RELATIVE COST OF STRUCTURAL STEEL BASICS AND TUTORIALS

RELATIVE COST OF STRUCTURAL STEEL BASIC INFORMATION
How To Compute Relative Cost Of Structural Steel?

Because of the many strength levels and grades now available, designers usually must investigate several steels to determine the most economical one for each application. As a guide, relative material costs of several structural steels used as tension members, beams, and columns are discussed below.

The comparisons are based on cost of steel to fabricators (steel producer’s price) because, in most applications, cost of a steel design is closely related to material costs. However, the total fabricated and erected cost of the structure should be considered in a final cost analysis.

Thus the relationships shown should be considered as only a general guide.

Tension Members. Assume that two tension members of different-strength steels have the same length. Then, their material-cost ratio C2 /C1 is

C2/C1 = A2P2/A1P1

where A1 and A2 are the cross-sectional areas and p1 and p2 are the material prices per unit weight. If the members are designed to carry the same load at a stress that is a fixed percentage of the yield point, the cross-sectional areas are inversely proportional to the yield stresses. Therefore, their relative material cost can be expressed as

C2/C1 = Fy1p2/Fy2p1  (1.2)

where Fy1 and Fy2 are the yield stresses of the two steels. The ratio p2 /p1 is the relative price factor. Values of this factor for several steels are given in Table 1.4, with A36 steel as the base.

The table indicates that the relative price factor is always less than the corresponding yield-stress ratio. Thus the relative cost of tension members calculated from Eq. (1.2) favors the use of high-strength steels.

TESTING APPARATUS FOR SITE SOIL LABORATORY BASICS AND TUTORIALS

TESTING APPARATUS FOR SITE SOIL LABORATORY BASIC INFORMATION
What Are The Testing Apparatus For Site Soil Laboratories?

The usual apparatus suitable for a small soils laboratory on site, to be run by the resident engineer’s staff after proper instruction from a geotechnical engineer, is set out below.

For moisture content determinations
1. Beam balance weighing by 0.01 g divisions.
2. Drying oven, thermostatically controlled. (Not absolutely essential. For rough measurement of moisture content the sample can be dried on a flat tray over a stove.)
3. Six drying trays.

For grading analyses of soils
4. Aset of BS sieves (woven wire) with lid and pan for each different diameter: (a) 300 mm dia – 38, 25, 19, 13, 10 mm. (These can also be used for testing concrete aggregate gradings.) (b) 200 mm dia – 7, 5 and 3 mm, and Nos. 7, 14, 25, 52, 72, 100 and 200.
5. Balance weighing up to 25 kg.
6. Balance capable of weighing up to 7 kg by 1 g divisions.

For in situ density test (sand replacement method)
BS 1377 Part 9:1990 gives four tests of which Test 2.2 is the most useful because it can be used on fine, medium and coarse grained soils. A metal tray with a 200 mm diameter hole cut in it is placed on the formation and material is excavated via the hole.

The volume of the excavation is measured by pouring uniformly graded sand into it whose bulk density has been measured.

Apparatus required (additional to 1, 2, 3 and 6 above):
7. Small tools for excavating hole.
8. A rigid metal tray 500 mm square or larger with a 200 mm diameter hole cut in it.
9. Dried clean sand all passing No. 25 sieve but retained on No. 52 or 100 sieve and suitable airtight containers for storing it. (About 20 kg of this sand will be required initially.)
10. A pouring cylinder (as BS 1377 Part 9 Fig. 4).
11. Acalibrating container 200 mm diameter by 250 mm (as BS 1377 Part 9 Fig. 5).
12. Air-tight containers for the excavated soil.

The method can be applied to larger test holes in soils containing some gravel; the sand being poured in layers from a can with a top spout. A length of hose is attached to the spout with a conical tin shield wired to the lower end, so the sand has only a short standard free fall. Tests to fill measured containers can show the accuracy in ascertaining the bulk density of the sand as poured.