Validation issues for SSI codes

The paper describes the results of a recent work which was performed to verify computer code predictions in the SSI area. The first part of the paper is concerned with analytic solutions of the system response. The mathematical derivations are reasonably reduced by the use of relatively simple models which capture fundamental ingredients of the physics of the system motion while allowing for the response to be obtained analytically. Having established explicit forms of the system response, numerical solutions from three computer codes are presented in comparative format

Thermally conductive cementitious grouts for geothermal heat pumps. Progress report FY 1998

Research commenced in FY 97 to determine the suitability of superplasticized cement-sand grouts for backfilling vertical boreholes used with geothermal heat pump (GHP) systems. The overall objectives were to develop, evaluate and demonstrate cementitious grouts that could reduce the required bore length and improve the performance of GHPs. This report summarizes the accomplishments in FY 98. The developed thermally conductive grout consists of cement, water, a particular grade of silica sand, superplasticizer and a small amount of bentonite. While the primary function of the grout is to facilitate heat transfer between the U-loop and surrounding formation, it is also essential that the grout act as an effective borehole sealant. Two types of permeability (hydraulic conductivity) tests was conducted to evaluate the sealing performance of the cement-sand grout. Additional properties of the proposed grout that were investigated include bleeding, shrinkage, bond strength, freeze-thaw durability, compressive, flexural and tensile strengths, elastic modulus, Poisson`s ratio and ultrasonic pulse velocity

Standard problems for structural computer codes

BNL is investigating the ranges of validity of the analytical methods used to predict the behavior of nuclear safety related structures under accidental and extreme environmental loadings. During FY 85, the investigations were concentrated on special problems that can significantly influence the outcome of the soil structure interaction evaluation process. Specially, limitations and applicability of the standard interaction methods when dealing with lift-off, layering and water table effects, were investigated. This paper describes the work and the results obtained during FY 85 from the studies on lift-off, layering and water-table effects in soil-structure interaction

Literature Survey on Cements for Remediation of Deformed Casing in Geothermal Wells

Brookhaven National Laboratory was requested to conduct a literature survey for the best available cement to use in the proposed casing patch as part of the Geothermal Drilling Organization (GDO) project on remediation of deformed casings. A total of 50 wells have been identified with deformed production casing in Unocal`s portion of The Geysers geothermal field. A procedure to address the casing deformation and avoid abandonment of these wells has been developed as described in the Geysers Deformed Casing Remediation Proposal. The proposed remediation procedure involves isolation of the zone of interest with an inflatable packer, milling the deformed casing and cementing a 7 inch diameter liner to extend approximately 100 ft above and 100 ft below the milled zone. During the milling operation it is possible that the original cement and surrounding formation may slough away. In order to specify a suitable cement formulation for the casing patch it is first necessary to identify and understand the deformation mechanism/s operating in The Geysers field. Subsequently, the required cement mechanical properties to withstand further deformation of the repaired system must be defined. From this information it can be determined whether available cement formulations meet these requirements. In addition to The Geysers, other geothermal fields are at possible risk of casing deformation due to subsidence, seismic activity, lateral and vertical formation movement or other processes. Therefore, the proposed remediation procedure may have applications in other fields

A plane strain model of soil saturation effect on dynamic stiffness functions of embedded footings

Impedance functions associated with horizontal and vertical vibrations of rigid massless strip footings embedded in a saturated soil stratum are evaluated using a finite element approach The foundation medium is treated as a two-phase continuum which behaves according to Blot`s classical theory of wave propagation in fluid-saturated porous media. Parametric studies have been recently performed by the authors in an effort to verify that the adopted finite element approach and associated numerical procedures yield reasonable correlations with analytic solutions of soil-structure interaction problems. Horizontal and vertical impedance functions are presented for various embedment depth/soil layer thickness configurations. It is shown that saturation influences the foundation impedances especially their imaginary parts which can be reasonably explained as being the result of additional dissipation in the system associated with the motion of pore fluid relative to the soil skeleton. It is further shown that, as anticipated, soil stiffnesses increase with increasing embedment depth

Review of public comments on proposed seismic design criteria

During the first quarter of 1988, the Nuclear Regulatory Commission (NRC) prepared a proposed Revision 2 to the NUREG-0800 Standard Review Plan (SRP) Sections 2.5.2 (Vibratory Ground Motion), 3.7.1 (Seismic Design Parameters), 3.7.2 (Seismic Systems Analysis) and 3.7.3 (Seismic Subsystem Analysis). The proposed Revision 2 to the SRP was a result of many years' work carried out by the NRC and the nuclear industry on the Unresolved Safety Issue (USI) A-40: ''Seismic Design Criteria.'' The background material related to NRC's efforts for resolving the A-40 issue is described in NUREG-1233. In June 1988, the proposed Revision 2 of the SRP was issued by NRC for public review and comments. Comments were received from Sargent and Lundy Engineers, Westinghouse Electric Corporation, Stevenson and Associates, Duke Power Company, General Electric Company and Electric Power Research Institute. In September 1988, Brookhaven National Laboratory (BNL) and its consultants (C.J. Costantino, R.P. Kennedy, J. Stevenson, M. Shinozuka and A.S. Veletsos) were requested to carry out a review of the comments received from the above six organizations. The objective of this review was to assist the NRC staff with the evaluation and resolution of the public comments. This review was initiated during October 1988 and it was completed on January 1989. As a result of this review, a set of modifications to the above mentioned sections of the SRP were recommended by BNL and its consultants. This paper summarizes the recommended modifications. 4 refs

Integrated system for seismic evaluations

This paper describes the various features of the Seismic Module of the CARES system (Computer Analysis for Rapid Evaluation of Structures). This system was developed by Brookhaven National Laboratory (BNL) for the US Nuclear Regulatory Commission to perform rapid evaluations of structural behavior and capability of nuclear power plant facilities. The CARES is structured in a modular format. Each module performs a specific type of analysis i.e., static or dynamic, linear or nonlinear, etc. This paper describes the features of the Seismic Module in particular. The development of the Seismic Module of the CARES system is based on an approach which incorporates all major aspects of seismic analysis currently employed by the industry into an integrated system that allows for carrying out interactively computations of structural response to seismic motions. The code operates on a PC computer system and has multi-graphics capabilities. It has been designed with user friendly features and it allows for interactive manipulation of various analysis phases during the seismic design process. The capabilities of the seismic module include (a) generation of artificial time histories compatible with given design ground response spectra, (b) development of Power Spectral Density (PSD) functions associated with the seismic input, (c) deconvolution analysis using vertically propagating shear waves through a given soil profile, and (d) development of in-structure response spectra or corresponding PSD's. It should be pointed out that these types of analyses can also be performed individually by using available computer codes such as FLUSH, SAP, etc. The uniqueness of the CARES, however, lies on its ability to perform all required phases of the seismic analysis in an integrated manner. 5 refs., 6 figs

Experimental characterization and performance evaluation of geothermal grouting materials subjected to heating–cooling cycles

In recent years, the increasing rise in environmental awareness among energy consumers has led to an increasing use of renewable energies such as the geothermal energy. An important role in the efficient exploitation of the geothermal resource is played by the grouting material placed in the borehole between the pipes and the ground. Actually, the use of proper grouts is essential to provide an effective heat transfer between the ground and the heat carrier fluid in the pipes, and also to comply with the mechanical and environmental demands. However, when it comes to the construction of the GHP installations, the grout is especially required to be easy to work with (workable) and for this reason more water than required is sometimes added. In order to assess the suitability of grouting materials with significant water/solid ratios, the thermal conductivity, mechanical strength and permeability of five different grouts and grout–pipe specimens were measured for their laboratory characterization. In addition, the grouts were subjected to heating and cooling cycles to evaluate their durability with time in terms of the potential degradation of the materials and the loss of quality of the grout–pipe interface. According to the results obtained, the grouts here tested are appropriate for most of the geothermal heat pump installations, especially for those with low to medium ground thermal properties.The authors wish to express their gratitude to the Ministerio de Economía y Competitividad which funded this study within the Spanish National Plan for Scientific and Technical Research and Innovation (INNPACTO program) through the research project IPT-2011-0877-920000

Critical seismic load inputs for simple inelastic structures

The modelling of earthquake loads as design inputs for inelastic single-degree-of-freedom structures is considered. The earthquake load is modelled as a deterministic time history which is expressed in terms of a Fourier series that is modulated by an enveloping function. Subsequently, the coefficients of the series representation, and, the parameters of the envelope function are determined such that the structure inelastic deformation is maximized subject to a set of predefined constraints. These constraints include bounds on the total energy of the earthquake signal, peak values on ground acceleration, velocity and displacement and upper and lower bounds on the Fourier spectra of the ground acceleration. Additional mathematical limits on the envelope parameters are also considered. The quantification of these constraints is obtained based on numerical analysis of a set of past recorded ground motions at the site under consideration or other sites with similar soil conditions. The structure force?displacement relation is taken to possess an elastic?plastic behavior. The resulting nonlinear optimization problem is tackled by using the sequential quadratic optimization method. The study, also, examines influences of the structure yield strength and damping ratio on the derived earthquake load and the associated structure response. Issues related to the time-variation of various energy forms dissipated by the inelastic system are also explored. The proposed formulation is demonstrated with reference to the inelastic response analysis of a frame structure driven by a single component of earthquake load