The beneficial effect of the autogenous self‐sealing of cracks has been relied upon implicitly in the design of concrete water retaining structures for many years. The degree to which it can be relied upon to retard leakage through cracks in water retaining structures has, to date, not been quantified in probabilistic terms. Previous research identified the crack width as a critical parameter in the autogenous self‐sealing of flow through cracks in tension‐cracked, reinforced concrete. In this research, two experimental databases are collected and compiled, and are used to probabilistically model the prediction of initial flow through, and the subsequent leakage through tension cracks considering the effects of self‐sealing. The total leakage is characterized as a function of crack width range, identifying the notable effect of increasing crack width on increased leakage duration and magnitude. This research is a first step toward quantifying the achieved SLS reliability for water retaining structures.
The aim of this project was to study the structural design and material costing of various designs of tall wind turbine towers and the associated foundations in a South African context. Design guidelines are proposed for the design of tubular steel, concrete and concrete-steel hybrid towers and foundations for hub heights of 80, 100 and 120 m. The results indicate that concrete and hybrid towers become viable alternatives to the conventional steel towers at hub heights equal to and above 100 m. Three heights - 80 m, 100 m and 120 m - of each type of tower (steel, concrete and hybrid) and their foundations were designed according to the relevant design standards. The designs were verified using the Abaqus CAE finite element software (SIMULIA 2010). The material costs of the designs were calculated for a South African environment, according to the increases in material cost with increasing hub height. In this paper, the required foundation sizes for the concrete and hybrid towers were found to be smaller than for the steel towers. The material costs of the concrete and hybrid towers were shown to be lower than for the steel towers, especially at hub heights above 100 m. An increase in hub height caused an increase in energy generation of 3.52% and 6.28% for 80 m to 100 m, and for 80 m to 120 m hub heights, respectively. It is postulated that the concrete and hybrid towers become viable alternatives to the conventional steel towers at hub heights above 100 m.
The limit state that typically governs the design of circular reinforced concrete water retaining structures is the limitation of leakage through cracks. Current design codes prescribe target crack widths in the range of 0.05–0.2 mm, depending on the design situation, to limit leakage to acceptable levels. Fairly high model uncertainty exists in the prediction of load‐induced crack widths and the beneficial effect of autogenous self‐sealing has not effectively been quantified, so that the achieved levels of reliability using current codified procedures are unknown. This research uses a reliability analysis previously developed by the authors to assess the level of SLS reliability achieved in tension‐governed reinforced concrete reservoirs covering much of the scope of practice. The SLS reliability performance is evaluated using a limit state of allowable versus predicted leakage, including a probabilistic quantification of the effect of autogenous self‐sealing, and the uncertainty present in the prediction of load‐induced crack widths. Many permutations of practical reservoir geometries are considered for four combinations of stabilization period and water tightness test time (leakage regimes) typically used in water tightness tests. The target crack width recommendations of EN 1992‐3 and Model Code 2010 are evaluated across the range of geometries and leakage regimes. The commonly used target crack width of , recommended by Model Code 2010 and many other codes, was found to be inadequate to achieve a target SLS reliability index of . The values from EN 1992‐3 showed better performance but were found to result in reliability indices frequently in excess of , indicating that the values are perhaps too stringent. Results confirm that smaller target crack widths and longer water tightness test times increase the achieved reliability. However, even for a given target crack width and leakage regime, a substantial range of achieved reliabilities is observed depending on reservoir configuration. This shows that design to meet current target crack widths is not effective at meeting target reliability across the range of practical application. A suggestion is made to refine reservoir specific crack width targets to achieve target reliability more consistently.
Target reliability forms the basis of most modern design standards and is intended to represent an optimal balance of safety and risk of failure. Previous research noted discrepancies between target reliability obtained using generic and case-specific cost optimization for SLS cases. The source of the discrepancies was identified as the efficiency of the decision parameter at increasing reliability. This research extends the investigation to cases of ULS failures and found similar discrepancies. Generic cost optimization assumes a linear dependence between the decision parameter and the structural resistance. Where the dependence of resistance on the decision parameter is superlinear, the generic was found to under-predict target reliability by up to 15%. A factor is proposed to adjust generically-obtained ULS target reliability to be more appropriate to specific ULS cases. The factor accounts for the efficiency of the decision parameter, the case-specific cost of safety and parameter variation. The adjustment factor represents a first step towards mapping generic to case-specific target reliability in the ideal of promoting safer and more cost-effective structures.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.