高应变PDA试验正确的使用方法.ppt

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1、1975,1982,1992,1965,1997,PDA 试验,正确的方法,2008,新型测试设备很容易运送到现场,传统的“PAK”,PDA 试验现已被广泛采用,PAX:-有线；-无线-遥测,第一要注意安全,避开吊架,特别是当吊车移动、提升桩或打桩时。,导架,很幸运、没人受伤,用“CASE法”需在桩顶附近同一位置测力(F)和 速度(V),PDA 试验,PDA 试验,轻的应变和加速度传感器便于运输、适用于不同类型和尺寸的桩,由测得的应变()可用下式算力 F F(t)=E A(t)由测得的加速度(a)可用下式算速度 V V(t)=a(t)dt,PDA试验,在按到桩上前、应测试所有传感器 检查应变传

2、感器的零状态值（OFFSET）当传感器连到PDA(PAKS,PAX)时、轻敲触发传感器，检查其响应 可用提供的标定试验（CAL TEST，“CT”）来检查（PE）,VMX 4.06 m/s for A1 cal of 834 gs/V(PE)MEX 737 for F1 cal of 147.5/V 标定试验亦可检查 PDA 是否工作,PDA 试验-数据采集,PDA 试验-数据采集,考虑到由偏心锤击而引起的弯矩、至少需两个应变传感器 轴对称安装 如考虑两个方向上的弯矩、需 4 个应变传感器,PDA 试验-数据采集,PDA 试验-数据采集,应用高质量的传感器 应变传感器 小心保护 零状态读数“o

3、ffset”为什么重要?*,PDA 试验-数据采集:PAK,PDA 试验-数据采集:PAK,如初始值偏向正向、其正向范围被减小，大信号就有被切掉的可能,PAX的初始状态检查不同,A/D has a range-a,a voltIf a strain gage has an offset,i.e.,prestressed,a balance volt is added to bring the output of strain gage near zero,so extra force can have full range,Straingage,Balance volt,A/D,Close t

4、o zero volt,Strain Gage Balance,PAX的初始状态检查不同,PDA 试验-数据采集,应用高质量传感器(并保管好)应变传感器 应小心保护,PDA 试验-数据采集,PE 加速度传感器 一般来说比较结实 适用于一般情况(混凝土桩或钢桩)PR加速度传感器 适用于钢对钢锤击(亦可用于混凝土桩)*,PDA 试验-数据采集,传感器安装在桩顶附近,支持电缆重量,Back in notes,选定传感器安装位置 初打时 桩顶附近(离桩顶 2 倍直径),PDA 试验-数据采集,避开裂缝 避开非均匀处(如结合部,焊接处或截面变化处。这些地方下面一个 直径距离以上为好)保证在桩打完时、传感

5、器仍在地面和水上 应保证联接部分在水上 复打 地面上任何方便位置(避开裂缝。)灌混凝土的钢管桩(需要开窗口?)*,避开焊接处,带护筒的钻孔桩灌混凝土的钢管桩工字梁贯穿整个水泥浆/混凝土桩,沿长度均质的复合材料桩,混凝土:Ac,c,钢:As,s,沿长度均质的复合材料桩,平均比重=(Ac c+As s)/(Ac+As)平均弹莫 EM=(Ac Ec+As Es)/(Ac+As)估计波速 WS=EM/(如试验能确定 WS、用其),例:灌混凝土的钢管桩,测试灌混凝土钢管桩,假设:混凝土和钢管的应变相同,Important,必须满足,常常选择灌混凝土后进行测试的原因是：当复打时、由于恢复而拒打，更高的阻抗

6、能帮助激发更多的承载力。,混凝土和钢管的应变相同,如钢的成份少、应用窗口将传感器直接按到混凝土上如钢的成份高、可将传感器直接按到钢管上,非常重要,用木垫来保护桩顶,窗口会产生应力集中,测试灌混凝土钢管桩,Concrete filled casing,Calculate relative EA of steel versus concrete,F=ma,Force Transducer,Use 4 strains,Poor top preparation,Did not use template for drilling holes surface not“flat”,Poor attachme

7、nt leads to questionable data(damage sensor?),Sensors not 180O opposite,would not cancel bending,42 inch nom.shaft,25%increase AR,Sensors just below transition NOT ideal;strain not fully engaged,proportionality lost,沿长度非均质的复合材料桩,用钢送桩来打混凝土桩 混凝土桩、工字梁在桩底 混凝土桩、工字梁在桩顶.用非均质护筒的钻孔桩护筒壁厚变化护筒和桩不一样长,沿长度非均质的复合材料

8、桩,可按在钢上,E 和 A 已知，所以力可测得应避开端部和截面变化处、以避免应力集中。至少在混凝土一米以上 采集数据时、应用钢的材料参数(许多PDA算出的参数是错的)要得到正确得答案、需用 CAPWAP 来模拟非均匀性,安这里?,PDA-W,PDA 试验标定试验,CT,供电噪音,可用汽车电瓶来避免,PDA 试验 数据采集,V1 reduced by cosine of angle from axial,PDA 试验 数据采集,PDA 试验 数据采集,PDA 试验 数据采集,PDA 试验 数据采集,平均力满足比例、合理;显然 2 应变传感器能补尝弯矩,由于偏心锤击而引起的弯矩,PDA 试验 数据

9、采集,需多少传感器?至少 2 应变传感器 轴对称分布 需 4 个来克服 2 个方向的弯矩,对钻孔桩、建议用 4 个(F1 和 F2 相对,F3 和 F4 相对)对螺旋焊接的钢管桩、建议用 4 个 在关键试验中、建议用 4 个以防万一 至少 1 个加速度传感器 好的数据、速度基本上一样 建议用 2 个以防万一*,Back in notes,PDA 试验 数据采集,即使大的弯矩、两个速度仍然一致,PDA testingdata acquisition,Pile properties(at sensor location)Area“Diameter”(sensor location and circ

10、umference)Length below sensors Material properties Density SP Modulus EM Wavespeed WS EM=c2=(SP/g)WS2(watch dimensions!)Embedment(LP)for CAPWAP Uniform?*,Important,PDA testingdata quality,Typical Values for pile materials,EnglishSImetric,PDA testingdata quality,SI Example:Calculate WS from EM and SP

11、EM=35,000 MPaSP=24 kN/m3EM=c 2=(SP/g)x WS2WS=SQRT(EM x g/SP)WS=SQRT(35,000 x 9.8 x 1000/24)=3,780 m/s(MN/m2)x(m/s2)x(kN/MN)/(kN/m3)=(m/s),如何确定波速?,升起到升起 峰到峰,升起,峰,How to find WS?,Rise to rise Peak to peak,Use“proportionality”to get WS for long piles with no shaft resistanceChange WS by ratio of ZxVT1/

12、FT1Look at example,How to find WS?,?,?,Problems:High friction-early unloading No well defined reflection,VT1 x Z=6.62 x 141.6=937FT1=1014Znew=Zold x 937/1014=130.8,Solutions:Know WS from experience(other piles or from EOD)If no friction near top,use proportionality,Amount of data to collect?During d

13、riving as many blows as needed stresses,energy,capacity.as many blows as possible(PDA-W)can reduce amount of data later Restrike or Drilled shaft Save every blow Use as few blows as possible Higher bending and local stresses,PDA testingdata acquisition,Back in notes,Pile name,project name(if BOR,EOD

14、 date)Hammer description(name,weight,drop H)Capacity requirements(ultimate or design)Pile vertical or inclined Soils Visual observations about pile material(e.g.fy)Unusual occurrences Static load test results(and date)Blow counts or set per blow,PDA testingdata acquisition,问题常常由以下因素引起 传感器有问题 电缆有问题 联

15、接问题 桩有问题 错误的标定参数,PDA 试验 数据质量,PDA 试验-应变仪的标定,Accuracy to about 1 or 2%recent study says must tighten to 60 inch-poundsComparison traceable to calibrated micrometer,PDA 试验-加速度传感器的标定,Target,Ram,“Hopkinsons Bar”calibration,Two small rods suspended to minimize friction.PDI uses 75 mm OD hollow rods.The im

16、pact surface is flat for one rod and slightly rounded for other.The“Ram”is set in motion to impact the“Target”.,PDA 试验-加速度传感器的标定,X Target,Ram,“Hopkinsons Bar”calibration,Measure:unknown accCompare with:known acc known strain,PDA 试验-传感器的标定,应变仪的准确度达 2%加速度传感器准确度达 2%（NIST 震动台标定仅达 5%的精度）因此在进行CAPWAP前对标定参数

17、微调是可理解的 旧传感器应重新标定(ASTM 规定每两年标定一次)*,如何发现问题?锤击之间数据不一致 力和速度曲线比例失调 标定参数?波速?(=v/c)桩的非均匀性?传感器离地面很近?柴油锤?(precompression)长的升起时间?(软垫)结果不合理（承载力、应力、能量比等。检查材料参数）注意PDA警告信息和窗口,PDA 试验 数据质量,Important,PDA 试验 数据质量,F=F+ZV/2=WDF=F-ZV/2=WU,Important,F=F+F V=V+V ZV=ZV+ZVZV=F-F,WD 和 WU 的重要性:区分输入和反射（响应）WU 含有以下信息 土阻力及其分布 桩的

18、缺陷,PDA 试验 数据质量,PDA 试验 数据质量,F 和 V 成比例?,PDA 试验 数据质量,需看上行波,第一上升标志后平缓逐渐上升,PDA 试验 数据质量,比例?,PDA 试验 数据质量,Precompression of diesel hammer is often longer than 2L/c.Thus get reflections from toe even before T1Thus F can be larger than V prior to and at T1Look to see if waveup is smooth through impact time,PD

19、A 试验 数据质量,Proportional?,PDA 试验 数据质量,F2 应变传感器松动,PDA 试验 数据质量,如螺栓不紧、应变曲线将与 加速度曲线类似,PDA testingdata quality,PDA testingdata quality,V2 数据有问题,PDA 试验 数据质量,不是太好,PDA 试验 数据质量,PDA 试验 数据质量,得到改善,PDA 试验 数据质量,如何解决问题?换传感器 换电缆 注意正确的联接 螺栓或混凝土锚要紧 锤击偏心加速度传感器的方向,PDA 试验 数据质量,Back in notes,不根据低质量数据进行判定(垃圾进,垃圾出)检查所有输入值(LE

20、,AR.),PDA 试验-判定,错的 WS(3800 m/s)比例?,正确的 WS(3300 m/s),在分析混凝土桩时、波速和弹模是非常关键的参数,Pile type:Prestressed Spun Concrete PilePile size:OD 600mm X Thk 100mmMaterial Strength:80 MPaHammer:BSP 11t Hydraulic Hammer drop height:800mmTheoretical Max Energy=8.8 t.mEMX=10.5 t.mETR=120%Unreasonable!Proportional?,PDA 试

21、验-判定,Reduce WS 4400 3700 m/s for top sectionChange overall WC to 3920 m/s to match observed 2L/c reduce SP to 2.45EM reduced from 513 t/cm2 to 342 t/cm2What is real pile area?Theoretical Max Energy=8.8 t.mEMX=7.25 t.mETR=82%Possible!Proportional,PDA 试验-判定,PDA 试验-判定,WS 3911 m/sBN 3,WS 3911 m/sBN 2045

22、,波速变化,Use or to adjust WC,WC 3556 m/sBN 2045,WS still 3911 m/s,PDA testingdata interpretation,Free endR=0,Impact generated,Compressive wave down(+F=+Zv),Free end.Requires zero force.,Results in tension wave up(-F=+Zv),Free end:(easy driving)+F-F=zero+Zv+Zv=+2 ZvPile toe moves down and pulls pile top

23、 down at 2L/c,+F+v(down),-F+v(down),Important,Back in notes,PDA testingdata interpretation,F v,+F+v,-F+v,Free end(top or bottom)has zero stress and velocity doubles at top and bottom,FV,WD,PDA 试验-判定,+F+v,-F+v,易打,最大速度,PDA testingdata interpretation,2 L/c,4 L/c,6 L/c,8 L/c,?,What is it?,PDA testingdat

24、a interpretation,Fixed endR 2F,Impact generated,Compressive wave down(+F=+Zv),Fixed end.Zero movement.,Results in compression wave up(+F=-Zv),Fixed end:(hard driving)+F+F=+2 F+Zv-Zv=zeroPile toe does not move and pile rebounds up at 2L/c and force at toe doubles,+F+v,+F-v(up),Important,PDA testingda

25、ta interpretation,+F+v,+F-v(up),Assumed fixed top,Fixed end(top or bottom)has zero velocity and force doubles at top and bottom,WD,FV,PDA 试验-判定,+F+v,+F-v,难打,PDA testingdata interpretation,Easy driving,Hard driving,Wave down=(F+Zv)/2=“WDN”=WD Wave up=(F-Zv)/2=“WUP”=WUF=WD+WU V=(WD-WU)/Z,PDA testingda

26、ta interpretation,Impact generated,Compressive wave down(+F=+Zv),Activates resistance(R),Results in tension wave down and compression wave up each with value(R/2),R,Important,PDA testingdata interpretation,R,+F+v,“Setup”,PDA 试验-判定阻力,R,R/2,Important,PDA 试验-判定阻力,Wave up gives information on Rs distrib

27、utionhigher slope equals higher unit friction,Important,PDA testingdata interpretation,Energy transfer to check Hammer Compute EMX=FV dt Compare EMX with rated energy(e.g.Wh)Compare with experience histograms Calc.stroke of o.e.diesels=4(60/BPM)2-0.3 ft Compare with hammer monitor(prox switch)If Ene

28、rgy is low Check cushions,helmet,alignment.Check hammer maintenance Diesel preignition or ECH preadmission*,PDA testingdata interpretation,Energy=F V dt,Energy from hammer to pile,Energy from pile to hammer,E,D,PDA testingdata interpretation,Net measured efficiencies(steel piles),Efficiencies on con

29、crete piles are lower 10%,规范允许的打桩应力,USA(AASHTO)钢桩材料屈服强度的90%混凝土桩压应力:85%混凝土抗压强度 预应力拉应力(预应力混凝土):预应力+50%混凝土抗拉强度 拉应力(一般混凝土):70%钢筋的屈服强度,BN595;yielding,PDA 试验-判定,高拉应力,高拉应力,Beta guidelines,Capacity of broken piles is meaningless,Small damage,Large damage,blow,1,2,3,4,toe,top,New toepile shorter,PDA testingd

30、ata interpretation,damage,damage,Start of damage,Major damage,Pile failed at pickup point.Due to early handling,or low concrete strength,or uneven toe stress(limerock),Extraction reveals damage,1200 psi prestress 5000 psi fc driven at 7 days,BN 1,BN 263(end),Final driving was at 100 bl/ft,We suggest

31、ed extracting the open end pipe pile.,The extraction confirmed the damage.,Pipe pile,H pile with shoe driven to sloped karst limestone,Discovered only because driven out of location,so piles were extracted.Caused more PDA tests found more damaged piles,Extracted-short,Reports-ASTM D4945,Graph of dat

32、a(F&V vs.time from PDA-W or CAPWAP)Each pile(EOD and/or BOR)Summary of Results(from PDIPLOT)Graphical and/or Tabular(with Statistics)CAPWAP results(plots and tables)Descriptions Pile,Hammer,Soils,Goals of test Results of tests,Conclusions or recommendations Stresses,Integrity,Energy,Capacity Driving Criteria(if requested),Reports-ASTM D4945,Reports-ASTM D4945,Reports-ASTM D4945,“PDIPLOT”program,Reports-ASTM D4945,