Eurocode Approach Research Articles

Reliable design rules for cold-formed ferritic stainless steel closed built-up beams

In the companion paper, test results were presented to explore the flexural performance of cold-formed ferritic stainless steel (FSS) closed built-up beams. Each specimen was fabricated by joining two lipped channels in a face-to-face configuration and securing them with spot welds at intermediate points along the beam span. Sectional aspect ratio, compression flange’s sectional slenderness and moment gradient were the key parameters varied to explore their influence on the flexural response of such members through tests. The current paper establishes a simplified finite element (FE) model of cold-formed FSS closed built-up beams and verifies it against the test results. Further, an extensive parametric study is carried out using the validated FE model to generate a large pool of data points. A wider database comprising of test results, numerical results obtained from this study and numerical results available in the companion paper were used to critically examine the adequacy of the current Australian Specifications (AS/NZ), American Standard (SEI/ASCE-8), European Code (EN 1993-1-4), Modified Eurocode approach suggested by Gardner and Theofanous, and Direct Strength Method (DSM) in North American Specification (AISI-S100: 2016), Modified DSM approach proposed by the authors in the literature and Continuous Strength Method (CSM) for cold-formed steel (CFS) flexural members. This makes the current study the first to extensively assess the accuracy of the various design guidelines available in the codes and other relevant literature, which explicitly highlighted their grave limitations. Accordingly, through suitable modifications and recommendations, new design rules are proposed to reliably and safely predict the flexural capacity of cold-formed FSS closed built-up beams.

Analysis of the transfer, flexural bond and anchorage lengths of pretensioned FRP reinforcement based on Eurocode

Current design codes in North America have guidelines for assessing the anchorage zone of pretensioned fiber reinforced polymer (FRP) reinforcement. However, there is no comparison of the Eurocode approach with experimental data or suggestions for its application for prestressed FRP reinforcement. Therefore, the main objective of this article is to provide a comparison of available data in the literature on the transfer, flexural bond, and anchorage length of different types of FRP reinforcement with Eurocode and to provide insight on the adaptation of this code. The database of more than 300 and 100 specimens with the results of the transfer and flexural bond lengths is used, respectively. This database is used to derive and propose the parameters that describe the type and surface of pretensioned FRP reinforcement based on the Eurocode approach. Furthermore, the influence of shear reinforcement and the type of pretensioned reinforcement release (gradual and sudden) is taken into account. The Eurocode approach with the coefficients proposed for different FRP reinforcements on average gave the best prediction of the experimental transfer, flexural bond, and anchorage length results compared to the North American design codes for FRP reinforcement and the Eurocode for steel strands.

Compressive strength of beech and birch at different moisture contents and temperatures

AbstractOwing to increased environmental demands to replace petroleum-derived materials with more environmentally friendly materials, research has been directed towards the potential of using wood in the automotive industry. This study extensively investigates the compressive strength (fc) of two hardwood species (beech and birch) with different anatomical directions, at various moisture and temperature levels, in an attempt to understand the wood’s behaviour during the forming process. The experimental tests were performed at 20, 100 and 140 °C on specimens with five moisture levels, ranging from completely dry to wet conditions. Overall, irrespective of the investigated direction, the measured compressive strength exhibited a clear exponential trend with increasing moisture content over the whole temperature range. This was capitalised on to present a simple predictive equation to roughly estimate the fc of beech and birch in different moisture and temperature conditions by relating to their dry fc at a reference temperature of 20 °C. The proposed approach was compared with other procedures and trends reported in the literature for the effect of moisture and temperature on the fc of wood. Furthermore, the reduction factors for the effect of temperature on the fc of softwoods, as set out in Eurocode 5 (EN 1995-1-2), were discussed in comparison with the present study findings. It was shown that, although the Eurocode approach is conservative, it may still be applicable for estimating the fc of hardwood species.

Proposed Modified Formula for Predicting Shear Strength of Reinforced Concrete Beams Based on Eurocode Approach

In order to predict the shear strength test values from the literature, shear strength calculations have been carried out per SNI 2847:2019, ACI 318M-19, EN 1992-4, NZS 3101.2, and CSA A23.3. In order to investigate the predicted shear strengths of various concrete beams, 129 experimental concrete beams have been selected as the representative data for validation. After the shear strength calculations of the beams using the five code formulas, the results obtained have been compared with the corresponding experimental data. The investigation of low- and high-strength concrete beams is the primary focus of the study. Based on the comparisons between predicted values from various code formulas and the test data, which code formula has provided the best prediction on the shear strength of the test beams but still fall on the safe side can be determined. Accordingly, a proposed formula has been also developed to improve the beam’s shear strength prediction accuracy. Overall, the results have indicated that the SNI 2847:2019 has given the most over-prediction in shear strengths compared to those obtained from the other four code formulations. In contrast, it is also found out that the CSA A23.3 has the most conservative formula. The proposed formula has modified the EN 1992 formula in order to enhance the prediction and maintain it on the safe side in the majority. The proposed formulation shows better agreement with the test data compared with all the existing formulations.

Basal reinforcement of embankment over voids and soil subsidence area – new standard XP G38065

The use of geosynthetic reinforcement to limit the consequences of a localized collapse of the ground under road and railway structure started in the 90s. The new French standard XP G 38065 for basal reinforcement establishes the rules for justifying works on potential cavity risk areas and will provide users with a tool adapted to this use. This paper shows the different steps of a design, considering the Eurocode approach with deformation and stress criteria, and the lateral displacement design model.

Flexural buckling of extruded high-strength aluminium alloy SHS columns

The structural performance and design of extruded high-strength aluminium alloy square hollow section (SHS) columns were presented in this paper. A total of 12 extruded 7A04-T6 aluminium alloy SHS column specimens were tested under axial compression, together with tensile coupon tests and initial global geometric imperfection measurements. The flexural buckling failure mode and axial load versus end shortening and mid-height lateral deflection curves were reported. Based on validated finite element (FE) models, 480 numerical results were generated by means of parametric studies over a broad range of cross-section dimensions, member lengths, proof strengths and strain hardening exponents of the aluminium alloy material. The applicability of current design rules used for normal-strength aluminium alloy columns in European, Chinese and American standards to extruded 7A04-T6 high-strength aluminium alloy SHS columns was evaluated through comparisons with the test and FE results. The analysis results showed that the three standards consistently yielded conservative axial compression resistance predictions by about 9% for extruded 7A04-T6 high-strength aluminium alloy SHS columns. New flexural buckling curves with linear and nonlinear imperfection terms for the Chinese code, as well as modifications to the American specification, were separately proposed, resulting in improved accuracy with significantly reduced scatter. Additionally, the continuous strength method (CSM) was further extended for the flexural buckling design of extruded 7A04-T6 high-strength aluminium alloy SHS columns, and was shown to provide accurate and consistent resistance predictions. Reliability analyses of the codified and the proposed design methods were performed, confirming that the design proposals meet the target reliability indices except the Eurocode approach.

Validation and application of bearing and block tearing resistance; background to prEN1993-1-8:2021

An investigation of bolted connections with a specific geometry and bolt arrangement that require high local ductility to achieve the predicted resistances according to the design rules of the new prEN 1993-1-8 is presented. The experimental campaign includes tensile and shear tests on mild steel coupons to calibrate the parameters used for the true stress-strain relationship, damage initiation criterion and fracture evolution, while a numerical model for the high strength steel grade S690 was selected from the literature. The FEA results were satisfactorily validated by experiments on bolted connections for which the rules of the new prEN 1993-1-8:2021 were used to predict the resistance and deformation behaviour. The deformation behaviour was predicted by applying the new analytical model to calculate the deformation at the bolt hole due to the bearing action. The resistances of the tested connections were also predicted using EN 1993-1-8:2005. It is clearly shown that the new design formulae predict the experimental results significantly better than the results obtained according to EN 1993-1-8:2005. The FEA of a bolt group in bending, representing a high web splice, provides new proof for an analytical model for the distribution of forces between the bolts in the elastic stage and at ultimate resistance. Furthermore, the new Eurocode approach for predicting the bearing deformation behaviour at the bolt hole agreed well with the experimental and numerical results.

Numerical analysis of the influence of curling on the strength of connections with one bolt

AbstractCurling failure typically appears in bolted connections with thin plates, where the force is transferred by bolt bearing. The curling phenomena is related to the high compressive stresses caused by bolt bearing, which cause the plates to buckle, reducing the bearing strength of connections. Since the reduction of the bearing strength due to curling is not considered in design codes, the curling phenomenon has been studied numerically to understand the mechanical behaviour and to develop simple design rules that take into account reduction in bearing strength. The reduction factor for reducing the bearing resistance by curling was developed taking into account the Eurocode approach, i.e. by calculating the elastic critical force associated to curling and the relative slenderness. Therefore, the elastic critical force in relation to curling was obtained by parametric buckling analysis in finite element software Abaqus. These results were used to develop a simple analytical model for the calculation of the elastic critical curling force. The reduction factor was obtained from the relationship between the results of parametric GMNIA and relative slenderness. The strength of single bolt connections was determined by geometrical and material nonlinear analysis with imperfections (GMNIA) considering various parameters, namely ratio of the bolt diameter to plate thickness, end distance e1, edge distance e2, material grade (S235, S690), shape and amplitude of imperfections and boundary conditions. The accuracy of the reduction factor for bearing strength is checked on the basis of experimental data given in literature.

Wind load on façade scaffolding without protective cover – Eurocode and in-situ measurement approaches

This paper presents an analysis of scaffolding response to static wind action, based on different approaches. The static wind load was adopted according to Eurocode standard that required separate calculations for the load acting perpendicular (load case B) and parallel (load case C) to the façade of the building on which the scaffolding was attached. In the second approach, the wind load was calculated on the basis of in-situ measurements performed on scaffolding structures set on construction sites (load case A). The research was carried out on 61 façade scaffolding structures without protective covers. Models of every scaffolding were created in the Finite Element system, based on their real geometry taken from geodetic measurements. Static-strength analysis allowed comparison of the scaffolding response determined by node displacements, normal stress and axial force in structural elements. It was found that in most of the analyzed cases the wind load based on Eurocode approach resulted in the greatest axial force or normal stress in elements. In a few cases, the load based on in-situ tests caused greater response of the structures and the permissible stress and axial force value in the elements were exceeded. These scaffolding structures were usually detached from the wall and twisted out of plane. Analyses pointed out that the scaffolding during its operational use could experience a load other than perpendicular or parallel to its façade as it is given in Eurocode.

Viewpoint. A new approach to floor loading

Alastair Hughes sets out a proposal to simplify the Eurocode approach to floor loads by moving from an occupancy-based categorisation to one based on loading.

The Comparative Study of Biaxial Bending Analysis of Steel Sections Using AISC and Eurocode Approaches

ABSTRACT
 This study investigates the capacity of the steel section using both AISC and Eurocode approaches by Robot Structure Analysis software. Three types of steel sections were subject to biaxial bending by applying loads to both main axes and examined by both approaches. The concept of Fisher was also adopted as an approach. The findings suggested that the Eurocode approach is more conservative in the design of steel sections subject to biaxial bending as it takes into account the level at which the load is applied, the type of the section whether rolled or welded and its height-to-width ratio (lateral buckling effect), the effects which are not considered in AISC approach. The AISC approach considers the shear center of the section as the level at which the loads are applied. The conservatism of the results was more pronounced when the section is close to H-section. Fisher`s concept of structural design of biaxial bending of structural steel is more conservative than both AISC and Eurocode approaches of analysis.

Contribution to the seismic behaviour of steel silos: full finite-element analysis versus the Eurocode approach

Under earthquake loading, the behaviour of storage structures such as grain silos represents, since the beginning of the 20th century until now, a field of study and investigation; for this aim, the present study investigates the reliability of the European guidelines employed for designing the steel silos subjected to seismic excitations. Via a 30 finite element analysis of a flat-bottomed slender steel silo taking into account the nonlinear time history analysis, wall flexibility, geometric imperfections, soil–structure interaction and multidirectional components, on one hand the stored matter is modeled by a continuum part with the hypoplastic law and a contact–friction law for the matter–silo interface, on the other hand, the stored matter is equivalently included according to Eurocode rules; the obtained results: at silo base, at matter–silo interface and on silo wall, were discussed to provide more clarifications on silos behaviour at filling state and under seismic excitation. The obtained results were also compared to underline the specification of both simulations and make a judgment on the actual European guidelines, especially the stress state and the profile of dynamic material pressure which seem inadequate.

An adjusted design approach for concentrically braced frames in low-to-moderate seismicity areas

Steel concentrically braced frame (CBF) configuration is a common construction application in Europe. In the low-to-moderate seismicity context, European building codes provide two alternative design methods for CBFs; engineers have to choose between a “non-dissipative” method (DCL) neglecting all seismic provisions, and a “dissipative” one (DCM), applying its complex and expensive ductility requirements. Currently, the preferred method is the former one, because of its simplicity. Such a choice may lead on one side to oversized profiles that are unduly expensive, on the other side to possibly unsafe solutions due to the unpredictable nature of the regions characterized by low-to-moderate seismicity, where rare but strong earthquakes are foreseeable. On the other hand, enforcing engineers to apply strict “high-dissipative” rules seems too conservative for this case, which would result in over-safe, but uneconomic structures. This article proposes an adjusted design approach for the low-to-moderate seismicity design of CBF structures, aiming to satisfy both economy and safety criteria. The proposed approach is based on the exploitation of the three features of CBF systems, which have not been deeply investigated so far: “frame action provided by gusset plates”, “contribution of compression diagonal and its post-buckling strength and stiffness”, and “energy dissipation capacity of non-ductile bracing joint connections”. The paper investigates these aspects by means of incremental dynamic analysis of case studies, based on the numerical models calibrated on full-scale experimental tests published elsewhere by the authors. As a result, it provides design recommendations and presents economic comparisons between the buildings designed with current Eurocode approach and the proposed one.

05.27: Resistance of mono‐axially bent beams of welded I‐sections: FEM verification of Eurocode's buckling curve formulation

ABSTRACTPresent Eurocode's approach to design of steel I‐section beams is based on the analytical resistance evaluation yielding from the interaction resistance criteria established for beam‐columns that cover two design situations: a) the flexural in‐plane failure (second order biaxial bending and compression), and b) the flexural‐torsional out‐of‐plane failure (second order spatial bending, warping torsion and compression). The Eurocode's unified resistance ultimate limit state criteria of I‐sections are depended upon the technological aspects of steel section production via the buckling curve differentiation for the evaluation of reduction factors for buckling in compression and lateral‐torsional buckling in bending about the major axis. This paper attempts to verify the Eurocode's buckling resistance criteria in case of welded I‐section in mono‐axial bending on the basis of finite element simulations and on the separate inclusion of material and geometrical imperfections. The finite element shell model is utilized and built within the ABAQUS software. The Eurocode's resistance criteria are verified by results of FEM simulations in case of moment gradient loading conditions. Concluding remarks in relation to analytical formulations presented in Eurocode 3 are drawn.

Blast effects on steel columns under fire conditions

Detailed finite element modelling of key elements is necessary to improve the robustness assessment of structures subjected to a coupled effect of fire and blast loads. This paper presents a method for a realistic multi-hazard approach by studying the residual load bearing capacity of steel columns under fire conditions and followed by an explosion. The approach adopts the use of a material constitutive law able to take into account both the strain rate sensitivity and the thermal softening. Explicit nonlinear dynamic analyses are performed using the explicit commercial code LS-DYNA. Results show that the residual load bearing capacity is influenced by the stand-off distance. The time of fire loading at which an explosion is triggered is a critical parameter as well. High strain rates in the typical blast range (102 ÷ 103 s−1) are numerically obtained as a consequence of explosions in the close proximity. A comparison with the Eurocode approach is also reported. The results can be of great interest to establish the initial conditions that could potentially lead to the onset of progressive collapse in steel framed structures subjected to a combined effect of fire and blast loadings.

Flexural strength of circular concrete-filled tubes

The flexural strength of circular concrete-filled tubes (CCFT) can be estimated by several codes such as ACI, AISC, and Eurocode 4. In AISC and Eurocode, two methods are recommended, which are the strain compatibility method (SCM) and the plastic stress distribution method (PSDM). The SCM of AISC is almost the same as the SCM of the ACI method, while the SCM of Eurocode is similar to the ACI method. Only the assumption of the compressive stress of concrete is different. The PSDM of Eurocode approach is also similar to the PSDM of AISC, but they have different definitions of material strength. The PSDM of AISC is relatively easier to use, because AISC provides closed-form equations for calculating the flexural strength. However, due to the complexity of calculation of circular shapes, it is quite difficult to determine the flexural strength of CCFT following other methods. Furthermore, all these methods give different estimations. In this study, an effort is made to review and compare the codes to identify their differences. The study also develops a computing program for the flexural strength of circular concrete filled tubes under pure bending that is in accordance with the codes. Finally, the developed computing algorithm, which is programmed in MATLAB, is used to generate design aid graphs for various steel grades and a variety of strengths of steel and concrete. These design aid graphs for CCFT beams can be used as a preliminary design tool.

Performance of unprotected and protected cellular beams in fire conditions

This paper describes an experimental study at elevated temperatures on the behaviour of full-scale composite floor unprotected and protected cellular steel beams with intumescent coating having different size and openings shape. All beams were designed for a full shear connections between the steel beam and the concrete flange using headed shear studs in order to fail in by web-post buckling. In fire, the temperature distribution across a composite member is non-uniform, since the web and bottom flange have thin cross-sections and a greater exposed perimeter than the top flange. The deterioration of the material properties of the web will therefore become an important effect on the overall performance of the member in the event of fire. Fire resistance and protection of cellular beams has been very controversial concerning their behaviour in elevated temperatures, the fire protection material and the required thickness. Two failure temperatures were observed in the fire tests indicated that cellular beams failed by web post buckling and Vierendeel bending associated with the buckling of the web posts of the steel section. The finite element modelling software TNO-Diana was used to complete the numerical investigation. Comparison of the experimental and FEM results is presented and both are in good agreement. However the Euro code approach can be improved by using the correct material specification of the intumescent coating used.

Design of Short Reinforced Concrete Bridge Columns Under Vehicle Collision

This paper presents the behavior of reinforced concrete bridge columns subjected to vehicle collision. An extensive parametric study consisting of 13 parameters was conducted, examining the peak dynamic force and the equivalent static force (ESF) of a vehicle collision with reinforced concrete bridge columns. The ESF was calculated by using the Eurocode approach and the approach of the peak of the 25-ms moving average of the dynamic impact force. The ESFs from these two approaches were compared with the AASHTO load and resistance factor design ESF of 2,670 kN (600 kips). This ESF was found to be nonconservative for some cases and too conservative for others. The AASHTO load and resistance factor design ESF was nonconservative when the vehicle’s velocity exceeded 120 km/h (75 mph) and when the vehicle’s mass exceeded 16 tons (30 kips). This paper presents the first equation that calculates a design impact force, which is a function of the vehicle’s mass and velocity. The equation covers a wide range of vehicle velocities, from 56 km/h (35 mph) to 160 km/h (100 mph), and a wide range of vehicle masses, from 2 tons (4.4 kips) to 40 tons (90 kips). This approach will allow departments of transportation to design different bridge columns for different highways depending on the anticipated truck loads and speeds collected from the survey of roadways. A simplified equation based on the Eurocode equation of the ESF is proposed. These equations do not require finite element analyses.

Critical assessment of Eurocode approach to stability of metal cylindrical silos with corrugated walls and vertical stiffeners

The paper deals with stability of steel cylindrical silos composed of corrugated walls and vertical open-sectional stringers. Comprehensive three-dimensional finite element analyses were carried out with perfect slender, semi-slender and squat silos by means of a linear buckling approach. Corrugated walls were simulated as an equivalent orthotropic shell and vertical open-sectional stringers as beam elements. The FE results were compared with the Eurocode approach. In addition, comprehensive FE computations for axially compressed cylindrical shells composed of an orthotropic shell and stringers were carried out. An improvement of standard formulae was proposed.

Study of Accelerated Production of Prestressed Concrete Sleepers Using Strut-and-Tie Model

When designing the technological process for producing prestressed concrete sleepers on a large scale, it is especially important to achieve substantial reduction of production time due to the economic aspect. In this study, an estimation of the earliest possible time to release prestressing force from the wire with respect to bond development is presented, thus, allowing earlier removal and reuse of a prestressed concrete sleeper formwork. Time-dependent development of concrete compressive and tensile strength is defined according to fib Model Code 2010. A Strut-and-Tie Model has been adapted as a design method for establishing the transmission length required for anchoring prestressed wires in a prestressed concrete sleeper in accordance with the bond stress. Additional calculations have established that the method is consistent with the Eurocode approach.