Version Of Eurocode Research Articles

Assessment of existing PC structures according to EN 1992-1-1:2023

The paper aims to present a number of additional standard provisions and changes included in EN 1992-1-1:2023, published in November 2023. Among other features, the new version of Eurocode 2 includes informative annexes on the assessment of existing structures and safety formats for non-linear analysis, which previously were not standardised. In addition, the paper summarises the basic changes of the new standard for the analysis of prestressed concrete structures. The paper also presents an example of the assessment of an existing post-tensioned concrete member in compliance with the recommendations of the EN 1992-1-1:2023 standard. The analyses were performed in two levels of accuracy, i.e. I – analytical method, II – nonlinear FEM analysis. Comparison of the obtained results indicates the potential of nonlinear analysis for optimal assessment of existing structures in accordance with Eurocode 2, especially for non-standard structures, such as prestressed structures.

Interactive local instability of aluminium angles

A theoretical approach for the evaluation of the ultimate resistance of aluminium angles subjected to local buckling under uniform compression is presented and compared with simplified approaches used for codification purposes. In particular, a theoretical procedure has been developed by considering the interaction of the outstand elements constituting the cross-section and the mechanical non-linearity of the material. To evaluate the accuracy of the theoretical approach, the results have been compared with experimental tests provided in the scientific literature. Then, a new mathematical formulation has been also derived to estimate the interaction effects of the section plates and it has been used for the extension of the Effective Thickness Method (ETM) according to the new version of Eurocode 9. Finally, the accuracy of simplified approaches as well is investigated by comparing the obtained values with the experimental results derived from the stub column tests reported in the scientific literature.

Second Generation of Eurocode 8: Seismic Design Rules for Cold‐Formed Steel Buildings

AbstractThe seismic design of Cold‐Formed Steel (CFS) building structures is not covered by the current edition of Eurocode 8. In order to update Eurocode 8 to reflect the findings of extensive research undertaken over the last ten years, the University of Naples “Federico II” is taking part in the evaluation of current seismic design criteria and the creation of new guidelines for the design of CFS systems. This paper especially examines various Lateral Force Resisting System (LFRS) types that may be found in the second version of Eurocode 8. It also provides background information on the research initiatives and reference design standards in use in various parts of the world that served as the basis for the development of design criteria included in the new version of Eurocode 8.

Estimation of the shear capacity of decks in existing shorter reinforced concrete bridges

AbstractIt has been recognized that the shear capacity of old bridges can play a crucial/key role in evaluating their structural safety. Determination of the shear capacity of critical cross‐sections presents a much greater challenge than the assessment of their bending capacity.Due to abovementioned problems, the shear capacity of shorter reinforced concrete bridges with T‐beams has been evaluated with various models. Four different models were examined, the currently valid Eurocode 2, draft of the new version of Eurocode 2, the currently valid Eurocode 8‐3 and the model corresponding to modified compression field theory (MCFT). According to all the models, the capacity of deck of existing reinforced concrete bridge was calculated. This bridge was previously inspected and the actual amount and shape of the shear and bending reinforcement was determined.The results obtained with different models were compared and the typical parameters which influence the shear capacity were analyzed. The results in terms of shear capacity show that different models can give quite different results for the same bridge.

Shear Resistance of Members Without Shear Reinforcement in Presence of Axial Forces in the Next Eurocode 2

The second generation of Eurocode 2 incorporates formulations based on physical models which are general enough for the assessment of existing structures but can be simplified for the design of new structures, in order to improve the ease-of-use. One of the areas where these improvements are addressed is the shear verification of members without shear reinforcement, such as solid slabs, walls, cut-and-cover tunnels, precast ribs or hollow core slabs, which in some cases are prestressed or subjected to external axial loading.In current Eurocode 2, the shear verification of these structures is based on an empirical formulation proposed by Zsutty in 1968. The final draft of the new version of Eurocode 2 has adopted the Critical Shear Crack Theory (CSCT) as the theoretical basis for the formulation of the shear resistance, which allows a better understanding of structural behaviour in many different conditions, not only for the design of new structures, but also for the assessment of existing structures. This formulation accounts for some aspects that are not well considered in current Eurocode 2, which have been underlined as shortcomings in recent years.The formulation for design of new structures in the final draft of the new version of Eurocode 2 (General Model) is easy to use for the verification of the shear resistance, but requires an iterative process to calculate the shear capacity of sections in the presence of axial forces. For this reason, the final draft of the new version of Eurocode 2 also provides an alternative non-iterative formulation (Linear Approach) to calculate the shear capacity in presence of compressive axial forces, based on the linearisation of the CSCT shear failure criterion and formulated with the same additive structure as in the current Eurocode 2, useful for the most common cases.This paper presents the General Model formulation provided in the next Eurocode 2 for the shear verification of axially loaded members without shear reinforcement, as well as the alternative formulation (linear approach). In addition, the agreement of both formulations with experimental results from an available shear test database on prestressed concrete beams is shown and the consistency of the safety treatment between the two formulations is also discussed.

Embedded Fibre Reinforced Polymers (FRP) in Concrete Structures According to the New Version of Eurocode 2

The new version of Eurocode 2 will include for the first time an informative annex, Annex R “Embedded FRP reinforcement”, to design reinforced concrete structures with fibre reinforced polymer (FRP) reinforcement. FRP embedded reinforcement has some advantages such as their low susceptibility to corrosion, high‐strength, and low life‐cycle cost. FRP rebars can be used as longitudinal or transverse reinforcement in a similar way than conventional steel rebars, but considering some particular aspects, such as their linear elastic behaviour up to failure or their lower modulus of elasticity, which may condition the design by the verification of theserviceability limit state. Since, the content of Annex R is new, a summary and background related to all aspects required for designing with FRP reinforcement are given in this paper.

Strengthening Existing Concrete Structures with Fibre Reinforced Polymers (FRP) in the New Version of Eurocode 2

This paper aims to introduce the content of Annex J “Strengthening of Existing Concrete Structures with CFRP” of Eurocode 2 [1]. This is first time that the design of adhesively bonded reinforcement with CFRP has been introduced in the European regulations through an informative annex. Annex J considers two different bonded strengthening techniques: externally bonded reinforcement (EBR) that consists of bonding CFRP strips or sheets to the surface of concrete elements, and near surface mounted reinforcement (NSM) that consists of embedding a CFRP strip or rod to a slot cut in the concrete cover. Since, the content of Annex J is new, asummary and background related to all aspects required for designing CFRP strengthened systems for concrete structures, are given in this paper.

Mechanical behaviour of welded high strength steel rectangular hollow section joints

The material reduction factor of rectangular hollow section (RHS) joints in a new version of Eurocode 3 part 1–8 is validate for steel with the nominal yield strength up to 700 MPa. In this paper, finite element simulations of gap K-joints are conducted to investigate effects of material properties, gap size of the joint, the brace to chord width ratio and welds type on the secondary bending stresses and the resistance. The governing failure mode considered for all the FE models is the chord face failure followed by brace sidewall failure. The ratio of axial stresses to the nominal stress was lower in the compressive brace made of higher strength steel grades compared to the mild strength grades. The maximum secondary bending stresses is 0.12–0.32 yield strength. The secondary bending stresses are increasing with the increase of the steel grade and the brace to chord width ratio and with reducing the gap size. The level of secondary bending stresses varied between 38% and 56% of the average normal axial stress. The secondary bending stresses of fillet-welded joints are larger than the butt-welded joints. The yield line model is used to predict the ultimate load and good agreement is obtained compared with FE results.

Advancement in prediction of shear strength and stiffness of cross laminated timber beams

Cross laminated timber (CLT) beams are mainly used within wall panels, but also standalone in design situations where cross layers have a reinforcing effect concerning stress perpendicular to the beam axis. The stress state in CLT beam members is complex and shear failure is mainly governed by stresses and strains acting in the crossing areas between orthogonally bonded laminations, known as shear failure mode III. The current model suggested for the next version of Eurocode 5 regarding shear strength prediction has certain limitations. Based on model improvement, design proposals regarding shear failure mode III for CLT beams composed of 3 and 5 layers are expanded for CLT with 7 layers. Based on test results of small shear specimens, both design proposals successfully predict shear strength experimentally obtained on beam specimens. Evaluated full-field deformations by a digital image correlation (DIC) system and the improved model and design proposal coincide in regards to the critical crossing area position. The influence of reduced lamination widths on beam shear strength and shear strength ratio on the position of critical crossing areas are further analysed indicating a fairly minor contribution. The improved analytical model and design proposals were further modified to calculate the effective shear modulus of CLT beams. A good agreement between the analytical and test results is obtained for the slip modulus of the crossing areas proposed in the literature. However, a higher slip modulus seems appropriate for both design proposals in the design situation to avoid too conservative effective shear modulus and corresponding shear stiffness.

PROS and CONS of linear and nonlinear seismic analyses for existing URM structures: Application to a historical building

Seismic capacity assessment of existing buildings is of paramount importance for mitigating the seismic risk in earthquake-prone areas. In Europe, the next version of Eurocode 8 and the current version of the Italian standards suggest the adoption of both linear and nonlinear approaches to perform seismic analyses of existing masonry buildings.This paper discusses with the main issues concerning linear and nonlinear analyses methodologies provided by the Italian standards for existing unreinforced masonry buildings. An historical building located in Southern Italy, representative of the Mediterranean basin buildings, has been chosen as a case study and modelled through the equivalent frame model. According to the Italian standards, the influence of in-plane stiffness of floors and spandrels on the overall seismic capacity of the structure has been considered in the analyses. Beyond the code prescriptions, the effect of different ultimate drifts values assumed for the spandrels on nonlinear behavior of the structure has been analysed.The results of two types of linear analyses (lateral static force method and modal response spectrum analysis) have been compared among them and with those provided by the nonlinear static method. Conclusions show that either behavior and overstrength factors provided by the Italian standards are conservative than those estimated through the nonlinear static analyses. Moreover, it has been remarked that the value of ultimate drift adopted for the spandrel can affect significantly the nonlinear response of the structures, although this topic still represents an open issue.

The Effect of Long Duration Earthquakes on the Overall Seismic Behavior of Steel Structures Designed According to Eurocode 8 Provisions

Premature and simultaneous buckling of several steel braces in steel structures due to the prolonged duration of a seismic motion is one of the issues that must be addressed in the next version of Eurocode 8. In an effort to contribute towards the improvement of the seismic design provisions of Eurocode 8, an evaluation of the overall behavior of some steel building-foundation systems under the action of long duration seismic motions is performed herein by means of nonlinear time-history seismic analyses, taking into account soil–structure interaction (SSI) effects. In particular, the maximum seismic response results—in terms of permanent interstorey drifts, overturning moments and base shears of the steel buildings as well as of the permanent settlement and tilting of their foundations—are computed. It is found that the seismic performance of steel buildings when subjected to long duration seismic motions is: (i) acceptable for the two and five-storey fixed base steel buildings and for the two-storey steel buildings with SSI effects included; (ii) unacceptable for the eight-storey fixed base steel buildings and for the five and eight-storey steel buildings with SSI effects included. In all cases of steel buildings with SSI effects included, the seismic performance of the mat foundation, as expressed by the computed values of residual settlement and tilting, is always acceptable.

On the Lateral-Torsional Elastic Post-Buckling and Strength of Channel Steel Beams

This paper aims at shedding new light on the elastic post-buckling behavior and strength (elastoplastic collapse) of steel channel section beams undergoing lateral-torsional (LT) buckling. This new insight is acquired using a two-node geometrically exact beam finite element developed by the author, which can handle large displacements, including torsion-related warping, Wagner effects, plasticity, residual stresses and arbitrary initial configurations (namely geometrical imperfections). Several cross-sections and loading/support conditions are analyzed. The results obtained show that the LT buckling behavior of channels is asymmetric, meaning that the direction of the geometric imperfection can influence significantly the strength of the beams. Moreover, it is demonstrated that the loading and support conditions play a major role, leading to a significant scatter of results which hinder the definition of a single buckling curve for design purposes. Nevertheless, in all cases considered, the buckling strengths obtained fall significantly above those predicted by the current version of Eurocode 3.

Numerical evaluation of the plastic hinges developed in headed stud shear connectors in composite beams with profiled steel sheeting

For composite beams using novel steel sheeting, the current Eurocode 4 rules sometimes overestimate the load-bearing capacity of headed stud shear connectors. This is due to the larger rib heights and the smaller rib widths in comparison with the old studies, which have been carried out to calibrate the current design equations. The RFCS Project “DISCCO” investigated this phenomena and the working group under mandate M515, CEN/TC250/SC4/SC4.T3 is enhancing this equation and working on a proposal to be taken over in the new version of Eurocode 4.The proposed new equation covers the failure behaviour of the shear connection more in detail. The test results show, that the failure consists in a combined concrete cone and stud in bending. Due to the geometry of novel steel sheeting, the load bearing capacity of the headed stud shear connector is no more limited by its shear capacity, but by its bending capacity.A 3D non-linear finite element model is developed and validated through the support of the DISCCO push-out tests. A good agreement between numerical and experimental results in terms of force-slip behaviour is achieved. Special attention of this work lies on the numerical evaluation of the number of plastic hinges ny: a stress-based procedure is presented and the results are compared to the equations presented for new Eurocode 4.The numerical simulations show that the upper plastic hinge moves up as the slip increases due to the progressive crushing of the concrete in the rib. From the parametric study, it turns out that ny is linearly proportional to the embedment depth. Compared to pre-punched hole decking, through-deck welding specimen activates less plastic hinges in the studs because of the higher stiffness provided at the base of the stud.

Código Modelo 2020: Un proyecto fib para el avance del hormigón estructural

El Código Modelo es uno de los documentos más importantes producidos por fib. Desde su primera edición en 1970, se han publicado ediciones en 1978, 1990 y, recientemente, en 2010. Todos estos documentos han influido en la producción de códigos nacionales y regionales. Los Códigos Modelo de 1978 y 1990 han tenido una gran influencia en las diferentes versiones del Eurocódigo 2. El Código Modelo de 2010 sirve de guía de manera similar al trabajo preparatorio de CEN para las nuevas ediciones de los Eurocódigos. Los Códigos Modelo siempre han sido una referencia importante para investigadores, diseñadores y constructores. La nueva edición del Código Modelo que se publicará en 2020 pretende abordar, al mismo nivel, las estructuras nuevas y existentes y presentar modelos más generales y más racionales, eliminando cualquier rastro de reglas de diseño empírico previas. Será un Código Modelo operativo y orientado a las necesidades prácticas. Este documento muestra el contenido del nuevo Modelo de Código 2020 y el trabajo en curso para su preparación.

Experimental and numerical investigations of cross-laminated timber elements at in-plane beam loading conditions

Abstract Cross laminated timber (CLT) at in-plane beam loading conditions presents a complex stress state wherefore several failure modes and geometry parameters need to be considered in design. The work presented here includes experimental investigations of CLT beams for comparison and validation of an analytical model and design proposals previously suggested by the authors. All relevant failure modes are considered; bending failure and shear failure modes I, II and III. The main focus is, however, on shear failure mode III relating to shear failure in the crossing areas between orthogonally bonded longitudinal and transversal lamination. The analytical model presented is an improvement of the analytical model which has been suggested to be used as the basis for design equations for the next version of Eurocode 5. The two design proposals presented are based on that improved analytical model. Experimental results show good agreement with the improved model and both design proposals. In order to study the influence of different lamination placements and varying lamination widths, comparisons between the improved analytical model and FE-analyses regarding magnitude and distribution of internal forces are presented and good agreement is obtained. Experimental and analytical results indicate only a small influence of reduced lamination widths close to the beam edges. This is a finding which is of practical interest since CLT beams in general are cut from larger elements, with no consideration of the location of the individual laminations with respect to the edges of the beam.

Cross laminated timber at in-plane beam loading – Comparison of model predictions and FE-analyses

The work presented concerns validation of a specific analytical model for Cross Laminated Timber (CLT) at in-plane beam loading conditions. The original model (model A) has previously been presented in the literature and is also suggested to be used as a basis for design equations for the next version of Eurocode 5. An improved version (model B) of that original model (model A), regarding basic assumptions relating to the internal force distribution, has recently been presented in the literature. Here, comparisons between the original model (model A), the improved model (model B) and FE-analyses regarding magnitude and distribution of internal forces are presented. The main focus is on forces and torsional moments acting in the crossing areas between longitudinal and transversal laminations and relevant for shear mode III failure, meaning the relative sliding and rotation between two flat-side bonded laminations. The results show that the improved analytical model (model B) outperforms the original model (model A) in terms of giving predictions very close to the predictions of the FE-model. A further extension of the improved model (model B) regarding distribution of forces and torsional moments in the beam width direction is also presented.

SOIL REINFORCEMENT AND EC7 (202x)

Soil reinforcement is not really covered in current version of Eurocode 7 and therefore during the proposals for 2<sup>nd</sup> generation of EC7 the soil reinforcement was highly promoted for inclusion in new EC7 based on the comments from practising engineers. In new EC7 which is now being written in newly created part 3 there will be next to other clauses also complete clause on Reinforced Ground. The paper will inform on the proposed contents of this clause.

Cross laminated timber at in-plane beam loading – Prediction of shear stresses in crossing areas

Cross Laminated Timber (CLT) at in-plane beam loading conditions present a very complex stress state and many failure modes need to be considered in design. The work presented here aims at finding improvements of a specific analytical model for stress analysis and strength verification that has been suggested in literature and which is also suggested as a basis for design equations for the next version of Eurocode 5. Although the model has appealing properties it suffers from some drawbacks related to the assumed distributions of internal forces which, based on comparison to finite element analysis, appear to be inaccurate. The main focus in this paper is on model predictions regarding the distribution and magnitude of internal forces acting in the crossing areas between longitudinal and transversal laminations. The proposed modified model assumptions regarding the distribution of lamination shear forces, which in turn influence the forces acting in the crossing areas, are suggested to be taken into account in design of CLT beams.

Recent developments regarding the next version of Eurocode 3 part 1‐1 on steel structures.

AbstractThis paper gives an overview of the work necessary and underway for the next version of part 1‐1‐of Eurocode 3 on steel structures: EN 1993‐1‐1. This work is done by Working Group 1 (WG1) of subcommittee CEN/TC250/SC3 and by Project Team 1 (PT1) responsible for the technical content of the next version of EN 1993‐1‐1. In the past, WG1 collected a longlist of items that may need improvement and recently carried out a systematic review that also yielded topics that need to be considered for the next version of EN 1993‐1‐1. The work of WG1 already resulted in amendments for EN 1993‐1‐1 which were accepted by CEN/TC250/SC3. PT1 is currently implementing these amendments in the next version of EN 1993‐1‐1, that is due in a few years’ time. In this paper, an overview is given of the amendments and of other developments related to EN 1993‐1‐1. The amendments concern among others several strength and stability related design rules. This paper is an extended and updated version of [1].

Editorial: New Advances in Seismic Design and Assessment of Steel Structures

In recent years, rapid advances have taken place in earth-quake engineering as applied to steel structures with major emphasis given to (1) development of advanced procedures for seismic performance assessment, (2) development of advanced design procedures for plastic mechanism control, (3) improvements in structural design detailing, (4) better modeling of members and connections for dynamic non-linear analyses, (5) development of new damping devices for supplementary energy dissipation, (6) development of self-centering structural systems, (7) development and testing of new design strategies for reducing structural damage under severe ground motions. Even though such advances have reached in some cases a refinement level justifying their in-troduction in seismic codes, the updating of Eurocode 8 with design criteria and new design strategies reflecting newly developed knowledge is still in delay. In the actual version of Eurocode 8, some advances, such as new structural ty-pologies like braced frames equipped with buckling re-strained braces and dissipative truss moment frames, are still not codified even if they have already gained space in American codes. Because of these rapid advances, weaknesses of Euro-code 8 and new structural typologies to be codified have been recognized and a document focusing on such weak-nesses and new research needs has been published [1]. In particular, the sharing of knowledge obtained has been rec-ognized to be critical to improve the seismic design of steel structures. Therefore, a Thematic Issue on “New Advances in Seismic Design and Assessment of Steel Structures” can be considered timely. Many researchers, all joined by the common interest in design, testing, analysis and assessment of steel structures in seismic areas, have accepted to contribute to this special is-sue. As a result, this thematic issue is composed by eleven contribution covering important design topics for seismic resistant steel structures. Two works [2, 3] are devoted to the seismic design of Concentrically Braced Frames (CBFs), pointing out the drawbacks of the design provisions suggested by Eurocode 8 and also reported in the Italian Technical Code for Construc-tions. In particular, the need to revise the design procedure suggested for columns of CBFs is discussed showing that both the stability and resistance indexes of columns are often exceeded. The results obtained are in agreement with those presented by other researchers [4-8] who recommended de-sign procedures based on a rigorous application of capacity design principles. Also the third manuscript of the thematic issue is devoted to CBFs, but aiming to the development of a new buckling restrained system which can be easily dis-mounted [9]. As it is well known, buckling restrained braces (BRBs) are basically constituted by two parts: an internal slender steel member, known as the “core” and a restraining member, known as the “casing”. The core component has the key role of dissipating energy, while the casing component restrains the brace core from overall buckling in compres-sion. The buckling restraining mechanism can be obtained by enclosing the core (rectangular or cruciform plates, circu-lar rods, etc.) either in a continuous concrete/mortar filled tube or within a “all-steel” casing. Despite of the use of such braces allows to obtain wide and stable hysteresis loops, thus overcoming the main drawbacks of traditional braces due to the poor cyclic response resulting from overall buckling, and their design is already codified in ANSI/AISC 341-10 [10], their use is still not codified in Europe testifying an impor-tant weakness of Eurocode 8. Two papers of the present thematic issue are devoted to beam-to-column connections [11, 12]. The first one [11] presents the results of a wide experimental program recently carried out at Salerno University dealing with extended end plate connections, with and without Reduced Beam Section (RBS), connections with bolted T-stubs and, finally, innova-tive connections equipped with friction dampers. The second work [12] is mainly devoted to the theoretical development of the analysis of the influence of gravity loads on the seis-mic design of RBS connections. In particular, it deserves to be underlined that such influence is commonly neglected in codified rules, such as ANSI/AISC 358-10 [13], because experimental tests constituting the base of the recommended design procedures are typically based on cantilever schemes where gravity loads are not applied.