Optimisation and design of post-tensioning anchorage corner blisters in concrete box girder bidges

The design of anchorage blisters of internal continuity post-tensioning tendons of bridges built by the cantilever method, presents some peculiarities, not only because they are intermediate anchorages but also because these anchorages are located in blisters, so the prestressing force has to be transferred from the blister the bottom slab and web of the girder. The high density of steel reinforcement in anchorage blisters is the most common reason for problems with concrete cast in situ, resulting in zones with low concrete compacity, leading to concrete crushing failures under the anchor plates. A solution may involve improving the concrete compression and tensile strength. To meet these requirements a high-performance fibre reinforced self-compacting mix- ture (HPFRC) was used in anchorage corner blisters of post-tensioning tendons, reducing the concrete cross-section and decreasing the reinforcement needed. To assess the ultimate capacity and the adequate serviceability of the local anchorage zone after reducing the minimum concrete cross-section and the confining reinforcement, specified by the anchorage device supplier for the particular tendon, load transfer tests were performed. To investigate the behaviour of anchorage blisters regarding the transmission of stresses to the web and the bottom slab of the girder, and the feasibility of using high performance concrete only in the blister, two half scale models of the inferior corner of a box girder existing bridge were studied: a reference specimen of ordinary reinforced concrete and a HPFRC blister specimen. The design of the reinforcement was based in the tensile forces obtained on strut-and-tie models. An experimental program was carried out to assess the models used in design and to study the feasibility of using high performance concrete only in the blister, either with casting in situ, or with precast solutions. A non-linear finite element analysis of the tested specimens was also performed and the results compared

column connections under cyclic lateral loading

For their help in the laboratory, the authors also acknowledge Rafael Sanabria Díaz, Peyman Ghaderi and Bruno Moniz. Publisher Copyright: © Fédération Internationale du Béton – International Federation for Structural Concrete.Punching shear reinforcement has already proved to be a reliable solution to improve the deformation capacity of flat slab – column connections subjected to seismic actions. Alternative approaches are becoming attractive with the development of materials such as High-Performance Fibre Reinforced Concrete (HPFRC) with better performance in tension and compression compared to conventional concrete. Motivated by the promising results obtained during an experimental campaign on hybrid HPFRC flat slabs under monotonic centred vertical loading, this paper investigates the possibility of using HPFRC to improve the behaviour of flat slabs under lateral loading (such as during earthquakes). Four reversed horizontal cyclic loading tests, under constant gravity loads, are presented. The flexural reinforcement ratio, the extent of HPFRC zone from the face of the column and the gravity load were the experimental variables considered. Results show that HPFRC can be a promising alternative to conventional punching shear reinforcement in slab column connections subjected to seismic actions, leading to increased deformation capacity. Furthermore, the results show that even a small extent of the HPFRC zone (up to 1.5 times from the face of the column) can lead to significant benefits in terms of seismic behaviour of slab – column connections, opening the possibility for an optimization of use of HPFRC.authorsversionpublishe

Behavior of flat slabs with partial use of high-performance fiber reinforced concrete under monotonic vertical loading

Funding Information: This work was financially supported by the Fundação para a Ciência e Tecnologia – Ministério da Ciência, Tecnologia e Ensino Superior through project PTDC/ECI-EST/ 30511/2017 funded by national funds (PIDDAC). EUROMODAL, Secil, Omya Comital, Sika and Dramix are gratefully acknowledged for their collaboration and supply of materials. Publisher Copyright: © 2022 Elsevier LtdReinforced concrete flat slabs are used worldwide in multi-story buildings. In these slabs, the design is often governed by punching shear and serviceability. The mitigation of these issues during design usually leads to increased raw material consumption and costs. Previous studies have shown that using Fiber Reinforced Concrete (FRC) or High-Strength Concrete (HSC) only at the vicinity of the column, while casting the rest of the slab with Normal Strength Concrete (NSC), can lead to an improved behavior under gravity loads in terms of both serviceability and ultimate capacity. Motivated by these results and the scarcity of previous tests, the present paper experimentally investigates the applicability of High-Performance Fiber Reinforced Concrete (HPFRC) as an alternative material that can be seen as an improvement over FRC and HSC, allowing a combination of ductility and strength. In addition, the HPFRC used in this paper is self-compacting, thus reducing the labor costs associated with concrete vibration. Five 150 mm thick flat slabs were tested under monotonically increasing punching load. The experimental variables were the flexural reinforcement ratio and the extent of the HPFRC zone. One of the specimens was cast only with NSC and served as a reference slab. Results show that the solution was effective for both flexural reinforcement ratios considered. Cracking load, maximum load, as well as the displacement capacity were increased significantly, even for a small extent of HPFRC (1.5 times the effective depth from the face of the column). Regarding the ultimate load capacity, it was observed an increase of 44% to 58% for the specimens with lower reinforcement ratio (0.64%) and between 15%–21% for the specimens with higher reinforcement ratio (0.96%). The results indicate that the use of HPFRC is a promising solution regarding both serviceability and ultimate limit state design of reinforced concrete flat slabs under gravity loading, with obvious advantages in material savings and labor costs.publishersversionpublishe

Characterization of soil macrofauna in grain production systems in the Southeastern state of Piauí, Brazil

O objetivo deste trabalho foi caracterizar a macrofauna edáfica em sistemas de produção de grãos sob plantio direto e convencional no Sudoeste do Piauí, na região de Matopiba. Amostras de solo foram coletadas nas camadas de 0,0-0,1, 0,1-0,2 e 0,2-0,3 m, com serrapilheira, em áreas cultivadas predominantemente com milho e soja, sob preparo convencional e plantio direto, em solos com diferentes texturas. Remanescentes de vegetação nativa adjacentes foram amostrados como referência. A macrofauna edáfica nos diferentes sistemas de uso do solo foi identificada até o nível de famílias, as quais foram agrupadas de acordo com suas funções ecológicas. Os grupos mais abundantes nas áreas amostradas foram Isoptera, Hymenoptera e Coleoptera, este com o maior número de famílias. A análise de componentes principais revelou que os grupos funcionais geófago/bioturbador, fitófago/praga e predador/parasita estão associados a solos de textura argilo-siltosa; enquanto o grupo detritívoro/decompositor, a solos mais arenosos. Os sistemas de manejo do solo alteram a estrutura da comunidade de macroinvertebrados edáficos em relação à condição natural de Cerrado. O plantio direto proporciona maior abundância e riqueza de espécies que o preparo convencional, e minimiza o impacto de sistemas agrícolas sobre a biodiversidade da macrofauna edáfica.The objective of this work was to characterize the edaphic macrofauna in agricultural grain production systems under no-tillage and conventional tillage, in the Shoutheastern state of Piauí, in the Matopiba region, Brazil. Soil samples were taken from the 0.0-0.1, 0.1-0.2, and 0.2-0.3-m layers, with litter, in areas predominantly cropped with corn and soybean, under conventional and no-tillage systems, in soils with different textures. Fragments of native vegetation in adjacent areas were used as a reference. The edaphic macrofauna in the different land uses was identified down to family level, and the families were grouped according to their ecological functions. The most abundant groups in the sampled areas were Isoptera, Hymenoptera, and Coleoptera, the latter with the highest number of families. Principal component analysis revealed that the functional groups geophages/bioturbators, phytophages/pests, and predators/parasites were associated with clayey-silty soils, and detritivores/decomposers with sandy soils. Soil management systems change the community structure of edaphic macroinvertebrates in comparison with the natural Cerrado condition. No-tillage system promotes greater abundance and species richness than conventional tillage, and minimizes the impact of agricultural systems on edaphic macrofauna biodiversity

Soil macrofauna associated with cover crops in an Oxisol from the southwest of Piauí state, Brazil

ABSTRACT: The soil macrofauna is fundamental for the maintenance of soil quality. The aim of this study was to characterize the soil macrofauna under different species of cover crops, including monoculture or intercropping associated to two types of soil management in the southwest region of Piauí state. The study was carried out in an Oxisol (Latossolo Amarelo, according to Brazilian Soil Classification System) in the municipality of Bom Jesus, Piauí, distributed in 30 m2 plots. Testing and evaluation of the soil macrofauna were conducted in a 9 × 2 strip factorial design, with combinations between cover crops/consortia and soil management (with or without tillage), with four replications. Soil monoliths (0.25 × 0.25 m) were randomly sampled in each plot for macrofauna at 0‒0.1, 0.1‒0.2, and 0.2‒0.3 m depth, including surface litter. After identification and counting of soil organims, the relative density of each taxon in each depth was determined. The total abundance of soil macrofauna quantified under cover crops in the conventional and no-tillage system was 2,408 ind. m-2, distributed in 6 classes, 16 orders, and 31 families. The results of multivariate analysis show that grass species in sole cropping systems and no-tillage presents higher macrofauna density, in particular the taxonomic group Isoptera. No-tillage also provided higher richness of families, where Coleoptera adult were the second more abundant group in no-tillage and Hemiptera in conventional tillage

Previous cultivation of palisade grass and soil correctives: influence on growth and yield of soybean cultivated under various soil compaction levels Cultivo prévio de braquiarão e corretivos de solo: influência sobre o crescimento e produção da soja cultivada sob vários níveis de compactação do solo

Soil compaction directly interferes on crop yield. The objectives of this work were to evaluate the effect of previous cultivation with palisade grass [Urochloa brizantha (C. Hochstetter ex A. Rich.) R. Webster cv. Marandu] and the use of soil correctives on the growth and yield of soybeans (Glycine max L.) cultivated under various soil compaction levels, in greenhouse conditions. The experiment was conducted in pots (columns) of 0.2 m diameter PVC tubes, composed of two rings: the lower ring, 0.4 m in height, received the soil (dystrophic Red Latosol, clayey texture) without corrective and a density of 1.0 Mg m-3; and the upper ring, 0,2 m in height, received the treatments of soil correctives and density. The experimental design was fully randomized in a 4 x 6 x 2 factorial outline, being four soil density levels (1.0; 1.20; 1.40 and 1.60 Mg m-3), six soil correctives (without corrective, lime, calcium silicate, gypsum, lime + gypsum and calcium silicate + gypsum) and two cultivation systems of the soybean (with and without previous cultivation of palisade grass). Starting from 1.2 Mg m-3 of soil density the soybean growth and yield were decreased. The use of soil correctives and previous soil cultivation with palisade grass decreased the harmful effects of the soil compaction on the soybean growth and yield. For the treatments that received previous cultivation with palisade grass, the soybean growth and yield were higher with application of lime + gypsum and calcium silicate + gypsum.<br>A compactação do solo interfere diretamente sobre a produção das culturas. Neste trabalho, objetivou-se avaliar o efeito do cultivo prévio do braquiarão e o uso de corretivos do solo sobre o crescimento e produção da soja cultivada sob solo com vários níveis de compactação, em condições de casa de vegetação. O experimento foi conduzido em vasos (colunas) de tubos de PVC de 0,2 m de diâmetro, compostos por dois anéis: o anel inferior, de 0,4 m de altura, recebeu o solo (Latossolo Vermelho distrófico de textura argilosa) sem corretivo e densidade de 1,0 Mg m-3; e o anel superior, com 0,2 m de altura, recebeu os tratamentos de corretivos do solo (sem correção, calcário, silicato de cálcio, gesso, calcário + gesso e silicato de cálcio + gesso) e de compactação (1,0; 1,20; 1,40 e 1,60 Mg m-3 de densidade) do solo. O delineamento experimental foi inteiramente casualizado em esquema fatorial 4 x 6 x 2, sendo quatro densidades de solo, seis corretivos de solo e dois sistemas de cultivo da soja, com e sem cultivo prévio do braquiarão. A partir de 1,2 Mg m-3 de densidade de solo, foi observada redução no crescimento e produção de grãos da soja. O uso de corretivos e o cultivo prévio do solo com braquiarão amenizam os efeitos deletérios da compactação do solo sobre o crescimento e produção da soja. Para os tratamentos que receberam cultivo prévio de braquiarão, a mistura de calcário + gesso e silicato de cálcio + gesso foram os corretivos que proporcionaram maior crescimento e produção da soja