Simulation of Crack Propagation in Concrete Hydropower Dam Structures

Transcription

1 Simulation of Crack Propagation in Concrete Hydropower Dam Structures Richard Malm 1,, Manouchehr Hassanzadeh 1,3 Tobias Gasch, Daniel Eriksson 1 KTH Royal Institute of Technology / Concrete Structures Vattenfall Research and Development / Civil Engineering 3 Lund University / Building Materials Crack Propagation in Concrete Hydropower Dam Structures Ongoing extensive program to upgrade the Swedish hydropower plants - Generator foundation - Influence of cracks on the dam safety Water level Upstream side Front-plate Buttress wall Downstream side Inspection gangway Insulating wall

2 .5 m Storfinnforsen hydropower dam Storfinnforsen concrete buttress dam - Total length of 1 m (8 m concrete) - 1 concrete monoliths Several different types of cracks found in-situ Water level Upstream side Front-plate Buttress wall Downstream side Inspection gangway Insulating wall Numerical simulations One monolith is modeled with 3D shell elements - Reinforced concrete Nonlinear material model CDP (Concrete Damaged Plasticity) in ABAQUS v 6.1 Thermal analyses - Winter air temperature 15 C - Summer air temperature +5 C Simulation steps - Static loads (gravity, water pressure) - Cycle winter and summer temperatures for the initial design of the monolith - Cycle winter and summer temperatures after the insulating wall was installed c15 mm Two layers of rebars φ19 mm Each 5 mm below the concrete surface c4 mm c4 mm c4 mm c4 mm c3 mm c4 mm

3 Steady State Thermal Calculations Cyclic steady state thermal calculations were performed - Summer winter (without an insulating wall) - Summer winter (with an insulating wall) Coupled thermo-stress analysis - Importing the steady state temperatures into a model that calculate resulting stresses and predict cracking Winter conditions Summer conditions Simulation - Seasonal temperature variation Before the insulating wall Inclined cracks in the buttress Horizontal cracks in the front-plate After the insulating wall Inclined crack in the buttress

4 Animation of the crack propagation Cyclic seasonal temperature variation (summer/winter) Deformation scale factor 4 Probabilistic analyses Study the influence of material properties and material distribution on the crack trajectory - Starts from an analysis where the inclined crack is initiated and simulate further crack propagation Monte Carlo Simulation - 1 analyses - Sub-model of the area of interest with a significantly refined mesh Sub-model

5 Stochastic material properties Probability Generated 1 random material properties with log-normal distribution Statistics ofrandom generated properties N = 1 µ =.53 MPa σ =.78 MPa COV = Tensile strength (MPa) Probability Statisticsof random generated properties N = 1 µ = 1.9 Nm/m σ = 35.8 Nm/m COV = Fracture energy (Nm/m ) Elastic modulus (GPa) Assuming a high correlation between the material properties, above 95% Probability Statistics ofrandom generated properties N = 1 µ = 5. GPa σ = 3.8 GPa COV =.15 Tensile strength (MPa) 6 4 Tensile strength (MPa) 6 4 Fracture energy (nm/m ) Fracture energy (Nm/m ) Elastic modulus (MPa) Elastic modulus (MPa) Material distribution Randomly assigning a set of material properties (f t, E c, G f ) for each element in the sub-model and simulating the crack propagation Tensile Strength [MPa] Regions With Low Tensile Strength [MPa] Max Mean f t =.54 MPa 1 Min

6 Area subjected to cracking Based on all simulations - All cracked elements summarized in one plot - Calculated probability of cracking Crack Pattern Calculated probability of cracking Cracked element from the all simulations Cracked element in the original analysis (with mean values).1.5 Conclusions Several, more or less cracked dams in Sweden. - In many cases due to the new pattern of generator operation - Extensive ongoing program to upgrade the dams In this project, the non-linear finite element method have been used to - Explain the cause of cracks in a concrete buttress dam - Study the influence of distribution in material properties on the crack trajectory - Preliminary results shows a difference in crack trajectory obtained from a deterministic analysis with mean values compared to the most probable crack trajectory obtained from probabilistic analyses

7 Thanks for your attention! Richard Malm, PhD KTH Royal Institute of Technology Concrete Structures Vattenfall Research and Development Civil Engineering