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Self‐compacting concrete (SCC) is a type of flowable, high‐strength and high‐performance concrete in the construction field, which can flow and compact under its own weight. The damage of concrete is often caused by internal microstructural defects. Nano silica (NS) has excellent pozzolanic properties, and with an appropriate content of NS as auxiliary cementing material, it can promote the generation of C‐S‐H gels in addition to serve as internal filler, thus improves the micro‐scale defects in concrete. This paper extracts data from studies published over the last decade which focus on the application of NS in SCC and discusses the similarities and differences between the studies. Ultimately, a systematic review of the physical and chemical characteristics of NS, and the effect of NS on the workability, mechanical and durability properties of SCC is presented. Based on the review, the most common NS content is 0%–6%, where the negative effect of 0%–6% NS on the workability of SCC can be controlled by increasing the dosage of superplasticizer. The NS content of 2%–3% is optimum for improving the mechanical strength and the ability of SCC to resist water permeability, corrosion, acid and sulfate attacks, elevated temperature as well as shrinkage. [ABSTRACT FROM AUTHOR]

The next edition of the fib Model Code for concrete structures, Model Code 2020 (MC2020), is under development with the aim of issuing a first partially harmonized draft for comment in early 2023. MC2020 is a single code dealing with both new and existing concrete structures, that is both the design of new structures and the various activities associated with the assessment, interventions upon and life‐cycle management (LCM) of existing concrete structures. The paper outlines the overarching sustainability framework and the performance‐based or outcomes‐based approaches (PBA) adopted by MC2020. There is a pressing need to reduce barriers to the evolution in concrete construction materials and the technical aspects of design and the LCM of existing structures, in order to meet pressing climate change drivers and the goal of achieving lower carbon construction. MC2020 also addresses significant advances made on a wide range of issues including those relating to structural design and analysis methods, seismic design and assessment procedures, durability, structural monitoring, service life design, structural assessment through‐life and making interventions to adapt existing structures or enhance their performance or extend their useful life. [ABSTRACT FROM AUTHOR]

High‐performance fiber‐reinforced concrete (HPFRC) can be considered a promising material for the construction of precast concrete girders for road bridges. This paper presents conceptual considerations and numerical analysis to support this statement. The HPFRC is a compromised alternative between FRC and UHPFRC mixes. Specifically, a tailor‐made mix design of HPFRC jointly developed by ACCIONA and the authors is presented, and then compared with the other types of fiber‐reinforced concretes collected from the technical literature. In addition, some trends observed in the database are described. This material characterization is followed by a conceptual analysis of the advantages of the application of HPFRC to road bridges. Specifically, a proposed bridge for the case of a 60 m‐span box girder is analyzed. A comparison between alternatives based on the use of HPFRC and conventional reinforced concrete is discussed. The results shed light on the viability of this material for bridge application. Specifically, the main finding show potential significant material savings in structural elements of the superstructure. Finally, ongoing and future research for a wide application to the construction sector are briefly discussed. [ABSTRACT FROM AUTHOR]

Despite the good balance between notable mechanical properties and a reasonable cost, high‐performance fiber reinforced concrete (HPFRC) is not widely employed in the construction of bridges. This work is part of a larger research addressed at exploring the potential of this material for replacing standard concrete in the construction sector. Specifically, this paper focuses on the use of HPFRC to build precast simply supported I‐girders for road bridges. This work investigates the influence of several design variables on the material consumption to identify the key features that can lead to possible material savings. The variables, explored through a parametric analysis, are: (i) the concrete class (C80/95, C100/115, and C120/140); (ii) the number of beams to form the deck (from 3 to 5); (iii) the girder span‐to‐depth ratio (17, 20, and 23); (iv) the bridge span (L) (20, 40 and 60 m). One specific case of study is described in detail, and then the same procedure is applied to all the case studies. In addition, the effect of different hypotheses and formulations for the bending and shear verifications are analyzed. The results shed light on the relevance that these variables play in the final solution and how they affect the dimensioning of these elements. As main finding, this work proves that the use of HPFRC represent a material‐efficient solution for slender and long‐span precast I‐girders. [ABSTRACT FROM AUTHOR]

Crack initiators in reinforced concrete structures can facilitate fulfilling the serviceability requirements. They can be used as a design parameter to diminish the minimum reinforcement for members subject to imposed deformation and exposed to the environment as they reduce the crack spacing and width when arranged close enough. While crack initiators in conventional concrete construction are cumbersome to provide (e.g., by construction joints or taperings), they are inherent to layered extrusion processes with digital fabrication technologies: the tensile strength is typically reduced locally in interfaces between layers. Rather than trying to avoid these weak interfaces, this paper discusses the potential of taking advantage of them to act as crack initiators reducing the minimum reinforcement content. A tension chord‐based model is developed to (i) account for the local strength reduction and (ii) predict the effect of weak interfaces on the expected crack spacing and width. As a key finding, the model predicts a reduction of the required minimum reinforcement ratio proportional to the locally decreased concrete tensile strength for a specified maximum crack width requirement under imposed deformations. An experimental campaign on five layered and three reference tension ties confirmed the clearly positive impact of weak interfaces on crack spacings and widths. [ABSTRACT FROM AUTHOR]

Compressive strength is considered to be one of the most important mechanical properties of high‐strength concrete (HSC). In this study, three machine learning models, ELM, PSO‐ANN, and GS‐SVR were employed to predict the compressive strength of HSC using 681 data records. The five ingredients and the compressive strength of HSC were regarded as input variable features and output target, respectively. Results indicated that the GS‐SVR model showed the best performance in forecasting with the R of 0.992, MAPE of 0.016, RMSE of 1.241, MAE of 0.842, and RRMSE of 0.024, which could be an alternative candidate for strength prediction. Additionally, a sensitivity analysis was performed within the GS‐SVR model to achieve an in‐depth examination of the effect of each single input variable on the compressive strength. The sensitivity of input variables demonstrated that the water is the most sensitive parameter to the compressive strength of HSC, while the superplasticizer is less sensitive. The research of this paper can provide reference and guidance for concrete design and construction. [ABSTRACT FROM AUTHOR]

Employing non‐metallic reinforcement made of fiber‐reinforced polymers (FRPs) as textile grids is one promising extension of the utilization range of FRP in concrete construction, and thin planar elements reinforced in this manner have high application potential in bridge or parking garage decks, in façades, or in webs and flanges of hollow core cross‐sections. Existing models for predicting the shear resistance of such elements were derived for solid cross‐sectional dimensions similar to conventional steel‐reinforced structures, and their application to thin slabs is debatable. This paper presents the results of an extensive experimental program on the one‐way shear capacity of slabs without and with carbon FPR textile shear reinforcement. A variation of member height, shear slenderness, and shear reinforcement ratio allowed for analysis of the most relevant influencing factors on shear resistance. Both planar and preformed C‐shaped grids enhance the shear capacity and are suitable as shear reinforcement in thin slabs. The experimental results are the foundation for the extension of shear models to thin slabs with FRP reinforcement and for derivation of new unifying shear models that are applicable to a wider range of reinforcement materials and member dimensions. [ABSTRACT FROM AUTHOR]

In order to develop a calculation method for the ultimate flexural capacity of high strain‐hardening ultra‐high performance concrete (UHPC) T‐beams, four‐point loading tests on five specimens were carried out. The design parameters were the ratio and the strength of reinforcement. Based on the assumption of plane section, a linear regression analysis was carried out and the ultimate tensile strain of high strain‐hardening UHPC was obtained. The analysis results proved that the bond between reinforcement and UHPC is reliable and these two materials can maintain strain consistency before the reinforcement reaches its yield strain. A finite element model of the specimens was established using ANSYS and distributed reinforcement was added to simulate the behavior of UHPC after cracking. Considering the tensile contribution of the high strain‐hardening UHPC after cracking, the calculation method for flexural capacity of high strain‐hardening UHPC T‐beams was derived. The finite element simulation method and the theoretical formula calculation method proposed in this paper are in good agreement with the experimental values, and they can be applied for the theoretical analysis and the design of high strain‐hardening UHPC beams. The theoretical calculation method proposed in this paper is compared with calculation methods proposed by standards. The study shows that the proposed calculation method is accurate and generally applicable. [ABSTRACT FROM AUTHOR]

The anchorage capacity of anchor plates under tensile loads is typically limited by the resistance of concrete against cone failure. This resistance can be increased by using supplementary reinforcement in the concrete member. Several authors cited in this paper have discussed the applicability of current normative design methods for a cost‐efficient design of anchor plates or headed anchors combined with supplementary reinforcement in the concrete member. A novel analytical approach has been recently developed by Sharma et al. (2017) to allow for a more efficient design of such anchorages. The applicability of the new analytical approach for the design a proprietary model of anchor plate is discussed in this paper. [ABSTRACT FROM AUTHOR]

Disposal of fresh concrete waste is a worldwide problem. In recent years, many studies have claimed that fresh concrete waste from a reclaiming system can be efficiently recycled into concrete. This paper gives a comprehensive review of the characteristics and applicability of fresh concrete waste in phase of slurry wastewater, fresh paste, and recycled solids. The effects of fresh concrete waste in the three phases on workability, strength, and durability such as permeability, water absorption, shrinkage, and acid resistance of concrete have also been reviewed in this paper. [ABSTRACT FROM AUTHOR]

In this paper, the deformation of a sealed low-calcium fly ash-based geopolymer concrete during heat curing was investigated. The sealed sample underwent thermal deformation due to temperature change and possible autogenous deformation related to alkaline activation of the fly ash. For the separation of the both deformation types the coefficient of thermal expansion ( CTE) is a paramount issue. The CTE evolution of the geopolymer concrete from plastic to hardened state was determined by means of a new method proposed in this paper. Based on the experimental results, the CTE is mathematically described as a function of the so-called equivalent time. The thermal dilation during heat curing was then calculated using the CTE equation. The autogenous shrinkage of the fly ash-based geopolymer concrete is comparatively low. The thermal dilation during the heat curing cannot completely reverse, if the concrete is cooled down to its temperature at the beginning of the heating. After the heat curing no further autogenous deformation was observed on sealed samples continuously cured at room temperature. [ABSTRACT FROM AUTHOR]

Concrete shells are very efficient structures, spanning wide areas with very little construction material. Unfortunately the formwork needed to erect concrete shells is still very labor and material intensive. An alternative construction method which is more time and resource friendly is Pneumatic Forming of Hardened Concrete. A simple air cushion in combination with additional post‐tensioning tendons are used to transform a flat concrete plate into a double curved shell. This paper describes the design and construction of the first practical large‐scale application of this building method for the construction of the deer pass "AM 2" over the newly built two‐track rail Koralmbahn in Carinthia in the south of Austria. The plan measurements of the bridge are 36.2 m by 38.7 m with the height of the shell from the top edge of the foundations to the vertex mounting to 7.6 m. Within the construction process a flat 100 mm thick hardened concrete plate with a weight of 546 t was lifted to the designed double curved shell. This thin concrete shell served as lost formwork for the final bridge. [ABSTRACT FROM AUTHOR]

Ultra‐high performance fiber‐reinforced concrete (UHPFRC) is usually applied for thin‐walled and lean constructions because of its excellent mechanical properties. However, these lightweight constructions such as bridge girders, masts, towers, and railway tracks, for example, are susceptible to oscillations due to cyclic loading. A model describing the fatigue behavior of UHPFRC is required. Therefore, the material behavior of all mixture components and the composite itself, each subjected to cyclic tensile loading, is studied experimentally and numerically on the mesoscale at iBMB, Division of Concrete Construction and Institute of Structural Analysis both at TU Braunschweig. In this paper, first findings concerning bond processes of single and multiple micro steel fibers embedded in ultra‐high performance concrete as well as a new geometrically and physically nonlinear bond model are presented. [ABSTRACT FROM AUTHOR]

This paper concerns the shear capacity of keyed joints that are transversely reinforced with overlapping U-bar loops. It is known from experimental studies that the discontinuity of the transverse reinforcement affects the capacity and the failure mode. However, to the best knowledge of the authors, previous theoretical works and current design equations in standards do not account for this important effect. This paper introduces a detailed model based on finite element limit analysis to assess the effect of the discontinuous reinforcement. The model is based on the lower bound theorem and uses the modified Mohr-Coulomb yield criterion, which is formulated for second-order cone programming. The model provides a statically admissible stress field as well as the failure mode. Twenty-four different test specimens were modelled and the calculations compared with the experimental results. The results of the model show satisfactory agreement with the experimental observations. The model produces estimates of the shear capacity that are significantly better than those of the Eurocode 2 design equations. [ABSTRACT FROM AUTHOR]

Encapsulation‐based self‐healing technology is an effective method for healing the crack‐deteriorated cementitious material. Encapsulation‐based self‐healing initiates by crack occurrence and progresses by chemical reaction of released self‐healing agents in the cracks, which are contained in capsules. In this paper, a review has been conducted on various healing agents, encapsulation techniques, as well as experimental approaches, basing on existing substantial studies. Recently, there is no consistent agreement on the effective criteria for evaluating encapsulation‐based self‐healing and mature solution for increasing the survival ratio of capsules during mixing. However, the polyurethane‐based healing agents filled in glass or ceramic tubes are popularly applied for self‐healing cementitious materials. Besides, the polymer capsules present promising attractions for engineering application. Mechanical strength and durability are the most widely used self‐healing efficiency assessment indexes. On the other hand, nondestructive technique and numerical modeling have also extensively adopted to visualize and evaluate the self‐healing behavior of cementitious materials. However, there are still some challenges, which require further investigations, such as behavior of crack propagation, kinetics of healing agent in discrete crack surfaces, effect of inserted capsules on the mechanical properties of self‐healed cementitious materials. [ABSTRACT FROM AUTHOR]

This paper is concerned about the lateral load response and associated working mechanism of a precast reinforced concrete shear wall involving horizontal connections. An assembling method is proposed using dry connection through a horizontal steel connector (H‐connector) and high strength bolts. To investigate the effectiveness of such an assembling method, two identical wall‐connector assembly specimens have been constructed and tested under monotonic loading and cyclic loading, respectively, while subjected to a constant vertical compression. The test results showed that the performance of the shear wall assembly was generally satisfactory in terms of ensuring the full development of the shear wall strength and ductility. To assist in the interpretation of the experimental results and enable further study on the design approach, a detailed mechanism analysis has been subsequently conducted. The stress in H‐connector flange and shear force transferred through each high strength bolt has been deduced on the basis of mechanism analysis. The further sliding analysis within the bolted connections agrees well with the experimental results and therefore confirms the derived formulae for H‐connector and high strength bolt. [ABSTRACT FROM AUTHOR]

This paper analyzes the existing problems in the practical engineering design, resulting from the mechanical properties of two‐way composite concrete slabs with precast ribbed panels (CSPRPs). Due to the influence of the structurally orthotropic characteristic, the calculation formulas for the deflection and bending moments of a CSPRP with three supported edges and one clamped edge under a uniformly distributed load are solved using the load superposition method and the orthotropic plate theory. The CSPRP is calculated as an equivalent isotropic cast‐in‐place two‐way slab using the transformation of function, and the application of the equivalent span ratio. The simplified elastic design method is presented for a CSPRP with three supported edges and one clamped edge under a uniformly distributed load. The elasticity coefficients of the CSPRP with the equivalent span ratio, ranging from 0.5 to 1.0 and stiffness ratios of 0.5 and 2 are obtained using the programming calculation. The linear interpolation method is applied using the equivalent span ratio of an isotropic cast‐in‐place two‐way slab, and one example of a CSPRP with three supported edges and one clamped edge is given to verify. The results show that the simplified elastic design method is accurate and feasible. [ABSTRACT FROM AUTHOR]

This paper proposes new strength models to predict compressive, splitting tensile and flexural strengths of steel, synthetic and hybrid fiber reinforced concretes. The strength models depending on fiber reinforcing index, concrete compressive strength, and fiber volume fraction have been developed by multiple regression analyses of the experimental results obtained from a comprehensive experimental program. Twenty‐five concrete batches, one control and 24 fiber reinforced concrete with target compressive strength of 40 MPa were produced. Steel and synthetic fibers, namely hooked‐end steel (HF) and polyamide (PA) synthetic fibers of total volume of 0.25, 0.5, and 0.75% were added in single and hybrid forms to concrete mixes. Moreover, the predictions of the proposed strength models have been compared with the existing strength models in the literature. The test results clearly showed that the predictions of the proposed strength models are more accurate than the existing strength models for compressive, splitting tensile and flexural strengths of all the fiber types. Although the existing strength models may be applicable to the prediction of compressive strength of steel, synthetic, hybrid fiber reinforced concrete (FRC), they may not be safely used for splitting tensile and flexural strength of steel, synthetic and hybrid FRC. [ABSTRACT FROM AUTHOR]

The use of fibers can improve the behavior at serviceability limit states (crack and deflection control) and ultimate limit states (bearing capacity) of reinforced concrete (RC) elements under flexure. Fibers reinforcement provides a postcracking resistance, leading RC element to have a more diffused crack patterns characterized by narrower and more closely spaced cracks. Some doubts are instead related to RC element ductility, which can be affected by crack localization after rebar yielding. However, most of experiments present in literature relate only to elements in steel fiber reinforced concrete with significant residual strengths (fR,1 and fR,3 greater than 3.5–4.0 MPa). This paper aims to evaluate the influence of different fiber type (steel, glass, or polymer macrofibers) on the cracking and strength capacity of RC beams under flexure by using a broad range of Fiber Reinforced Concrete (FRC) toughness (1.6 ≤ fR,1 ≤ 5.1 MPa and 0.8 ≤ fR,3 ≤ 4.5 MPa). Twenty‐one small scale RC beams with a typical value of longitudinal reinforcement ratio (0.87%) were tested under flexure. Crack and deflection control, as well as bearing capacity and crack localization were evaluated as a function of FRC toughness. Finally, results were compared against mean crack spacing and strength capacity predictions of fib Model Code 2010. [ABSTRACT FROM AUTHOR]

Concrete possessing high‐passing ability needs to be flowable and cohesive. Hence, passing ability cannot be improved by solely adding superplasticizer, which increases both flowability and segregation of concrete simultaneously. Decreasing the maximum size of aggregates so that concrete segregates at lower cohesiveness is a possible but undesirable way as it narrows the aggregates' grading and decrease dimensional stability of concrete. With the same maximum size of aggregates, passing ability can be improved by raising the concurrent flowability‐segregation envelope of concrete. In this paper, fly ash and silica fume (cementitious fillers) and limestone (inert filler) were selected to replace cement partially and subsequently the passing ability of concrete was studied. From the results, it was evident that when either type of fillers were used, the passing ability and maximum limits of flowability and segregation achieved simultaneously increase. It is because these fillers are finer than cement that provides better filling effect to increase packing density and excess water leading to better flowability. Concurrently, the cohesiveness of concrete also increases as the content of fine particles increases. These allow concrete to hold the coarse aggregates more firmly when passing through narrow gaps, after which the concrete will keep flowing rapidly. [ABSTRACT FROM AUTHOR]

Two simple finite element models denoted as FEM‐B and FEM‐BC are developed in this paper to investigate the structural behavior of fiber‐reinforced polymer (FRP) strengthened reinforced concrete (RC) beams under static and cyclic loading. First, the FEM‐B is developed for analysis of FRP‐strengthened RC beams under static loading and the bond‐slip effect between FRP, adhesive and concrete is included. Then FEM‐BC is developed based on FEM‐B for analysis of structural behavior of FRP‐strengthened RC beams under cyclic loading, and degradations of material properties of concrete, steel reinforcement, and FRP due to cyclic loading are taken into account. The developed FEMs are validated against experimental results and demonstrated to be effective for structural analysis of FRP‐strengthened RC beams. Furthermore, parametric studies are carried out to learn the effects of types, thickness, and length of FRP on the structural behavior of FRP‐strengthened RC beams based on the FEM‐BC model. The research findings are summarized finally. [ABSTRACT FROM AUTHOR]

When designing fiber‐reinforced concrete (FRC) structures, one of the basic design issues is represented by the choice of a proper combination of fibers and conventional reinforcement that allows to obtain the best structural performance with the minimum amount of materials. The combination of rebars and fibers in the concrete matrix is generally known as Hybrid Reinforced Concrete (HRC). HRC represents a feasible solution in many structures; among these, slabs are gaining an increasing interest among practitioners. In fact, slabs are the most widespread structural elements in common practice as they are typically used to construct slabs on ground (industrial floors or foundations), slabs on piles (foundations) or elevated slabs. This paper focuses on the flexural design of FRC elevated slabs by using the most recent design provisions reported in the fib Model Code 2010. A simplified design procedure based on a consolidated design practice is proposed. Emphasis is given to the use of HRC to minimize the total reinforcement (fibers + rebars) in order to get practical and economic advantages during construction (ie, construction time and costs reduction). In more detail, a procedure for proportioning the hybrid reinforcement and then verifying the structural safety will be presented and discussed. Numerical nonlinear finite element analyses will be carried out to assess the effectiveness of the proposed design method. [ABSTRACT FROM AUTHOR]

This paper investigates the effects of expanded perlite aggregate (EPA) on the properties of mortar and concrete. A volume of 10, 20, and 30% EPA were used instead of 0–2 mm fine aggregate. Water/binder ratio of 0.30 was constant for all the mortar and concrete mixtures. The compressive strength, ultrasonic pulse velocity (UPV), and linear autogenous shrinkage tests were performed on both mortar and concrete mixtures. Furthermore, the heat of hydration test was only made for mortar mixtures and restrained shrinkage test was only employed to measure cracking time and strain for concrete mixtures. For both mortar and concrete mixtures, the experiments show that the compressive strength, UPV, and linear autogenous shrinkage were generally decreased with increasing the amount of EPA according to control sample, while the heat of hydration is generally increased. However, the reduction ratios in the compressive strength of mortar and concrete samples gradually decreased with increasing the curing time. In addition, the increases in the heat of hydration for EPA10, EPA20, and EPA30 were 5, 7, and 8%, compared with the control. [ABSTRACT FROM AUTHOR]

In this paper, the influence of heating up to 400°C on properties of the self‐compacting concrete containing recycled copper slag fine aggregate was investigated. The residual mechanical properties such as compressive strength, splitting tensile strength, elastic modulus, and stress–strain curve of the heated concrete were measured with the change in the porosity of concrete. Moreover, the resistance against the penetration of chloride ions (Cl−) into the concrete after the heating was also evaluated. For observing the micro‐structure around the fine aggregate in the concrete, scanning electron microscopy was employed. The experimental results showed that the compressive strength of the concrete decreased with the mixing of copper slag fine aggregate, although the residual compressive strength increased after heating up to 300°C with the rise in temperature. Mixing copper slag fine aggregate into concrete also reduced the residual elastic modulus and accelerated Cl− penetration into the self‐compacting concrete when the maximum temperature exceeded 200°C. [ABSTRACT FROM AUTHOR]

In this paper, a novel method is presented for quantifying damage to cast‐in‐place self‐centering concrete stepping walls via a proposed numerical model. By conducting a parametric study, an equation is derived to estimate the plastic hinge length of the wall as a function of the axial prestress ratio. To estimate the state of damage in various parts of the wall, including boundary element, wall‐footing interface, and plastic hinge zone, different ratios were introduced. In order to calculate the ratios, damage was calculated at various levels of drift for different values of the prestress ratio. The estimated damage was then compared with the expected damage for the basic performance objective to calibrate the ratios. According to the results, the proposed method can provide insight and valuable information about the probable state of damage. Moreover, to satisfy the basic performance objective requirements, the value of prestress ratio should be limited to 0.125. [ABSTRACT FROM AUTHOR]

This paper investigates the punching behavior of reinforced concrete flat slabs supported on rectangular columns under concentric loading. Based on the critical shear crack theory, a new model is proposed to determine the punching shear strength of slabs. In this model, a rectangular slab is replaced with an elliptical surface with the same area. The efficiency of the model is validated through comparisons made with experimental studies in the literature. Furthermore, results are compared with three different codes, namely, ACI, Eurocode 2, and FIB Model Code 2010. Finally, an alternative approach is introduced to facilitate the calculation of the punching shear capacity of slabs with column rectangularity considerations. For the experimental tests available in the literature, good shear strength predictions were obtained by the two proposed models. [ABSTRACT FROM AUTHOR]

This paper focuses on the development of energy dissipaters for rocking precast systems. The energy dissipaters developed in this work are to be used externally, having the advantages of being easy to inspect and replace after an earthquake. The main parameters to take into account for the development of the energy dissipaters are the cyclic behavior, the strength, and the ductility. The cyclic behavior has to be stable from cycle to cycle. The developed dissipater has to respond with adequate strength. The ductility is also important as the dissipater has to sustain the displacements applied by a major seismic event without failure. For this purpose, the experimental campaign using steel structural angles as dissipaters is described and solutions able to deliver the desired behavior are shown. To support and complement the experimental tests, two‐dimensional numerical models using a finite element software are shown and an analytical method is also presented to describe the behavior in both elastic and plastic ranges and thus design the elements. In both cases, good agreement with the experimental results is achieved. The analytical method has the advantage of being easy to implement for estimation of the steel angle response. [ABSTRACT FROM AUTHOR]

A review of current studies in concrete shear walls shows considerable uncertainty in the effective stiffness of these elements. Based on statistical analyses of 154 existing experiments on slender and squat walls, this paper proposes relations to determine the effective stiffness. Linear regression analyses are applied to determine the relationship between effective stiffness parameters such as axial load, reinforcement ratio, and aspect ratio. The results show the axial load plays a major role in the effective stiffness of the slender wall with correlation coefficient of 0.81. While, in case of squat shear walls, the axial load and the aspect ratio of the wall are the most significant parameters with correlation coefficient of 0.75 and 0.65, respectively. Finally, 2 relations are suggested for the effective stiffness of the slender and squat shear walls by linear regression analyses and are compared with the existing relations. [ABSTRACT FROM AUTHOR]

In steel-concrete composite girders, innovative composite dowels can be used to transfer the shear forces between the concrete slab and the steel section. Today, composite dowels are predominately used in engineering structures such as prefabricated composite bridges. However, due to their ease of manufacture, good loadbearing and deformation properties and suitability for slender concrete slabs, these composite dowels are being used more than ever in building construction as well. The present article describes shear tests on puzzle-shaped composite dowels for slender concrete slabs with a depth of only 10 cm. Aside from different reinforcement configurations, the influence of different longitudinal stress states and transverse cracking in the concrete slab have been investigated. In previous studies of the shear force capacity of composite dowels, the influence of transverse cracking has been neglected. However, our own experiments described in this paper show that the shear capacity of composite dowels is significantly affected by concrete cracking. In order to simulate the experiments performed and to analyse the shear behaviour of the composite dowels in cracked and uncracked concrete, a three-dimensional, non-linear finite element model of the shear tests was set up. The results of both the experimental and numerical investigations are summarized in this paper. [ABSTRACT FROM AUTHOR]

The present paper describes a design approach for textile-reinforced concrete (TRC) shells which reflects the interaction between normal forces and bending moments based on the cross-sectional strength characteristics of the material determined experimentally. The influence of oblique loading on the composite strength of TRC elements with flexible reinforcement is included in a normalized interaction diagram for combined loading. As an example, the design approach is applied to the ultimate limit state assessment of a TRC shell in double curvature. Furthermore, the general applicability of the design approach is discussed in the light of the non-linear loadbearing behaviour of TRC. Due to its strain-hardening tensile response, stress redistributions within the shell result in loadbearing reserves. Details of the structural design and production solutions developed and applied during the realization of the TRC shell structure are described in the companion paper (Part I). [ABSTRACT FROM AUTHOR]

The paper presents the results of an experimental program carried out on 96 concrete pullout specimens prepared with natural and recycled aggregates using 10 and 12 mm diameter deformed steel bars. Steel rebars were concentrically embedded in pullout specimens with two embedded length of 5 and 10 times the rebar diameter. The present work includes six recycled concrete aggregate mixtures and two conventional concrete mixtures with C25/30 and C35/45 target class of compressive strength and S4 class of workability. For both series, specimens were fabricated with different incorporation ratios of fine and coarse recycled aggregates and only coarse recycled aggregates. Tensile load was applied gradually until the pullout failure occurred and the slip between the rebar and concrete was measured at the free and loaded ends for each loading level. Furthermore, systematic observations of failure surface have been made at both macroscopic and microscopic scales. Test results showed that for the same class of compressive strength the bond strength and related failure mechanisms remain very close and the obtained values are, at least, four times higher than the predicted values by Eurocode 2. The experimental results of this study, together with an extensive number of results reported in the literature, were used to describe the variation of bond strength with concrete compressive strength, embedded length, and concrete cover. In addition, an analytical bond-slip relationship is proposed and the parameters of bond-slip law were calibrated by an optimization algorithm. [ABSTRACT FROM AUTHOR]

This paper presents basic parameters test and an efficient numerical model for the bond between reinforcing bars and concrete after elevated temperatures. The chemical adhesive and friction coefficient are measured by self-designed setups, and the variation law of the parameters is summarized. In the 3D modeling, bar-to-concrete interface has been modeled by means of an explicit discretization of the bar ribs. Surface-to-surface contact pair elements are employed for the interface, and the tangential contact behavior is elastic-plastic with a Coulomb-type friction model. Comparison between experimental and numerical results shows that the proposed model describes the behavior of steel bar relatively well in the pull-out process after elevated temperatures. The 3D modeling makes up some deficiencies of macro pull-out test, such as the detailed stress distributions and crack patterns. [ABSTRACT FROM AUTHOR]

T-beams are acknowledged as economic and efficient structural members widely used for floor slab construction systems. In many cases, according to practice in some countries, the beams do not present transverse reinforcement, and their shear strength is governing for dimensioning the width of the web. Although experimental investigations have shown that the presence of the compression flange enhances the shear capacity with respect to equivalent rectangular cross sections, most current design codes neglect this phenomenon, which leads to the overdesign of these members. In this paper, the role of the compression flange of slender T-beams with concentrated loads is investigated with reference to its influence on the shape of the critical shear crack and to the associated shear transfer actions (STA) of the beam. The flanges are considered elements that allow the smearing of applied loads over a certain length of the web. This consideration, in combination with the mechanical model of the Critical Shear Crack Theory ( CSCT), allows a consistent treatment of the phenomenon and leads to simple design expressions accounting for the role of flanges. The results of the proposed model are compared together with design codes (Model Code 2010, Eurocode 2, and ACI 318-11) and other shear design approaches to a database of 239 beams on T-shaped members. The comparison shows that the role of flanges is finely accounted with the proposal based on the CSCT, leading to consistent agreement and to strength predictions that are more suitable for design purposes than the other investigated design models. [ABSTRACT FROM AUTHOR]

To the authors' knowledge, the West Seventh Street Bridge in Fort Worth, Texas is the first precast concrete network arch bridge in the world. Completed in 2013, this bridge consists of 12 identical arches that were precast and post-tensioned near the bridge site. The prefabricated arches, which were 49.8-m long and weighed approximately 2,500 kN, were then transported to the bridge site and erected. To evaluate the structural behavior throughout construction and under subsequent live (truck) loading, 224 vibrating wire gauges were embedded in the 12 arches prior to concrete placement. Three-dimensional finite element models of the arches were also developed to evaluate the structural response under different loading and boundary conditions. Relatively small bending moments were observed in the arches, and the response of the arch elements was generally governed by axial forces. This paper describes the bridge, the instrumentation, and the modeling effort, in addition to the short-term response of the arches. [ABSTRACT FROM AUTHOR]

In this paper, experimental results about the shrinkage and creep behavior of an alkali-activated slag concrete ( AAS-concrete) are presented. The autogenous shrinkage of AAS-concrete is pronounced at a relatively high water to binder ratio of 0.41. The ultimate value of autogenous shrinkage is determined to be higher than that of high-strength concrete ( HSC). The observed self-desiccation at a later concrete age can be one of the reasons for the autogenous shrinkage. In a drying environment of 65% relative humidity AAS-concrete exhibits a significantly higher total shrinkage compared to normal-strength concrete composed of Portland cement. In the contrary to normal and HSC carbonation shrinkage must not be neglected for AAS-concrete in the early concrete age. The sum of drying and carbonation shrinkage develops much more rapidly for AAS-concrete in the first weeks after the beginning of drying. Based on the experimental results the shrinkage behavior of AAS-concrete cannot be predicted by conventional models. The creep behavior of the AAS-concrete was investigated under sealed and unsealed conditions. The creep coefficients for both conditions are higher than those calculated when using conventional models. [ABSTRACT FROM AUTHOR]

The design philosophy of the new fib Model Code for Concrete Structures 2010 represents the state of the art with regard to performance-based approach to the design and assessment of concrete structures. Given the random nature of quantities determining structural behaviour, the assessment of structural performance cannot be well established by deterministic methods, instead requires a probabilistic approach. The performance-based approach is introduced in Part I of fib Model Code 2010 by applying the concept of performance requirements and reliability management during service life. Correct understanding of the reliability concept of fib Model Code 2010 is a basic prerequisite for applying its design philosophy in an appropriate manner. Therefore, the main objective of this paper is to explain some decidedly non-trivial issues related to safety and reliability management aspects. In this context, this paper indicates how this general philosophy in fib Model Code 2010 is further developed into a set of operational rules for the design and assessment of concrete structures. [ABSTRACT FROM AUTHOR]

Concrete became the most used material on Earth over 200 years following the invention of modern cement. The design concept has undergone a transition from the allowable stress design method, limit state design method, and to the performance-based design method, in response to the evolution of materials, sophistication of experimental facilities, and advancement of computation skills. From the issues on resources and energy depletion, global warming, and resilience etc., it is necessary to create a new design framework taking into consideration the required performance beyond the conventional concept, in order to construct infrastructure and buildings in a more rational way. In other words, one should construct a design system which sets the continued existence of the diverse and rich global environment as its most important criterion of value. In this paper, the authors review the design and technology system developed in the past and discusses it based on the above-mentioned new viewpoint, while constructing and presenting a new design system for concrete structures, focusing mainly on the concept of sustainability which is regarded as the most important in achieving conservation of the Earth's rich resources as well as sound socioeconomic activities of humankind in the future, and discusses its feasibility. [ABSTRACT FROM AUTHOR]

When constructing reinforced concrete (RC) building structures, knowing the loads to which the shoring system will be subjected during the entire process is one of the key aspects for ensuring safety during the work. Although various simplified methods of estimating the load transmission between shores and slabs during construction have been proposed to date, none of these methods can estimate the loads on individual shores during the different construction phases. This paper proposes a calculation method that allows the loads on individual shores to be calculated for each construction phase without having to resort to the use of advanced software. The proposal was validated by comparison with the results obtained from two actual buildings under construction and represents a step forward in the construction of RC building structures, as it is the first method that offers the possibility of estimating the loads acting on each shore during all the construction phases. [ABSTRACT FROM AUTHOR]

With correct design, specification and construction, concrete structures provide high-performance durable assets with long service lives. Owners can maximise the benefits to be gained from concrete structures, while minimising through-life cost and sustainability impacts, by taking a through-life perspective on the design, specification and management of their structures; rather than simply focusing on first cost. This first part of a two-part paper provides an overview of the advice given in the fib guide to good practice entitled Concrete Structure Management-Guide to Ownership and Good Practice (fib Bulletin 44): the paper deals with general issues associated with concrete structure ownership, giving owners an insight into their responsibilities and obligations, what they should do and seek to achieve in the context of concrete structure management, and information regarding potential deterioration mechanisms and the merits of adopting proactive as opposed to reactive structure management. [ABSTRACT FROM AUTHOR]

The well-known capacity of concrete to withstand high temperature and fire is put to the test by the most recent, high- and ultra high-performance cementitious composites, since their more closed pore structure favours pressure build-ups in the pores filled with water, turning to vapour at high temperature. The ensuing spalling phenomena can be prevented by adding polymeric fibres to the mix, while material toughness can be improved - at any temperature - by adding metallic fibres. However, concrete mechanical behaviour depends on the thermal field, which is strictly related to the type of fire and to the thermal properties of the material. Hence, special concretes for special structural applications should be thoroughly characterised at high temperature and after cooling, to evaluate their thermal and mechanical properties. These properties are recalled in the first part of this paper, with reference to thermal diffusivity, compressive and tensile strength, elastic modulus and fracture energy. Furthermore, to maximise the benefits coming from the use of better materials, a parallel rethinking of some aspects of structural analysis is needed.With regard to this point, in the second part of the paper some suggestions and proposals are formulated with reference to the analysis of reinforced concrete sections subjected to combined bending and axial force, and some considerations are made on two rather underrated aspects of the analysis: the role of the thermal self-stresses and the increasing slenderness of fire-exposed columns. [ABSTRACT FROM AUTHOR]

Concrete is by far the largest component of tunnels. Given the high relative humidity in tunnels (e.g. 75%) when compared with buildings in general (e.g. 50%), there is a higher risk of the occurrence of explosive spalling in tunnels during a fire, which increases with increase of the level of pore filling with water in the concrete. Tunnel fires described by hydrocarbon-type fire scenarios are also more severe than building fires described by cellulose fire scenarios (e.g. ISO 834 fire scenario) owing to their confined nature. Passive fire protection in tunnels involves the use of thermal barriers and/or polypropylene fibres in the concrete mix. The latter operates on the pore pressure mechanism of explosive spalling. This paper presents the concept and methodology of the separation of pore pressure spalling from thermal stress spalling for the first time in large-scale experiments as part of the NewCon international research project, by the use of thermally stable lightweight aggregate of negligible thermal expansion. This paper also presents the concept of the pressure induced tangential space (PITS) as a mechanism for increased permeability during fire even before the fibre is melted. The prediction of explosive spalling is still not a fully developed science. Prediction methods include large-scale testing, use of nomograms, theoretical models and numerical models. Numerical modelling, in addition to costly large-scale testing, offers a promising way forward. This paper also introduces for the first time the concept of the expert assessment of spalling in tunnels with a tentative example following a risk-based approach for a given concrete, different traffic conditions and initial pre-fire stress in an example separating tunnel wall. Finally, definitive conclusive calculations for a tunnel example in a severe fire indicates negligible toxicity from the combustion of polypropylene fibres used in tunnel concretes to combat explosive spalling. This work was carried out as part of the NewCon international research project. [ABSTRACT FROM AUTHOR]

Concrete is known to be an excellent structural material, owing especially to its many favourable properties, to its constituent materials available from many local sources, unlimited forms, easy placement, economy and aesthetics. The question remains whether concrete is also an attractive material in terms of its properties with respect to fire. The present paper aims to discuss this question, reach some conclusions and give some indications for the future. The paper also provides an introduction to selected topics concerning fire design of concrete structures, such as the influence of fire on concrete properties (strength, deformation and spalling), member and structural analysis, and the role of both the restraints and the boundary conditions. Only few technical or scientific details are given in the paper, since the author's main objective is to present some topical ideas, on-going research activities and possible future development. [ABSTRACT FROM AUTHOR]

The bond clauses in the CEB/FIP Model Code 1990 (MC90) were written for steel reinforcement in concrete. Since then, fibre reinforced polymer (FRP) reinforcing bars have been introduced as an alternative. To make use of fibre composites, it is necessary to bring these materials into codes of practice and the easiest way is to adapt the code clauses for steel reinforced concrete to FRP reinforced concrete. Proposals for the design bond stress code clauses have been presented in an earlier paper. This paper covers proposals for the design lengths and tension stiffening code clauses. [ABSTRACT FROM AUTHOR]

Bearing pads are used in precast concrete connections to provide a more uniform distribution of contact stresses over the bearing areas and to allow relative movements between precast concrete elements, in order to prevent cracking at the connection area. This paper presents the study of an alternative material made with styrene- butadiene latex modified on Portland cement mortar, polymeric fibres, and, eventually, lightweight aggregate (vermiculite). The developed material showed a good compression strength and low elasticity modulus. These characteristics make it suitable for use as bearing pads in precast concrete connections, such as beam-to-column connections or wall-to-wall connections. The paper shows the main characteristics of this material and the application and tests on: (a) beam-to-column connections and (b) samples that reproduce a wall-to-wall connection. [ABSTRACT FROM AUTHOR]

This paper provides a brief overview of Session 8 `Durability of Concrete Structures' of the fib 2002 congress on Concrete Structures in the 21st Century, which was held in Osaka on 13-19 October 2002. The keynote speaker of the session, Dr Odd E. Gj&3x00F8;rv, Professor and Head of the Department of Building Materials at the Norwegian University of Science and Technology at Trondheim, has conducted concrete research for more than 40 years. His research has focused on a broad range of topics related to the durability of reinforced and prestressed concrete structures in severe environments. His paper addressed durability and service-life issues of concrete structures. In addition to the keynote address, more than 50 papers were considered for this session, covering topics in the following areas: general issues related to concrete serviceability and durability, corrosion of reinforcement, and grouting of post-tensioned systems, as well as several case studies. The highlights of some of the papers are described here. [ABSTRACT FROM AUTHOR]

In steel-concrete composite structures, innovative composite dowels can be used for the connection of ultra-high-performance concrete (UHPC) slabs and high-strength steel members. In addition to sufficient shear capacity, composite dowels have to ensure the transmission of tensile forces in the composite connection in order to prevent lifting of the concrete slab. This may lead to structural problems, particularly in the very slender concrete slabs of high-strength composite beams, where composite dowels have very small embedment depths. Although findings concerning the structural anchorage behaviour of composite dowels under static loads are already available, studies on the fatigue of composite dowels under cyclic pull-out loading are still lacking. As fatigue behaviour is crucial for applications in bridge construction, the present paper introduces cyclic pull-out tests on composite dowels in UHPC slabs in which the influence of different load-dependent parameters (upper load level and load range) as well as the use of transverse reinforcement has been investigated. Furthermore, an approach to assess the lifetime of composite dowels in UHPC under cyclic pull-out loading is proposed. [ABSTRACT FROM AUTHOR]

The coupling of subsequent rings in the circumferential joints of tunnel lining systems is of particular interest in mechanized tunnelling and a controversial issue in discussions. On the one hand, interlocking systems such as "cam & pot" can be of use in limiting the lining's deformation. But on the other hand, unfavourable conditions often lead to repetitive and significant damage that decreases the tunnel's lifetime. This paper describes the experimental results of a three-part optimization concept (structural analysis, topological optimization and experimental verification) that was tested for concrete linings using the example of the shear coupling mechanism. First, geometrical dependencies are analysed which reveal predominantly stronger cams than corresponding pots. Hence, pot bearing capacities are increased, transferring topological optimization results to reinforcement concepts featuring micro-mesh reinforcement, steel fibre cocktails and rebars welded to anchor plates. The latter especially resulted in comparatively stronger pots along with considerably better ductility. Nevertheless, pots still represent the weaker part and are crucial for the design. Therefore, a concept with steel dowels and predefined static boundary conditions was tested. The results are characterized by a significantly lower scatter of bearing capacities accompanied by much better ductility. [ABSTRACT FROM AUTHOR]

Birmingham New Street is the busiest UK rail station outside of London. Growing demand following upgrade works to the West Coast Main Line has seen passenger numbers exceed the design capacity of the current station, which was constructed in 1967. To meet projected increases in passenger numbers, a redevelopment of the historic station is currently underway. Retaining all major structural features, the redevelopment is being undertaken over a live railway in the heart of Birmingham while maintaining existing passenger capacity. This paper describes the structural assessment and strengthening design work undertaken to facilitate the regeneration of Birmingham New Street. The assessment methodologies used in examining this historic concrete structure are discussed before the design of subsequent strengthening works is presented. [ABSTRACT FROM AUTHOR]

Inspection and maintenance of concrete bridges is a major cost factor in transportation infrastructure, and there is significant potential for using information gained during inspection to update predictive models of the performance and reliability of such structures. In this context, this paper presents an approach for assessing and updating the reliability of prestressed concrete bridges subjected to chloride-induced reinforcement corrosion. The system deterioration state is determined based on a Dynamic Bayesian Network (DBN) model that considers the spatial variability of the corrosion process. The overall system reliability is computed by means of a probabilistic structural model coupled with the deterioration model. Inspection data are included in the system reliability calculation through Bayesian updating on the basis of the DBN model. As proof of concept, a software prototype is developed to implement the method presented here. The software prototype is applied to a typical highway bridge and the influence of inspection information on the system deterioration state and the structural reliability is quantified taking into account the spatial correlation of the corrosion process. This work is a step towards developing a software tool that can be used by engineering practitioners to perform reliability assessments of ageing concrete bridges and update their reliability with inspection and monitoring data. [ABSTRACT FROM AUTHOR]

According to current design codes, many existing road bridges exhibit shear capacity deficits. This is partly due to increased traffic loads and partly due to changes in the code provisions. In order to extend the service lives of these bridges, either refined design approaches may be used or strengthening measures performed. This paper describes the results of experimental investigations into how additional external prestressing influences the shear capacity of continuous prestressed concrete beams. Within the research project, six shear tests were performed on three test beams with parabolic internal post-tensioning and additional, variable external prestressing. The aim of the project was to determine the effect of external prestressing on the shear capacity of existing bridges, and whether current design approaches lead to conservative results when used for recalculating existing bridge structures. [ABSTRACT FROM AUTHOR]