harbour cay condominium failuare

8/9/2019 Harbour Cay Condominium failuare

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School of Engineering And Technology

Structural Engineering

Forensic Engineering: Structural Evaluation and Retrofitting of S

CE 72.62

Instructor: Dr. Thanakorn Pheeraphan


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A Failure Case Study ofHarbour Cay Condominiuin Cocoa Beach, Florida

Presented By:

Chandani Chandra Neupane

ST 115587


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Overview

Background Objectives

Problem

Design and Construction

Investigation

Causes of Failure Prevention of the Failure

Conclusion

Lessons Learned


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During construction on March 27, 1981, Harbour Cay Conbuilding, collapsed during the placement of concrete foslab, the entire structure collapsed vertically.

11 workers were killed and 23 were injured.


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Objectives

To determine what causes the failure.

To suggest a way to prevent this type of failure.


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Problem

Figure : Before the Collapse (Image courtesy of National Bureau of Standards)


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Figure : After Collapse (Image courtesy of National Bureau of Standards)


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Figure : After Collapse (Image courtesy of National Bureau of Standards)


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Design and Construction

Five story flat plate structure of overall area 242ft x 58ft (74for residential use.

Stairwells at north ends and a structurally detached elevatothe east end.

The slabs spanned up to 6.75 and 8.43 m in two directions.

Interior columns 10x18 in. (254 x 457 mm)

Exterior columns 10x12 in. (254 x 305 mm)


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Compressive Strength Concrete = 27.6 MPa (4000 lb./in.2)

Reinforcing Steel - Deformed bars ASTM Grade 60.

Floor slab 8 in. (203 mm)

Story Height = 8- 8 (2.64 m)

At foundation level, columns were supported by pile caps co2 to 9 piles each.


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Construction Rate 1 floor per week (with each floor cast in twtwo days apart)

Roof Slab was to be cast in one continuous placement and r80% complete when the collapse occurred.

At the time of collapse, shores were in place on the fifth flooreshores were in place on the second, third, and fourth floo

Some of the reshores may have been removed by other tradis possible that not all were replaced. There were no reshorethe second floor.


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At the time of Collapse:

Occurred at approximately 3:00 pm, on March 27, 1981.

Based on workers statements,

As the workers were finishing the concrete, they heard a lo

that sounds like wood splitting.

It appears to have been triggered by a failure in fifth floorcenter portion of the building and propagate straightground.


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Figure : Location of Workers in Building at Time of the Collapse


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Investigation

NBS)

Site Investigation

Slab had broken away from the column at the slab columninterfaces, so the failure node appeared to be a punching shfailure type.

There was no evidence of overturning.

Measurement of outside dimension of column and slab sect

indicated conformity with structural drawing. Some columns in first story did not meet

the clear spacing requirement of ACI Code.

Figure: Field Me

L b t I ti ti


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Laboratory Investigations

Property Description

Quantities of ingredients Insufficient documentation

Comp. Strength of slab Core Satisfied with ACI Code for 27.6 MPa

Comp. Strength of Column Core Does not Satisfied with ACI Code

for fifth floor and have high variability.

Reinforcing steel Grade 60

Cement Content Lower (calculated value imprecise)

Tensile strength Characteristics- Normal Weight Concrete


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Fig: Compressive strength of drilled slab core Fig: Compressive strength of d


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Structural Analysis

At the time of collapse, gravity loads were only significant.

Finite Element Analysis for response measurement.


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Fig: Result of FEM analysis of fifth floor

Maximum shear


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Causes of Failure

Collapse of Harbour Cay Condominium (NBS findings)

Design errors + Construction errors

Design Errors

Slab thickness = 8 in.

Minimum slab thickness required by ACI code to resist punshear for the given loads, spans, and column sizes= 11 in.


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After the collapse, many of the columns remained standing wfloor slabs stacked on top of each other on the ground. This sfurther strong evidence of a punching shear failure.

StandingColumns


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A punching shear failure happens when the concrete floor slaand breaks away from its column connection.

Figure: Punching shear failure mechanism.


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The punching shear strength of a flat slab for a simplified caseinterior column is:

Vc = 4((fc)^(1/2))(b0)(d)

fc = 28-day cylinder compressive strength of the concrete

d = effective depth of slabb0 = the perimeter of the failure surface around the column mat distance d from the face of the column

For our case, max. punching shear force= 454 KN (102 kip)

Required D = 11 in. but provided d = 6.3 in. (D= 8 in.)


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The structural engineer was a retired NASA engineer who hired anretired NASA engineer to perform the calculations.

Overall, design errors included:

There were no calculations for deflection or minimum thickness

There were no calculations for punching shear or beam shear.


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There were no code checks for column reinforcement spacin

Calculations used Grade 40 steel whereas the structural draspecified Grade 60 steel.

Congested column reinforcement prevented concrete from around the steel bars and thus caused a deficient bond betwreinforcement and concrete.

Fig: Congested reinforcement


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Construction Errors

The top reinforcement steel was placed too low, whieffective slab depth and hence the punching shear capacity

The top reinforcement bars were placed on chairs that werewhich reduced the effective slab depth d from 6.3 in. to 5top cover was increased to 1 5/8 whereas it was designed t

Figure: Field Measurement of Chair heig


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Bottom slab bars were not placed through many columns and thslabs broke away from the columns where the slabs and column

In addition, some vertical reinforcement was found to have been

bent during fabrication.

Laboratory-cured test cylinders were used instead of field-curedcylinders to determine the actual strength of slabs prior to the stformwork.

Fig: Severely Bend Column Reinforceme


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Also

Many workers stated that, The spider-web-type cracks wereonce the flying forms were removed.

Most cracks were located near mid spans and around columsome were said to have extended 4 to 5 inches into the floo

Excessive deflections were reported once the forms were re

1 (44 mm) deflection was noted and the structural enginrequested to recheck the design, which he did, reporting bawas O.K.


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Workers also noted that some of the concrete from the onplant had a non-uniform consistency and was difficult to fin

One worker stated, Twenty-two years Ive been pouringand theyve never pulled the forms in two days like theyThey usually set there for a week or 10 days.

Shores and reshores initially supported the dead load

structure and transferred the loads to the ground. Once thbelow the first floor level were removed, the concrete sforced to carry the weight of the structure through theirshear capacity at the columns.


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Figure: Lateral sequence of flying form removal Figure: Assumed State of Construction a


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Prevention of the Failure

Punching shear failure could have been avoided by simpledesign checks for punching shear and minimum slab thickne

The most economical way to increase the punching shear cthe slabs would have been to increase the size of the coluwould also have created more space for casting concrete bevertical column reinforcement bars.

Increasing the thickness of the slab would have required mconcrete than increasing the size of the columns. Hence,the column sizes would have provided a more economica


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In addition,

Paying attention to warning signs of a potential collapse iswork on the building should have stopped after thedeflections and spider-web-type cracks had formed. Insteadthe building continued without properly addressing these obvof possible failure.


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Conclusion

The Harbour Cay Condominium collapse due to both impropand construction procedures.

A punching shear failure on the fifth floor initiated a progrescollapse of the entire structure.

Punching shear calculations were omitted by the structural when the structure was designed.


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Lessons Learned

Punching shear strength must be checked when designing flat slapunching shear is the most common mode of failure for concrete

Minimum depth of a flat slab much be checked to account for dand strength requirements.

It is crucial to place reinforcing bars directly within the column to prevent progressive collapse. This can be done at no addition

Proper design of formwork, shoring and reshoring plans and schand procedures for successful field construction control.


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Another important lesson is that

All work on a project must be stopped if warning signs offailure are encountered. Workers should evacuate theimmediately, and professional evaluation of the problemsperformed before work can be resumed.

We should also learn from Charges


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We should also learn from Charges

Harold Meeler (primary structural engineer), surrenderedand said he would never practice again. Meeler said he wou

maximum fine of $3,000 to avoid a hearing on the collastructure (Engineer 1981).

The other structural engineer also surrendered his licensnever practice in the state of Florida again.

The Florida Department of Professional Regulation charged

parties involved in the project with negligence. Additiocontractors were disciplined, and the architect was suspepracticing in Florida for ten years.


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We must remember that

Major failures in low-rise projects are still possible despite all knowledge available to avoid them.


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References

1. Delatte, Norbert J. Beyond Failure: Forensic Case Studies for C

Engineers, ASCE Press, 2009, p. 149-155.

2. Feld, Jacob and Kenneth Carper, K. Construction Failure. 2nd EWiley &Sons, New York, N. Y., 1997, p. 271-274.

3. Kaminetzky, D. Design and Construction Failures: Lessons fromInvestigations. McGraw-Hill, New York, N. Y., 1991, p. 72-78.

4. Lew, H. S. et al. Investigation of Construction Failure of HarboCondominium in Cocoa Beach, Florida. Rep., U.S. Dept. of ComBureau of Standards, S/N 003-003-02405-8, Washington, D. C.


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Thank You.

harbour cay condominium failuare

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