This project was the ACEC Tennessee Engineering Excellence Awards Grand Award, Structural Systems, Small Projects winner in 2022.

Nestled underground, adjacent to the Memphis Light Gas Water (MLGW) administration building, sits a concrete parking structure. Originally constructed in the late 1960s, the garage is a cast-in-place, two-way concrete slab. In February of 2021, a significant weather event in the Memphis area caused or contributed to a break around one of the support columns on the upper level of the garage. MLGW immediately reached out to SSR as their on-call consultant to help assess the situation and direct a contractor that was already engaged in work at the administration building to install shoring at the failed slab level and at a lower level to carry the load to the ground slab. This work was performed over the course of two days.

During the next four weeks SSR engaged in regular inspections to ensure that no further movement occurred. During this time, the SSR team began to conduct analyses of the existing structure to formulate repair plans. Repair plans consisted of three main elements: repair of the break, installation of additional steel beam supports in specific areas of the garage, and regrading of the grass roof.

 

Uniqueness/Innovative Application of New or Existing Techniques

There were several key items that made the repairs to the MLGW parking garage a unique project:

• Emergency nature of the project
• Complexity of repairs
• Future mitigation efforts

The first aspect of the project that is unique is the sheer emergency nature of the situation. It’s not every day that a large, monolithic concrete structure fails in some capacity. The flexibility of the team to act quickly to stabilize the structure and prevent additional damage was critical to the overall success of the project.

The second unique aspect of the project was the complexity of the repairs. The existing structure was a cast-in-place waffle slab. This presented several challenges in terms of repair. The analysis of the damage and the design of the repair to maintain the existing force profile presented several engineering challenges. Following design, the demolition of the damaged portion, though time consuming, was vital to maintaining as much of the intact rebar as possible. Construction presented its own challenges with the recreation of the existing cast-in-place waffle pattern in some locations.

Finally, the additional efforts to ensure the longevity of the structure were two-fold. Steel beams were placed in several locations in the garage to reinforce the existing structure. These additions were made on the opposite side of the garage in the mirror image location of the break, as this area experiences similar loads to the damaged location, and a secondary location where cracking had begun to occur. In addition to these efforts, the grass roof was regraded to reduce the load created from above. Special considerations were taken during this effort due to the condition of the garage including the weight of equipment and placement of moved earth and materials.

 

Future Value to the Engineering Profession

In today’s world, “replace” is often preferred over “repair.” It’s refreshing when a project team comes together and is intentional about repairing an existing structure, especially in an emergency situation.  Following conventional wisdom is the easiest path, but the partnership between SSR and MLGW to find the best solution to the specific needs of their facility and community is a testament to the ability of the profession to drive the industry forward through conservation. While the MLGW project may not redefine current engineering thinking, it does illustrate the ability of the team to successfully navigate the range of challenges presented by a complex repair project and speaks to the ingenuity that continues to be inherent in the profession.

 

Social, Economic, and Sustainable Development Considerations

SSR’s approach to the MLGW emergency parking garage repairs provided the owner with social, economic, and sustainable development benefits.

Social. If the parking garage failed, or incurred further damage, staff access and quality of life would be impacted given the location of the garage and administration building in the busy downtown district and the limited alternative parking. The performed repairs allow the structure to continue to serve as a resource to MLGW and their staff.

Economic. MLGW is a public utility, meaning the stewardship of their resources and funds have a direct impact on the community. The combination of these repair and mitigation efforts made for a fiscally responsible solution to prolong the life and use of the existing parking structure.

The approach taken by SSR was to extend the life of the facility as much as possible. While repairing the damaged area was imperative, additional measures were taken to ensure the continued functionality and safety of the structure for the future. Additional steel beams were placed to reinforce sections of the garage that could be subjected to similar forces that damaged the current repair area. In addition, the grass roof was regraded, reducing the earth levels by two and a half feet in most areas, and the subsequent loads on the structure.

Sustainable Development. With any situation where you are repairing or reusing an existing structure, your environmental impacts are reduced in comparison to replacement. The reduction in new raw materials used as well as the smaller amount of construction waste created makes for a more sustainable project overall.

 

Complexity

The repair of the MLGW garage offered several challenges. The first was the emergency nature of the project. The SSR team’s response had to be immediate, thorough, and collaborative with the contractor to protect the facility from further damage and prevent injury to those on site. Another challenge with working in a repair environment is the differences in codes. There have been significant changes in building codes since the construction of the garage in 1968, complicating the design of the repairs and mitigation efforts to meet current codes while not changing the distribution of the loads and adversely effecting other portions of the structure.

 

Successful Fulfillment of Client/Owner Needs

The SSR team took an active approach to ensuring project success, working closely with the owner and contractor on this challenging repair. Throughout the project, SSR’s team was in constant communication with our partners at MLGW. At all times, they were aware of the project’s status — from the initial emergency shoring efforts through the analysis, design, and repair of the facility. This level of communication allowed the project team to reduce delays and better navigate challenges across the life of the project.