Improving tunnel resilience against fires: A new methodology based on temperature monitoring

Monitoring temperatures during tunnel fires is of major importance for both the firefighters extinguishing the fire, and the engineers in charge of the subsequent repair work. However, current methods of assessing fire damage have limitations when applied to tunnels and only provide estimates of the maximum fire temperatures at specific locations of the tunnel. This is not a desirable situation, as the temperature time curves associated with the fire event should be available for use in assessing the residual strength of the tunnel structure. This is the key parameter in defining repair work and the length of time the tunnel will need to be closed and thus the socio-economic cost of the tunnel fire. In addition, real-time recording of the temperature time curves would provide valuable information to the firefighters engaged in extinguishing the fire. This paper presents a new general methodology for the optimal placement of sensors in a tunnel to obtain the temperature evolution at any point along its lining during a fire. The methodology was applied to the Virgolo Tunnel in Italy, in which 100 potential high-temperature sensor configurations were tested and a set of optimal sensor configurations was proposed. The results of the analysis show that: (a) the proper location of the sensors is crucial; (b) it is possible to define a set of sensor configurations that minimize the cost of the monitoring system and maximize the accuracy of the estimated temperatures; (c) it is important to place at least three high-temperature sensors in each monitored cross section (at the crown and symmetrically on the haunches/side walls). The proposed methodology improves tunnel resilience against fires, as it enables safer infrastructure and a faster and more economic recovery of the tunnel after a fire eventThis work has been possible thanks to the financial support of the Spanish Ministry of Science and Innovation (Research Project BIA 2011-27104). Funding for this research was provided to Paula Rinaudo by the European Commission (Project Erasmus Mundus Action 2 ARCOIRIS). The authors are also grateful to Eduardo Cassiraga from the Universitat Politecnica de Valencia and to Eduardo Loma Ossorio for all the support provided.Rinaudo, P.; Paya-Zaforteza, I.; Calderón García, PA. (2016). Improving tunnel resilience against fires: A new methodology based on temperature monitoring. Tunnelling and Underground Space Technology. 52:71-84. https://doi.org/10.1016/j.tust.2015.11.021S71845

Load transmission between slabs and shores during the construction of RC building structures A review

[EN] Shoring successive floors is at present the most frequently used technique when constructing reinforced concrete (RC) building structures. This technique allows the recently poured slabs to be supported by the lower slabs by means of shores. Considering the particular characteristics of shoring successive floors, it is very important to be able to estimate how loads are transmitted between shores and slabs in order to maintain adequate structural safety and avoid situations of risk or even collapse in buildings under construction. The transmission of loads from shores to slabs during all the construction stages is a complex phenomenon and has been the subject of numerous studies, especially in recent years. The research carried out to date has included experiments on fullscale buildings and the development of advanced numerical models, the estimation of the loads acting on slabs during construction, the definition of simplified calculation methods to estimate loads on slabs and shores during building construction and estimating the appropriate construction times taking into account the evolution of the mechanical properties of early-age concrete. This paper was conceived in order to give an answer to: (1) advances in the field of constructing RC building structures, (2) the growing interest of the scientific community, and (3) the need for the structural and construction engineering sector to have the tools available to increase the safety and design of building construction processes. The paper is unique in the field of RC building structures in that it is the widest, most complete and most ambitious review carried out to date and includes the most important advances in the study of slab-shore load transmissions. This work will be of interest to researchers who wish to go deeper into the field of building construction, and to more experienced professionals who require all the up-to-date information in a single document. However, engineers, architects and builders could also find the paper an excellent guide that will help them to improve their daily work in the field of designing and constructing buildings.The authors would like to express their gratitude to the Spanish Ministry of Education, Culture and Sport for funding received under the FPU Program [FPU13/02466] and also to the Generalitat Valenciana [GV/2015/063].Buitrago, M.; Adam, JM.; Moragues, JJ.; Calderón García, PA. (2018). Load transmission between slabs and shores during the construction of RC building structures A review. Engineering Structures. 173:951-959. https://doi.org/10.1016/j.engstruct.2018.07.04695195917

Cement-based mortar patch repair of RC columns. Comparison with all-four-sides and one-side repair

[EN] This paper describes an experimental study on patch-repaired reinforced concrete columns subjected to axial loads until failure. The behaviour of four series of columns repaired with Class R3 and R4 cement-based mortar was analysed both with and without a bonding agent. The results obtained were compared with control series of undamaged and damaged but unrepaired columns to determine the effectiveness of the repairs and the subsequent improvement in the behaviour of the columns. The results of this study were compared with those of previous work by the authors on the analysis of all-four-side repairs and one-side repairs. The conclusion reached was that patch repairs are highly effective as compared to the other techniques studied and that using Class R3 mortar achieves better results on damaged columns made with low-quality concrete. It was also concluded that applying a bonding agent does not improve the results, although this element was found to be necessary to prevent the premature detachment of the repair when there is a substantial difference between the stiffness of the column concrete and that of the mortar used in the repairs. (C) 2018 Elsevier Ltd. All rights reserved.The authors wish to express their gratitude to the HADES CONSTRUCCIONES Y CREACIONES 2003 company for their human and material contributions to this work.Ortega, I.; Pellicer, TM.; Calderón García, PA.; Adam, JM. (2018). Cement-based mortar patch repair of RC columns. Comparison with all-four-sides and one-side repair. Construction and Building Materials. 186:338-350. https://doi.org/10.1016/j.conbuildmat.2018.07.148S33835018

Effects of core position uncertainty on optical shape sensor accuracy

[EN] Optical fiber sensors are now widely recognized as extremely reliable instruments to sense strain. Optical shape sensors consist of multiple single-core optical fibers or multicore optical fibers capable of sensing bending direction and curvature by comparing the longitudinal strain of different cores in an instrumented section and reconstructing the sensor shape. This paper describes a study on the effects of core position errors on the precision of optical shape sensors when measuring strain, bending direction and curvature, and identifies the role of measured curvature and core spacing (distance between section center and external cores), considering 7, 4, and 3-core fiber geometries, three of those most widely employed for sensing applications. The Monte Carlo technique was utilized to reproduce the measurement process. Forty-five simulations, including 3.10(6) trials, were carried out for each geometry with the aim of investigating the law of uncertainty propagation. The results of the analysis, applicable to both multiple single-core fibers and multicore optical sensors equipped with distributed or quasi-distributed strain-sensors, show the effects of core position uncertainty and will be useful for new sensor designs and user options by predicting the achievable performance of these devices.This work was carried out within the ITN-FINESSE framework, funded by the European Union's Horizon 2020 Research and Innovation Program under the Marie Sklodowska-Curie Action Grant Agreement No 722509. It was also supported by the Ministry of Economy and Competitiveness of Spain under the project DIMENSION TEC2017-88029-R.Floris, I.; Calderón García, PA.; Sales Maicas, S.; Adam, JM. (2019). Effects of core position uncertainty on optical shape sensor accuracy. Measurement. 139:21-33. https://doi.org/10.1016/j.measurement.2019.03.031S213313

Load limiters on shores: Design and experimental research

[EN] When constructing reinforced concrete building structures, shores are normally used to transmit the loads from freshly poured slabs to lower floors. However, certain problems are involved in this process, including: (a) the loads on the shores may be higher than expected, which can lead to the collapse of the shoring system or even of the whole structure, and (b) the limited range of shore types in commercial catalogues, which often means that the shores used are oversized. This paper describes the study carried out on the development of a new loadlimiter (LL) that can be fitted to shores to improve safety and reduce the cost of constructing building structures. The study shows that combining mechanical and civil engineering fields made it possible to produce a novel device that could revolutionise the shoring techniques at present in use. The method of designing and implementing the LLs involved: (a) the design of prototypes by using numerical simulations, (b) the use of the design of experiments technique, (c) an ambitious experimental campaign in which LL were tested, (d) the detailed simulation of the final design, and (e) the formulation of a simplified model that considers the behaviour of the shore-LL as a unit.The authors would like to express their gratitude to the Spanish Ministry of Education, Culture and Sport for funding received under the FPU Program [FPU13/02466], also to the Generalitat Valenciana [GV/2015/063] and to Professor Salvador Ivorra from University of Alicante for helping us to carry out the steel characterization tests.Buitrago, M.; Adam, JM.; Calderón García, PA.; Moragues, JJ. (2018). Load limiters on shores: Design and experimental research. Engineering Structures. 173:1029-1038. doi:10.1016/j.engstruct.2018.07.063S1029103817

Axially loaded RC columns repaired on one side with cement-based mortars

[EN] This paper describes and analyses the results of an experimental programme carried out at the Universitat Politecnica de Valencia on 18 reinforced concrete (RC) columns, 12 of which had been repaired on one side with cement-based mortar before being subjected to axial loading until failure. The objective of the research was to determine the performance of the columns that had been repaired using different mortars, evaluate the influence of Class R3 and R4 mortar used and of the application of a binder or bonding agent. The results obtained were compared with those of the undamaged control columns and those of the unrepaired damaged columns to obtain values for the efficiency of the repairs and for the improvement in the load-bearing capacity of the columns. The results obtained indicate that the columns repaired with Class R3 mortar, with a lower elasticity modulus, function in better way than the Class R4 repaired ones. The presence or absence of a binder was not found to be a determining factor in improving the behaviour of the repaired elements. The chief novelty of the study lies in the fact that it is the first experimental study on RC columns totally repaired on one side only, using different types of mortar with and without the application of a binder. (C) 2018 Elsevier Ltd. All rights reserved.The authors express their gratitude to HADES CONSTRUCCIONES Y CREACIONES 2003 for their material, human and financial support.Ortega, I.; Pellicer, TM.; Calderón García, PA.; Adam, JM. (2018). Axially loaded RC columns repaired on one side with cement-based mortars. Construction and Building Materials. 177:1-9. https://doi.org/10.1016/j.conbuildmat.2018.05.102S1917

Measurement uncertainty of multicore optical fiber sensors used to sense curvature and bending direction

[EN] This paper describes a study of the influence of strain measurement uncertainty on sensing curvature and bending direction, considering one of the most widely used fiber geometries for sensing applications (7-core Multicore Fiber) with different core spacings (distance between outer cores and fiber axis). The Monte Carlo method was proposed to simulate the real measurement process and 33 simulations with 106 iterations were performed to determine the laws of propagation of strain measurement uncertainty in calculating curvature and bending direction. The outcomes, which show the strong influence of strain uncertainty and core spacing on the precision of Multicore Fiber sensors, can be used to support the design of new sensors or new fiber geometry and to predict their achievable performance.This work was carried out within the ITN-FINESSE framework, funded by the European Union's Horizon 2020 Research and Innovation Program under the Marie Sklodowska-Curie Action Grant Agreement No 722509. It was also supported by the Ministry of Economy and Competitiveness of Spain under the project DIMENSION TEC-2017-88029-R.Floris, I.; Sales Maicas, S.; Calderón García, PA.; Adam, JM. (2019). Measurement uncertainty of multicore optical fiber sensors used to sense curvature and bending direction. Measurement. 132:35-46. https://doi.org/10.1016/j.measurement.2018.09.033S354613

An experimental study on RC columns repaired on all four sides with cementitious mortars

[EN] This paper describes a study carried out in the ICITECH laboratories (Universitat Politècnica de València) on RC columns repaired on all four sides with cementitious-based mortars. A total of 18 specimens were tested, representing a group of square 200 x 200 mm2 columns subjected to compressive axial loads. Different repair scenarios were considered in order to study the influence of the type of mortar used and the presence or absence of bonding agents between the mortar and the column concrete. The results obtained showed that bonding agents have no appreciable effect on the behaviour of the repaired columns. Of the two types of mortar used in the study (Classes R3 and R4), the columns repaired with the lower grade mortar (R3) were seen to behave better. The main novelty of this work lies in the fact that this is the first time that two types of mortar are compared in the repair of four column sides, in addition to the possible use of bonding agents between the mortar and the column.The authors are grateful to the HADES CONSTRUCCIONES Y CREACIONES 2003 company for their material and financial assistance, without which the study would not have been possible. They also wish to express their gratitude to Professor Jose L. Bonet, Dr. Javier Pereiro-Barcelo and Mr. Lino Martinez for their assistance in planning and performing the tests.Ortega, I.; Pellicer, TM.; Adam, JM.; Calderón García, PA. (2018). An experimental study on RC columns repaired on all four sides with cementitious mortars. Construction and Building Materials. 161:53-62. https://doi.org/10.1016/j.conbuildmat.2017.11.126S536216

New fiber optic sensor for monitoring temperatures in concrete structures during fires

Monitoring temperatures in structures during fires provides valuable information to 1) the firemen engaged in extinguishing it, 2) those who assess its security, and 3) the organizations who have to decide on its possible repair, renovation or demolition. Developing sensors able to measure extremely high temperatures in actual blaze conditions is therefore a fundamental requirement. This paper proposes a new fiber optic sensor based on Regenerated Fiber Bragg Gratings specially designed to be embedded in concrete structures to monitor temperatures during fire events. A practical test was carried out on a 5.8m long beam subjected to the ISO-834 fire curve for 77 minutes under the typical loads borne by beams in conventional structures. Nine optical sensors were installed at the mid-span section of the beam and were submitted directly to flames and high temperature gradients (of the order of 200ºC/min) that make them measure maximum temperatures of 953º C. The temperatures recorded by the new sensors were compared with those obtained from electrical sensors (thermocouples) and a numerical model, with which they showed a good fit, except in those places in which concrete spalling caused distortions in the results and/or failure of the sensors. The paper thus demonstrates the viability of optical technologies in monitoring reinforced concrete during fires and analyzes sensor behavior to point out areas in which additional research is required.This work was made possible by the support from the Universitat Politecnica de Valencia, the Spanish Ministry for Science and Innovation (Research Project BIA2011-27104 and TEC2011-29120-C05-05) and the Spanish Ministry of Public Works (Project Sopromac P41/08).Torres Górriz, B.; Paya-Zaforteza, I.; Calderón García, PA.; Sales Maicas, S. (2017). New fiber optic sensor for monitoring temperatures in concrete structures during fires. Sensors and Actuators A: Physical. 254:116-125. https://doi.org/10.1016/j.sna.2016.12.013S11612525

Experimental and numerical analysis of a hybrid FBG long gauge sensor for structural health monitoring

This paper presents a new long gauge sensor for structural health monitoring based on the use of Fiber Bragg gratings. The proposed sensor has the advantage over existing sensors that it does not require prestressing of the optical fiber. The development consisted of numerical studies complemented by experimental tests to analyze: (1) the strain transfer between the sensor and the host structure; (2) the in!uence of sensor axial stiffness on the structural behavior of the host structure; (3) the in!uence of the mechanical properties of the adhesive used to fix the sensor and (4) the failure modes of the sensor (buckling and shear stress of sensor anchors).This work was made possible by the support from the Universitat Politecnica de Valencia, the Spanish Ministry for Science and Innovation (Research Project BIA2011-27104) and the Spanish Ministry of Public Works (Project Sopromac P41/08).Torres Górriz, B.; Calderón García, PA.; Paya-Zaforteza, I.; Sales Maicas, S. (2014). Experimental and numerical analysis of a hybrid FBG long gauge sensor for structural health monitoring. Measurement Science and Technology. 25:1-15. https://doi.org/10.1088/0957-0233/25/12/125107S11525Glišić, B., & Inaudi, D. (2007). Fibre Optic Methods for Structural Health Monitoring. doi:10.1002/9780470517819Kissinger, T., Charrett, T. O. H., & Tatam, R. P. (2013). Fibre segment interferometry using code-division multiplexed optical signal processing for strain sensing applications. Measurement Science and Technology, 24(9), 094011. doi:10.1088/0957-0233/24/9/094011Abang, A., & Webb, D. J. (2013). Effects of annealing, pre-tension and mounting on the hysteresis of polymer strain sensors. Measurement Science and Technology, 25(1), 015102. doi:10.1088/0957-0233/25/1/015102Calderón, P. A., & Glisic, B. (2012). Influence of mechanical and geometrical properties of embedded long-gauge strain sensors on the accuracy of strain measurement. Measurement Science and Technology, 23(6), 065604. doi:10.1088/0957-0233/23/6/065604Torres, B., Payá-Zaforteza, I., Calderón, P. A., & Adam, J. M. (2011). Analysis of the strain transfer in a new FBG sensor for Structural Health Monitoring. Engineering Structures, 33(2), 539-548. doi:10.1016/j.engstruct.2010.11.012Majumder, M., Gangopadhyay, T. K., Chakraborty, A. K., Dasgupta, K., & Bhattacharya, D. K. (2008). Fibre Bragg gratings in structural health monitoring—Present status and applications. Sensors and Actuators A: Physical, 147(1), 150-164. doi:10.1016/j.sna.2008.04.008Li, D. (2006). Strain transferring analysis of fiber Bragg grating sensors. Optical Engineering, 45(2), 024402. doi:10.1117/1.2173659Moyo, P., Brownjohn, J. M. W., Suresh, R., & Tjin, S. C. (2005). Development of fiber Bragg grating sensors for monitoring civil infrastructure. Engineering Structures, 27(12), 1828-1834. doi:10.1016/j.engstruct.2005.04.023Leng, J. S., Winter, D., Barnes, R. A., Mays, G. C., & Fernando, G. F. (2006). Structural health monitoring of concrete cylinders using protected fibre optic sensors. Smart Materials and Structures, 15(2), 302-308. doi:10.1088/0964-1726/15/2/009Kesavan, K., Ravisankar, K., Parivallal, S., Sreeshylam, P., & Sridhar, S. (2010). Experimental studies on fiber optic sensors embedded in concrete. Measurement, 43(2), 157-163. doi:10.1016/j.measurement.2009.08.010Hill, K. O., & Meltz, G. (1997). Fiber Bragg grating technology fundamentals and overview. Journal of Lightwave Technology, 15(8), 1263-1276. doi:10.1109/50.618320Chung, W., & Kang, D. (2008). Full-scale test of a concrete box girder using FBG sensing system. Engineering Structures, 30(3), 643-652. doi:10.1016/j.engstruct.2007.05.003Adam, J. M., Brencich, A., Hughes, T. G., & Jefferson, T. (2010). Micromodelling of eccentrically loaded brickwork: Study of masonry wallettes. Engineering Structures, 32(5), 1244-1251. doi:10.1016/j.engstruct.2009.12.05