Document 3NqxqXD1mrb1jOoGN4qeKQN63

Soil's Load-Bearing Ability Is Checked Prior to Driving Piles for Turbine TEST BORING bcforo pile driving. Figures PIPE PILE being driven os port of the AFTER DRIVING pipe shell to full depth to right show bio** needed to drivo I ft foundation for a 50,000-kw extension compressed air hondlos finol cleonout Structural Support for Plant Loads Briefing on fundamentals of concreting, equipment founda tions, plant structures How piles and spread foot ings support heavy loads Problems that may crop up when conduit is laid in con crete during construction By A O MULT, Structural Feglneer Berm end Rm tue Today's rowcn rLAHT ouildinc Is designed primarily lo support and en close turbine generators, switchgear boilers and fuol-handUng equipment. Crouping ouch equipment into o rela tively small plant area always means a highly concentrated weight for the foun dation. Average unit load on the soil beneath a typical modern plant falls somewhere between 3000 and 4000 pat. These pressures ore higher directly un der the boilers, turbines ond coat bunk ers. Since concrete is a common miterisl lor foundations and general building construction, lei us first con sider its makeup and how it ts used. CONCRETE Concrete Is cement, sand, stone and water, mixed together ond allowed to harden. To get concrete of a specified strength, core must be taken in select ing each of the materials, including the water, and then proportioning the mis. Gravel ond sand form a mass of loose particles of various sites. Then cement is added to coat each bit of sand and, stone. Water is Introduced to hydrsto the cement, causing the bits of and and gravel to adhere lo each other. This in a nutshell is concreto. Concrete Specs. Concrete is frequent ly specified by either of two ways: a volume mix ratio or the desired strengthIn specifying o mix by volume ratio* such as 1-2-4 or 1-3-5, we mean one pari cement or two parts sand to fee*' parts of gravel. More often the specify cation calls for concrete to bo of certalp minimum ultimate strength, say 2000. 3000,- or 4000 psi at the end of 26 day* When mixing concrete remember tb*. ' SO ENOtNCERINO AND MANAGEMENT SECTION fOWO ; And Building Supports STEEL CORE is then lowered Into shell for transmitting load to, the rock bed leu witch used the stronger the con crete. And after pouring the concrete, the more water you use in keeping it wet, the stronger it will be. Concrete may be kept from drying out too fast by using waterproof paper coverings r water sprays. Specifications often limit the water per bag of cement to about 6 gel, for 3000 lb concrete. About 2)4 gal of water is needed to hydrate one bag of cement fully, if thoroughly mixed. But additional water U added to make concrete easier to mix nil place. Added water increases **umP a measure of fluidity of given mi*. The greater the slump, the more Buld a mix become-and the easier it ** to place. So on irresponsible con tractor is ipt to ute lots of water. A *a7 to Increase slump is to add both cement and water to keep watercement ratio constant. Concroti Tnti. To make mra con. ."? It of proper Urolith, aamplea are wen as H U being placed. Records re kept of where it was placed, noting the time and weather. Samples are sent to a testing laboratory. One sample of a "set" is tested dt the end of seven days and another at the end of 26 days. Tbe 7-day test is considered an indica tion of what to expect from the 26-day test, which is the one that must come up to specified strength. Portland ce ment concrete will develop about twothirdaof its design strength in the first seven days and its full design strength in 26 days. Good concrete will keep growing stronger throughout its life. Don't pour concrete In cold weather, without protection. It freezes oasily and, when frozen, hydration completely stops, so, os a result, you may have only an uncemented mass of stone and sand. Concrete is an excellent structural material in compression, but weak in tension. So to take tension in beams, slabs, footings, and ao on, steel rods are used to reinforco it It Is assumed for design purposes that all tension is taken by the sled rods used as reinforcing. . CONDUIT When conduit is run io concrete, keep it at least four Inches from the surface. Reason is that localized healing of conduit may break the bond between it and, concrete. I feel tbe only lime con duit .should be run in concrete ineldo o building is when there is no other way to run it. When going through floor slabs and concrete walls, use pipe sleeves larger than the conduits. Heat ing of bare grounding cable or conduit laid near concrete surface will result in concrete spalling. Thus the bond be tween cable or conduit and concrete will be broken. When cooduits must be placed in a floor slab put an additional slab atop the structural slab. This is most feasible where we have small floor areas and mony conduits. It wouldn't be practical to do over a large floor area just to take a few conduits. An alternative would be conduit sleeves in the slab, then inserts in underside o( slab to hang conduits. Below the basement Roof, conduits may be laid directly on top of the fill ond basement-floor slabs poured right over them. Grounding. Pumps, motors, pipes, conduits and other mechanical and electrical equipment may be grounded to the building steel framework. All steel, tn turn, is lied to the ground mesh or mat. More positive protection results from using a grounding cable for tbe complete column length. Then ground connections from this cable tie into the ground mesh. In laying a ground mesh, one method is lo lay cable directly on the ground right below the basement floor slab, stringing it along under the column lines. Then a ground lead is brazed to each column, tied to the column ground ing-cable, through the floor slab and lu the ground mesh. This mesh is then lied at intervals to pipes or ground rods driven 20 ft opart, 6 to 10 ft deep. EQUIPMENT FOUNDATIONS Within the plant building, concrete is used mostly lor building foundations, equipment foundations and floor slabs. It mokes n excellent equipment foun dation because of its strength end weight, lu'weighl, when properly used, tends to dampen the vibration of moving* equipment such as turbines, compres sors, pumps, motors. A safe rule lo follow in the design of moil equipment foundations Is that the weight of foundation should be two to three times the total weight of ma chine, or three lo four limes the weight of moviog parts. Foundation is usually a little larger than the machine bed and minimum depth is determined by weight requirements. Machine founda tion is. generally tied into the building alsb or mat supporting it. An exception is made (or large equipment like tur bine-generators and pulverizers. Here are a few design rules of thumb for turbine-generator founda tions. Depth of every member, vertical or horizontal, is about one-third the length ol span. 'Sometimes you can cut this to one-fourth the span length by using structural steel beams for rein forcing. So for an 16-ft span between bents, you should havo about a 6-fideep beam; width about one-half to two-thirds beom depth. Don't make square-corner intersec tions. Use a 12-Inch or larger haunch. And for appearance, chamfer all cor ners. Soil loads. Almost any soil will take a spread load of 500 to 1000 paf. And if the soil is dry with much sand and gravel, or even dry clay, it will probably be good for 5000 or 6000 paf, or more. About 3000 to 4000 lb Is a safe guess for average soils. But a guess wouldn't do for a major structure. Soil investigation! are almoal always necessary. Adequate soil study and proper foundation design is of top importance. Test Methods. There are two general methods of soil investigation: visual in spection and test loading. Visual in spection coils for digging a test pit to required depth, then studying the soli. This is OK for shallow foundations and light loads. But with deeper foundations and heavy loads, core borings are always desirable. In this test a small pipe is driven into the ground. Inside the pipe a spoon lifts the material out as the Unuaiy tojj ENOINIIIINO AND MANAGEMENT SECTION fit