in which the first term represents the entire live and dead loads upon the bay, exclusive of the weight of the drop, and the second term the additional weight of the drop. The value of j in this case cannot be taken from Table I on page 20, as there is an excess of concrete in compression, but it can be determined by trial, as follows: In general a value taken from Table I, page 20, corresponding to the stresses employed, may be used in the computation for the steel section-area, as the error, on the safe side, is usually within 5% of the exact computed value. Accept seven 5%-in round deformed rods each way. Since these rods serve both the inner and mid-sections they may be bent as shown in Fig. 11, and their length is (L+ forty rod-diameters) + 6 in allowance for bend, or, 20 ft + 2 ft + 6 in 22 ft 6 in. The rods are arranged as shown in Fig. 8. It is not necessary to hook the ends. (b) Column-head sections: By Formula, in which the value of j is taken from Table (I), page 20, corresponding to the stresses Accept ten 5%-in round, deformed rods each way. Since these rods must lap past the column centers, so that twenty 5%-in rods are available across the column-head section, they are bent as shown in Fig. 8 and the length is in which the value of j is taken from Table I, page 20, corresponding to the Accept eleven 5%-in round, deformed rods, each way (one only additional to the number already computed). Since the sectional area of steel in this section is more than one-half of that in the column-head section, it is necessary to introduce short rods, as shown in Fig. 8. As there are ten 5%-in round rods, as determined for the column-head section, already available, only one additional rod is needed to give the required area. The length is, 17. Typical Design of Exterior Panel, Two-Way System. American Concrete Institute Ruling, 1920. Specification-data and panel-data are the same as in the preceding article. Example 2. (See Fig. 9.) (1) Band-steel perpendicular to the wall. (a) Outer section. Typical interior panel-requirement is increased 20% Accept fourteen 5%-in round, deformed rods. At least one-third of these rods shall be carried through to the wall in the bottom of the slab. Five are so treated, and as they must be raised over the first row of interior columns and extend to the line of inflection of the adjoining span, their length is 26 ft 3 in. The remaining nine, 27 ft long, are raised over both the interior and exterior columns. At the wall the raised rods, only, are hooked. (b) Column-head section over first interior row of columns. The typical interior panel-requirement is increased 20% Accept twenty-five 5%-in round, deformed rods (one only additional to the number already computed). As there are fourteen rods from the exterior panel and ten from the adjacent interior panel crossing this section, one additional rod, only, is needed. It is placed in the top of the slab, extending on either side of the column twenty rod-diameters beyond the lines of inflection of adjoining spans. Their length is 14 ft. (c) Column-head section at exterior columns. An area equal to 80% of the typical interior panel-requirement is used, or Accept seventeen 5%-in round deformed rods (eight only additional to the number already computed). As there are nine rods raised from the outer section, it is necessary to add eight more. They should extend twenty roddiameters beyond the line of inflection, which makes the length 8 ft, with a hook at the wall. (2) Slab steel perpendicular to the wall. (a) Inner section. Typical interior panel-requirement is increased 20%, Accept eight 5%-in round deformed rods. At least one-half of these rods should be carried through to the wall in the bottom of the slab. Four are so treated, and as they must be raised over the first row of interior columns and extend to the line of inflection of the adjoining span, their length is 27 ft. The remaining four, 16 ft 9 in in length, raised at the wall and cut off at a distance 0.25L 1 ft, outside of the exterior row of columns (see Fig. 9). (b) Mid-section at first interior row of columns. The typical interior panel is increased 20%. This requirement is the same as for the inner-section. Accept eight 5%-in round, deformed rods (none additional). As there are four raised from the inner portion of the exterior panel, and four more from the inner portion of the adjacent interior panel, the required section-area is already provided. (c) Mid-section at wall. A section-area equal to 80% of the typical interior panel-requirement is used. Accept six 5%-in round, deformed rods. (Two additional to those already chosen.) As there are four rods raised from the inner section, it is necessary to add two more. They should extend 20 rod-diameters beyond the assumed line of inflection, which makes the length 8 ft with a hook at the wall. (3) Band-steel at wall and parallel thereto. (a) The reinforcement required for the one-half column-head section may be considered, in this case, to be one-half of that at the interior columnhead section. Accept five 5%-in round, deformed rods of length 32 ft 6 in. (b) The reinforcement required for the one-half outer section is one-half of that for similar interior bands. Accept six 5%-in round, deformed rods (one additional to those already chosen). As there are five rods available from the one-half column-head section, only one rod, 14 ft long, is added. 18. Typical Design of Interior Panel, Two-Way System. Chicago Code. This design to be made irrespective of exterior panel requirements. Specification-data: f. 18 000 lb per sq in Panel-data: = = v = 12 = 700 lb per sq in 60 lb per sq in (shearing unit stress around periphery of drop) 120 lb per sq in (shearing unit stress around periphery of column capital.) Dimensions center-to-center of columns, 20 ft by 20 ft Drops are to be used Under this code the panel is divided into two strips known as strip A and strip B. Strip A corresponds to two column-strips of the Joint Committee designation (Fig. 7), and strip B corresponds to the middle strip. A slab thickness of 8 in is assumed. Then, allowing 4 lb per sq ft of bay for the weight of the drop in which (4 × 84) is the periphery of the drop and 6.5 the effective depth of the slab, both in inches. As 60 lb per sq in is permitted, accept a square drop with side equal to 7 ft 0 in. (4) Size of column capital. A circular capital with a diameter equal to 0.225L, is assumed. in which M = the bending moment, in inch-pounds, in band A over the columnhead, computed as in Paragraph (6) following, and based upon an assumed depth of 111⁄2-in. The values of k and j are taken from Table I, page 20, correspond to (b) Punching-shear around periphery of column capital. and in which (3.14 X 54) is the periphery of the column capital, and 10.25 the effective depth of the combined slab and drop, both in inches. As 120 lb per sq in is permitted on this section, the depth of the drop is controlled by the compressive strength of the concrete, see Paragraph (a) above. and the offset may be 31⁄2 in, making the total depth 1111⁄2 in. |