Static and Dynamic Analysis of Concrete Turbine Foundations0 pages

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Static and Dynamic Analysis of Concrete Turbine

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Foundations

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Peter Nawrotzki, Dr-Ing., Managing Director, GERB Engineering GmbH, Essen, Germany; Giinter Hiiffmann, Dr-Ing., Senior

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Adviser, GERB Vibration Control Systems, Berlin, Germany and Timur Uzunoglu, Dr-Ing., Managing Director, convex ZT GmbH,

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Graz, Austria

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Summary

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The paper presents a systematic overview of the static and dynamic analysis of

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turbine foundations made of reinforced concrete. It discusses the load cases to

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be applied, the required ultimate limit and serviceability limit state checks, the

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assessment of the static and dynamic foundation stiffness and special provisions

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required in seismic areas. Turbine foundation design is an ambitious task, requir-

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ing attention to detail and plausibility checking of all input/output parameters, as

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a shut down of a turbine caused by an insufficiently designed and built founda-

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tion will lead to damage that is in no proportion to its cost.

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Keywords: turbine foundation; block foundation; table foundation; spring

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support; structural dynamics; vibration amplitude; vibration velocity; misalign-

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ment matrix.

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Introduction

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During the first half of the twentieth

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century, engineering of turbine foun-

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dations was limited to a static analysis

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based on dead loads plus an additional,

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arbitrary vibration charge amounting

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to 3 to 5 times of the machine weight

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acting as a vertical, equivalent static

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load.

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In 1955, the publication of the first edi-

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tion of DIN 4024 provided for the first

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time rules for a standardised static and

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dynamic analysis. Although it was ob-

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vious that the calculation of the first

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order natural frequency alone was not

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sufficient to characterise the dynamic

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behaviour of turbine foundations, it

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needed the development of computers

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to allow models and methods for the

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analysis of turbine foundations to pro-

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vide a more precise assessment of the

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dynamic behaviour.

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turbine leading to a table-type foun-

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dation (Fig. 2), with two possible ar-

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rangements: either, the condenser is

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welded to the LP turbine nozzle with

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a smaller part of the condenser weight

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^^^^^^

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^A^A^A^A^AAAA

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Fig. 1: Bedding types of a block foundation2

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hanging at the LP turbine, and the re-

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maining bigger part of the condenser

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dead load supported by springs, allow-

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ing heat expansion of the condenser

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downwards, or the condenser is fixed

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at the bottom with a bellow between

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condenser and LP turbine nozzle to

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allow heat expansion upwards. In this

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case, neither dead load nor heat ex-

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pansion will be part of the foundation

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analysis, but the vacuum pull will be

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an additional load case.

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Block and table foundations may be

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placed directly on the ground or may

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be supported by piles, if only a deeper

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layer of soil has sufficient load-bearing

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capacity. These foundations should be

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separated from the surrounding struc-

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ture by a joint filled with an elastic ma-

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terial.

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XAAVA>

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^A

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I

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^A^A^A^A^ASAA

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General Information about

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Turbines and their Foundations

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The present paper deals, particularly,

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with foundations of gas and steam

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turbines coupled to a generator for

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power production. For gas turbines,

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typically block foundations are used

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(Fig. 1). For steam turbines, the con-

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denser arrangement in the low pres-

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sure (LP) turbine area leads to

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different foundation designs. In most

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cases, the condenser sits below the LP

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n

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^^^AAAAA^/A

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L □

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'AAsA/AÏ,

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E

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11

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m$ ^AAAA^A^AA/A

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Fig. 2: Bedding types of a table foundation

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Structural Engineering International 3/2008

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Reports 265

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