Net width for zigzag-connected members can be calculated by subtract­ing the overall width of the first hole located in the cross-section in question, and the W obtained by the following equation subsequently for each hole. For steel angles or channels as illustrated in Fig. 5.6-2, their effective cross-sectional area should be determined by developing

them, and by subtracting the plate thickness from the sum of the dis­tances from the hole center to the corner of the steel angle when fixed on different legs. The net cross-sectional area for combined T- or H- shapes should be the sum of the net cross-sectional areas obtained in this paragraph for each member.——~~

where d

Pi g

Fig. 5.6-1 Arrangement of Tightening Holes and Direction of Load

Example (1) Net width of the arrangement of tightening holes as il- lustrated in Fig. 5.6-1 is as follows:

A -A net width = b-2d

A-B-A net width = 6 — d —(d — -~f-) — (d — -^~)

4g 4g ⁷

A-B-C net width = 6-d-(£f--~~) - (<7-“^—)

4g 4g

Example (2) Effective cross-sectional area for steel angle

g = (/i_t + h₂) - t

Fig. 5.6-2 Example of Arrangement of Tightening Holes on Steel Angle

The effective cross-sectional area for the above example (2) means the shaded part in Fig. 5.6-3.

Fig. 5.6-3 Effective Cross-sectional Area for Steel Angle as Tension Member

Article 7. Fabrication of Joint

Sheared edges of the plates to be connected shall be planed away as wide as at least 1/4 of the thickness of plate (minimum 3mm) but the plates can be used without any process provided that they are under 9mm thick and their sheared sections are smooth, or they are cut off by an automatic gas cutting machine.

When making holes in plates thicker than 12mm, punching shall not be allowed. Except for secondary members, when punching plates under 12mm thick,'the diameters shall be increased by drilling at least 3mm after aligning the holes.

Holes shall be made vertically to the plate surfaces and finished smooth.

Description:

At the sheared edges of the plates to be tightened, the properties of the material change due to shearing, and some notches may be induced by inadequate cutting. Thus, edge planing is required to remove these defective portions, irregularity and shoulder-sagged portions of the sheared edges. In addition, as a long sized plate is sheared several times due to the operational limit of the machine, thus causing iregularities on the edge, the plate should be finished by planing away those irregularities.

For these reasons, it is specified that sheared edges of plates of con­nections to be tightened should be planed away at least 1/4 of the plate thickness (min. 3mm), and that the edges should be finished smooth to the required dimmensions.

As for plates under 9mm thick, the change in the properties of materi­al is relatively small because of easy shearing, and thus it is specified, that plates with smooth sheared sections and accurate cut sections may be used as they are without finishing. When an automatic gas cutting machine is used, the change in the properties of the material due to gas cutting is relatively small in range, and cut lines and sections can be smoothly and accurately processed. Accordingly, the plates cut thus are permitted to be used without any finishing.

When using a semi-automatic gas cutting machine, the above may be applied depending upon the face accuracy.

In the case of manual gas cutting, poor workmanship is likely to hap­pen, so it is necessary to finish smooth by planing, chipping, grinding, etc.

There are two ways to make holes: punching and drilling.

> Although punching is most efficient, the material is likely to be damaged and holes cannot be made accurately in a cylindrical shape because the steel around the hole is subjected to extremely unnatural force as is illustrated in Fig. 5.7-1.

Fig. 5.7-1 Punch and Dies for making Rivet Holes

Consequently, punching holes with the. required diameters is permis­sible as long as plates are under 12mm thick.

When punching plates under 12mm thick, the portion punched is sheared and passed through the dies, and it is said that the difference in diameter between the punch and the dies should be under 1.5mm in practical use. This difference in diameter makes the inner face of the sheared hole rough and also produces burrs. Thus it is specified that, except for secondary members, in order to remove these portions and to make the inner face smooth, the diameter should be enlarged at least 3mm with holes aligned after punching.

The secondary members here mean fillers, tie plates, bracings, over­flow plates, etc., in structures of a hydraulic gate or steel structures.

Since drilling causes less damage to material than punching, it is ad­visable to use drilling even for plates under 12mm thick when making holes in the main pressure portions of a steel penstock and the main structural-portions of a hydraulic gate. There are two ways to drill? to make holes with the required diameters from the outset or to make smaller holes than the ones needed and apply reaming or drilling to get the required diameters after the members are temporarily assembled.

When drilled with the required diameter from the outset, the holes should be placed with an accurate pitch. When reamed, each member must be sufficiently tightened with bolts so that the contact faces will < be in close contact with each other, after adjusting the position of each member. •

Holes must be of a cylindrical shape to be in accordance with the shapes of rivets, high strength bolts or bolts, and the direction of holes should be vertical to the plate surfaces. When making holes either by drilling or by punching, holes should be made exactly at a previously marked point so as not to produce eccentricity or tears. Burrs produced around the holes must be removed, and they must be clean-finished to the re­quired dimensions by chamfering the edges of the holes.

In case of a circular face like circumferential joints of pipe shell of a steel penstock, the holes should be concentric and drilled in the direc­tion, of the center.

Thus it is necessary to obtain the required diameteres by reaming.