Analytical mechanics solution for measuring the deflection of strengthened RC beams using FRP plates

Partial-interaction due to sliding between the steel bars, adhesively attached FRP plates and their bordering concrete surface, accompanied with the detachment of the FRP plates due to intermediate crack (IC) debonding make the deflection of strengthened RC beams difficult to anticipate. Previous research and design rules on determining the deflection of strengthened RC beams using FRP plates have opted for a full-interaction moment-curvature design technique where the deflection was measured by either deriving average effective moment of inertia and using elastic deflection equations or integrating the curvature along the beam’s length. Therefore, IC deboning of the plate and the slip resulting from the formation and broadening of new cracks were not directly considered. In this study, a partial-interaction moment-rotation analysis of an adhesively plated beam segment was used to derive analytical equations for the rotation of individual crack faces. The analytical expressions were used to compute the rotation at a crack for a given moment; subsequently, the influence of each crack to the midspan deflection of the RC beams was calculated. As for the uncracked region of the beam, the deflection contribution was measured by integrating the curvature over the uncracked span. The deflection results from the mechanics solution seem to compare well with experimental results. The analytical mechanics solution accounts for the partial-interaction between the steel bars, externally bonded FRP plate and their bordering concrete surface, and also the detachment of the external plate through IC debonding. Further, due to its generic nature and non-reliance on empirical data, the mechanics solution can be adopted to forecast the deflection of strengthened RC beams with novel types of reinforcement materials

Were Fertile Crescent crop progenitors higher yielding than other wild species that were never domesticated?

During the origin of agriculture in the Fertile Crescent, the broad spectrum of wild plant species exploited by hunter-gatherers narrowed dramatically. The mechanisms responsible for this specialization and the associated domestication of plants are intensely debated. We investigated why some species were domesticated rather than others, and which traits they shared. We tested whether the progenitors of cereal and pulse crops, grown individually, produced a higher yield and less chaff than other wild grasses and legumes, thereby maximizing the return per seed planted and minimizing processing time. We compared harvest traits of species originating from the Fertile Crescent, including those for which there is archaeological evidence of deliberate collection. Unexpectedly, wild crop progenitors in both families had neither higher grain yield nor, in grasses, less chaff, although they did have larger seeds. Moreover, small-seeded grasses actually returned a higher yield relative to the mass of seeds sown. However, cereal progenitors had threefold fewer seeds per plant, representing a major difference in how seeds are packaged on plants. These data suggest that there was no intrinsic yield advantage to adopting large-seeded progenitor species as crops. Explaining why Neolithic agriculture was founded on these species, therefore, remains an important unresolved challenge

Structural behavior of out-of-plane loaded precast lightweight EPS-foam concrete C-shaped slabs

This study aimed to develop optimum lightweight expanded polystyrene foam (LEPSF) concrete with a compressive strength of 35 MPa at a density of 1980 kg/m3, to produce precast LEPSF concrete C-shaped slabs with different parameters. LEPSF beads and quarry dust were used as partial replacements for coarse and fine aggregates at different percentages of (15%, 22.5%, and 30%) and (7.5%, 15%, and 22.5%), respectively. From the findings of this investigation, it was noticed that the use of LEPSF beads resulted in acceptable early age strength; however, a reduction in strength was observed at a mature age. Meanwhile, the use of quarry dust improved the compressive strength of LEPSF concrete by more than 30% compared to the mixtures with EPS alone. Totally, 256 samples were prepared to examine the physical and engineering properties of LEPSF concrete mixtures. Results revealed that the deflection of the full-scale LEPSF concrete C-shaped slabs was 31.5%–45.7% more than that recorded in comparable normal concrete slabs. Meanwhile, results have shown that the ductility of the precast LEPSF concrete C-shaped slabs improved in comparison to the normal concrete samples and they also exhibited 20% reduction in the self-weight. It was also seen that precast LEPSF concrete C-shaped slabs give more warning time before failure occurs. As such, it was concluded that the developed precast LEPSF concrete C-shaped slabs have a significant potential to be adopted in flooring systems of modern buildings today

Mechanics-based approach for predicting the short-term deflection of CFRP plated RC beams

Most design codes available today for predicting the deflection of adhesively plated RC beams use a full-interaction moment-curvature approach that requires the flexural rigidity to be quantified empirically. Due to their empirical nature, these design rules can only be applied within the bounds of the tests from which they were derived. Furthermore, as these design rules follow a full-interaction analysis, the slip between the reinforcement and adjacent concrete was not considered and the method does not cope with the discrete rotation of the cracks; that is, the deflection associated with crack widening was not directly considered. As an alternative, partial-interaction mechanics-based methods can be used. In this study, a mechanics-based approach for quantifying the deflection of adhesively plated RC beams was presented. The approach took into account the slip between the reinforcement and adjacent concrete, the formation and widening of flexural cracks, and the intermediate crack debonding mechanism of the externally bonded plate. The deflection from the mechanics-based approach was determined by considering the discrete rotation of individual cracks and the curvature of uncracked regions of the beam. The deflection results derived from the mechanics-based approach were compared with the experimental results of seven adhesively plated CFRP RC beams bonded to their tension face and a significant correlation between the results was observed. The mechanics-based approach does not require any components on the member level to be quantified empirically; thus, it could be useful in predicting the deflection of adhesively plated RC beams with new types of reinforcement material

Flexural strength of FRP plated RC beams using a partial-interaction displacement-based approach

esigning FRP plated RC beams using full-interaction moment-curvature analysis would often suggest that the RC structure is brittle with debonding often occurring prior to yielding of the reinforcement steel. For that reason, researchers have looked into a displacement-based approach that takes into account the member debonding mechanism. The force in the plate within the debonded region was assumed to remain at the intermediate crack debonding force, PIC, and the ultimate strength was determined by considering compatibility of displacements along the member length. However, from laboratory testing, it is seen that the force in the externally bonded FRP plate keeps building up until failure occurs. Therefore, in this study, an extension to the displacement-based approach developed by previous researchers for FRP plated beams is presented where the residual bondstress of the plate within the debonded region is incorporated in the analysis. This is achieved by adopting a bond-slip model with a residual shear component that allows for the force in the plate to increase beyond PIC. The ultimate strength of the FRP plated beams is determined when the plate displacement matches that of the concrete near the plate end. A comparison with the experimental results of seven adhesively plated beams shows that incorporating the residual bondstress of the externally bonded plate yields significant improvement in accuracy and give better correlation with experimental findings

RC beam strengthening using hinge and anchorage approach

Retrofitting of existing structures using adhesively bonded plates has been a major growth area in civil engineering and has gained well-deserved popularity over the past few years. This strengthening technique is in line with sustainable practices in construction and can be used to preserve eminent structures of historical or cultural values. This study aims to present an ideal design model for strengthening reinforced concrete elements using the hinge and anchorage design philosophies for retrofitting and plating existing structures. This includes a check on the intermediate crack (IC), critical diagonal crack (CDC), and plate end (PE) debonding mechanisms. The results of a theoretical model for an FRP plated reinforced concrete beam element were presented, and the findings showed that plating increased the shear at the datum point to cause a diagonal crack by 46.7%. The increase in moment capacity due to plating the hogging region was 64.3% while allowing for 30% moment redistribution from the sagging region to the hogging region. The accompanying increase in uniformly distributed load due to 30% moment redistribution was 42.8%. The results of the theoretical model were compared with previous design models for IC debonding to which it has been shown that following the anchorage approach, a higher strain in the plate may be allowed as compared to the hinge approach. In addition to the theoretical model presented, analysis on an FRP plated RC beam and slab were also presented to show the effect of different plate widths on the moment capacity and PE moment capacity