Ram weight – Drop height

500 kN´s påle

The capacity of the pile is both a geotechnical and a structural issue

Lastkapacitet En slagen påle kan betraktas som en av jorden sidostöttad pelare. Lastkapaciteten beror av: Initialkrokighet Jordens hållfasthet Antalet slag för att slå pålen Tabellvärden finns i Pålkommissionens rapporter samt i typgodkännanden.

Geotechnical Capacity The geotechnical capacity of a driven pile is the ability of the surrounding soil and/or the rock to withstand loads without harmful movements.

Geotechnical capacity The rule of thumb in Sweden for driven piles to set less than 10mm/10bl Concrete piles: 1 kN per cm 2 Steel piles: 13 kN per cm 2

Geotechnical capacity Often much higher capacities is used, for concrete piles up to 1,6kN/cm 2 and steel piles 22kN/cm 2. This require that the pile is driven to solid rock in order to verify capacity. To verify capacity 5% to 25% of the piles are normally tested.

Geoteknisk bärförmåga För stålpålar testas 10 % av pålarna om pållasten är max cirka 17 kN per cm 2 (under förutsättning att erforderlig bärförmåga kan verifieras). För laster mellan 17 och 22 kN per cm 2 testas 25 % av pålarna.

Nedåtgående våg F= Zv Z=EA/c Z=EA/c Tryckvåg Kraft + Partikelhastighet + Dragvåg Kraft - Partikelhastighet -

FdLFdx F dL F dL EA EA F dL F dL EA EA v = dx = F dL = F c dt EA dt E A dt EA dt E A v = dx = F dL = F c dt EA dt E A dt EA dt E APartikelhastighetVåghastighet dx =

Ram weight One condition in order to install the pile to the desired capacity is to have sufficient ram weight. A rule of thumb in Sweden is that for micro piles it is recommended that the piston in hydraulic hammers has a weight at least 2 times the pile weight per meter.

Ram weight – Drop height In order to mobilize available capacity the pile final set for the test blow has to be a few millimeters. This require both drop height and ram weight. Rule of thumb: Drop height 7-8 % of the length of the pile Ram weight 1-1,5 % of desired capacity

Ram weight- Drop height The relationship between impact velocity and drop height Kinetic Energy = Potential Energy mv 2 /2 = mgH H = v 2 /2g or v = √2gH To drop one kg on the toe from one meter is equally painful as dropping 10kg from the same height. Only the the 10kg hurts for a longer time ;-)

Drop height Example 1: Calculation of Z (EA/c) steel pipe pile 140mm x 8mm A (Area): 33 cm 2 (0,0033 m 2 ) E (Elasticitetsmodul): MPa c (wavespeed): 5120 m/s Z=210000*10 6 *0,0033/5120= Ns/m= 135 kNs/m

Ram weight-Drop height If a pile is struck by a impact velocity of 3 m/s, the force in the pile will be: F = v*Z = 3*135 = 405 kN To achieve this partical velocity (force) the drop height has to be: H = v 2 /2g = 3 2 /2*10 = 0,45 m Due to loss of energy in the cap, cushioning and so forth the drop height has to be higher

Ram weight –Drop height If the pile is struck by an impact velocity of 6 m/s the force in the pile will be: F = 6*135 = 810 kN To achieve this partical velocity (force) the drop height has to be: H = v 2 /2g = 6 2 /2*10 = 1,8 m Due to loss of energy in the cap, cushioning and so forth the drop height has to be higher

Ram weight-Drop height Piles driven to solid bed rock the downward traveling compression wave is superimposed which results in higher stresses than that induced by the hammer (specially on short piles)

Ram weight – Drop height The stresses in micro piles are commonly very close to the yeild stress for the test blow. Important that the pile is cut correct prior to test and that the hammer is lined up correctly.

Ram weight – Drop height Example 2: Calculation of Z (EA/c) for a concrete pile (side=235mm) A (Area): 552 cm 2 (0,0552 m 2 ) E (Elastic modulus): MPa c (Wave speed): 3900 m/s Z=40000*10 6 *0,0552/3900= Ns/m= 566 kNs/m

Ram weight – Drop height If the pile is struck by an impact velocity of 3 m/s the force in the pile will be: F=3*566=1698 kN To achieve this partical velocity (force) the drop height has to be: H=v 2 /2g = 3 2 /2*10 = 0,45 m Due to loss of energy in the cap, cushioning and so forth the drop height has to be higher

Ram weight – Drop height If the pile is struck with a drop height of 1,2m the partical velocity will be: V= √2gH = √2*10*1,2 = 4,9 m/s The force in the pile will than be (energy losses are neglected): F=4,9*566=2773 kN, which is equal to a stress of 2,773/0,0552 = 50 MPa. The pile will only withstand a few of these blows!

Ram weight – Drop height Warning! Modern machinery are often equiped with accelerating hammers. These hammers can quite easily over stress the pile.

Datorsimulering En förfinad beräkning av erforderlig hejarvikt och fallhöjd kan utföras med hjälp av datorprogrammet WEAP (Wave Equation Analysis Program).

Dragbärförmåga För brostöd och vindkraftverk (och även andra byggnadsverk) kan dragkraft uppträda i pålarna i vissa lastfall. Riktlinjer för beräkning av en påles dragkraft finns i BRO 2004 eller i den nya Eurokoden. Alternativt kan datorprogrammet CAPWAP användas. Om en dragkrafts-beräkning skall baseras på CAPWAP är det nödvändigt att pålarna får ”växa fast” några dagar innan mätning utföres.

CAPWAP CAPWAP (Case Pile Wave Analysis Program) är ett datorprogram som utifrån uppmätta signaler beräknar pålens spets- och mantel- bärförmåga. Dessutom erhålles last-deformations- sambandet för pålen i jorden (motsvarar en simulerad provbelastning).

Provbelastning Dynamisk provbelastning (stötvågsmätning) används i cirka 90 länder. Statisk provbelastning (den traditionella metoden för att verifiera pålars bärförmåga) används fortfarande runt om i världen.

Kuriosa Vissa typer av byggnadskonstruktioner kan få detaljerade regelverk att framstå som mindre relevanta.