(part1/2)collapse of the hyatt regency walkways 1981

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Mechanics of Materials (CASE STUDY) Investigation & Analysis for the Collapse of the Kansas City Hyatt Regency Walkways (1981) Group Members (ME-05 B) Ali Faizan Wattoo NUST201305057BSMME Farhan Ellahi NUST201304475BSMME Muhammad Umair Qazi NUST201305329BSMME Gohar Shoukat NUST201305490BSMME Usama Zaid Malik NUST201304802BSMME Submitted to Dr. Irfan-Ul-Haq Dr. Amir Mubashir

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Page 1: (PART1/2)COLLAPSE OF THE HYATT REGENCY WALKWAYS 1981

Mechanics of Materials

(CASE STUDY)

Investigation & Analysis for the

Collapse of the Kansas City Hyatt Regency Walkways (1981)

Group Members (ME-05 B)

Ali Faizan Wattoo NUST201305057BSMME

Farhan Ellahi NUST201304475BSMME

Muhammad Umair Qazi NUST201305329BSMME

Gohar Shoukat NUST201305490BSMME

Usama Zaid Malik NUST201304802BSMME

Submitted to

Dr. Irfan-Ul-Haq

Dr. Amir Mubashir

Page 2: (PART1/2)COLLAPSE OF THE HYATT REGENCY WALKWAYS 1981

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CONTENTS

1) ABSTRACT ------------------------------------------------------------------------ 2

2) INTRODUCTION ----------------------------------------------------------------- 2

3) ANALYSIS & RESEARCH -------------------------------------------------------- 3 3.1- Theoretical Analysis 3

3.1.1 Given Data and Assumptions

3.1.2 Tensile stress in Hanger Rods

3.1.3 Transverse Shear Stress in Box Beam

3.1.4 Bending stress in Box beam

3.1.5 Bearing Stress on Nut Cross-section

3.1.6 Bearing Stress on Washer Cross-section

3.1.7 Welded Area Strength

3.2 Conclusion drawn from theoretical analysis 9

4) RESULTS & FINDINGS ----------------------------------------------------------- 10

5) DISCUSSION & CONCLUSION -------------------------------------------------- 10

6) FUTURE PROSPECTS ------------------------------------------------------------------ 11

7) REFRENCES ------------------------------------------------------------------------- 11

* APPENDIX (Attached with the report)

Finite Element Analsis of the walkway structure on SolidWorks

3

5

5

6

7

7

8

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1-ABSTRACT

In this research, an investigation of the collapse of two walkways in the Hyatt Regency Hotel

Kansas City (1981) has been carried out. The proposed design of the engineers was altered by

the fabricators due to the unavailability of required length of the rod. They replaced the single

long rod with two individual ones due to which there was a design load variation in the

supporting rods. After careful theoretical and mathematical analysis of the original design and

the fabricated design we found that the force distribution in one of the rods was doubled which

resulted in the failure of the beam-rod joint. We also found the original design also lacked

perfection. These findings were validated by simulating the original and the fabricated designs

through finite element analysis (FEA) on Solidworks. This report covers all the investigation and

analysis for both the designs.

2-INTRODUCTION

On July 17, 1981, during a dance party, the collapse of two walkways in the Hyatt Regency Hotel

in Kansas City resulted in the deaths of 114 human lives with a loss of millions of dollars. It was

one of the worst structural engineering failures in the history of United States.

The Hotel had lavish walkways connecting the two sides of the second floor and the fourth floor

which were designed by Jack D. Gillum and Associates, a structural design firm. Their original

proposed design consisted of a single continuous rod supporting both the walkways tying them

up to the roof truss. Due to difficulty in fabricating and setting up the single continuous rod the

fabricators altered the design for easy construction without being warned by the designers.

They replaced the one long rod with two individual shorter ones.

Investigations and forensic reports found the alteration in the original design as the major

cause of the incident. The engineering firm which proposed the design was held responsible. It

was supposed to point out the flaws and should’ve noticed the design alteration by the

fabricator. As a result the principal structural engineers lost their Missouri engineer’s licenses,

and the firm, Jack D.Gillum and Associates got dissolved.

This report covers the mathematical and structural analysis for both the designs to point out

the reason for this structural failure that consumed 114 precious lives.

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3-ANALYSIS & RESEARCH

3.1 THEORETICAL ANALYSIS

Here we will analyze the stresses produced as a result of redesign in hanging rod, nuts, beam

and welded area near the hanger rod and compare them with the allowable stresses to find out

the cause of failure.

For this we will proceed as follows:

3.1.1 Given Data and Assumptions

Pressure 90 kN

Material of beam A36 steel

Yield strength of A36 steel 250 MPa

Ultimate Tensile Strength of A36 steel 400 MPa

Shear Yield Strength of A36 Steel 0.5 × Sut = .5 × 400 = 200 MPa

Material of Bolts and Nuts A325

Yield strength of A325 234 MPa

Electrode used in weldings 620MPa

Ultimate Tensile Strength of A325 E60xx

Yield strength of E60xx 345 MPa

Ultimate Tensile Strength of E60xx 427MPa

Length of weld 2340mm

Type of weld between two C section Beams to

form a bonded Box Beam

Butt Welding

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Standard Specifications of C Beams (MC8x8.5)

Load supported by hanger rod = 2P = 180 kN as shown in figure below:

We will consider the cross-section of hanger rod to be 1¼ in. in diameter.

Assuming the same thread sizes for nuts and washers; using ANSI standards:

Max. Nut Width across Flat = bn = 2 in.

Max. Washer diameter = 3 in.

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3.1.2 Tensile stress in Hanger Rods

To calculate the tensile stress in the hanger rods consider following calculations:

A = 𝜋𝑑2

4 =

𝜋(1.25×0.0254)2

4 = 7.917 X 10-4 m2

σ= 𝑃

𝐴 =

180000

7.917×10−4 = 226 MPa < 234MPa

As it is less than the tensile strength of A36 steel so the stress in hanger rods is satisfactory.

3.1.3 Transverse Shear Stress in Box Beam

To calculate the shear stress in the box beam consider the following calculations:

𝐼 =2

12(95 × 10−3 × (7.9 × 10−3)3 + 2(. 095 × .0079) ×. 10552 +

2

12(. 00455 ×. 18743)

= 2.17 × 10−5 𝑚4

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𝑄𝑚𝑖𝑑−𝑝𝑜𝑖𝑛𝑡 = 𝛴𝑦′𝐴 = 2 × .04685 × .00455 × .09370 + .095 × .00790 × .09765

= 1.13 × 10−4 𝑚3

𝜏 =𝑉𝑄

𝐼𝑡=

180000 × 1.13 × 10−4

2.17 × 10−5 × (.00455 × 2)= 103𝑀𝑃𝑎 ≪ 200𝑀𝑃𝑎

Where

V : Shear Force

Q : Static Area above the axis about which we measure the thickness of the cross-section

I : Moment of Inertia about the Neutral Axis

t : Thickness

3.1.4 Bending stress in Box beam:

We will now be taking a look at bending moment in the box – beam. We have the following

cross-section.

A free body diagram of a section of the beam is as follows.

Maximum shear force will 180 kN, anyplace between the two opposing forces.

Maximum bending moment will lie infinitely close to the 90kN force, with magnitude

M =180,000 x 0.1 = 18,000 Nm

For cross section properties:

w = 9.5 cm = 0.095 m

d = 20 cm = 0.200 m

Maximum radius (at the corners) = 0.100 𝑚

Bending stress = 𝜎 = 𝑀𝑐

𝐼=

18,000 ×0.100

2.17×10−5 = 82.9 𝑀𝑃𝑎 ≪ 250 𝑀𝑃𝑎

This is much less than the yield strength of the material, so it is safe.

180 kN

90 kN

0.100 m

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3.1.5 Bearing Stress on Nut Cross-section:

In the redesign of walkway supports, the nut and washers on the fourth floor walkway beam

supports double the load as compared to original design i.e.

F = 90 kN X 2 = 180 kN

Cross-sectional Area of Nut = A = 3√3𝑠2

2 -

𝜋𝑑2

4

Where, s = 𝑏𝑛

√3 =

2

√3

d = 1¼ in.

Thus we get:

A = 2.237 in2 = 2.237 x 0.02542 m2

A = 1.443 x 10-3 m2

σb = 𝐹

𝐴 =

180000

1.44×10−3 = 125 MPa < 234 MPa

This value is less than the tensile strength of A325 steel so value of stress is satisfactory.

3.1.6 Bearing Stress on Washer Cross-section:

To calculate the bearing stress on washer cross-section consider following calculations:

Here F = 180 kN

Cross-sectional area of washer = A = 𝜋

4(𝑑2

2 − 𝑑12) =

𝜋

4(32 − 1.252)

= 5.84 in2 = 3.77 x 10-3 m2

Bearing Stress σb on washer cross section = 𝐹

𝐴 =

180000

3.77×10−3 = 47.74 MPa

This value is considerably less than the tensile strength of A325 steel so stress on

washer didn’t cause failure.

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3.1.7 Welded Area Strength:

The load supported by nut and washer is acting on the welds as a reaction i.e.F = 180 kN

We consider that butt welds were used to join the two MC 8x8.5 beams to form box beams.

As discussed above:

Max. Nut Width across Flat = 2 in.

Max. Washer diameter = 3 in.

Since, the weld extends to about 2300mm, it is a very long welded region, and the force is

localized, its immediate affects will also be localized. By Saint Venant's Principle we assume any

localized effects of a localized force to be contained within 2-3 times the thickness ‘t’ of the

beam", so that makes, 2.5 x .3 = 0.75 in.

This distance is measured from the ends of the nut, which has a diameter of 2 inch, so in total,

it makes a distance of: 2 + 2 (0.75) = 3.5. So,

Effective weld length L = 3.5 in.

For MC 8x8.5 box beam of A-36 steel material,

We find out its toe thickness to be t = 0.311 in.

Thus taking effective weld throat to be equal to toe

thickness i.e.

h = 0.311 in.

Butt weld area under consideration:

A = h x l

=3.5 in. x 0.311 in

=1.0885 in2

=1.0885 x (0.0254 m) 2 = 7.023 x 10-4 m2

For butt weld, shear stress is given by following equation:

τ = 𝐹

ℎ𝑙

= 180 𝑘𝑁

7.023 𝑥 10−4

= 180000

7.023 𝑥 10−4

τ = 256.3 MPa

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For butt weld, the allowable shear stress is given by:

τall = 0.30 Sut

Taking E60XX to be the electrode material:

Sut = 427 MPa

So τall = 0.30 (427)

= 128.1MPa

Thus, the shear stress acting is appreciably greater than allowable shear stress. Hence, it is

concluded that failure occurred due to the breaking of welds in the vicinity of nuts

and washers where the hanger rods were bolted.

It is to be noted that these values are calculated on maximum constraints. When we use 90

kN force (which is the case of single hanger rod), the stress comes out to be 128.1 MPa on

same maximum constraints. This value is equal to the allowable stress. But if the weld

length and throat are less than considered say:

l = 3.25 in.

h = 0.25 in.

So, τ comes out to be 171.69 MPa for 90 kN force i.e. it exceeds the limit.

Hence, the original design can also not be considered safe.

*See appendices for complete Finite Element Analysis (FEA) of the walkway structure

3.2 Conclusion drawn from theoretical analysis

- Hanger Rods bent Under the Impact of Fall

A = 5.24 x 10-4

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4-RESULTS & FINDINGS

From the above Analysis of the walkway structure, we found following results:

The Box beam fabricated by welding two C Beams, proves to be stable under Transverse, Bending and Normal Stresses.

Forces exceed their design load only on the contact surface between the nut of the hanger rod and the Box Beam.

The load applicable on the contact area becomes twice the maximum design load.

Structural analysis of the entire beam indicates failure at the joint of the top floor.

The weld is ripped apart by the shearing force induced by the nut of the hanger rod.

Weld Metal strength was unsatisfactory.

This increases the Bearing Stress causing the Beam to bend at its welded edges

producing plastic deformation and the nut to go through it.

The original design too was marginally safe.

The factor of safety for the weld group was equal to 1.

5-DISCUSSION & CONCLUSION

The structural analysis was conducted using Simplistic theory of Mechanics of Materials and

verified by Finite Element Analysis conducted on SolidWorks. Both the methods indicated that

the joint connecting the beam and the hanger rod was the failing point. However, weak joint

was not the cause of failure. The new design induced shearing forces and moments which

caused the loading on the top floor to almost double. The structure with a factor of safety

marginally over 1 could not withstand any further loading which triggered its collapse.

The sequence of events as indicated by the debris assessment could be that the weld failure

created a gap between the two C beams. This caused a reduction in area in contact with the nut

which increased the bearing stress several folds. Support structures must transfer their loading

to the ground instead of other critical members of the structure. When the member is

experiencing maximum design load, any further load or moment transmitted to it from

members shedding their load on it will cause it to exceed the design load and hence, fail.

Another important aspect mentioned by the report is the miscommunication between the

designers and constructors and the lack of quality control. Clearly, this episode only further

enhances the importance of a well-coordinated and controlled engineering approach.

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A better design would have been to use Columns or Pillars as support structures instead of

hanging rods. Failure under compressive loading is unlikely compared to tensile loading.

The essential problem was a lack of proper communication between

the design engineers (Jack D. Gillum and Associates) and the manufacturers (Havens Steel).

6-FUTURE PROSPECTS

Transverse Shear Stress and Bending Stress Distribution Mapping over the Box Beam

cross Section.

Making assumptions more realistic.

Increase Accuracy of FEA of model by improving boundary conditions.

Fatigue Analysis to observe the affect of fatigue on the bridge.

Detailed alternative design proposal with Mathematical Reasoning and FEA for analysis.

Due to Limited number of pages, for further analysis and discussions, please refer to the

Appendix added.

7-REFERENCES

1. MECHANICS OF MATERIALS R. C. HIBBELER 9th EDITION, Publisher: Pearson Prentice Hall

(2014c)

2. *Marshall, Richard Detal. (May 1982). Investigation of the Kansas City Hyatt Regency

walkways collapse. Building Science Series 143. U.S. Dept. of Commerce, National Bureau of

Standards. Retrieved 2012-03-13

3. National Bureau of Standards (May 1982). "Investigation of the Kansas City Hyatt

Regency Walkways Collapse" (PDF). US Department of Commerce. Retrieved 2011-

01-26.

.

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THE END