1,721,087 research outputs found
Analytical Modelling of Transmission and Anchorage Length in Corroded Pre-Tensioned Concrete Elements
No full textPre-tensioned concrete (PC) elements are widely used in the construction industry, and the bond between strands and concrete is a key factor to evaluate their behavior. However, bond mechanisms are complex and existing design rules provide simplified formulations, which do not always ensure a good estimate of experimental evidence. Moreover, bond evolves during the service life of PC elements due to long term effects and external actions, that can lead to its deterioration. In this work, corrosion effects on bond of PC elements are analyzed through the development of analytical models, based on the Thick-Walled Cylinder (TWC) theory. New analytical models are presented, to estimate transmission and anchorage length in corroded PC elements
Effect of axial cyclic loading on frcm confined concrete
No full textThis study presents the results of an experimental campaign aimed at testing the behavior of fiber-reinforced cementitious matrix (FRCM) confined concrete subjected to axial cyclic and monotonic loading. Several parameters were investigated in the campaign, including fiber material (glass and carbon), number of layers applied (1-4 layers) and loading protocol. The results of 22 cylindrical specimens, between control and confined ones, were tested while carefully monitoring axial stress and strain developments. Lateral strain development was also monitored, through electrical strain gauges (eSGs), directly on the fibers of each confinement layer applied to better understand fiber exploitation during cyclic loading. Test results show that even though concrete strength was enhanced in all confined specimens, ductility is the one that is most improved. Both strength and ductility enhancements strongly depend on fiber properties and have a linear proportional enhancement with an increase in the FRCM layers applied. Additionally, no significant difference was observed between the envelope stress-strain curve from cyclic tests with respect to the monotonic ones
Experimental behavior of FRCM-confined concrete under high temperature
Full text linkThe paper investigates the behavior of concrete confined through FRCM (Fiber Reinforced Cementitious Matrix) composites subjected to high temperatures. Small scale cylindrical specimens (150x300 mm) were confined using two types of carbon fiber (dry and resin impregnated). For the sake of comparison two layers of FRCM were applied to all confined specimens. After curing, cylinders were exposed to four ranges of increasing temperatures being 20°C (ambient), 80°C, 100°C and 250°C and then tested under cyclic loading. The experimental results show that thermal stress significantly influences the confinement effectiveness of FRCM composites. Exposure to high temperatures reduces the ultimate confined strength and strain. For specimens confined with resin impregnated fibers, the observed stress-strain trend of confined elements tested after high temperatures exposure significantly differs from specimens tested under standard ambient conditions
Recycled materials in concrete
Full text linkThis chapter reviews the main recycled materials that can be introduced in concrete mix design to achieve the sustainability goals asked for by the construction industry. Outcomes from the most recent research work about the use of recycled components in concrete are reported. First, the use of supplementary cementing materials such as fly ash and ground granulated blast-furnace slag is discussed. Then, the application of recycled materials as aggregates is analyzed, paying special attention to recycled aggregates coming from construction and demolition waste, whose use is already regulated in almost all of the developed countries. By-products will also be presented, because their application in concrete is gaining increasing attention by researchers, such as in the case of steel slags. Lastly, some innovative research results about other recycled materials are included, such as recycled glass and plastics, scrap tires, hemp fibers, and ashes from incinerator facilities
FRCM-Confined Concrete: Influence of Cross-Section Geometry on Cyclic Stress–Strain Behavior
No full textThis work presents the results of an experimental campaign aimed at assessing the influence of cross-section geometry on the confinement of concrete samples. Four geometries were investigated: circular, square and two rectangular ones, characterized by different aspect ratios. Carbon fibers were used in the Fiber Reinforced Cementitious Matrix (FRCM) employed to realize the confining jackets. Samples were tested under uniaxial compressive stress, both adopting a cyclic and monotonic loading, to evaluate compressive strength, ductility and fibers strain exploitation ratio. Results indicate that the best performance is achieved by circular specimens, displaying the highest lateral pressure
Model Uncertainty Assessment for the Anchorage Length Formulation of fib Model Code 2020
No full textIn the design of pre-tensioned concrete elements, it is important to avoid the anchorage failure of tendons. This can be done by predicting the anchorage length through any of the empirical or semiempirical models provided by the main design codes. However, the models in these codes are based on experimental evidence gathered many years ago, when the 7-wire strands manufacturing process was significantly different from now. The objective of this contribution is to evaluate the model uncertainty for the anchorage length formulation of the last draft of the fib Model Code 2020 and to ensure that all the main influencing factors are properly considered. Since a direct measure of anchorage length is not experimentally feasible, a large data set of flexural tests has been gathered from the scientific literature, and each failure mode has been compared to the corresponding anchorage length prediction, to obtain a censored sample of the model uncertainty from which an appropriate probability distribution could be estimated. Then, the minimum values of the partial safety factors that consider both model and material uncertainties and ensure the achievement of the target reliability in anchorage length predictions have been derived through Monte Carlo Simulations. Finally, these results have been validated through a FORM approach for some case studies and compared to the current fib Model Code 2020 proposed partial safety factors, showing that they guarantee the achievement of the expected level of reliability in all the evaluated situations
Seismic reliability assessment of code-conforming reinforced concrete buildings made with electric arc furnace slag aggregates
No full textRecent studies have demonstrated how Electric Arc Furnace (EAF) concrete represents a sustainable alternative to ordinary concretes, and that it could be satisfactorily employed to realize reinforced concrete (RC) elements. However, a comprehensive study about the effects of its use in RC structural systems, both in terms of structural safety under static and dynamic loads, and environmental impacts along the whole life cycle, has not been investigated yet. This work analyzes the seismic reliability of standard residential buildings (cast in place RC frames), considering three different configurations (3-, 6- and 9- story building type) designed considering ordinary concretes made with natural aggregates (NA) according to the novel Italian seismic code, which is similar to the Eurocode 8 approach. Non-linear time history analyses have been carried out to investigate the seismic response of the analyzed cases comparing results obtained from the benchmark structures (i.e. the NA ones) with those coming from the same made with EAF mixes, in order to verify the suitability in using sustainable EAF concrete mixes in seismic areas. Lastly, a seismic reliability analysis has been carried out for comparative purposes, demonstrating how EAF concrete overstrength compensates for the extra efforts that the analyzed RC frames may undergo during seismic events
Environmental impacts of recycled aggregate concrete
No full textConcrete is the most diffused building material worldwide; its large availability is however responsible for great environmental emissions, causing the production of up to 5% of worldwide man-made emissions of carbon dioxide. In this contribution, the effects of using recycled concrete aggregate (RCA) to produce recycled aggregate concrete (RAC) are analyzed, both in terms of mechanical and environmental performances. Four concrete mixtures have been designed: a control, made with only natural aggregates, and three containing RCA. Fresh and hardened concrete properties have been analyzed, and then savings in environmental emissions due to the use of RCA have been quantified. Environmental analysis has been conducted through Life Cycle Assessment (LCA). Results show that the quality of the adhered mortar in RCA is a key parameter to allow recycled concrete to be designed with satisfying mechanical properties, and about 50% of carbon can be saved using RCA instead than NA
New trends in assessing the prestress loss in post-tensioned concrete bridges
Full text linkThe evaluation of the current prestress force represents often a challenging issue during the assessment of existing post-tensioned concrete (PTC) members. In this contribution, two case studies are presented to show
the efficiency of some experimental methods applied both to laboratory beams and to an in-service PTC bridge. First, the outcomes of an experimental campaign carried out on three PTC beams with a straight post-tensioned, non-grouted tendon are discussed. For each beam, three point bending tests (3PBTs) were carried out applying increasing load steps until failure and varying the prestress force; at each load step, nondestructive
tests (NDTs) were performed, namely, dynamic free vibration and ultrasonic tests. The variation of non-destructive parameters was evaluated as a function of the prestress force and of the structural damage. The second case study deals with a 50-year-old PTC bridge with grouted ducts. In this case, other than evaluating the existing geometry, structural details, and material properties, the following NDTs were performed: endoscopies, tests based on stress release, i.e., both sawcut and wire-cut tests, and lastly, X-ray diffractometries (XRDs). The results indicate the high potential of this latter technique, which resulted more
reliable and less invasive than the previous ones
A new confinement model for FRCM confined concrete
No full textConfined concrete by means of FRCM (Fabric Reinforced Cementitious Matrix), also known as TRM (Textile Reinforced Mortar), may exhibit alternative stress–strain behaviors, depending on different variables including the unconfined concrete strength, concrete cross-section, fibers type and number of layers. Specifically, increasing the confinement level, the experimental observed response changes from a softening to a hardening one, after an initial peak that coincides roughly to that of the unconfined strength. To consider the peculiar behavior of FRCM-confined concrete, a new analytical model is proposed in this work. The formulation allows to calculate both the first and ultimate peak strength values, being more adherent to the real observed experimental behavior of FRCM-confined concrete members. The model is calibrated on a set of experimental data obtained by the same authors, and then its accuracy is validated on a different, larger dataset. Model performance indicators are compared to those calculated for other existing formulations, demonstrating the goodness of the new proposal
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