Unusual soil deposits can form, such as varved silts or varved clays Marine deposit Soil deposited in the ocean, often from rivers that empty into the ocean Granular shore deposits but offshore areas can contain soft clay deposits Colluvial deposit Soil transported and deposited by gravity, such as talus, hill-wash, or landslide deposits Can be geologically unstable deposit Pyroclastic deposit Material ejected from volcanoes. Examples include ash, lapilli, and bombs Weathering can result in plastic clay. Ash can be susceptible to erosion. NOTE: The first four soil deposits are man-made, all others are due to geologic processes.  c   tan  (6.9) n where  shear strength of the soil c  effective cohesion  n effective normal stress on the shear surface   effective friction angle The mechanisms that control the shear strength of soil are complex, but in simple FIGURE 6.10 Direct shear apparatus. terms the shear strength of soils can be divided into two broad categories: granular (nonplastic) soils and cohesive (plastic) soils. Granular Soil. These types of soil are nonplastic and include gravels, sands, and nonplastic silt such as rock flour. A granular soil develops its shear strength as a result of the frictional and interlocking resistance between the individual soil particles. Granular soils, also known as cohesionless soils, can only be held together by confining pressures and will fall apart when the confining pressure is released (i.e., c  0). The drained shear strength (effective stress analysis) is of most importance for granular soils. The shear strength of granular soils is often measured in the direct shear apparatus, where a soil specimen is subjected to a constant

The unit-price technique is frequently used for preparation of cost estimates. It can be used for any level of estimate but does require that some design be performed. Data for the technique are obtained from commercially available handbooks of unit prices, which are usually updated at least once a year. The industry approach to development of preliminary or higher-level cost estimates for a warehouse using the unit-price technique usually proceeds as follows: The warehouse is divided into categories, for example, loading dock, storage facilities, aisles, restrooms, and offices. The special equipment required, such as cranes, crane rails, and docks, is listed. Then, the estimator looks up in a unit-price book the cost of each of the items specified above. For each category, the unitprice book gives the total cost of materials, labor, and equipment to construct an item. For instance, for a loading dock, the unit price would be specified as either the cost per linear foot or the cost per truck accommodated by the dock; for rest rooms, the unit price would be specified as the total cost of all the fixtures needed or as the total cost per square foot. Finally, the estimator sums the preceding costs to arrive at the total cost of the warehouse. The discipline approach to development of a preliminary or higher-level cost estimate for a warehouse using the unit-price technique typically proceeds as follows: From the design documents, the estimator determines the ground area the building occupies (the footprint of the building). The costs of grading and the building floor slab are obtained from a unit-price handbook. With information from the contract documents, the estimator calculates the amount and cost of the structural materials and finishes needed. The unit cost of illumination and air-conditioning are also obtained from a unit-price handbook. Finally, the estimator adds the preceding costs to arrive at the total costs. Crew Development Technique. This is used to prepare the estimate based on the costs for the specific personnel and equipment that would be needed to complete each item during each phase of construction. The crew development technique differs from the unit-price technique, where the activity is priced without assignment of specific workers and equipment. For a specific project, the size and mix of crew selected depend on project needs. If early completion is the key consideration, a large crew working multiple shifts and much overtime might be advisable. If access to a site is difficult, a small crew might be necessary. Size and mix of crew can also vary during the course of construction. For example, for a typical high-rise structure, construction may start with personnel and equipment that provides the lowest cost per unit of production. As work progresses and access to work areas grows more difficult, a smaller crew using more equipment may be used. In the final construction stages, when the investment in the building is large and interest costs are high, the contractor may employ a large crew working shifts and overtime to finish as soon as possible, thereby minimizing total project costs. Estimators tend to use the crew development technique for high-level estimates, the definitive and above. Unlike the unit-price technique, the crew development technique is based on the way the facility actually will be erected. Consequently, it is the most accurate of the estimating techniques. Hence, it is the principal technique for fixed-price estimates; where accuracy is critical. The crew development technique is based on data from production handbooks. These may be organized in accordance with the use of a facility or by building


20 1   (9.8) b For example, suppose a 20-ft interior span of a continuous slab with equal spans is made of concrete with a strength of 4 ksi and reinforced with bars having a
c yield strength y of 60 ksi. Factored dead and live loads are both 0.100 ksf. The factored moments are determined as follows: Maximum negative factored moments occur at the supports of the interior span when this span adjacent spans carry both dead and live loads. Call this loading Case 1. For Case 1 then, maximum negative factored moment equals M
(0.100  0.100)(20)2 /11
7.27 ft-kips / ft u The corresponding positive factored moment at midspan is 2.73 ft-kips / ft. Maximum positive factored moment in the interior span occurs when it carries full load but adjacent spans support only dead loads. Call this loading Case 2. For FIGURE 9.11 Factored bending moments in an interior 20-ft span of a continuous oneway slab: (a) factored moments for Case 1 (this and adjacent spans fully loaded) and Case II (this span fully loaded but adjacent spans with only dead load); (b) Case I factored moments after redistribution. Case 2, then, the negative factored moment is (10.00  5.00)
5.00 ft-kips / ft, and the maximum positive factored moment is 5.00 ft-kips / ft. Figure 9.11a shows the maximum factored moments. For the concrete and reinforcement properties given, the balanced-reinforcement ratio computed from Eq. (9.27) is b
0.0285. Assume now that reinforcement ratios for the top reinforcement and bottom reinforcement are 0.00267 and 0.002, respectively. If alternate bottom bars extend into the supports, 

0.001. Substitution in Eq. (9.8) gives for the redistribution percentage The negative factored moment (Case 1) therefore can be decreased to Mu
7.27(1  0.188)
5.90 ft-kips / ft. The corresponding positive factored moment at midspan is 10  5.90
4.10 kips / ft (Fig. 9.11b). For Case 2 loading, if the negative factored moment is increased 18.8%, it becomes 5.94  5.90 ft-kips / ft. Therefore, the slab should be designed for the factored moments shown in Fig. 9.11b. For two-way slab systems, the ACI 318 Building Code permits a three-dimensional (space-frame) analysis in which the equivalent frame combines the flexibility (reciprocal of stiffness) of the real column and the torsional flexibility of the slabs or beams attached to the column at right angles to the direction of the bending moment under consideration. This method, applicable for all ratios of successive spans and of dead to live load, is an elastic (exact) analysis called the equivalent