Tension Zone Research Articles

Flexural response of reinforced concrete beams with full and partial depth of steel fiber-reinforced layer at severe conditions

The investigation aims at studying the behavior of reinforced concrete (RC) beams under flexure, with varying amount of steel fiber; variation in depth of fiber layer; and extreme environmental conditions. The test beams were exposed to artificial saline environment prepared from 3.5% NaCl solution. A total of three exposure conditions namely normal (NCC– normal casting and normal curing), mild (NSC- normal casting and saline curing) and extreme (NSC- saline casting and saline curing) were taken. In addition to the conventional reinforcement, the steel fibers were provided across full thickness, half tension zone and quarter tension zone thickness of the beam. The chopped steel fibers dose of 0.6% and 0.8% was used for each of the above-mentioned depth. In all a total of 63 beam specimens, corresponding to 21 groups of beams with 3 replications each, were prepared. For all the exposure conditions, the load and deflection values decrease as the depth of fiber layer decreases to bottom half tension zone. With further reduction in fiber layer depth i.e., to bottom quarter tension zone, the first crack load almost remains same. For all the beam specimens, the load carrying capacity and deflection decreases as the level of salinity is increases from mild to extreme exposure. The beam specimen, with 0.6% fiber content provided in the bottom quarter depth of tension zone, exhibits excellent ductility, load carrying capacity and ensuing deflection. About 20% savings in the unit cost is attained for almost same level of structural integrity as obtained when fibers are provided across the full thickness of the beam. The present investigation validates the effectiveness of additional fiber reinforcement provided in the bottom quarter tension zone of the flexural members. An analytical model is suggested for predicting the flexural behavior of reinforced concrete beams with steel fibers under saline exposure conditions. The model is in good agreement with the observed values and the mid span deflection is predicted well.

A comparative review on bubble-voided reinforced concrete slab – An innovative concept for lightweight concreting

The bubble-voided reinforced concrete (RC) slab is a relatively new concept of light-weight concreting, introduced to the industry. In this concept, the consumption of unnecessary concrete between the tension zone and the neutral axis, inside a RC slab (one-way or two-way), can be avoided by the introduction of voids at that very zone in the form of hollow plastic bubbles. The bubble-voided slab is lightweight in comparison to the solid slab, and self-weight can effectively decrease upto 30% to 40%, through the application of spherical voided-formers. Although, the bubble-voided slab’s load capacity is slightly less, compared to the equivalent solid slab. But, unlike the hollow-core slab, bubble-voided slab performs well against bi-axial loading. As, the concrete consumption is less in bubble-voided slabs, so less amount of cement needs to be manufactured, and, this way, the bubble-voided concreting method can indirectly be beneficial in reducing the Carbon-Di-Oxide (CO2) emission in the atmosphere. The bubbles can be made of plastic waste, which is an innovative way to recycle that waste plastic to use in industry, and, also reduce plastic wastage from the nature. So, it can be understood that bubble-voided concreting is very much eco-friendly. The present authors have explored through the evolution in the researches on the bubble-voided concrete slab, and, discussed about the critical findings of previous researchers. A comparative discussion is also, presented in this study on various input parameters and load vs deflection curves presented in previous studies. The comparisons showcase that the depth of slab (DS), grade of concrete, and, percentage of void, are the key factors which influence the load vs deflection behaviour of bubble-voided RC slabs. Future scopes in this field of study are identified, such as, studies on the effect of thermal loading, impact loading, and, cyclic loading on the bubble-voided RC slabs.

Flexural Behavior of Ultra-High Performance Concrete (UHPC) Deck with Joints subjected to an Improved Steel Wire Mesh (SWM) Treatment

Prefabricated Ultra-high performance concrete (UHPC) decks are often connected using UHPC wet joints to create the overall deck structure. The UHPC deck is, nevertheless, made weak by the fiber discontinuity at the contact interface. In this study, the fiber at the interface was made to serve as a bridge using an embedded steel wire mesh, and experiments were utilized to determine how the contact between the fiber and the steel bar affects the flexural behavior. The results show that the fiber significantly affects the ductility and flexural strength without reinforcement. The combined action of the fiber and reinforcement of the reinforced specimen somewhat increases the flexural capacity and ductility. The flexural capacity of decks with joints was finally calculated using three different ways, and it was found that the method that simplifies the tension and compression zones into rectangles is the most appropriate.

Effect of compression reinforcement on modulus of elasticity of RC beams under flexure

In structural analysis, precise estimation of modulus of elasticity, cross-sectional area and moment of interia of the section play an important role. It is a key factor while carrying out structural analysis for indeterminate structures. Most of the international codes quantify material behaviour for concrete as well as steel in elastic zone and is equally correct. Indian codal provisions express modulus of elasticity of concrete in terms of characteristic strength of concrete only similar to all other international codes. Structural analysis of a high rise building demands cross-sectional area of unreinforced concrete. However, area of reinforcement and stirrups provided are overlooked in the analysis. Contemporary design practice necessitates additional cycle of analysis along with design. First cycle of analysis shall yield the conventional design of sections and are of reinforcement. Based on calculated area of steel in first cycle, it is possible to arrive at effective area of concrete and respective moment of inertia by considering reinforcement in tension and compression zone. The analysis of sections can further be carried out in pre and post cracking conditions. At this stage, material as well geometrical properties play an important role. Present aim of study is to determine modulus of elasticity of reinforced concrete beams with percentage of compression reinforcement ranging from 0.29 to 0.43%. The outcomes are used to propose an empirical equation for evaluation of modified modulus of elasticity of reinforced concrete material which is a dependent on concrete grade along with percentage of tension and compression reinforcement.

Residual strength capacity of reinforced reactive powder concrete two-way slabs subjected to drop weight

This paper presents an experimental investigation of the effect of the impact force on the residual strength capacity of simply supported reactive powder slabs. Eight specimens of reinforced reactive powder concrete slabs with dimensions of 500 x 500 mm and 70 mm in four categories were used. The influences of slab compressive strength (conventional concrete and reactive powder concrete), steel fiber proportion (1, 1.5, and 2%), percentage of reinforcement in the tension zone (ρ1=0.007, ρ2=0.011, ρ3=0.0179), and the number of impacts (two impacts, four impacts, and six impacts) were all investigated in this test. Investigations were carried out to ascertain each slab's residual response, including first cracking load, residual failure load, residual steel reinforcement strain, maximum central deflection, and crack pattern. The results showed that using reactive powder concrete instead of normal concrete increased the mechanical properties of concrete and resulted in a significant increase in failure load. In addition, the central deflection and strain increased. Increasing the reinforcement ratio increased the failure load while simultaneously decreasing the deflection due to the improvement in slab moment resistance. Furthermore, it was discovered through experiments that the addition of steel fiber to the mixture enhanced the slab’s post-cracking reactivity. The presence of steel fiber raised the slab strength resistance by 21.63% as the steel fiber ratio increased from 1% to 2%. This is because the addition of steel fiber increased the slab's tension resistance.

Experimental study and performance analysis of the flexural strength of reinforced ice slabs

In recent years, interest in the prefabricated ice rink for international competition has increased. The ice sheet, whose support is extruded polystyrene foam board, is prone to bending failure. To maintain the advantage of recycling prefabricated ice rinks, the method of reinforcing ice slabs with welded steel mesh (SRI) was proposed. However, the flexural properties of SRI remain unclear. Therefore, three-point bending tests, theoretical derivation, and finite element analysis were conducted in this study to better understand SRI. First, the three-point bending tests with 17 specimens were performed considering the effects of reinforcement ratio (0%∼0.812%). The results showed that the SRI's cracking load capacity and ultimate load capacity improved significantly with 1.84 and 4.49 times higher than the plain ice slab at most. Additionally, reinforcement can reduce the stiffness drop caused by cracking, which can be increased to 0.913 at most. Then, the calculation formula of the cracking load, which is a segmentation function, is derived based plane section assumption and gets good agreement with experimental results. At the same time, the calculation formula of the ultimate load is derived, although the calculation result is conservative, it can reflect the trend of the ultimate load with the variation of reinforcement ratio. Finally, finite element simulation analysis of three-point bending tests of SRI were conducted, using the brittle cracking model and the Coulomb-Moore plasticity model, respectively. Simulation results show that using both models alone have the limitation of use range. As a result, a B + C combined numerical model (the brittle cracking model is used for the tension zone and the Coulomb-Mohr plasticity model is used for the compressive zone) was proposed, and the simulation results agree well with the cracking load of both experiment and formula. Taken together, the welded steel mesh effectively improves the flexural performance of ice slabs and the findings of this study are beneficial for the design and finite element analysis of SRI in the future.

Experimental study on flexural behavior of precast hybrid UHPC-NSC beams

The main objective of this research was to evaluate the flexural behavior of precast hybrid Ultra-High Performance Concrete-Normal Strength Concrete beams. In this paper, a new precast hybrid Ultra-High Performance Concrete-Normal Strength Concrete beam was proposed, in which Ultra-High Performance Concrete was used in both the tension and compression zone of the cross section, while Normal Strength Concrete was adopted in the middle part, respectively. All six concrete beams were constructed and tested to study the flexural performance of precast hybrid Ultra-High Performance Concrete-Normal Strength Concrete beams. The results showed that (1) the proposed precast hybrid Ultra-High Performance Concrete-Normal Strength Concrete beams can still provide satisfactory bearing capacity, stiffness and ductility; (2) a larger crack width was observed in the precast hybrid Ultra-High Performance Concrete-Normal Strength Concrete beam when compared with Ultra-High Performance Concrete beams, which was mainly affected by the ratio of Normal Strength Concrete and Ultra-High Performance Concrete area and the reinforcement ratio; (3) the cost performance of precast hybrid Ultra-High Performance Concrete-Normal Strength Concrete beams can be improved by increasing the reinforcement ratio and the ratio of Normal Strength Concrete and Ultra-High Performance Concrete area; (4) the proposed model can accurately predict the moment capacity and deflection of the precast hybrid Ultra-High Performance Concrete-Normal Strength Concrete beam based on the experimental results. It is a new attempt to make reasonable use of such superior characteristics of Ultra-High Performance Concrete.

Carbonation Resistance of Marine Concrete Containing Nano-SiO2 under the Action of Bending Load

In order to study the influence of nanomaterials on the carbonation resistance of marine concrete under bending loads, an appropriate amount of nano-SiO2 was added to plain concrete, and a self-developed carbonation box and bending loading device were used to conduct a coupling test. Four different stress levels were set to measure the carbonation depth of nano-concrete at different ages. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used to analyze the concrete interfacial transition zone. The carbonation depth was used as the test index to evaluate the durability of nano-SiO2-based concrete under the combined action of bending load and carbonation. The test results showed that the compressive and flexural strengths of concrete remarkably improved when the nano-SiO2 concentration was 2%. Compared with regular concrete, the compressive and flexural strengths of nano-SiO2 based concrete improved by 15.5% and 15.3%, respectively. When the stress level was 0.15 and 0.6, the carbonation depths of NS20 were 20.5 and 18.4% lower than those of PC in the tensile zone and 18.9 and 23.7% lower than those of PC in the compression zone. The carbonation depth of the NS20 tensile zone was lower by 31 and 18.4% at 3 and 28 days than that of PC. Compared with PC, the carbonation depth in the compression zone of NS20 decreased by 50 and 23.7%, and the carbonation depth of nano-concrete was significantly lower than that of conventional concrete under the same stress level and age. When the stress level is constant, the carbonation depth of the tension zone and compression zone increases gradually with the increase in age, and the carbonation depth of the concrete in the first 7 d was 50% that at 28 days. Under the same age, the carbonation depth in the tension zone increased with increasing stress levels, while the carbonation depth in the compression zone decreased with increasing stress levels. When the stress level was 0.3–0.45, the slope of the carbonation depth curve significantly increased. SEM and XRD analysis results revealed that nano-SiO2 significantly improved the internal structure of concrete by reducing the width of the microcracks, the number of pores, and the number of microcracks. The number of C3S/C2S and CaCO3 crystals in nano-SiO2 based concrete was significantly less than that in plain concrete, and the amount of C-S-H gel was more than that in plain concrete. Under bending loads, the nano-SiO2 significantly improved the carbonation resistance of concrete. When the dosage of nano-SiO2 was 2%, its improvement effect was the most significant.

Flexural Behavior of Two-layers Reinforced Concrete Beams

High-strength concrete is used to reduce the size of the beams in addition to enhancing the strength, this leads to overestimated cost in comparison with normal-strength concrete while using normal-strength concrete leads to the overestimated amount of concrete (layer size) of the beam section. For balancing the condition between the cost and size of beams, the benefit of both materials is used, by using beams in two layers, high-strength concrete in the compression zone (top layer), which is more beneficial for beam strength, and normal strength concrete in tension zone (bottom layer), which is no need using high strength concrete the in-tension zone. This study investigates the flexural and shear behavior of reinforced concrete beams consisting of two layers with different concrete strengths (grades), for beams with and without shear reinforcement (stirrups), considering the effect of shear-span ratio, layer thickness, layer compressive strength, and the overlap time casting of the two layers. The experimental program consists of a total of nineteen reinforced concrete beams of dimension (125 mm x 250 mm) with a total length of 1200 mm, the beams are reinforced with longitudinal reinforcement (4Ø12mm) and using (Ø8mm) bar as transverse reinforcement (stirrups). The experimental results show that the crack pattern of the two-layer reinforced concrete is closer to the crack of the control beam with one layer. Increasing the compressive strength of the concrete of the top layer, the ultimate failure load increased by (8.35%, 15.6%, and 18.85%), with respect to the (control beam) with the full depth of normal concrete. By increasing the high-strength layer thickness, the value of shear strength (Vc) and ultimate shear strength (Vu) increased linearly. The casting overlap time of up to (60 min) can be used for casting two-layered reinforced concrete beams, which is recommended, beyond this time the strength of the shear strength (Vc) and, ultimate shear strength (Vu) decreases. With increasing the shear span ratio (a/d) from (1 to 1.5 and 2) the ultimate load failure decreased by (33% and 50%). The shear strength capacity decreases with increasing stirrup spacing.

Fatigue Crack Growth Behavior of Different Zones in an Overmatched Welded Joint Made with D32 Marine Structural Steel

Applying fracture mechanics theory to heterogeneous welded joints might lead to an uncertain assessment of fatigue crack propagation behavior and, consequently, an inaccurate estimation of the cyclic loading capacity and fatigue life of welded structures. Combining experimental testing and analytical equations of the marine overmatched welded joints of D32 marine structural steel provided a view of the influence of strength heterogeneity on fatigue crack growth (FCG) behavior under constant cyclic loading. FCG testing was conducted using compact tension specimens under different stress ratios. The effect of residual stress on the FCG behaviors of the heat-affected zones (HAZs) and fusion zones (FZs) of the compact tension (CT) specimens was examined in the overmatched welded joints. Subsequently, the welding residual stresses were removed by post-welding heat treatment (PWHT) to focus the FCGR assessment on the microstructural effect. The results indicated that the FCG rates (FCGRs) of the FZ and HAZ materials obviously varied in as-welded and stress-relieved states. The existence of residual stress in the overmatched welded joints led to a decrease in FCG rates and prolonged the fatigue crack propagation life for the FZs and HAZs. Moreover, the FCGR increased in the base metal (BM), HAZ, and FZ with the increase in the stress ratio. The FCG curves of these materials were fitted to correct the stress ratios using the NASGRO equation. Finally, an analytical analysis of the FCGR based on the NASGRO equation revealed the relationship between different stress ratios for different materials.

Seismic Upgradation of RC Beams Strengthened with Externally Bonded Spent Catalyst Based Ferrocement Laminates

Globally, since there are more systems of civil infrastructure, there are also more degraded buildings and structures. If upgrading or strengthening is a practical option, complete replacement is likely to be an escalating financial burden and may be a waste of natural resources. It is necessary to repair or strengthen a number of reinforced concrete buildings and structures in order to boost their load-bearing capabilities or improve their ductility under seismic stress. Additionally, due to changes in service circumstances, a structure might need to be modified to reduce deflections or manage cracking. Strengthening may be preferable to limiting usage, capping applied loads, and regularly inspecting the structure rather than removing the existing structure or part and building a new one. This study aims to examine the flexural, shear, and combined effect of flexural and shear behavior of reinforced concrete (RC) beams strengthened with externally bonded spent catalyst-based ferrocement laminates and compare them to the control beams (unstrengthened) under two-point loading conditions. This study involves researching laminates with various spent catalyst doses, such as 3, 6, 9, and 12%, in an effort to determine the best amounts that will improve the structural performance of ferrocement laminates. Twelve spent catalyst-based ferrocement laminates measuring 500(L) × 125(B) × 20 mm (thickness) with 3% volume fraction of meshes each were cast and tested in the lab as part of the preliminary investigation. For repeatability, three laminates per case were employed. Eight numbers of under-reinforced RC beams measuring 75(L) × 100(B) × 150(D) mm were cast for the main study; six numbers were strengthened with optimized spent catalyst-based ferrocement laminates bonded with flexible epoxy systems at the tension zone, shear zone, and combination of tension and shear zone. Two of the beams were cast as control specimens. The beams were then evaluated using a Universal Testing Machine (UTM) with a 1000 kN capacity under two-point loading conditions. As a result, the strength, yield load, ultimate load, stiffness, ductility, and related failure modes of all tested beams' flexural and shear performances were examined. According to a preliminary analysis of laminates made of spent catalyst, the dosage of 9% provides good flexural strength in comparison to other doses. In comparison to the strengthened beam, the control beam's initial cracks appeared earlier. In comparison to the control beam, the strengthened beam has an increase in load-carrying capacity of 18% for flexure, 16% for shear, and 30% for the combined impact of flexure and shear. In comparison to the control beam, the deflection of the strengthened beam was decreased by close to 20 to 40% for flexure, 10 to 30% for shear, and 15 to 20% for the combined effects of flexure and shear at the same load level. In relation to control beams, the ductility also improved up to 30% for flexure, 25% for shear, and 25% for the combined impact of flexure and shear. Similar to this, the retrofitted beam is stiffer than the control beam by approximately 40% for flexure, 48% for shear, and 30% for the combined effect of flexure and shear. Theoretical formulation by section analysis is also derived and it gives close agreement with control and strengthened beams. The flexural and shear strengthening of the RC beam retrofitting system is effectively increased by using spent catalyst-based ferrocement laminates. No beam showed signs of premature and brittle failure. According to the test findings, it can be said that spent catalyst-based ferrocement reinforced beams perform better in every way than control beams. Doi: 10.28991/HIJ-2023-04-01-013 Full Text: PDF

Evaluation of YLT method to estimate the load carrying capacity of one-way patched reinforced concrete slab under concentrated load

An unsaturated polyester resin (UPR) mortar was applied to repair the damage to the tension zone's one-way reinforced concrete (RC) slabs. The load carrying capacity of the patched RC slab is of interest to justify the effectiveness of the repair. The Yield Line Theory (YLT) may be used to estimate the load carrying capacity of patched RC slabs under concentrated load. The results of the YLT are compared with the experimental results to evaluate the validity of the YLT method. The results confirm that patching alters the yield line formation, mainly when the concentrated load is applied close to the patching zone. Subsequently, the YLT method provides a higher load carrying capacity estimation deviation for slabs with a loading point near the patching zone. On the other hand, the YLT method estimates load carrying capacity accurately when the loading point is away from the patching zone.

Comparing structural models of linear elastic responses to bending in inosculated joints

Key messageMechanical models of inosculations benefit from moderate geometric detail and characterisation of the structurally optimised area of interwoven tension-resistant fibres between the branches.Living architecture is formed by shaping and merging trees, often in combination with non-living technical elements. These structures often employ the mechanical and physiological adaptations of living trees to support structural loads. Designed and vernacular buildings utilise inosculations to redistribute forces, redirect growth, and provide redundancy. Mechanical models of inosculations in living architecture must be built according to the adaptations available to the tree. Here, mass allocation and fibre orientation are examined. Under typical gravity loads, a zone at the top of the inosculation is subject to tension. This is of particular interest because a trade-off in fibre orientation between mechanical and physiological optimisation is necessary. In tree forks, this results in specifically adapted interwoven fibres. In this study, Finite Element Analysis (FEA) is used to develop different mechanical models to fit bending experiments of four Salix alba inosculations, comparing the models’ accuracy in replicating rotations in the joint. Nine models were developed. Three levels of detail of mass allocation are considered for global isotropic (3 models) and orthotropic (3 models) mechanical properties as well as a model including the interwoven tension zone, a model of local branch and trunk orthotropy, and a model combining these two localised features. Results show significant accuracy gains come from moderate geometric accuracy and consideration of the tension-zone optimisation. The construction of the tension zone in FEA is simple and applicable to natural and artificially induced inosculations.

Investigation of flexural performance and effective width of composite wide flat beams

To investigate the flexural performance and effective flange width of composite wide flat beams (CWFBs) with composite hollow core slabs (CHCSs), four CWFB specimens with double-sided CHCSs were tested and analyzed. The test results indicated that all specimens showed typical flexural damage. The CWFB with CHCSs had shear lag effect in both tension and compression zones. Increasing the width of the CHCSs resulted in a greater effective width, stiffness, and load carrying capacity of CWFB with CHCSs. Compared with the three-point loading method, the effective width of CWFB with CHCSs was larger for the four-point loading method and the uniform loading method. In addition, finite element models (FEMs) of the tested specimens in MSC. Marc software were validated by the test results, and 30 FEMs were further analyzed. Finally, the equations for calculating the effective width were obtained for the CWFB with CHCSs under uniform, four-point and three-point loads.

Research on stress performance of universally wrapped assembled joints of lattice wind power tower with concrete-filled steel tube

With the control parameters of the wall thickness of the ball table and the thickness of the pressure plate of the ball table, four universal wrapped assembled joint models were designed for the research of stress performance via static loading test. The failure mode of the joint, the axial force–displacement curve of the web member, the equivalent stress distribution of the ball table and the pressure plate of the ball table were analyzed, and the ABQAUS finite element software was used for the analysis of parameter expansion of the specimen. The research results show that the failure modes of universally wrapped assembled joints can be divided into the buckling failure of the ball table and the strength failure of the material. The wall thickness of the ball table is the key parameter affecting the failure mode of the joints, and the thickness of the pressure plate of the ball table is the crucial parameter influencing the ultimate bearing capacity of the joints. The maximum equivalent stress of the pressure plate and the ball table at compression zone for all the joints is occurred at the side squeezed by the bolt ball, and the growth rate of the equivalent stress for the ball table at compression zone is more uniform than that at tension zone. According to the finite element analysis results, when the wall thickness of the ball table is greater than 7 mm, the thickness of the pressure plate of the ball table is greater than 16 mm, the growth rate of the ultimate bearing capacity of the joint is significantly decreased, therefore, it is recommended to use the wall thickness of 7 mm and the pressure plate thickness of 16 mm in the actual design of the project.

Flexural behaviour of RC one-way slabs reinforced using PAN based carbon textile grid

Textile reinforced mortar (TRM) is mainly used for strengthening of existing structural members whereas, on the other hand Textile reinforced concrete (TRC) is a technology implied in construction of new members for enhancing the structural behaviour. Application of TRM on the tension zone of the reinforced concrete (RC) slabs to improve the flexural capacity has been investigated by many researchers in the past. However, the effectiveness of textile fabrics, used as internal reinforcement in the RC slab (TRC technology) needs to be studied. The paper, therefore, presents the experimental research conducted on three one-way RC slabs specimens reinforced using textile grid. An innovative Polyacrylonitrile (PAN) based carbon textile grid was used as internal reinforcement in combination with the steel bars. Two textile-reinforced RC slabs having one and two layers of textile grid (SRC + 1T and SRC + 2T respectively) and one reference slab (SRC) was fabricated to investigate the flexural behaviour under a four-point loading system. The internal textile reinforcement layer(s) was confirmed to be effective, particularly in terms of improving the cracking load, ductility, deformability and toughness. The material ductility of SRC + 1T and SRC + 2T slabs were increased by 41% and 44% compared to SRC slab. Also, the deformability ratio was found to be greater than 4, indicating a ductile failure of textile-reinforced slabs. Further, based on the load-deflection relation, moment-curvature curves were derived. Moreover, these curves were also developed using Eurocode two prediction model. The experimental and the predicted moment-curvature curves showed good agreement.

Modelling non-linear deforestation trends for an ecological tension zone in Brazil

Tropical deforestation is a recent phenomenon that started in the second part of the twentieth century. One may argue that the Brazilian state of Maranhão is an excellent case study for ex-amining deforestation trends and the effects of environmental policies. A man-made line sepa-rates Maranhão into two sections. Due to the administrative divide between the Legal Amazon Maranhão (LM) and the Cerrado Maranhão (CM), one may hypothesize about differences in deforestation between the two regions. This research employs a nonlinear modelling approach based on Generalized Additive Models (GAMs) with a quasi-Poisson distribution and a logarith-mic function to detect deforestation patterns in these areas. Deforestation is linked to the year and a variety of climatic variables. These covariates differ substantially across seasons (rainy and dry) and regions. During times of above-average precipitation, including in the dry and wet seasons, deforestation occurred in the LM area. However, in the non-enforced region, this regime was not followed. According to the statistics, deforestation decreased in the LM region when precipitation levels were below average.

Crack Shape Coefficient: Comparison between Different DFOS Tools Embedded for Crack Monitoring in Concrete.

The article presents research on the performance of different distributed fibre optic sensing (DFOS) tools, including both layered cables and monolithic composite sensors. The main need for the presented research was related to the growing applications of the DFOS techniques for the measurements of cracked concrete structures. There are no clear guidelines on the required parameters of the DFOS tools, which, despite their different designs, are offered for the same purpose (strain sensing). The state-of-the-art review and previous experiences show noticeable differences in the quality of the results depending on the applied DFOS tool. The technical construction of selected solutions was described with its theoretical consequences, and then laboratory tests on full-size reinforced concrete beams were discussed. Beams equipped with embedded tools were investigated in four-point bending tests, causing the formation of multiple cracks in the tension zone along the beams' length. The results in the form of strain profiles registered by selected DFOS tools were analysed regarding the qualitative (crack detection) and quantitative (width estimation) crack assessment. The comparison between crack-induced strain profiles was based on a new parameter called crack shape coefficient CSC, which could be applied to assess the effectiveness of the particular DFOS tool in crack detection and analysis. It was one of the world's first research allowing for such direct comparison between the layered and monolithic sensing tools. The summary indicates practical guidelines referring to the preferable design of the tools best suitable for crack measurements, as well as the field proofs based on data from two concrete bridges in Germany.

Chloride Resistance of Concrete under Complex Stress and Environment

The presence of stress is shown to have a significant impact on chloride ions in concrete. Reinforced concrete is usually durable and cost-effective which has resulted in its widespread use for construction, however, the concrete subjected to environment and load has become increasingly apparently that attacked by aggressive agents such as chloride ion. In this study, the coupling influences are stress effects and environmental problems on the coastline concrete durability have been investigated. A series of cyclic of a wet-dry cycle and submersion tests were performed onto the stressed concrete to obtain an understanding of the physical mechanisms causing the accumulation of chlorides in the interior pores of concrete under different stress types and exposure environments, based on the same duration. Specimens were prepared and subjected to NaCl solution in a wet-dry cycle and submersion, the chloride in the tension zone is gradual with increasing the stress level, as well as the chloride ion in the wet-dry cycle, is increasing the number of cycles. The apparent diffusion coefficient of each specimen was calculated respectively, the profile of concentration at a different section of tension and compression zones were presented in influence factors of the number of cycles, the length of drying phase, and periodic wetting cycles with sodium solution was discussed. After employed Fick’s second law, the results suggested Da in a wet-dry cycle is much higher than the Da in submersion zones.

Application of external prestressing to timber-concrete composite beams

Timber-concrete composite beams are classified as modern constructions. They are created by connecting a timber and concrete element. They are designed in such a way that the concrete part of the beam is placed in the compressed zone, and the timber part is placed in the tension zone. Different types of fasteners can be used for connecting, from mechanical (screws, nails, perforated plates, parts of steel profiles, etc.) to chemical (various types of glues). In this work, the possibility of active strengthening for this type of beam by external prestressing, is examined. One way for applying an external prestressing force is shown. By experimental testing are determined results for prestressed and beam without prestressing. Obtained results are presented and compared.