This section is from the book "A Treatise On Architecture And Building Construction Vol3: Stair Building, Ornamental Ironwork, Roofing, Sheet-Metal Work, Electric-Light Wiring And Bellwork", by The Colliery Engineer Co.. Also available from Amazon: A Treatise On Architecture And Building Construction.
44. In fireproof buildings it is a common practice to combine the elevators and stairs in one shaft. In such cases the elevator usually occupies the center of the shaft, and the stairway is constructed around it. Such a combination is shown in plan in Fig. 65, where the arrangement of stairs and elevator shaft on the first floor is shown at (a), and on the upper floors at (b). An elevator shaft 6 ft. X 6 ft. 9 1/2 in. is thus provided, around three sides of which rises a stairway 3 ft. 2 1/2 in. in the clear. So far as the details of the stairs are concerned, they are precisely the same in principle as those described in Arts. 18, 19, and 20; the wall strings are first set in place, then the face strings (which in this case are the well strings), and finally the risers and treads. The well strings, however, have to be considered with the elevator shaft, as they form a part of that structure; and the details of the grille-work screen around the elevator shaft must include a treatment that will take the place of a balustrade on that side of the stairs.
The elevations of the wall strings, the outside strings, and the sides and back of the enclosure, also the front elevation of the enclosure, are shown at (a), (b), (c), and (d), in Fig. 66.
The grille-work on the first story is of brass, and on the stories above of iron.
45. As in the previous examples of stair work, the first procedure is to fix the number of risers and the width of the stairs. The height, as shown at (a), is 14 ft. 8 1/4 in. between the first and second stories; and to determine the number of risers, the size of the well hole, as well as the approximate space that the elevator will occupy, must be considered, though the latter may be modified to work out the stairs.
It will be seen that 26 risers at 6.77 inches high, counting from the top to top of the treads, gives 9 risers each side of the well and 8 at the back. This will permit the treads to be 10 inches wide on the sides and back, all finishing nearly symmetrically at the corners. The face of the first riser, as G8 shown in Fig. 65 (a), is 1/2 inch from the corner of the angle-iron frame of the well, and the ninth riser is 1 inch from the corner of the corresponding angle at the back of the shaft.
The upper part of the opposite side is similar, and the run at the back has the tenth and seventeenth risers, each 1 inch back of the angle iron, thus in each case allowing sufficient room for the finished tread to stop inside the edge of the angle. In planning any stair that is broken by intermediate platforms, the starting riser of each section should, if possible, be kept the same distance from a fixed point; in this example these points are represented by the angles at the corners of the well. Circumstances may arise, as in the present case, when this arrangement is not possible, and then the space is divided equally, in place of having the eleventh riser 1/2 inch back, and the seventeenth 1 1/2 inches; this also allows the platform to be the same breadth.
The upper stories being less in height than the first story, fewer risers are required; and by making them 7.66 inches high, the plan of the stair on each side of the well remains the same as the first story, while at the back the platform extends across the full width of the well. In fact, the stairs in every case should be planned as a whole, and not simply flight by flight.
46. The plans being determined, the wall and outside, or well, strings, and the sides and back of the enclosure should be laid out on the section lines j k, l m, and n o, shown in Fig. 65 (a), the developments of which are shown at (a), (d), (c), and (d), Fig. 66, and (a), (b), and (c), Fig. 67. The elevation of the front is also shown at (d), Fig. 66. In most stairs, the platforms are of slate or marble, and must be supported at the center or diagonally by either cast or wrought iron ribs or arches, as indicated by the dotted lines shown on the plans, Fig. 65. The development and details of the parts of the enclosures and stairs are shown in Fig. 68. (a) shows the head of the outside string in plan and section at the first platform, between the first and second stories; (b), the foot of the outside string in plan and section at the first platform, between the first and second stories; (c), the wall string in plan and section at the first platform between the first and second stories, and an elevation of the arch rib supporting the platform and the springing block to which the rib is bolted. At (d) is shown the plan and section of the head and foot of the outside string, with the enclosure of basketwork and grille as they exist in the upper stories, and (e) shows the plan and section of the wall string of the same run. At (f) is shown a plan and section of the head and foot of the outside string on all the platforms and landings of the upper stories. At (g) is shown the wall string and the platforms and landings of the same run. In Fig. 09 is shown the elevation and section of the rib arches that support the platforms. The ends are checked out 3/4 in. x 1 in. where they rest on the springing blocks as shown. Fig. 69 shows at (a) the plan of these platform arches for the first story, and at (6) for the upper stories, while the springing blocks that support these ribs are shown at (c). They are cast channel shape, with the web, or socket, and the lug on the face.