Testing to Develop Design Methods and Code Language
Presented By: Eric Kreiger
Affiliation: U.S. Army Engineer Research and Development Center
Description: Additive Construction (3D printing for construction) has attracted interest within the DoD for installation and expeditionary construction. Demonstrations have outpaced the development of codes and standards, leading to difficulty in enforcing standard practices. Structural design and performance has been a primary thrust area for ERDC's Additive Construction program. This presentation will discuss structural testing of walls and beams and the development of structural performance for informing design and code language for the Unified Facilities Criteria.
Full-Scale Testing of Low-Rise Additively Constructed Concrete (ACC) Walls Designed for Seismic Applications
Presented By: Mohammad Aghajani Delvar
Affiliation: Texas A&M
Description: Additive Construction (AC) methods, such as concrete 3D printing (also termed additively constructed concrete – ACC), has recently gained popularity. AC methods have the potential to revolutionize the construction industry and the structural engineering discipline by offering reduced production costs and achieving reduced construction times via automation that permits continuous operation. AC methods can also achieve much lower environmental impact by using materials only where it is needed and, in the case of concrete 3D printing, by eliminating the need for formwork. While early applications have mostly focused in areas of low or negligible seismicity, there is interest by the engineering community for applications in earthquake prone areas. This presentation will discuss major findings of an experimental program on four full-scale 3D printed concrete (or ACC) walls. These walls have been designed as part of a proposed seismic force resisting system that the authors deem suitable for ACC structures and will discuss in this presentation. These walls combine two different aspect ratios (height/length) that result in shear and flexural failure mechanisms (by design), and two cross-section designs: one with and one without infill. All walls adopt a proposed reinforcing strategy that includes integrated internal reinforced concrete (RC) elements, similar to boundary elements in masonry walls. All walls are subjected to a constant vertical load simulating gravity effects as well as displacement-controlled in-plane horizontal cyclic loading simulating seismic demands. The cyclic loading will be applied with increasing magnitude until complete failure/collapse. The experimental data provide information on strength, deformation capacity and damage progression. Practical aspects, such as reinforcement placement, connectivity to the foundation and connectivity to slabs and other flooring systems will also be discussed.
Additive Manufacturing of Intelligent Concrete Columns with Embedded Self-Sensing
Presented By: Khalilullah Taj
Affiliation: Louisiana State University
Description: Performing structural health monitoring (SHM) of infrastructure in areas with limited access consistently presents formidable challenges. However, the rapid advancements in additive manufacturing (AM) within construction, combined with innovative self-sensing materials, have enabled the integration of emerging technologies and novel materials into structural components. This research explores the practicality and effectiveness of additive manufacturing methods to develop intelligent concrete structural components with embedded self-sensing cementitious materials. The self-sensing materials were integrated into various locations of the 3D-printed concrete columns during the printing process. In this study, monotonic and cyclic axial compressive loading was applied, and the strain changes in the column were quantified through the electrical resistivity measurements of the sensing segments. In addition, digital image correlation (DIC) was employed as a reference to validate the effectiveness of the self-sensing capabilities. Preliminary results reveal that the gauge factor of the 3D-printed self-sensing segments offers commendable sensitivity, accurately detecting strain behavior under various loading conditions. These observations highlight the merit of leveraging AM technique in embedding functional materials within structural elements, signaling a promising trajectory for the broader incorporation of AM technologies in the dynamic landscape of concrete construction.
Structural Performance of Unreinforced 3DPC Buried Structures
Presented By: Alireza Hasani
Affiliation: University of North Dakota
Description: There is a lack of information about structural performance and failure behavior of large-scale load-bearing 3DPC. It is also argued that reinforcement can change the failure behavior of 3D-printed objects because of introducing voids. Concrete pipes are among few unreinforced structures that can be constructed in accordance with available standard specifications. Thus, unreinforced 3DCP pipes were opted for the study to investigate the influence of different materials and 3D printing processes on their structural performance. In this regard, small-scale fresh and hardened tests, and large-scale structural tests were conducted. Additionally, other aspects, such as, geometry accuracy of printed structures was studied.
Methodology for Structural Design of Low-rise Additively Constructed Concrete (ACC) Buildings
Presented By: Sumedh Sharma
Affiliation: Texas A&M University
Description: Three-dimensional (3D) extrusion-based concrete printing is a novel construction method within the broad family of additive construction (AC) methods that has the potential to revolutionize the construction industry and the field of structural engineering due to the rapidity of onsite construction and the low construction cost it offers, as well as via the freedom to pursue non-conventional building geometries. One of the first applications of this technology targets affordable housing to address the housing crisis as well as homelessness. However, compared to traditional building construction, structural design and analysis methods for ACC buildings, such as 3D printed concrete buildings, are not as well established. We aim to address this gap by proposing a design methodology for low-rise ACC buildings. First, the load transfer path for gravity and wind-induced lateral loads are identified based on proper assumptions on diaphragm (in-plane) flexibility and the selection of load-bearing and non-load-bearing (or non-participating) walls. The axial, out-of-plane, and in-plane demands on all ACC walls are subsequently determined based on critical load combinations. The ACC walls are designed at the component level using strength equations derived by the authors on the basis of a limit-states mechanics-based approach for in-plane, out-of-plane and axial loading conditions. The design includes geometry and dimensions, infill patterns, shear reinforcement, grouted cell design, boundary reinforced concrete (RC) columns designs, and RC bands and ties. RC columns ties are provided at wall intersections and openings to ensure structural integrity. To validate the design methodology, a prototype 3DPC building was analyzed under gravity and wind-induced lateral load via finite element modeling. This presentation will finish with a discussion on a seismic design methodology that the authors are currently developing for applications of ACC buildings in seismic areas.
A New Methodology to Characterize the Intralayer Bonding Capacity of a 3D Printing Reinforced Concrete
Presented By: Francesco Soave
Affiliation: Politecnico Di Milano
Description: The multifaceted nature of 3DCP presents challenges to fully harness its capabilities. The paramount focus is on the examination of bond strength between successive layers, a parameter that has profound implications for structural integrity and the overall quality of printed structures. The robustness of this bond depends on various variables, including surface moisture, laying temperature, surface roughness, and the formation of cold joints, collectively influencing structural quality and reliability.
Within existing literature, a variety of methodologies has been investigated to enhance the interlayer bond, employing wire mesh, U-nails, steel reinforcement, and fibers. This study introduces an innovative approach that leverages stainless steel-reinforced nails for creating interlayer connections, exploiting its modular characteristics, allowing for solutions tailored to specific scenarios. Additionally, its potential for full process automation further amplifies its value.
Interfacial Behavior of 3D-Printed Concrete Structures at the Interfaces
Presented By: Pedram Ghassemi
Affiliation: Ohio State University
Description: Currently, the construction industry is facing some challenges such as labor shortage and low productivity. Additive construction, also known as 3D Concrete Printing (3DCP), is an emerging technology that has the potential to revolutionize conventional construction owing to its advantages. In 3DCP, the concrete material is extruded through a nozzle using a 3D concrete printer. Although a lot of efforts have been made to improve the knowledge about this technology, it is still in the primary stage and a lot more study should be performed to obtain sufficient knowledge and understanding. One of the main differences between 3D-printed concrete elements and conventional concrete elements is the layer-by-layer nature of 3D-printed concrete which introduces interfaces within the structures. The interfaces are the bottleneck of 3D-printed concrete structures since they are not only the weak region but also, they cause the anisotropy. As a result, considering the roles of the interface in both experimental and numerical investigations as well as structural design is of utmost importance. This study aims to study the interfacial shear bond-slip relationship at the interfaces using a direct shear test considering various printing parameters such as printing time interval and nozzle height. The authors are in the process of starting the experimental tests. The outcomes of the research are constitutive models that govern the interfacial shear behavior of the interfaces within 3D-printed concrete structures. The constitutive models can be used in computational modeling, numerical analysis, structural design, and establishing building codes.