Climent Molins

Experimental and analytical study of the structural response of segmental tunnel linings based on an in situ loading test.: Part 1: Test configuration and execution

During the last years the use of segmental linings in tunnels bored with tunnel boring machines (TBMs) have increased considerably. Despite this, uncertainties remain on the structural behavior of segmental tunnel linings. To overcome them, a new methodology for an in situ real scale test on this kind of tunnels was developed and applied on an experimental section placed at the new Line 9 (L9) of the metro of Barcelona. The main particularity of this test falls on its performance in the definitive placement of the rings and, therefore, in the real work conditions of the tunnel. The main advantage to previous real scale test experiences was the consideration of the real ground–structure interaction. The experimental section was composed by 15 rings built using steel fibers as a unique reinforcement. Significant loads were applied to the tunnel crown (max 3000 kN) by means of three hydraulic flat jacks embedded at the extrados of the loaded ring. A complete set of internal and external instrumentation was placed on the experimental section to obtain the necessary measurements to characterize the lining behavior. Such measurements were intensively treated and its main results are presented and analyzed in detail in this paper. This in situ test provides significant evidences of the structural response of SFRC segmental tunnel linings in hard ground conditions.

Experimental and analytical study of the structural response of segmental tunnel linings based on an in situ loading test.

During the last years the use of segmental linings in tunnels bored with tunnel boring machines (TBMs) have increased considerably. Despite this, uncertainties remain on the structural behavior of segmental tunnel linings. To overcome them, a new methodology for an in situ real scale test on this kind of tunnels was developed and applied on an experimental section placed at the new Line 9 (L9) of the metro of Barcelona. The main particularity of this test falls on its performance in the definitive placement of the rings and, therefore, in the real work conditions of the tunnel. The main advantage to previous real scale test experiences was the consideration of the real ground–structure interaction. The experimental section was composed by 15 rings built using steel fibers as a unique reinforcement. Significant loads were applied to the tunnel crown (max 3000 kN) by means of three hydraulic flat jacks embedded at the extrados of the loaded ring. A complete set of internal and external instrumentation was placed on the experimental section to obtain the necessary measurements to characterize the lining behavior. Such measurements were intensively treated and its main results are presented and analyzed in detail in this paper. This in situ test provides significant evidences of the structural response of SFRC segmental tunnel linings in hard ground conditions.

FLEXIBILITY-BASED LINEAR DYNAMIC ANALYSIS OF COMPLEX STRUCTURES WITH CURVED-3D MEMBERS

A flexibility-based formulation of a new mass matrix for the dynamic analysis of spatial frames consisting of curved elements with variable cross-sections is presented. The main characteristic of such formulations is the exact equilibrium of forces at any interior point, with no additional hypotheses about the distribution of displacements, strains or stresses. Accordingly, the derived element mass matrix takes into account the exact stiffness and mass distribution throughout each element. In validation tests, results obtained with this method are compared with those obtained by other numerical or analytical formulations, showing the accuracy of the proposed method. The comparison of experimental results for a multispan arch bridge subjected to a dynamic load with those achieved by means of the proposed method are finally included to illustrate its efficiency in the treatment of complex structures.

Improved Tensile Performance with Fiber Reinforced Self-compacting Concrete

The use of self-compacting concrete (SCC) eliminates the need for compaction, which has benefits related to economic production, the durability, the structural performance and working circumstances. SCC is able to transport fibers which can replace in some structures conventional reinforcement. By taking into account tailor-made concrete characteristics, new fields of structural application can be explored. This paper discusses the potential for an improved performance of fibers in self-compacting concrete. In flexural tests significant differences were observed between conventional and self-compacting concrete at a given fiber type and dosage concerning the variation of results and the flexural performance. Mechanical testing and image studies on concrete cross-sections indicate how the flow influences the performance, the orientation and the distribution of the orientation of fibers. Differences between traditionally compacted and flowable concrete are pointed out.

Efficient preliminary floating offshore wind turbine design and testing methodologies and application to a concrete spar design

The current key challenge in the floating offshore wind turbine industry and research is on designing economic floating systems that can compete with fixed-bottom offshore turbines in terms of levelized cost of energy. The preliminary platform design, as well as early experimental design assessments, are critical elements in the overall design process. In this contribution, a brief review of current floating offshore wind turbine platform pre-design and scaled testing methodologies is provided, with a focus on their ability to accommodate the coupled dynamic behaviour of floating offshore wind systems. The exemplary design and testing methodology for a monolithic concrete spar platform as performed within the European KIC AFOSP project is presented. Results from the experimental tests compared to numerical simulations are presented and analysed and show very good agreement for relevant basic dynamic platform properties. Extreme and fatigue loads and cost analysis of the AFOSP system confirm the viability of the presented design process. In summary, the exemplary application of the reduced design and testing methodology for AFOSP confirms that it represents a viable procedure during pre-design of floating offshore wind turbine platforms.

Case study of damage on masonry buildings produced by tunneling induced settlements

This study analyzes the structural response of a group of masonry buildings subjected to real ground movements experienced during the construction of the L9 Metro tunnel in Barcelona, bored by a earth pressure balance machine (EPB) tunnel boring machine (TBM). The studied one-story small dwellings represent a common building typology frequently used in those days in Barcelonas outskirts (more than 1000 were erected). Real settlement profiles are compared with the ones provided by empirical methods, which estimate the shape and the area of the trough according to the ground properties and the volume loss. The first aim of the study is to evaluate the effectiveness of two techniques used to predict damages in buildings resulting from tunneling subsidence: 1) the equivalent beam and its subsequent refinements, and 2) the use of a non-linear finite element (FE) macro-model. The real structural damage presented in the buildings is compared with the predictions given by these two methods. Main model parameters have been determined by means of characterization experiments developed on the site and in the laboratory, thus giving a much higher significance to the analysis. The obtained predictions present a high correspondence with the actual damage registered, particularly in crack patterns and widths.

Double-Punch Test of Fiber-Reinforced Concrete: Effect of Specimen Origin and Size

One of the main advantages of the Barcelona test is that the properties of fiber-reinforced concrete (FRC) can be determined by using cylindrical specimens, thereby permitting the use of cores to control the quality of concrete used in construction.; Using the results of an extensive experimental campaign, this paper establishes the relationship between the unitary load of cracking, residual strength and toughness of molded specimens, and cores of concretes reinforced with different types of fibers but with the same aspect ratio. The fiber diameter is observed to signifidantly influence the properties of molded specimens, whereas in the cores, the number of fibers that lose anchoring due to drilling determines the response of the FRC.

Experimental RAO’s Analysis of a Monolithic Concrete SPAR Structure for Offshore Floating Wind Turbines

Nowadays the offshore wind energy market is clearly oriented to be extended around the world. Bottom fixed solutions for supporting offshore wind turbines are useful in shallow waters which are available in a limited extent unless a continental shelf exists. Considering the Oil & Gas background knowledge, move from bottom fixed solutions to floating solutions is not a technical challenge, but the cost of each structure in terms of industry profit is currently the main issue for its commercial implementation. That point has induced huge research efforts on the topic.Recently, a new concept consisting of a monolithic concrete SPAR platform was experimentally and numerically studied in the framework of the AFOSP KIC-InnoEnergy project (Alternative Floating Platform Designs for Offshore Wind Towers using Low Cost Materials) [1] [2]. The studies comprised a set of hydrodynamic tests performed in the CIEM wave flume facility at UPC, with a 1:100 scaled model assuming Froude similitude.The whole test campaign includes free decay tests, RAO’s determination, regular and irregular waves with and without wind mean force. For the determination of the platform RAO’s, a set of 21 regular waves trains with periods ranging from 0.8s up to 4.8s were applied. The 6 DOF motions of the platform were measured with an infrared stereoscopic vision system.In this paper, a summary of pitch and heave RAO’s tests will be presented with the main objective to calibrate and validate the accuracy of the Morison-based numerical model for floating wind turbine platforms developed at the Universitat Politecnica de Catalunya.Because the wave flume spatial constraints, both Airy and Stokes wave theories are necessary to reproduce the correct wave kinematics. The numerical model includes both theories and a comparison between them has been done, checking the validity range of each one.The simulations revealed a reasonable good agreement with the experimental results, as well with the computed RAO’s in commercial software.Copyright

Material Characterization and Micro-Modeling of a Historic Brick Masonry Pillar

ABSTRACT A masonry pillar composed of solid clay bricks, cement mortar and infill is extracted from a historical structure and tested in concentric compression. It is subjected to cyclic and monotonic loads up to compressive failure. In parallel, samples are extracted from the pillar and are subjected to destructive tests. Non-destructive tests are performed on the pillar, as well. The properties of the constituent materials are critically examined and their role in the maximum load reached and the failure mode obtained are discussed. Finally, a finite element micro-model of the pillar is used for the simulation of the pillar test. The influence of the existing damage on the pillar is investigated using the model, resulting in a fair approximation of the global Young’s modulus, maximum load and the failure mode. Highlights ● A brick masonry pillar extracted from a historical building is tested in compression. ● Material samples extracted from the pillar are characterized by mechanical tests. ● A finite element micro-model of the pillar is used for the simulation of the compressive test. ● The effect of damage on the compressive strength of the pillar is numerically investigated.

Analysis of two medieval stone masonry bridges

The studies performed upon two medieval bridges are presented with the conclusions obtained in regard to their actual stability and needs of repair. Special attention is given to the description of the methodology of analysis, which consisted of detailed structural analyses by numerical simulation combined with experimental measurements. The studies included the performance of a dynamic loading test in one of the bridges, also simulated numerically in order to allow a direct comparison between experimental and analytical results.