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Composite dowels are powerful shear connectors in steel-concrete composite structures, especially for prefabricated composite bridges. The advantages of composite dowels over other shear connectors are their increased strength and sufficient slip capacity even in high-strength concrete. The National Technical Approval for Germany [1], [2] from 2013 allows the design of composite structures with composite dowels for hogging and sagging moments under static and cyclic loading. However, the design of structures with cyclic loading in combination with centric tension perpendicular to the composite dowels (transverse tension) is neglected. Therefore, one part of national project P967 “External reinforcement for composite bridges”, funded by FOSTA, the Research Association for Steel Application, was to determine how transverse tension affects the static capacity and fatigue resistance of composite dowels. To investigate this effect, two test series, each with six push-out tests, were carried out. The test setup and the results of the static and cyclic shear tests in combination with transverse tension are presented in this paper.

In the case of frame bridges with external reinforcement, the reinforcing elements have to be anchored in the abutment wall. Owing to the interaction of negative bending moment and longitudinal shear force in the abutment area, the force transfer between concrete, external steel reinforcement and normal steel reinforcement is complex. Two frame structure tests were carried out to investigate the loadbearing behaviour and rational anchorage length of external reinforcement in abutments. Two different anchorage lengths were tested, and the structural behaviour and failure modes of the two specimens were compared and analysed. The results indicate that the anchorage length has a great influence on the loadbearing capacity, and the pull-out effect at the end of the external reinforcement should be paid special attention. The detail stress distribution and the M-V interaction in the anchored external reinforcement were obtained from the tests and the results fit well with the theoretical calculation. Mechanical models are proposed to evaluate the pull-out effect and optimize the anchorage length of the external reinforcement.

Composite dowels with different shapes have been developed and used in composite members during the last two decades. At the Chair of Concrete and Masonry Structures at Technical University of Munich (TUM), composite dowels with a clothoid shape are used for filigree composite beams and columns. In both types of application the composite dowels are used as external reinforcement and Ultra-High Performance Concrete (UHPC) is chosen instead of normal-strength concrete. This article describes mainly the results of the preliminary push-out tests that were carried out in order to determine the structural behaviour of composite dowels in thin UHPC elements and verify the influence of the UHPC web thickness, the steel thickness of the shear connector, the concrete compressive strength and the influence of reinforcement on the loadbearing capacity and failure modes. The paper also includes an overview of and the outlook for the experiments with composite beams and composite columns.

In steel-concrete composite beams, lifting effects between the steel section and the concrete slab usually occur incidentally and have comparatively small load ordinates compared with the shear forces transferred. For this reason, lifting forces are generally irrelevant for the dimensioning of the composite joint. Nevertheless, this statement does not apply if shear connectors are used for the systematic anchorage of pull-out forces. Although the anchorage behaviour of conventional shear connectors, e.g. headed studs, has already been studied extensively, appropriate investigations into the anchorage behaviour of concrete composite dowels are lacking, especially for composite dowels in slender or cracked concrete slabs. In this paper, the anchorage behaviour of a puzzle-shaped concrete composite dowel is investigated in cracked and uncracked concrete. To this end, particular test setups were developed. All tests were simulated using a three-dimensional, non-linear finite element model. Finally, an engineering model for calculating the anchoring capacity of single composite dowels and composite dowel groups in reinforced and unreinforced concrete is presented.

Cuauhtémoc Stadium, a first division football stadium in Puebla, México, with more than 51 000 seats, has recently been completely renovated. The brand-new façade has become an icon for the club and for the city. The façade is designed as a skin of single-layer ETFE foil in a combination of three different shades of blue and translucent white. The design and construction of the façade is the result of an international collaboration between local contractor DÜNN Lightweight Architecture, from Zapopan, Mexico, and LEICHT Structural engineering and specialists consulting GmbH, based in Munich, Germany. This paper will elaborate on the boundary conditions of the project and the technical decisions made for the construction of the façade.

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This paper includes a presentation of a shear test database that contains 278 tests conducted on reinforced concrete beams with vertical stirrups and no horizontal skin reinforcement. These beams are commonly referred to as non-slender beams since they were tested using loading arrangements that created shear span-to-depth ratios a/d < 2.4. In an effort to arrive at a database that can be used for the purposes of evaluating the accuracy and conservativeness of design provisions, several control and filtering criteria were applied. After this process, 178 beams remained in the evaluation database. The analyses conducted using this database indicated that the application of the strut-and-tie models (STM) of Eurocode 2 (EC2) to non-slender beams with stirrups is unconservative, i.e. the database analyses yielded results that were above the desired 5 % fractile. Almost all unconservative strength estimations were obtained for test specimens containing large numbers of stirrups. Conversely, statistical evaluations showed that the FIP Recommendations model for beams with point loads near supports is conservative.

Progressive collapse is a phenomenon in which local failure of a structural component due to a gas explosion or blast may lead to failure of the entire structure or a significant part of it. RC structures can resist progressive collapse through various mechanisms such as frame action and catenary action.
In this paper, the effect of catenary action on the resistance of concrete frame structures to progressive collapse is modelled using limit analysis. Non-linear optimization is performed for this. It is observed that although frame action is known to be the main mechanism resisting progressive collapse, at the end of this action, after rupture of bottom bars, catenary effects may bring about a noticeable increase in the resistance of the structure. The results show good agreement with the experimental results of other researchers.

Software for calculating the internal forces, moments and deflections of sandwich elements with reinforced concrete facings has been developed as part of a research project at Technische Universität Kaiserslautern. Sandwich elements with stiff concrete facings are internally statically indeterminate. Cracking of the concrete facings leads to a redistribution of the internal forces and moments over the length and across the cross-section of the element. This redistribution must be considered in the structural design of such elements.
An existing program for calculating metal-faced sandwich elements was considerably extended by an iterative approach that allows the internal forces and moments to be calculated with the exact stiffness of the cracked facings. This iterative approach and the calculation algorithm behind the new software, called swe2+, are explained in this paper. A verification of the calculation results and a parametric study of a two-span sandwich element are also presented.

Chloride-induced corrosion of reinforced concrete (RC) bridge girders has led to a huge loss of national resources. One of the important concerns affecting RC bridge girders is corrosion of the stirrups, which can even cause the failure mechanism to change from a ductile flexural mode to a brittle shear mode. Hence, analysis of the reduction in shear capacity overtime is essential in the reliability assessment of bridge girders, which is the topic of the paper. This paper proposes a stochastic modelling approach for estimating the time-variant shear capacity and reliability within the framework of a Monte Carlo simulation, which assists in the sustainability-based service life design of bridge girders. Such modern design concepts require methodologies for estimating whole life cost at the design stage itself. The development of such methodologies would provide the designer with various options for arriving at an optimum design having the desired performance level during the service life. The proposed approach takes into account: 1) the randomness in basic variables, 2) the effect of micro-environments and the spatial variation of corrosion, 3) the number of stirrups resisting web shear failure, and 4) the ductile to brittle transition of stirrup steel as corrosion propagates. The incorporation of this transition is found to have a significant influence on the time-variant reliability of the girder. Although PFA concrete is known to have better durability characteristics than OPC concrete, this paper gives a framework for its quantification in terms of time-variant reliability.

Strut-and-tie models (STMs) have been wildly used for the design of disturbed regions in structural concrete members. The STM developed based on the load path method or with the aid of stress trajectories is not unique and varies with the designer's intuition and past experience. As a result, topology optimization methods have been adopted to generate STMs in reinforced concrete structures. However, such models are just a preliminary configuration and the detailed layout of ties in an STM cannot be determined by the optimal topology. This is because reinforced concrete is assumed to be a uniform elastic continuum. Therefore, the effect of the steel reinforcement on the load transmission cannot be considered in the optimization process. Recently, the criterion of minimum strain energy has been proposed to determine the optimal layout of STMs obtained by the modified optimization method. However, the strain energy criterion does not work when the minimum strain energy in ties is zero when evaluated by mathematical equations. To address this issue, the maximum stiffness criterion is proposed to discover the optimal layout of ties in STMs by evaluating the stiffnesses of strut ties.

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.

This paper is a comprehensive background document on the state of the art in European seismic design provisions which was assembled by fib committee 5.1 to support the development of design guidelines regarding the use of externally applied fibre reinforced polymer (FRP) materials in the seismic retrofitting of reinforced concrete structures. In the context of developing design guidelines, the underlying mechanistic models that support the derivation of provisions were assembled following critical evaluation of the existing proposals and with careful reference to the experimental evidence available, the comparative assessment of past models in the literature and requirements established from first principles.

The behaviour and modelling of concrete columns confined with FRP composites under monotonic compression has been extensively studied, but far fewer studies of the cyclic behaviour of FRP-confined circular and rectangular columns have been carried out. A reliable model indicating the cyclic stress-strain behaviour of FRP-confined columns is of great importance, especially for seismic retrofits and the design of these columns. In this paper, based on the results from a series of cyclic compressive loading tests on FRP-confined specimens, a unified cyclic stress-strain model is proposed for circular, square and rectangular columns confined with FRP composites. The model contains different parts of the cyclic stress-strain curve, including plastic strain, maximum strain in unloading path and corresponding stress, stress deterioration, effect of loading history, partial unloading and partial reloading. New expressions are also proposed for predicting unloading and reloading paths. The proposed model agrees well with the test results.

The behaviour of the bond between fibre-reinforced polymers (FRP) and concrete greatly influences the behaviour of concrete structures strengthened with FRP composites. Although numerous experimental studies have investigated this bond, experimental data concerning fatigue tests on carbon FRP plates attached to concrete blocks are still lacking. Therefore, a series of double-lap shear tests under monotonic and fatigue loadings were performed on concrete prismatic specimens reinforced with CFRP plates. First, a series of experimental investigations are summarized. Thereafter, the fatigue behaviour of CFRP plate debonding is characterized using S-N diagrams that represent the relationship of the upper-limit fatigue load with the monotonic load strength and the number of cycles to debonding on a semi-logarithmic scale.

Fibre orientation and volume distribution affect the post-cracking tensile strength, which is one of the main design parameters of fibre-reinforced concrete (FRC). This paper discusses the influence of unidirectional and grid reinforcement on fibre orientation and distribution in FRC slabs. Slabs without conventional reinforcing bars were used as a reference. The slab size was 1200 × 1200 × 150 mm. Numerical simulations were used to predict the fibre orientation and X-ray computed tomography (CT) to determine the actual fibre orientation and distribution. Beams were sawn from each slab, CT-scanned and tested in three-point bending tests in accordance with EN 14651. Both the numerical simulations and the CT results show that the rebars caused a more isotropic fibre orientation in the lower halves of the slabs. This was confirmed in the bending tests, where the lowest variation and highest residual tensile strengths were documented for beams sawn from slabs with grid reinforcement. Fibre migration from the upper layer to middle and lower layers of the slabs due to gravity was observed in all slabs, and in the reinforced slabs, migration also depended on the distance from the casting point. The reinforcement led to an accumulation of fibres above the rebars in the middle layer of each reinforced slab. A set of mechanisms is proposed to explain the experimental results.

Cross-section deformation is considered an important indicator for assessing the structural safety in the inspection and maintenance of tunnels. The way it increases over its lifetime is an indication of the gradual degradation in structural performance. In order to take timely and appropriate maintenance measures before the tunnel reaches the ultimate limit state, a predictive degradation model of cross-section deformation should be established. In this paper, a probabilistic degradation model is developed based on an average uniform rigidity ring model for circular tunnels assembled from segmental linings. By considering the uncertainties and relevant performance of parameters that vary over time, the model is able to supply probabilistic and time-dependent predictions. Critical parameters are identified and the model is simplified following sensitivity analysis. Based on the measuring data, a Bayesian updating method is proposed to improve the input assumptions and predictions of the model. This research provides a perspective on the degradation modelling of the cross-section deformation of circular tunnels assembled from segmental linings and methods for improving the proposed predictive model.

Durability at the corners of the cross-section is relatively weak in the concrete beams of bridges; the reinforcement at the corners therefore corrodes first. In order to delay durability failure at the corners, measures should be taken such as the application of corner concrete coatings or adjustments to the reinforcement at the corners. In this way, the durability resistance would be adjusted to be equal in the section, which is called the equal durability design method. In this paper, the life cycle analyses of a component designed with equal durability and one designed in the traditional way - both in a carbonation environment - are conducted and compared. A probabilistic model of service life is established based on empirical degradation models. Service life distribution is calculated with the Monte Carlo simulation method. Costs associated with durability failure are estimated based on the service life distribution. Related influencing factors are analysed as well. Finally, life cycle cost analyses of the component designed with equal durability and the one designed in the traditional way are conducted and compared. The results show that the component designed with equal durability is more economic over the life cycle if construction cost is kept within about 1.1 times that of the component designed traditionally.

The growing concern for the ready-mixed concrete industry is the disposal of returned unused concrete. In its plastic state, the concrete is a perishable product and the disposal of any unused concrete presents a set of challenges. An increase in environmental regulations requires the industry to implement the best practices that effectively reduce the quantity of by-product materials requiring disposal. This paper describes a preliminary experimental study on the effect of commercial stabilizer on the plastic and hardened properties of concretes made with three different types of cement commonly used in Australia, namely, general-purpose Portland cement (GP) (100 % ordinary Portland cement (OPC)), general-purpose blended (GB) cement (75 % OPC + 25 % class F fly ash (FA)) and low-heat (LH) cement (35 % OPC + 65 % blast-furnace slag). The effect of various stabilizer dosages on the efflux time (flow time) of GP, GB and LH cement grouts was studied in the initial phase. The results show that for a constant efflux time, the holding duration of the grouts increases with increasing stabilizer dosages (or amounts) and in the case of GB and LH cement grouts, the holding duration is longer than the GP cement grout for the same stabilizer dosage. In the next phase, the predicted stabilizer dosage was added to concretes made with the above three cements to evaluate the plastic and hardened properties of fresh concretes, stabilized concretes and blends of fresh concretes with 10, 25 and 50 % stabilized concretes. The results show that the initial slump values are within the tolerance, except they are higher when the stabilizer dosage is added after 1 h, but the final slump is within the tolerance of the control concrete. After stabilization of the concretes, the initial and final setting times of stabilized concretes increased to > 24 h. The initial and final setting times of the blended concrete containing fresh concrete and 10, 25 and 50 % stabilized concretes are similar to those of fresh concrete for all cement types. The stabilized concretes do not have any significant effect on the compressive strength and shrinkage compared with the control concrete.