fire testing and design of stainless steel structure

8/13/2019 Fire Testing and Design of Stainless Steel Structure

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Fire testing and design of

stainless steel structures

Presented by:-

Ajit Choudhary : 06010404

Chandu Namewar : 06010416

Hemant Kumar Bhaskar : 06010421

Kamal Kumar : 06010424

Nidhi Gupta : 04010419


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62-story First Interstate Bank Building fire in Los Angeles, 1988


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Things to be taken care of

Structural elements should possess anappropriate fire resistance to resist collapse.

Fire resisting partitioning walls and slabsshould resist flame penetration or excessivetemperature rise on their unexposed faces.

Any failure of the structure in the fire zone

should be gradual, involving large plastictype deformations.

The parts of the building away from the fire

should remain intact.


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Hp/A Concept

The heating rate of steel section in fire

depends upon section factor:

The perimeter of the steel exposed toflames-Hp(m)

The cross-sectional area of the section-

A(m2)


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Heavy sections (lower Hp/A)heat up more

slowly than light sections (higher Hp/A), a

heavy section will require less insulationthan a light section to achieve the same fire

resistance.


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Fire Resistance Time:

The temperature developed in the member

at the required fire resistance time is less

than the critical temperature necessary tocause failure.

Steel members will collapse in a fire whentheir temperature reaches a critical level.


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This critical temperature varies according to

a) The load conditions

b)The temperature distribution across thesection, which typically is in the range 500to 900C.

In a building in which a natural fire occursthe heating rate is also influenced by themember location


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Effect of Fire on Stainless

Steel Column and Beam


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Test procedure for column

Fire tests were carried out on 6 stainless steel columns.

Four tests were carried out by SCI on columns of 3.4 m length, threeof them were rectangular hollow section and the other one was of I-

section with both the ends fixed in all four columns. The other two tests were carried out by CTICM on square hollow

section columns with pinned end connections with overall length of3.9 m. A small eccentricity of loading of 5mm was applied on bothCTICM columns to induce the overall buckling failure mode .

In all the six tests the load was applied through hydraulic jacks and

the load was kept constant through out the test by allowing thecolumn to expand against load.

The columns were exposed to fire on all four sides.


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Measured material properties and C/S dimensions of tested column:


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Performance criteria for column

BS:476 part 20 and part 21 states that fire resistance of a

column is minimum of the time elapsed between

commencement of heating to the termination of heating or

until failure to meet the load bearing capacity criterionoccurs.

According to European standard EN 1363-1 (1999) a

column fails when :

(I ) Vertical contraction=h/100mm(II) Rate of vertical contraction=3h/1000mm/min

where h is initial column height in mm

Testing was stopped before the rate of vertical contraction

reached 3h/1000


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Column test results

All the six columns tested were failed by overall flexural

buckling.

I- section column also displayed evidences of localbuckling which was expected due to slender nature of the

constituent plate elements.

I-section columns showed significant lateral deflectionswere which was absent in other columns


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Column before and after Testing

.


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Test Procedure for Beams

Four fire tests on grade 1.4301 stainless steel

beams supporting a concrete slab were carried out.

SCI tested one RHS beam and one I-section beam

CTICM tested two I-section beams one with

simply supported at 1.9m and one continuous overthree support with two equal span of 2.37m


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Measured material properties and

C/S dimensions of tested beams


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Appliedloads and load ratios for testedbeams

In all cases, the load was applied via a concrete slab by means of a hydraulic

loading


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Temperature rise followed the standard time temp.relationship specified in EN 1991-1-2.

The beams were exposed to fire on three sides, with theconcrete slab on the top flange of the members.

All test were anisothermal.


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Location of thermocouples on 2001256.0 RHS beam


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Performance criteria for Beam

The criteria for failure of beam is taken as when:

deflection of L/20

rate of deflection = L^2/9000d mm/min

whichever exceeds first.where

L=clear span of beam (in mm)

d=distance from the top of the structural section to the bottom

of the design (in mm)*BS 476: Part 20 (1987)


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Beam test results

1. Critical temperature of bottom flange and fireresistance

2. All beams failed by in-plane (major axis) bending


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2001256.0 RHS beam after testing


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Numerical modeling:

The four columns and two beams tested by SCI were modeled using thenon-linear finite element package LUSAS, Version 13.1

Analysis was done in two steps:

In the first step, load was applied to the columnat room temperature, and in the second step, temperature was increasedfollowing the measured temperaturetime relationships until failure.

Column were fully fixed and beam were taken as simply supportedwith load applied on web.


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Results of the numerical analyses:Predicted (FE) critical temperature for column and beam


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Results of the numerical analyses:FE model gives the slightly lower value of critical

temperature This slight change is due neglecting the

enhanced strength in the corner regions of the cross-section

or the application of a uniform temperature development

along the length of the member, while in the test the

members were protected from direct heat application near

the supports

In the I section non uniform temperature across cross

section was introduced which resulted in same lateraldeflection behavior as in the test.


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Conclusion

It is concluded that the described finite element

models are capable of replicating the non-linear

large deflection response of structural stainless

steel members in fire.

Recommendation from given result are included

in euro code : part1.2

Improvements of 6% for column bucklingresistance and 14% for in plane bending resistance

over the current Euro code methods are achieved.


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References

http://www.corusconstruction.com

http://www.kuleuven.ac.be/bwk/materials/T

eaching/master/wg04b/l0400.htmhttp://911research.wtc7.net/talks/wtc/highri

sefires.htm

http://www.sciencedirect.com/http://www.jotun.no/
http://www.corusconstruction.com/http://www.kuleuven.ac.be/bwk/materials/Teaching/master/wg04b/l0400.htmhttp://www.kuleuven.ac.be/bwk/materials/Teaching/master/wg04b/l0400.htmhttp://911research.wtc7.net/talks/wtc/highrisefires.htmhttp://911research.wtc7.net/talks/wtc/highrisefires.htmhttp://www.sciencedirect.com/http://www.jotun.no/http://www.jotun.no/http://www.sciencedirect.com/http://911research.wtc7.net/talks/wtc/highrisefires.htmhttp://911research.wtc7.net/talks/wtc/highrisefires.htmhttp://www.kuleuven.ac.be/bwk/materials/Teaching/master/wg04b/l0400.htmhttp://www.kuleuven.ac.be/bwk/materials/Teaching/master/wg04b/l0400.htmhttp://www.corusconstruction.com/

fire testing and design of stainless steel structure

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