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COMMONWEALTH OF PENNSYLVANIA

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The Pennsylvania Code website reflects the Pennsylvania Code changes effective through 52 Pa.B. 3204 (May 28, 2022).

34 Pa. Code § 15.18. Allowable stresses.

§ 15.18. Allowable stresses.

 (a)  For steel. Parts of the structure shall be so proportioned that the sum of the maximum stresses in pounds per square inch does not exceed the following:

   (1)  Tension. Tension shall be regulated as follows:

ItemMaximum Stresses
(pounds per square inch)
Structural steel, net section20,000
Butt welds, section through throat20,000
Rivets on area based on nominal diameter20,000
Bolts and other threaded parts, on nominal area at root of thread20,000

   (2)  Compression. Compression shall be regulated as follows:

     (i)   For the purposes of this paragraph, symbols represent the following:

       L = The unsupported length of the column.

       r = The corresponding least radius of gyration of the section.

     (ii)   Rolled steel, on short length or where lateral deflection is prevented, may not exceed 20,000 pounds per square inch.

     (iii)   On a gross section of columns, L/r does not exceed 120:

       1,700 - .485 L2 /r2

   if L/r exceeds 120:

       1 + [(18,000 ÷ L2) ÷ 18,000r2 ]

     (iv)   The ratio of unbraced length to least radius of gyration L/r for compression members and for tension members other than rods shall not exceed the following:

Item
Maximum Stresses
(pounds per square inch)
For main compression members120
For bracing and other secondary members in compression200
For main tension members240
For bracing and other secondary members in tension300

   (3)  Bending. Bending shall be regulated as follows:

     (i)   For the purposes of this paragraph, the following designations will apply:

       L = The unsupported length of the column.

       b = The width of the compression flange.

     (ii)   Extreme fibres of rolled shapes, and built up sections, net section, if lateral deflection is prevented, may not exceed 20,000 pounds per square inch.

     (iii)   Where L exceeds 15 times b, the stress in pounds per square inch in b may not exceed the following:

       1 + [(20,000 ÷ L2 ) ÷ 2,000b2 ]

     (iv)   The laterally unsupported length of beams and girders may not exceed 40 times b in width of the compression flange.

     (v)   Extreme fibres of pins, when the forces are assumed as acting at the center of gravity of the pieces may not exceed 30,000 pounds per square inch.

   (4)  Shearing. Shearing shall be regulated as follows:

     (i)   For the purposes of this paragraph, the following designations will apply:

       A = The gross area of the web in inches.

       V = The total shear.

       h = The height between flanges in inches.

       t = The thickness of the web in inches.

     (ii)   The following table will apply:

ItemMaximum Stresses
(pounds per square inch)
Pins15,000
Power-driven rivets15,000
Turned bolts in reamed holes with a clearance of not more than 1/50 inch15,000
Hand-driven rivets10,000
Unfinished bolts10,000
The gross area of the webs of beams and girders where h is not more than 60 times t13,000

     (iii)   The gross area of the webs of beams and girders if the web is not stiffened, where h is more than 60 times t, the thickness of the web, the maximum shear per square inch, V/A may not exceed:

       1 + [(18,000 ÷ h2 ) ÷ 7,200t2 ]

     (iv)   A section through the throat of a fillet weld may not exceed 13,600 pounds per square inch.

   (5)  Bearing. Bearing shall be regulated as follows:

     (i)   For the purposes of this paragraph, the letter ‘‘d’’ shall designate the diameter of the roller in inches.

     (ii)   The following table will apply:

Maximum Stresses
(pounds per square inch)
Item Single Shear
Double Shear
Pins32,000
32,000
Power-driven rivets32,000
40,000
Turned bolts in reamed holes32,000
40,000
Hand-driven bolts20,000
25,000
Unfinished bolts20,000
25,000

     (iii)   On expansion rollers, pounds per linear inch, -600d.

   (6)  Combined stresses. Combined stresses shall conform with the following:

     (i)   For the purposes of this paragraph, the following designations will apply:

       Fa = Axial unit stress that would be permitted by this specification if axial stress only existed.

       Fb = Bending unit stress that would be permitted by this specification if bending stress only existed.

       fa = Axial unit stress (actual) = axial stress divided by area of member.

       fb = Bending unit stress (actual) = bending moment divided by section modulus of member.

     (ii)   For stresses due to wind sway loads, combined with those due to dead or live loads, the permissible total working stress may be increased 33 1/3%, if the section thus found is not less than that required by the dead or live loads alone.

     (iii)   Members subject to both axial and bending stresses shall be so proportioned that the quantity fa/Fa+fb/Fb does not exceed unity.

   (7)  Members carrying wind and sway only. For members carrying wind and sway stresses only, the permissible working stresses may be increased 33 1/3%.

   (8)  Welding. Welds shall be made only by operators who have qualified by the tests prescribed in the Standard Qualification Procedure of the American Welding Society to perform the type of work required, except that this provision need not apply to tack welds not later incorporated into finished welds carrying calculated stress.

 (b)  For wood. Allowable unit stresses for wood parts of grandstands shall be considered in light of the following:

   (1)  Wood parts shall be so designed and proportioned that their stresses do not exceed the allowable unit stresses in the following table:

Allowable Unit Stresses in Pounds Per Square Inch for Wood parts of Grandstands Based on the American Lumber Standards

   (2)  A species or grade of wood excluded from paragraph (1) may not be used except when permitted by the Department and after the wood is determined to be satisfactory.

   (3)  For stresses produced by wind loads or impact only, or by a combination of wind or impact loads and dead and live loads, allowable stresses may be increased 50% if the resulting sections are not less than those for dead and live loads alone.

   (4)  Connections to wooden members shall be by means of rivets, bolts, lag screws, except lag screws in tension or for field connections or approved modern timber connectors. It is recommended that a bulletin issued in the United States Department of Commerce entitled, ‘‘Modern Connection for Timber Construction’’ be consulted. The use of nails and wood screws is permissible for holding parts together, but for designing purposes the nails or screws shall be considered incapable of transmitting calculable stresses.

   (5)  Nails or screws may not be used if their loosening or splitting of the surrounding wood causes stresses in excess of those permitted or would jeopardize the strength and stability of the structure or the safety of its occupants.

   (6)  Connections to wooden tension members may be by means of not less than two bolts, rivets or lag screws or approved modern timber connectors. Reference should be made to the bulletin referred to in paragraph (4). Adequate provision shall be made to prevent wood splitting at such connections.

   (7)  The bearing values of bolts in wood shall be calculated by the following tables:

     (i)   Basic stresses for calculating safe loads for bolted joints shall be subject to the following:

Basic Stress
(pounds per square inch)
GroupSpecies of Wood Parallel with
the Grain
Perpendicular
to the Grain
Softwoods (conifers)
2Cedar, Alaska, Port Oxford and western red1,000200
2Douglas fir (Rocky Mountain region)1,000200
2Hemlock, western1,000200
2Pine, Norway1,000200
3Cypress, southern1,300275
3Douglas fir (coast region)1,300275
3Larch, western1,300275
3Pine, southern yellow1,300275
3Redwood1,300275
3Tamarack1,300275
Hardwoods (broad-leaved species)
2Maple (soft), red and silver1,200250
2Elm, American and slippery1,200250
2Gum, black, red, and tupelo1,200250
2Sycamore1,200250
3Ash, commercial white1,500400
3Beech1,500400
3Birch, sweet and yellow1,500400
3Elm, rock1,500400
3Hickory, true and pecan1,500400
3Maple (hard), black and sugar1,500400
3Oak, commercial red and white1,500400

       (A)   The stresses set forth in subparagraph (i) apply to seasoned timber used in dry covered locations. Exposed parts of grandstands which may be used outdoors require 7/8 of those values.

       (B)   When the stress is neither parallel nor perpendicular to the grain of the wood, the maximum basic stress in pounds per square inch shall not exceed the following:

Equation to Title 34—§ 15.18

       in which P is the allowable basic stress parallel with the grain, Q is the allowable basic stress perpendicular to the grain, and O is the angle between the direction of the grain and the direction of the load normal to the face considered.

     (ii)   The percentages of basic stress parallel with the grain for calculating safe bearing stresses under bolts shall be derived as follows:

Length of
Bolt in
Main
Percentage of Basic Stress for—
Member
Divided
Common BoltsHigh-strength Bolts
by its
Diameter
Group 1Group 2Group 3Group 1Group 2Group 3
(L/D) WoodsWoodsWoodsWoodsWoodsWoods
1.0100.0100.0100.0100.0100.0100.0
1.5100.0100.0100.0100.0100.0100.0
2.0100.0100.0100.0100.0100.0100.0
2.5100.0100.097.7100.0100.0100.0
3.0100.0100.099.0100.0100.0100.0
3.5100.099.396.7100.0100.099.7
4.099.597.492.5100.0100.099.0
4.597.993.886.8100.0100.097.8
5.095.488.380.0100.099.896.0
5.591.482.273.0100.098.293.0
6.085.675.867.2100.095.489.5
6.579.070.062.098.592.285.2
7.073.465.057.695.888.881.0
7.568.560.653.792.785.076.8
8.064.256.950.489.381.273.0
8.560.453.547.485.977.769.6
9.057.150.644.882.574.266.4
9.554.147.942.479.071.063.2
10.051.445.540.375.868.060.2
10.548.943.338.472.564.857.4
11.046.741.436.669.761.954.8
11.544.739.635.066.859.252.4
12.042.837.933.664.056.750.2
12.541.136.432.261.454.448.2
13.039.535.031.059.152.446.3

       (A)   The product of the basic stress parallel with the grain selected from the table set forth in paragraph (7)(i), and the percentage for the particular L/D ratio and species group taken from the table set forth in subparagraph (i), is the safe working stress at that ratio for joints with metal splice plates. If wood splice plates are used, each of which is 1/2 the thickness of the main timber, 80% of this product is the safe working stress.

       (B)   The common bolts referred to in subparagraph (i) are those having a yield point of approximately 45,000 pounds per square inch.

       (C)   The high-strength bolts referred to in subparagraph (i) are those having a yield point of approximately 125,000 pounds per square inch.

     (iii)   The percentages of basic stress perpendicular to the grain used in calculating safe bearing stresses under bolts shall be derived as shown in the following tables:

TABLE I


Percentage for Common Bolts
Length of
Bolt in
Main
Member
divided by its
Diameter
(L/D)
Group 1
Conifers
and
Group 1
Hardwoods
Group 2
Conifers
Group 2
Hardwoods
and
Group 3
Conifers
Group 3
Hardwoods
Percentage
for High-
Strength
Bolts
(all groups)
1.0100.0100.0100.0100.0100.0
5.5100.0100.0100.099.0100.0
6.0100.0100.0100.096.3100.0
6.5100.0100.099.592.3100.0
7.0100.0100.097.386.9100.0
7.5100.099.193.381.2100.0
8.0100.096.188.175.0100.0
8.598.191.782.169.999.8
9.094.686.376.764.697.7
9.590.080.971.960.094.2
10.085.076.267.255.490.0
10.580.171.662.951.685.7
11.076.167.659.348.481.5
11.572.164.155.645.477.4
12.068.661.052.042.573.6
12.565.358.049.040.070.2
13.062.255.345.937.566.9


TABLE II


Diameter of Bolt
(in inches)
Diameter Factor
1/42.50
3/81.95
1/21.68
5/81.52
3/41.41
7/81.33
11.27
1-1/41.19
1-1/21.14
1-3/41.10
21.07
2-1/21.03
3 and over1.00


       (A)   The safe working stress for a given value of L/D is the product of three factors:

         (I)   The basic stress perpendicular to the grain taken from the table in paragraph (7)(i).

         (II)   The percentage from the table set forth in clause (A).

         (III)   The factor for bolt diameter, as set forth in clause (B).

       (B)   No reduction need be made when wood splice plates are used except that the safe load perpendicular to the grain should never exceed the safe load parallel to the grain for any given size and quality of bolt and timber.

       (C)   The common bolts referred to in Table I are those having a yield point of approximately 45,000 pounds per square inch.

       (D)   The high-strength bolts referred to in Table I are those having a yield point of approximately 125,000 pounds per square inch.

   (8)  For other materials. Other materials when used shall be so designed and proportioned that their stresses do not exceed the allowable unit stresses generally accepted as safe by engineering practice.

Source

   The provisions of this §  15.18 adopted August 15, 1933; amended through July 1, 1968.

Cross References

   This section cited in 34 Pa. Code §  15.11 (relating to applicability); and 34 Pa. Code §  15.17 (relating to materials).



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