This work enrolls in the context of eco materials. It concerns the field of transformation of local shrub forest resources and lateritic earth with low market values into building materials and is ...developing a process for the valorization of lateritic nodules,
Borassus aethiopum
(palmyra) and
Calamus deerratus
(rattan) in the engineering of modern reinforced concrete structures. The objective of this process is to promote the rational use of these local materials in the realization of the floors of social housing. Experimental studies of physical and mechanical characterizations of the lateritic concrete formulated, of the palmyra and rattan woods were carried out. Through tests of tearing and sliding of the interface between normal concrete and laterite concrete (push-out tests), it has been highlighted the adhesion of palmyra wood to concrete and the contribution of rattan lianas to oppose the longitudinal sliding of the interface between two concretes of different nature. The case study of a hollow body slab in mixed concrete (normal and laterite concrete) reinforced with palmyra and rattan woods, showed the structural effectiveness of lateritic earth, of palmyra and rattan woods for their implementation for the realization of a social housing floor of span, of up to 5 m.
Graphic Abstract
Stresses of a structure are determined with a first or a second order analysis. The choice of the method is guided by the potential influence of the structure’s deformation. In general, considering ...their low rigidity with regard to those of buildings, scaffolding and shoring structures quickly reach buckling failure. Imperfections, such as structural defects or residual stresses, generate significant second order effects which have to be taken into account. The main challenge is to define these imperfections and to include them appropriately in the calculations. The present study suggests a new approach to define all the structure’s imperfections as a unique imperfection, based on the shape of elastic critical buckling mode of the structure. This study proposes a method allowing to determine the equation of the elastic critical buckling mode from the eigenvectors of the second order analysis of the structure. Subsequently, a comparative study of bending moments of different structures calculated according to current Eurocode 3 or 9 methods or according to the new method is performed. The obtained results prove the performance of the proposed method.
This paper deals with strengthening statically indeterminate reinforced concrete (RC) beams with carbon and glass Fiber Reinforced Polymers (FRP) rods by using the Near Surface Mounted (NSM) ...technique. The test program consisted of six two-span beams; one control beam, which had exploited for comparison purposes, and five others initially strengthened in flexure with NSM-FRP rods in both hogging and sagging regions. The main test parameters were type, ratio and length of the FRP bars as well as characteristics of the filling material. The study presents and discusses their impacts on the global flexural behavior of continuous RC beam that mainly includes investigating the overall capacity, failure mode, moment redistribution and ductility state.
All NSM-FRP strengthened beams displayed higher overall capacity than the control beam; the test results showed that implementing the NSM technique in an appropriate way could significantly improve the yielding capacity and load-carrying capacity of RC beams without large decrease in the ductility index or the moment redistribution degree despite the non-conventional failure mode. The beam failure was primary affected by the strengthening length; terminating the FRP bars before the zero moment point caused to change the failure mode from pull out of the FRP bars to premature peeling off of the concrete cover. On the other hand, moment redistribution and ductility of the NSM-FRP beams were negatively affected by: (I) Increasing the FRP reinforcement, (II) Decreasing the FRP length or (III) Using mortar as a filling material instead of epoxy-resin. Adopting a nonlinear analysis of the cross-sections could accurately quantify the moment–curvature and the ultimate load of the NSM-FRP continuous beams.
This paper presents an experimental program that was carried out for the purpose of studying the global flexural performance of reinforced concrete beams strengthened internally with Carbon Fiber ...Reinforced Polymer (CFRP) rods using the Side Near Surface Mounted (SNSM) technique. The CFRP rods were placed laterally, adjacent to the longitudinal steel bars inside precut grooves. The strengthening length and position of CFRP rods as well as the type of filling material were the main variables investigated in this study. Moreover, a detailed comparison between the Side Near Surface Mounted (SNSM) and the Near Surface Mounted (NSM) techniques for the strengthening of RC beams using CFRP rods was conducted as well; in order to validate and assess the effectiveness of the SNSM technique.
The test results showed that using the SNSM-CFRP rods technique allowed improving in a significant way the load carrying capacity of RC beams but decreased their ductility along the deflection at maximum load. The results obtained indicated that the failure mode was influenced by the length of CFRP rods and the filling material characteristics, while the strengthening position did not have significant impact. The SNSM strengthening technique can be used as an alternative method to the NSM method, and in some cases, it may be used to prevent the non-conventional failure modes, due to degradation of the NSM strengthening system, such as the pull out of CFRP-rods or premature debonding failure. The conventional analytical model accurately predicted the strength capacity and mid-span deflection of the SNSM strengthened beams.
•The overall experimental program of this study consisted of 14 bending tests on large-scale RC continuous beams.•The beams were strengthened with EB-CFRP sheets or plates or by NSM FRP ...techniques.•The performance of each strengthening system is presented and discussed in terms of failure mode, yielding and load-carrying capacities, ductility and energy absorption capacities, FRP debonding strain, and serviceability state.•The failure modes of EB FRP (sheets or laminates) beams were mainly dependent on the type and position of the CFRP reinforcement.•The failure modes of NSM FRP (bars) beams were mainly dependent on the length and position of the strengthening bars as well as the type of the filling material used.•Using carbon plates or increasing the CFRP reinforcement ratio could considerably reduce the ductility performance by 70% and the energy capacity by 80% of EB beams compared to the control beam.
Statically indeterminate RC elements such as continuous beams are the most widely used structural form. Their flexural behavior and failure modes are considerably different from those of simply supported ones. The use of FRPs for flexural strengthening and retrofitting continuous RC beams has hardly been studied. Therefore, this paper compares the impacts of NSM-FRP and EB-FRP systems in two-span beams. The overall experimental program of this study consisted of fourteen large-scale bending tests. The performance of each strengthening system is presented and discussed in terms of failure mode, yielding and load-carrying capacities, ductility, and energy absorption capacities, FRP debonding strain, and serviceability state. The experimental results showed that the failure mode is mainly dependent on the type, length, and position of the FRPs, however, a general improvement in the flexural performance of strengthened beams was observed. The NSM technique allows the FRP tensile strength to be better exploited than the EB technique.
AbstractThis study presents a new design of a wood–concrete connector that meets ductility and stiffness requirements in accordance with Eurocode 4. An analytical approach and a numerical model ...developed on Abaqus are proposed. The study is completed by experimental push-out tests and a specially made composite beam. Two types of timber concrete composite (TCC) are considered in this study. The first connector (stud connector), was applied in construction and its performance compared to that of a recently developed connector. The analytical calculation of stiffness was performed using the relevant standard. In addition, different connector configurations and spacing were tested in push-out and beam tests. The results showed that this new connector has interesting characteristics such as stiffness (4,068.12 kNm2) and maximum strength (24,70 kN) compared to existing connectors.
The study of the properties of Recycled Aggregates (RA) and the basic properties of RA concrete has been on going over the last few decades, leading a number of countries to establish standards or ...recommendations supporting their use. In all the cases, the full and partial replacement of the Natural Aggregates (NA) with recycled alternatives has been proven a feasible option. This study focuses on the effects of small and high replacement ratios of recycled coarse and fine aggregates on shear behavior of reinforced concrete beams. The originality of this work is the investigations of the effect of the addition of recycled fines on the structural properties of recycled concretes. Both materials were compared with conventional concrete as a reference. All the beams are tested statically in four-point loading up to failure. The failure modes, the cracking behavior and the mechanical performance of all beams were studied. The experimental results were compared with the shear provisions of selected standards.
In order to predict the ultimate resistance of members by means of numerical simulations (GMNIA – geometric and material non-linear analysis with imperfection), it is indispensable to realistically ...assume geometric and material imperfections. For I-shaped profiles, it is possible to find several studies concerning the influence of geometric (for example member out-of-straightness) and material imperfections (residual stresses) on the ultimate resistance of the member. However, the sensitivity of hot-rolled U-shaped members to geometric and material imperfections has not been addressed in detail before. Moreover, the research projects concerning hot-rolled U-shaped members performed in the past often assumed different forms of geometric imperfections and residual stresses. Sometimes one may even find contradictory recommendations concerning the form of the geometric imperfection to be applied to the member.
Therefore, it seemed interesting and necessary to conduct a comprehensive study explicitly addressing the sensitivity of the ultimate resistance of U-shaped members on the assumption of the geometric imperfections and residual stresses. The results of this study are presented hereafter and recommendations on the form and amplitude of geometrical imperfections and residual stresses to be included into numerical simulations are derived.
•An auto-equilibrated residual stress pattern is proposed for U sections.•The influence of imperfections on the ultimate resistance of U-shaped members is studied.•Recommendations on the imperfections to be used for GMNIA calculations of U-shaped members are derived.
This paper aims to present and analyze the results of an ongoing research project on the use of NSM and side-NSM-FRP composites for the purpose of increasing the load-carrying capacity of two-pan ...continuous RC beams. This research study comprises two parts; an experimental part and a finite element (FE) part. First, three large-scale two-span beams were statically investigated; one control beam and two other beams initially strengthened in bending with two 6 mm diameter CFRP bars. Second, a three dimensional (3D) FE model was developed, using the computer software ABAQUS, in order to predict the flexural performance of the tested beams and to investigate the influence of the models applied to the CFRP-resin-concrete interfaces. The results obtained indicated that the side-NSM-CFRP bars system is a convenient alternative to the conventional one for strengthening continuous beams. For some strengthening configurations, the side-NSM technique proved to be more efficient than the NSM technique, particularly when the CFRP bars were applied solely in the hogging region or the sagging regions. The moment redistribution of strengthened beams was negatively affected when the steel reinforcement ratio in the hogging region was increased. Nevertheless, the moment redistribution degree was significantly affected by the position and arrangement of the CFRP bars. The 3D-FE analysis developed with the cohesive zone model can capture the main aspects observed from the experiments.
•The NSM and side-NSM techniques could be used to improve the load-carrying capacity of the continuous RC beams.•The side-NSM-CFRP system is a convenient alternative to the NSM system for strengthening continuous beams.•The moment redistribution degree of NSM/side-NSM CFRP beams is affected by the position and arrangement of the CFRP bars.•The 3D FE analysis developed with the CZM can capture the main aspects observed from the experiments.
•The side bonding technique is a convenient technique for strengthening RC beams.•Increasing the fiber weight may serve as an alternative to multiple sheet layers.•The majority of the moment ...redistribution occurred before yielding of the steel.•The design codes can predict strength of RC beams strengthened with one CFRP layer.•The test results confirm that the NSM system is more efficient than the EB system.
This paper presents an experimental study of the use of carbon fiber-reinforced polymer (CFRP) composites to strengthen two-span reinforced concrete (RC) beams. Six large-scale beams were strengthened in hogging and sagging regions according to the external bonding (EB) technique and then statically tested to investigate the impact of the CFRP position , CFRP form , CFRP layers , and weight of carbon fibers on the flexural performance of continuous beams. The experimental results of the strengthened beams were carefully studied in terms of load-carrying capacity, failure modes, cracking patterns, moment redistribution, and reinforcement strain and compared with the results of an unstrengthened control beam. The efficiency of the EB technique in strengthening continuous RC beams was assessed through a comparative study with the near surface mounted (NSM) technique. For this purpose, another two beam specimens strengthened with NSM-CFRP bars were considered.
Based on the experimental results, a general improvement in the flexural performance of strengthened beams was observed. By applying the EB-CFRP composites, the yield and ultimate load capacity could be improved up to 59.1% and 49.8% respectively. . The results also showed that increasing the carbon fiber weight was found to be effective in improving the strength capacity of beams and it may use as an alternative to multiple sheet layers… Comparisons regarding the global flexural performance allow confirming the higher efficiency of the NSM system in comparison to the EB one.
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