Canadian Dam Association Bulletin - Fall 2016 - 28

1 GENERAL The Otto Holden Generating Station (GS) is on the Ottawa River, near Mattawa. It has been in operation since 1952. The powerhouse has eight generating units, referred to as G1 to G8, with a total output capacity of 240 MW under a gross head of 23.5 m. The concrete substructure contains the eight turbines with their associated RC scroll cases and draft tubes. All eight units have the same Westinghouse generators. G1 to G4 have Allis Chalmers turbines and G5 to G8 are John Inglis turbines. Effects of concrete movement/ growth have been observed since the early 1970s. Lots of concrete cracking was observed in the 1970s and 1980s. Major overhauls were conducted on all eight units from 1980 to 1988 and the effects of concrete movement were noticed during turbine/generator component alignments. Since 1983, runner clearance data has been collected for all eight units and this data has helped in determining the rate and direction of unit component movements. Petrographic analysis of concrete samples collected in 1992 proved alkali-aggregate reaction (AAR) in the concrete. As per the recommendations of the Concrete Movement Investigation Study conducted in 1997, instrumentation was installed at various locations in the dam to monitor concrete movement. Concrete instrumentation data confirmed AAR in the concrete and also helped in determining the growth rate and strains in different parts of the dam. G8 encountered a major operational problem of sticky wicket gates in 1999. This initiated a second set of major overhauls and turbine/generator component modifications. A second set of overhauls were done from 2000 to 2008. During these overhauls, the turbine bottom rings were made adjustable to compensate relative movement between the top and bottom speed rings. At the beginning of 2014, a turbine assessment program was started to find the current condition of the generating units. One of the main objectives of this program was to assess the 28 condition of the turbine stay ring and determine the scope of work for the next set of unit overhauls. AAR is a complex phenomenon and concrete growth rate is not uniform across the dam. The concrete growth rate as measured by turbine clearances and concrete instrumentation varies from unit to unit. The majority of the generator and turbine components can be moved around to compensate for AAR related concrete movements. However, the stay ring is the most critical turbine component because it is embedded in the concrete and is being distorted by AAR induced movements. Previous studies indicated that the stresses in the stay vanes and in the stay ring anchor bars are beyond the yield strength of the material. High tensile stresses in the stay vanes were confirmed by the linear FEA model. However, the residual stress measured by the X-ray diffraction method in the stay vanes indicated that they are under compressive stresses. These conflicting stress estimates in the stay vanes may be due to questionable boundary conditions and loading applied in the stay ring FEA model. A better way to estimate loading on the stay ring due to AAR was to do an FEA of complete concrete structure of one unit. FE modeling of RC members is performed in order to develop numerical models for the nonlinear behavior of the Otto Holden substructure under the concrete expansion due to AAR. In Section 0 of this report, the nonlinear properties of the construction materials, (Concrete, Steel reinforcement and Steel plates of the Stay Vanes and Speed Rings) are discussed. Also, this section describes the various modeling features of ABAQUS/CAE. 2 FINITE ELEMENT PROGRAM ABAQUS/CAE The FE analysis is performed using ABAQUS/CAE Version 6.12-1(Dassault Systèmes Simulia Corp., 2012). ABAQUS/CAE provides an interactive and graphical technique and allows a model to be created easily by producing the geometry into meshable regions. Material properties, loads, and boundary conditions can be assigned to the geometry. ABAQUS/CAE has easy interface and it is suitable for simulation of nonlinear engineering problems. Additionally, its visualization module is an efficient option to interpret the results. ABAQUS/CAE consists of two main analysis products: ABAQUS/ Standard, and ABAQUS/Explicit. ABAQUS/Standard is typically used for general-purpose analysis problems where a system of equations is solved implicitly at each solution increment. ABAQUS/Explicit is used for special purpose analyses which use an explicit dynamic finite element formulation. It uses a central difference method to integrate the equations of motion explicitly through time. It is suitable for modeling brief, transient dynamic events, such as impact problems, and is also very efficient for nonlinear problems. For analyzing a nonlinear problem with a large number of degrees of freedoms (DOFs), using ABAQUS/Explicit is recommended. This is because for each iteration, ABAQUS/Standard requires a solution of a large set of linear equations through the iteration process. The ABAQUS/Explicit was used for the following reasons: * Concrete degradation can cause severe convergence difficulties in the ABAQUS/Standard (implicit) analysis program but in the ABAQUS/Explicit can perform well. * Reduces the computational time. 3 MATERIAL PROPERTIES 3.1 Concrete Model There are three different models to simulate the concrete behavior in ABAQUS/CAE: * The smeared cracking model. * The brittle cracking model. * The concrete damaged plasticity model (Dassault Systèmes Simulia Corp. 2012). Because the stiffness recovery effects during load reversals can be controlled by the user, the concrete damaged plasticity model is used in this nonlinear analysis. View past issues of the CDA Bulletin online at www.naylornetwork.com/cda-NXT/ http://www.naylornetwork.com/cda-NXT/

Table of Contents for the Digital Edition of Canadian Dam Association Bulletin - Fall 2016

Board of Directors
Board of Directors Nominations
Remedial Work at Lake Major Dam
CDA Conference Report: Otto Holden Generating Station Alkali-Aggregate Reaction Investigation
DSR Bulletin
Icold Corner
Notice of Annual General Meeting
Call for Papers, 2017 Conference
Young Professional Activities
Buyers’ Guide and Trade List
Canadian Dam Association Bulletin - Fall 2016 - cover1
Canadian Dam Association Bulletin - Fall 2016 - cover2
Canadian Dam Association Bulletin - Fall 2016 - 3
Canadian Dam Association Bulletin - Fall 2016 - 4
Canadian Dam Association Bulletin - Fall 2016 - 5
Canadian Dam Association Bulletin - Fall 2016 - 6
Canadian Dam Association Bulletin - Fall 2016 - Board of Directors
Canadian Dam Association Bulletin - Fall 2016 - 8
Canadian Dam Association Bulletin - Fall 2016 - Board of Directors Nominations
Canadian Dam Association Bulletin - Fall 2016 - Remedial Work at Lake Major Dam
Canadian Dam Association Bulletin - Fall 2016 - 11
Canadian Dam Association Bulletin - Fall 2016 - 12
Canadian Dam Association Bulletin - Fall 2016 - 13
Canadian Dam Association Bulletin - Fall 2016 - 14
Canadian Dam Association Bulletin - Fall 2016 - 15
Canadian Dam Association Bulletin - Fall 2016 - 16
Canadian Dam Association Bulletin - Fall 2016 - 17
Canadian Dam Association Bulletin - Fall 2016 - 18
Canadian Dam Association Bulletin - Fall 2016 - 19
Canadian Dam Association Bulletin - Fall 2016 - 20
Canadian Dam Association Bulletin - Fall 2016 - 21
Canadian Dam Association Bulletin - Fall 2016 - 22
Canadian Dam Association Bulletin - Fall 2016 - 23
Canadian Dam Association Bulletin - Fall 2016 - 24
Canadian Dam Association Bulletin - Fall 2016 - 25
Canadian Dam Association Bulletin - Fall 2016 - CDA Conference Report: Otto Holden Generating Station Alkali-Aggregate Reaction Investigation
Canadian Dam Association Bulletin - Fall 2016 - 27
Canadian Dam Association Bulletin - Fall 2016 - 28
Canadian Dam Association Bulletin - Fall 2016 - 29
Canadian Dam Association Bulletin - Fall 2016 - 30
Canadian Dam Association Bulletin - Fall 2016 - 31
Canadian Dam Association Bulletin - Fall 2016 - 32
Canadian Dam Association Bulletin - Fall 2016 - 33
Canadian Dam Association Bulletin - Fall 2016 - 34
Canadian Dam Association Bulletin - Fall 2016 - 35
Canadian Dam Association Bulletin - Fall 2016 - 36
Canadian Dam Association Bulletin - Fall 2016 - 37
Canadian Dam Association Bulletin - Fall 2016 - DSR Bulletin
Canadian Dam Association Bulletin - Fall 2016 - Icold Corner
Canadian Dam Association Bulletin - Fall 2016 - 40
Canadian Dam Association Bulletin - Fall 2016 - Notice of Annual General Meeting
Canadian Dam Association Bulletin - Fall 2016 - Call for Papers, 2017 Conference
Canadian Dam Association Bulletin - Fall 2016 - 43
Canadian Dam Association Bulletin - Fall 2016 - Young Professional Activities
Canadian Dam Association Bulletin - Fall 2016 - Buyers’ Guide and Trade List
Canadian Dam Association Bulletin - Fall 2016 - 46
Canadian Dam Association Bulletin - Fall 2016 - cover3
Canadian Dam Association Bulletin - Fall 2016 - cover4
Canadian Dam Association Bulletin - Fall 2016 - outsert1
Canadian Dam Association Bulletin - Fall 2016 - outsert2
Canadian Dam Association Bulletin - Fall 2016 - outsert3
Canadian Dam Association Bulletin - Fall 2016 - outsert4
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