International Concrete Abstracts Portal

This paper presents a new concept in designing a structure which is used as falsework, and utilized as reinforcing, which incorporates construction features for a turbine generator supporting structure. The turbine generator is supported by a massive concrete structure. In order to eliminate the falsework required for supporting the fresh concrete at the operating floor level, steel trusses are embedded in the concrete beams. The stress in the truss chord members are low for the construction loading, thereby allowing the trusses to be used as reinforcing in the beams. The trusses can be shop assembled in modules which can be transported by rail or truck to the site. In the assembly yard, the modules are completed for transporting to the turbine generator area and placing on the pedestal columns. The complete operation consists of adding side and soffit forms, rebar, anchor bolts, embeds, embedded conduits and penetrations. This construction sequence allows the turbine building outer framework to be erected prior to the placement of concrete pedestal. An enclosed building will also provide better control and environment for placing the concrete in the pedestal. This paper will provide an example pedestal design for a 1200Mw turbine generator. The details of fit-up of the truss modules, erection sequence, type of materials used, typical detai1s and concrete placement will be presented.

Grout, shims, or both, plus anchors form the vital link between machines, equipment, and column bases and their foundations. Grout and/or shims hold the equipment up and anchors hold it down. Grout, as used in this paper, is any fluid, flowable, plastic, or packable material that can be used to fill the space between the underside of a machine or column and the foundation on which the unit is to rest, then harden there to support the unit. The most widely used materials for grouts are combinations of hydraulic cements, fine aggregates including graded iron particles, various additives including chemical admixtures, and water. In recent years, various epoxy combinations with and without suspended fine aggregate have also been employed. This paper discusses hydraulic cement base grouts that are intended to not only completely fill the space under a base plate initially, but also harden in tight contact with the plate and permanently support or participate in the support of that plate. Such grouts are generally referred to as "nonshrink." Reasonably obtainable properties that the engineer may require of such a grout and tests he may specify to assure the results he desires are described. The pluses and minuses of fluid, flowable, plastic, and dry-pack grouts are covered and techniques for placing grouts at each consistency are described and illustrated. A measurable definition of the terms fluid, flowable, plastic, and dry-pack is offered.

Past attempts to analyze pile supported foundations included many simplifying assumptions regarding the pile-soil impedence functions (stiffness and damping) for a single pile. Further simplification was required to evaluate the effects of the pile group. In recent years significant studies relating to pile-soil dynamic behavior have been made and good agreement was reported in comparison with relatively small scale field tests. Also, generalized analyses of pile groups have been developed. In this paper the authors have used what they consider to be the current State-of-the-Art techniques for evaluating pile-soil impedence functions, group behavior, and embedment effects to calculate the dynamic response of pile supported machines and compared the calculated results to actual field measurements. Three similar operating plants, each using an identical reciprocating large compressor, were the basis of the study. The soil investigations included in-situ measurement of dynamic properties. The soil conditions at the sites were such that all sites required pile foundations and different pile types, including friction and end bearing piles, and batter piles. The results indicate that good agreement is achieved using the methods proposed for the rocking, and horizontal and vertical translation modes of vibration. .Further analyses are recommended to further investigate the behavior in the torsional mode. Also, further comparisons should be made with actual foundations where vibrations could be monitored at varying frequencies.

A dynamic analysis of an Induced Draft Fan and Foundation, subjected to unbalanced rotor loadings, is described and discussed. The installation selected for analysis is supported on piles, and consists of a reinforced concrete foundation and bearing pedestals, fan motor, fan, housing, and exhaust duct (evase’). The modeling techniques presented by the author in this case study will illustrate a method for the Design Engineer to completely analyze complex coupled systems involving both oil film and pile/soil stiffness and damping. The techniques presented do not require that the structural analysis computer program have discrete element damping (dashpot) capabilities. The model is all inclusive and can be used for both static and dynamic analysis. Dynamic responses, particularly modal frequencies and peak-to-peak journal bearing amplitudes of motion are compared with those calculated from relatively simplified lumped mass stick models of the same installation. Insight is gained into the dynamic behavior of the coupled system and the comparison study points out the limitations of the stick model responses. This paper presents a case study of an Induced Draft Pan and Foundation with special emphasis on the computer modeling techniques utilized. The model illustrated idealizes the COMPLETE system installation, and as such, is capable of directly predicting static deflections and internal forces, as well as coupled dynamic responses to earthquake and unbalanced rotor loads. The modeling techniques described are readily adaptable to commercially available structural analysis programs with finite element capabilities (i.e., Nastran, Strudl, Stardyne, Ansys).

This paper describes the design and construction of low-tuned, spring supported foundations for boiler feedpumps units installed in the Big Stone coal-fired power plant in South Dakota. Each system consists of a variable speed 9,500 HP (7084 Kw) steam turbine which drives a pair of feedpumps and is mounted on a prestressed concrete inertia block set on steel springs. This vibration isolation design required dynamic analysis of the inertia block systems since the variable speed pumps could present a range of forcing frequencies and hence a series of possible resonances. The concrete inertia blocks were prestressed in order to prevent cracking which could cause significant changes in the dynamic behavior. The concrete inertia blocks were fabricated and prestressed outside the turbine building. Each weighed about 96 tons (854 kN) and they were lifted into position on their steel springs on the operating floor level. The flexible isolation of the inertia blocks from the building floor facilitated the alignment of the machinery and the attachment of the piping. Vibration tests were conducted during plant start-up in order to anticipate potential problems and to verify dynamic characteristics. These units have now performed successfully for several years.