Michael J. McGinnis

Design and measured behavior of a hybrid precast concrete wall specimen for seismic regions

This paper presents the measured behavior from the testing of a 0.4-scale “hybrid” precast concrete wall specimen under reversed-cyclic lateral loading and provides an assessment of the seismic design and analysis of the wall by using the experimental results. The hybrid precast wall system investigated in the paper utilizes a combination of mild (i.e., Grade 400) steel and high-strength unbonded posttensioning (PT) steel for lateral resistance across horizontal joints. A seismic design procedure that conforms to ACI 318 and ACI ITG-5.2 was used for the design of the test specimen based on ACI ITG-5.1. The behavior of the specimen was measured with conventional data acquisition techniques and also full-field digital image correlation of the base panel and the critical joint between the base panel and the foundation, providing unprecedented information on the wall performance. The paper compares these measurements with the design and analytical predictions, focusing specifically on the applied lateral load...

Application of three-dimensional digital image correlation to the core-drilling method

We present a non-destructive technique for the determination ofin situ stresses in concrete structures, reterred to as the core-drilling method. The method is similar to the American Society for Testing and Materials (ASTM) hole-drilling strain gage method, except that the core-drilling method is formulated in the current work are performed with traditional photogrammetry, and the more novel (and more accurate) three-dimensional digital image correlation. In this paper we review the background elasticity theory and we discuss the results of verification experiments on steel plates. Calculated normal stresses are within 17% of applied values for photogrammetry, and 7% for three-dimensional digital image correlation.

Behavior of Precast Concrete Shear Walls for Seismic Regions: Comparison of Hybrid and Emulative Specimens

AbstractThis paper discusses the lateral load behavior of two, 0.40-scale, hybrid, precast concrete shear wall test specimens and the behavior of a third precast specimen designed to emulate monolithic cast-in-place RC shear walls. The walls had identical overall geometry and were constructed by placing rectangular precast panels across horizontal joints. The hybrid walls used mild steel bars [Grade 400 (U.S. Grade 60)] and high-strength unbonded posttensioning (PT) strands for lateral resistance, whereas the emulative wall used only mild steel bars. The mild steel bars crossing the base joint were designed to yield and provide energy dissipation, with the PT steel in the hybrid walls reducing the residual displacements of the structure. The mild steel bars at the base of the emulative wall and one of the hybrid walls used Type II mechanical splices, while the other hybrid wall used continuous bars grouted into the foundation. Because of the lack of PT steel, the emulative wall developed a large residual ...

Application of the Incremental Core-Drilling Method to Determine In-Situ Stresses in Concrete

The incremental core-drilling method (ICDM) is a nondestructive technique to assess in-situ stresses in concrete. These stresses may be constant or vary through the thickness of the concrete member under investigation. In this method, a core is drilled into a concrete structure in discrete increments. The displacements that occur locally around the perimeter of the core at each increment are measured and related to the in-situ stresses. This paper presents results from experimental tests in which simple concrete beams were subjected to controlled loads and in-situ stresses measured via ICDM were compared to known stress distributions.

LATERAL LOAD BEHAVIOR OF A POST- TENSIONED COUPLED CORE WALL

A 40%-scale multi-story reinforced concrete coupled core wall structure with unbonded posttensioned coupling beams was recently tested under quasi-static reversed-cyclic lateral loading. This paper provides an overview of the design and experimental results from this test. Conventional reinforced concrete coupling beams in seismic regions are often designed with two intersecting groups of diagonal reinforcing bars crossing the beam-to-wall joints. The placement of these reinforcing bars is a major challenge during construction. The new system eliminates the diagonal reinforcement by using a combination of high-strength unbonded post-tensioning (PT) steel and top and bottom horizontal mild steel reinforcing bars crossing the beam-to-wall joints to develop the coupling forces. The coupled wall specimen that was tested represented the most critical bottom three stories of an eight story prototype structure, consisting of two C-shaped wall piers, six post-tensioned coupling beams (two beams at each floor because of the C-shaped piers), tributary post-tensioned slabs at each floor, and the foundation. The less critical upper stories of the prototype structure were simulated analytically to obtain the axial forces and overturning moments imposed at the top of the bottom three stories. In addition to a dense array of conventional sensors, the deformations of the test specimen were monitored using a total of 14 two and three-dimensional digital image correlation (DIC) sensors, providing near-full-field response data of the most critical regions of the structure in the wall piers, floor slabs, and coupling beams. Ultimately, the high-fidelity measured data from the test specimen will be used to validate seismic design procedures and modeling/prediction tools for post-tensioned coupled wall structures. These procedures and tools may form the basis for the future implementation of this novel structural system as “special” reinforced concrete shear walls in medium and high seismic regions of the U.S.

3-D Digital Image Correlation - An Underused Asset for Structural Testing

Over the past several decades, structural testing has become ever more expensive, and researchers from many leading funding agencies are pushing to capture more and better data with each structural test conducted. Three dimensional digital image correlation (3D-DIC), is a tool that is gaining popularity as one way that more detailed information can be captured as part of testing programs. In 3D-DIC, the measured object is photographed with a pair of digital cameras before, during and after a load event and a stochastic pattern marked on the object is tracked from one set of images to the next such that a full field of displacements is derived. Historically, along with the cost of the system, factors such as how to correctly specify appropriate testing protocol and how to correctly interpret the results have limited the application in structural testing. The current paper focuses on three main aspects of 3D-DIC technology. First, a treatment of the basic theory behind the method is provided, highlighting the strengths and limitations of use for structural testing. Included are recommendations and guidelines for accuracy and other lessons learned during deployment over a broad range of projects. Second, the flexibility of the technique and the wide range of applications where it can prove useful will be discussed. Several case studies show how the technology has enhanced understanding of structural behavior in applications as far ranging as testing of rammed earth walls under gravity loads, testing of concrete bearing walls under fire and gravity loading, testing of post-tensioned shear walls under earthquake loading, and dynamic testing of a moment frame under earthquake loading. Finally, an experimental set-up designed to develop a protocol for deploying multiple 3D-DIC sensors simultaneously during the same structural test will be presented. The experiment is designed to allow four camera pairs to capture the deformations of key structural components of a coupled post-tensioned shear wall system.

Water-Induced Swelling Displacements in Core Drilling Method

This paper discusses the nondestructive technique of core drilling to evaluate stresses in concrete. Core drilling measures the displacements found near a hole drilled in concrete and relates this to stresses present in the structure by using elasticity theory. During core drilling, the introduction of water causes concrete to swell. These swelling displacements directly lead to errors in estimating the stresses. In this paper, the author provides a way to correct these water-induced swelling displacement errors. Using the values presented in the research literature as a basis, the author estimates the depth of water penetration and the swelling strain due to water exposure. The apparent stresses are estimated using finite element modeling. Results, which are applied to an earlier non-related hole-drilling investigation, show that proper accounting for water-induced swelling displacements significantly improves accuracy in prediction.

Testing and behavior of a coupled shear wall structure with partially post-tensioned coupling beams

A 40%-scale coupled core wall structure with C-shaped wall piers and novel unbonded post-tensioned (PT) coupling beams was tested under quasi-static reversed-cyclic lateral loads combined with tributary gravity loads. This paper describes the design, analysis, and testing of this specimen, which included the bottom three stories, the tributary floor slabs, and a large portion of the foundation from an eight-story prototype structure. The upper five stories of the prototype structure were simulated analytically to impose forces and moments at the top of the test specimen. In addition to conventional sensors, the specimen was monitored using 14 digital image correlation (DIC) sensors, providing near-full-field response data of the most critical regions. Overall, the structure performed as predicted, validating the design approach. Strength loss at the end of the test was largely caused by the fracture of the vertical reinforcing bars in the wall pier toes at the base. The coupling beams performed well, demonstrating the advantages of the new PT system.

Experimental Evaluation of a Multi-Story Post-Tensioned Coupled Shear Wall Structure

This paper discusses the design and experimental evaluation of a novel seismicresistant reinforced concrete (RC) coupled shear wall system. In this system, the widely-used unbonded post-tensioned floor slab construction method is adapted to couple (i.e., link) two RC wall piers, providing significant performance and construction benefits over conventional RC coupling beams in high seismic regions. Previous experiments of post-tensioned coupled wall structures are limited to floorlevel coupling beam subassemblies. The current paper extends the available research to multi-story structures by presenting the design of an 8 story prototype test specimen consisting of two C-shaped shear walls. The design is validated through the testing of a simplified 15% scale specimen in the laboratory. The experimental specimen includes the foundation, the first three floors of the shear walls, and the associated coupling beams. The upper stories of the building are simulated with hydraulic jacks that supply the appropriate bending moment, shear, and axial forces at the top of the laboratory structure. This paper compares the measured load displacement response of the laboratory structure with predictions from design models. Experimental and design predictions of several key behavior parameters are shown to match well. Future work involves the construction and testing of large scale (40%) specimens to validate the approach. Ultimately, the measured information from the test specimens will be used in the development of validated design procedures and modeling/prediction tools for multi-story post-tensioned coupled wall structures.

Behavior Comparison of Prestressed Channel Girders from High-Performance and Ultrahigh-Performance Concrete

In response to the demand for sustainable and improved bridge design practices, the development of emerging materials like ultrahigh-performance concrete (UHPC) is at the forefront of structural innovation. UHPC offers significant advantages to bridge superstructure design as it provides advanced mechanical and durability properties, including high compressive strength and increased tensile capacity. With the introduction of high-strength steel fibers into mixture proportions, postcracking tensile and flexural tensile capacities are increased. These increased tensile capacities provide greater ductility and reduce or possibly eliminate the need for mild steel reinforcement. The present research investigated the behavioral response of full-scale prestressed bridge girders subjected to four-point flexural loading. Two channel-shaped girders were designed to provide equal design moment capacities to facilitate comparative analyses of performance. The first of these girders was designed with high-performance concrete [HPC; 9.5 kips per square inch (ksi; 66 MPa)] and mild steel reinforcement typical of that used in New Mexico bridge designs. The second girder used nonproprietary UHPC [20 ksi (138 MPa)] mixture proportions consisting primarily of local materials, local mixing procedures, and a local curing regimen, all of which were developed at New Mexico State University, Las Cruces. Digital image correlation was used to capture deformations throughout the testing. This information creates a full field of displacements that captures tensile and compressive strain behaviors in the pure moment region. This investigation demonstrated the advantages and improved performance of UHPC and the contribution of steel fiber reinforcement to postcracking strength and flexural capacity.