The assessment of historical structures requires appropriate knowledge of the behaviour of the investigated materials. Concerning masonry, its mechanical characterisation is a challenging task, since its composite nature requires the careful evaluation of the behaviour of its material components. In particular, the experimental assessment of the strength of existing mortar in historical structures still encounters several difficulties. This study investigates a novel Minor Destructive Testing (MDT) technique virtually equivalent to the vane test used for soils. The instrumentation, called herein Torque Penetrometric Test (TPT), is composed of a steel nail with four protruding teeth and a torque wrench. The test consists in inserting the toothed nail into a mortar joint and then applying a torque by means of a dynamometric key, until reaching the failure of the material. This work presents a novel interpretation theory based on basic concepts of fracture mechanics and applied to the micro-mechanical analysis of the stress state induced by the instrument on the investigated mortar. The proposed interpretative theory is validated through the execution of experimental tests in the laboratory and in a historical masonry building. The test proves to be effective for a quick in-situ MDT evaluation of the strength of existing mortars.
In this paper, the flexural response of extruded wrought aluminium girders is presented. This structural element is intended for usage in marine structures such as light docks, marinas and yacht ports. Ease of use, durability, reduced weight, manoeuvrability and the potential development of bespoke sections are appealing properties in such structures that are fulfilled satisfactorily by this type of aluminium elements. Both experimental and numerical analyses are presented. Experimentally, modules of the girders are tested with loading about both minor and major axes. Numerically, the tests are satisfactorily reproduced for the sake of validation and a subsequent exploitation of the model is addressed for further study of the structural response of the girders. A discussion of the results is presented with some design recommendations of these particular structural elements.
This paper presents a comprehensive study on the application of global plastic design methods, not currently allowed in European specification provisions, to stainless steel rectangular and square hollow section continuous beams. The analysis of experimental and numerical continuous beam strengths highlighted that ultimate capacity predictions calculated based on global elastic analysis result in a considerable conservatism due to strain hardening and bending moment redistribution effects. Alternatively, the assessment and reliability analyses of the traditional plastic design methods demonstrated that the Class 1 cross-section limit provided in the European specification can be safely applied for the partial safety factor ¿M0 currently provided. However, the analysis evidenced that including bending moment redistribution in capacity predictions is not enough since strain hardening effects play an important role when stocky cross-sections are analysed. Thus, the Continuous Strength Method for indeterminate structures was also assessed and it was found to provide accurate capacity predictions for all analysed stainless steel grades. Finally, an alternative Direct Strength Method design approach is proposed for stainless steel continuous beams based on the Direct Strength Method bending capacity. The proposed method, statistically validated, accounts for strain hardening effects and moment redistribution and provides the best resistance predictions among the different design methods considered
This article presents a mechanical formulation to estimate the strength of transversally stiffened steel plate girders subjected to patch loading, in this particular case, with closely space stiffeners. Steel plate girders with closely spaced stiffeners are occasionally found in bridge design and for such cases, the current EN1993-1-5 rules underestimate the strength of the webs to transverse forces. A FE-based parametric investigation is conducted to estimate the web strength to patch loading. The results are compared to the results obtained from classical beam theory in combination with the proposed formulation. A notional plate girder is analyzed to demonstrate the potential of the formulation for daily routine designs. Results indicate that the proposed formulation does a better job in predicting the web strength of transversely stiffened girders subjected to patch loading than the EN1993-1-5 specification, and thus yield a lighter and more economical design for these specific girder geometries.
The behaviour of austenitic, ferritic and duplex stainless steel Rectangular and Square Hollow Section members subjected to compression and combined loading is investigated in this paper. A full slenderness range Direct Strength Method (DSM) approach is proposed based on experimental results and numerical strengths obtained from FE parametric studies. The method accounts for local buckling effects and enhanced material properties are also incorporated for those members stable enough to allow partial yielding of the cross-sections. The proposed method is based on strength curves previously provided for cross-sections although additional limitations have been adopted. The DSM approach for columns is based on existing buckling curves and provides accurate resistance predictions for slender and stocky cross-sections. The proposed DSM approach for beam-columns also improves capacity predictions for stocky and slender cross-sections obtained from the traditional methods for different bending moment distributions. This is attributed to the fact that the beam-column behaviour is directly calculated with a unique strength curve, considering the member and section slendernesses based on the elastic instabilities of the section subjected to the actual stress distribution instead of calculating the compressive and flexural strengths independently and combining these through an interaction equation, as is the traditional uncoupled approach. Finally, a reliability study of the full slenderness range DSM approach is presented to determine resistance factors for the different stainless steel grades columns and beam-columns
In structural frames, second order effects refer to the internal forces and moments that arise as a result of deformations under load (i.e. geometrical nonlinearity). EN 1993-1-1 states that global second order effects may be neglected if the critical load factor of the frame ¿cr is greater than 10 for an elastic analysis, or greater than 15 when a plastic global analysis is used. No specific guidance is provided in EN 1993-1-4 for the design of stainless steel frames, for which the nonlinear stress-strain behaviour of the material will result in greater deformations as the material loses its stiffness. A study of the effects of material nonlinearity on the stability of stainless steel frames is presented herein. A series of different frame geometries and loading conditions are considered. Based on the findings, proposals for the treatment of the influence of material nonlinearity on the global analysis and design of stainless steel frames are presented.
The Continuous Strength Method provides excellent resistance predictions of stocky cross-sections under different loading conditions as it accounts for enhanced material properties, although the method is currently limited to crosssectional resistance. The axial stress in short columns potentially exceeds the yield strength as members are stable enough to allow partial yielding of non-slender cross-sections and the flexural buckling resistance prediction of these short columns is therefore usually underestimated, since equations currently codified in standards do not account for strain hardening effects. This paper presents the extension of the Continuous Strength Method to stainless steel Rectangular and Square Hollow Section columns, allowing strain hardening effects to be incorporated in the resistance prediction of members subjected to compression. The proposed approach is equivalent to the traditional approach for columns codified in different standards based on the Ayrton-Perry formulation but considers a different generalized
imperfection parameter that depends on the cross-sectional slenderness and considered material, so strain hardening effects are directly introduced in the formulation. Results show that the proposed Continuous Strength Method approach provides improved predictions of the resistance of Rectangular and Square Hollow Section columns for all stainless steel grades. The reliability of the proposed approach has been demonstrated through the corresponding statistical analyses. Given the purely analytic nature of the proposed approach, it can be used for several materials, such as stainless steel, carbon steel and aluminium, and cross-section types for which the Continuous Strength Method has been defined. Finally, the better estimation of the flexural buckling behaviour of columns will have a direct impact on the accuracy of beam-column checks.
Link elements are dissipative devices in form of beam segments that are typically included in eccentrically braced frames (EBF) subjected to lateral loads and seismic hazard. Studies related to short links, energy dissipation and plastic hinge formation have been presented for carbon steel elements with several conclusions at material, member and structural levels. Stainless steel is a nonlinear metallic material with particular appeal for its structural use due to a considerable amount of capabilities such as corrosion resistance, circular life-cycle, sustainability, strength, ductility and aesthetics. Despite the increase of the use of stainless steel for structural elements in construction, the behaviour of this material for structural purposes is not defined accurately as the carbon steel in all applications. The most important difference between these types of steel is the shape of the stress-strain curve. Whereas carbon steel typically exhibits linear elastic behaviour up to the yield stress and a plateau before strain hardening is encountered, stainless steel has a more rounded response with no well-defined yield stress, leading to a non-linear material behaviour. The elastic stiffness, maximum load, shear deformation capacity as well as the energy dissipation in short links are generally affected by the defined geometrical parameters such as link length, web stiffening and connectivity. Due to the material nonlinearity of stainless steel, this influence may be considerably affected by the stress-strain curve and its corresponding energy dissipation since a nonlinear kinematic hardening branch must be adequately provided in numerical simulations for the sake of accurately reproducing the cyclic behaviour. In this paper, a numerical model aimed at studying the cyclic behaviour of short stainless steel links subjected to seismic lateral loads is presented. The model accounts for the material and the geometrical nonlinearities. Several geometrical as well as material configurations (length, web stiffening and constitutive equations) are studied. The results and conclusions obtained in this research are used for a subsequent definition of a research program related to stainless steel frames subjected to seismic loading including several structural configurations in both concentrically (CBF) and eccentrically (EBF) braced frames assembled with plastic or slender members.
Loaiza, N.; Graciano, C.; Chacon, R.; Casanova, E. European Conference on Steel and Composite Structures p. 4199-4204 DOI: 10.1002/cepa.477 Data de presentació: 2017-09-13 Presentació treball a congrés
Incremental launching is one of the common steel bridge assembly methods used nowadays, its practical application consists in passing the bridge assembly through the launching shoes as well as over each support pile. In some cases, when plate girders are used, it is usual to find longitudinal stiffeners reinforcement in order to prevent web local buckling produced by the vertical reaction acting in the support pile. A considerable number of studies have focused on evaluating the impact of a single stiffener on the resistance of plate girder subjected to patch loading. However, the effect of multiple longitudinal stiffened plate girders subjected to lengthy compressive load has received little attention. Therefore, this paper aims at studying the influence of load bearing length on the ultimate strength of multiple longitudinally stiffened webs subjected to compressive loads. Patch loading resistance is numerically calculated using a previously validated nonlinear finite element analysis. Subsequently, a parametrical study is conducted to investigate the effect of the aforementioned load length and the relative position and size of the stiffeners on the ultimate strength
The use of stainless steel structures has increased during the last decade due to their durability, aesthetics and mechanical properties such as ductility, considerable strain hardening and excellent fire resistance. However, the majority of conducted research works have only focused on single isolated stainless steel members and advances in the analysis of stainless steel frames are limited. EN1993-1-4 does not provide global plastic design rules for indeterminate stainless steel structures, such as frames, despite their proved high ductility. On the other hand, the lack of guidance on plastic design is an obstacle for the optimal design of stainless steel structures, leading to uneconomical design. This paper presents a preliminary study on non-sway stainless steel frames with stocky hollow cross-sections. The study of the behaviour of stainless steel frames is based on numerical parametric studies, considering the nonlinear material behaviour and different stainless steel types (austenitic and ferritic). The paper deals with the redistribution of internal forces and assesses the existing methods based on global plastic design for frames with stocky cross-sections, where alternative design approaches accounting for moment redistribution and strain hardening effects are analysed in addition to traditional plastic design method. Preliminary results demonstrate that including bending moment redistribution and strain hardening effects in capacity predictions is essential for an efficient design of stainless steel structures.
Lauwens, K.; Jonas, D.; Fortan, M.; Arrayago, I.; Mirambell, E.; Van Gysel, A.; Rossi, B. European Conference on Steel and Composite Structures p. 1909-1918 DOI: 10.1002/cepa.235 Data de presentació: 2017-09-13 Presentació treball a congrés
Steel-concrete composite floors are commonly used in construction due to their favourable weightto- depth ratio and erection time. Typically, concrete is poured onto a galvanised steel deck acting as formwork. However in case of floors exposed to corrosive environments, stainless steel is likely to be chosen over galvanised steel. Besides its better corrosion resistance, stainless steel also offers desirable aesthetic appearance and good mechanical properties. Composite slabs can fail in bending, vertical shear or longitudinal shear. The latter failure mode is the most common, and its prediction depends on values obtained through full-scale tests. However, for stainless steel decks, no specific treatment exists in current design standards. This paper investigates the longitudinal shear resistance of stainless steel composite slabs through an experimental study. One short and three long span slabs,
made using a Cofraplus 60 ferritic EN1.4003 stainless steel corrugated deck, are tested in accordance with Eurocode 4, annex B.3 . The Partial Shear Connection (PSC) method is used to assess the longitudinal shear resistance. The experimental results together with the results provided in  are used to draw conclusions on the applicability of ferritic stainless steel decks in composite floors.
Chacon, R.; Loaiza, N.; Graciano, C.; Casanova, E. European Conference on Steel and Composite Structures p. 4223-4229 DOI: 10.1002/cepa.480 Data de presentació: 2017-09-13 Presentació treball a congrés
In the construction of traditional composite bridges whose structure consists of plate girders, the concrete slabs of the decks are often casted before launching. These thin-walled webs are occasionally reinforced with longitudinal stiffeners to increase bending and shear strengths, and for bridges erected by incremental launching, these stiffeners also provide an enhancement for patch loading resistance. Experimental works have shown that ultimate resistance to patch loading is highly dependent on the size, relative position and shape of the longitudinal stiffener. Nonetheless, a comparison between those three factors should be carried out in order to establish the optimum configuration of longitudinal stiffening for webs under compressive forces. Hence, this study attempts to compare the increase of ultimate strength of a slender I-girder subjected to concentrated load using open and closed section types of stiffeners, evaluating three different stiffeners configurations: i) a single open section stiffener, ii) multiple open section stiffeners, and iii) a single closed section stiffener. The nonlinear computations were performed using a finite element analysis parametric model, where the relative position and size of the stiffeners are varied to cover a wide range of geometries.
Etxeberria, M.; Ming-Zhi, G.; Maury-Ramirez, A.; Poon, C. Journal of Environmental Engineering Vol. 143, num. 9, p. 1-10 DOI: 10.1061/(ASCE)EE.1943-7870.0001239 Data de publicació: 2017-09 Article en revista
The day-to-day negative effect of contaminating substances on the NOx removal effectiveness of photocatalytic surfaces and their recovery capacity after undergoing cleansing is of real academic and practical interest. This paper analyzes the NOx removal effectiveness of two different types of photocatalytic concrete surface layers incorporating nano-TiO2 particles. Both types of surfaces are examined before and after being subjected to dust accumulation and oil impregnation. The recovery of their NOx removal capacity after undergoing various cleansing processes is also evaluated. The results are compared to those of their respective reference samples. The results show that the high NOx removal capacity of the spray-coated samples is partially maintained even after a high concentration of dust accumulation. However,
the water-cleansing process employed is sufficient to recover the lost NOx removal capacity. It is also discovered that the nano-TiO2 particles lose nearly all their photocatalytic capacity after being subjected to oil impregnation, and that the cleansing processes, either by an alkaline detergent or using an n-hexane solvent, fails to recover the initial NOx removal capacity.
Petracca, M.; Pelà, L.; Rossi, R.; Zaghi, S.; Camata, G.; Spacone, E. Construction & building materials Vol. 149, p. 296-314 DOI: 10.1016/j.conbuildmat.2017.05.130 Data de publicació: 2017-09 Article en revista
A novel damage mechanics-based continuous micro-model for the analysis of masonry-walls is presented and compared with other two well-known discrete micro-models. The discrete micro-models discretize masonry micro-structure with nonlinear interfaces for mortar-joints, and continuum elements for units. The proposed continuous micro-model discretizes both units and mortar-joints with continuum elements, making use of a tension/compression damage model, here refined to properly reproduce the nonlinear response under shear and to control the dilatancy. The three investigated models are validated against experimental results. They all prove to be similarly effective, with the proposed model being less time-consuming, due to the efficient format of the damage model. Critical issues for these types of micro-models are analysed carefully, such as the accuracy in predicting the failure load and collapse mechanism, the computational efficiency and the level of approximation given by a 2D plane-stress assumption.
The amount and the quality of the old cement mortar attached to the aggregates influence the quality of the recycled concrete aggregate (RCA) produced. The characteristics of RCA adversely affect the physical, mechanical and durability properties of concretes. Due to these adverse effects, it is necessary to improve the RCA properties, not only changing their surface but also their internal microstructure. The main objective of this research work was to analyse the influence of chemically treated RCA on the properties of recycled aggregate concrete (RAC). The RCA was exposed to three chemical treatments, namely; silica fume (SF), waterglass (WG) and silica nanoparticles (Nano). Once the physical properties of both the untreated and treated RCA had been determined they were then employed in concrete production. RAC were produced employing 25% and 50% of RCAs in substitution of natural coarse aggregates. The obtained results by the RAC produced employing treated RCA were compared to those of the conventional concrete as well as to those of the RAC employing untreated aggregates. According to the results, the RAC produced employing RCA treated with WG and Nano achieved better compressive strength and durability properties than the RAC or CC concrete at 28 and 90 days.
The Equivalent-Frame Method (EFM), a simplified procedure for structural modelling of masonry constructions, is having a great success for the good balance that it allows between the accuracy of the geometrical description and the simplicity of the mechanical calibration.
Despite the widespread use of EFM in scientific and professional field, some uncertainties affect its application to the specific problem of the existing unreinforced masonry (URM) buildings. For these structures, in fact, irregular geometries, the presence of deformable diaphragms and the interaction with other structures in aggregate configurations represent hard-to-model features that limit the accuracy of EFM.
The paper presents a comparative study in the linear field between EFM and the more accurate Finite Element Method (FEM), assumed as reference. The comparative analysis involves a wide set of geometrical schemes, characterized by both regular and irregular configurations, and it is aimed at providing a measure of the EFM modelling accuracy as a function of the geometry of the wall. Non-dimensional parameters allow exploring the limits of applicability of EFM for both regular and irregular walls.
Based on the parametric analyses, some recommendations are given for improving the effectiveness of the method and preserving the simplicity of application that makes EFM models so popular and widely used.
This paper proposes an improved theoretical prediction equation for Concrete-filled steel tubes (CFT) subjected to compressive forces. This ultimate load capacity is inferred from a database of 344 experimental results reported in the literature by using Gene expression programming (GEP). Moreover, a series of structural comparisons between design provisions, other mechanically-derived expressions and the proposed prediction are addressed. The levels of accuracy, practical use and phenomenological understanding of the phenomenon are pinpointed. The results obtained are in good agreement with both the experimental and theoretical predictions. Advantages and disadvantages of such type of predictions are pinpointed.
A description of the deformations and damage that occurred in a segmental tunnel lining as a consequence of an unplanned surface load is presented, as well as the numerical analyses performed for its safety assessment. The tunnel in study is located in soft soil conditions and presents a low overburden. Few months after tunnel drilling, a new bridge was constructed at surface level, placing an access embankment over the tunnel path. Monitoring points were installed along the affected section which recorded the deformation of the tunnel caused by the embankment weight. More worryingly, despite no additional loads were introduced, the deformation of the lining continued increasing significantly along the next months, indicating the existence of soil consolidation phenomena. As a consequence, structural cracks emerged along the affected section. Non-linear finite element models that realistically simulate the behaviour of the non-linear segment joints and the concrete cracking were used to characterize the actual response and strength of the lining. The results showed that most significant damages should occur at the non-visible extrados side, and characterized how they evolve along the soil consolidation process. Finally, the adopted tunnel strengthening procedure is described.
First published by the International Association for Bridge and Structural Engineering (IABSE), Zurich, Switzerland, www.iabse.org; in Structural Engineering International 2017, Vol.27, issue 3, pg. 422-428.
The main objective of this experimental work is to analyse the effect of recycled aggregates (RA), on the basis of the study of the various qualities, of the physical, mechanical and durability properties of high performance concrete (HPC). Five types of recycled aggregates: three coarse RA sourced from parent concretes of 100, 60 and 40 MPa, as well as one coarse mixed recycled aggregate and one fine ceramic waste aggregate were used as replacement for natural aggregates (NA). Two types of coarse NA and two types of river sands were employed for concrete production. On the basis of the findings of our research it was determined that the reduction in quality and the increase in the amount of RA substitution produced a decline in the properties of HPC. According to our analysis of the mechanical properties, a 100 % replacement of coarse NA for recycled concrete aggregates can be employed, providing the RA has been sourced from a 60 MPa minimum-strength concrete. Nevertheless, durability behaviour was greatly influenced by the use of RA, and consequently replacement ratios of high quality RA should be reduced to 50 % to achieve similar behaviour patterns to those of NA concrete. Moreover, severe reductions of RA qualities (sourced from 40 MPa strength concretes or mixed waste) only permitted 20 % replacement ratios on HPC production. However, those concretes containing fine ceramic RA (up to 30 %) reached higher compressive strength, higher chloride-ion penetration resistance and higher improvements of durability properties at longer ages than those concretes produced using NA concrete.
The final publication is available at Springer via http://dx.doi.org/10.1007/s12649-016-9637-7
Chacon, R.; Oller, S. Journal of professional issues in engineering education and practice Vol. 143, num. 3, p. 1-9 DOI: 10.1061/(ASCE)EI.1943-5541.0000315 Data de publicació: 2017-07 Article en revista
In engineering, traditional approaches aimed at teaching concepts of dynamics to engineering students include the study of a dense yet sequential theoretical development of proofs and exercises. Structural dynamics are seldom taught experimentally in laboratories since these facilities should be provided with expensive equipment such as wave generators, data-acquisition systems, and heavily wired deployments with sensors. In this paper, the design of an experimental experience in the classroom based upon digital fabrication and modeling tools related to structural dynamics is presented. In particular, all experimental deployments are conceived with low-cost, open-source equipment. The hardware includes Arduino-based open-source electronics whereas the software is based upon object-oriented open-source codes for the development of physical simulations. The set of experiments and the physical simulations are reproducible and scalable in classroom-based environments.
The punching-shear strength of slabs reinforced with FRP bars without transverse reinforcement is a complex phenomenon. The main difference with the conventional reinforced concrete is that the passive reinforcement has a linear elastic behaviour up to failure. In this paper, a comparative analysis of the reliability of the existing formulations to evaluate the punching strength of FRP RC slabs without transverse reinforcement is performed through an assembled database of 88 existing tests. In addition, a preliminary proposal based on the multiaction shear capacity model has been made and its reliability has also been evaluated by means of the assembled database.
This paper presents a comparative analysis of the performance of some the existing formulations to evaluate the FRP contribution to the total shear strength of reinforced concrete beams strengthened in shear by externally bonded FRP sheets. This analysis has been performe through the use of a wide database of 275 experimental tests of rectangular RC beams distinguishing those cases with and without internal steel transverse reinforcement and the different FRP strengthening configurations.
A punching shear strength mechanical model for RC slabs with and w/o punching reinforcement, based on a previous shear model developed by the authors, is presented. The identified differences between shear and punching resisting mechanisms have been incorporated into the governing equations and failure mode. The model provides consistent explanations to the experimentally observed behavior, such as the position of the critical perimeter, the influence of the moment transferred to the slab or the efficiency of the shear reinforcement. Good agreement has been obtained between the model results and those of an available large database of punching tests.
En esta comunicación se presenta un método de diseño sísmico directo basado en prestaciones desarrollado para estructuras irregulares. Este método es una extensión del método de diseño no lineal estático; ambos, a través de un doble análisis lineal, son métodos rápidos y robustos. El método doble análisis lineal (DLA) para cargas sísmicas permite elegir la demanda de ductilidad, la intensidad de daños y comportamiento tanto global como local de una estructura mediante un parámetro de control (¿¿). En este artículo se muestra un ejemplo de aplicación del DLA, el cual se compara con resultados de análisis no-lineales como validación y muestra de la bondad del método.
Axial forces affect the shear strength of concrete members. The estimation of such effects on the shear strength depends on how the axial force influences the various shear transfer mechanisms, since a very different behavior has been experimentally evidenced in front of compressive and tensile forces, due to their influence on cracking. A mechanical model for the shear strength of reinforced concrete members previously developed by the authors was recently extended for prestressed concrete and, in this paper, the extension for tensile forces is presented. The comparison of the predictions with the results of experimental tests included in large databases shows very good agreement
Se presenta una campaña experimental de elementos de hormigón parcialmente pretensado y una formulación a cortante basada en modelos mecánicos. Se compararán los resultados experimentales con diferentes normativas y se analizarán los parámetros más relevantes para la resistencia a cortante. Concluyendo que las normativas son muy conservadoras y que el nuevo modelo predice muy bien la resistencia a cortante
La fisuración es inevitable en las obras de hormigón armado pero debe de ser controlado para asegurar un adecuado comportamiento en servicio y la durabilidad. El análisis de los patrones de fisuración es esencial para el diagnóstico, monitorización y mantenimiento; para identificar deficiencias o situaciones comprometidas. Una parte importante de esto el patrón de fisuración como un indicador de la distribución tensional del hormigón. Un método de búsqueda y medición de fisuras en imágenes en color de elementos de hormigón ha sido desarrollado e implementado como un programa de MATLAB. El algoritmo usa diversas herramientas de procesamiento digital de imágenes para medir la orientación de las fisuras y su orientación, y entre estas herramientas destaca un tipo especial de filtros llamados “orientation kernels” desarrollados especialmente para detectar el ángulo y ancho de las fisuras.
The use of fibre reinforced concrete (FRC) to produce segmental linings of TBM-constructed tunnels is an increasing tendency. So far, more than 50 tunnels have been constructed with this structural material, in some of these even using solely fibres as reinforcement. Moreover, several design guidelines (e.g., fib Model Code 2010) already include the FRC as structural material. There also exist specific guidelines for the design of FRC precast segment linings (e.g., ITAtech Report/7-15 and ACI 544.7R-16). These guidelines deal with the design of FRC considering the traditional limit state safety format. Therefore, partial safety factors for both the loads (¿L) and material strengths (¿M) must be considered. In particular, the magnitude of ¿M considered for compressive and tensile FRC strengths are assumed to be the same. Nonetheless, this assumption can be unrealistic, particularly in terms of flexural residual strength (fR) since this property present higher scatter than the compressive strength (fc). This is particularly true for elements with a reduced cracking surface (e.g., beams) due to the higher impact that uncertainties like fibre orientation and distribution have on the variability of fR. Therefore, this assumption can lead to lower reliability indexes (ß) than those established for traditional reinforced concrete structures. However, this variability tends to decrease with the increase of the width of the cracked sections (e.g., slabs). The results of a structural reliability analysis carried out to calibrate partial safety factors for fR is presented. Full-scale bending tests on precast segments with different dimensions, amounts and type of fibers were considered. This partial safety factors could be used in the design of future precast FRC tunnel linings.
de la Fuente, A.; Bairan, J.M.; Pialarissi Cavalaro, S.H.; Goodier, C.; Palmeri, A. fib Symposium p. 1530-1537 DOI: 10.1007/978-3-319-59471-2_176 Data de presentació: 2017-06-12 Presentació treball a congrés
Improvements in concrete technology, reinforcing systems and manufacturing processes enable the use of increasingly long reinforced precast concrete girders, contributing to the competitiveness of girders in concrete in comparison with other alternatives. The weight of the girders should be limited however, in order to achieve an optimum between span length and lifting and transportations costs. The current tendency in design is to minimize the width of the flanges, thus the girder becoming more flexible laterally and more prone to suffer instability phenomena during transient loading situations. An increasing number of accidents and damages associated with this instability problem are reported in the technical literature (e.g., Hurff 2010; Rose 2013). The main objective of this study is to describe a real case of lateral instability of a long prestressed concrete bridge girder during lifting as well asto perform a parametric study to understand the limits of the problem observed. Special attention is paid to the evaluation of the provisions gathered in the Model Code 2010 (MC - 2010) regarding the lateral stability, since these might not be sufficient to cover limit cases.
The shear resisting actions in reinforced concrete elements without transverse reinforcement is analyzed by means of optimized strut-and-tie models with concrete ties. Biaxial failure criteria are used for uncracked and cracked regions. The stress transfer capacity across cracks is accounted for by including the inclination between the stress field and the crack opening and sliding. An experimental case-study is analyzed. It is shown that that different shear resisting actions can occur in different regions of the beam. The strut-and-tie scheme in the critical region is consistent with the Multi-Action Shear Strength Model (MASM).
Analysis of shear resisting actions by means of optimization of strut and tie models taking into account crack patterns. Available from: https://www.researchgate.net/publication/317724351_Analysis_of_shear_resisting_actions_by_means_of_optimization_of_strut_and_tie_models_taking_into_account_crack_patterns [accessed Aug 28, 2017].
This paper presents the study of the structural performance of a set of timbrel vaults belonging to the so-called Administration Pavilion of the Hospital de Sant Pau, a large-scale hospital complex located in Barcelona. The paper includes three parts. First, the Administration pavilion of Hospital de Sant Pau is described by putting the emphasis on the geometry of the masonry vaults and the combined utilisation of steel and masonry structural members. Second, laboratory and in-situ experiments are discussed. Finally, the behaviour observed during the dynamic-identification and the static-loading tests is simulated by means of FEM analysis. The FEM models prepared to analyse the vaults take explicitly into account the direct effect of secondary masonry structural elements, such as the upper slab and the extrados stiffening diaphragms. The comparison indicates that the consideration of these structural elements is essential for an adequate FEM simulation of both the dynamic and the static behaviour of the timbrel vaults.
This is an Accepted Manuscript of an article published by Taylor & Francis Group in International Journal of Architectural Heritage on 2017, available online at: http://www.tandfonline.com/10.1080/15583058.2016.1277566
This paper studies the cross-sectional behaviour of austenitic, ferritic and duplex stainless steel hollow sections subjected to several loading conditions and presents a full slenderness range DSM approach for the prediction of cross-sectional strengths. Pure compression, pure bending moment and combined uniaxial bending and compression loading resistances are predicted using the same strength curve, which is based on experimental data gathered from the literature and ultimate strengths generated through parametric studies. The proposed approach is applicable to slender and stocky cross-sections leading to an accurate full slenderness range DSM design approach since the resistance reduction due to local buckling and the effect of strain hardening are taken into account, as is the effect of partial yielding of the cross-section in bending. A new method based on the actual stress distribution of the cross-section is also presented for combined loading conditions, where the cross-sectional behaviour is directly tackled through the same strength curve, providing more accurate results than the methods considering the uncoupled problem. Finally, a statistical analysis is presented to demonstrate the reliability of the proposed DSM approach.
La presente invención se refiere, en estructuras flotantes de soporte de turbinas eólicas, a la materialización mediante una lámina de hormigón pretensado de la zona de transición entre la torre, de menor diámetro, y el flotador de hormigón de mayor diámetro, tanto si la torre es metálica como de hormigón. Dicha lámina de revolución presenta una geometría óptima para la correcta transmisión de esfuerzos entre ambas partes, torre y flotador, con un espesor reducido y sin necesidad de elementos de rigidización y refuerzo exteriores a sus superficies que aumentarían el peso y el coste de la estructura.
This paper shows new possibilities of using novel, open-source, low-cost platforms for the structural health monitoring of heritage structures. The objective of the study is to present an assessment of increasingly available open-source digital modeling and fabrication technologies in order to identify the suitable counterparts of the typical components of a continuous static monitoring system for a historical construction. The results of the research include a simple case-study, which is presented with low-cost, open-source, calibrated components, as well as an assessment of different alternatives for deploying basic structural health monitoring arrangements. The results of the research show the great potential of these existing technologies that may help to promote a widespread and cost-efficient monitoring of the built cultural heritage. Such scenario may contribute to the onset of commonplace digital records of historical constructions in an open-source, versatile and reliable fashion.
Under general seismic loading, reinforced concrete columns may be subjected to lateral loads in more than one direction. Available experimental data on columns subjected to bidirectional forces indicate that higher levels of damage and a higher loss of ductility and strength have been observed compared to similar tests under unidirectional shear forces. In this study, an experimental program was conducted in which six lightly reinforced concrete columns were subjected to unidirectional and bidirectional cyclic shear forces. This observation was used to identify the mechanisms and parameters governing the behavior of columns subjected to cyclic bidirectional lateral loads. Hence, a new conceptual model was developed to obtain the capacity of member. The shear forces were analyzed and an analytical formulation was derived to account for the effects in the concrete stress-strain relationship, the moment-curvature diagram and the plastic hinge length. These equations were used along with a structural model with concentrated plastic hinges to obtain the capacity curve of the column. The results of the formulations developed were verified using the results of the experiments performed on columns subjected to unidirectional and bidirectional cyclic lateral forces.
Mortar is of all masonry components the most difficult to be experimentally characterised in heritage buildings. This paper investigates the possibility of combining different in-situ and laboratory minor destructive testing (MDT) techniques to assess the strength of mortar in historical brickwork. Lime mortar and clay brick walls were built in the laboratory and then tested in order to derive empirical correlation rules among three different MDT techniques: double punch test (DPT), helix pull-out test (HPT) and pin penetration test (PPT). The outcomes of this activity were used eventually to assess the mortar properties of an important historical heritage structure, Casa Puig i Cadafalch, located near Barcelona. The research is intended to promote the use of MDT in studies and conservation works on built cultural heritage by providing criteria for the evaluation of the strength of existing mortar with respectful sampling and testing techniques.
Finite element macro-modelling approaches are widely used for the analysis of large-scale masonry structures. Despite their efficiency, they still face two important challenges: the realistic representation of damage and a reasonable independency of the numerical results to the used discretization. In this work, the classical smeared crack approach is enhanced with a crack-tracking algorithm, originating from the analysis of localized cracking in quasi-brittle materials. The proposed algorithm is for the first time applied to a large-scale wall exhibiting multiple shear and flexural cracking. Discussion covers structural aspects, as the response of the structure under different assumptions regarding the floor rigidity, but also numerical issues, commonly overlooked in the simulation of large structures, such the mesh-dependency of the numerical results.
This paper presents the results of an experimental program carried out in the laboratory to evaluate the shear strength of aerial lime mortar brickwork. Masonry triplets and walls were tested after one year from their construction by adopting two different testing methods. The first approach consisted in the shear tests of masonry triplets, whereas the second technique was based on core drilling from walls of 90 mm diameter cylindrical specimens to be subjected to Brazilian tests with varying inclination of the diametric mortar joint. The first method is more adequate to characterize new masonry, whilst the second one is a suitable MDT procedure for the analysis of existing structures. The experimental results from standard and non-standard tests were properly investigated in order to obtain the shear failure envelope of the bond interface and mortar joint. The comparisons between the different tests and their interpretative theories show the possibilities of the novel non-standard testing method for the evaluation of the shear strength of structures of the built cultural heritage.
The paper presents an integrated approach aimed at assessing the seismic safety of Mallorca cathedral. This cathedral is an extraordinary historical construction dating back to the middle-ages. The experimental modal parameters of the cathedral were identified using Ambient Vibration Testing (AVT). The cathedral numerical model was updated using the identified modal parameters. This updated model was then used to study the seismic response of the cathedral using non-linear static (pushover) analysis. A sensitively analysis was carried out to reveal the dependency of the seismic capacity on the input materials properties. To assess the seismic performance and the safety of the cathedral, the N2 method was employed. It was found that the cathedral is safe when subjected to the earthquakes expected in Mallorca Island.
Currently, the AISC code provides guidance for the calculation of the ultimate strength of unstiffened plate girder webs subjected to concentric edge loads. Specifications consider three categories: local web yielding, web crippling, and sideway web buckling. Based on previous studies, the presence of longitudinal stiffeners in the web has not been considered in the calculation procedures. Longitudinal stiffeners in steel plate girders are primarily used to increase bending and shear strength. In the last two decades, a number of projects regarding the positive effect of longitudinal stiffening on the strength of plate girder webs to concentrated load have been conducted around the world. The results have shown that this type of stiffening enhances ultimate strength for web crippling depending on the position of the stiffener that modifies the slenderness of the directly loaded panel; and flexural and torsional rigidities of the stiffener. This paper presents a methodology for the consideration of longitudinal stiffening on the ultimate strength of plate girders webs subjected to concentrated loads. The methodology is based on the plastic collapse mechanism observed experimentally, in which plastic hinges are formed in the loaded flange and yield lines result in the portion of the web limited by the loaded flange and stiffener. Then, a closed-form solution accounting for the influence of the stiffener is developed following the current expression available in the AISC specifications. Theoretical predictions are compared with available test results, showing that the predicted ultimate loads are in good agreement with experimental results.
Numerical simulations have been widely applied, for the determination of the resistance of steel structural elements, when experimental analysis are not possible (due to cost or size limitations) or when parametric studies with high number of variables are needed. However, the numerical models must be properly validated with experimental tests in order to deliver reliable studies. With the purpose of studying the behaviour of stainless steel plate girders in fire situation, a total of 34 experimental tests from the literature have been numerically modelled. The tested girders had different configurations: rigid and non-rigid end posts, 2 and 4 panels, and transversal and longitudinal stiffeners were considered. Comparative analyses between those experimental and numerical results have been done. Good approximations to the experimental results at normal temperatures have been achieved with differences on average lower than 5%. Afterwards, the developed numerical model has been used to perform a sensitivity analysis on the influence of the initial geometric imperfections at both normal and elevated temperatures, considering different values for its maximum amplitudes, concluding that 10% of the web thickness is an appropriate value for the maximum amplitude of the geometric imperfections when modelling experimental tests. The effect of the residual stresses has also been analysed, being obtained differences lower than 2%. Finally, comparisons between the numerical results and the Eurocode 3 design procedures have been performed considering different uniform elevated temperatures.
The final publication is available at Springer via http://dx.doi.org/10.1007/s10694-016-0602-6
Petracca, M.; Pelà, L.; Rossi, R.; Oller, S.; Camata, G.; Spacone, E. Computer methods in applied mechanics and engineering Vol. 315, p. 273-301 DOI: 10.1016/j.cma.2016.10.046 Data de publicació: 2017-03 Article en revista
This work presents a multiscale method based on computational homogenization for the analysis of general heterogeneous thick shell structures, with special focus on periodic brick-masonry walls. The proposed method is designed for the analysis of shells whose micro-structure is heterogeneous in the in-plane directions, but initially homogeneous in the shell-thickness direction, a structural topology that can be found in single-leaf brick masonry walls. Under this assumption, this work proposes an efficient homogenization scheme where both the macro-scale and the micro-scale are described by the same shell theory. The proposed method is then applied to the analysis of out-of-plane loaded brick-masonry walls, and compared to experimental and micro-modeling results.
Time-dependent strains, when restrained, can lead to important tensile forces and damage, affecting, among other aspects, the shear response and ultimate load carrying capacity of shear-critical RC frames. This paper presents a detailed study of this problematic by means of an extension of a shear-sensitive fibre beam model to time dependent behaviour of concrete. The model is firstly validated with experimental tests on diagonally pre-cracked beams under sustained loads. From these analyses, the contributions of shear distortions and bending curvatures to the total long-term deflection of the beams are discerned. Afterwards, the model is applied to study the influence of restraining strains due to long-term creep and shrinkage in the service and ultimate shear response of frames. In contrast with flexural resistant mechanisms, delayed strains may influence the latter shear resistance of integral structures by reducing the concrete contribution to shear resistance and leading to a sooner activation of the transversal reinforcement. These aspects can be relevant in assessing existing structures and this model, due to its relative simplicity, can be advantageous for practical applications.
The final publication is available at Springer via http://dx.doi.org/10.1617/s11527-016-0875-8