Precast+Concrete+Element+Failure+Patterns,+Highlighting+the+Beam+Collapse+at+Pittsburgh+International+Airport+Terminal,+Airside+ Building

Precast Concrete Element Failure Patterns, Highlighting the Beam Collapse at Pittsburgh International Airport Terminal, Airside Building //Oluwatobi S. ////Jewoola ////, B.A.E./M.A.E., Penn State 2015 // toc
 * Pittsburgh, Pennsylvania - August 14, 1990 **

=**Introduction **= The Failure in Airside building occurred on Tuesday, August 14, 1990 at about 9.45 AM during construction when a cantilevered beam in the roof framing, dapped at its ends, collapsed. The beam (RB-35) supports an arched beam on its cantilevered end. RB-35 was made of precast concrete. Due to the method of project delivery, design-bid-build with separate prime construction contracts for different engineering disciplines, design for the precast concrete beam was passed onto the precast concrete subcontractor’s engineer. Series of events were observed and concluded to causes of the failure of beam RB-35. In this paper, other precast concrete failures and their causes are also presented. Possible patterns of failure for precast concrete construction are then discusses.



=**Events leading to failure **= Project delivery method adopted for this project was design bid build with separate prime construction contracts for the different engineering disciplines. Contract documents, which consisted of all applicable building design loads, building performance criteria, and complete design for some structural elements and the foundation system were provided by the professional engineer of record (EOR). However, the design for the precast concrete members were not completely executed by the EOR. (Thornton and DeScenza, October, 1997) The professional EOR attempted to pass some of the design responsibilities to the precast concrete subcontractor. A greater portion of the engineering services that are usually performed by the EOR during the contract documents phase of the project were transferred to the precast subcontractor and were executed during the production of the shop drawings (Thornton and DeScenza, October, 1997). The EOR provided incomplete specifications for the precast concrete members, which led to the final design being done by the contractor’s engineer. A huge section of the design specifications such as the dimension of the rebar embedment, position of the rebar and calculation of erecting stresses were omitted. These documents are generally required to be included in the contract documents but were ignored.

=**Description of Collapse **= The building is framed of precast concrete members. The structural element in question, beam RB-35 which lies between column grid lines B20 and 17 as seen in Figures 2 and 3, is a cantilevered precast concrete beam dapped at the ends to accommodate mechanical and architectural features in the roof framing. The dapped end, approximately 2m long, reduces the 1000 mm deep beam to 600 mm. The beam also supports an arched beam at its cantilevered end.

According to OSHA investigations, the interview statements of the workers and field observations made by OSHA representatives, a series of events occurred as beam RB-35 fell. (Scannell, December, 1990) On the day of the collapse, three planks were placed on the roof framing between column lines B20, B21, 16 and 17 and supported by beam RB-35. Later in the morning, a loud sound, indicative of severe cracking, was heard. Following the crack sound, the choker attached to one of the planks spanning between beam RB-14 and RB-35 was released. (Scannell, December, 1990) A set pattern or sequence of failure was not necessarily observed. However, it was certain that the collapse of beam RB-35 and the rest of the system ultimately occurred following the release of the choker.



=**Cause of Failure **= Beam RB-35 failed at two different locations. (Scannell, December, 1990) The beam split across its vertical plane at the dapped end causing a reduction in depth as the top portion of the failed segment remained in place due to the support of the top reinforcement (see Figures 4 and 5). At another location adjacent to the vertical split, a deduction in beam depth was also observed. (Thornton and DeScenza, October, 1997) The primary cause of collapse of beam RB-35 was insufficient embedment of reinforcement. The amount of reinforcement provided at the beginning of the dapped end where rebars transition into a smaller cross section was insufficient. As illustrated earlier, design of the precast members were performed by the engineer of the precast subcontractor. Even though length of critical rebar, like the transition rebar described, was highlighted on the shop drawings, the position of the bar was not clearly indicated. Likewise, the dimension for the embedment of the bar was not provided (Thornton and DeScenza, October, 1997). Further research also showed that the ultimate moment capacity of beam RB-35, based upon the as-built condition, was incapable of handling the total ultimate applied moments. (Thornton and DeScenza, October, 1997) No comment was made by the EOR regarding the embedment of the critical rebar upon the submittal of the shop drawings.







=**<span style="font-family: Arial,sans-serif; font-size: 14pt;">Other Precast Concrete Failures **=

** __<span style="font-family: Arial,sans-serif; font-size: 10pt;">Severe Cracking of Double-T beams at Pittsburgh International Airport Parking Garage __ **
<span style="font-family: Arial,sans-serif; font-size: 10pt;">At the same airport, Pittsburgh International Airport, major structural defects were noticed in a parking garage. The parking garage, built in 1992, is a 3-story concrete structure with about 2100 parking spaces. Supporting the 2nd and 3rd floors of the garage are precast concrete double-T beams which bear on L-shaped girders (ledger beams). Similar to the Airside building, the double-T beams were dapped at the ends where they sit on the ledger beams. <span style="font-family: Arial,sans-serif; font-size: 10pt; line-height: 1.5;">Long after the garage had been in frequent use, severe cracks were noticed close to the dapped ends of nearly all the double-T beams in the garage. Baker Engineering, a firm that performs forensics testing was employed as a third party to perform tests on the double-T beams and determine the cause of failure. (Sawyer, December 1998) After performing analyses on the structure, the county concluded that the cracks were indicative of shear failure caused by inadequate prestressing and/or bonding between reinforcing tendons and concrete. (Sawyer, December 1998) Improper prestress at the end zones, improper placement of hanger and/or reinforcing bars at the beams’ dapped ends were also contributors to the failure.

**__<span style="font-family: Arial,sans-serif; font-size: 10pt;">Collapse of Tilt-Up Precast Concrete Wall Panel __**
<span style="font-family: Arial,sans-serif; font-size: 10pt;">A tilt-up wall panel made of precast concrete collapsed during the construction of a Home Depot Store in Greensboro, NC. The 23 ft. tall wall panel, located at the perimeter of the building, weighs about 40,000 pounds with a 20 ft. length and 6 ½ in thickness. The wall supports the joists located at the exterior bay. It is supported by the foundation walls over shims at its ends as seen in Figure 6. (Ayub and Dinesh, September, 2002) At the time of failure, the space between the wall panel and the foundation wall was scheduled to be grouted and the wall panel was to be connected to the slab on grade (SOG) by a closure strip which will occupy the last 4 ft. of the SOG.



<span style="font-family: Arial,sans-serif; font-size: 10pt;">At about 11.30 AM during construction the wall suddenly fell over three workers. (Ayub and Shah, September, 2002) Prior to the collapse, the tilt up wall contractor instructed the subcontractor to remove the pipe bracing the wall based on a report obtained from the Testing Agency. This report states that the welds holding the roof joists and the embedded steel plates of the wall together had been completed. Therefore, bracing the wall will be redundant. However, the bottom connection involving the attachment of the wall to the slab on grade was not yet placed leaving the shims at the ends of the wall as the only support for the wall after the temporary bracing was removed. (Ayub and Shah, September, 2002). A situation of substandard construction was also observed. (Ayub and Shah, September, 2002) 1 in grout was specified for the space between the underside of the tilt-up wall and the foundation. This is well below the 2 in to 4 in range required by the structural engineer.

<span style="font-family: Arial,sans-serif; font-size: 10pt;">**__Additional Precast Failure – Parking Garage__**
<span style="font-family: Arial,sans-serif; font-size: 10pt;">A precast failure took place in a parking garage. The name and location will not be stated due privacy concerns as this case was settled out of court. The garage was originally designed as cast in place concrete. During the construction phase, it was decided that the cast in place members be changed to precast members. The floor framing, like Pittsburgh International Airport parking garage, was to consist of double T precast beams and L-shaped ledger beams supporting the double T beams. Also, some site layout issues were observed at the foundation footings. These issues were rectified by moving the foundation footing away from the obstructions observed. However, the footing was not redesigned to account for the increased soil pressure due to the different load. <span style="font-family: Arial,sans-serif; font-size: 10pt; line-height: 1.5;">Several issues were observed in the site prior to the failure that if corrected in time, could have prevented the collapse. The base plate at the base of the column around which the collapse surfaced wasn’t grouted on time leaving the base plate and column connection at a substandard for a long period of time. The column in question was also unbraced during construction. In addition, extra live load incurred from lifting the double T precast beams and ledger beams in place with heavy equipment was not accounted for when the precast members were designed.

=**<span style="font-family: Arial,sans-serif; font-size: 14pt;">Repair measures Adopted for Airside Building **= <span style="font-family: Arial,sans-serif; font-size: 10pt;">RB-35 design was used at different locations in the building. (Thornton and DeScenza, October, 1997) After the collapse, particular attention was paid to erection loads associated with the handling of the precast members. A procedure for quality assurance was enacted to verify the contents of contract documents and shop drawings. <span style="font-family: Arial,sans-serif; font-size: 10pt; line-height: 1.5;">(Thornton and DeScenza, October, 1997) Shoring was placed at the different locations where RB-35 beam design was used, as well as other areas where similar deficiencies were suspected. In addition to the shoring, repairs were also made to increase the ultimate capacity of the beams.

=**<span style="font-family: Arial,sans-serif; font-size: 14pt;">Possible Patterns of Failures observed for Precast Concrete Construction **= <span style="font-family: Arial,sans-serif; font-size: 10pt;">After critically examining cases of precast concrete failures, I noticed that there are no specific patterns or identical technical reasons for precast concrete failures as conditions and circumstances surrounding the event may vary with respective collapse. However, I found hints of carelessness or inattention of professional personnel involved (engineers or contractors) to be major facilitators of most of these failures. In the collapse of RB-35, it was stated that the main cause of failure was the inadequate provision of rebar embedment at the dapped end of the beam. This could have been avoided if the design specifications were completely provided by the EOR or the shop drawings were properly documented by the precast subcontractor and critically reviewed by the EOR. Similarly, ensuring proper prestressing and bonding between reinforcing tendons and concrete, preventing an early removal of the temporary bracing for the tilt-up wall panel, and grouting the base plate to the column on time could have prevented the failures at the Airport Parking garage, the Home Depot store and the additional parking garage discussed respectively. All of these scenarios are representative of human errors that could have been avoided. Nevertheless, technical causes are also attributed to these failures as described earlier. Technical errors vary with respect to collapse as circumstances leading up to the failure may differ with respect to the project. = =

=**<span style="font-family: Arial,sans-serif; font-size: 14pt;">Lessons learned to Prevent Precast Concrete Failures **= <span style="font-family: Arial,sans-serif; font-size: 10pt;">(Thornton and DeScenza, October, 1997) It is important that the lines of design responsibilities be clearly stated in a project delivery. Performance criteria should be issued and possible assumptions that may be detrimental to the design of the structure should be highlighted. Special attention should be made to interconnecting members and their connections. <span style="font-family: Arial,sans-serif; font-size: 10pt; line-height: 1.5;">Unlike cast in place construction where formwork is created for concrete assemblies, erecting precast members requires critical observation of their connections to neighboring members and supports. The precast concrete tilt-up wall may have eluded a collapse if it was designed as a cast in place member. Formwork could have been constructed and a monolithic assembly consisting of the wall and slabs maybe have reduced the need for additional bracing as long as proper formwork erection and reinforcement installation are ensured. For precast concrete members as it is the case of the tilt-up wall and the other precast failure discussed, special attention needs to be paid to the separate members (wall, floor, foundation, column etc.) as they come together. Similarly, critical analyses of the design of reinforcement, rebar placement and reinforcement embedment should be ensured.

=**<span style="font-family: Arial,sans-serif; font-size: 14pt;">Summary and Conclusion **= <span style="font-family: Arial,sans-serif; font-size: 13.3333px;">The investigation of the precast concrete failures at the airside building and parking garage of Pittsburgh International Airport, Home Depot store and the additional parking garage show that there are no specific patterns to the failures of precast concrete construction. A series of technical and human errors were observed to have caused the failures. Inadequate design and construction were some of the technical causes of failure observed. Nevertheless, I found human errors to be more apparent in most cases. Failure to pay attention to contract documents, shop drawings, connection details and on-site irregularities were contributors to the failures. Precast concrete failures can be limited in project deliveries if personnel associated with the delivery of the project can ensure that their respective duties are properly handled.

=Bibliography=
 * <span style="font-family: Arial,sans-serif; font-size: 10pt;">ACI Committee (2005) “ACI 318-11 Building Code Requirements for Structural Concrete” American Concrete Institute. **
 * <span style="font-family: Arial,sans-serif; font-size: 10pt; line-height: 1.5;">ACI 318-11 provides minimum requirements for designing and constructing concrete members.

<span style="font-family: Arial,sans-serif; font-size: 10pt;"><>
 * <span style="font-family: Arial,sans-serif; font-size: 10pt;">Ayub, Mohammed and Shah, Dinesh (September, 2002) “Investigation of the August 5, 2002 collapse of tilt-up precast concrete wall panel in Greensboro, NC” OSHA. **
 * <span style="font-family: Arial,sans-serif; font-size: 10pt; line-height: 1.5;">This report presents OSHA investigation on the 2002 precast concrete wall collapse in Greensboro, which involved post incidental field observations. It also includes testing results of material properties of the concrete beams and structural analysis to determine cause of the accident.

<span style="font-family: Arial,sans-serif; font-size: 10pt;"><>
 * <span style="font-family: Arial,sans-serif; font-size: 10pt;">Chavanic, James (2013), “Pittsburgh International Airport parking garage precast double-T structural defects, Pittsburgh, PA (1998)” Failures Wiki. **
 * <span style="font-family: Arial,sans-serif; font-size: 10pt; line-height: 1.5;">In this paper, James discusses the structural defects that occurred at the parking garage of Pittsburgh International Airport, events leading up to the incident and possible causes of the failure.

<span style="font-family: Arial,sans-serif; font-size: 10pt;"> < https://failures.wikispaces.com/Parking+Garage+Collapse+in+San+Antonio>
 * <span style="font-family: Arial,sans-serif; font-size: 10pt;">Li, Jiang (2012) “San Antonio Parking Garage Collapse, San Antonio, Texas (February 14, 2011)” Failures Wiki. **
 * <span style="font-family: Arial,sans-serif; font-size: 10pt; line-height: 1.5;">In this paper, Jiang discusses the 2012 collapse that occurred at the parking garage in San Antonio, events leading up to the incident and possible causes of the failure.

<span style="font-family: Arial,sans-serif; font-size: 10pt;"><>
 * <span style="font-family: Arial,sans-serif; font-size: 10pt;">Sawyer, Tom (December, 1998) “Airport beam cracks are filled, wrapped in time for holidays NMP/DCG” Engineering New-Record. **
 * <span style="font-family: Arial,sans-serif; font-size: 10pt; line-height: 1.5;">This article discusses the parties involved in the repair and an overview of the legal filings regarding the failure of the beams.


 * <span style="font-family: Arial,sans-serif; font-size: 10pt;">Scannell, Gerard F. (December, 1990), “Investigation of August 14, 1990 collapse of precast concrete beams at Airside Building, Midfield Terminal Project, Greater Pittsburgh International Airport” Occupational Safety and Health Administration (OSHA). **
 * <span style="font-family: Arial,sans-serif; font-size: 10pt; line-height: 1.5;">This report presents OSHA investigation on the 1190 collapse at Airside Building, which involved eyewitness accounts, interviews of the designer, engineers, and a quality control and precast fabricator personnel. It also includes observation of the collapsed structural elements; testing of material properties of the concrete beams and structural analysis to determine cause of the accident.

<span style="font-family: Arial,sans-serif; font-size: 10pt;"><[]>
 * <span style="font-family: Arial,sans-serif; font-size: 10pt;">Schwartz, Eileen and Wood, Debra. (February 14, 2011) "Contractor Sounds Evacuation Alarm Prior To Texas Parking Deck Collapse." Engineering News-Record. **
 * <span style="font-family: Arial,sans-serif; font-size: 10pt; line-height: 1.5;">This article provides a background information of the parking garage and describes how the contractors reacted after the accident.


 * <span style="font-family: Arial,sans-serif; font-size: 10pt;">Thornton, Charles H and DeScenza, Robert P. (October 5, 1997), “Concrete collapse of precast concrete framing at Pittsburgh’s Midfield Terminal” American Society of Civil Engineers. **
 * <span style="font-family: Arial,sans-serif; font-size: 10pt; line-height: 1.5;">This article presents the events leading to the 1990 collapse of portions of the precast concrete structure frame at the Airside Passenger Terminal. The basic structural framing system and construction approach are defined and factors contributing to the collapse are outlined. The paper includes suggested approaches to help minimize the potential for similar failures occurring in the future.

=Additional Resources and References=
 * <span style="font-family: Arial,sans-serif; font-size: 10pt;">Prestressed Concrete Institute (2004). PCI Design Handbook, Precast and Prestressed Concrete. 6th Edition. **
 * <span style="font-family: Arial,sans-serif; font-size: 10pt; line-height: 1.5;">PCI Design Handbook provides methods of designing precast concrete and prestressed concrete members.