Grantee Research Project Results
Final Report: IsoTruss-Reinforced Concrete Foundations for Increased Resiliency to Natural Disasters
EPA Contract Number: 68HERC22C0029Title: IsoTruss-Reinforced Concrete Foundations for Increased Resiliency to Natural Disasters
Investigators: Jensen, David
Small Business: IsoTruss Inc.
EPA Contact: Richards, April
Phase: I
Project Period: December 1, 2021 through May 31, 2022
Project Amount: $99,966
RFA: Small Business Innovation Research (SBIR) Phase I (2022) RFA Text | Recipients Lists
Research Category: Small Business Innovation Research (SBIR)
Description:
Infrastructure has a significant impact on human health and the environment, particularly as disasters increase in intensity and frequency. Telecommunications, one of 16 critical infrastructure sectors recognized by CISA, plays a vital role during disasters in providing emergency communications, contact with first responders, and coordination of relief efforts.
IsoTruss patented composite lattice technology is inherently more resilient to natural disasters due to corrosion-resistant material and reduced wind load experienced by the structure compared to traditional designs. During this Phase I project, IsoTruss, Inc. designed and prototyped a resilient tower foundation solution that increases resiliency to disasters and simplifies debris cleanup without substantially increasing installation time or cost.
Summary/Accomplishments (Outputs/Outcomes):
The IsoTruss team was led by Dr. David W. Jensen, original inventor of the IsoTruss geometry, with consultant Dr. Hayder A. Rasheed, a world expert in composite-reinforced concrete. The foundation was designed for four common soil types utilizing the International Building Code (IBC), American Concrete Institute 440, and the unique properties of the IsoTruss geometry.
There are two important ways that IsoTruss structures increase resiliency of reinforced concrete: corrosion resistance and structural strength. Composite materials, such as the carbon fiber reinforced polymer used in IsoTruss structures, are inherently corrosion resistant. This is a significant feature for reinforced concrete in humid, coastal areas such as the hurricane-prone regions in the southeast US because corrosion resistance increases product lifetimes up to 5X. In comparison to steel structures, the combination of longer life and less material in IsoTruss products results in a 70% reduction of carbon emissions over the lifetime of the product, making IsoTruss a perfect fit for corrosion-susceptible situations.
IsoTruss structures also have unique structural capabilities compared to typical steel or composite rebar that allow added resiliency through structural redundancy, combination of shear and axial strength into a single structure, easier installation, and reduction of concrete volume. Typical rebar does not resist shear leaving the concrete to carry the full shear loads, however, IsoTruss rebar does have shear capacity. This adds redundancy to the design so that if the concrete cracks the IsoTruss rebar carries the shear load in the structure and prevents failure. IsoTruss rebar also carries bending loads, like other rebar, but each IsoTruss is the equivalent of six rebar members without the added installation time and cost of tying members onsite. The significant weight savings – up to 10X compared to steel – also makes installation easier and faster because the rebar can be maneuvered by hand. In order to increase resiliency and eliminate the potential for the tower to tip in extreme wind, drilled shafts reinforced with IsoTruss rebar were also added to the design. The drilled shafts stabilize the foundation and reduce the concrete volume 20-40% depending on the soil type.
Figure 1. Model of the resilient IsoTruss-reinforced foundation that was designed and prototyped during the project. The foundation has added structural redundancy compared to typical foundations because of the ability of the IsoTruss reinforcement to carry both shear and bending loads. The drilled shafts allow added stability even during extreme wind loads and reduce the concrete volume by 20-40% depending on the soil type.
Conclusions:
This project proved the feasibility of an IsoTruss-reinforced foundation for telecom towers. The foundation design was optimized to take advantage of the unique properties of IsoTruss structures with a focus on increasing resiliency without increasing installation cost or time.
The design consists of a cylindrical concrete footing about 13 feet in diameter and 2.5 feet deep with the bottom of the tower inserted directly into the concrete. This removes the need for additional hardware to connect the tower and foundation which is a potential failure point under heavy loading. There are two layers of IsoTruss reinforcement spread radially around the diameter of the footing that transfer load from the tower to the six drilled shafts around the circumference. The drilled shafts provide stability to the tower and foundation, particularly in extreme wind conditions, and are also reinforced with IsoTruss structures. The diameter and height of the drilled shaft changes based on the bearing capacity of the soil. The foundation design with IsoTruss reinforcement was completed for four common soil types – ordinary clay, gravel or coarse sand, cemented sand or gravel, and bedrock.
Analysis of the foundation design showed that it is completely stable even at the highest wind speeds experienced in the US. The IsoTruss reinforcement adds resiliency compared to typical rebar with its ability to carry both bending and shear loads if the concrete cracks. The corrosion-resistance of the IsoTruss reinforcement also ensures that water damage or humidity will not weaken the foundation or reduce its lifetime. One of the most exciting discoveries with the IsoTruss-reinforced foundation design was the reduction of concrete volume, resulting in thousands of pounds of CO2 saved for every foundation.
The feasibility of the design was also confirmed with a scaled prototype. The prototype process allowed IsoTruss the opportunity to experience the manufacturing including concrete embedment and placement of reinforcement pieces. Prototype manufacturing went smoothly and provided physical models to be able to show the design to potential customers.
The targeted market for this application is the global telecommunications industry. Based on previous experience introducing new technology to the telecom market, customers tend to feel more comfortable with a design that has a stamped design package by a reputable civil engineering firm. Steps were planned during the Phase I project to get to a stamped design package including component testing, full-scale testing, and a beta deployment. After testing is completed, consultant Dr. Rasheed will be able to stamp the designs as a professional engineer which will allow easier approval in the future with other civil engineering firms when specific sites are selected.
Customer relationships and understanding customer needs are key to marketing and design of the technology. Customer discovery surveys have revealed the tower owners in the US are most concerned about capital cost and lead time. The foundation design addresses both concerns by reducing cost by reducing the volume of concrete and decreasing lead time with ready-made IsoTruss reinforcement that makes installation times faster. The cost and time benefits of the IsoTruss-reinforced foundation were presented to prospective customers with positive response. Several contacts expressed interest in seeing the technology advance and being involved with a beta deployment in the future.
The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.