It is therefore important, in designing riveted joints, to determine whether the shearing strength of the rivets or the bearing values of the plates is the stronger, and to proportion the joint accordingly.

Table XXIX gives the shearing and bearing values for the principal sizes of rivets and plates used in steel construction.

The greatest economy in material is obtained when the net area of the plates or members joined is the greatest possible; that is, when the percentage or ratio existing between the net section and the gross section is as great as can be. It is usual, in proportioning riveted work, where the rivets are driven by hand in the field, to increase the number of rivets 25 or 50 percent, to allow for faulty riveting.

It has previously been said that rivets fail by shearing; they are, however, in rare instances liable to fail by bending. This occurs only when the rivets are long and it is impossible to drive them enough to have them upset sufficiently to fill the holes. In such case the only remedy is to so design the joint as to lessen the grip of the rivet, or increase the number of rivets, and consequently reduce the tendency to bending. Rivets are never proportioned to withstand flexure.

Rivets.

Character of Work,

Pounds per Square Inch.

Shearing.

Ordinary Bearing.

Web

Bearing.

Iron rivets

Railroad bridges

6,000

12.000

16,000

Iron rivets

Highway bridges and buildings

7,500

15,000

20,000

Steel rivets

Railroad bridges

7,500

15,000

20,000

Steel rivets

Highway bridges and buildings

9,000

18,000

24,000

Table XXIX. Shearing And Bearing Values Of Rivets

Diameter of Rivet. Inches.

Single Shear at 6,000 Lb. per Sq. In.

Bearing Value at 12,000 Lb. per Sq. In. for Different Thickness of Plate in Inches.

1/4

5/16

3/8

7/16

1/2

9/16

5/8

3/8

660

1,120

1/2

1,180

1,500

1,880

2,250

5/8

1,840

1,860

2,320

2,790

3,250

3,720

3/4

2,650

2,250

2,810

3,370

3,940

4,500

5,060

7/8

3.610

2,630

3,280

3,940

4,590

5,250

5,910

6,560

1

4,710

3,000

3,750

4,500

5,250

6,000

6,750

7,500

Diameter of Rivet. Inches.

Single Shear at 7,500 Lb. per Sq. In.

Bearing Value at 15,000 Lb. per Sq. In. for Different Thickness of Plate in Inches.

1/4

5/16

3/8

7/16

1/2

9/16

1

3/8

830

1,410

1/2

1,470

1,880

2,340

2,810

5/8

2,300

2,340

2,930

3,520

4,100

3/4

3,310

2,810

3,520

4.220

4,920

5,630

6,330

7/8

4,510

3,280

4,100

4,920

5.740

6.560

7,380

8,200

1

5,890

3,750

4,690

5,620

6,560

7,500

8,440

9,380

Diameter of Rivet. Inches.

Single Shear at 9,000 Lb. per Sq. In.

Bearing Value at 18,000 Lb. per Sq. In. for Different Thickness of Plate in Inches.

1/4

5/16

3/8

7/16

1/2

9/16

5/8

3/8

990

1,680

1/2

1,770

2,250

2,820

3,370

5/8

2,760

2,790

3,480

4,180

4,870

5,580

3/4

3,970

3,370

4,210

5,050

5,910

6,750

7,590

7/8

5,410

3,940

4,920

5,910

6,880

7,870

8,860

9,840

1

7,060

4,500

5,620

6,750

7,870

9,000

10,120

11,250

Example

Fig. 31 shows the riveted joint for a tension member. The allowable stress for the rivets in single shear is

7,500 lb. per sq. in., and the safe bearing and tensile values of the wrought-iron bars 15.000 and 12,000 lb. per sq.in., respect-ively; what will be the safe resisting strength of the member at the connection? Solution - Determine whether the shear of the rivets the bearing value of the bars, or the tensile strength of the members connected, is the strongest. The combined sections of bars a and c are equal to that of b. The safe tensile strength of members connected is equal to strength of net section of the bar 6, obtained by deducting from the gross section of 6 the area of metal cut out for rivet holes. The rivet hole is considered as 1/8 in. larger than the rivet, to compensate for the deterioration of the metal, due to punching. The gross section is equal to 5/8 in. (thickness) x 2 in. (width) = 1.25 sq. in. The section of metal cut out for the rivet hole is equal to .625 in. X .875 in. (diameter of rivet hole) = .5468 sq. in.; the net section of the bar is therefore equal to 1.25 sq. in. - .5468 sq. in., or .7032 sq. in. The safe tensile strength of bar b is equal to .7032 sq. in. X 12,000 lb. (safe tensile strength per sq in. of material) = 8,438 lb., which is also the combined strength of the bars a and c.

In Fig. 31 it is evident that the two 3/4" rivets are in double shear along the lines e d and b a, but, by referring to Table XXIX, it will be seen that the safe bearing value of a 3/4 " rivet upon a 1/4" plate is 2,810 lb., which is less than the safe shearing stress of the rivet, and is therefore the one to be used. The bearing value of the 3/4" rivet upon the 3/8" bar c is greater than the shearing stress of the rivet; therefore, in this case the shear of the rivet should be taken as its resistance. The safe resistance of the 3/4 " rivets is then as follows:

Shear of two 3/4" rivets on line ed = 3,310 X 2 = 6,620 lb. Bearing value of two 3/4" rivets on 1/4" plate 2,810 X 2 = 5,620 lb

Total = 12,240 lb.

Table XXIX Shearing And Bearing Values Of Rivets 268

Fig. 31

To this add the safe shearing stress of the 5/8" rivet, which is 2,300 lb. or less than its safe bearing value against the 1/4" bar. Thus, 12,240 + 2,300 = 14,540 lb., the safe resistance of the rivets to shear, and the plates or bars to crippling. From these results, it is seen that the net section of the bars is weaker than the connection; hence, the safe strength of the tension member is 8,438 lb., the strength of bar 6, or the combined strength of bars a and c.