Structural Design Examples

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Bisalloy Design Examples

Design

Examples

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DESIGN EXAMPLES

The following five structural design examples demonstrate the significant savings which can

be achieved in the areas of weight and cost by using Grade 690 MPa Bisplate 80 steel

instead of the more commonly used lower grade structural steels. These examples primarily

compare Bisplate 80 to Grade 300 Plus Steel which is currently the most commonly usedstructural steel in Australia. Comparison with other steels are noted where appropriate.

The design examples are as follows:

Heavily Loaded Column

Heavily Loaded Beam - I section

Heavily Loaded Beam - Box section

Heavily Loaded Truss

70 MI Water tank

Where appropriate, these examples have been simplified as much as possible in order tofacilitate ease of comparison between the different steels. Each example contains a brief

explanation of the structural element and the loading applied. Also provided are some typical

examples of applications in which the structural element may be utilised.

DESIGN CODES RELATING TO THE USE OF HIGH STRENGTH QUENCHED AND TEMPERED PLATE

MEMBERS IN STRUCTURAL ENGINEERING APPLICATIONS.

There is currently no Australian Standard covering the design of structural elements utilising

high strength quenched and tempered steels. The SAA Steel Structures Code, AS 4100-1990,

may be used for the design of structures in steel grades up to 450 MPa, beyond which the

general provisions of the code are not applicable.

AS4100 does not exclude the use of structural steels in excess of 450 MPa yield stress.

However, in order to adequately design and demonstrate the validity of a design in such

steels, it is necessary to engage an appropriate international standard which has been

specifically developed to cater for the use of high strength steels.

One such code, and the most commonly used in Australia for design in high strength steels is

the American Institute of Steel Constructions (AISC) Specification For Structural Steel

Buildings - Allowable Stress Design and Plastic Design, June 1, 1989. This code has been

proven to provide relatively simple and efficient methods of structural design for all types ofstructural elements, and has been used in the development of each of the design examples

contained within this publication.

A limit state version of the AISC specification is also available, and should be equally

effective in the design of High Strength Steel structures. It should also be noted that Bisplate

80 steel, at 690 MPa yield stress, is right on the upper limit of 100 ksi yield stress steel

covered by the AISC specification. Above this yield stress the AISC specification is not

applicable.

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EXAMPLE 1

HEAVILY LOADED COLUMN

Consider a braced column, 10m high, loaded

axially with an 11,000 KN factored live load

(Fig. 1).

Some examples of practical applications where

such a column may be required are as follows:

In multi-storey construction

Heavy industrial structures

Storage silos/Hopper supports

Structural column design was carried out

for Grade 300 MPa steel using AS4100-1990. C

Corresponding design was carried out forGrade 690 MPa Bisplate 80 Steel using the

AISC specification.

The results of each design are summarised in Table 1. Representative calculations are

provided on following pages.

STEEL GRADE MPa SECTION WEIGHT Kg/m300 500WC383 383

690tf = 20 d1 = 400tw = 16 bf = 500

207

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COLUM DESIGN USING GRADE 300STEEL COLUMN DESIGN USING GRADE 690MPA YIELDDesign in accordance with AS4100 1900.

Fig 3

AS4100 500WC383Reference

Section Capacity6.2.1 NS = KfAnfy

An=Ag=Ae

Kf = 1.0

Ns = 13664 KN

Ns = 12,298 KN > N* OK

Member Capacity6.3.3 Nc = c Ns N

c = {[1-[1-(90/)2]}= 0.8945Nc = 12,222 KN

Nc = 11,000 KN N* OK

Nominal Mass of Column = 383 kg/m

STRENGTH BISPLATE 80

Design in accordance with American Institute of Steel

Construction Specification for Structural Steel Buildings - 1989.Ag = 48,800 mm

2

Ix = 1,890 x 106mm4

Iy = 751 x 106mm4

rx = 197mm

ry = 124mm

fy = 280 MPa

AISC Spec. Design Load = 11,000 =7,333KN

Reference 1.5

fa = 7,333 = 277.78 MPaAg

Fa = 40.29 ksi

B5 Check Local Buckling

Table B5.1 Flanges : 95 = 95 = 9.5 < b = 12.1

Fy 100 t

Kc 1.0

Slender Element

Table B5.1 Web: 253 = 253 = 25.3 > b = 25.0

Fy 100 t

Non-Compact Element

Slender elements involved

Design by Appendix B

App. B Stress Reduction Factor for Flange,

B5a Qs = 1.293 0.00309 b Fy = 0.907

t Kc

Stress Reduction Factor for Web,

Qa = 1.0

Member stress reduction factor,

Q = QsQa = 0.907

Ag = 26,400 mm2 = An = Ae

Iy = 416.8 x 106mm4

Ry = Iy A = 125.7mm

fy = 690 MPa

= 100 Ksi

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COLUMN DESIGN USING GRADE 690MPA YIELD

STRENGTH BISPLATE 80(CONTINUED)

AISC Spec.

Reference

B5c Allowable Stress, Fa

C1c = 79.44 > kl

r

kl2

r

Q 1 - Fy2Cc

,2

Fa =

Eq A-B5-11 kl kl3

5 3 r r

3 + 8Cc 8Cc3

Fa = 43.13ksi > fa OK

Nominal mass of Column = 208 kg/m

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EXAMPLE 2

HEAVILY LOADED BEAM (ISECTION)

Consider a beam with full lateral restraint spanning 10m, loaded continuously with a live load of 470

KN/m (factored) as shown in Fig.5.

Practical applications where such a beam ma

required are:

In multi-storey construction


Roof support in underground mining

Structural beam design was carried out for Grade 300 MPa steel using AS4100-1990. Corresponding

design was carried out for Grade 690 MPa Bisplate 80 steel using the AISC specification.

The results of each design are summarised in Table 2. Representative calculations are provided on the

following pages.

STEEL GRADEMPa

SECTION WEIGHT Kg/m

300 1200WB392 392

690

tf= 25 d1 = 850

tw = 12 bf = 450 256

Note that a significant reduction in the depth of the beam was achieved through the use of Bisplate 80, in addition to the

weight waving, while still satisfying the permissible deflection requirements. This is of great importance in underground

mining and multi-storey construction applications, where head room is at a premium.

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BEAM DESIGN USING BEAM DESIGN USING GRADE 690MPA

GRADE 300STEEL YIELD STRENGTH BISPLATE 80Design in accordance with AS4100 1990.

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EXAMPLE 3

HEAVILY LOADED BEAM (BOX SECTION)

Consider a beam with full lateral restraint spanning 10m, loaded continuously with a live load of 470

KN/m (factored) as shown in Fig 9.

Practical applications are :


Roof support in mining

A box section is effective in long spans where additional lateral restraint is required within the

beam section to compensate for a lack of external restraints.

A common application ofabox section fabricated from high strength Q & T steel in

which the load configuration varies significantly from that described above, is in the

lifting booms ofmobile cranes.

Structural beam design was carried out for both Grade 250 MPa steel and Grade 690 MPa

Bisplate 80 steel using the AISC specification.

The results of each design are summarised in Table 3. Representative calculations are

provided on the following pages.

Table 3:

STEEL GRADEMPa

SECTION WEIGHT Kg/m

250

tf= 40 d1 = 1120

tw = 10 bf = 500 490

690tf= 25 d1 = 850

tw = 8 bf = 450284

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BOX SECTION BEAM DESIGN USING BOX SECTION BEAM DESIGN USING

GRADE 250MPA ASTMA36 GRADE 690MPA BISPLATE 80

In accordance with AISC Spec. In accordance with AISC Spec.

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EXAMPLE 4

HEAVILY LOADED TRUSS

Consider a heavily loaded truss spanning 40m.

Some examples of practical applications where such a truss may be required include :

Underground construction supporting a trafficable roof

(e.g. a hydro-electric power station).

Multi-storey construction supporting several floors.

In this example the following loading parameters have been considered.

Truss spacing 10m

Live Load 3 KPa

Dead Load 1 KPa

Occasional Load 20 KN mid span

The resulting load configuration is illustrated in Fig.13.

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Structural member design was carried out for Grade 300 and 350 MPa steels using AS4100

1990. Corresponding design was carried out for Grade 690 Bisplate 80 steel using the

American Institute of Steel Construction Specification for Structural Steel Buildings. Results

are summarised in Tables 4 and 5.

TRUSS DESIGN SUMMARY

Grade 300 & 350 MPa AS4100 1990

Table 4:MEMBER SECTION kg/m TOTAL LENGTH

mTOTAL WEIGHT

TONNES

Top Cord 310 UC 137 137 40 5.480

Bottom Cord 310 UC 96.8 96.8 40 3.872Webs 250 UC89.5

* (250 x 250 x 6 SHS)

89.5

(45)

87.3

(87.3)

7.814

(3.929)

Total Weight = 17.166(13.281)

*Figures in brackets correspond to the use of Grade 350 square

Hollow Sections as web members.

All other members are Grade 300.

Grade 690 Bisplate 80 AISC Spec.

Table 5:MEMBER SECTION kg/m TOTAL LENGTH

mTOTAL WEIGHT

TONNES

Top Cord tf = 10 d1 = 212tw = 8 bf = 256

55 40 2.200

Bottom Cord tf = 10 d1 = 212tw = 10 bf = 260

58 40 2.320

Webs tf = 8 d1 = 225tw = 6 bf = 256

43 87.3 3.754

Total Weight = 8.274

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EXAMPLE 5

REVISED DESIGN FOR A LARGE WATERSTORAGE TANK

A water storage tank was originally designed in AS3678-1990 Grade 250 and 350 steel plateto the following parameters:

Height = 14.25m

Diameter = 83.8m

Capacity = 70 MI

The stress calculations for the original design are as shown in Table 6.

Table 6::DEPTH (m) PRESSURE

(KPa)

HOOP

TENSION(KN/m)

PLATE YIELD

STRENGTH(MPa)

PLATE

THICKNESS(mm)

STRESS

(MPa)

2.85 28.5 1194 250 10 1195.70 57.0 2388 250 20 119

8.55 85.5 3582 250 25 14311.40 114.0 4777 350 28 17114.25 142.5 5971 350 36 166

A revised design incorporating 690 MPa yield strength Q & T steel plates in the lower two

sections produced the following set of values, shown in Table 7.

Table 7:

DEPTH (m) PRESSURE(KPa)

HOOPTENSION

(KN/m)

PLATE YIELDSTRENGTH

(MPa)

PLATETHICKNESS

(mm)

STRESS(MPa)

2.85 28.5 1194 250 10 1195.70 57.0 2388 250 20 1198.55 85.5 3582 250 20 17911.40 114.0 4777 690 20 23914.25 142.5 5971 690 20 298

As shown in Fig. 15, this revised design resulting in a saving of 25% in the mass of steelwork

in the walls of the tank.

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Please Note:Every care has been taken to ensure the accuracy of the design examples, however, the information is provided

as a guide only. A structural engineer should be consulted with respect to use for specific projects. Bisalloy doesnot warrant the suitability of the design examples for a particular purpose. The purchaser relies on its own skilland judgement as to the suitability of Bisalloy 80 (Bisplate 80) for its purpose.Bisalloy Steels shall not be liable for any loss or damage howsoever caused arising from the application of such

information.

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