Shear transfer capacity along pumice aggregate concrete and high-performance concrete interfaces

This paper aims to present an experimental investigation on the behaviour of interfaces between pumice LWAC (lightweight aggregate concrete) and HPC (high-performance concrete-high-strength and fibre-reinforced), typically found in the faces and core, respectively, of hybrid precast structural sandwich panels. The evaluation of the experimental data resulted in the derivation of a semi-empirical relationship that relates the interface strength with materials strength, interface geometry and loading parameters. A brief overview of existing shear friction theories and proposed relationships, as well as a somparison among existing models and that proposed by the authors, are also outlined in the paper.     

Influence of the design materials on the mechanical and physical properties of repair mortars of historic buildings

Historic buildings are subjected to deterioration by natural weathering or by corrosion due to polluted atmosphere and the materials more susceptible are the mortars used. This study examines the influence of the type and quantity of design materials on compressive strength, creep, water absorption and length change of repair mortars produced. The design materials used were lime, natural pozzolan, sand and brick fragments in order to obtain the compatibility required between historic and repair mortars; different quantities of Portland cement were also used in order to quantify his influence. Nine mixtures were then designed and produced considering as parameters two binder: aggregates ratios, three pozzolan: cement ratios and three sand: brick fragments ratios. The experimental measurements continued until the age of 3 years or the stabilization of the test values. The results indicate that compressive strength is strongly affected by cement content and aggregates dosage and type. It appears that the increase of cement as well as brick fragments leads to confinement of creep deformation, while the mixtures with high pozzolan and sand content experience considerably high creep values. Water absorption reaches higher values when pozzolan or aggregate dosage arises and brick is in excess. Shrinkage increases when binder or brick quantity arise and is considerably influenced by cement content.     

Debonding in foam-core sandwich panels

The strain energy release rate is used to give a criterion for debonding in structural sandwich beams with isotropic faces and a foam core. The critical strain energy release rate of the interface is measured on double-shear specimens and the results of the debonding analysis are compared with experiments on sandwich beams with aluminium faces and foamed polyurethane cores. The analysis describes debonding failure well. Comparison of the load for bebonding with that for other failure modes shows that debonding occurs only if relatively large cracks exist at the interface between the face and the core.     

Topic detection and tracking on heterogeneous information

Given the proliferation of social media and the abundance of news feeds, a substantial amount of real-time content is distributed through disparate sources, which makes it increasingly difficult to glean and distill useful information. Although combining heterogeneous sources for topic detection has gained attention from several research communities, most of them fail to consider the interaction among different sources and their intertwined temporal dynamics. To address this concern, we studied the dynamics of topics from heterogeneous sources by exploiting both their individual properties (including temporal features) and their inter-relationships. We first implemented a heterogeneous topic model that enables topic–topic correspondence between the sources by iteratively updating its topic–word distribution. To capture temporal dynamics, the topics are then correlated with a time-dependent function that can characterise its social response and popularity over time. We extensively evaluate the proposed approach and compare to the state-of-the-art techniques on heterogeneous collection. Experimental results demonstrate that our approach can significantly outperform the existing ones.     

Design of Concrete Flexural Members Strengthened in Shear with FRP

The present study describes a simple design model for the calculation of the fiber-reinforced polymer (FRP) contribution to the shear capacity of strengthened RC elements according to the design formats of the Eurocode, American Concrete Institute, and Japan Concrete Institute. The key element in the model is the calculation of an effective FRP strain, which is calculated when the element reaches its shear capacity due to concrete diagonal tension. Diagonal tension failure may be combined with FRP debonding or tensile fracture, and the latter also may occur at a stage beyond the ultimate shear capacity. An upper limit (maximum) to the FRP effective strain also is defined and aimed at controlling crack opening. The effective strain, obtained through calibration with >75 experimental data, is shown to decrease with the FRP axial rigidity divided by the concrete shear strength. It also is demonstrated that the contribution of FRP to shear capacity is typically controlled by either the maximum effective strain or by debonding and, for a given concrete strength, it increases linearly with the FRP axial rigidity until the latter reaches a limiting value beyond which debonding controls and the gain in shear capacity is relatively small. However, proper anchoring (e.g., full wrapping) suppresses the debonding mechanism and results in considerable increases in shear capacity with the FRP axial rigidity. Finally it is demonstrated that, when compared with others, the proposed model gives better agreement with most of the test results available.     

Experimental Investigation of Nonconventional Confinement for Concrete Using FRP

The present study investigates experimentally the behavior of concrete confined with fiber reinforced polymers (FRP) in the form of jackets which are applied according to a number of nonconventional techniques. First, the effectiveness of various jacketing configurations combined with anchors as a measure of increasing the strength and deformability of L-shaped columns is investigated. It is concluded that easy to install and low-cost anchors made of resin impregnated fibers properly placed at the reentrant corner of L-shaped columns enable excellent mobilization of confining stresses supplied by the FRP jackets. Next, a number of alternative confinement methods are investigated on concrete cylinders, aimed at quantifying the effectiveness of (1) unbonded jacketing, (2) spirally applied strips attached only at their ends, and (3) jacketing directly on concrete with mortar plastering. Although the study may be regarded as preliminary, it provides useful experimental support to a number of techniques which have the potential to open new horizons in the field of externally applied FRP for enhancing concrete confinement.     

Experimental Investigation of FRP-Strengthened RC Beam-Column Joints

The results of a comprehensive experimental program, aimed at providing a fundamental understanding of the behavior of shear-critical exterior reinforced concrete (RC) joints strengthened with fiber reinforced polymers (FRP) under simulated seismic load, are presented in this study. The role of various parameters on the effectiveness of FRP is examined through 2/3-scale testing of 18 exterior RC joints. Conclusions are drawn on the basis of certain load versus imposed displacement response characteristics, comprising the strength (maximum lateral load), the stiffness, and the cumulative energy dissipation capacity. The results demonstrate the important role of mechanical anchorages in limiting premature debonding, and they provide important information on the role of various parameters, including: area fraction of FRP; distribution of FRP between the beam and the column; column axial load; internal joint (steel) reinforcement; initial damage; carbon versus glass fibers; sheets versus strips; and effect of transverse beams.     

Recommendation of RILEM Technical Committee 250-CSM: Test method for Textile Reinforced Mortar to substrate bond characterization

Textile Reinforced Mortar (TRM), also known as Fabric Reinforced Mortar or Fabric Reinforced Cementitious Matrix, composites are an emerging technology for the external repair and strengthening of existing structures. For most applications, the effectiveness of the TRM reinforcement relies on its bond performance. This recommendation identifies the best practice to characterize the bond behaviour of TRM. A shear bond test method is proposed to determine the peak axial stress (associated with the maximum load that can be transferred from the structural member to the externally bonded TRM reinforcement), the stress–slip relationship and the failure mode that controls the TRM-to-substrate load transfer capacity. Guidelines on specimen manufacturing, experimental setup, test execution, and determination of test results are provided.     

Creep and shrinkage analysis of composite systems under axial load and biaxial bending

The instantaneous and creep and shrinkage behaviour of composite steel-concrete sections subjected to axial load and biaxial bending is examined analytically using the age-adjusted effective modulus method and a stress relaxation procedure. Any cross-section that can be discretized in rectangular elements can be analysed using the approach described in this study. Material non-linearities (concrete cracking and crushing as well as steel yielding) are included in the formulation by empolying an interative numerical procedure. The analytical method was implemented in a computer program and case studies demonstrate that composite columns under complex loads experience a considerable redistribution of stresses and strains, causing the degree of cracking and the secondary load effects (P-delta) to increase.