Euro Code Research Articles

11.44: An integrated experimental and numerical assessment of force‐based design for concentrically braced steel frames

ABSTRACTThis study uses an integrated experimental and numerical approach to assess the use of the force‐based design (FBD) methodology presented in Eurocode 8 (EC8) for multi‐storey steel concentrically‐braced frames (CBFs).In the EC8 approach, the design seismic action is defined by first generating an elastic response spectrum. This spectrum is reduced to create the design spectrum by applying an appropriate behavioural factor (q) to account for energy dissipation. The value of q chosen depends on the form of the lateral‐load resisting structure, the structural material(s) to be used, the ductility class and the degree of irregularity in the structural layout. The design base shear force calculated from the design spectrum is used to estimate the seismic forces on the structure and hence determine the final member cross‐section sizes.In this study, the FBD approach to the design of structures presented in Eurocode 8 is described and applied to 4‐ and 8‐storey CBF structures. Both dissipative (Ductility Class High – DCH) and non‐dissipative (Ductility Class Low – DCL) design is considered for each structure.A numerical modelling approach developed using the OpenSees seismic analysis software and validated from a series of full‐scale experimental tests of single‐storey CBFs is outlined. The two‐dimensional reference model assigns appropriate out‐of‐plane rotational stiffnesses to the ends of the bracing members based on the strength and geometry of gusset plates specified.The experimental work used to validate the model, carried out as part of the BRACED transnational research project funded by the European Commission's Seventh Framework Programme (FP7) is briefly described. The experimental observations support model validation at different levels of earthquake ground motion including elastic, inelastic and ultimate response conditions.The validated numerical modelling approach is used to perform a series of non‐linear time history analyses (NLTHA) of the designed 4‐ and 8‐storey frames by subjecting them to appropriately scaled simulated ground motion accelerations. The key recorded responses of the NLTHA of the modelled frames (displacements, drift, brace forces and ductility demands) are compared, and the implications of the assumed energy dissipations are discussed.

04.02: Plastic behaviour of polygonal hollow sections in bending

ABSTRACTSteel poles of polygonal sections are an economic alternative to circular hollow sections for use as lighting towers or transmission line pylons. Especially for transmission lines, the design of the poles is intended to become more compact to avoid land usage and to obtain an inconspicuous appearance. If the pole diameter is reduced, the slenderness of the sections needs to be reduced as well to achieve the desired resistance, but an increasing wall thickness disproportionately reduces the cost‐effectiveness of the structure. The European design rules for overhead electrical lines [1] do not allow using the plastic behaviour of stocky sections, which reduces the advantages of compact sections.In modern standards for steel structures, such as Eurocode 3 (EC3) [2], activating plastic reserves is generally acknowledged state of the art. According to EC3‐1‐1, the slenderness of the profile decides on the allocation to cross section class 1 or 2, where plastic design is allowed, class 3, where only elastic behaviour is used or class 4, where local buckling is assumed. When changing from class 2 to class 3 sections, this standard provides a sudden drop in resistance, which has long been recognised to be unjustified. Research has been done to overcome this mismatch for circular hollow sections [3].In this paper the transition between the plastic bending moment capacity and the limit state of buckling is investigated to identify the ultimate load of polygonal sections. The investigated polygon of 16 edges can be treated as a collection of plate strips using the plate buckling design rules EC3‐1‐5 for cross sections class 4. Detailed examinations illustrate the inconsistency of EC3 in the bending capacity of compact sections right before the start of stability problems.On the basis of experimental data gained from full‐scale bending tests, along with imperfection measurements via laser scanning, numerical investigations have been performed. These results suggest that the bending moment capacity can be increased above the calculated elastic capacity with more compact sections, but might be overestimated when calculating the full plastic capacity according to EC3‐1‐1.

Design Guideline for Shear Strengthening of Reinforced Concrete Beam Using CFRP Strip to Eliminate Debonding Failure

Background: Design guideline to obtain the dimension of CFRP laminate for eliminating premature deboning failure is vital to acquire the ultimate strength of shear strengthened reinforced concrete beam. Objectives: The main objective of this research is to offer a design guideline for shear strengthening of reinforced concrete beam using CFRP laminate by eliminating debonding failure. Methods/Statistical Analysis: In the guideline, the design strain of CFRP laminate was obtained based on the bond strength of concrete and finally the beam was designed for shear in accordance with Euro Code (EC 2). To verify the guidelines, three reinforced concrete beams were experimentally investigated including un-strengthened control beam, beam strengthened with proposed guideline and beam strengthened in accordance with ACI 440. Findings: Results showed that the strengthened beam with proposed guideline prevented the complete separation of CFRP shear strips before failed by flexure. The strains of CFRP laminate were found to be compatible with shear reinforcement. Strengthened beam of proposed guideline had 35% and 20% higher failure loads as compared to un-strengthened control beam and strengthened beam with ACI guideline respectively. In terms of design parameters, the proposed guideline had been satisfactorily verified through experimental investigations. Application/Improvements: The proposed guideline is recommended for shear strengthening of RC beam using CFRP laminate. However, future research is suggested to further investigate the effects of concrete cracks on bond strength of concrete. Keywords: CFRP Laminate, Debonding, Design, Shear Strengthening

Investigation of minimum shear strength of reinforced concrete elements without transverse reinforcement

The paucity of experimental research and several incongruences in boundary conditions of actual sectional design procedures of empirical nature may raise doubts about the validity of the minimum value for the shear strength of reinforced concrete members in Eurocode 2 (EC‐2). Although a minimum reinforcement due to bending is supposed before shear strength checking, EC‐2 Commentary gives an explanation about a conservative value for a minimum on the basis of the tensile strength of the concrete. This manuscript highlights the gaps in the state of present knowledge and incorporates a new proposal.

Suggestion for allowable additional compressive stress based on track conditions

A continuous welded rail has immovable zones due to its structural characteristics. In an immovable zone, thermal expansion and contraction of rails are restricted when the temperature changes, thereby causing excessive axial force on the rail. When the immovable zone of the continuous welded rail is located on a bridge, additional stress and displacement occur through track–bridge interactions. Additional stress and displacement of the rail compared to the embankment area are restricted when constructing the bridge under the continuous welded rail track to prevent problems with the track–bridge interaction according to UIC 774-3R and Euro codes. According to the various codes, the maximum allowable additional compressive stress is 72 MPa, with the conditions of a curve with a radius (R) ≥ 1500 m, UIC 60 continuous welded rail (tensile strength of at least 900 MPa), ballasted track with concrete sleepers and 30 cm of deep for a well-consolidated ballast. However, the lateral resistance that has the greatest effect on track stability can depend on the conditions mentioned above. Therefore, an additional review of various track conditions is required. In this paper, an evaluation of the current criteria was performed using the minimum buckling strength calculation formula, and the allowable additional stress on the rail suggested by codes could only be used on tracks with a large lateral resistance above 18 kN/m/track. Thus, a three-dimensional nonlinear analysis model was developed and analyzed to calculate the allowable additional compressive stress considering various track conditions. According to the results of the analysis, the allowable additional compressive stress was reduced with a comparatively small lateral resistance. The freedom of design can be enhanced with respect to the parameters of various track and bridge conditions using this model.

EXPERIMENTAL AND ANALYTICAL COMPARISON OF TORSION, BENDING MOMENT AND SHEAR FORCES IN REINFORCED CONCRETE BEAMS USING BS 8110, EURO CODE 2 AND ACI 318 PROVISIONS

This study investigated the effect of combined actions of torsional moments, bending moments and shear forces in reinforced concrete beams with concrete compressive strength of 30N/mm 2 . The ultimate torsional moments, bending moments, and shear forces of the beams were determined experimentally, through a simple test arrangement set-up on fifteen beam specimens grouped from BC1 to BC5, three beam specimens in each group. The combined loads were induced by loading the test beams at an eccentricity of  from the beam’s principal axis at the mid-span, using Computerized Universal Testing Machine TUE-C-100. BS 8110, Euro code 2 and ACI 318 were used to calculate the ultimate torsional moments provided by both longitudinal and transverse reinforcements, bending moments and shear forces induced. The values obtained from the codes were compared with those of experimental results for validation. It was observed that Eurocode 2 predicted the highest bending moment of 21.1530kNm, the highest torsional moments of 9.8470kNm and 12.6193kNm, for torsional resistance provided by longitudinal and transverse reinforcements respectively, at an angle crack of 45°, while BS 8110 predicted the least values. ACI 318 predicted the highest value of internal shear forces that the beams possessed before yielding to the applied loads.  http://dx.doi.org/10.4314/njt.v36i3.7

EXPERIMENTAL AND ANALYTICAL COMPARISON OF TORSION, BENDING MOMENT AND SHEAR FORCES IN REINFORCED CONCRETE BEAMS USING BS 8110, EURO CODE 2 AND ACI 318 PROVISIONS

This study investigated the effect of combined actions of torsional moments, bending moments and shear forces in reinforced concrete beams with concrete compressive strength of 30N/mm2.The ultimate torsional moments, bending moments, and shear forces of the beams were determined experimentally, through a simple test arrangement set-up on fifteen beam specimens grouped from BC1 to BC5, three beam specimens in each group. The combined loads were induced by loading the test beams at an eccentricity of  from the beam’s principal axis at the mid-span, using Computerized Universal Testing Machine TUE-C-100. BS 8110, Euro code 2 and ACI 318 were used to calculate the ultimate torsional moments provided by both longitudinal and transverse reinforcements, bending moments and shear forces induced. The values obtained from the codes were compared with those of experimental results for validation. It was observed that Eurocode 2 predicted the highest bending moment of 21.1530kNm, the highest torsional moments of 9.8470kNm and 12.6193kNm, for torsional resistance provided by longitudinal and transverse reinforcements respectively, at an angle crack of 45°, while BS 8110 predicted the least values. ACI 318 predicted the highest value of internal shear forces that the beams possessed before yielding to the applied loads. http://dx.doi.org/10.4314/njt.v36i3.7

Punching shear behavior of recycled aggregate reinforced concrete slabs

Preservation of environment and natural resources has recently attracted researchers to study the use of recycled aggregates from demolished concrete in new concrete structures. This paper presents an experimental study on punching shear behavior of simply supported natural and recycled coarse aggregate concrete slabs. The punching shear behavior of interior slab–column connection in flat plates is tested in “The Reinforced Concrete Laboratory of the Faculty of Engineering, Alexandria University”. Eight two-way slab specimens using two different types of aggregate “natural and recycled” and two aggregate nominal sizes (12.5 and 25mm) were cast and tested to failure. The slabs were designed such that they would fail in punching shear only. The experimental work was conducted on (6) recycled coarse aggregate concrete (RCAC) slab specimens and (2) natural coarse aggregate concrete (NCAC) slabs. All the slabs were simply supported on four edges and tested under a central patch load. The ACI mix design procedure was adopted to achieve strength of concrete at 28days of 35MPa. Four concrete mix proportions were used with (0%, 30%, 60% and 100%) replacement of natural coarse aggregate with recycled coarse aggregate for each aggregate size. The test results showed that the first punch crack load, ultimate punch load, stiffness and energy absorption decrease as the replacement of natural coarse aggregate with recycled coarse aggregate increases. Also as the recycled aggregate size increases the cracking and failure load increases. The measured ultimate failure loads have been compared with code predictions (ECP 203, ACI 318, JSCE code, Euro code 2 and yield line theory). The Euro code – 2 equations gave the best correlation with the experimental results.

Seismic design criteria for Chevron CBFs: European vs North American codes (Part-1)

Chevron concentrically braced frames are one of the most cost-effective solutions for seismic resistant steel buildings. Therefore, this system is widely used in Europe and North America. Both European and North American codes adopt capacity design rules aiming at enforcing the dissipative behaviour into the braces and at preventing the damage in the remaining structural members. However, in order to achieve this purpose, European and North American codes recommend some different requirements and detailing rules, which substantially influence the overall performance and energy dissipation capacity. The research presented in this paper is addressed (i) to verify the effectiveness of the design requirements prescribed by Eurocode 8 (EC8) compared to North American codes (i.e. both AISC 341 and CSA-S16), (ii) to identify the criticisms of EC8 needing revision and upgrading. In order to achieve these objectives, a comprehensive parametric numerical study based on nonlinear dynamic analyses is carried out. 2D frames extracted from low, medium and high-rise buildings are analysed and the main structural parameters affecting the performance against lateral loads are described and discussed. The critical review of the examined standards and the discussion of numerical results highlight that the design rules given by North American codes are more effective than those recommended by the current version of EC8. In particular, EC8-compliant frames show the poorest energy dissipation capacity with tension bracing members almost in elastic range and severe demand on those in compression. On the contrary, both CSA- and AISC-compliant cases exhibit satisfactory energy dissipation capacity.

Minimum cost plastic design of steel beams using Eurocode 3

This paper presents a model for minimum cost plastic design of steel beams according to the Eurocode3 (EC3). The objective function comprises material cost and fabrication costs. The constraint functions are set to meet design requirements of Eurocode3 (EC3). They consist on plastic bending resistance constraints, plastic vertical shear resistance, design constraints derived from Eurocode3 (EC3), deflection due to both dead and live loads and current practices rules.The minimum cost plastic design process is developed through the use of the Generalized Reduced Gradient (GRG) algorithm. Two numerical examples are given to illustrate the applicability of the proposed model. The optimized results are compared to traditional design solutions from conventional design office methods to evaluate the performance of the developed cost model. Substantial savings were achieved through this approach. In addition, this study shows the difference between steel beams optimized for minimum cost and minimum weight. The proposed approach is practically simple, reliable and computationally effective compared to classical designs procedures used by designers and engineers.

A finite element approach to develop track geometrical irregularity thresholds from the safety aspect

Riding quality and safety of rail tracks are directly influenced by track geometry; hence, their degradation along time could reduce safety and cause serious accidents. Standards propose thresholds for track geometrical parameters to keep track safety and riding comfort at an acceptable level. In this study, a method is proposed to select or define a set of proper thresholds for geometrical parameter irregularities according to desirable to safety level. The impact of track geometry irregularities on the derailment index has been investigated through the finite element model. The results suggest that twist and gauge shortage have a greater effect on the derailment index compared to the vertical profile of the track. Having the critical values of geometrical irregularities that result in derailment, safety factors of Iranian and Euro code standards in determining their thresholds are calculated and compared. It is shown that each standard has a unique set of safety factors that depend on speed and geometrical parameters.

Cost optimum design of doubly reinforced high strength concrete T-beams

This paper presents a method for optimizing the design cost of a doubly reinforced High Strength Concrete (HSC) T-beam. The objective function used in the model includes the costs of HSC, steel and formwork. The constraint functions are set to satisfy design requirements of Eurocode 2 (EC-2). The cost optimization process is developed by the use of the Generalized Reduced Gradient algorithm. An example problem is considered in order to illustrate the applicability of the proposed design model and solution methodology. It is concluded that the present approach is economically more effective when compared to conventional design methods and can be extended to deal other sections without major alterations.

Effects of transient creep strain on post-tensioned concrete slabs in fire

The effects of transient creep strain of concrete on post-tensioned concrete slabs in fire were investigated by means of numerical modelling. Employing the commercial package Abaqus, three-dimensional non-linear finite-element (FE) models were established. The thermal creep strain of prestressing steel tendons was explicitly incorporated into the FE models. Three concrete constitutive models were considered – a basic model without considering transient creep strain, a transient model explicitly considering transient creep strain and the Eurocode 2 (EC2) model, implicitly considering transient creep strain taken from BS EN 1992-1-2. Through comparing the numerical results with those obtained from available tests in the literature, excellent agreement was achieved. Based on this, the basic model was verified at ambient temperature and both the EC2 model and the transient model were also verified in test fire scenarios. A main conclusion from this study is that transient creep strain should be considered either explicitly or implicitly in numerical modelling for its positive contribution to the fire resistance of slabs.

Influence of the bracing scheme on seismic performances of MRF-EBF dual systems

The work herein presented has the aim to investigate the influence of the bracing scheme on the seismic performances of Moment Resisting Frames-Eccentrically Braced Frames (MRF-EBF) dual systems, designed according to two design approaches: the first one is the Theory of Plastic Mechanism Control (TPMC) while the second one is based on Eurocode 8 (EC8) design provisions. Even though TPMC design approach is not introduced in modern seismic codes, it has earned the reputation of being a robust design approach because of its strong theoretical background, based on the kinematic theorem of plastic collapse extended to the collapse mechanism equilibrium curve to assure a collapse mechanism of global type. Conversely, the design approach based on EC8 promotes the application of the so-called beam-column hierarchy criterion which is usually able to avoid soft-storey mechanisms but does not assure the yielding of all the dissipative zones, because a collapse mechanism of global type is very rarely attained. The main purpose of the present work is to compare, given the above mentioned design approaches, the different seismic performances resulting from the use of the four different bracing scheme proposed by codes. For this reason, 5 bay buildings with 4, 6 and 8 storeys have been examined considering four bracing schemes providing a total number of 12 structural schemes analyzed. The seismic performances have been evaluated by means of Incremental Dynamic Analyses (IDA) carried out until the achievement of structural collapse and repeated for a set of ten earthquake ground motion.

The evolution of shrinkage strain of pet-mortar composite eco-materials

Concretes and mortars are subjected to several kinds of shrinkage strains which represent the volumic variations resulting from the cement hydration and are governed by various physical and chemical aspects. The use of polyethylene terephthalate PET plastic wastes which are available in quantity and within low cost in our country yields a very important economic and environmental impact in the construction industry. Thus, we are interested to investigate the effect of PET volumetric additive amounts for cement substituting and for the behavior of the total, drying and autogenous shrinkage. Comparison study of obtained experimental results with codale prediction models were performed according to Eurocode 2 (EC2) in order to analyze the evolution of shrinkage strain with PET-mortar composite ages and for several rates of PET waste additions. According to obtained results, PET additions acts to reduce shrinkage strains of PET-mortar composites which promote the use of these modified mortar Eco-materials in the field of construction industry.

Performance of squat 3D sandwich walls with longitudinal reinforcement and boundary elements under lateral cyclic loading

Three-dimensional (3D) sandwich precast concrete walls are often used in building construction due to their superior performance, thermal efficiency, and speed of fabrication. When applied to low-rise buildings, this technology facilitates a cellular structure composed of squat sandwich walls sustaining gravity loads and performing as shear wall against lateral loads. Not much research information is available on squat 3D sandwich walls under in-plane lateral loading. This paper discusses experimental investigations on eight squat 3D sandwich walls were tested, in which four were without and four with boundary elements. In each group of four walls, two were provided with only weld mesh as reinforcement and remaining two were provided with additional longitudinal reinforcement. The shear span-to-width ratio of walls was 1.0 or 0.87 subjected to lateral quasi-static reversed loading cycles, while the vertical load was kept constant. The dimensions of unstiffened 3D sandwich walls are 1250 mm × 1250 mm, whereas the dimensions of the stiffened 3D sandwich walls are 1125 mm × 1250 mm (size of stiffening element: 370 mm × 1250 mm). The behavior of squat 3D sandwich walls has been investigated in terms of load–displacement response, crack pattern, mode of failure, ductility, stiffness degradation, and energy dissipation. Also, the present study attempts to validate the current design practices, both in Europe (Euro code 8) and in the United States (ACI 318) in relation with the experimental results. Also, other available design equations established for reinforced concrete walls to verify the applicability of these empirical formulae for sandwich walls have been examined. From the test results on 3D sandwich walls, it has been observed that the addition of longitudinal reinforcement and the boundary elements exhibited strong coupling action of shear due to the squat nature of the walls. The 3D sandwich walls with additional longitudinal reinforcement showed significant strength and stiffness.

Calculation of Punching Shear Strength of Steel Fiber Reinforced Concrete Flat Slabs

The paper deals with analysis of calculation of punching shear strength of reinforced concrete flat slabs with or without steel fibers in punching shear zone. The analysis shows, that the type, shape and strength of steel fibers has an influence on punching shear strength. The empirical method, evaluating these factors and calculating the punching shear strength according to Lithuanian and Euro Codes, is presented and discussed.

The maximum sloshing wave height evaluation in cylindrical metallic tanks by numerical means

The metallic cylindrical storage tanks are very common structures in the field of civil engineering; These facilities are especially used in the industry in which they are used to store all kinds of products-which are for the most toxic or flammable. The tanks are also used in the storing of drinking water. When earthquakes, these structures must be strictly maintained in order to avoid that they lose their precious contents causing reactions that can cause more damage than the earthquake itself. In this study, the effects of the liquid height, the geometric parameters of tanks in the variation of the maximum sloshing wave height are studied: For this purpose, the software ANSYS V11.0 is used for modelling the tanks, the results found are compared with thus given in the Euro code 8

Vulnerability Assessment of Building Frames Subjected to Progressive Collapse Caused by Earthquake

Progressive collapse is an initial local failure of the structural component and leading to the additional collapse of the building frames. This study investigated the vulnerability of four- and six-storey moment resisting concrete frame (MRCF) buildings subjected to progressive collapse. The four- and six-storey MRCF buildings were designed based on British Standard (BS) and Eurocode (EC). The differences between these two codes were investigated. Nonlinear static analysis, which is also known as pushover analysis (POA), and nonlinear dynamic analysis or incremental dynamic analysis (IDA), were performed for each model to obtain capacity curve and explore vulnerability measures. IDA was conducted using a sample of ground motion from an earthquake that occurred in Ranau, Sabah in 2015. The four-storey building was more vulnerable than the six-storey building.

Self-terminated carbonation model as an useful support for durable concrete structure designing

The paper concerns concrete carbonation, the phenomena that occurs in every type of climate, especially in urban-industrial areas. In European Standards, including Eurocode (EC) for concrete structures the demanded durability of construction located in the conditions of the carbonation threat is mainly assured by the selection of suitable thickness of reinforcement cover. According to EC0 and EC2, the thickness of the cover in the particular class of exposure depends on the structural class/category and concrete compressive strength class which is determined by cement content and water-cement ratio (thus the quantitative composition) but it is not differentiated for various cements, nor additives (i.e., qualitative composition), nor technological types of concrete. As a consequence the selected thickness of concrete cover is in fact a far estimation -sometimes too exaggerated (too safe or too risky). The paper presents the elaborated self-terminated carbonation that includes abovementioned factors and enables to indicate the maximal possible depth of carbonation. This is possible because presented model is a hyperbolic function of carbonation depth in time (the other models published in the literature use the parabolic function that theoretically assume the infinite increase of carbonation depth value). The paper discusses the presented model in comparison to other models published in the literature, moreover it contains the algorithm of concrete cover design with use of the model as well as an example of calculation of the cover thickness.