Euro Code Research Articles

Seismic Behavior of Historical Masonry Bridges: The Case Study of Irgandi Bridge

In Anatolia, numerous bridges have been constructed throughout history for essential reasons. It is important to preserve the bridges and hand them down to the future generations as they have hints regarding the materials and construction techniques used in the past. Irgandi Bridge located on Gökdere in Bursa city, which is the first capital of the Ottoman Empire, has a special importance among bridges around the world. It is one of the few bridges around the world, which have had commercial activities with shops on it along with the purpose of transportation. This symbolic structure in terms of cultural, historical and constructional aspects is located in Bursa which includes 1st degree seismic hazard zone. Therefore, preservation of the bridge requires investigation of its seismic performance and taking necessary precautions. Irgandi Bridge was modeled by ANSYS software using finite element method (FEM). Convergence study was performed to determine the accurate number of elements. Modal and linear dynamic analysis of the Irgandi Bridge was conducted after the number of elements were determined by the convergence study. Therefore, seven earthquake records were scaled and performed to the system according to EC-8 (Eurocode-8). Stress distributions and displacements were examined as a result of linear dynamic analysis. It was determined that the maximum displacement occurred at the top of the bridge and the principal stress occurred in the support regions. As a result of the analyses, it was proposed to strengthen the support parts of the bridge, which were determined to be damaged under earthquake impact.

A comparative study of beam design curves against lateral torsional buckling using AISC, EC and SP

Introduction. Structural stability is an essential part of design process for steel structures and checking the overall stability is very important for the determination of the optimum steel beams section. Lateral torsional buckling (LTB) normally associated with beams subject to vertical loading, buckling out of the plane of the applied loads and it is a primary consideration in the design of steel structures, consequently it may reduce the load currying capacity. Methods. There are several national codes to verify the steel beam against LTB. All specifications have different approach for the treatment of LTB and this paper is concentrated on three different methods: America Institute of Steel Construction (AISC), Eurocode (EC) and Russian Code (SP). The attention is focused to the methods of developing LTB curves and their characteristics. Results. AISC specification identifies three regimes of buckling depending on the unbraced length of the member ( Lb ). However, EC and SP utilize a reduction factor (χ LT ) to treat lateral torsional buckling problem. In general, flexural capacities according to AISC are higher than those of EC and SP for non-compact sections.

Reinforced recycled aggregate concrete slabs: Structural design based on Eurocode 2

This paper presents the design of simply supported one-way recycled aggregate concrete slabs in compliance with Eurocode 2 (EC2), to illustrate the design process of slabs with these materials. Calculations were based on various evidence-based assumptions from previous studies, namely the effect of incorporating RA on several properties of concrete. The design process followed conventional methods and the solutions were attained by altering the geometry of the slab’s cross-section to exhibit the same pre-determined service life, load bearing capacity and deflection limit in accordance with the ultimate limit state and serviceability limit state of EC2. Four variables were evaluated: increasing incorporation of recycled aggregates with different quality classes; two environmental exposure classes; choice of maintaining target strength class or accepting loss with increasing recycled aggregates; structural design in conservative vs. average conditions. The results showed that an increase to nominal cover and slab thickness was required with increasing replacement level, in order to maintain the same service life and mitigate deflection, the effect of which was most impacted using lower quality recycled aggregates. Between the two exposure classes, marginal relative changes were observed with the incorporation of recycled aggregates. Maintaining target strength was found to be a more practical approach and with less changes to the slabs’ cross-section dimensions. As expected, using the values corresponding to the fiftieth percentile, obtained in previous studies involving meta-analyses of data, resulted in less changes to the geometry of the slabs’ cross-section. Nevertheless, several cases in more conservative settings also required minimal alterations to limit maximum deflection within the EC2′s serviceability limit state.

Coupled element and structural level optimisation framework for cold-formed steel frames

Optimisation of cold-formed steel (CFS) structures can be challenging due to the complex behaviour of thin-walled CFS sections affected by different buckling modes. In this paper, a coupled framework is presented for element and structural level optimisation of CFS portal frames, under serviceability limit state (SLS) and ultimate limit state (ULS) conditions, using Genetic Algorithm. First, CFS lipped-channel beam sections are optimised with respect to their flexural capacity determined in accordance with the effective width method specified in Eurocode 3 (EC3). The relative dimensions of the cross-section are considered as the main design variables, while the EC3 plate dimensions and slenderness limits and a number of manufacturing and end-use constraints are taken into account in the optimisation process. The results show that the optimum CFS sections exhibit significantly higher (up to 84%) ultimate capacity compared to the standard lipped channel sections with the same plate width and thickness. The structural level optimisation is then carried out to obtain the optimal design solution for a long-span CFS portal frame with knee braces under SLS and ULS conditions. Compared to conventional optimisation using standard cross-sections, it is shown that the proposed coupled framework leads to more cost-effective solutions (up to 20% less structural material) by using the more efficient CFS cross-sectional shapes optimised for generic applications. The results also indicate that optimising the frame geometry and knee brace configuration can noticeably improve the structural performance and reduce the required structural weight, especially when both ULS and SLS conditions are considered.

Experimental study on time-dependent deformation of hybrid steel–PRC girder with headed stud shear connections under sustained loading

In a hybrid girder, the connections at the steel–prestressed reinforced concrete (steel–PRC) junction must be designed to resist steel–concrete interfacial tensile and shear forces. Headed stud shear connections are most commonly and widely used for such an application. In Japan, the Japan Road Association specifies a stud capacity that is 0.12, 0.13, and 0.22 times those of the American Institute of Steel Construction, Japan Society of Civil Engineers, and EURO code specifications, respectively. Hence, in Japan, the existing design method uses less than 50% of the actual nominal shear capacity of connectors. Owing to a low design shear force, the influence of sustained loads has not yet been considered nor studied comprehensively. Moreover, in a hybrid girder, the prediction of the time-dependent deformation behaviour under sustained loading is crucial for ensuring serviceability; however, few studies have focused on this subject. Five scaled-down hybrid steel–PRC girder specimens of a real bridge with headed stud connections were tested under sustained and static loads. The time-dependent deformation behaviour was sensitive to the exposure time, previous loading history, prestress level, concrete strength, and creep and shrinkage phenomena. The results of this study provide an important basis and reference data for designing such girders while considering their long-term response with time effects.

Nonlinear Finite Element Analysis of Punching Shear Strength of Eccentrically Loaded RC Flat Slabs with Opening

The aim of this paper is to investigate the influence of eccentric load and the presence of an opening near the column on the punching shear strength of reinforced concrete (RC) flat slab without shear reinforcement using analytical investigation and numerical simulations. A model based on the finite element method is proposed and its validation is confirmed in this study, by comparing the results with the existing experimental studies available in published literature. Twenty slabs supported directly on columns were analyzed, along with variation of load and opening position in the slab. The punching shear strength for all slabs was calculated according to Eurocode 2 (EC2) and numerically. It was found that the obtained punching shear strength was significantly underestimated by EC2. In addition, this research has shown that the opening position in relation to the direction of the bending moment caused by the eccentric load significantly affects the punching shear strength, while EC2 neglects this position.

Tests of CHS-to-SHS tubular connections in stainless steel

A test program was conducted in this study on hybrid tubular T-, Y- and X-connections made of circular hollow section (CHS) braces and square hollow section (SHS) chord in stainless steel. A total of 18 specimens including 4 T-, 5 Y- and 9 X-connections were tested by applying axial compression to the end of circular brace. The failure modes, failure strengths and deformation curves of all specimens were obtained from experimental investigation. The influences of the key geometrical parameters including the brace diameter/chord width ratio (β), the brace/chord thickness ratio (τ), the chord width/thickness ratio (2γ) and the inclined angle (θ) between brace and chord on the load-carrying capacities of CHS-to-SHS tubular connections in stainless steel were carefully evaluated. Experimental results show that the initial stiffnesses and the failure strengths of hybrid tubular T-, Y- and X-connections increased with the increment of the β value, and increased with the decrement of the θ value. However, the influences of other geometrical parameters of τ and 2γ on the initial stiffnesses and the failure strengths are insignificant. Furthermore, the test strengths are compared with the nominal design strengths calculated using the design formulae of the current design specifications including CIDECT, Eurocode 3 (EC3), Australian/New Zealand Standard (AS/NZS) and Chinese Code, in which AS/NZS is the only design guideline for stainless steel structures. The comparison indicates that the design formulae of CIDECT, EC3 and Chinese Code are all conservative, in which the design formulae of EC3 are most conservative with the largest scatter of predictions. While, the design formulae of AS/NZS are generally appropriate for CHS-to-SHS tubular connections in stainless steel.

Experimental Investigation on Behavior of High-Strength Light weight Concrete-Filled Steel Tube Strut Under Axial Compression

This investigation was conducted for experimental and analytical study on the behavior of lightweight concrete-filled steel tube strut (short column) concentrically loaded in compression to failure. Sintagg (expanded clay aggregates) light-weight aggregate was used to prepare high-strength structural lightweight concrete of 40 N/mm2 grade. Sixty-four specimens were tested to failure to investigate the axial compressive behavior of lightweight concrete-filled tube strut (LWCFT). Different strut lengths, sectional sizes, and thickness were used to enumerate the influence of member geometry and constituent material properties on the structural behavior of CFT struts. Ultimate strength results were compared to current specifications governing the design of concrete-filled steel tube struts. This investigation provided a review of the current design rules for concrete-filled sections in Euro code 4 (EC4) and American standards (AISC). Consequently, deadweight of strut member was reduced by 25.30% as compared to normal concrete-filled steel tube strut. The buckling failure pattern for square CFT strut was observed as local buckling takes place, while for circular and rectangular CFT struts plastic buckling takes place. Also, it was observed that the experimental results were adequate to predict the current design specifications. Experimental results suggest that circular tubes offer substantial post-yield strength and stiffness, not available in most square or rectangular cross sections. The calculated confining strengths show that Euro Code-4 provides more realistic results than in case LWCFT strut under axial compression.

Optimum Design of Cold‐formed Steel Beams: Particle Swarm Optimisation and Numerical Analysis

ABSTRACTCold‐formed steel (CFS) members, when subjected to optimisation, can significantly increase their ultimate load carrying capacity leading to a more economical and efficient structural system. This paper presents the details of an investigation on optimisation of CFS beams subjected to bending capacity and an investigation of shear and web crippling capacities of optimised sections. The optimisation was aimed to meet construction constraints reported in Eurocode 3 (EC3). In this research, 4 different CFS sections were considered including the introduction of 2 novel sections (Super Sigma and Smart Beam) which has closer shear center to the web and less susceptible to web buckling. The bending capacity of the available sections were obtained based on the effective width method reported in EC3, while the optimisation procedure was performed using particle swarm optimisation (PSO). The capacities of the optimised CFS beams were also obtained using the nonlinear finite element (FE) analysis and the FE results were compared with EC3. The FE results showed that the Smart beam and Super Sigma claim dual advantage of increase in section moment capacity and restrain against torsional effect than the conventional CFS channel sections with the same amount of material. These optimised cold formed steel beams can be employed in light gauge steel building constructions.

The influence of joint modelling on the seismic design of steel frames

ABSTRACTJoints play an important role in design and performance of steel structures. Recently, two European projects, EQUALJOINTS (1) and EQUALJOINTS+ (2), addressed seismic prequalification of four types of moment resisting beam‐to‐column joints: extended end‐plate joints with haunches, stiffened and unstiffened extended end‐plate joints and dog‐bone joints. Beam‐to‐column joints with haunches are frequently employed by structural engineers in seismic design of steel moment resisting frames. Their large stiffness and strength allows coping with stringent drift limitation requirements and avoiding experimental validation of partial‐strength/semi‐rigid ones requested by Eurocode 8 (EC8). In current design practice, when modelling steel frames, the finite size of the joints is often neglected for the reasons of simplifying the task. The present paper examines the potential benefits of explicitly modelling beam‐to‐column joints with haunches in structural analysis, and aims at identifying possible simplifications of the structural model, accounting the advantages, but, at the same time, keeping the model as simple as possible. Two types of steel structures are addressed within this study: moment resisting frames and dual frames combining moment resisting frames with eccentrically braced frames. The two configurations are designed and their seismic performance is assessed, using different modelling approaches.

Equivalent-Resistance-Capacity-Method (ERCM) for the design of steel Elliptical-Hollow-Sections (EHSs) under axial compression

The robustness of the equivalent Circular-Hollow-Section (CHS) diameter expressions for the Elliptical-Hollow-Sections (EHSs) under pure axial compression proposed in earlier studies is assessed and found to be conservative and inconsistent with respect to the Eurocode 3 (EC3) CHS cross-section classification criteria. Thus, to promote consistent application of the cross-section slenderness parameter limits and design strength curves specified for CHSs, also to the EHSs, an improved empirical expression for the equivalent CHS diameter is derived in this study using the results of EHS stub column analyses from the literature, based on a novel Equivalent-Resistance-Capacity-Method (ERCM). Additionally, a unified empirical expression based on the Direct-Strength-Method (DSM) approach for predicting the axial compressive capacity is also determined by using an exhaustive data of EHS and CHS stub-column analyses from the literature.

Compression capacities of cold-formed high strength steel tubular T-joints

The paper presents a test programme on cold-formed high strength steel tubular T-joints with fully supported chord members. The T-joints consist of brace members made up of square, rectangular and circular hollow sections, while chord members were made up of square and rectangular hollow sections. The T-joints were fabricated by both brace and chord members made up of square and rectangular hollow sections as well as circular hollow section braces were welded to square and rectangular hollow section chord members. The brace and chord members were welded by semi-automatic gas metal arc welding process. The steel grade of 900 MPa was used for the square, rectangular and circular tubular members, while the steel grade of 960 MPa was used for the square and rectangular tubular members only. A total of 22 tests was conducted where an axial compression was applied through the brace members, while the chord members were resting on a solid flat base. The ratio of brace-to-chord width (β) ranged from 0.33 to 1, brace-to-chord thickness (τ) from 0.53 to 1.27, chord width-to-thickness (2γ) from 20.6 to 38.7, and chord side wall slenderness (h0/t0) from 12.7 to 38.6. The test results were compared with the nominal strengths obtained from the Eurocode 3 (EC3) and CIDECT for the assessment of the existing design rules for tubular T-joints with fully supported chord members. It is found that the existing design rules are not applicable for the design of cold-formed high strength steel tubular T-joints with fully supported chord members.

Coefficient of Moment of Inertia for Ribbed RC Slab Beams

During the design process of monolithic ribbed slabs, engineers face a common issue how to correctly evaluate stiffness of the beams. When Bar and Plate elements are used for analysis of the slabs, the neutral axis of those members are in the same level, therefore the stiffness of (T) shape cross-section is not considered correctly in the calculations. In this case the internal forces are obtained incorrectly as well as deflections of the beams are overestimated. A simple method is discussed in this paper, which allows engineers to calculate internal forces and deformations of mentioned type slabs more accurately with FEM programs by using Bar and Plate elements. The method is based on Bar elements moment of inertia adjustment. After the comparative analysis of differences between moment of inertia of (T) and (+) shape cross-sections as well as deflection discrepancies, the adjustment coefficient expression is presented. In order to reflect the actual behaviour of ribbed slabs even more accurately the influence of shear deformations is also considered. In this case not only the member geometry but the material properties, loading scheme and even supports are taken into account in the calculations of the adjustment coefficient. Selection of the most appropriate (effective) flange width of (T) shape cross-section is also analysed in this paper. Comparative calculations were done using different effective flange widths beff calculated by EC2 (Eurocode 2), “STR” (Lithuanian Construction Technical Regulations) and ACI (American Concrete Institute) methods. In order to assess the reliability of the proposed calculation method and the calculation results all plates were also analysed using Solid elements. Application of the presented expressions of moment of inertia coefficient will allow engineers to evaluate stiffness of (Γ) and (T) shape cross section beams simply, fast and accurately enough for most of structural engineering calculations.

Tests of cold-formed high strength steel tubular T-joints

The paper presents an experimental investigation on cold-formed high strength steel tubular T-joints. The fabricated T-joints include brace members made up of square, rectangular and circular hollow sections, while chord members were made up of square and rectangular hollow sections. The nominal yield strengths of square and rectangular tubular members were 900 and 960 MPa, while the nominal yield strength of circular tubular members was 900 MPa. Two configurations of tubular joints were fabricated, first, where both brace and chord members were made up of square and rectangular hollow sections, and second, where circular hollow section braces were welded to square and rectangular hollow section chord members. The brace and chord members were joined together by automatic gas metal arc welding process. In total, 24 tubular T-joint tests were conducted where an axial compression was applied through the brace members of the T-joints, while the ends of the chord members were supported on rollers. The ratios of brace-to-chord width (β) ranged from 0.34 to 1, brace-to-chord thickness (τ) ranged from 0.52 to 1.27 and chord width-to-chord thickness (2γ) ranged from 20.63 to 38.55. The resistances and deformations of tubular T-joints were carefully examined. In order to evaluate the applicability of the existing design provisions for high strength steel tubular T-joints, test results were compared with the nominal strengths obtained from the Eurocode 3 (EC3) and CIDECT. It is shown that the existing design provisions are not capable of providing accurate and reliable predictions for the design of cold-formed high strength steel tubular T-joints made up of S900 and S960 steel grades.

On the value of a reliability‐based nonlinear finite element analysis approach in the assessment of concrete structures

AbstractThe objective of this paper is to explore the value of reliability‐based nonlinear finite element analysis (NLFEA) over the currently available, standardized assessment methods. To our knowledge, no studies are available on this subject, and this paper provides a first insight into the value and reliability level of these assessment methods. The exploration is illustrated through three reinforced concrete structural members: a continuous girder, a continuous deep beam, and a high‐strength deep beam. The analysis is performed gradually: step by step advancing the approximation level of the mechanical and the probabilistic models. The added value of the reliability‐based NLFEA over the semi‐probabilistic Eurocode (EC) method is found to be on average 0.60. In other words: even if according to the semi‐probabilistic EC method the design action (Ed) is 60% higher than the design resistance (Rd), the compliance with the target reliability criterion can be demonstrated by a reliability‐based NLFEA. Furthermore, it is observed that the gain and its cause (i.e., more advanced mechanical or probabilistic models) are different for the three cases. Though this outcome is restricted to the analyzed cases and should be interpreted as an upper limit added value, it indicates that a more detailed physical representation of the problem and an explicit treatment of uncertainties may uncover substantial reserves compared with the currently available, standardized assessment methods. Hence, the reliability‐based NLFEA method offers a promising alternative in the assessment of existing structures, enabling to avoid expensive measures that might be needed based on simplified methods.

Tests of Slab-Column Connections Subjected to Reversed Cyclic Moments in Addition to Different Levels of Gravity Shear Load

Reinforced concrete flat slab-column structures are widely used because of their practicality. However, this type of structures can be subjected to punching-shear failure within the slab-column connections. Without shear reinforcement, the slab-column connection can undergo brittle punching failure, especially when the structure is subjected to lateral loading in seismic zones. This research is a part of an extensive investigation about the punching shear behaviour of interior RC slab-column connections under seismic loading. The main objective is to discuss the effect of the gravity shear level on the punching shear behaviour[1].The current paper represents only the results of the first four tested specimens without shear reinforcement. The first specimen was tested subjected to vertical gravity load only without cyclic loading while the other three specimens were tested under different vertical loads V which was kept constant during testing in addition to a reversed displacement controlled cyclic loading which was increased up to punching shear failure. The gravity load V was chosen as 0.4, 0.6 and 0.8 V0 respectively, where V0 is the vertical load causing punching shear failure according to ACI318-14[2]. All tested specimens have the same slab dimensions of 2000x2000mm, slab thickness 200mm, flexural reinforcement ratio of 1.62% and the same column dimensions 250mm x 250mm. Finally, the experimental results are analyzed and compared to international codes such as American Code ACI318-14 and Euro Code EC2-2004[3]. In light of these results, some preliminary conclusions are presented.

REINFORCEMENT OF THE BRIDGE RABOVCE

The overall objectives of the project is to identify and describe the repair and strengthening bridges on the N2 Road, on Rabovce on the road Pristina – Blace section, in order to meet the required level of safety and service for international heavy road traffic. This in accordance with the design criteria of Euro code.Optimal repair and strengthening methods are sought considering the entire assemblage of bridges. Alternative methods may be described for the individual bridge, if relevant. If possible, the total amount of repair and strengthening works will be described as a set of additive works in such a way that the parts of works to be carried out in the near future can be selected. These works should then be selected dependent on a prioritisation of aspects related to load capacity, traffic safety and durability.The repair and strengthening works are defined from comparison of the actual condition of the bridges with the requirements as laid down in Euro codes. The condition of the bridge is evaluated by considering the condition of the structural elements combined with an estimation of the load bearing capacity of the bridge.

Earthquake loss assessment of steel moment-resisting frames designed according to Eurocode 8

Current design and assessment guidelines define several seismic performance levels, aiming to ensure that structures exhibit adequate behaviour at different seismic intensity levels. Typically, the acceptance criteria at different performance levels are met by ensuring that local deformation demands are lower than pre-defined capacities. Despite the proven effectiveness of such an approach, it provides an ambiguous measure of the performance of the building, which, in most cases, is neither meaningful nor appropriate for building owners, stakeholders or decision-makers. The main objective of the research presented in this paper is to evaluate the expected direct economic seismic losses of steel moment-resisting frame structures designed according to Eurocode 8 (EC8). A set of 120 archetype buildings, representative of the current building stock in Portugal, were designed according to Part 1 of EC8 using three different behaviour factors, q: a) code-prescribed upper bound limits for medium and high ductility classes; b) behaviour factor defined according to an Improved Force-Based Design (IFBD) procedure. The PEER-PBEE methodology with the improvements proposed by Ramirez and Miranda [1] was employed for the estimation of expected seismic losses evaluated for the seismic intensity levels considered in Part 3 of EC8. The results obtained indicate that the buildings designed in accordance with EC8 comply with the non-collapse criteria. However, the level of damage could imply significant repair costs. Importantly, the results also highlight that a rational selection of the behaviour factor can result in a reduction of steel weight but still ensuring acceptable levels of expected annual losses.

Structural behavior of self – drilling screws applied in steel structures of prefabricated buildings

Since the fast development of prefabricated building industry facilitate the light thin – walled steel application in both low residential building and fast construction, better understanding of the labour intensive fabrication of connection indicates the problems of optimized connection design and reduced manufacturing cost can be addressed. Several parameters such as number of screws and configurations of the screw layout were varied to study the impact on shear strength. Since the connection strength governs the structural behavior of the truss system which is the main part of modern thin – walled steel structure, the connection strength is calculated according to the American Iron and Steel Institute (AISI), Euro code, and Chinese specification respectively. The main failure mode occurred in self – drilling screw connections are found to be the tilting and bearing failure based on 84 single lap shear test. All testing specimens have experience four stages. When the spacing is fixed to certain number and the screw is less than six, the effect of configuration patter on the resistance capacity is very limited. In contrast, if the screw number is more than six, certain patter layout could lead to better overall strength compare with normal layout patter and the group effect factor is becoming as a constant. The strength of connection can be increased by enlarging the screw spacing with certain range.

Shear Behaviour of Reinforced Self-Compacting Concrete Beams Made with Treated Recycled Aggregate

In this paper, an experimental work was conducted to investigate the possibility of improving the structural performance of reinforced self-compacting concrete (SCC) beams cast with 100% treated and untreated recycled aggregate (RA). RA was first exposed to a simple treatment method to reduce the amount of its adhered mortar and to improve its performance by the impregnation in polyvinyl alcohol (PVA) polymer solution. After completing RA treatments, rectangular simply supported reinforced SCC beams cast with RA, treated recycled aggregate (TRA) as well as normal aggregate (NA), were prepared and tested under two-point loading up to failure. Half of the prepared beams were tested to evaluate the shear behaviour of normal strength (NS) SCC mixes, while the other half was tested for high strength (HS) SCC mixes. The results were evaluated with regards to load deflection response, ultimate failure load, first crack load, and cracking pattern. The main experimental results demonstrated that using treated RA considerably improved the shear capacity of reinforced SCC beams in comparison with that of untreated RA. Based on the ACI 318-14 and Euro codes, the shear strength values showed that the treated RA beams were considered more conservative compared to the RA beams in both strength grades.