1

Investigation into the Progressive Collapse

of a Rack Supported Structure

Lomira, Wisconsin

July 12, 2002

(Photograph of completed structure taken by Quad Graphics)

2

EXECUTIVE SUMMARY

On July 12, 2002 at approximately 9:29 PM the Quad Graphics Automated Storage and Retrieval

System (ASRS) high bay rack structure in Lomira, Wisconsin collapsed resulting in the death of

a 22 year old male employee. The collapse of the structure resulted in a fire, which burned for

nearly two weeks. The Quad Graphics plant produces printed material such as catalogs and color

newspaper supplements. The ASRS structure was designed to store materials that had been

partially completed, along with materials ready for shipping or mailing. At the time of the

collapse the building was approximately 80% loaded with materials. The ASRS structure

construction is identified as a “rack supported structure.” Essentially, the rack structure is

installed and a roof and exterior skin are attached to the rack structure to form the building. The

rack structure provides the structural elements of the building. Within a historical perspective

this type of structure is relatively new in design and application.

This document is the culmination of the investigation originated by the Wisconsin Department of

Commerce, Division of Safety and Buildings and concluded after the Division closed the

investigation and issued a violation report. The Division of Safety and Buildings has regulatory

authority over the construction and use of public buildings and places of employment within the

state of Wisconsin. On July 15, 2002 the Division organized a team of investigators to:

1) Determine if any codes were violated in the construction of the facility.

2) Determine if the design of the building was done in accordance with the requirements

of the codes and applicable standards.

The investigation team consisted of an architect, a professional engineer with expertise in

structural requirements, a professional engineer with expertise in building code requirements,

and a management representative with expertise in fire protection engineering and investigation.

3

ANALYSIS OF COLLAPSE CAUSATION

In order to determine the effectiveness of the Wisconsin Commercial Building Code the cause or

causes that may have attributed to the collapse had to be investigated. This report examines

probable causes for the collapse. This report does not establish absolute certainty as to the cause

of the collapse.

METHOD OF ANALYSIS

The Lomira collapse is considered to be a unwitnessed collapse. The building is normally

unoccupied and robotic cranes conduct work activities. At the time of the event there were two

workers present at the south conveyor area, and one worker at the north conveyor area.

Eyewitness accounts of the collapse are limited to those areas, which are visible from the north

and south ends of the building in the low bay areas.

Photograph of the North Low Bay area at the approximate location of the witness.

(Photograph by Commerce investigator.)

Because the actual point of

origin was unwitnessed this

evaluation can only provide

probabilistic analysis of the

origin based on available

information. In most

catastrophic events a single

cause is rare, and in most

cases a multitude of causes

culminates to form the result.

In an effort to identify the

cause of the collapse the

investigation and this report

has been developed using the

probabilistic analysis method.

Probabilities are assessed for

each key element associated

with failure modes. The analysis begins with defining the four major categories associated with

building failure, which include the design of the structure, the construction of the structure, the

operation or use of the structure, and any other external forces such as weather, foreign object

damage, etc. Given that the building did collapse the total probability for failure was 100%.

The four major categories begin with an equivalent probability for failure of 25%. The

probabilities are then adjusted up or down based on data assessments. During the initial phase of

the investigations there no identified probabilities for external events such as weather, foreign

objects, missile impact, or explosion. Based upon the determination that the external category

had a small probability factor the remaining categories are adjusted. Probabilities were adjusted

to reflect that three primary categories (design, construction and operation) remained equivalent

4

pending additional information. These categories were then reassessed to greater than 30% with

the external category lowered to less than 10%. The initial assessment of probabilities is shown

in Table 1.

Table 1 – Initial Assessment of Probabilities

Category Predominant Issues

Building Design

>30 %

Defective or Inadequate Design

Building

Construction

>30%

Defective Fabrication or Construction

Building Operation

>30%

Internal Event (crane accident, excessive loads, etc.)

External

<10%

Event (wind, snow, tornado, missile, etc.)

As discussed previously, single causes rarely result in a catastrophic event. This analysis further

separates the event into an “incident precipitators” and “progressive collapse factors.” In

comparison to a house of cards, the collapse begins at a single point where structural integrity is

lost. The loads begin to shift and the collapse progresses through the structure until one of two

events occurs, a total collapse or a portion of the structure resists and results in a partial collapse.

The category of external events was developed using historic information. Items in the category

were then reduced as probabilities due to the lack of any evidence that these forces existed.

In this method of analysis there is an inherent difficulty in reaching absolute certainty, with

regard to the conclusions. Mathematical and scientific modeling for this specific type of

structural event was not available during the investigation. Scientific modeling was gathered

from similar or related types of events as noted in the report.

The evaluation of the causes begins with an understanding of the building type and method of

construction.

5

BUILDING TYPE AND METHOD OF CONSTRUCTION

RACK SUPPORTED STRUCTURES

(Photographs taken during construction by Quad Graphics)

The pictures above are of the Lomira rack supported structure under construction. Photos from

top left to bottom right – first rack modules; installation of roof modules; east side exterior wall

covering; west side wall covering and precast concrete installation. In this form of construction

the rack system forms the structural elements. The rack structure is installed in modules. Each

module is aligned, plumbed and squared. After a significant number of modules are installed the

roofing structure is installed to provide cross aisle support, a cross aisle support is known as a

“cross aisle tie” (CAT). Support along the length of the module is provided by down aisle

supports. This type of a support is known as a “down aisle tie” (DAT).

The Quad Graphics ASRS structure was 763 feet long, 88 feet wide and 103 feet tall to the top of

the rack frames. The total height including roof structure was 106 feet.

6

The ASRS structure was adjacent to a north low bay area, a south low bay area and a corridor

low bay area on the east side (depiction above). The ASRS structure high bay area was

constructed by the Rack Structures Incorporated, the rack manufacturer. A construction division

of Quad Graphics and their sub-contractors constructed the low bay areas. The low bays were

constructed using standard beam and column construction. The north low bay area included the

shipping docks and was used as the primary area for handling finished product.

Photograph of North Low Bay looking towards conveyors to cranes. (Photograph taken by Quad

Graphics.)

The south low bay area was

predominately used for

handling partially

completed materials. The

north and south ends of the

high bay had “run out”

areas for the cranes. The

run out areas were open to

the full height of the

structure. The run out areas

provided space for the

cranes to operate near the

conveyor areas. The south

run out area included a

catwalk for maintenance on

the cranes. The south run

out area was longer than the north run out area due to the catwalk maintenance platforms.

Six aisles divided the high bay; each aisle had a robotic crane. The cranes were designed to

move full distance of the aisle. On each side of the aisle the racks storage cells were single deep.

The exterior racks on the east and west side were single wide, the interior racks were double

wide. Along the north – south axis the rack structures were identified as rows and aisles. Along

the east – west axis the rack structures were known as bays. There were a total of 136 bays, with

Bay 1 located at the south end, and Bay 136 located at the north end. Each rack had 19 storage

cells from floor to roof line. Each crane had access to 5,168 cells. The total number of cells in

the structure was 31,008. Cells near the run out areas were left open to allow employees access

to the cranes, which slightly reduced the total number of cells available to the cranes.

7

Photograph of Crane “B” and Aisle 2. Cranes A, C and D also shown.

(Photograph taken by Quad Graphics.)

At the time of the collapse Quad Graphics personnel had been in the process of loading pallets

into the ASRS system. The final cell loading is indicated in the table below.

Final Cell Loads as of July 12, 2002

Aisle Full Cells Empty Cells Total Cells Percent Full

1 5103 63 5166 98.78

2 5023 143 5166 97.23

3 4336 826 5162 84.00

4 3983 1185 5168 77.07

5 3362 1803 5165 65.09

6 3172 1994 5166 61.40

Totals 24979 6014 30993 80.60

8

RACK FRAME STRUCTURE

The rack structure was composed of rack frames. Each frame had two upright sections of cold

rolled steel. The uprights were constructed using heavier gauge steel for the lower half, and

thinner gauge steel section for the upper half. The two sections were spliced using welded

plates. Two uprights were then connected by a “Z” brace welded into place forming the rack

frame. Shelf units composed of “load

arms” and “load rails” were welded to the

rack frame. The shelf units were designed

to cantilever from the rack frame to support

pallet loads.

Photograph of a north end rack module

suspended by a crane during installation.

Note the down aisle ties, lateral bracing and

run out area without cells. (Photograph

taken by Quad Graphics)

Rack frames connected together formed rack modules. On each side of a rack row there were

nine down aisle ties, for a total of eighteen for each rack row. Cross aisle ties were only present

at the roof structure.

With an understanding of the building type and construction the collapse of the building was

then evaluated.

9

EVALUATION OF THE COLLAPSE

COLLAPSE SCENARIO

Collapse scenarios for rack systems generally fall into two main categories, localized (confined)

and progressive. The Lomira collapse was a progressive collapse. The eyewitnesses identified

the movement of the collapse from the east exterior rack (Row A) to the west in a domino effect.

Photograph of southeast section of the building. Exterior rack structure, cross aisle roof

structure, some remaining exterior wall covering. (Photograph taken by Commerce staff on July

15, 2002.)

The movement of the rack structure and the nature of the amount of damage would indicate a

progressive collapse. The movement of a progressive collapse begins with an initiating event,

which causes shifting of loads and subsequent failures. Load shifting from one element to

another would have a tendency to accelerate due to the addition of loads as each structural

member fails. Load shifting from structural elements would occur in a 360 direction with the

exception of the exterior racks. The exterior racks along the east and west walls would have load

shifting in a 180 direction. Acceleration along the exterior wall would be greater than an

interior rack row due to the limitation of elements by direction to accept loads. The acceleration

10

along the exterior rack would also be impacted by the width to height relationship. Interior racks

were double deep and exterior racks were single deep.

This depiction is an elliptical model based on a progressive collapse with an acceleration rate,

which is greater along the exterior wall than through the interior rack structure. It should be

noted that observers located in relation to the dots saw the movement of the east exterior rack

prior to movement of the interior racks.

View from the west side of the North Low Bay. Left side of photograph is the east exterior wall.

View is from the general area of the witness at the north end.

(Photograph taken by Commerce investigator)

11

COLLAPSE PROGRESSION

To define the collapse progression, the status of the building is evaluated in a reverse

chronological order. The ASRS building was completely razed within 48 hours of the incident

initiation.

The image below, left is from the Milwaukee Journal Sentinel from the night of the July 12,

2002; the image below right was taken on July 17, 2002 at 8:11 AM, by the investigation team.

The area shown is in the south end of the ASRS adjacent to the low bay conveyor area. The

south end of the ASRS was an area of total collapse.

The south end of the building is defined as the area south of the underground pedestrian tunnel,

which was located ~288 feet north of the south exterior wall of the ASRS high bay. Initial

observations by responders to the site indicated that this area was completely collapsed.

Responders also noted the area north of the pedestrian tunnel was damaged but standing. The

individual killed by the collapse was a car parked near the pedestrian tunnel.

Fire department responders during the initial hours after the collapse reported that the structure

north of the pedestrian tunnel stood until sometime between 12:30 and 1:00 AM on the morning

of July 13, 2002. At approximately midnight the fire that had been burning in the south area

progressed into the north end and a flashover occurred. The fire further weakened the damaged

north end resulting in the total collapse of building except for an area on the west exterior wall.

The area that did not collapse extended from ~446 feet north of the south exterior high bay wall

to a point ~588 feet north along the wall. The free standing area extended into the building ~36

feet and probably included bays 78 – 106 along rows E, F, and G (aisles 4, 5 and 6). The

freestanding area was pulled down by cranes at the direction of the fire department to prevent

injury due to the possibility of further collapse. It should be noted that aisle 4 was 77% full, aisle

5 was 65% full and aisle 6 was 61% full. It is highly likely that this area of the building was

12

resistant to collapse due to the decreased loads. Rack structural elements would have been able

to carry loads shifted during the collapse. It should also be noted that there were additional

bracing posts along east – west axis just north and south of the freestanding area.

(The Milwaukee Journal Sentinel took the photograph below on July 13, 2002.)

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1

In the photograph arrow #1 indicates the location of the south low bay, #2 indicates the location

of the freestanding area, and #3 indicates the north low bay.

The area north of the freestanding section along the west exterior wall was reported by witnesses

as being pushed out along the base of the concrete precast walls, and buckled near the top

northwest corner of the building. The east exterior wall in an area across and just north of the

freestanding area was described by witnesses as leaning towards the east, with some of the

exterior wall covering missing.

13

The collapse at the Lomira plant began as a partial collapse, and then due to the subsequent fire

resulted in a near total collapse. The total collapse of the structure did not occur within the first

few minutes of the event. The building had four areas, which are defined as the area of origin, an

area of total collapse, an area of partial collapse, and an area of resistance to collapse.

The area depicted in shaded gray is approximately the area of the building, which exhibited

internal collapse, and some external damage. This area of partial collapse was further weakened

by the fire and completely collapsed around 12:30 AM on July 13, 2002.

The “X” is the location of the Crane A, the “P” is the approximate location of the witness in the

north low bay. The “PP” is the approximate location of the two witnesses in the south low bay.

The two black dots indicate the approximate locations of the sprinkler system supply lines to the

rack structure.

During the collapse Crane A was toppled severing the electrical connection in the base of the

crane. The Crane Trace Report indicates loss of contact with Crane A at 21:30 hours (July 12,

2002). The cranes were polled by the computer system every 500 milliseconds. At 21:29 the

fire alarm system recorded a fire pump start. The fire pump started due to a decrease in water

pressure. Because water is essentially non-compressible the rapid drop in water pressure

(exceeding the capability of the jockey pump) was probably due to the severing of one or more

of the branch lines or one of the main supply lines. The time differences between the fire alarm

system and the trace report computer could not be verified. A lighting strike caused a outage and

reset of the fire alarm system at a time period after the collapse and prior to the collection of

data. Time sequencing based on information available would seem to indicate that the fire pump

started before Crane A was toppled. This sequencing would indicate that given the speed and

acceleration of the collapse a sprinkler line at some distance north of Crane A was the first

sprinkler line severed.

Interviews of the witnesses indicated that the individuals in the south end low bay reported a

loud noise followed by the sound of thunder moving towards them. Looking towards Crane “A”

the witnesses reported the movement of Row A1 (east exterior rack), progressing towards the

west. The witness at the north low bay reported banging sounds, or pinging, something like a

metal drum being hit. The banging increased to a roar. At that time the witness identified the

movement of Row A1 progressing towards the west. Witness statements were focused on Row

A1, with a progressing west. The noises heard by the witness in the north end of the building

could be related to welds or bolt connections breaking. The thundering sound is likely related to

an acceleration of cells collapsing in downward direction.

14

The information garnered from the witnesses’ lead the investigation team towards the probability

that the initial point of origin was along the east wall and closer to the north end than the south.

The pinging sound followed by an increase in noise at the north end would be more indicative of

the point of origin than the thundering sound heard at the south end. This theory may be

supported by the time sequencing between the fire pump alarm and the Crane Trace Report.

Photograph of area along the east side, south of the North Low Bay. This section of the rack had

indications of compressed buckling of uprights above the splice and just above the base plates.

Debris in this area slumped on to the East Low Bay and the adjoining roof. (Photograph by

Commerce investigator.)

Photograph of slumped

rack structure on eastside,

shows debris accumulation

on adjoining East Low Bay

roof.

15

EVALUATION OF PROBABLE COLLAPSE CAUSES

LOAD SHIFTING

Load shifting is the action that occurs when a structural member fails to support all or some of

the loads and the loads are completely or partially shifted to another structural member. The

most prominent examples of load shifting in recent history include the collapse of the World

Trade Center, and the Murray building in Oklahoma City. Load shifting can occur in macro or

micro scale. Micro shifts in loads can occur without obvious indicators, or a load shift can result

in deformations of the structural member.

The progression in the collapse of the Quad Graphics ASRS Building appears to be due in part to

load shifting.

In a paper by J. R. Gilmour and K S. Virdi the following description of load shifting was

presented:

1“Improvements in structural analysis and knowledge of materials over the last 100 years

have led engineers to build structures that are structurally more efficient than in the past.

This leads increasingly to stretching constituent materials to the limit of their operational

envelope. The result is that modern structures lack the strength reserve that was inherent

in older structures engineered by empirical knowledge and instinct, and hence thought

must be given as to how they will perform when subjected to abnormal loads. A

progressive collapse occurs when a structure has its loading pattern or boundary

conditions changed such that elements within the structure are loaded beyond their

capacity and fail. The residual structure is forced to seek alternative load paths in order

to redistribute the loads applied to it. As a result other elements may fail causing further

load redistribution. The process will continue until the structure can find equilibrium

either by shedding load as a by-product of elements failing or by finding stable

alternative load paths.”

The collapse progression and effect of load shifting in the World Trade Center were presented in

an article in the Member Journal of The Minerals, Metals & Materials Society by Thomas W.

Eagar, and Christopher Musso,

2“Nearly every large building has a redundant design that allows for loss of one primary

structural member, such as a column. However, when multiple members fail, the shifting

loads eventually overstress the adjacent members and the collapse occurs like a row of

dominoes falling down.”

16

A technical article published by Gross and Associates on micro-shifting states the following:

3“Over the past several years there has been a notable rise in the number of rack system

collapses, although seismic activity is rarely the cause of such structural failure. It is

much more likely that a series of pre-existing (man-made) conditions caused the rack

structure to be inherently unstable.

Forensic engineers conclude that lift truck damage, overloading, or inadequately

engineered systems account for nearly all rack failures. One or more of the above factors

can cause the center of gravity to shift away from the center of the rack column and

compromise structural integrity. As the center of gravity shifts further from the column

center (at the baseplate), this "offset" subjects the column to a bending moment, which

creates horizontal force on the column pushing it towards the load center. The column

deforms and the load center continues to shift further away from the column center,

creating an even greater moment. This cycle (called micro- shifting) continues until the

rack structure becomes so unstable that a relatively minor impact may trigger a major

collapse.”

In the 1994 edition of the Uniform Building Code, Table 16-B Special Loads, includes the

following note regarding rack storage.

“Vertical members of storage racks shall be protected from impact forces of operating

equipment, or racks shall be designed so that failure of one vertical member will not

cause collapse of more than the bay or bays directly supported by that member.”

HEIGHT AND WIDTH RELATIONSHIPS

In an article published by Rack Manufacturers Institute the following information was provided

on single row racks, height and width, and considerations with building interaction.

4“BUILDINGS USED TO BRACE RACKS

Wherever the racks have been tied to the building in any way, be absolutely certain the

building has been checked for its adequacy to resist these applied forces. I have seen

installations where a leaning rack was “braced” to the roof by welding an angle from the

top of the rack post to the bottom chord of the roof joist. This may be fine for the rack

except that when it snows, the roof tries to sag and the rack post ends up supporting the

roof as well as the pallet loads. Just because a rack is tied to a wall does not guarantee the

wall is capable of sustaining the applied loads.

Generally, single row racks create the major concern. Some specifications require

additional support for racks where the height to depth ration is greater than 6 to 1. The

height is the height to the top of the topmost load and the depth is the depth of the upright

frame. Stability requirements are a function of the imposed lateral loads. My own

judgment would be not to require additional support, including floor anchoring, for

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Cross Aisle

Tie (CAT)

Down Aisle

Tie (DAT)

structures whose ratio is 6:1 when the height is to the topmost beam. From 6:1 to 8:1 is a

matter of judgment based upon the overall conditions and loads. Above 8:1 must be

either floor-anchored, wall-tied, or top-tied across the aisle. When racks are top-tied, post

must line up so that the tie runs from post to post. Otherwise the top assembly is too

flexible. “

Photograph of collapsed rack section showing top of rack frame to roof section. (Photograph by

Commerce investigator)

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MECHANISMS OF COLLAPSE

In a study conducted by 5R.E. McConnel, Phd, CEng, MICE; and S.J. Kelly, Phd, the progressive

collapse of warehouse racks systems was evaluated by the use of computer models and half-scale

tests. The following report was presented and published in the periodical The Structural

Engineer, vol 61A, No. 11, Nov 1983 (figures are copied from the report):

“Mechanisms of Collapse

Taken together, the results of joint pull-out tests, computer program, and half-scale

collapse tests, lead to the following observations.

(i) After bottom leg failure (the most common

form of collapse initiation) a mechanism forms in

the two bays supported by the failed leg as

shown in Fig 5. This mechanism will hereafter

as the ‘joint rotation mechanism.’

(ii) The progress of the joint rotation mechanism

is partly retarded by the bracing connecting the

failed leg to the leg behind it.

(iii) The bracing in most racking systems is

incapable of transferring the load originally

carried by the failed leg to the rear leg; hence the

bracing fails.

(iv) The joint rotation mechanism can develop

only by drawing in the adjacent bays, and this

motion is resisted by the inertial damping and

structural resistance of the adjacent bays. Axial

forces are thus induced in the inclined beams.

Confined collapse

The pull out strength of the joints determines

whether the inclined beams in the joint rotation

mechanism separate from the ‘stationary’

adjacent bays. If separation occurs, a confined

collapse will result, as shown in Fig 6.

Progressive collapse

Alternately, if the beams do not separate, there

are two possible sequences of collapse. Which

of these is followed will depend on where the

initiation point is in relation to the ends of the

rack.

(1) If the initiation point is relatively close to a free end (within four or five bays),

and noting that significant inertial resistance of the adjacent bays occurs only in

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the early stages of the sequence, the major resistance to the progress of the joint

rotation mechanism is the sway resistance of the bottom columns to the free end.

If the axial force in the bottom beam line is greater than the total sway resistance

of these bottom columns, a ‘bottom leg sway mechanism’ will result, as shown in

Fig 7.

(2) If collapse initiation is far from the free end, e.g. in the middle of a long rack,

the total sway resistance of all the columns either side of the failed leg is likely to

be high. Hence a bottom leg sway mechanism will not form.

An analysis of the forces in joint A in Fig 8 shows that the load lost by the

failed leg is transferred to the legs immediately adjacent to the joint rotation

mechanism. If the axial strength of these bottom columns is exceeded, the legs

must fail. Consequently, two ‘half’ joint rotation mechanisms are set up in

adjacent bays, as shown in Fig 9. Further bottom leg failures can be envisaged as

successive leg failures result from overloads, hence a ‘successive leg buckling

mechanism’ is set up.

Both the bottom leg sway and successive leg buckling mechanisms contain

several bottom leg failures in only the front frame, i.e. in the legs nearest the aisle.

An obvious consequence of this is rigid body rotation of the rack into the aisle, as

shown in Fig 10. A domino-type failure of the racks across the aisles of the

warehouse can then follow. This is the most likely mechanism of progressive

collapse that involves a complete racking installation.”

20

21

Compressed

buckling at

baseplate – aisle

side.

Photographs of rack frame uprights located in the north end of the building east side exterior

rack row. This rack row was a single deep rack structure.

(Photographs by

Commerce

Investigator)

Compression

buckling located

above splice on

aisle side upright.

Splice

Buckle of

upright

located above

splice

Failed

brace

22

The photograph below was taken of a rack frame upright, which was located along the east

exterior wall, single deep row rack. This upright was located nearer to the south end then

photographs shown previously.

(Photographs by Commerce investigator)

Compressed buckling

of non-aisle side

upright located above

splice - specific

distance undetermined.

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STRUCTURAL WELDING

Documents reviewed by the investigators indicated that weld failures were known to have

existed from the construction of the first rack frame. The lack of weld quality was due in part to

the lack of certification of welders, the lack of procedures and quality assurance. Welding

problems existed in materials due to the inadequacy of seam welds in cold-formed steel tube

stock.

The design professionals including the supervisory design professional reviewed the welding

issues and provided updated engineering data to support continued construction of the facility.

Welding issue were never resolve throughout the construction process as evidenced by

communications between the parties. A weld failure during the loading phase of the project

resulted in visual examination, engineering evaluation and planning for weld replacement. The

loading of the racks did not cease, nor was product removed from the rack based on engineering

assessments of the extent of the problem.

SCOPE OF THE GENERAL CONTRACTOR

At the outset of the project the owner of the site and the contractors set up an unusual working

relationship. The owner contracted the company responsible for the automated cranes as the

general contractor, while retaining responsibility for elements of the building not specifically

associated with the rack structure such as the footing and foundation. This is an important

element of design considering that the site had to be elevated to meet the same floor level as the

rest of the graphics plant. Backfilling of the site and foundation work was accomplished by the

owner. The owner had a nationally renowned reputation for super level concrete design and

construction. The level of the concrete and shifting of the soils became a discussion during the

construction due to shifting of ceiling to rack elements and placement of upright spacers and the

floor level. During the investigation these issues were discussed as they related to load shifting

due differences rack height and roof leveling.

Another element that became an issue during load testing and as it related to the investigation

was the operation of the loading system between the forklifts and the automated racking system.

The conveyer system installed by the owner resulted in load shifting from the front of a rack cell

to the back of the rack cell. Analysis during this phase of the project by the engineering team

determined that a load shift to the back of the cell within the rack did not result in a load

problem. However, this condition was not thoroughly evaluated with respect to the single rack

rows located at the east and west walls. The rack structures at the east and west walls were

designed and evaluated to have the majority of the weight placed at the aisle side of the rack

rather than at the wall side (back of the cell) of the rack. This issue may have been a contributor

to the increase of load and resultant load shift.

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The table indicates adjustments in the probability factors based on design issues in consideration

of the evaluation by the design professionals regarding construction defects.

Category Predominant Issues Incident Initiators Catastrophic Factors

Building Design

>60 %

Defective or Inadequate

Design

Code Compliance

Peer Documents –

Standards

Load Calculation

Safety Factors

Load Calculation –

Allowable Stress Design

with Impact Load of

10%; see RMI/ANSI

standard for load

calculations and 25%

load impact requirement.

Load Arm to Load Rail

weld correction analysis

and mechanical repair.

Load Rail deflection and

oscillation.

Single vs. double load

stops causing loads to be

skewed.

Calculation on load

stops in racks due to

conveyor system

placement of loads on

cranes.

Height to width ratio,

note in particular to

exterior rows.

Beam to column joints,

torsional and flexuaral

buckling of thin wall

cold formed steel

columns during load

impact moments.

Distortional buckling

and the formation of

Micro shifting of

loads and deflection

of frame posts.

Progressive collapse

analysis due to a

single column failure,

Cambridge Study,

also see UBC 1994

Table 16-B, storage

racks and note 12.

25

plastic hinges in steel

columns.

Soil capacity – Loading

Requirement due to soil

compaction.

Load shifting as a result

of placement of loads to

the back of the cell due

to the conveyor system.

Building

Construction

>30%

Defective Fabrication or

Construction

Welds

Mechanical

Connections

Plumb or Square

Base Material Defect

Load Arm to Load Rail

weld failures.

Load Arm to Rack

Frame weld failures.

Rack Frame post seam

failures.

Anchor Bolts –

Improper size and depth.

Shim – Improper height

of shims and subsequent

burning out shims.

Compression of rack

frames due to load

transfer through DAT

and CAT.

26

Bent posts in at least

three locations.

Roof frame alignment

problems due to post

height.

Use of welders without

certification on type of

weld or credential in

Wisconsin.

Building

Operation

>10%

Internal Event

Crane Operation

Rack Loading

Rack Damage

Rack load procedures –

Aisle A, B, and C were

loaded to greater degree

than D, E, and F.

Manual operation of

cranes and use of spider

crane.

In situ load test of

rack structures with

known weld failures.

External

0%

Event

Wind

Snow

Rain

Tornado

Flood

Foreign Object

Missile Damage

No items identified. No Items identified

27

Elevation view of slumped rack structure located on eastside near the East Low Bay.

28

Location of through-bolt

installed for sprinkler

system.

29

Poor quality weld from

upright to base.

30

Separation of rack structure at the point where the south run-out area was attached. Area on the

left (run-out area) folded towards the west. Area on the right indicates that the section pulled

down and away from the section on the left. Down aisle ties are all bent in a similar manner.

Mechanical repair installed

after load arm to load rail

weld failure.

31

South run-out area viewed from the south. Wall has folded over and the roof area is to the far

left.

32

Looking from the North Low Bay towards the south along the East Low Bay. Fire fighters

responding to this area stated that the area was blocked due to collapse debris. Debris was

present from the time of the initial partial collapse in this area. Further collapse occurred after

the fire degraded the remaining elements that were still standing. (Picture taken by Commerce

investigator)

33

Bowed uprights

Tear

Section of rack structure along the south end, exterior single-deep row. Uprights are bowed, note

the tear on upright at the approximate location of connection to the low bay.

Seam weld on upright.

34

Seam weld failures on

upright.

35

Seam weld failure

36

Load arm to upright weld failure

37

FINDINGS of THE DEPARTMENT OF COMMERCE:

The following findings are a result of the investigation. Following these findings the Department

issued Violation Orders, which are attached.

In accordance with Wisconsin State Statutes ch. 101.11 stats. the owner of a facility is

responsible for providing a safe workplace in conformance with the codes. The building was

not in conformance with the codes as identified by the violation orders.

The design of the structure did not include adequate safety factors to prevent the collapse of

the structure. The supervising professionals did not comply with requirements to submit a

compliance statement. The continued placement of loads in the rack structure resulted in an

uncontrolled in-situ load test. The loading of the rack structure was done with the approval

of the supervising engineer. The engineer signed the compliance statement with full

knowledge that welds had failed and needed to be repaired.

Ineffective welding techniques resulted in a reduction in the strength of the rack structure and

is a likely precipitator to the initial event. Welders working for two contractors did not have

the required credentials or certifications for the types of welding they performed.

A progressive collapse occurred in the ASRS building due to load shifting. Acceleration of

the collapse occurred in areas of the building, which were loaded to near capacity. Areas

within the building that were only partially loaded resisted collapse.

Further analysis may be necessary to determine if additional safety factors should be considered

to prevent a progressive collapse. Designs may need to include either a method to shed loads or

absorb loads during a load shifting progression.

DISCUSSION

The findings of the Department of Commerce were based only on those facts that could be

substantiated and did not expand into conjecture or theory due in part to the political and legal

nature of the Department. This purpose of this document is to expand into the probabilities and

discuss hypothetical causes based on probability.

The theory of initiation of the event begins with the welding failures. At the time of the collapse

the owner and contractors were investigating a failure of a weld that resulted in the load shifting

from an upper cell to a lower cell. This failure occurred in a double row rack in the south end of

the building. The report of the Nondestructive Testing Inspection NDI contractor indicated that

the probability of bad welds was more likely in the north end of the building. Inspection began

in the south end of the building and had not progressed to the north end at the time of the

collapse.

Based upon eyewitness accounts it is more likely the collapse began at the north end and

progressed to the south end. The witnessed also indicated that the motion moved from the east

wall to the west.

38

Based on the crane trace reports and the rack loading information the east wall, single row rack

was loaded to at least 98% of capacity. Again based on reports by the NDI contractor and the

eyewitness accounts the initiating event probably began in the single row rack along the east wall

at a point proximate to the north end. Although numerous investigators on site during the

investigation were focused on the south end of the ASRS, this location only seemed to provide

information relative to the collapse due to comments made by some of the individuals at the

plant. Investigative interviews with the eyewitnesses and with the first responders did not

support the theory that the collapse began at the south end.

The theory proposed in this report is that the collapse was initiated along the east wall at the

north end of the single row rack. The event may have been precipitated by a weld failure or and

in concert with the load placement of the load within the cell (at the back of the rack). Load

shifting in a micro scale was probably already present. Weld failure may have been the last

element necessary to begin a catastrophic load shift.

The progressive collapse was likely a result of design. The Down Aisle Ties were by design

bolted elements and would not have released without tearing metal elements of the rack uprights.

This was evident in examination of rack uprights during the investigation.

Imagine for a minute the playfull game of kids, each hold the others hands as they collapse to the

ground in a game called “ring around the rosey”. If there hands are grasped at the fingers, they

would lose grasp without much effort. If they grasp each other by wrists or forearms, then they

are more likely to hold on longer as they drop to the ground. Referring back to the testing done

on rack structure collapses in 1983, the stronger the down aisle tie, the greater the probability of

progressive collapse. Within the structural system designed for Quad Graphics, there was no

method of reliving or preventing a progressive collapse. In fact the design likely increased the

probability of a progressive collapse.

It is surprising that the requirement in the Uniform Building Code to prevent progressive

collapse has ceased to exist in codes developed from that document. If that code or the results

from the Cambridge study had been fully considered in the design of this building it is probable

that a progressive collapse could have been averted. Current building codes do not require

inherent safety factors to prevent a progressive collapse. The lack of this type of safety factor

was discussed within the State of Wisconsin Department of Commerce, Division of Safety and

Buildings, but was not addressed in the development of future projects or in the development of

future codes adopted by the Department.

It should be noted that after the economic downturn following September 11th

, the Wisconsin

Department of Commerce began a significant move away from state level enforcement and

began shifting enforcement duties to local communities and contractors. This was a primary

political platform of the election of the governor including the elimination of thousands of state

employees. The genesis of this report began within the Department of Commerce, but was

shelved due to cost, political and economic repercussions.

The importance of the release of this information has exceeded the need to maintain political and

economic viability for a few.

39

Hopefully, this report will generate renewed efforts to understand the probability of load shifting

and the need for designing elements to resist loads shifts that can result in catastrophic

progressive collapses.

40

1) ”NUMERICAL MODELLING OF THE PROGRESSIVE COLLAPSE OF FRAMED

STRUCTURES AS A RESULT OF IMPACT OR EXPLOSION.” J.R. Gilmour and K.S. Virdi;

Dept of Civil Engineering, City University, London, UK, EC1V OHB.

2nd

Int. Phd. Symposium in Civil Engineering 1998 Budepest.

2) “WHY DID THE WORLD TRADE CENTER COLLAPSE?, Science, Engineering, and

Speculation”

Thomas W. Eagar, the Thomas Lord Professor of Materials Engineering and Engineering

Systems, and Christopher Musso, graduate research student, are at the Massachusetts Institute of

Technology. MIT, 77 Massachusetts Avenue, Room 4-136, Cambridge, Massachusetts

JOM: The Member Journal of The Minerals, Metals & Materials Society

3) "PALLET RACK SYSTEMS DESIGN CRITERIA & SEISMIC CONSIDERATIONS"

Gross & Associates, Corporate Headquarters,167 Main St.,Woodbridge, NJ 07095

4)“DESIGN IT RIGHT AND IT WON’T GO WRONG”

William T. Guiher, V.P. Simulations & Material Handling, Inflection Point, Inc., 3045 Logan

Road, Greenbrier, TN 37073-4886

5) “STRUCTURAL ASPECTS OF THE PROGRESSIVE COLLAPSE OF WAREHOUSE

RACKING”; R.E. McConnel, Phd, CEng, MICE; and S.J. Kelly, Phd, University of Cambridge

Engineering Department; The Structural Engineer, vol 61A, No. 11, Nov 1983: