Reinforced-concrete, folded-plate construction is a versatile concept applicable to a variety of long-span roof construction. Applications using precast, simple V folded plates include segmental construction of domes and (vertically) walls (Fig. 9.60). Inverted folded plates have also been widely used for industrial storage bins. (Standard Practice for Design and Construction of Concrete Silos and Stacking Tubes for Storing Granular Materials, ACI 313, and Commentary, ACI 313R, American Concrete Institute.) Determination of stresses in folded-plate construction is described in Art. 5.15.5. Formwork for folded plates is far simpler than that for curved thin shells. Precasting has also been a simpler process to save formwork, permit mass-production construction, and achieve sharp lines for exposed top corners (vees cast upside down) to satisfy aesthetic requirements. For very long spans, posttensioned, draped tendons have been used to reduce the total depth, deflection, and reinforcing-steel requirements. The tendons may be placed in the inclined plates or, more conveniently, in small thickened edge beams. For cast-in-place, folded-plate construction, double forming can usually be avoided if the slopes are less than 35 to 40. Since larger transverse bending moments develop in folded plates than in cylindrical shells of about the same proportions, a minimum thickness less than 4 in creates practical problems of placing the reinforcing steel. A number of area in the plates will require three layers of reinforcing steel and, near the intersections of plates, top and bottom bars for transverse bending will be required. Ratios of span to total depth are similar to those for cylindrical shells, commonly ranging from 8 to 15. (See also F. S. Merritt, Standard Handbook for Civil Engineers, Sec. 8, Concrete Design and Construction, McGraw-Hill Publishing Company, New

Programmable thermostats conserve energy by automatically raising or lowering the space temperature to preprogrammed settings several times each day. Building temperature adjustment is performed during occupied or unoccupied hours, again conserving energy. Other types of thermostats are available that produce energy savings: Reduction of overshoot on recovery from the setback temperature, limiting the rate of temperature rise Selective recovery from the setback temperature by utilizing lower stages (singlestage and multistage only) Selective recovery from the setback temperature using a heat pump in lieu of an auxiliary heat source (heat-pump thermostat) Prevention of room temperature from deviating from a setpoint under varying load conditions Microprocessor-Based Systems. Computerized energy-management systems are available to control complex HVAC systems. These microprocessor-based systems are capable of saving enough energy that they can pay for themselves in 2 years or less. Energy management systems are available in many variations and with many features. The most common include the following capabilities: equipment scheduling, duty cycling of equipment, temperature compensated control, demand limiting, optimum start / stop, and night setback. Equipment Scheduling. Running HVAC equipment on a continuous basis, including periods when operation is not required, results in excessive and nonproductive energy consumption. These periods include lunch hours, evenings, weekends, and holidays. By using a scheduling program, the control panel promptly shuts down HVAC units and other units at preset times. A typical scheduling program may provide four start / stop times for each load on an 8-day cycle. It will also allow automatically for holidays, leap year, and daylight savings time. Duty Cycling. Duty cycling applied to HVAC equipment utilizes an on-off control to reduce operating time and increase energy savings. The duty-cycling program will permit up to eight cycle patterns for each load. On-off protection timers are provided for each piece of equipment to assure equipment safety. Temperature-Compensated Control. Maximum occupant comfort is ensured by use of a computerized control that provides equipment cycling with automatic temperature override. Cycling will be reduced or stopped, depending on whether room temperatures fall outside present comfort levels. Hence, the guesswork of selecting proper cycling strategies is eliminated. Demand Limiting. As much as 50% of bills for use of electrical energy may be attributed to kW demand charges. A demand-limiting program may save a substantial amount of utility energy costs over a short period of time. A computerized control, in particular, can limit costly demand charges by use of a predictive demand program that anticipates electrical demand peaks. When the control panel senses that a peak is about to occur, it simply turns off selected loads on a priority basis until the peak subsides, thereby reducing the energy bill. Optimum Start /Stop. Energy can be wasted by HVAC equipment that is scheduled to start and stop on worst-case conditions. This scheduling results in operations that begin too soon and run too long. Computerized control monitors indoor and outside temperatures and determines the most efficient start and stop times without sacrificing individual comfort. Optimum start / stop also allows independent control of individual comfort zones. Night Setback. Utilization of night setback temperatures saves energy by automatically converting the specific comfort zone to a predetermined nighttimetemperature setpoint. The setpoint overrides the daytime setting for every load or zone. HVAC equipment will operate to maintain the nighttime setting until morning warm-up or cool-down is required. Night setback also allows independent control

D2
D2 area ratio (%)  100 o i (6.2) D2i where De  diameter at the sampler cutting tip Di  inside diameter of the sampling tube Do  outside diameter of the sampling tube In general, a sampling tube for undisturbed soil specimens should have an inside clearance ratio of about 1% and an area ratio of about 10% or less. Having an inside clearance ratio of about 1% provides for tip relief of the soil and reduces the friction between the soil and inside of the sampling tube during the sampling process. A thin film of oil can be applied at the cutting edge to also reduce the friction between the soil and metal tube during sampling operations. The purpose of having a low area ratio and a sharp cutting end is to slice into the soil with as little disruption and displacement of the soil as possible. Shelby tubes are manufactured to meet these specifications and are considered to be undisturbed soil samplers. As a comparison, the California Sampler has an area ratio of 44% and is considered to be a thick-walled sampler. It should be mentioned that using a thin-walled tube, such as a Shelby tube, will not guarantee an undisturbed soil specimen. Many other factors can cause soil disturbance, such as: Pieces of hard gravel or shell fragments in the soil, which can cause voids to develop along the sides of the sampling tube during the sampling process Soil adjustment caused by stress relief when making a borehole Disruption of the soil structure due to hammering or pushing the sampling tube into the soil stratum Expansion of gas during retrieval of the sampling tube Jarring or banging the sampling tube during transportation to the laboratory Roughly removing the soil from the sampling tube Crudely cutting the soil specimen to a specific size for a laboratory test The actions listed above cause a decrease in effective stress, a reduction in the interparticle bonds, and a rearrangement of the soil particles. An undisturbed soil specimen will have little rearrangement of the soil particles and perhaps no disturbance except that caused by stress relief where there is a change from the in-situ stress condition to an isotropic perfect sample stress condition. A disturbed soil specimen will have a disrupted soil structure with perhaps a total rearrangement of soil particles. When measuring the shear strength or deformation characteristics of the soil, the results of laboratory tests run on undisturbed specimens obviously better represent in-situ properties than laboratory tests run on disturbed specimens. Soil samples recovered from the borehole should be kept within the sampling tube or sampling rings. The soil sampling tube should be tightly sealed with end caps or the sampling rings thoroughly sealed in containers to prevent a loss of moisture during transportation to the laboratory. The soil samples should be marked with the file or project number, date of sampling, name of engineer or geologist who performed the sampling, and boring number and depth. 6.2.4 Field Testing There are many different types of tests that can be performed at the time of drilling. The three most common types of field tests are discussed in this section: Standard Penetration Test (SPT). The Standard Penetration Test (SPT) consists of driving a thick-walled sampler into a sand deposit. The SPT sampler must have an inside barrel diameter (Di)  3.81 cm (1.5 in) and an outside diameter (Do)  5.08 cm (2 in). The SPT sampler is shown in Fig. 6.1. The SPT sampler is driven into the sand by using a 63.5-kg (140-lb.) hammer falling a distance of 0.76 m (30 in). The SPT sampler is driven a total of 45 cm (18 in), with the number of blows recorded for each 15 cm (6 in) interval. The measured SPT N value (blows per ft) is defined as the penetration resistance of the sand, which equals the sum of the number of blows required to drive the SPT sampler over the depth interval of 15 to 45 cm (6 to 18 in). The reason the number of blows required to drive the SPT sampler for the first 15 cm (6 in) is not included in the N value is that the drilling process often disturbs the soil at the bottom of the borehole and the readings at 15 to 45 cm (6 to 18 in) are believed to be more representative of the in-situ penetration resistance of the sand. The data below present a correlation between the measured SPT N value (blows per ft) and the density condition of a clean sand deposit. N value (blows per ft) Sand density Relative density 0 to 4 Very loose condition 0 to 15% 4 to 10 Loose condition 15 to 35% 10 to 30 Medium condition 35 to 65% 30 to 50 Dense condition 65 to 85% Over 50 Very dense condition 85 to 100% Relative density is defined in Art. 6.3.4. Note that the above correlation is very approximate and the boundaries between different density conditions are not as distinct as implied by the table. The measured SPT N value can be influenced by many testing factors and soil conditions. For example, gravel-size particles increase the driving resistance (hence increased N value) by becoming stuck in the SPT sampler tip or barrel. Another factor that could influence the measured SPT N value is groundwater. It is important to maintain a level of water in the borehole at or above the in-situ groundwater level. This is to prevent groundwater from rushing into the bottom of the borehole, which could loosen the sand and result in low measured N values. Besides gravel and groundwater conditions described above, there are many different testing factors that can influence the accuracy of the SPT readings. For example, the measured SPT N value could be influenced by the hammer efficiency, rate at which the blows are applied, borehole diameter, and rod lengths. The following equation is used to compensate for these testing factors (A. W. Skempton, Standard Penetration Test Procedures, Geotechnique 36): N  1.67 E C C N (6.3) 60 m b r where N60  SPT N value corrected for field testing procedures. Em  hammer efficiency (for U.S. equipment, Em equals 0.6 for a safety hammer and Em equals 0.45 for a donut hammer) Cb  borehole diameter correction (Cb  1.0 for boreholes of 65 to 115 mm (2.5 to 4.5 in) diameter, 1.05 for 150-mm diameter (5.9-in), and 1.15 for 200-mm (7.9-in) diameter hole) Cr  Rod length correction (Cr  0.75 for up to 4 m (13 ft) of drill rods, 0.85 for 4 to 6 m (13 to 20 ft) of drill rods, 0.95 for 6 to 10 m (20 to 33 ft) of drill rods, and 1.00 for drill rods in excess of 10 m (33