S - Kam Ng PhD Dissertation Final.pdf - Digital Repository of CCEE ...

562.5.2. Hammer modelHammers can be divided into either internal or external combustion hammers. Alldiesel and vibratory hammers are internal combustion hammers, and the hydraulic and drophammers are external combustion hammers. Diesel hammers can be classified as liquidinjection, atomized injection, open end, and closed end. Hydraulic hammers can becategorized into single acting, double acting, drop, and power assisted, and their energy canbe transferred by steam, compressed air, pressurized hydraulic fluid, or simply a hoist and arope.In WEAP hammer modeling, a ram segment is usually about 900 mm (3 ft) long anda slender ram is connected with a series of ram springs. Different hammer types are modeledwith different combination of masses, springs, and/or dashpots, and the hammer assembly forthe external combustion hammer is shown in Figure 2.12. The WEAP 2005 version has adatabase of various hammer types, and modifications of hammer efficiency, pressure, andstroke values that represent the actual hammer used are allowed.2.5.3. Driving system modelThe WEAP driving system model consists of a striker plate, hammer cushion, helmet,and a pile cushion which are represented by masses and springs. The weight of each pieceshould be included in the mass. The driving system model also has a dashpot that is placedparallel with the hammer cushion spring as illustrated in Figure 2.12, and its dampingconstant can be computed using√ (2.30)where,C dhC dhik rm a= damping constant for hammer cushion, kN-s/m or kip-s/ft,= non-dimensionalized input value, default value of 1.0, dimensionless,= hammer cushion stiffness, kN/m or kip/ft, and= either the impact block mass density for diesel hammer or helmet massdensity for external combustion hammer, kN-s 2 /m or kip-s 2 /ft.