Axial Capacity

Capacity of open-ended pipe piles (a) unplugged and (b) plugged. 

Terms used to define incremental filling ratio (IFR = Akp/AL). 

There are a number of computational techniques available to determine the axial capacity of a pile (Bea, 1975 Cox et al., 1979 Poulos, 1981b). These techniques vary from simple empirical procedures to more refined methods that look at the components of pile strength. The methods available to predict the axial capacity of offshore piles can lead to calculated capacities that vary by 25% from the mean of the predictions (Kraft et al., 1981). 

The methods to calculate the end-bearing resistance (Qp) and the skin friction (QJ depend upon whether the soil is a sand or clay. The relationship for capacity (QJ of a pile minus the weight of the pile (W) is given by Equation 10.2  

The capacity in compression for a pipe pile is based on two criteria, representing two extreme conditions (1) the pile is considered as closed-ended, or (2) the pile behaves purely open-ended. 

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Loads applied to panels on the short wall will be resisted by the three end columns. The roof panels will act as a diaphragm to distribute the loads but they must also resist vertical blast loads in bending which reduces in-plane capacity. To avoid this problem, the top of the center column will be supported by a truss in the roof of the end bay. This truss will utilize the rigid frame beams as chord members with additional angles added to form the struts Braced frames in the end bay wall will provide the support reaction for the roof truss as well as the load from the corner columns. The end bay braced frame will consist of the rigid frame columns and x bracing. Since the columns must resist loads from both directions, the axial capacity in each direction is artificially reduced for the analysis. 

Equations 10.2 through 10.5 present the fundamental basis of any axial capacity determination, irrespective of the method to establish the soil parameters/and q. Several computation techniques are available to derive unit skin friction and unit end bearing either from laboratory and sampling data or from in-situ test data. The in-situ test most utilized is the cone penetration test (CPT). Details on the performance of the CPT can be found in Andresen et al. (1979) and de Ruiter (1971,1975). 

End-bearing component of an axial capacity can be determined from bearing capacity theory as given in Equation 10.8 ... 

Bea, R.G. 1975. Parameters affecting axial capacity of piles in clays. Proceedings of the 7th Annual Offshore Technology Conference. OTC, Houston, TX, pp. 611-623. 

The primary load on a drilled shaft is usually axial, either downward or uplift. Therefore, it is necessary to select a diameter and length that produce sufficient skin friction and end bearing capacities. There are several methods of determining the axial capacity of drilled shaft. The important methods are ... 

For walls with moderate to high axial stress (more than 30 % of the wall axial capacity), cracks start to initiate within the bricks themselves due to diagonal tension in the bricks exceeding the tensile strength of the bricks. These cracks are also often complemented by staggered step cracking in head and bed joints, especially with wet mortar constmction. 

Bending moment on r.c. section acting before FRP strengthening Axial capacity of FRP-confined concrete member Axial capacity of FRP-confined masomy Factored axial force... 

S.IO.I Design Axial Capacity Under Concentric and Slightly Eccentric Force of the Confined Member... 

FRP confinement can also be applied to conaete members subjected to combined bending and axial loads, so as to enhance their ductility and, only marginally, their axial capacity. 

Enhance flexural capacity or combined bending and axial capacity through the application of composites with fibers ranning in the same direction as the member axis and then in different directions as well... 

General Axial Capacity of Pile Group Settlement of a Pile Group Lateral Capacity and Deflection of a Pile Group... 

Inclined or battered piles should not be used together with vertical piles unless the inclined piles alone have enough lateral capacity. Inclined piles provide partial lateral resistance from their axial capacity and since the stiffness in the axial direction of a pile is much larger than in the perpendicular directions, inclined piles tend to attract most of the lateral seismic loading. Inclined piles will fail or reach their ultimate axial capacity before the vertical piles are activated to take substantial lateral loads. 

The axial capacity of a pile group is the combination of piles in the group, with consideration of interaction between the piles. One way to account for the interaction is to use the group efficiency factor which is expressed as... 

TABLE 9.14 Group Efficiency Factor for Axial Capacity... 

Davis, M. P., Robertson, P. K., Campanella, R. G., and Sy, A. 1988. Axial Capacity of Driven piles in Deltaic Soils Using CPT, Proceedings of the first International Symposium on Penetration Testing, ISOPT-1, Ed. J. De Ruite, March 21-24, Orlando, FL. 

Elwood K, Moehle JP (2005b) Axial capacity model for shear-damaged columns. ACI Struct J 106(S45) 578-587... 

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