A recently developed numerical methodology is demonstrated for the analyses of concrete structures subjected to extreme loading and large deformations. This methodology combines a discrete particle formulation with non-linear finite element modelling to improve analyses of i.e. penetration phenomena. The penetration of a projectile into a concrete target is studied by the use of this numerical methodology. Experimental results for impacts of both reinforced and unreinforced concrete targets are used for comparisons with the simulation results, and the simulations show reasonable results for these two simulation cases.

In earlier times, the generators of the hydropower plants ran more or less continuously, while nowadays there are many planned starts and stops. The hydropower stations are thereby, due to the new pattern of operation, subjected to loads that they were not originally designed for. The aim of this study is to understand the complex interaction between the power generating system and the supporting concrete structure, during this new operational pattern.

During inspections, cracks were discovered in the concrete structure of the power house, near the stator and rotor spider supports, at several hydropower stations in Sweden. In a previous phase of this project it was shown that these cracks initiated due to the combined effect of drying shrinkage, mechanical loads and variations in temperature due to starts and stops. Cracking of the concrete structure reduces its stiffness, which may result in larger loads acting on the structure and vibrations exceeding the unit’s strict tolerance limits.

In this part of the study, the behaviour of a concrete support structure subjected to rotor dynamic loads during normal operation has been studied. A detailed 3D numerical model has been developed which include hydropower unit. The results of this study show that a reduced structural stiffness of the concrete support structure, due to cracking, influences the behaviour of the rotating system.

Numerical analysis is a suitable tool in the design of complex reinforced concrete structures under extreme impulsive loadings such as impacts or explosions at close range. Such events may be the result of terrorist attacks. Reinforced concrete is commonly used for buildings and infrastructures. For this reason, the ability to accurately run numerical simulations of concrete elements subjected to blast loading is needed. In this context, reliable constitutive models for concrete are of capital importance. In this research numerical simulations using two different constitutive models for concrete (Continuous Surface Cap Model and Brittle Damage Model) have been carried out using LS-DYNA. Two experimental benchmark tests have been taken as reference. The results of the numerical simulations with the aforementioned constitutive models show different abilities to accurately represent the structural response of the reinforced concrete elements studied.

An extensive program for improvement of the hydropower plants in Sweden is currently on-going. The aims are to secure future production and to maintain and further develop an already high dam safety.

During inspection, cracks were discovered in the concrete foundation, near the stator and rotor spider supports, at some hydropower stations in Sweden. The cracks were believed to be related to new patterns for generator operation, thereby changing the dynamic loading of the stator and rotor spider supports. Previously the generators ran continuously, while nowadays there are an increased number of stops and starts, sometimes even several times during one day. Increased dynamic forces due to runaways, and also other dynamic events such as emergency stops, may also contribute to increased stress levels and cracking of the foundation. Furthermore, although extreme loads such as short circuits of the generator seldom occurs, the influence on the dynamic forces acting on the supporting structure and concrete foundation may be strongly influenced during such events.

The objective of this study is to understand the complex interaction between the power generating system (stator, rotor, turbine, etc.) and its supporting concrete structure. It is important from a dam safety perspective to determine the causes of existing structural cracks in the foundation. Furthermore, to be able to predict further crack propagation of the concrete foundation will help to determine future maintenance requirements.

A three dimensional non-linear finite element model developed earlier was used to evaluate a methodology for analyses of the interaction between the generator and the concrete foundation. The influence of cracks in the concrete foundation was investigated by including the fracture pattern obtained in earlier FE analyses of time-dependent thermal and moisture gradients. These analyses showed that the drying shrinkage induced cracking inside the concrete foundation and especially close to the supports of the stator and the rotor spider. The obtained fracture pattern for the previous analysis was used as input for this study, with the concrete foundation’s changed structural properties and their influence on the interaction with the generator considered in the analyses. Furthermore, deadweight and operational load were also included in the analyses.

The study show that FE models with a cracked concrete foundation can be used to analyse structural interaction betwee foundation and generator components during operation of a hydro power generator. The crack pattern can be determined by FE analyses, or by in-situ measurements of existing concrete cracks for a specific concrete foundation. The analyses show that further studies are needed regarding the combined effects from thermo-mechanical loads, drying shrinkage, creep and dynamical loads caused by the generator. The combined effects may further increase the stress levels for the concrete foundation, especially locally near perforations, and stator and rotor spider supports. These analyses should be performed with an increased numerical resolution for both the concrete foundation and the supporting structure for the generator, with an increased accuracy for the local stress variations near perforations of the foundation and also at the supports for the generator. This research area will be further investigated within a recently started research project at KTH, financed by the Swedish Hydropower Centre.

Ett kontinuerligt arbete med utvärdering och uppgradering av vattenkraften pågår i Sverige. Syftet med projektet är att säkerställa bibehållen långvarig och säker drift av vattenkraftens konstruktioner ur ett byggnadstekniskt perspektiv.

Vid inspektioner av svenska vattenkraftsstationer har, i vissa fall, sprickor observerats i de betongfundament som utgör generatorns upplag och i synnerhet kring stator- och rotorupplagen. En av de bidragande orsakerna till dessa sprickor tros vara dynamiska påkänningar som orsakas av ett nytt driftsmönster, samt även andra dynamiska påkänningar. Dessa dynamiska påkänningar kan utgöras av lastfrånslag/snabbstopp och ökade dynamiska laster vid övervarvning, samt även sällan förekommande påkänningar som t.ex. kortslutning av generatorn. Tidigare användes generatorerna kontinuerligt medan vattenkraften idag används för att balansera energitillförseln, vilket leder till många starter och stopp, ibland under ett och samma dygn. Syftet med föreliggande projekt är att förstå den komplicerade samverkan mellan generator (stator, rotor, turbin, etc.) och betongkonstruktionen som utgör generatorns upplag. Från ett dammsäkerhetsperspektiv är det viktigt att bestämma orsaken till de sprickor som observerats i fält, samt att kunna prediktera både sprickor i betongfundament och framtida underhållsbehov.

En tredimensionell finita-elementmodell av ett generatorfundament har definierats i ett tidigare projekt och denna modell har använts för utvärdering av metodik för analyser av interaktionen mellan betongkonstruktionen och generatorn. Inverkan av sprickor i fundamentet har studerats baserat på beräknat sprickmönster erhållet vid tidigare genomförda FE-analyser. Dessa analyser visade att uttorkningskrympningen huvudsakligen orsakar uppsprickning på fundamentets insida och främst vid upplagen för stator- och rotorbalkar. Dessa analysresultat användes som indata för denna studie, varvid fundamentets ändrade egenstrukturella beteende och dess inverkan på fundamentets interaktion med generatorn har beaktats med hänsyn till effekter från egentyngder och driftsbelastningar.

Resultatet från projektet visar att analyser av strukturinteraktion mellan en generator och ett betongfundament kan genomföras med hänsyn tagen till sprickornas geometri. Detta spricksystem kan vara bestämt med hjälp av FE-analyser, eller baserat på befintliga sprickor för ett specifikt betongfundament. Resultaten visar att fortsatta studier krävs avseende samverkan mellan de termomekaniska laster, inverkan av uttorknings-krypning och krympning för betongen under långtidsbelastning, samt dynamiska lasteffekter orsakade av generatorn. Detta då samverkan av de olika belastningarnas antagligen resulterar i ökade påfrestningar på betongfundamentet. Dessa analyser bör genomföras med ökad geometrisk upplösning avseende betong- och stödstrukturens uppbyggnad, detta för att möjliggöra analyser av lokala spänningsvariationer vid fundamentets perforationer och generatorns upplag. Den aktuella problemställningen kommer att beaktas inom ett doktorandprojekt vid KTH, med stöd av SVC Svenskt VattenkraftCentrum.

Skyddskonstruktioner av betong har fått större aktualitet inom forskningen eftersom farligt godsnu oftare passerar nära boendeområden och trafikerade leder i växande städer. Användandet av höghållfast betong för konstruktioner som riskerar att utsättas för extrema laster aktualiseras även det aktuella forskningsområdet.

The structural response of a stainless steel plate subjected to the combined blast and sand impact loading from a buried charge has been investigated using a fully coupled approach in which a discrete particle method is used to determine the load due to the high explosive detonation products, the air shock and the sand, and a finite element method predicts the plate deflection. The discrete particle method is based on rigid, spherical particles that transfer forces between each other during collisions. This method, which is based on a Lagrangian formulation, has several advantages over coupled Lagrangian-Eulerian approaches as both advection errors and severe contact problems are avoided. The method has been validated against experimental tests where spherical 150 g C-4 charges were detonated at various stand-off distances from square, edge-clamped 3.4 mm thick AL-6XN stainless steel plates. The experiments were carried out for a bare charge, a charge enclosed in dry sand and a charge enclosed in fully saturated wet sand. The particle-based method is able to describe the physical interactions between the explosive reaction products and soil particles leading to a realistic prediction of the sand ejecta speed and momentum. Good quantitative agreement between the experimental and predicted deformation response of the plates is also obtained.

The ability to predict penetration resistance in concrete is necessary to evaluate the vulnerability of protective designs for impacts by penetrating weapons, or deformable projectiles. The paper presents experimental work regarding oblique projectile impact of both normal strength and high performance concrete targets with modern type of hard target penetrators. Furthermore, finite element (FE) analyses of non-normal projectile impacts of the normal strength concrete targets are presented, and its limitations discussed.

Penetration and perforation of concrete targets are studied by the use of numerical simulations to enhance the understanding of the penetration phenomenon. Comparisons were made with test results obtained for both reinforced and unreinforced 48.0 MPa normal strength concrete. The studied projectiles were made as generic models of penetrators for buried hardened target defeat. Varying impact velocities and angles for the penetrators were investigated. The simulations gave reasonable results for the different simulation cases, with the best results were obtained for reinforced concrete targets.

The results from this investigation demonstrate the ability to perform numerical simulations of dynamic structural response of concrete elements subjected to air blast loading. Beams of both high-strength concrete (HSC) and normal-strength concrete (NSC) were studied. Also beams with two concrete layers of different strength were simulated. It is of particular interest to investigate the use of material models for implementation with software for the explicit analysis of non-linear dynamic events. The influences of concrete strength, amounts of reinforcement, the bond between concrete and reinforcement, bi-linear strain softening of concrete, the strain rate dependence of reinforcement and boundary conditions at the supports were studied. The simulations were performed with the text data as reference through comparison between numerical examples and experimental test results. It was possible numerically to analyse the dynamic behaviour of beams tested in situ and to describe the observed failure modes of these beams. The analysis tool will be used for evaluating the dynamic strength of future protective structures of HSC, possibly with parts consisting of NSC elements.