigidity of buildings in a simple Mindlin beam. Why do we need the rigidity of the building to come into our numerical models? We have many evidences that show us greenfield deformations (which are deformations due to tunnelling on level ground without any structure.) are much higher and narrower than building deformations caused by tunnelling. One evidence is given my Frischman et. al. (1994) and reported by Mair, Taylor and Burland (1996). So, we need the rigidity of the structure to be modelled and we need it as close as possible to the reality. How? We can model the structure every time we model a tunnel problem, this is an option of course, but an option for people with lot of time. We need a simpler solution. The simpler solution is equivalent beam method. To determine the EI and EA of the beam, we have to come up with a methodology that allows us to simplify the building. Potts and Addenbrooke (1997) have proposed calculating moment of inertia of the building with respect to neutral axis, considering only slabs using parallel axis theorem. (If you forget: Moment of inertia of a beam at point P at a distance y to its neutral axis is I_P=I+Ay². As authors state, this is an over-estimation since this assumption holds true only for rigidly framed structures. But they also summarize another method which is also described in CIRIA report 200 by Mair and Taylor (2001). Using this method, authors have predicted the deformations before the construction (Class A prediction) and results are very close to measurements. In this method, moment of inertia of each slab is summed up by neglecting Ay² term. Note that in both methods equivalent area of the beam can be calculated using sum of the area of each slab. Goh and Mair (2014) developed a third approach which adds column stiffening factor, C of Meyerhof to approach given in Mair and Taylor (2001). However, calculation of C requires detailed information on column and beam positions which may not be readily available in every project. But, to make a note, I should state that, if you will perform a detailed analysis for a significant building, you should definitely use this paper (if you will not model the building in full detail.)s Goh and Mair (2014) states that parallel axis method is over-estimation of the building rigidity while algebraic sum of moment of inertias is under-estimation. To be honest, parallel axis method was looking better for me. However, a very very simple experiment proved me wrong. I have modelled a building in almost-full detail. Of course, there are still many simplifications such as connections of slabs and columns, but it is a simple trial, so this should do. I have created three models using Plaxis 2D 2019: ...