PIMC Occupancy Safety Evaluation 2011.pdf

DURRANT ®

Progress by Design.

May 2, 2011

Indian Health Service

Phoenix Indian Medical Center

Occupancy Safety Evaluati on

HVAC REPLACEMENT

Analysis of Crane and HVAC Impact on Existi ng Structures

HHSI161200700007C

410 North 44th Street

Suite 800

Phoenix, AZ 85008

T 602.275.6830

F 602.275.4331 www.durrant.com

Architecture

Engineering

Planning

Project Delivery

Financing

Interior Design

Graphic Design

Denver, CO

Des Moines, IA

Dubuque, IA

Phoenix, AZ

May 2, 2011

Mr. Scott Fillerup

Project Engineer

Phoenix Indian Medical Center

4212 North 16 th Street

Phoenix, AZ 85016

Re: Occupant Safety Regarding HVAC and Crane Impact

DW: 07073.10

Dear Mr. Fillerup:

We understand your need for an operational facility during HVAC placement. Due to your need to keep operational during the placement of the units, Durrant has been requested to determine the structure’s capacity to protect occupants in the event of failure during HVAC replacement and crane failure. Failure modes include dropping AHU mechanical units 10 to

20 feet above the roof and a lattice jib or boom falling into the structure. The maximum crane assumed to be used is 550 ton Grove Model with possible lattice jib extensions.

Several crane modes of failure can occur such as crane overturning, member failure and connection failures. These modes of failure can result in various impact conditions on the structure. Failure modes of the crane and how it impacts the structure can have various results. This report focuses on conditions regarding the possible impact to structural systems. It is based on engineering judgment and limited calculations on the structural systems. Structural modeling, lab and field testing were not completed in preparing this report. This report offers further methods and insight into the actual performance of the structure. This report provides overview of systems, methods of research, data and analysis, present conclusions and offers guidance to the client. An overview summary is below, however the full guideline should be followed and understood for all occupant risks.

Location Structural

System

Failure Mode Occupant Risk

Tower Two-way concrete slab

HVAC Safe

*Crane Safe to potential

One-story One-way concrete slab

HVAC Safe to limited

*Crane Limited to significant

One-story Double Tee’s HVAC Safe to potential

*Crane Potential to removal

Parapet Block *Crane **Safe

*All occupants’ risk for failure of lattice jib crane perpendicular to the surface is extensive.

**Interior occupants safe, however exterior individuals at risk from falling debris.

Structural Systems:

Built in 1968, the hospital’s structure consists mostly of drilled concrete piers, concrete floor slabs, concrete walls, beam and columns. Different framing systems for areas are described below.

• Tower: Roof structure is a nine inches thick, monolithic pour, mild-reinforced two-way slab system with bay spacing being between 20’-0” and 24’-8”on center. The two-way system has flat concrete caps over columns, perimeter concrete beams

12’-24” wide and 20’-30” deep wraps the entire perimeter.

• One story: Roof structure over non-mechanical unit locations consists of two inch concrete topping on twelve inches deep concrete double tee’s with two inch concrete flanges. The concrete stems are spaced two feet on center. Structure over mechanical units is a one way seven-inch thick, monolithic slab supported by concrete beams. Reinforcing for the double tee’s and concrete slab is not known.

Concrete beams span to concrete columns.

• Parapet walls: Parapet walls are four inch concrete block units tied into the perimeter concrete beam and roof systems described above.

Research:

There is fairly limited research documentation regarding assessment of structures regarding crane failures and HVAC units impacting structures. A report concludes by the Federal

Emergency Management Agency document “FEMA 361: Design and Construction

Guidance for Community Safe Rooms” offers some insight. The FEMA 361 document provides guidelines to the professional community for safe and unsafe structure assemblies regarding hurricane and tornado shelters. The document engages in impact load testing of assemblies of 2’x4’s striking the surface at a particular speed. This type of impact testing is smaller in scale but results of these systems can be correlated to performance under HVAC impact and to less extent steel impact striking the surface. Other documents regarding this topic are specialty related. These documents delve into the particular situation with structural modeling, forensic investigations, field and lab testing and other methods used to determine and understand the likely outcome of the events. We have not taken the fee, time or effort to engage in this type of study.

Occupant safety is maximized with uniform depth, reinforced, redundant type systems for impact loadings. A conclusion on non-uniform depth and reinforced systems is non-predictable, therefore these systems are not recommended to protect occupants. In non-uniform systems, occupant safety depends on how and where the object strikes the surface.

The non-uniform depth double tee’s system with two inch flanges and twelve inch stems with a two inch concrete topping will have various results regarding the same object striking the surface. Thin flange locations would not meet FEMA shelter criteria as they are very susceptible to objects punching through the thin non-reinforced sections. However, reinforced stem depths provide considerable support and capacity for impacts, and can support the load if the impact engages these components. Given non-uniform system performance is randomly based on object strike locations, these systems are an unsafe overall protection for occupants. However, they can and will support impact loadings if the stems are engaged upon impact.

Uniform one-way and two way slab systems would likely meet the FEMA shelter criteria.

These systems are a premium choice for these shelters and perform exceptionally well under impact loading. The main concern and issue is how deep a system is needed to support the impact required. Nine-inch deep two-way slab systems and seven-inch one way slab systems are present in the tower and one-story roofs. Though not specifically designed for FEMA shelters, they meet the criteria will perform well and can withstand significant impact loadings before structural.

Research indicates object rigidity is the important consideration when determining the force impact on structure and these fall into three main categories: Highly deformable, semi-deformable, non-deformable. A solid piece of concrete is non-deformable, steel and wood can be semi-deformable, mechanical HVAC units are highly deformable. The force and energy produced by a highly deformable object is dissipated (crushing) into the object, a semi-deformable object less dissipated and non-deformable objects incur the full impact force.

Determining the deformable objects impact load to the structure can be highly subjective and inaccurate, unless significant efforts in modeling or testing occur regarding these objects.

Per FEMA 361 Section 6.2.2 discussion regarding mechanical units concludes “1500lb units falling 30 feet on a reinforced concrete structure performed adequately.” The results on double tee systems are less confirming and really depend on how the unit impacts the roof.

When the units fall and engage the flanges and stems, acceptable performance occurs. If the unit first impacts only the flanges then spalling and ejection of the concrete tee flange occurs, however the unit did not go through the double tee. Rigid and semi-rigid objects went through the double tee flanges. If engaging the stem of the double tees, the object may be stopped with minor damage to the structure with flange issues discussed above.

Crane failure impact on structures is beyond FEMA scope and there is limited research completed. There is currently no formal research documents discovered discussing this type of scope, and extensive modeling should be completed for accurate analysis of this event.

The information going forward is based on engineer judgment, limited analysis and design, and highlights from available information. This report has not taken those measures and is using guideline documents and research provided by others to provide the client with sound engineering judgment.

Data and Analysis:

• Tower: The tower roof can support an impact loading of singular HVAC units. The method applied was to determine capacity and residual capacity and remove design safety factors as the system is to be evaluated at failure. AHU should be is brought up in sections so unit weight is not more than 9,000 lbs.

The two-way slab performance for crane boom or lattice jib impact depends on the failure method, perpendicular or parallel to the structural system. Parallel impact spall and ejection of concrete may be evident with repair may be needed.

Perpendicular impact the two-way system is to result in failure of the system as it will be punched through by the crane. The small surface area of impact, semi-deformable material, and high impact force will all contribute to the crane jib penetrating the structure. Due to the semi-deformable nature, weight and height the impact force and damage will be greater than the HVAC unit drop. More accurate analysis should be completed to determine the extent of damage that occurs.

Based on engineering judgment the system is likely damaged but the extent unknown without further information. Localized failure with perpendicular crane impacts is likely. As discussed, the system is repetitive and the entire roof system will be able to redistribute loads. This avoids the chain reaction of progressive collapse of the entire roof, so only localized punching of the roof slab will occur.

• One-story: Double tee system may not be adequate for the AHU unit drop.

Reviewing the documents reinforcement information is unknown. A baseline approach of the likely reinforcing was used to determine capacity. The expectation is the flanges will be damaged significantly, while the stems will hold the HVAC unit when engaged. The close concrete stems spacing in two foot intervals will assist this condition.

Lattice jib impacting the surface indicates significant damage. Perpendicular to the surface impacts will result in punching through the concrete roof system. Roof system redundancy is present; however failure of both double-tee stems will result in the roof collapsing along the double tee span. The one-way concrete slab system was not analyzed due to lack of rebar information on the documents. However; the conclusion is these sections will perform similarly, though not quite as well as the two-way tower roof structure. One-way slabs perform well for HVAC unit drops, fair for lattice jib parallel impact, and perform poorly for perpendicular to surface impacts

Span lengths are short and a heavy reinforced slab is anticipated for the mechanical unit locations.

• Parapet walls: Exterior parapet walls are lightly reinforced cantilevered parapets and will be damaged significantly and fail. The concrete beams and the concrete roof have the ability to resist crane booms impacting the side of the building. A likely scenario is the crane impacting and removing the parapet and stopping when hitting the concrete beam and roof system.

Conclusions:

• Tower: The nine-inch two-way slab system roof will perform well for mechanical unit impact and crane jig impact parallel to the surface. Anticipated damage includes threshold spalling and shear cracking around columns. Other issues may need repair after impact occurs. However the occupants are relatively safe during these events. Crane lattice jig or boom impact perpendicular to the surface can result in concrete slab ejecting a portion of concrete similar to the size of the lattice crane.

This condition of crane failure perpendicular to the surface is extremely unlikely.

Under this condition, the jib crane member/connection failure would need to occur over the roof location and may allow a perpendicular impact to the surface. In addition, the weight of the mechanical unit would assist the crane to falling perpendicular to punch into the roof. The roof system likely meets FEMA 361 documents for tornado shelter and can be considered a relatively safe place for occupants. The roof system is very redundant. Failure on one area or section of the roof will not result in failure of other locations.

• One story: The impact from dropping mechanical units from the specified height is questionable over a double tee’s type system. Various depths occur over the roof surface - four-inches total at flanges and fourteen-inches at the concrete stems.

Main reinforcing occurs in the stems. Secondary reinforced flanges and topping slab offers little capacity to resist impact loads. Depending on how the unit drops, minor to extensive damage can be expected. Impact occurring at only the flange location should expect damage as reinforcing is not present to take significant impact loads. Damage includes likely threshold spalling, possible ejected flange sections, and possible roof puncture. However, it is unlikely the unit would collapse the double tee completely once the stems are engaged. It may “catch” the unit before falling completely through. The roof system is semi-redundant as two stems would need to fail. Flanges are connected together at four to six feet intervals to offer possible load redistribution. During crane boom or lattice jib impacts the system will perform somewhat acceptable for parallel impacts, while perform poorly for perpendicular impacts. The system redundancy is better than a single span joist system but not nearly as good as a two-way reinforced slab system.

• Parapet walls: The crane falling into the building is the likely result. The four-inch concrete block parapet would incur significant damage as the crane boom or jib would remove this portion during impact. The crane would come to rest on the perimeter beam and roof system as these components are adequate to protect the occupants and stop the crane from continuing into the building

Guidelines:

Occupant safety concern can be eliminated if crane failure and safe handling of the

HVAC units occur. All parties to take adequate measures to insure safety occurs, especially if occupants remain below during installation. Below are general guidelines

• Follow OSHA current crane standard guidelines.

• Follow manufacturer guidelines for crane usage.

• Follow all procedures outlined by crane operators.

Recommendations:

My recommendation for occupants is below and broken into the following self-explained categories:

Safe, limited risk, potential risk, significant risk, removal.

• Tower:

• Occupants are safe if all HVAC units drop.

• Occupants are safe from crane failure if lattice jib fails fairly parallel to surface being impacted.

• Occupants are at potential risk if lattice boom impacts nearly perpendicular to the surface.

Occupants’ safety is the best in the towers.

• One-story:

• Double Tee System:

o Occupants’ risks varies if HVAC unit drops dependent upon unit weights:

� 0-1500lb safe

� 1500-3000lb limited risk

� 3000lb-9000lb potential risk o Occupants have potential risk if lattice boom fails fairly parallel to surface being impacted.

o Occupants need removal if lattice boom impacts nearly perpendicular to the surface.

• One-Way Slab System:

o Occupants are safe if all HVAC units drop.

o Occupants have limited risk for lattice boom fails fairly parallel to surface being impacted.

o Occupants have significant risk for lattice boom impacts nearly perpendicular to the surface.

Occupants risk potential is higher under the double tees than the one-way slab system. High jib height swings for tower units leads to more occupant risk over the one-story locations.

• Exterior wall:

• Parapet o Interior occupants are safe and have no risk in this area.

o Exterior individuals have risk to falling debris.

• Perimeter concrete beam o Occupants are safe for crane impacts into building.

Please contact me if you have any questions regarding this guidance report. Its intent is to serve as a decision making process for occupant safety. As discussed earlier, structural modeling, laboratory and field testing were not completed in issuance of this guidance.

Overall the building will perform very well in protecting occupants during crane failure or

HVAC drops, except for perpendicular to surface boom or lattice jib failure. If further in-depth requirements are needed to actually predict the outcome of such events, we would be happy to offer our services or direct you to agencies that can provide this service.

Sincerely, DURRANT

Eric D Neuharth

P.E. S.E. LEED

BD+C