The uniform pressure distribution for concentric

loading is based upon the assumption that the base

tored loads should be performed on each monolith

slab of the monolith behaves as a rigid base. To

that can be dewatered. For further information, see

compute the pressure distribution, the sum of all

ETL 1110-2-307. Drag loads will not be used to

vertical forces acting on the base of the monolith is

resist uplift (flotation) due to the varying nature of

distributed equally across the monolith bottom. An

drag loads. If insufficient capacity exists to keep the

example of this computation is given in Figure A-2.

monolith from floating, the monolith can be held

This uniform pressure is modified to account for

down with anchors, heels, or more concrete mass, or

loads eccentric to the centroid of the monolith base.

improved foundation drainage systems can be added

An example of this computation is given in Fig-

to the monolith.

ure A-3. The stepped pressure distribution is an

approximation based upon observed data from instru-

ment occurs between adjacent monoliths due to the

mented U-frame locks founded on soil. In this distri-

difference in size and weight of the monoliths as well

bution, the pressure beneath the lock wall is increased

as differing foundation conditions beneath each mon-

to a set percentage of the pressure beneath the

olith. Differential settlement should be held to the

remainder of the monolith. These two pressures are

practical minimum possible. There are several ways

modified proportionately until the total pressure

to handle this problem, including use of keys, dowels,

equals the sum of the vertical forces. Observed data

and construction sequencing. Keys can be formed

from Port Allen Lock suggest the amount of increase

between adjacent monoliths. Dowels can be added

should be 75 percent. An example of this computa-

between the base slabs of adjacent monoliths. The

tion is given in Figure A-2. This stepped base pres-

construction sequence for adjacent monoliths can be

sure is modified to account for loads eccentric to the

specified such that the heavier monolith is partially

centroid of the monolith base. An example of this

placed prior to placement of the lighter monolith.

computation is given in Figure A-3. For further

The magnitude of the forces being carried by dowels

information on the amount of increase to use, see

or keys is difficult to predict, but the designer must

Sherman (1968) and (1972).

try to account for these forces by some rational

method.

location analysis using unfactored loads should be

performed on each two-dimensional and three-

dimensional monolith. The analysis consists of deter-

mining the location of the resultant of all loading in

Once the design criteria have been established, all

relation to the kern of the monolith base. The resul-

reasonable load cases have been identified, and the

tant location for usual load cases should be the mid-

initial foundation parameters have been established,

dle third of the base. The resultant location for the

the analysis of the structure may be performed. The

unusual load cases should be the middle half of the

structural analysis is necessary for ensuring that the

base. The resultant location for the extreme cases

wall and slab thicknesses are sufficient and for deter-

should be within the base. Usually the location of

mining the reinforcement requirements of the struc-

the resultant is not a problem.

ture. Before performing an analysis of a U-frame

lock, the designer must decide whether each monolith

behaves in a two-dimensional or a three-dimensional

manner. The method of analysis must also be

unfactored loads should be performed in accordance

selected, which can be a frame analysis, a finite

with ETL 1110-2-256. The CASE computer program

element analysis, hand calculations, or a combination

CSLIDE can perform this analysis (Pace 1987).

of these. These decisions are based on experience

and good engineering judgment. A parametric study

which bounds the extremes of behavior of a structure

sis should be performed using unfactored loads. The

can also be used as a tool to ensure adequacy of a

foundation capacity should be developed taking into

structure. As a result of these analyses, the designer

account such items as soil type and stratification.

can then determine final member sizes and

The computed bearing pressures must be less than the

reinforcement.

foundation capacity.

A-12

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