•Tests of eccentrically loaded column bases allow an analysis of the influence of moment-shear interaction on the punching shear capacity.•A more brittle failure is observed for column bases with ...larger shear slenderness whereby increasing load eccentricities positively affect the ductility.•Innovative measurements allow the continuous measurement of inner concrete strains close to the column revealing new insights on the punching failure of column bases.•The slab deformations are significantly affected by load eccentricities due to a skewing rotation.•Current design approaches reveal further potential for optimizing coefficient β to allow for more progressive design approaches in the future.
In the past, the punching shear behavior of centrically loaded column bases has been predominantly investigated even though eccentric loads frequently occur in engineering practice. To consider this corresponding uneven shear stress distributions around the column, many design approaches define coefficients to increase the acting load. Due to the limited test data for eccentric punching tests, an assessment of the design approaches is not reliably possible. To fill this gap of experimental test results, four centrically loaded and fourteen eccentrically loaded punching tests were conducted to analyze the effects of systematically graded load eccentricities.
The tests reveal a significant influence of load eccentricity on the punching shear capacity and the load-bearing behavior. With increasing eccentricity, the crack formation shifts to the higher loaded side going along with an incompletely developed punching cone. Innovative measurements of the strains in the slab allow to analyze the circumferential multi-axial stress state inside the concrete. In contrast to centrically loaded column bases, this compression ring does not fully develop under eccentric loads. Based on these measured tangential strains, an experimental approach for describing the influence of the load eccentricity on the punching shear strength is derived and compared with the design approaches of Eurocode 2, Model Code 2010 and the stable version of the next generation of Eurocode 2. Overall, the results indicate optimization potential for more advanced design provisions of column bases with eccentric loads.
•A large experimental database was used and compared with the ACI 440.1R-06 and EC2 predictions.•Regression analysis was conducted to discuss the influence of parameters on the capacities, and ...cracking moment.•The reliability analysis was conducted, and partial safety factors were suggested.
In the last few years, there has been a significant increase in the utilization of Fiber Reinforced Polymer (FRP) materials as reinforcing elements in concrete structures due to their excellent properties. Unlike traditional steel rebars, FRP rebars do not rust, which helps to prevent degradation and deterioration of the concrete structure over time. This growth has resulted in a rise in the application of design regulations for FRP-reinforced concrete (RC) members. There are currently no European standards that offer suggestions about FRP RC structures. This paper aims to assess the load- carrying capacity and deflection of FRP RC beams with large number of test data available against design standards. The results are compared with ACI 440.1 R-06 specifications and EC2 concepts available in fib Bulletin No. 40. It was found that both ACI and EC2 underestimate the shear flexural capacity. Both design codes presented 38% and 62% of the collected data that overestimated and underestimated the calculation of the deflection, respectively. A parameter influence analysis is performed considering the database collected, and a reliability analysis based on Annex D EN 1990 (2002) is conducted. The reliability analysis allowed suggestion new partial safety factors values of 1.45 and 1.65 for moment and shear capacities, respectively, which can be used by design engineering communities.
Experimental investigations on centrically loaded column bases provide the basis for current punching shear design provisions. However, this symmetric loading condition represents an exception in ...daily engineering practice since usually load eccentricities occur leading to uneven shear stress distributions along the control perimeter. To account for this effect, design approaches define different factors to either increase the acting shear force or to decrease the punching shear resistance in design. New punching test results of 14 eccentrically loaded and four centrically loaded column bases now allow the evaluation of design approaches depending on different geometric boundary conditions. In this new test series, the load eccentricities were systematically graded to analyze their influence on the punching behavior. Strain measurements in the multiaxial compression zone of the concrete in the column‐footing connection reveal new insights on the punching failure of column bases. As a result, a correlation between tangential concrete strains and the reduction of punching shear strength can be recognized for increasing load eccentricities. The comparison of experimentally determined load increase factors with the design results according to Eurocode 2, Model Code 2010 and the stable version of the next generation of Eurocode 2 reveals optimization potential for deriving more advanced design provisions in the future.
•Evaluation of punching shear design provisions according to Eurocode2.•New Uniform Design Method for punching shear in flat slabs and column bases.•New databank consisting of 476 punching tests on ...flat slabs and column bases.
The punching shear design of flat slabs and column bases was revised with the introduction of Eurocode 2. While in many former codes the punching shear resistance was determined regardless of the type of member, in Eurocode 2 two different design equations for flat slabs and column bases were introduced. Additionally, different control sections for flat slabs and column bases were defined. The differentiation between flat slabs and column bases and especially the iterative design procedure for the determination of the punching shear resistance of column bases require great effort in daily practice.
Based on the punching shear provisions according to Eurocode2, a new Uniform Design Method (UDM) for flat slabs and column bases is developed. The derivation of the design method is described in detail. To verify the changes in the current design provisions, the new design method is evaluated using large databanks for flat slabs and column bases without and with shear reinforcement as well as systematic test series.
•Experimental programme on full-scale RC members with a green alternative BFRP rebar.•The experimental results are compared with international design standards.•Design recommendations for reinforced ...concrete with BFRP rebars are proposed.
The durability of reinforced concrete structures is an ongoing challenge for engineers, particularly in harsh environments. In these conditions, concrete is susceptible to excessive cracking which allows water or other aggressive agents to penetrate the structure, thereby accelerating the deterioration, mainly through corrosion, of the steel reinforcement. The deteriorated concrete structures require frequent maintenance to achieve and extend their service life and may need expensive rehabilitation measures. The use of fibre-reinforced polymer (FRP) rebars, such as carbon and glass FRPs, can be an effective, sustainable and durable solution to enhance the durability of reinforced concrete structures in aggressive environments. Another type of FRP that has gained popularity in construction in the last two decades is basalt fibre-reinforced polymer (BFRP), which is the subject of the current paper. In order to investigate their behaviour, an experimental programme comprising five reinforced concrete beams and seven one-way spanning slabs has been conducted, and is described herein in detail. Three different types of reinforcement were included in the tests, namely sand-coated BFRP bars, ribbed BFRP bars as well as regular carbon steel reinforcement, for comparison. All of the members were tested up until failure. The test results are presented and analysed, with particular focus given to the cracking moment, ultimate moment capacity, deflections and also crack opening widths. The results are compared with the guidance currently available in several international design codes. In addition, based on the results and analysis presented herein, design recommendations for reinforced concrete with BFRP rebars are proposed.
•Improved Eurocode 2 truss model with two variable-inclination compression struts.•The upper compression strut may have lower inclination than the lower strut.•The two strut angles determined via ...equilibrium conditions and plasticity theory.•A wider class of statically admissible solutions, excluded by EC-2, is constructed.•Good agreement with ACI-DafStb databases and better performance than EC-2 approach.
The shear strength of reinforced concrete beams with stirrups can be assessed with strut-and-tie models based on the truss analogy. The Eurocode 2 formulation exploits such a possibility with a variable-angle inclination of the compression struts that is determined through the lower-bound theorem of plasticity. This approach tends to underestimate the shear capacity of lightly shear-reinforced beams where the concrete contribution, which is neglected in this formulation, is more significant. Based on this consideration but adopting an identical theoretical framework without adding a concrete contribution explicitly, this paper presents an upgrade of the EC-2 truss model incorporating two variable-inclination compression struts, whose inclination angles are determined through equilibrium conditions and the theory of plasticity. In this model, the upper compression strut may have lower inclination than the lower compression strut, which is mechanically motivated by the increase of shear stresses observed in the upper portion of the beam, in the neighborhood of the crack tip, following the trend of the principal compressive stress direction. This improved truss model enables the construction of a wider class of statically admissible solutions compared to the EC-2 single-strut approach. Closed-form expressions are derived for a variant of this model in which the two compression struts extend equally for half of the inner lever arm, which allows a simple and compact formulation for practical design purposes. Based on comparison with the well-established ACI-DafStb databases including more than 200 tests, the proposed model leads to values of the shear strength that are in very good agreement with experimental results and more accurate than the values obtained from the EC-2 procedure, despite the relatively comparable simplicity.
Abstract Recycled aggregate concrete contributes to the recovery of construction and demolition waste, which is a growing societal concern. The technical feasibility of recycled aggregate concrete ...has been extensively tested and validated and the revisions of codes are already including clauses for recycled aggregate concrete specification and design. However, there are still doubts regarding its structural behavior. This article assesses the suitability of Eurocode 2 design clauses for concrete elements under compression when used for recycled aggregate concrete design. This is done through the analysis of model uncertainties that are estimated from a database collected from laboratory experiments on columns. Both the current version of Eurocode 2 (with and without taking confinement into account) and the upcoming (second generation) Eurocode 2 are considered. A database was collected with clearly defined criteria and includes coarse recycled aggregates produced from concrete waste, since columns made with other types of recycled aggregates are scarcely tested and do not represent the current status for structural recycled aggregate concrete design and production. The statistics of the model uncertainty for natural and recycled concrete columns were compared and it was observed that the mean model uncertainty tends to decrease slightly when recycled aggregates are used. However, a preliminary assessment of whether a partial factor for recycled aggregate concrete compression design should be used concluded that this partial factor is not necessary to ensure reliable design and the design of columns may be carried out using the same formulae used for conventional concrete. The format proposed may be used for other resistance models, provided that the partial factor is calibrated for each resistance model.
•Influence of recycled aggregates on the model uncertainty of beams with and without stirrups.•Recycled aggregate incorporation may result in unsafe designs.•Resistance models that explicitly account ...for aggregate interlock are more affected.•Probability distribution of the model uncertainty of recycled concrete beams without stirrups.•Preliminary partial factor for shear design of elements without transverse reinforcement.
The model uncertainty of the shear resistance equations of three design codes {the current Eurocode 2 (2004), Model Code (2010), and the final draft of the Eurocode 2 (2020)} was investigated for coarse natural and recycled aggregate concrete beams. Databases of beams with and without shear reinforcement were made with clearly defined criteria. The statistics of the model uncertainty of natural and recycled concrete beams were compared and it was found that recycled aggregate incorporation has detrimental effects on the model uncertainty of shear design. Surprisingly, recycled concrete aggregate beams designed following the current version of Eurocode 2 (2004) are safer than those designed using the other codes. This is due to the shear resistance equations of the latter overestimating the aggregate interlock of recycled aggregate. A preliminary partial factor was proposed, offsetting the influence of recycled aggregate on the safety of beam designs. The database of beams with shear reinforcement lacks representativeness but hinted that recycled aggregate incorporation also reduces the safety of this type of shear design. The paper finishes presenting suggestions of experiments that would complement the current knowledge on this topic.
•Definition of an equivalent functional unit for Life-Cycle Assessment (LCA) analyses.•Concrete with recycled aggregates (RA) versus conventional structural concrete.•Equivalent properties of RAC in ...function of the same property in RC are used.•The methodology was validated in 100% of the slabs and 95% of the beams tested.
This research intends to determine an equivalent functional unit in concrete with recycled aggregates (RA) to conventional structural concrete in the context of Life-Cycle Assessment (LCA) analyses. The work intends to contribute to a better understanding and greater confidence in the use of concrete products with RA. The relationship between recycled aggregates concrete (RAC) and conventional concrete (RC) is expressed by fundamental parameters α, which describe the relevant equivalent properties of RAC in function of the same property of RC. Using those parameters, the study performs a thorough analysis according to Eurocode 2 (EC2): the various compliance checks with the limit states are performed in order to obtain the amount of recycled aggregates concrete required to reach the same performance as a given volume of conventional structural concrete. Conversion criteria for concrete structures with RA (concerning its structural performance) are established and the conversion formulas are tested in case studies. This study is developed particularly for slabs and beams, but remarks are made concerning other main structural elements, namely columns and footings. The results show that the method is valid for slabs and beams and that the conversion formulas yield good results.
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