Graduation Year

2011

Document Type

Thesis

Degree

M.S.C.E.

Degree Granting Department

Civil Engineering

Major Professor

Austin G. Mullins

Keywords

Foundation Movement, Slab Lifting, Slab Support, Structure Displacement, Underpinning

Abstract

The restoration of foundations of residential and light commercial structures that have been affected by differential displacement resulting from problematic soil conditions has been an ongoing issue since early times. In Florida, the issue of structures being affected by subsidence of soils related to sinkhole activity has been a problem that has gained more interest and exposure within the last 20 years. Structures affected by sinkholes have been historically addressed by remediating the soil mechanism which caused the structure to displace and then structurally addressing the portions of the structure that have displaced with steel underpins installed on the foundation. More comprehensive soil investigations are revealing that multiple soil mechanisms are contributing to the displacement of structures. Based on case studies of structures being partially underpinned on soils affected by multiple problematic conditions, Engineers have been forced to develop more comprehensive foundation restoration plans. These comprehensive plans were intended to address the potential for differential movement between portions of the structure supported by post-construction deep foundations and those portions of the structure that remain bearing on the soil.

With limited products available for Engineers to rely on to adequately support cast-in-place concrete slabs on grade, the comprehensive restoration of structures on problematic soils has become cost prohibitive and structures throughout the state of Florida are either being left in a distressed state or are being repaired with substandard repair methods. Being exposed to this ongoing trend manifested the need to develop a solution to this detrimental problem.

Having been involved in the design phase and the restoration process of structures affected by displacement, a comprehension was developed on the products available to support and restore slabs on grade and where those products were deficient. After several prototypes, the development of a new support bracket was invented which would more efficiently support and lift displaced slabs. This slab support bracket was named the ISB-07.

This thesis is based on the research and development that was conducted on the ISB-07 and on different slab specimens. This research was performed to demonstrate that a slab supported by the multi pivoting arm ISB-07 slab bracket can be more efficient than previous support methods.

It was concluded, after performing full scale testing, ultimate load testing, stress analysis, computation and finite element analysis, that the influence area of support provided to a cast-in-place concrete slab by the ISB-07 is greater than previous support methods. Therefore, the required spacing between interior slab supports when the ISB-07 is utilized is significantly increased and therefore the amount of interior supports warranted is reduced. With this reduction in interior supports, the disturbance of the existing structures slab is minimized. This reduction in disturbance and materials needed to stabilize structures directly translates to a cost savings which in turn will lead to more structures being properly repaired.

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