Identification of the Influence of Concrete Cover Thickness and ∅/ρ Parameter on Crack Spacing.

Cracks due to the service load in the reinforced concrete structures are controlled at the design stage, by limiting the calculated crack width. Widely used crack width calculation models (Eurocode 2 and Model code 2010), estimates the crack width by multiplying the crack spacing with the mean strain difference of concrete and reinforcement. Concrete cover thickness and the ratio of diameter to reinforcement area to effective tensile area of concrete (∅/ρp,ef) are the two main crack spacing governing parameters in the aforementioned models. The existing models are mostly applicable when concrete cover thickness is within the specified limit. For example, Model Code 2010 model limits the concrete cover thickness to 75 mm. In order to identify the influence of aforementioned two governing parameters on crack spacing, the results of recent experiments have been considered. According to some recent studies, it is found that the concrete cover thickness has a significant influence and the ∅/ρp,ef parameter has a negligible effect on crack spacing. To investigate the reasons why the ∅/ρp,ef parameter has a negligible effect on crack spacing, the involvement of bond properties is needed to study. Some authors have specified that the large diameter bars consist of higher bond force per unit surface area than the small diameter bars, due to the high rib area. Due to this reason, the similar bond behavior could be identified, from low number of large bar diameters and high number of small diameter bars. A literature review has been carried out to study the bond behavior on specimens subjected to pure tension. With the facts and available data, it is further verified that the ∅/ρp,ef parameter has a negligible influence and concrete cover thickness has a significant effect on crack spacing

Experimental investigation of crack width variation along the concrete cover depth in reinforced concrete specimens with ribbed bars and smooth bars

Crack width variation along the concrete cover depth has been studied from the past for better understanding of the cracking phenomenon in reinforced concrete (RC) structures. Previous studies have highlighted important cracking behaviors like internal cracks. The behavior of ‘slip’ between the reinforcement and concrete and the formation of a nonuniform crack face along the concrete cover depth are still not very clearly understood. An experimental program has been conducted to study the crack width variation along the cover depth in concrete prisms reinforced with a central ribbed bar and smooth bar, by varying the concrete cover depths. Both in specimens with smooth bars (SS) and specimens with ribbed bars (SR), crack width is larger on the concrete surface than at the steel bar surface. The crack width at the reinforcement is considerably larger in the SS than in the SR. In the SR, the crack width increases from the reinforcement along the cover depth bi-linearly, while, in the SS, it increases linearly. For the SR, the aforementioned behavior is due to the occurrence of internal cracks. In the SS, significant slip has been identified at the reinforcement and concrete interface, whereas negligible slip has been observed in the SR. A surface crack width calculation model has been developed, considering both the strain difference and the effect of the nonuniform crack face along the concrete cover depth. Its predictions showed good agreement with the experimental surface crack widths from the conducted study and with the results from the experiments in literature.publishedVersio

Influence of actual environmental factors on shrinkage behaviour of concrete containing mineral compounds

This study was carried out to check whether the shrinkage can be reduced by using mineral admixtures and the shrinkage behavior of concrete containing mineral admixtures in actual environmental conditions. Since there are several environmental factors affecting on this shrinkage of concrete. Observation of shrinkage cracks in concrete structures is the most important aspect. Other than the observed data, it was necessary to get the predicted measurements of shrinkage from specific codes and models. But all these equations and models have been modeled in specific environmental situations. For most of them temperature and relative humidity values have taken as constants or under the control lab conditions. These codes or equations don’t represent the exact situation for the structures in the local environmental conditions. Therefore in this study, one of the main aims is to find out, which model or code equation gives the most relevant relationship for the shrinkage strain in structures under actual environmental conditions

DICER1 syndrome and its various paediatric presentations: case series and review of the literature

DICER1 syndrome is a rare tumour predisposition syndrome, associated with a range of benign and malignant tumours, which may occur during childhood. A high index of suspicion is required to ensure appropriate diagnosis and testing, with early treatment and surveillance of at-risk individuals. In this report, we present 5 patients with variants in DICER1 identified following diagnosis of a minimally invasive thyroid follicular cell carcinoma, a pineoblastoma, a pleuropulmonary blastoma, a urethral rhabdomyosarcoma and on sibling testing. Each of these children have presented at a young age, and 2 have presented with characteristic tumours prior to the ages currently recommended for initiation of routine screening. We discuss their presentation, management and follow up, as well as a review of the current literature on each associated tumour in relation to our patients. Overall, we demonstrate that DICER1 is a heterogenous condition and that there is a need for cascade testing of family members as well as regular screening for tumour development in affected children, although consideration should be made regarding initiating this screening at an earlier age depending on clinical findings

Cracking Behavior of Reinforced Concrete Structures Subjected to Service Load: Experimental and Numerical Investigation

PhD thesis in Mechanical and Structural Engineering and Materials ScienceCracks in reinforced concrete (RC) structures are controlled to enhance the service life, for a better aesthetic appearance, and to avoid leakages in liquid retaining structures. The most widely used crack controlling method at the structural design stage is to limit the calculated crack width to an allowable crack width limit. With an understanding of the economic and social benefits, there is a trend to build RC structures with a long service life. To enhance the durability of these structures, large concrete cover thicknesses are required to protect the embedded reinforcement from corrosion. These enhanced concrete cover thicknesses are larger than the limitations of existing crack width calculation models. From a literature survey and a parametric study conducted with the results from recent experiments in the literature, it can be identified that the existing crack width calculation models require improvement, to predict the crack widths in RC specimens with large concrete cover thicknesses. The next objective is to study the different theoretical approaches discussed in the literature regarding the approaches to cracking and to identify the most relevant method for the actual cracking behavior in RC members subjected to service load. To achieve this objective, an experimental program was conducted to test large-scale RC specimens in axial tension. Then it was identified that the actual cracking behavior in RC members with ribbed reinforcement is more related to the ‘no-slip approach’ (perfect bond between reinforcement and concrete) than the classical bond-slip approach. This finding has been further confirmed with a literature survey focused on the previous experimental studies that measured the slip between the reinforcement-concrete interface. After studying the ‘no-slip approach’, an experimental program was conducted to investigate the governing parameters for crack spacing. From the experimental program, it was identified that both concrete cover thickness and the clear distance between bars have an influence on crack spacings and therefore on the crack widths in RC specimens. Then, with the results of the conducted experiments and the results of a series of calibrated 3D non-linear finite element method simulations, an improved crack spacing model was developed, to predict the crack spacings in RC members with multiple bars that are subjected to axial tension. The crack width variation along the large concrete cover thickness has been studied by means of an experimental program. From this study, it was found that the effect of shear lag has an influence on the surface crack widths of RC members. Based on the findings, an improved crack width calculation model has been proposed, and its predictions gave good agreement with the experimental results in recent literature

Determinants of Social Entrepreneurial Intention of Sri Lankan Entrepreneurs (An Evidence from Current Entrepreneurs of Ratnapura District)

Today the whole world is embraced by harsh problems than ever in the history of mankind. People are suffering due to many kinds of social and environmental issues; climate changes, environmental pollution, natural disasters, diseases, poverty, crime, corruption, economic crises etc. Mankind has to provide innovative and sustainable solutions since they are the root causes to occur such as disasters to the world. To solve these harsh problems, social entrepreneurs have a big role to play. They are the change agents who combine change and innovations and they should possess the behavioural intention to start social enterprises. However, as per the preliminary findings, Sri Lankan entrepreneurs do not intend to start social enterprises or convert their existing businesses into social enterprises. Accordingly, the current study was dedicated to investigating the impact of the determinants on low social entrepreneurial intention (SEI) of Sri Lankan entrepreneurs which was proved by the preliminary findings. Further, the study investigated the significance of SEI in Sri Lanka. The study was conducted as a quantitative study and the deductive approach was used. Mair and Noboa’s model (2006) adopted by Hockerts (2015) was used with five latent constructs; prior Experience with social problems/social organizations, social entrepreneurial self-efficacy, empathy, moral obligation and perceived presence of social support. Out of 1,800 Registered entrepreneurs in Ratnapura District to the date, 317 entrepreneurs were selected as the sample based on Krejcie and Morgan (1970) table. Convenience sampling technique was deployed, and data collection was done through a questionnaire survey. Structural equation modelling was performed to analyse the variable interested with the assistance of AMOS 16 and SPSS 21. Social entrepreneurial self-efficacy and moral obligation were not validated and analysis was done by using the rest of the three variables. Analysis results indicated that the empathy, prior experience and perceived presence of social support have a direct positive impact towards SEI. Empathy and perceived presence of social support are the partial mediators of the model which significantly affect the relationship exist between prior experience and social entrepreneurial intention. Hence, it is concluded that both the partial mediators create mechanisms for prior experience to impact the SEI rather than individual impacts. Keywords: Social Entrepreneurial Intention, Empathy, Prior Experience and Perceived Presence of Social Suppor

A new crack spacing model for reinforced concrete specimens with multiple bars subjected to axial tension using 3D nonlinear FEM simulations

Crack spacing is a governing parameter in widely used crack width calculation models. Axial tensile experiments are conducted to examine the crack spacing behavior of reinforced concrete specimens with multiple reinforcement bars. To reduce the time, cost, and labor of the experiments, nonlinear finite element simulations are widely used. In this study, 3D non-linear finite element simulation models have been developed with the smeared cracking approach to predict the average crack spacings. These models are calibrated and validated using both the experiment conducted by the authors and an experiment given in the literature. The governing crack spacing parameters have been identified as concrete cover thickness and clear distance between tensile bars. After conducting a series of 3D nonlinear finite element method simulations with the calibrated model, an equation is developed to predict the average crack spacings using multiple linear regression analysis. The validity of the proposed crack spacing equation has been checked with 18 recent experimen tal results in the literature. The proposed crack spacing equation gives a good agreement with the results of these experiments.publishedVersio

Applicability of Existing Crack Controlling Criteria for structures with Large Concrete Cover Thickness

Widely used crack width calculation models and allowable crack width limits have changed from time to time and differ from region to region. It can be identified that some crack width calculation models consist with limitations for parameters like cover thickness. The current Norwegian requirement for cover thickness is larger than these limitations. The applicability of existing crack width calculation models and the allowable crack width limits must be verified for structures with large cover thickness. The background of crack width calculation models in Eurocode, Model Code 2010, Japanese code, American code and British code have been examined. By comparing the experimental crack widths with the predictions of the aforementioned models, the existing codes can be identified as requiring modification. Considering the durability aspect, it can be identified a long-term study proving that the allowable crack width can be increased with the increase in cover thickness. When considering the aesthetic aspect, the authors suggest categorizing the structures based on their prestige level and deciding the allowable crack widths accordingly. The paper proposes potential solutions for future research on how to improve both crack width calculation methods and allowable crack width limits to be used effectively in structures with large cover thickness.publishedVersio

A new crack spacing model for reinforced concrete specimens with multiple bars subjected to axial tension using 3D nonlinear FEM simulations

Crack spacing is a governing parameter in widely used crack width calculation models. Axial tensile experiments are conducted to examine the crack spacing behavior of reinforced concrete specimens with multiple reinforcement bars. To reduce the time, cost, and labor of the experiments, nonlinear finite element simulations are widely used. In this study, 3D non-linear finite element simulation models have been developed with the smeared cracking approach to predict the average crack spacings. These models are calibrated and validated using both the experiment conducted by the authors and an experiment given in the literature. The governing crack spacing parameters have been identified as concrete cover thickness and clear distance between tensile bars. After conducting a series of 3D nonlinear finite element method simulations with the calibrated model, an equation is developed to predict the average crack spacings using multiple linear regression analysis. The validity of the proposed crack spacing equation has been checked with 18 recent experimen tal results in the literature. The proposed crack spacing equation gives a good agreement with the results of these experiments