Building 55 - Structural Report.pdf

Engineered Solutions for Building Envelopes®

James A. Haley VA Medical Center

Building 55 – Parking Garage Structural Investigation Report

KMK Construction, Inc.

c/o Ms. Jessalyn DiSclafani, AIA 730 South Sterling Ave., Suite 306 Tampa, FL 33609

Building Envelope Consultants and Scientists, LLC Traci Powell, P.E., Project Manager

437 Grant Street, Suite 1801 Pittsburgh, PA 15219

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Engineered Solutions for Building Envelopes®

January 26, 2021

ATTENTION: KMK Construction, Inc.

c/o Ms. Jessalyn DiSclafani, AIA 730 South Sterling Ave., Suite 306 Tampa, FL 33609

SUBJECT: Structural Investigation Report

Building 55 – Parking Garage Tampa, FL 33612

BECS #VA.2020.073

Dear Ms. DiSclafani:

Building Envelope Consultants and Scientists, LLC (BECS) is pleased to submit the following report summarizing the findings of our visual observations and assessment of the tee-to-tee connectors in the precast concrete parking garage at the referenced address.

Background

On October 5, 2020, BECS personnel, accompanied by KMK Construction Inc. (KMK) personnel, visited Building 55 of the James A. Haley VA Medical Center complex in Tampa to observe the nature and extent of tee-to-tee connector issues reported at the precast concrete parking garage structure. Following our onsite review, BECS was provided with the original construction documents, including architectural and structural drawings by HDR Architecture Inc. dated July 24, 2009. All comments in this report related to “drawings” reference this drawing set and all captioned images of drawings contained herein were taken from them. The precast concrete design submittal was requested by BECS but was not available for our review. The following is a summary of our findings.

Observations

The parking garage is an approximately ten-year-old, six level, precast concrete structure. The elevated garage decks are four bays wide by nine bays long and constructed of precast double tees. The western two bays, A-B and B-C, are inter-level ramps while the eastern two bays, C-D and D-E, are level (reference Images 1 and 2 on the following page). The double tees are supported by haunched lite walls on grid lines B and C, inverted T-beams on line D, and inverted L-beam spandrel panels on lines A and E. The precast T and L-beams are conventionally supported by precast columns, which bear on shallow, spread footing foundations.

The double tees comprising the garage floor decks are primarily pretopped (the entire tee flange was cast in the precaster’s shop) with the exception of the four corner bays, which are field topped (two-inch, plant-cast tee flanges topped in the field after erection with a concrete topping slab).

Structural Investigation Report

Building 55 – Parking Garage Tampa, FL 33612

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Image 1 - Typical Floor Plan Image 2 - Isometric

It was reported to BECS personnel that in certain locations within the garage, floor framing members were perceived to be excessively “bouncy” as vehicles drive over them. This phenomenon commonly occurs in precast garages framed with double tees when connectors between the tees have fractured or failed. The investigation of these connectors was the primary objective of BECS’s onsite review.

With this type of slab system, the double tee (“TT” shaped) members are placed side by side and their horizontal top flanges create the parking deck surface. Adjacent tees are commonly connected along their length by welding together aligning steel hardware that is embedded in the tee flanges on either side of the joint. While the primary purpose of the connectors is not to support gravity loads (downward-acting loads including vehicular live loads), they do serve several other important functions. In terms of load resistance, they counteract movement induced by thermal expansion and contraction forces and they resist shear across the joints induced by lateral wind and seismic forces. They also allow tee flanges to mutually support one another to resist differential deflections. When connectors fail, the adjacent tees deflect independently as vehicles drive over them, causing the perceived bounciness, often accompanied by loud noises, as tires cross the uneven joints between tees.

The tee-to-tee connectors in Building 55 were observed to be smooth, round, stainless steel bars, commonly referred to as slugs, that are designed to be welded on both sides to reinforcing bars embedded within the adjacent tee flanges. BECS observed that the connectors generally conform with the connectors depicted in the original structural drawing detail for field topped tees (see Image 3 of Detail 7 from structural sheet S-511). These connectors were present throughout the garage, including locations with pretopped tees, where the structural drawings indicate that a different connector detail was to be used (consisting of proprietary connectors by JVI, as shown in Image 4 of Detail 10 from structural sheet S-511).

BECS counted ten connectors per joint at the typical joint conditions. The required spacing of connectors is not provided on the structural drawings as this information would typically be specified on the precast shop drawing submittal, therefore BECS is unable to comment on the adequacy of the connector spacing.

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Image 3 - Connector Detail for Field Topped Tees Image 4 - Connector Detail for Pretopped Tees

In several locations, BECS observed failed connectors where the slugs were missing, indicating that the welds on both sides of the connection fractured, causing the slug to fall to the level below. In one instance, BECS located a slug on the grade beneath the first floor level (see Image 5 of recovered slug). The slug was observed to be stainless steel, 1-1/4” in diameter by 3-1/2” long. Weld material was observed to be intact on both side of the slug. On one side, the weld is an approximately 1/8” flare-bevel groove weld that appears to be a shop weld. On the opposite side, the weld is an approximately 1/4” flare-bevel groove weld that appears to be a field weld.

KMK personnel drove a vehicle around the various levels of the garage while BECS personnel observed, on foot, the deflection of the tees beneath the tires and listened for the sounds indicative of failed connectors. While it would be difficult to locate individual failed connectors in this manner, locations where multiple or perhaps all, of the connectors along a single joint were able to be detected. BECS isolated these locations to eight joints between pretopped tees on the first floor level ramps (see joints indicated in red on Image 6). In most locations where failed connectors were observed, little to no deterioration of the concrete tee flange edges was observed.

BECS observed that the sealant at the weld pockets over the connectors was deteriorated throughout the garage, most notably on the top level, where sealant was observed in several locations to be missing entirely, exposing the connector below (see Image 7).

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Image 5 - Recovered Slug Image 6 - First Floor Ramps

Image 7 – Missing Sealant at Weld Pocket

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Evaluation

Failed tee-to-tee connectors are a common occurrence in precast concrete double tee garages. Connectors can fail for various reasons, including design, fabrication, and installation deficiencies as well as fatigue caused by heavy garage traffic.

Another common cause is corrosion of the embedded connector hardware. In the presence of water (and dissolved chlorides in other locales where deicing salts are used), the steel components of the connectors corrode. Corrosion can cause the embedded steel hardware to expand, and the pressure exerted by the expanding steel causes the surrounding concrete to crack and spall. Deterioration of the concrete leads to further exposure of the connector hardware and welds to moisture. Exacerbated by cyclical loading of vehicular traffic across the joints, this leads to a fracture of the embedded bar or the weld between the bar and the slug (as was the case for the slug recovered by BECS, where the welds were observed to have fractured at the interface with the embedded bars on both sides). BECS noted very little deterioration of the concrete surrounding the connectors, which suggests that corrosion of the embedded steel components may not be a factor.

BECS noted non-conformance between the as-built conditions and the structural drawings as they relate to the type of connectors to be used. The connector detail used at the pretopped tees did not match the specified pretopped tee connector detail, but instead corresponded with the field topped detail. While it is presumed by BECS that both details would have been designed for a similar load capacity, the welds used for a round slug detail may be less resilient and more susceptible to corrosion-induced deterioration, and would be more appropriate for a condition where the concrete topping covers the connector hardware (as would be the case for field topped tees). When used with pretopped tees, the connector’s only protection from moisture is the sealant in the pocket above, which BECS observed to be deteriorated and missing throughout the garage.

BECS did not find any other evidence during our onsite review or subsequent document review and analysis to suggest a design or capacity related issue with the tee-to-tee connectors. The difference in weld sizes observed on the two sides of the recovered slug could be indicative of an issue with the welds, however, it is more likely that the field welds were upsized to account for variability in field conditions as opposed to the shop welds being undersized. BECS cannot state whether the welds provided are adequate with respect to the those designed without performing a review of the precast concrete shop drawing submittal, which was not available. This delegated submittal is where the final, formal design of the connectors would be specified and may differ from the detail provided on the structural drawings. (Though the precast manufacturer uses the structural drawings as a basis for their design, it is common for the designer to modify or adjust certain aspects or details of the precast members to conform with their shop’s standard practices.)

BECS did find it unusual that the welds on both sides of the recovered slug were fractured. Typically, when the weld on one side fails, the slug remains connected to the other side (though the connection no longer provides any load resistance).

It is possible that after the weld on one side failed, movement of the adjacent precast flanges due to thermal effects and cyclical, vehicular loading caused the weld on the other side to fracture due to cyclical impact of the slug into the adjacent tee flange. At the failed connectors which BECS observed, we were unable to determine which weld failed, the shop weld or the field weld (or which failed first, in the instances where both welds failed) as the sealant in the weld pockets were intact in these locations. Therefore, it is not definitive whether a potential weld issue lies in the shop welds or field welds.

Either way, the potential exists that the incorrect welding electrode could have been used to connect the stainless steel slug to the presumably stainless steel embedded bars. The structural drawings indicate E-308 electrodes, which are the correct welding electrodes to be used with stainless steel, however BECS cannot confirm whether the as-installed welds conform with this specification.

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It is the opinion of BECS that fatigue due to vehicular loads, possibly in combination with deterioration due to corrosion or deficiencies in the welds, is the primary contributor to the failure of the connectors. This opinion is supported by the fact that the heaviest vehicular traffic occurs at the lowest level, where cars enter, and tapers off as you move up the levels of the garage. Also, the first level ramps near the entrances have a high exposure to moisture, as cars track moisture into the garage during rain events. With the increased exposure to moisture caused by failed sealant at weld pockets, the welds between the round slugs and embedded reinforcing bars are particularly susceptible to deterioration.

Tee-to-tee connectors tie the flanges of precast concrete double tees together, allowing the individual tees to function as a unified slab system, where forces are distributed across multiple connectors. Therefore, one failed connector does not result in a catastrophic failure of the double tees nor does it result in a significant reduction in the load-carrying capacity of the floor system. Double tees do not rely on the connectors to support gravity (vehicular) loads and therefore do not pose a significant safety risk in that regard. The reduction in load capacity of the tees to resist tension and compression forces due to thermal expansion and contraction is minimally affected by a single failed connector. Similarly, the reduction in shear load resistance due to lateral wind and seismic forces is minimal for a single failed connector.

Failed connectors become problematic when there are multiple connector failures along a single joint. When all of the connectors along a joint between two adjacent tees fail, the integrity of the floor slab diaphragm to resist wind and seismic loads is compromised. This can happen relatively quickly after one connector fails; the loads previously resisted by that connector are redistributed to the adjacent connectors. As adjacent connectors become overloaded, they too fracture, and the joint begins to unzip.

Recommendations

At the locations observed by BECS to have multiple connector failures along a joint (eight locations at the time of BECS’s onsite review), BECS recommends remediation of the connectors within the short-term future (six months). BECS estimates that approximately 80 connectors will require short-term remediation. As stated, BECS did not pinpoint the locations of individual failed connectors. Isolated connector failures, while not of an immediate structural concern, can lead to a progression of connector failures along a single joint. Therefore, BECS recommends that the locations of all visibly failed connectors throughout the garage be determined by a contractor and that the remediation of any connectors not previously addressed during the short-term repair phase be performed within the intermediate-term future (two years).

Furthermore, BECS recommends that visual inspections of connectors be implemented into the garage’s maintenance program, and that the failed connectors be remediated on a regular basis. BECS also recommends replacement of all deteriorated tee-to-tee sealant joints.

There are many available options for the remediation of failed connectors, including replacement, repair, and retrofit.

Replacement of failed connectors involves demolition and repair of the concrete surrounding the embedded portions of the failed connector on both sides of the joint. There are many options available for replacement, including proprietary connector hardware such as the JVI vector connectors (see Image 8) which were specified on the original structural drawings for pretopped conditions. Replacement is likely to be the most costly option, but provides the most effective solution in terms of long-term durability and load-carrying capacity.

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Repair of failed connectors involves determining the locations of fractured welds; and cleaning, preparing, and re-welding the existing embedded reinforcing bars to the slugs; and replacing the sealant pocket. This option eliminates the cost of the new connector hardware but does not improve the susceptibility of the connector to corrosion due to moisture as the only protection provided for the connector is the sealant which will degrade over time. Therefore, this option is not recommended by BECS.

Retrofit of failed connectors involves leaving the failed connectors in place and supplementing with new connectors, oftentimes located at the mid-points between the existing connectors. Several options for retrofit are available. One potential option is the installation of external steel members to the underside of the tee flanges. These members can be steel plates, angles, or channels running perpendicular to the joint and bolted to the underside of the slab with post-installed anchors (see Image 9). This option is cost-effective in terms of eliminating concrete repairs and is particularly well suited to applications where minimal deterioration of the concrete flange edges is present at the existing connectors to otherwise require concrete repairs. However, because the connector is external to the concrete slab, over time it is susceptible to deterioration from corrosion.

Another option for retrofit is the installation of proprietary carbon fiber reinforced polymer (CFRP) biscuits (see Image 10 of T-Biscuit Connector by V2 Composites, below). The installation of the biscuits involves saw-cutting a slot in the top surface of the slab across the joint, inserting the biscuit into the slot, and filling the slot with a bond paste. This option also eliminates the cost of concrete repairs and can be installed relatively quickly and easily. During our analysis, BECS compared the shear load capacity provided by a 3-1/2” long, 3/16” flare-bevel groove weld using E-308 electrodes (as was depicted on the original structural drawing detail) to that of a T-Biscuit connector, manufactured by V2 Composites, and found the connectors to be of a similar capacity. Therefore, BECS considers this product to be a structurally acceptable alternative for retrofitting the existing connectors.

Image 8 - JVI Vector Connector Image 9 – Steel Angle Connector

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Image 10 – V2 T-biscuit

Limitations

Evaluations of existing buildings and their components require that certain assumptions be made regarding existing conditions. Some assumptions cannot be verified without performing intrusive investigations, which can prove costly and may damage existing features of the building. We did not remove additional finishes, take samples, or perform tests. Our evaluations do not consider conditions that may become, or cause, structural deficiencies or defects and are limited to the visually apparent condition of the components at the locations observed and at the time of the investigation. We are not responsible for other portions of the property that are not a part of this investigation or for components unrelated to those reported such as heating, AC, electrical, and plumbing. We did not investigate for the presence or absence of any hazardous substances including but not limited to toxins, carcinogens, mold, noise, and or contaminants in soil, water, and air.

We performed these services in a manner consistent with the level of skill and care ordinarily exercised by professional engineers and consultants practicing in this region under similar conditions. No other representation, warranty or guarantee is given. Our opinions are based on our engineering judgment. We will not be responsible for latent defects that may appear in the future or for differing opinions of others that may arise. The intent of our investigation was not to perform an exhaustive study to locate every existing defect, but rather focuses on overall condition of the elements of concern, and specific conditions brought to our attention by the Client. Should additional information become available that we were not aware of, did not see, or which was unknown at the time of our investigation, we reserve the right to revise our report as needed.

This report is to be read in its entirety; thus no portions of this report may be used outside the context of the entire report.

This report is not a construction document and is not intended to be used for construction or actual repairs based on this report alone. This report is intended solely for the use of the Client or Owner; any third party use, third party reliance, or third party decisions made on the basis of this report shall be the sole responsibility of such third parties.

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Closing

It is recommended that the details and design of the remediation options described above be established for Building 55 by an experienced registered professional engineer, and that all repairs be performed by a qualified concrete repair contractor. Upon request, BECS may provide drawings showing replacement, repair, or retrofit connector details.

We appreciate the opportunity to be of service and look forward to our continued service as your engineering consultant.

If you have questions regarding this report or require additional assistance, please contact our office at your convenience.

Sincerely, Building Envelope Consultants and Scientists, LLC

Traci Powell, P.E. JP McDonald, P.E.

Project Manager Vice President