动力设备基础设计

1、hve土建/结构工程设计方法 动力设备基础设计参考资料 design of structure and foundation for vibrating machines dynamic analysis of stg foundation procedures and guidance american concrete institute (aci318) asce 7 minimum design loads for buildings and other structures (asce)土壤资料剪切波速，弹性模量重度。其他条件基础标高，周围环境，或结构的敏感性vender dwg频率

2、，静荷，动荷不平衡力，容许振幅确定基础形式：块式/构架/隔振确定基础尺寸，埋深on soil or pile基础桩尺寸静力分析，土壤承载力，抗倾覆及沉降计算土壤静，动弹簧系数，及阻尼比计算动力分析，频率，振幅，速度，加速度基础强度，配筋计算确定基本荷载及其组合形式：块式/构架/隔振endngng基础分析及设计流程基本概念vibration modes possible. translations: 3. rotation: 3 一个质点有六个自由度(dof),在外力作用下会产生六种振型(mode)。设备基础被认为是由多个质点组成的结构，根据需要可以建立成能任意数量的质点模型，也就会产生无数种振

3、型和振型组合，每一种振型组合都有不同的振动频率。根据质量参与程度（mass participation）的不同，通常把参与度最高的几种振型对应的频率作为基础的主频率。只有主频率位于机器自频20%之外，才能有效避免“共振”的产生。solid block base rests in the ground 动力设备主要是指turbine、steam generator、pump等由于机器转子围绕传动轴偏心转动产生不平衡力(unbalanced load，也称“扰力”)的设备，设备自有频率(natural frequency)和扰力大小的不同，对承载设备的基础危害程度也不相同。结构计算的主要目的就是通

4、过分析防止设备“共振”和偏心扰力对基础的破坏。 动力设备主要由发电机、蒸气机、变速箱、耗能 压缩机、发电机、涡轮机等部分组成，相对于传动轴，不同部分有不同的频率，频率大小从100hz-8000hz不等，一般来讲，频率小于3000hz的被称作低频设备，大于3000hz的被称为高频设备。低频设备由于频率接近于承载设备的基础固有频率，容易产生“共振”，因此破坏极大。 扰力的大小不是一成不变的，它是按照简谐波的运动方程f= fo * sin (wt + a)做简谐运动，其中fo是机器最大扰力，w是机器圆频率，a是相位角。在扰力简谐波作用下，设备基础会在运动简谐波波峰处产生最大扰力。一般设备机组有至少一

5、台设备存在简谐扰力，通常为两台或三台。因此，动力分析时还需要考虑不同机组间的扰力简谐波干涉。 damping阻尼是机器振动过程中必须考虑的因素。machine、foundation、soil都存在阻尼，阻尼越大，振动对设备基础的影响越小。动力分析时，必须将三部分阻尼同时考虑。 一般情况下动力设备基础必须与其它周边的建/构筑物分开，并采取必要的隔振措施。the concept of primary and secondary unbalance force of reciprocating machine 动力设备基础主要分为三种类型：基础类型基础特点示例块式基础（block-type）主要是指

6、小型设备的基础，如泵基础。，承载的设备扰力不大，只需按照构造要求保证基础与设备的质量比，不需要动力分析。板式基础（mat slab）指大型动力设备的基础，如发电机基础等。此类基础外形为超大厚板，直接作用于地基或桩上。由于基础本身刚度大， 构架式基础（elevated frame / table top）由顶板、柱（墙）、底板组成。按工艺要求，某些压缩机蒸汽需冷凝，这就要求支撑压缩机的顶板与基础底板间有一定的空间。由于构架式基础自身刚度较小，不适于承载低频动力设备。1. initial sizing基本外形尺寸的确定 详细请见：aci351.3r -04(foundation for dynam

7、ic equipment). page 27动力基础基本外形尺寸的确定可参考design of structure and foundation for vibrating machines第三章trial sizing of a block foundation & trial sizing of a elevated foundation部分设备基础的型心与设备型心必须一致5%，避免扭转基础外形尺寸定义完成后，需通过计算验算基础与设备的质量比，如果比值小于3，则需要重新调整尺寸。同时，还需要通过简单计算，初步验算基础的倾覆和滑移系数，保证基础尺寸足够应对倾覆和滑移。2. geotechni

8、cal data土壤参数模拟及设计要求土壤动力参数和材料弹性刚度土壤在动力荷载作用下的参数计算与静力荷载作用的参数计算有所不同，应参照设计规定进行计算。动力荷载作用下，设备基础的材料弹性刚度提高1.1倍：ed = 1.1*es（aci351.3r-04 page 45） 2.1 确定给定频率下的土壤动弹簧参数，及阻尼。（使用dyna 或手工计算）阻尼damping modeling阻尼是自由振动过程中能量衰减的原因。动力分析过程中，需要考虑土壤、动力基础和设备自身的阻尼对简谐振动的影响，阻尼值采用临界阻尼值。staad/pro计算时，应使用“复合阻尼”（set sdamp）命令考虑上述三种阻尼

9、对振型的共同影响。土壤阻尼赋值命令：spring damping；设备基础阻尼赋值通过定义设备基础块体材料参数完成：define material / cdamp设备本身阻尼赋值通过定义刚性杆材料参数完成。damping is a phenomenon of energy dissipation that opposes free vibration of a system. damping is expressed in terms of % of critical damping. critical damping is the amount of damping that would c

10、ompletely eliminate free vibration. structural damping ratio: the concrete members are assigned a 2% critical damping value for both material and structures. machine damping: per asce suggestion, use 10% damping ratio for machine damping. composite damping: damping is specified by using composite mo

11、dal damping. composite modal damping permits computing the damping of a mode from the different damping ratios for different materials (machine, concrete, soil). modes that deform mostly the concrete would have concrete damping ratio, whereas modes that mostly deform the soil, would have the soil da

12、mping ratio.the sample of staad input for composite damping: 土壤抗压、抗剪刚度应根据地质报告提供的剪切刚度进行计算，具体计算方法可参考design of structure and foundation for vibrating machines第四章table 4-1。 2.2 确定土壤静弹簧参数(手工计算excel template)3. create staad model模型建立model block with cube element model mat with thick plate elementuse rigid

13、 link at all cube to mat for machine shaft alignment, stability and soil pressureuse rigid links only at periphery nodes of the structural block for reinforced concrete design 软件分析模型有两个：块单元(solid)模型和板单元(shell/plate)模型块单元模型：主要用于基础的刚度验算和动力分析板单元模型：地面以下底板部分采用板单元模型，地面以上部分仍然采用块单元，用于底板配筋计算和地面以上块体的配筋计算 设备质心

14、与基础的连接可通过刚性杆（刚性杆的刚度可以通过提高i值解决，单位设为米或者英尺），刚性杆为无质量杆件，模型中仅用于传递荷载。 块单元模型只接受点荷载，作用点上的弯矩需要转换成等效力偶。 不管建立何种模型，在有限元划分时，要考虑荷载作用点位置、结构高度、外形尺寸、梁柱尺寸、开洞位置、以及桩位（如果需要）的变化，必要时可通过细分有限元，考虑可变因素，避免模型返工。 无论是板单元还是块单元，模型单元的建立应尽可能的按照一定规律，建立统一的节点编号和杆件编号体系，这样有助于模型分析，减少工作量。 非桩基基础底板按照板单元分析时，可以使用plate mat direct all subgrade命令，将

15、抗压、抗剪刚度赋于各个板单元；按照块单元分析时，需要使用joint list plate mat y sub 1 print计算每个底板节点的土壤影响面积，然后将总抗压、抗剪刚度分配给各个节点。4.1荷载a=accident loadd=dead load基础自重主要是指设备基础材料重量以及操作平台、管架、维护结构自重等 e=seismic load地震荷载计算应考虑两个水平方向(纵向和横向)地震力，如果结构不规则，还需要考虑两个水平方向地震力的共同作用，即30%另一方向地震荷载与本方向地震荷载的组合,地坪以下的基础地板部分不参与地震荷载计算抗倾覆验算时需要考虑竖向地震力对基础的倾覆作用, 竖

16、向地震力可以按照0.2g计算得出gsc=generator short circuith=earth pressure loadsl=live load活荷载压缩机基础的活荷载主要是指操作荷载，一般根据设计经验确定动力设备的检修主要是对转动部分进行清洗维护。转动部分的质量很大，检修时多把该部分直接置于基础操作平台上，因此，操作平台的计算尤为重要，必要时还需划定设备放置区域。对基础的影响。如果维护结构直接置于设备基础上，则需要考虑该部分荷载，在活荷载组合中予以考虑。lr=live roof load acting on enclosure buildingna=turbine normal op

17、erational axial load ntg=generator normal operational torque load 扭转力ntt=turbine normal operational torque load 扭转力由于设备运动属于圆心运动，温度应力、扭转应力和紧急停车荷载必须考虑相反方向的共同作用，水平荷载还需考虑由于设备高质心产生的支座上下支撑荷载（up-and-down force）r=rain load (asce 7)s=snow loadt =loads due to structural effects and self-straining forces (i.e.

18、, creep, shrinkage, thermal) 温度应力tg=generator thermal friction loads.tlob=turbine loss of blade 叶片破损荷载tsc=turbine short circuit 紧急停车荷载（短路荷载/）tt=turbine thermal friction loads.w=wind load由于动力设备的重要性，此类设备一般都置于厂房或维护结构内，一般不考虑风荷载m=maintenance loads.4.2荷载组合loading conditionsnormal operating condition正常操作 u

19、 = d + l + op normal operating + seismic condition u = d + l + op + enormal operating + wind condition u = d + l + op + wabnormal operating condition非正常操作 u = d + l + a (turbine) u = d + l + a (generator) maintenance condition u = d + l + m service level load combinationsnormal operation load combin

20、ations: d d + l d + l + openvironmental load combinations wind: d + l + op w d wenvironmental load combinations seismic: d + l + op sh/1.4 0.9d sh/1.4accident load combinations: d + l + a alignment deflection load combinations op ( for normal operating live load condition) d ( for dead load conditio

21、n) a ( for emergency operating load condition, such as short circuit, loss of blade) strength level reinforced concrete load combinationsnormal operation load combinations: 1.4d 1.4d + 1.7l 1.4d + 1.7l + 1.7openvironmental load combinations wind: 1.2d + 1.6l + 1.6op 0.8w 1.2d + 1.0l + 1.0op 1.0w 0.7

22、5(1.4d + 1.7l 1.7w) 0.9d 1.3wenvironmental load combinations seismic: 1.2d + 1.0l + 1.0op sh sv 1.05d + 1.275l + 1.275op sh sv 0.9d shaccident load combinations: d + l + a seismic orthogonal effectsbased on cbc 2001 section 1633.1, the seismic orthogonal effects were considered by using 100% of desi

23、gn seismic force in one direction plus 30% of the design seismic forces in the perpendicular direction. the combination requiring the greater component strength was used for design. sh = shx sh = shz sh = shx + 0.3shz sh = shz + 0.3shx5. 动力计算分析动力计算时，设备质量仅考虑自重（不包括其它非刚性连接质点的重量，如物料重），设备质点位于设备传动轴轴线上（质心、

24、传动轴的位置需参考设备图纸），传动轴通过刚性杆与设备基础连接。基础底板分析时，一般情况下不允许出现拉力。仅在非正常操作工况（service level）情况下，可以出现局部拉力，且最大拉力值不允许超过该工况下各单元地基反力平均值的2%，最大压力需小于1.33最大承载力。在非地震工况荷载组合下，最大沉降不得超过设计承载力对应的沉降值。dynamic loadingharmonic loads forcing functionthe dynamic load for normal operating conditions is to be applied to the staad_pro in t

25、ime history type dynamic load.the general equation for the harmonic loading, fo (t), due to a rotating eccentric mass is given by the following equation:fo (t) = (m*e*w2 * sf/12) *sin(wt+a) lbf = fo * sin(wt+a) where:m = rotating mass, lbme = eccentricity of mass, inw = circular operating frequency

26、of machine, rad/sect = time, seconda = phase angle, radsf = 2, service factorfo = dynamic force amplitude (zero-to-peak), lbf . also is the max rotating unbalance forces. unbalanced force applied in staad modelsturbine rated speed max operable rotating unbalance forces at rated speed at cg point 360

27、0rpm 12.168 kips t1 = generator 3600rpm 11.712 kips t2 = turbineload case 1: z direction (horizontally perpendicular to machine shaft line)bearingxyzxyzt10.00.01.00.00.00.0t20.00.01.00.00.00.0load case 2: y direction (vertically perpendicular to machine shaft line)bearingxyzxyzt10.01.00.00.00.00.0t2

28、0.01.00.00.00.00.0load case 3: yz direction (diagonally perpendicular to machine shaft line)bearingxyzxyzt10.00.7070.7070.00.00.0t20.00.7070.7070.00.00.0 dynamic forces applied in-phase and out-phasein-phasefor bearing locations t1 & t2, in-phase unbalanced load orientation (phase angle) will be use

29、d for the dynamic analysis: t1: 0 degrees generator rotort2: 0 degrees turbine rotorout of phase for bearing locations t1 & t2, the following out of phase unbalanced load orientations (phase angles) will be used for the dynamic analysis: t1: 0 degrees generator rotort2: 90 ,180,270 degrees turbine r

30、otort1: 90, 180,270 degrees generator rotort2: 0 degrees turbine rotorstaad y-y direction t1 & t2 staad z-z direction t1 & t2 staad y-z direction t1 & t2 * ex. 90 deg phase angle = 1/4 cycle, so 0.25 cycle / 60.0 cps = 0.004167 sec0 0.004167analysis of foundation dynamic response by using staad time

31、 history (harmonic)harmonic response analysis the harmonic analysis is carried out by mode superposition method. staad is equipped with a facility to perform a response history analysis on a structure subjected to time varying forcing function loads at the joints and/or a ground motion at its base.

32、this analysis is performed using the modal superposition method. the mode superposition methodin the mode superposition method, step 1: a natural frequency analysis is performed firststep 2: the forced response analysis is then carried out on a mode-by-mode basis.transient response & steady state re

33、sponseharmonic response analysis was used to determine the steady-state response of a linear structure to loads that vary sinusoidally (harmonically) with time. the idea is to calculate the structures response at several driving frequencies and obtain a graph of some response quantity (such as displ

34、acement, velocity, acceleration) versus frequency. peak responses are then identified on the graph reviewed at those peak frequencies.the following figure shows typical harmonic response system -transient and steady-state dynamic response of a structural system . since there is no direct method in s

35、taad to separate the transient response from the steady state response, the way to achieve steady state dynamic response results from staad is to inspect the plot of time history (give longer time) of displacements (by giving a longer time) and then come to a conclusion based on that.5.1 foundation

36、natural frequencies自频验算自频验算的内容 一个动力设备基础，理论上有无数个振型，每个振型都对应一个频率，动力分析只关注质量参与最多（参与度大于5）的振型对应的频率。 staad/pro进行模型分析时，参与计算的振型数量不宜过多，否则影响计算速度，一般情况下保证x/y/z三个方向总质量参与度分别达到99即可满足需要，对于块式基础，选用前30个振型；对于构架式基础，选用前300个振型。动力基础振型、频率及其质量参与百分比 产生振动的设备至少有一个，一般来说，必须保证设备基础主频率在所有设备自频20%范围之外，才能避免“共振”的发生。 有些动力设备厂家要求，除需考虑正常操作情况下

37、的设备振动以外，还需要考虑设备冷启动过程和紧急停车时产生的振动，其中设备冷启动条件下频率和扰力都很低，可根据设备厂商提供的资料进行计算。 staad/pro计算分析时，一般采用时程分析法（time history load）输入简谐波，按照设备频率的不同输入不同类型的简谐波。不同简谐波之间存在着位相（phase）差：位相差为0时，称作同相位（in-phase），此时两个简谐波的初始相位角都为0；位相差大于0时，称作异相位（out of phase），此时两个简谐波的初始相位角分别按照0/90、0/180、0/270、90/0、180/0、270/0计算，分析时需要分别建模。 时程分析法定义的荷

38、载通过时间荷载（time load）施加于设备质点，分别作用y/z方向(y=z=1)以及45o斜向（y=z=0.707）。5.2 machine shaft alignment动力设备基础控制点位移验算要求 验算控制点间位移差，主要是指两个或三个控制点之间的相对位移，计算时应采用空间解析几何公式进行计算（具体计算方法参考计算模板）。5.3 staad harmonic analysis results for dynamic criteria (forced vibration 60hz) 节点位移、速度、加速度验算。动力荷载作用下，设备基础表面节点位移、速度、加速度的控制验算是评判基础设计是

39、否合理的关键因素，一些国家和主要动力设备生产厂家都对节点位移、速度、加速度的控制有严格的要求，以确保操作运转时的舒适感。 虽然前面的动力分析中已经保证了结构主频率位于设备自频20%范围之外，但设备基础表面最大节点位移、速度、加速度仍然出现在与设备自频相同的频率下对应的振型。staad/pro的缺省位移、速度、加速度图形出现在时间域（time domain），需要转换成频率域（frequency domain）才能得到最大值。the forced responses of machine-foundation-soil systemthe following displacement plots

40、 by staad post-processing show the evidence of steady state response of concrete of the foundation: the sample of steady-state response checks: convert time domain to frequency domain (fft method)often, a signal is not a simple sine or cosine wave, it looks more like the sum wave in figure below. ho

41、wever, fouriers theorem states that any waveform in the time domain (that is, one that you can see on an oscilloscope) can be represented by the weighted sum of sine and cosines. the sum waveform below is actually composed of individual sine and cosine waves of varying frequency. the same sum wavefo

42、rm appears in the frequency domain as amplitude and phase values at each component frequency (that is, f0, 2f0, 3f0).frequency domainvibration exists in time, and it is said to be in the time domain. the representation of a vibration signal in the time domain is a wave form, and this is what one wou

43、ld see if the signal were displayed on an oscilloscope. if the waveform is subjected to a spectrum analysis, the result is a plot of frequency vs. amplitude, called a spectrum, and the spectrum is in the frequency domain. the waveform is said to be transformed from the time domain to the frequency domain. most detailed analysis of machinery vibration data is done in the frequency domain, but certain information is more eas