Two-level stucco house with water damage on stairs
Elevated home in Nassau Bay, Texas (Source: Cedric Ling, August 11, 2020).

Rising Above the Flood: A Decision Tool for Structural Safety

Communities along the U.S. Gulf Coast experience severe flooding events that cause extensive casualties and property damage. In 2005, Hurricane Katrina generated storm surges as high as 11.45 feet (3.5 m) along the state of Louisiana’s coast and cost the country $161 billion in damage, according to the National Oceanic and Atmospheric Administration (NOAA). Robbie Berg at the National Hurricane Center reported that, in 2008, Hurricane Ike inundated the coastal communities of Texas with as much as 10 feet (3.1 m) of water and left damage worth a total of $19.3 billion.

After those and similar flooding events, homeowners may choose to elevate their homes above the base flood elevation, which is a viable mitigation method to reduce or eliminate flood damage. To do this, the existing concrete foundation slabs are typically cast in place directly on the soil support – about 4 inches (102 mm) thick with minimal reinforcement of a single layer of welded wire fabric. The slab perimeter is typically provided with a concrete-grade beam for added stiffness.

The elevation method involves raising the slab home and the attached beams to as much as 15 feet (4.6 m) and placing them on pier supports. For economy and practicality, solid concrete or stacked concrete masonry units are typically used for piers. These are usually placed below the grade beams or newly added steel beams if additional supports are required.

An Existing Knowledge Gap

Elevating a home above the base flood elevation is a viable option for flood damage reduction. However, the elevation process may cause unanticipated deformations and stresses due to the changed support conditions. Such slabs are typically lightly reinforced, and the concrete degrades with age, reducing the capacity and safety. The elevated slabs, therefore, must be properly supported, and inadequacies in these areas can result in possible slab failure, leading to casualties and economic losses. With the proliferation of home elevations in flood-prone areas, the structural safety of such projects is of critical concern.

A knowledge gap exists in the design of elevated home slabs. The American Concrete Institute (ACI) 318-19 Building Code or governing bodies such as the Federal Emergency Management Agency (FEMA) do not provide relevant guidelines or instructions. The former includes guidance on the design of concrete slabs for specific support conditions. However, it does not cover the design of elevated home slabs. The FEMA Homeowner’s Guide to Retrofitting defers such design aspects to trained engineers or contractors. Due to its comparatively low cost and simple design, the current home slab design process has found general acceptance among developers at the expense of an unknown risk of slab cracking, greater deflection, and possible failure. This unknown risk highlights the uncertainty of converting a soil-supported slab into an elevated frame slab without changing the original design.

Furthermore, under the International Residential Code (IRC), which is, by and large, the governing code for residential construction in the U.S., the floor of a single-family residential space must be able to support a minimum of 40 pounds per square foot (psf, or 1.9 kPa) of distributed live load. Any inability of the home floor to support at least that much live load is considered non-conforming according to the IRC provisions. Because of the inherent weakness of the elevated home slab support configuration, several elevated home collapses have been reported to date:

  • In 2011, a home in Louisiana collapsed while being lifted as part of the post-Hurricane Katrina relief effort.
  • In 2013, after Hurricane Sandy, during elevation, a home in New Jersey slid off its foundation and collided with another as the former was being raised.
  • A house in New York also collapsed as it was being raised in the wake of Hurricane Sandy. Many other such examples can be found in the literature.

To address the knowledge gap and safety concerns that exist when elevating a home, the authors conducted a study with two key objectives:

  • Examine the safety of elevated home slab configurations and determine the maximum allowed pier spacing to safely support the IRC minimum floor live load.
  • Develop a simple tool to check the safety of desired elevated slab configurations that FEMA guidelines or the ACI Building Code do not address.

Experimental Procedure

An experimental study was performed in 2020-2021 to determine how much floor load the typical raised concrete home foundations in residential homes around the Texas Gulf Coast region could safely carry (see Figure 1). Increased floor loads stress the slab to higher levels that can eventually cause the slab to fail through concrete or steel failure. The tests involved pouring water on top of plywood troughs built atop each slab to simulate typical floor loads from everyday use. Data gathered from testing showed how these types of slabs failed and where to expect such failure. It was found that the typical practice of limiting support pier spacing to 10 feet (3.1 m) was adequate to safely carry the building code-specified minimum load. Square-shaped slabs were more susceptible to failure than rectangular-shaped ones. Additional information about the experimental work may be found in the literature (Ling et al., 2023), which is currently under review with the Journal of Coastal Research.

In a parking lot, a wooden frame is on top of a concrete slab with eight concrete pillars underneath.
Fig. 1. Experimental two-way concrete slab with concrete masonry unit piers (Source: Authors, 2023).
The results from the experimental study were used to create computer models that replicated the behavior of real-life slabs. The verified models were then used to explore slabs of various sizes, shapes, and support conditions, such as the one shown in Figure 2. The model results were then configured to link to the decision tool, as discussed below. In these simulations, the maximum applied floor load was 80 psf (3.8 kPa), which is double the minimum value specified by the IRC for single-family residential homes.
Gray background with thick black grid pattern measuring 1,067 x 914 cm.
Fig. 2. Sample model home floorplan (dimensions in cm) (Source: Authors, 2023).

Tool Development

Based on the numerical modeling results, a Home Elevation Decision Tool was developed in 2022 by Nur Yazdani with assistance from Cedric Ling, Debashish Kar, Maria Koliou, and Yoo Yong as a software interface. It allows users to determine the floor load capacity of an elevated home slab rapidly and conveniently, based on the governing building code provisions. The user must log in or create a new account to access the full data set of features, or they may proceed as a guest to use a more limited portion of what the application offers. A disclaimer and a user manual are also available from the home screen (see Figure 3). The Excel-based tool is freely available on Android, iOS, and desktop platforms. It may be found by searching App stores for “Home Elevation Decision Tool.”

A screenshot of a two story house with a carport underneath.
Fig. 3. Decision tool application home screen (Source: Authors, 2023).

The user selects a home model from five available archetypes that most closely resemble the actual home being considered. The selection is tied to the home floor area, number of stories, and roof configuration. The pier spacings in the two directions are then selected, determining the total number of piers in the configuration (see Figure 4).

Form to enter the column and building information
Fig. 4. Decision tool application parameter selection screen (Source: Authors, 2023).

When prompted via the “submit” link, the tool compares the entered selections with a hidden internal database of numerical values. It then outputs whether the specific support beam-pier configuration can safely support the minimum floor loading. A sample results screen from the application is shown in Figure 5, showing the output when the entire elevated slab can safely support the minimum IRC live load.

Word table listing construction elements, safety check live loads, and remarks.
Fig. 5. Decision tool application results screen (Source: Authors, 2023).
Since its first release in 2022, the research team at the University of Texas Arlington and Texas A&M University College Station has expanded the study by including the superstructure of the elevated homes (walls, roofs) and considered the effects of applied lateral loads such as flooding and wind. The authors envision that the first version of the decision tool will be enhanced with additional results if future funding for such efforts becomes available.
Cedric Ling
Cedric Ling received a Ph.D. degree in structural engineering from the University of Texas at Arlington. He earned his Bachelor of Science degree in Ocean Engineering at Texas A&M University College Station and a Master of Engineering degree in Civil Engineering at the University of Houston. During his master’s program, he worked at Bechtel, Inc., in Houston as part of the offshore group as both a naval architect and a marine terminal engineer. Currently, he is working as a design engineer at Volkert, Inc., Houston.
Debashish Kar
Debashish Kar is a front-end User Interface (UI) developer specializing in creating engaging and responsive web applications. He has a master’s degree in computer science from the University of Texas at Arlington and has over three years of professional experience. He has developed six software applications in both private industry and public institutions, including a COVID Management System and the Home Elevation Decision Tool described in this article. He is currently working as a full stack developer at the Texas A&M AgriLife.
Nur Yazdani
Dr. Nur Yazdani is a professor and past chairperson of the Civil Engineering Department at the University of Texas at Arlington. He received his Ph.D. and master’s degrees from the University of Maryland College Park and the University of Oklahoma, Norman. A fellow of the American Society of Civil Engineers (ASCE), American Concrete Institute (ACI), and ASCE Structural Engineering Institute (SEI), he is the author of more than 180 articles in journals and proceedings and an invited speaker at conferences and seminars. Dr. Yazdani is well known for his research on bridge design, evaluation and rehabilitation, resilient and high-performing infrastructure design and rehabilitation, natural and man-made hazards, coastal infrastructure, and engineering education. He has secured more than $18 million from research projects. He has been highly successful in finding and applying technology to improve the inspection, repair, rehabilitation, safety, durability, and performance of concrete bridges. Research results have been widely adopted and practiced, primarily by state and federal agencies. Leadership roles included the chair of national professional chapters. As part of the committee activities, he was instrumental in developing and modifying governing codes, standards, and guidelines from ACI and ASCE. Dr. Yazdani has served as an ASCE-certified civil engineering program evaluator for the Accreditation Board for Engineering & Technology (ABET).
Eyosias Beneberu
Dr. Eyosias Beneberu is an associate professor of research in Civil Engineering at the University of Texas at Arlington and a practicing bridge engineer. His academic experience ranges from teaching to researching various topics in structural engineering and hazard mitigation. His areas of expertise include repair and rehabilitation of structures, structural fire engineering, non-destructive evaluation, and health monitoring of bridges. Dr. Beneberu is a member of the ASCE-SEI Technical Activities Division for Bridge Management, Inspection and Rehabilitation Committee, ASCE Fire Protection Committee, and reviewer for various ASCE, ACI, and Elsevier journals. Dr. Beneberu’s industry experience encompasses the structural design of high-rise buildings and bridges as well as construction inspections of transportation infrastructure. He is a licensed professional engineer in multiple states and a fellow of the ASCE-SEI.
Maria Koliou
Dr. Maria Koliou is an associate professor at the Zachry Department of Civil and Environmental Engineering (CEE) at Texas A&M University. Her research contributions focus on developing resilient and sustainable structures and communities against extreme events to safely and functionally accommodate growing populations in urban areas. Her work includes system-level and community-level simulations that analyze the performance of structures and communities to extreme events. She is developing novel resilient structural designs and systems against various natural hazards and formulating fundamental mathematical frameworks to assess risk-based system functionality and community resilience. Dr. Koliou has received over $3 million in external research funding from federal, state, and private sources, and she is currently leading a multi-institution National Science Foundation (NSF) project on the “Gulf Resilience Coastlines and People Focused Research Hub” focusing on the recovery of tribal communities in the Gulf region. Dr. Koliou received the 2018 Structural Engineering Institute’s Young Professional Scholarship, 2021 Research Impact Award by the Department of CEE at Texas A&M, 2021 Engineering Genesis Award for multi-disciplinary research by the Texas A&M College of Engineering, and the 2021 NSF CAREER award. She has very recently been selected as one of the NSF and Kaleta A. Doolin Foundation Ocean Decade Champions.
Yong Yoo
Yong Yoo has a Ph.D. in civil structural engineering with 11 years of research experience. In particular, Yong Yoo has conducted various research projects using Finite Element (FE) and structural analysis programs.



Translate »