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Heavy Duty Riveted Bridge Deck AASHTO H20 Loading and Fatigue Testing: Long Service Life Explored

IQS Newsroom — Wed, 08 Dec 2010 16:22:00 +0000

Originally Presented at the Heavy Movable Structures, Inc. 13th Biennial Symposium October 25-28, 2010

Kenneth P. Apperson, PE – Ohio Gratings Inc.
Dr. Craig C. Menzemer, PhD, University of Akron

Introduction
Heavy Duty Riveted Bridge Deck Grating has been field proven to provide long service life for heavily loaded bridges. Examples presented include riveted steel decks that are in almost new condition after over 15 years in service and others that are still in good condition after nearly 60 years of service with no evidence of significant damage or deterioration. This is in stark contrast to the service life exhibited by some welded type bridge decks. This paper begins to examine the fatigue resistance of heavy duty riveted style bridge decks. The results from static load and fatigue cycle testing of riveted grating under AASHTO H20 loading with a 30% impact factor are presented. The testing conducted during 2009 and 2010 at the University of Akron Civil Engineering Lab has examined the static behavior of the riveted grating and has included fatigue testing of full-scale decks to well over 1 million cycles. The extra heavy load levels and worst case load location were used to accelerate the testing, and show where cracks might originate. The results also provide insight into the best methods for attachment of the riveted grating to the support structure.
Background and History of Steel Bridge Decks
Riveted heavy duty steel bridge deck was one of the first grating types developed in the early 1900’s. Because of this long history, there are many examples of riveted decks that have been in service for decades with no fatigue failures. Presented below are some examples of both riveted decks and welded type decks that contrast the life span issues. What is not known with certainty is the ADTT or Average Daily Truck Traffic for each structure.
Examples of Riveted Steel Decks:
Bay City, Michigan:
The Veterans Memorial Bridge in Bay City Michigan carries the four lane MI highway 25 over the Saginaw River. This Bascule Bridge was originally constructed in 1957. In 1994 a major renovation of the bridge included a new 5” Deep Heavy Duty Riveted Bridge Deck. The photos below were taken in February 2009. After over 15 years of service the deck is still in almost new condition.

Veteran’s Memorial Bridge Bay City, Michigan Riveted Grating installed in 1994. Like new after over 15 years in service.

Chicago, Illinois
The historic LaSalle Street Bridge in the heart of Chicago was built in 1928, and a new riveted steel bridge deck was put in service during a 1971 renovation project. This busy bridge is exposed to annual average daily traffic of about 27,000 vehicles per day. An examination in June 2008, demonstrated that the riveted grating is still providing good service after over 37 years of heavy use.

The LaSalle St Bridge in Chicago, Illinois with Riveted Bridge Deck installed in 1971 is still in good condition after over 37 years in service.

Long Island, New York:
The Robert Moses Causeway Southbound Bridge at Captree State Park was built in 1951, and in 2007, when the photos below were taken; the original riveted bridge deck was still in service.

The Robert Moses Parkway Bridge in Long Island, New York with riveted steel deck installed in 1951 was still in service after 56 years.

Examples of Short Life with Welded Steel Decks:
Chicago, Illinois:
The welded type steel deck on the North Halsted Street Bridge in Chicago was installed in 1994. After less than 17 years, many of the transverse and diagonal bars have developed fatigue cracks and some bars have actually fallen out of the deck. Note the repair patch plates in several locations in the welded deck.

Grosse Ile, Michigan:
About 25 miles south of the city of Detroit, Michigan, the island of Grosse Ile is served by a 1,400 ft bridge span over the Trenton branch of the Detroit River. Most of the span is fixed, with a 340 ft swing portion near the east end. The bridge was built in 1930 with a concrete deck surface. In 1980 a welded steel deck was installed in order to lighten the dead load on the bridge to accommodate heavier trucks. By 2006 when the photos below were taken, many cracks had developed in the bars of the bridge deck. Some sections had so many missing bars that patch plates were required. In addition, the bridge deck was very noisy as the vehicles crossed. In 2007 the deck was replaced with a heavy duty riveted bridge deck.

Laboratory Testing of Riveted Deck
During 2009, a research and testing program sponsored by Ohio Gratings Inc. was started at the
University of Akron. The purpose of the project was to establish the fatigue resistance of various heavy duty riveted bridge deck types. One objective was to examine how the AASHTO H20 wheel loads with the 10” x 20” tire patch would be distributed to the various component bars within the riveted grating panel. Another objective of the research was to establish the fatigue behavior of the riveted deck, especially in the negative bending moment areas over stringer supports. It was assumed that one reason the riveted decks have performed so well in the field was due to the fact that there are no welds at the top surface where the negative bending puts the top surface in tension. The fact that the rivets are centered 0.75 inches below the top surface in a lower stress area is believed to be a major reason for the outstanding performance in the field. The test data presented is based on results for Ohio Gratings type 37R5 Lite 5” x ¼” with bearing bars of type ASTM A-36 steel.
Static Loading
Figure 1 and the photo below show the general arrangement for the static test set-up for testing of the two span continuous riveted steel bridge deck. Support spacing was 49 inches center to center of stringers. A spreader beam was utilized and loads were placed 72 inches apart to simulate a design truck axle located to provide the maximum negative bending response. Twenty inch long sections of steel “I” beam with reinforcement plates and a 10 in wide flange were used to provide the AASHTO tire patch for an H20 loading. High durometer rubber pads were placed between the short sections of each “I” beam and the deck to act like a “tire”

Figure 1: General arrangement of static test set-up for 37R5 Lite 5” x ¼” deck.

Figure 2 shows the longitudinal strain distribution for the bearing bars acting along the negative moment region of the continuous span. Each of the strains plotted in Figure 2 is from a gage mounted 0.25 in from the top of the bar, oriented in the longitudinal direction. The distribution of strain shown represents an axle load of about 41,600 lbs, representing a fully loaded H20 truck with 30% impact applied to the wheel loads. The diagram shown in Figure 2 shows the location of the load with respect to each tire patch, centered over bearing bars 5 and 6 near the center of the panel width. From the response shown in Figure 2, it is apparent that most of the resistance is supplied by the bearing bars located directly under the load. The bearing bars adjacent to those under the load participate in the resistance, but to a much smaller extent.

Figure 2: Longitudinal strain distribution across the top of bearing bars in the negative moment region. The 10 inch dimension of the loading plate was centered over bars 5 and 6.

Figure 3 shows the longitudinal strain near the top of the bearing bars in the negative moment region when the loading is applied at the edge of adjacent panels. As before, the strains were measured using gages 0.25 inches from the top of the bar oriented in the longitudinal direction. The load was again applied to produce the maximum negative moment. The strain distribution was taken under a load of about 41,600 lbs. With the load applied at the edge of the panel, the maximum response is from the three bearing bars directly under the simulated tire patch.

Figure 3: Longitudinal strain under the maximum negative moment with the load applied at the edge of a panel.

Fatigue Tests:
Fatigue behavior of structural connections depends primarily on the detail type and the applied stress range. Fatigue test results presented here are for the same 37R5 Lite 5” x ¼” riveted steel deck represented in the static tests. As with the static tests, loading was arranged to produce the maximum negative moment over the support, and was representative of 16 kip wheel loads plus 30% impact. A small positive loading ratio, R, was maintained: wheel loads varied from 1000 lbs to 21,800 lbs, producing an effective load range of 20,800 lbs. With the maximum negative moment occurring over the support, the details of interest were the rivet connections between the main bearing bar and adjacent reticuline bars as well as the attachment of the deck to the supporting structure. In this case, the supporting structure was represented by a series of “W” beams intended to act like stringers.
Figure 4 shows one crack that developed during fatigue testing after 1,300,000 cycles in one of the bearing bars of the deck. The section of deck where this piece was removed was directly over the center support, or that area subjected to maximum negative bending. What is interesting to note is that the crack originated from the fillet weld used to attach the deck to the test fixture. In a number of instances, field installation would require fillet welding of the bearing bars to supporting steel. For the tests conducted in the laboratory, a plate was welded to the bottom of the bearing bars and was then mechanically fastened to the simulated steel stringers.

Figure 4: Section of bearing bar after fatigue test of 37R5 Lite 5” x 1/4” steel deck.

Located directly over a support, the fatigue crack that developed in Figure 4 would have experienced compression due to bending and shear. Tensile residual stress fields exist adjacent to a vast majority of weldments, due to the uneven heating and cooling that occurs during the joining process. Often these local residual stresses may be on the order of the yield point of the base metal. It is likely that the area close to the fillet weld experienced a net cyclic stress that was tensile. Inclination of the crack is most likely the result of the presence of shear as well.
Figure 5 is a Scanning Electron Micrograph (SEM) image of the fracture surface in the area near the fillet weld. While there is a significant amount of mechanical damage from the surfaces coming into contact during negative bending, there are a series of what appear to be ridges or striations present, indicative of fatigue crack growth.

Figure 5: Area near the weld showing mechanical damage with some indication of striations.

Figure 6 is an SEM micrograph taken in the overload region. The fracture surface has a rough macroscopic appearance. Upon closer examination, the matrix shows evidence of localized cracking and the formation of microvoids, indicative of tensile overload. Therefore, it is believed that the tensile fracture of this section up to the top of the grating resulted from the crack which started near the weld area. During the testing of this deck, no fatigue cracks were observed in the area of the rivet.

Figure 6: Overload region of fracture surface.

Conclusion:
The laboratory testing confirms that the heavy duty riveted bridge deck is very resistant to fatigue cracking. This type deck can be relied upon to provide decades of service even when exposed to heavy truck loading. When a crack finally was initiated in the test panel after 1,300,000 cycles of extreme worst case loading, it started in the area of the welded attachment at the bottom of the grating well away from the riveted connections. This suggests the design of the attachment to the stringers is important.
Alternate Attachment Systems:
Several options are available for modification of attachment system. One option is to raise the welded fastener plate closer to the neutral axis of the bearing bars as shown in figure 7. This will move the residual stress area around the welds into an area where they will be subjected to much lower levels of stress reversal during live loading. The fastener plates would then be attached to the stringers by bolted connections as shown. Another option is to use an attachment design that eliminates the need for welding the fastener plate to the bearing bars. One way to accomplish this is to use a bearing bar angle rather than flat bar. This configuration is shown in figure 8. This method allows direct bolting of the bearing bars to the support stringers thus eliminating the welded fastener plate. The continuing research and testing program will include fatigue cycle testing with heavy duty riveted bridge deck using these alternate attachment systems.

Figure 7 – Fastener Plate welded up 1 inch from the bottom of the bearing bar.

Figure 8 – Bearing Bar Angles provide a horizontal leg for bolted attachment to the stringers with no welding required.

HMS 13th Biennial Symposium Heavy Moveable Structures
Heavy Duty Riveted Bridge Deck
Long Service Life Explored

The post Heavy Duty Riveted Bridge Deck AASHTO H20 Loading and Fatigue Testing: Long Service Life Explored first appeared on IQS Newsroom.

The Plastic Pallet And Fire Protection

IQS Newsroom — Wed, 20 May 2009 16:37:00 +0000

by TMF Corporation

Abstract
This paper attempts to identify some of the specifics of the process used to obtain approval for use of plastic pallets as equivalent to wood pallets for use in warehouse storage. This paper is written to look at the issue in general and is not intended to cover all storage situations. Your specific situation should be evaluated by a fire protection specialist.
Identifying the Issue
Most plastic pallets are molded out of polyolefin materials such as high density polyethylene or polypropylene. These materials are more flammable than the wood used to make pallets. Over the years the industry has argued with the fire protection establishment that plastic pallets, while they burn hotter than wood, are much more difficult to ignite. Fire protection people counter with the fact that most warehouse fires are arson and if an arsonist wants to start a fire they will do what ever they need to do to get a fire started.
Eventually the plastic pallet industry and the fire protection establishment came to some general agreements. The National Fire Protection Agency, NFPA, took the many documents that in any way referred to plastic pallets and included them in one document. This document, NFPA13, “Installation of Sprinkler Systems” identifies what warehouse owners need to do when using pallets, both wood and plastic, for storage in warehouses.
In general plastic pallets can be used in warehouse storage the same as wood pallets depending on certain situations.
Warehouses built since the mid-1990 are required to have sprinklers designated as K-17 or higher. Testing done to approve the K-17 sprinkler was done using plastic pallets because it was determined that plastic pallets afforded the most severe challenge for sprinklers to control. Since the K-17 sprinkler tested and approved for protection in a plastic pallet fire, it followed that plastic pallets could be used in warehouses with K-17 or higher sprinkler protection.
Warehouses built before the mid-1990’s can be addressed in several different ways. One way is to upgrade the sprinkler system to present code. This can be done in some cases by simply replacing existing sprinkler heads with K-17 sprinkler heads as long as there is sufficient water volume and pressure, as described in NFPA 13.
In other cases the entire sprinkler system might need to be replaced. This is very expensive and in most cases impracticable. NFPA 13 addresses these cases by providing options in how the plastic pallets are handled and stored.
The following is taken from NFPA 13, 2007 edition for “Storage of idle plastic pallets” pages 13-121, 13-122 and 13-123.
“Plastic pallets shall be permitted to be stored in the following manners:
1. Plastic pallets shall be permitted to be stored outside.
2. Plastic pallets shall be permitted to be stored in a detached structure.
3. Plastic pallets shall be permitted to be stored indoors where arranged and protected in accordance with the requirements of indoor storage.
4. Indoor storage of plastic pallets shall be permitted to be protected in accordance with the following arrangements:
a. Maximum storage height of 10 ft.
b. Maximum ceiling height of 30 ft.
c. Sprinkler density 0.6 gpm/sq. ft. over 2000 sq. ft.
d. Minimum sprinkler K-factor of 16.8
5. Indoor storage of non-wood pallets having a demonstrated fire hazard that is equal to or less than idle wood pallets and is listed for such equivalency shall be permitted.
6. When specific test data is available, the data shall take precedence in determining the required protection of idle plastic pallets.
Plastic pallets where stored indoors shall be protected as follows:
1. Where stored in cutoff rooms the following shall apply:
a. The cutoff rooms shall have at least one exterior wall.
b. The plastic pallet storage shall be separated from the remainder of the building by 3 hour-rated fire walls.
c. Sprinkler protection by one of the following:
i. The storage shall be protected by sprinklers designed to deliver 0.6 gpm/sq.ft. for the entire room or by high-expansion foam and sprinklers with a density no less than 0.15 gpm/sq.ft.
ii. K-14 ESFR upright sprinklers when the storage is on the floor and the system is designed to supply all sprinklers in the room at 50 psi or a maximum of 30 ft. ceiling or 75 psi for a maximum 35 ft. ceiling.
d. The storage shall be piled no higher than 12 ft.
e. Any steel columns shall be protected by 1-hour fire-proofing or a sidewall sprinkler directed to on side of the column at the top or at the 15 ft. lever, whichever is lower. Flow from these sprinklers shall be permitted to be omitted from the sprinkler system demand for hydraulic calculations.
2. Where stored without cutoffs from other storage the following shall apply:
a. Plastic pallet storage shall be piled no higher than 4 ft.
b. Sprinkler protection shall employ high temperature rated sprinklers.
c. Each pallet pile of no more than two stacks shall be separated from other pallet piles by at least 8 ft. of clear space or 25 ft. of stored commodity.”
In most cases when plastic pallets are substituted for wood pallets, the commodity stored on the pallet suffers a one class higher penalty. In other words, if one were storing a class II commodity, say bags of flour or sugar, the sprinkler protection required would have to be sufficient to protect a class III commodity.
In a lot of cases this would not be a problem. However, in cases where the stored product is a Class III commodity the jump to a class IV commodity requirement can prohibit the use of plastic pallets. The reason for this is that the increase in required sprinkler protection from classes is not equal. From Class I to Class II to Class III can be relatively easy to address. Going from Class III to Class IV is a very large jump.
In this case, as well as all cases, NFPA 13 allows for testing of plastic pallets and using the results from this testing to compare to known test results from commodity tests conducted with wood pallets. In other words, if the results from burning plastic pallets are equal to or better than results from burning wood pallets, they can be protected by the same sprinkler scheme as approved for wood pallets.
The following is taken from NFPA 13, 2007 edition for “Pallet Types” page 13-25.
“Pallet Types”:
1. When loads are palletized, the use of wooden or metal pallets shall be assumed in the classification of commodities.
2. For Class I through Class IV, when unreinforced polypropylene or high density polyethylene plastic pallets are used, the classification of the commodity unit shall be increased one class.
3. For Class I through Class IV, when reinforced polypropylene or high density polyethylene plastic pallets are used, the classification of the commodity unit shall be increased two classes. Reinforced polypropylene or reinforced high density polyethylene plastic pallets shall be marked with molded symbol to indicate that the pallet is reinforced.
4. For Class I through Class IV when other than polypropylene or high density polyethylene plastic pallets are used, the classification of the commodity unit shall be determined by specific testing conducted by a national testing laboratory or shall be increased two classes.
5. No increase in the commodity classification shall be required for Group A plastic commodities stored on plastic pallets.
6. For ceiling only sprinkler protection, the requirements of 2 and 3 shall not apply where plastic pallets are used and where the sprinkler system uses spray sprinklers with a K-factor of 16.8.
7. The requirements of 2 through 4 shall not apply to nonwood pallets that have demonstrated a fire hazard that is equal to or less than wood pallets and are listed as such.”
The Approval Process
There are a number of testing facilities that can do the burn tests. However, only two companies actually have documented approval processes. These laboratories are Factory Mutual Approvals in Norwood, MA. and Underwriters Laboratories in Chicago, IL.
Factory Mutual’s test is ANSI/FM4996 and involves testing idle plastic pallets as equivalent to wood pallets.
The fire test hazard classification used in this standard consists of monitoring several performance criteria during actual fire test conditions. The values obtained during the fire tests are then compared to predetermined limits for each criterion. From this comparison, an assessment of performance can be made to determine if the pallet has met all requirements for fire hazard classification as equivalent to wood pallets. The performance criteria are:
· Number of sprinkler operations
· Maximum one minute average ceiling level gas temperature
· Maximum five minute average ceiling level gas temperature
· Maximum one minute average ceiling level steel temperature
· Maximum five minute average ceiling level steel temperature
· Extent of fire damage
· Extent of melted plastic pooling
The number of sprinkler operations is useful in determining how quickly a fire can be controlled and/or extinguished by automatic sprinkler protection.
The maximum one and five minute average ceiling level gas and steel temperatures are the energy convected upward and are responsible for the heating of exposed steel and the operation of automatic sprinklers. Some fires are intense but short lived and may give a thermal impact less severe than a fire of lower intensity but longer duration. To assess fire severity, these measurements are averaged over the most severe one and five minute intervals.
The extent of fire damage is a measure of a fire’s potential for spreading horizontally and causing damage to adjacent products.
The extent of melted plastic pooling is a measure of the potential of the fire to spread along the floor to adjacent products located across an aisle space.
In addition to the above test criteria, quality control tests shall be conducted as an aid in monitoring the quality controls exercised in the resin and pallet manufacturing process in order to characterize the materials used in the make up of the pallets. These tests can also be used as the basis for determining the anticipated performance characteristics of any future changes in the resin formulation.
Underwriters Laboratories’ test is UL2335 and involves testing in both commodity classes and idle pallet storage conditions.
While UL2335 is very similar to the Factory Mutual test there are a couple of notable differences. In UL2335 there is a series of burn tests where a simulated Class II commodity is placed on the plastic pallet to be tested and the loaded pallets are placed in a steel rack configuration. The arrangement is then set on fire. There are three separate tests that differ in that the sprinkler water flow is set at three different volumes. The heat release, gas temperatures, steel temperatures and amount of damage is then compared to know results obtained from the same tests using wood pallets.
The idle pallet part of the tests are conducted similar to Factory Mutual except the pallets are stacked 20 ft. high in three rows with two of the rows back to back and the third with an 8 ft. aisle between it and the back to back rows. Here the heat release, gas temperatures, steel temperatures and the amount of damage is then compared to know results obtained from the same test using wood pallets.
Based on known data from testing wood pallets the plastic pallet is then approved or not.
While the two tests are somewhat different, NFPA accepts test results from both laboratories in the determination of acceptability as relates to fire protection and sprinkler installations. Passing either test establishes a particular plastic pallet as equivalent to a wood pallet.
As of this date only four companies have developed pallets which are approved by either/or Underwriters Laboratories or Factory Mutual Global. One of these companies is a resin company and achieved this by using a very expensive engineered resin. The other three companies are plastic pallet manufacturers and all achieved approval by changing the resin makeup of either high density polyethylene or polypropylene. This method helps keep the individual cost of the pallets much more affordable.
For those interested in contacting these companies, you can contact Factory Mutual Global or Underwriters Laboratories and they will give you the companies contact information.

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How to Write a Specification For and Evaluate a Design/Build Cleanroom Proposal

IQS Newsroom — Thu, 22 Jan 2009 16:01:00 +0000

by Tim Loughran & John Burton of AdvanceTEC, LLC.
Introduction
With the increasing emphasis on utilizing the design/build method of delivery in the construction industry, and the desire to evaluate proposals using that old adage of “apples to apples”, it becomes incumbent upon the owner to create a specification which will insure that contractors have the appropriate information to propose the facility accurately. The specification (request for proposal) must be written to supply the contractor with enough pertinent information to accurately propose the requirements, yet not so detailed as to stifle the creative process and potentially limit the owner’s value received.
The contractor must then take on the responsibility of presenting its proposal in a manner by which the owner can accurately assess the value they are receiving. Value in and of itself is a relative thing: what is valuable to one may be less important to another.
The intent of this article is to put forth a guideline, which can assist in utilizing the process effectively, and to detail parameters that should be included in a specification to insure the contractor has the pertinent information to accurately assess the requirements. In addition, following the guidelines set forth, the owner can insure requirements do not inadvertently set parameters, which significantly impact price.
Writing a Specification and How Requirements Affect It
Many design/build cleanroom contractors utilize a “planner” to detail the parameters of a specification. Often times these planners are clouded with too much inappropriate detail which causes the owner to frame the design in a fashion that does not allow the design/builder to utilize ingenuity to deliver a proposal which best suits its needs. As an example, often the owner has a preconceived notion as to the type and finish of the wall or ceiling system it prefers, which precludes the design/builder from submitting information on less expensive or more appropriate products to fit the need.
The specification should begin with the general overview of the facility and proposal requirements, starting with the type of work which will be performed within the facility and the production schedule, if any. Production facilities which are required to operate 24 hours per day should not be designed the same as R&D cleanrooms, which would be utilized intermittently and never for more than 8 hours at a time.
After review of the general overview is complete, it is necessary to determine the scope of work that will be required from the contractor. Will the scope include the cleanroom design and construction only? Will the contractor need to incorporate requirements (such as electrical, exhaust, and process gases) for process equipment within the design and/or construction? Will your own Facilities Department deliver services to a point of connection or will the contractor be required to search out and determine the points of connection? These items all depend upon the depth and workload of your Facilities Department and the required involvement and Facilities Department’s regulations.
A required room completion date should be included, but don’t make one up, if the schedule is flexible. Let that be known and negotiate a schedule at contract time. Putting a false schedule on a project may have price implications, which may not surface in the evaluation process.
The taxable status of the project can impact price, so tell the design/builder clearly what your corporation’s tax position on the project is, and what it should or should not include in the proposal. Permits, stamps, and fees pose significant hidden costs in any construction project. Be clear to the design/builder what your organization’s intent is. If you require local permitting, the process will undoubtedly add time to your schedule and cost to your project. The division of responsibility and the posture with local code officials should be a fluid process with your design/builder: permit time and fees can vary based on the local building officials’ familiarity with your company or the design/build firm. How the cleanroom is classified by your organization (modular cleanrooms frequently are classified as capital equipment versus leasehold improvement) also affects permits and fees. At a minimum, insist that the design/builder include the cost to stamp the drawings and acquire the permits: it most probably will be in both parties’ best interest that fees be a negotiated passthrough cost. The design/builder or your in-house Facilities Department should be able to estimate permit fees to include in your capital appropriations.
Architecturally, the owner should supply the design/builder with a basic cleanroom floor plan, equipment plan, and facility plan in order for it to accurately assess the construction requirements logistically. In the absence of the availability of these items, the request for proposal should require a site survey to determine the issues (such as location of the cleanroom within the facility, possible location of support equipment for the cleanroom, equipment and material entry path, etc.) affecting the cleanroom design and construction. Architectural parameters, which must minimally be included with the request for proposal are: the required room classification (if you are unsure what cleanroom classification is needed. supply the design/builder with the particle size which you are trying to eliminate from the environment). This combined with the process information you supplied in the general overview should help an experienced cleanroom contractor determine the appropriate classification to satisfy your needs. In addition to classification, information on ceiling height, square footage of clean space required, support space required, clear ceiling height of the existing space, what floor of the building the room will go on, as well as any pertinent seismic or structural issues will be needed. The accuracy of the logistical information supplied is directly proportional to the accuracy of the design/builders proposal.
The mechanical section of the cleanroom design, specification, and proposal is invariably the portion that can differ greatly from concept-to-concept and proposal-to-proposal. This section is where the most painstaking effort should be directed in assessing and writing the requirements and, in turn, assessing the proposals. First and foremost, determine if the driving force of your requirements centers on precise temperature control or precise humidity control. Improper understanding of temperature and humidity and how they are affected by the process within the cleanroom; how they affect each other and equipment requirements and sizing, and how HVAC equipment is controlled, are without doubt the biggest issues in cleanroom design. The temperature and humidity control set points required are sometimes not as instrumental as the control bandwidth (the plus or minus variables). Comfort cooling for cleanrooms is widely accepted to be 68 degrees F; the most widely accepted humidity control point is 45%.
Temperature set point should be determined somewhat by the cleanroom classification, or more accurately by the garment requirements of the cleanroom classification. Garments utilized in more stringent cleanrooms are designed to encapsulate the worker and eliminate particle escape. This process in turn reduces the ability of the worker’s body to breathe and expound heat; therefore, the surrounding environment should take this into account. If precise temperature control is not a requirement of the process, the control bandwidth should be +/- 3 degrees, allowing for economical (industrial type) equipment, controls, and valves.
Humidity and its relationship to temperature is the single most costly and misunderstood factor in cleanroom design. “Relative Humidity” is just that: relative to the temperature it is measured at. If your process dictates that optimum performance is at 70 degrees F and 45% RH, that is not the same operating condition (i.e. moisture content) as 68 degrees F and 45% RH. To achieve the same grains of moisture (the amount of moisture in the air) at 70 degrees F and 68 degrees F, the corresponding relative humidity to 45% would be approximately 40%. This could be a significant delta in microelectronics applications. It is the reason that a 68-degree rainy summer day feels much cooler than a 68 degree dry fall day. The moral of the story is: that determining the process temperature and humidity requirements of the cleanroom is of utmost importance; and, if not accurately determined; it could significantly affect your process, therefore rendering the cleanroom improper for your needs. Be aware also: setting a cleanroom parameter that controls temperature and humidity more precisely than is required, or with added range to allow for flexibility, is significantly more expensive, and vice versa, if your cleanroom design/builder takes liberties with your specification.
Now that the temperature and humidity parameters have been set, other parameters which will affect the cleanroom’s HVAC systems, must be detailed. Heat load of the equipment to be utilized within the room is significantly important. A tool matrix, or cut sheets on the equipment to be installed, will help insure the assumptions made by the design/builder are correct. The number of people assumed to be working in the room also is significant. People add active (heat generation) and latent (moisture generation) load to a cleanroom system. Exhaust requirements (if any) of the room are important to determine make-up air for the facility (again, here is where the tool matrix or cut sheets come in handy) as well as where the make- up air will be drawn from (the facility or directly outside). The temperature of the surrounding area that the cleanroom will be installed within also affects cooling requirements, due to heat transference.
The requirements of the sprinkler system for the cleanroom are dependent upon the occupancy code and use, as well as local building codes. Some jurisdictions require sprinklers within plenums, on mezzanines, in the space, and under raised floors effectively requiring 4 levels of sprinkler coverage. The present facility system may be at capacity for the required area, and a new main may be required. In addition, the tie-in point may be directly overhead or hundreds of feet away. The contractor may expect to be able to arrange a shutdown of the system and you expect them to wet-tap. The contractor may assume the requirement to meet local codes and your insurance underwriter expects coverage in excess of code, to meet its requirements. This is an area where requiring code or insurance carrier compliance, within your specification, puts the burden on the design/builder to investigate the issues; however, you must give them information regarding tie-in points, and times, and what you will be classifying the room as.
Electrical requirements for the facility should be determined to avoid the potential costly, and schedule impacting, need to get additional power delivered to your facility at the last minute. Existing power, voltage, and amps available is a good thing to determine in advance of generating your RFP. This determination will help to delineate the scope of the cleanroom contractor. If you are sure you require additional facility power, in advance of the cleanroom proposal submission, have the cleanroom contractor bring the required power to a single point of connection (this will require they include all load centers and step-down transformers). Your facility personnel can deliver power from the source to the single point of connection at the same cost as the contractor, and you will save their overhead and profit without compromising cleanroom performance responsibility. This is another area where the tool matrix is valuable, in determining power requirements for process equipment.
Controls are another area that can be significantly impacted by requirements, or more appropriately, by the lack there-of. Your process, regulatory agency, or customer may require data logging or other monitoring which should be understood and communicated up front. Your Facilities Department may require interface with their existing Facilities Management Program. You may wish to have energy saving setback, operating parameters, if the cleanroom space is not actively utilized during certain portions of the day, month, or year. Controls are one of those items which you may not want to over-specify up front but will surely want to have detailed information on and review diligently when evaluating a proposal. A few words of caution: use a control system which has modem and remote interface capabilities which can save time and money when attempting to troubleshoot operating issues. Stay away from proprietary systems which do not have components, or are not serviceable on the open market: they can be costly down the road.
If you cannot deliver to the design/builder a significant portion of the requirements listed above, or at the very least be capable of making reasonable assumptions regarding these items, the design/build method of delivery may not be the most appropriate method for your needs. At a minimum, you may need to solicit assistance in determining those requirements prior to soliciting design/build proposals. Allowing for too many assumptions to be made by the design/build contractors will make your task of determining the most appropriately valued proposal nearly impossible.
Deliverables with the Proposal
Before evaluating the proposals from your design/build contractors you must first evaluate the design/builder themselves. Ideally this should be done before asking the contractor to develop and present a proposal. Ask for information that will help you determine their abilities and resources, solicit financials or D&B reports, ask for a listing of ongoing and recently completed projects (then pick the projects which you would like to call for references). Ask the contractor to submit a set of design plans for a project similar in scope. Ask for resumes of the project team proposed, to interview them, how many projects they’ve worked on together, and to tour a project that they have completed.
When requesting the proposal, ask for information which will help you compare the proposals for relative value and accuracy. At a minimum, you should be supplied with a proposed Project Schedule, Floor Plan, Reflected Ceiling Plan, Equipment Plan, and Air Balance Schematic, as well as details and catalog cuts of products and materials which were utilized in the basis of design. Heat Load Calculations and Power Requirements (rough order of magnitude) also should be asked for. These items should be readily available and part of an accurate estimating process as well as invaluable in understanding the similarities and differences from proposal to proposal. Don’t utilize them to compromise the process: any information supplied by a design/build contractor should be utilized for evaluation of, and discussions with, that contractor only.
Most important to evaluating the proposals: don’t accept one lump sum price. Ask for a price breakdown, per trade, allowing you to evaluate where there are differences in proposals. This is not to beat people down against their competition, but to concentrate on comparison of proposals in areas of significant difference.
Developing an Evaluation Criteria to Understand Value
Developing evaluation criteria whether in a formal matrix form (with details and ranking) or informal comparison format, is essential to understanding the value versus price issue always inherent when you are not going through the traditional design/bid/build form of construction. You misuse and discredit the design/build process (and ultimately your own organization) if you take the cheapest guy and scope him to the best proposal. You can be sure the best value is in between. Throw out non-responsive firms who have not submitted the information you requested in the RFP document. Compare the remaining proposals utilizing critical information. Do not select a contractor at this point: short-list 2 or 3 and interview them. The interview order should not be random; it should be based on the criteria you set to help determine which firm best suits your needs. Most importantly, interview: what you will learn about these organizations during the interview process is most valuable.
Some of the items you should look for in the proposal evaluation and subsequently discuss in the interview are as follows:
1. Architecturally your evaluation should consider the ceiling grid specified, filter type and efficiency (% filter coverage), walls system substrates, doors (number and type), windows, entrance and egress scheme and facility integration. This is why your RFP asked for the Floor and Ceiling Plans and catalog cuts.
2. The mechanical portion requires critical evaluation as we have stated previously. The heat load calculations and air balance schematic will help to evaluate cfm (in turn-air change rates), tons of cooling, make-up air, exhaust parameters, and what energy efficiency has been designed within the system, as well as redundancy. These issues affect operating costs and the ability of the room to function at times when equipment is down for service or repair. If your cleanroom is required to operate every working shift to meet production goals, what happens if a piece of equipment is down for repair for 2 days: what is the plan to continue to operate under reduced capacity? There would be none, if you have not designed in redundancy. During the interview process, a significant portion of time should be spent on reviewing the heat load calculations and air balance schematics to understand fully how the values were determined. In addition, the catalog cuts submitted for HVAC equipment will help to understand the value and intricacies from proposal-to-proposal. Are the recirc air handlers manufactured specifically for cleanroom usage; are they double wall insulated: are there belts (which generate contamination) within the air streams. All of these items affect the hidden energy consumption and operating and maintenance costs that could take an inexpensive proposal and make it more costly over a short period. During the evaluation process ask for energy calculations, if you require this information to accurately understand a proposal. Remember not to punish a contractor for thinking outside the box: if they develop a concept you don’t like but which shows thought and ingenuity, don’t throw them out: allow them to re-propose or amend their proposal after the interview.
Items which should be included in the electrical evaluation are the number of lights, the voltage, and whether they utilized energy efficient ballasts. Has the contractor included emergency lighting and exit signs? How many convenience outlets are incorporated in the design, and the overall facility power requirements including process, if within the scope?
Certification of the cleanroom should always be performed by an independent source with the criteria determined in the RFP document. The cost should be included in the design/builder’s estimate and the owner should reserve the right to remove the cost from the scope and contract it directly, if they see fit. Remember that contractually the certifier is bound to the firm they are contracted with.
Schedule should be negotiated and included with any design/builders contract to protect both parties against unforeseen delays which impact the contractor’s ability to control time related costs and the owner’s ability to expect completion and avoid delays.
When the interview is done, ask a simple question. What will I have to do (as the owner) to operate this facility after your work is complete? This will help determine scope gaps and confirm an appreciation for the contractor’s understanding of scope delineation.
Conclusion
Reviewing the outline we have set forth, the process for reaching an accurate design/build contractor selection should include setting a basic criteria, communicating the required proposal deliverables, preparing an evaluation matrix, interviewing the short-listed candidates, understanding the value inherent in the conceptual design, and choosing the most technically-sound respondent.
To be clear, this is not a foolproof plan to create those “apples-to-apples” situations. The design/build process is not an “apples-to-apples” process: it is a process to deliver alternate paths to a predetermined point. The proposals should be evaluated on their own merits (price vs. value) and a selection should be made based on that process. Cheapest isn’t less expensive and the lowest price isn’t always the best value.

The post How to Write a Specification For and Evaluate a Design/Build Cleanroom Proposal first appeared on IQS Newsroom.

Foam Inserts – Cutting Your Own or Having Them Custom Made

IQS Newsroom — Wed, 08 Oct 2008 14:06:00 +0000

by Steven Holand, Carry Cases Plus Owner
When it comes to creating custom foam inserts for your carrying case or shipping case, there are several options available.
If you’d like to cut your own inserts, purchasing a solid pad is a good way to go. Simply trace your item on the pad and cut the foam using a utility knife. The solid insert could also be used as is to protect thin items.
Solid pads are available in either Polyurethane or Polyethylene foam. Polyurethane foam is soft, durable (similar to the foam in your couch cushions) and great for light to medium-weight items. Polyethylene is dense (the material is the same as those “noodle” flotation toys that kids play with in the pool) and ideal for medium to heavy-weight materials.
Eggcrate (or “convoluted”) inserts, which are made of Polyurethane, work well on their own. The unique grooves in the foam grab the items and hold them in place when the case is closed.
Another option in creating your own inserts is to purchase Diced/Pick and Pluck foam, which comes in pre-scored cubes of Polyurethane. Make your own insert by putting your items on top of the pre-cut grid. Next, remove the cubes touching your item so that it fits nice and snug into the remaining foam piece.
Foam inserts can be custom-made for added protection and a perfect fit. Die cut foam inserts are cut using steel rule dies. Die cutting produces the most precise cut and in my opinion, it also produces the best product. For deep cases, wire cut inserts are a good option. These inserts are created using a computer-controlled abrasive wire-cutting machine. The machine is programmed with the use of a CAD (Computer Aided Design) drawing, which details all the cutouts and dimensions. Both processes allow for either Polyurethane or Polyethylene foam.
If all of these options are overwhelming you, don’t panic. Sometimes it is difficult to decide which insert would best fit your materials. If you have questions, be sure to contact a foam insert professional for guidance.
Steven Holand is the owner of Carry Cases Plus, a foam fabricator with over 20 years of experience creating foam inserts. For the second year in a row, the company was listed as one of Inc. Magazine’s 5,000 Fastest Growing Private Companies in America. Visit Carry Cases Plus at www.carrycasesplus.com.

The post Foam Inserts – Cutting Your Own or Having Them Custom Made first appeared on IQS Newsroom.