Analysis of the longitudinal distribution of pressures near the ends of the vertical and horizontal faces in stepped spillway of slope 1V: 0.75H

Abstract

Stepped spillways have been widely used for flood runoff due to of their constructive advantages and in regards to energy dissipation during the drop, allowing downstream dissipation structures to be designed in smaller dimensions. Due to the need for further studies on the effect of runoff in the chute of the stepped spillway and the analysis of dimensionless numbers used to characterize the longitudinal distribution of the pressures acting on the faces of the steps of a spillway, this study aims to characterize the acting forces on the steps of said spillways. Analyses were performed on a physical model of spillway with a slope of 1V: 0.75H and steps with a height of 6 centimeters. The pressure fields on the steps were analyzed and compared with results found in literature. As a general finding concerning the pressure in the horizontal faces, it was ascertained that the traction and the compression loads have relatively similar magnitudes, the negative pressures being more intense. Regarding the maximum pressures at the horizontal faces of the steps, it should be emphasized that the maximum values of compression have occurred at the end of the chute and that the lower discharges yielded higher values of pressure coefficients.Keywords: Dams; Stepped spillways; Pressures on spillways. RESUMOVertedouros em degraus vem sendo muito utilizados para escoamento de cheias devido às suas vantagens construtivas e em relação à dissipação de energia durante a queda, possibilitando que as estruturas de dissipação a jusante possam ser projetadas em menores dimensões. Devido a necessidade de estudos mais aprofundados sobre a ação do escoamento na calha de vertedouros em degraus e a análise dos adimensionais utilizados para caracterizar a distribuição longitudinal das pressões atuantes nas faces dos degraus de um vertedouro, o presente estudo objetiva a caracterização dos esforços atuantes nos degraus dos referidos vertedouros. Foram realizadas análises sobre um modelo físicos de vertedouro com declividade de 1V:0,75H e degraus de 6 centímetros de altura. Os campos de pressões nos degraus foram analisados e comparados com os resultados disponíveis na bibliografia. Como constatação geral sobre as pressões nos espelhos verificou-se que os esforços de tração e compressão têm magnitudes relativamente semelhantes, sendo mais intensas as pressões negativas. Sobre as pressões máximas nos patamares, destaca-se que os valores máximos de compressão ocorreram no final da calha, percebendo-se que as menores vazões geraram maiores valores de coeficientes de pressões. Palavras-chave:Barragens; Vertedouros em degraus; Pressões sobre vertedouros.RBRH, Porto Alegre, v. 23, e4, 2018Analysis of the longitudinal distribution of pressures near the ends of the vertical and horizontal faces in stepped spillway of slope 1V: 0.75H

Stepped spillways with aerators: hydrodynamic pressures and air entrainment

“…Pressure measurements on the vertical faces of the steps were performed using piezoresistive sensors (Omega PX419, Sitron SP96 and Hytronic TM25 The pressure behavior was evaluated based on the results of extreme pressures with non-exceedance probability of 5%, 1% and 0.1% (P 5% , P 1% and P 0.1% ) on the vertical faces of the steps. Similar statistical parameters of extreme pressures were used by Sánchez-Juny et al (2007,2008) and Osmar et al (2018). It was chosen to analyze only minimum extreme pressures on the vertical face due to the conclusions of Sánchez-Juny et al (2007).…”

“…Even though, in practical cases, stepped spillways have already been subject to notable floods without showing damage on the chute (Matos & Meireles, 2014;Chanson, 2015), the design practice usually restricts the specific design discharges to values in the order of 15 to 30 m 2 /s, as recommended by Pfister et al (2006a) and Amador et al (2009). Such recommendations are based on the understanding that stepped chutes are more prone to cavitation, when compared to smooth chutes, due to (i) the irregularities created by the steps protruding into the flow (Terrier, 2016) and (ii) the negative pressures that occur, especially, on the vertical faces of the steps, according to contributions of Sánchez-Juny And Dolz (2005), Sánchez-Juny et al (2007), Osmar et al (2018), Ferla et al (2019) and Marques et al (2019).…”

Influence of aeration induced by piers on the starting position of the flow aeration and extreme pressures in stepped spillways

“…Several studies on stepped spillways were developed to understand the flow behavior and hydrodynamic efforts that occur along the stepped chute, such as the studies published by Povh et al (2004), Sánchez-Juny et al (2007, 2008, Arantes et al (2009), Takahashi & Ohtsu (2012), Conterato et al (2015), Estrella et al (2015), Xu et al (2015), Dai Prá et al (2016), Zhang & Chanson (2016, 2017, Osmar et al (2018) and Nóbrega et al (2020). Based on the knowledge of hydrodynamic pressures on the steps, studies found the implementation of stepped spillways to be limited to a range of discharges due to the risk of cavitation damage.…”

Combination of experimental and numerical approaches to determine the main characteristics of skimming flow in stepped spillways

“…The physical hydraulic structure used in this work is described in Sanagiotto (2003), Sanagiotto & Marques (2008) and Gomes (2006) and is very similar to the structure used in other studies (Conterato, 2011(Conterato, , 2014Conterato et al, 2015;Novakoski et al, 2017aNovakoski et al, , 2017bOsmar et al, 2018), with small differences in the approach channel and the channel downstream of the steps.…”