LATERAL LOAD BEHAVIOR OF A POST-TENSIONED COUPLED CORE WALL

Steven Barbachyn,1 Yahya C. Kurama,2 Michael J. McGinnis,3 Richard Sause,4 and Kristen A. Peterson5

ABSTRACT A 40%-scale multi-story reinforced concrete (RC) coupled core wall structure with unbonded post-tensioned coupling beams was recently tested under quasi-static reversed-cyclic lateral loading. This paper provides an overview of the structural design and experimental results from this test. Conventional RC 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 energy-dissipating (ED) mild steel 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 three-story test sub-structure. In addition to a dense array of conventional sensors, the deformations of the specimen were monitored using 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 will be used to validate seismic design procedures and modeling/prediction tools for post-tensioned coupled shear wall structures. These procedures and tools may form the basis for the future implementation of this novel structural system as “special” RC shear walls in medium and high seismic regions of the U.S.

1Graduate Student, Dept. of Civil & Envir. Engin. & Earth Sciences, U. of Notre Dame, Notre Dame, IN 46556 2Professor, Dept. of Civil & Envir. Engin. & Earth Sciences, U. of Notre Dame, Notre Dame, IN 46556 3Associate Professor, Dept. of Civil Engin., U. of Texas at Tyler, Tyler, TX 75799 4Professor, Dept. of Civil & Environmental Engin., Lehigh U., Bethlehem, PA 18015 5Staff I-Structures, Simpson Gumpertz & Heger, Boston, MA 02453 Barbachyn S., Kurama Y., McGinnis M., Sause R., and Peterson K. Lateral Load Behavior of a Post-Tensioned Coupled Core Wall. Proceedings of the 10th National Conference in Earthquake Engineering, Earthquake Engineering Research Institute, Anchorage, AK, 2014.

Lateral Load Behavior of a Post-Tensioned Coupled Core Wall

Steven Barbachyn,1 Yahya C. Kurama,2 Michael J. McGinnis,3 Richard Sause,4 and Kristen A. Peterson5

ABSTRACT

A 40%-scale multi-story reinforced concrete (RC) coupled core wall structure with unbonded post-tensioned coupling beams was recently tested under quasi-static reversed-cyclic lateral loading. This paper provides an overview of the structural design and experimental results from this test. Conventional RC 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 energy-dissipating (ED) mild steel 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 three-story test sub-structure. In addition to a dense array of conventional sensors, the deformations of the specimen were monitored using 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 will be used to validate seismic design procedures and modeling/prediction tools for post-tensioned coupled shear wall structures. These procedures and tools may form the basis for the future implementation of this novel structural system as “special” RC shear walls in medium and high seismic regions of the U.S.

Introduction Reinforced concrete (RC) coupled shear wall structures are commonly used for primary lateral load resistance in medium and high-rise buildings in regions of moderate and high seismicity. The typical coupled wall system consists of two or more vertical shear wall piers connected by relatively short, deep beams called coupling (or link) beams at the floor and roof levels. Properly designed and detailed coupled walls can provide large strength, stiffness, and energy dissipation under lateral loads; however, the design and construction of the coupling beams remain

1Graduate Student, Dept. of Civil & Envir. Engin. & Earth Sciences, U. of Notre Dame, Notre Dame, IN 46556 2Professor, Dept. of Civil & Envir. Engin. & Earth Sciences, U. of Notre Dame, Notre Dame, IN 46556 3Associate Professor, Dept. of Civil Engin., U. of Texas at Tyler, Tyler, TX 75799 4Professor, Dept. of Civil & Environmental Engin., Lehigh U., Bethlehem, PA 18015 5Staff I-Structures, Simpson Gumpertz & Heger, Boston, MA 02453 Barbachyn S., Kurama Y., McGinnis M., Sause R., and Peterson K. Lateral Load Behavior of a Post-Tensioned Coupled Core Wall. Proceedings of the 10th National Conference in Earthquake Engineering, Earthquake Engineering Research Institute, Anchorage, AK, 2014.

challenging due to the presence of large reversed-cyclic nonlinear rotation demands combined with large shear forces, resulting in complex reinforcement details.

To meet the significant shear and rotation demands, the primary reinforcement for typical RC coupling beams in seismic regions consists of two intersecting groups of large diagonal reinforcing bars passing through the beam and anchored into the wall piers ([1-5]). This conventional system is difficult to construct [as shown in Fig. 1(a)] and can experience considerable damage under seismic loading. In comparison, the primary reinforcement in the coupling beams of the wall system described herein consists of unbonded post-tensioning (PT) strands placed in one or two tendons at the beam centroid, greatly simplifying construction [see Fig. 1(b)]. This new system represents a significant innovation and transformation, but one that can be realistically achieved by adapting the existing and widely-used post-tensioned slab technology. The deformations in the coupling beams occur primarily in the form of concentrated cracking at the ends, resulting in little damage to the rest of the beam as the structure displaces laterally during a large earthquake. Additionally, energy dissipating (ED) top and bottom horizontal mild steel bars (ASTM A615, Grade 60) are designed to yield in tension and compression as the beams rotate under reversed-cyclic lateral displacements. After the earthquake, the PT tendons provide a restoring (self-centering) force that closes the cracks and pulls the structure back toward its undeformed, plumb position. The combination of PT steel and mild steel reinforcement to develop the design coupling forces with self-centering capability and energy dissipation results in an efficient structure for seismic loading conditions.

The single major barrier to the use of post-tensioned coupling beams in seismic regions is the lack of experimentally-validated design methods, construction procedures, and numerical simulation models for multi-story structures. Previous experiments on the use of the proposed technology are limited to isolated floor level subassembly studies ([6-8]). To fill this knowledge gap, a 40%-scale physical laboratory experiment integrated with the analytical model of a multi-story coupled wall structure was recently conducted at the Network for Earthquake Engineering Simulation (NEES) laboratory site operated by Lehigh University. The laboratory specimen included the first three floors, tributary slabs, and foundation of an 8-story prototype system, representing the most critical regions of the structure. The other (less critical) regions of the structure were simulated in the computer to obtain the forces and overturning moments acting at the top of the 3-story laboratory specimen. Fig. 2(a) shows a three-dimensional rendering of the 40%-scale experimental setup in the laboratory, while Fig. 2(b) shows the completed test specimen. In addition to a dense array of conventional sensors (load cells, strain gauges,

(a) (b) Figure 1. RC coupling beams: (a) diagonally reinforced beam (courtesy, Magnusson

Klemencic Associates); (b) proposed post-tensioned beam

displacement/rotation transducers), the deformations of the laboratory structure were monitored using a total of 14 two and three-dimensional digital image correlation (DIC) sensors ([9]) 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 this test, as well as from a subsequent second specimen to be tested in 2014, is expected to lead the development of validated design procedures and modeling/prediction tools for the new system. The primary focus of the current paper is on an overview of the structural design and experimental results from the first 40%-scale laboratory test specimen.

Full-Scale Prototype Structure

A full-scale 8-story prototype building was designed to form the basis for the 40%-scale post-tensioned coupled shear wall test specimen. An overview of the design and detailing of this prototype structure is given in this section. Design Approach The prototype structure was designed for a site in Los Angeles, California with a seismic response coefficient of Cs = 0.136g. The plan and elevation views of the structure are shown in Figs. 3(a) and 3(b), respectively. The primary lateral load resistance was provided by a coupled core wall system at the center of the building, consisting of two C-shaped shear walls connected by post-tensioned coupling beams at each floor. This core included two slab openings to simulate the elevator shafts and stairwells in an office building. These slab openings were centered inside the core to prevent any significant asymmetric behavior during testing. The configuration, dimensions, and detailing of the prototype building were chosen with the assistance of Magnusson Klemencic Associates (MKA) in Seattle, Washington. The design strengths of concrete, mild steel, and PT steel were f’c=6 ksi, fy=60 ksi, and fpu=270 ksi, respectively.

To determine the design forces for the prototype structure, the Equivalent Lateral Force (ELF) procedure from ASCE 7 ([10]) was used with a response modification factor of R=6.0. The structure had a calculated fundamental period of T=0.74 s. The ELF procedure resulted in a

(a) (b)

Figure 2. 40%-scale experimental setup: (a) 3D rendering; (b) completed structure

design total base moment and total base shear force, which were distributed to the components of the coupled wall structure by making a number of design selections. First, a coupling degree of 30% was chosen, meaning that 30% of the design total base moment was to be carried by the coupling action between the two wall piers. This coupling moment was distributed to the post-tensioned coupling beams as a design shear force and corresponding moment at the beam ends, with the remaining base moment distributed evenly between the two wall piers. The reinforcement details of the wall piers and coupling beams were then selected to satisfy these design forces and achieve ductile behavior up to a maximum roof drift ratio of 3% for the 8-story structure. The specimen was intentionally designed not to have any significant over-capacity in force or displacement (e.g., no capacity reduction factor was used for axial-flexural design).

Figure 3. Full-scale prototype structure: (a) building plan (b) coupled wall elevation;

(c) wall pier base details; (d) 1st floor coupling beam end details Structure Detailing Fig. 3(c) shows the wall pier details at the base of the structure, which were symmetric in the N-S direction for each pier and symmetric in the E-W direction between the two piers. The pier

reinforcement plan was selected to be similar to typical reinforcement details used in conventional coupled shear walls. The 1st floor post-tensioned coupling beam end details are given in Fig. 3(d). Sixteen 0.5 in. diameter PT strands (ASTM A416) anchored at the outsides of the wall piers provided the total post-tensioning force for this beam. The strands were placed inside two ungrouted ducts to prevent bonding to the concrete, resulting in uniformly distributed strand strains over the entire length of the structure, thus, delaying the yielding of the strands and maintaining the initial post-tensioning force. Energy dissipation in the 1st floor coupling beams was provided by three No. 6 ASTM A615, Grade 60 ED reinforcing bars at the top and bottom of the beam, crossing the beam-to-wall interface at each end. A predetermined length of this reinforcement was unbonded from the concrete by wrapping each ED bar in a plastic sleeve to limit the maximum steel strains and delay low-cycle fatigue fracture. The beams were designed as T-beams considering an effective flange width from the slab, resulting in unequal amounts of unbonded length for the ED reinforcement as well as unequal amounts of confinement hoop reinforcement at the top and bottom of the cross-section. The coupling beams in the upper stories were designed similarly, but with smaller amounts of reinforcement due to the reduced beam shear and moment demands over the height of the structure. Preliminary analytical models of the structure were used to determine an estimate of the coupling beam design forces, resulting in three different beam designs over the height (1st floor, 2nd-4th floors, and 5th-8th floors).

The deliberate lack of bond (i.e., debonding) between the steel and surrounding concrete

was intended to result in the development of concentrated cracks at the beam ends rather than distributed cracks developing into the span. The post-tensioning steel was designed to create a large diagonal compression strut over the beam length, essentially eliminating cracking in the mid-span. This compression strut also resulted in large compression stresses at the beam ends; and thus, closely spaced transverse hoops were placed for concrete confinement in these regions. However, the transverse shear reinforcement away from the beam ends was significantly reduced compared with conventionally reinforced coupling beams. The simplified rectilinear orientation of the beam reinforcement and localization of damage under lateral loading represent significant improvements over diagonally-reinforced coupling beams.

The widely-used unbonded post-tensioned slab technology was used for the floor slabs.

These slabs were designed by MKA following typical methods for coupled core wall structures, but with slight modifications to account for the new post-tensioned coupling beam details. The final reinforcement layout consisted of a top and bottom mat of mild steel bars (continuous into and through the wall piers) and unbonded PT steel in both the N-S and E-W directions of the slab. The slab PT tendons were banded in the N-S direction and distributed evenly along the slab length in the E-W direction. The main deviation from a typical post-tensioned slab design was in the termination of the E-W mild steel bars running parallel to the coupling beams. In order to prevent these slab bars from interfering with the intended behavior at the beam ends, the bars placed within the effective slab width were terminated at the beam-to-wall interfaces (i.e., the slab bars were not continuous across the beam-to-wall interfaces).

Experimental Program

The construction and testing of the 40%-scale post-tensioned coupled core wall specimen took place at the Lehigh University NEES Equipment Site. All dimensions, reinforcement, and

structure demands for the test specimen were reduced from the full-scale prototype building using the 40% length scale factor. In some cases, the full-scale detailing did not scale exactly to a nominal reinforcement area or a regular dimension, requiring slight deviations from a perfectly-scaled structure. Despite these small deviations, the specimen still satisfied the scaled design demands very closely. The measured material strengths ranged between f’c=6.7-7.6 ksi, and fy=61-69 ksi for the concrete and steel, respectively, in the different parts of the structure.

The laboratory test specimen represented the most critical bottom three stories of the 8-story prototype structure. The upper five stories of the structure were simulated analytically using the DRAIN-2DX ([11]) software. Since the post-tensioning of the coupled core wall was an integral part of the floor construction, the test sub-structure included a tributary portion of the slab at each of the three floors. In the analytical simulation, a 40%-scale model of the 8-story structure was subjected to a reversed-cyclic lateral displacement history under the ELF profile from ASCE 7, combined with tributary gravity loads. The foundations of the structure were modeled as fixed. The analytical models for the wall piers and coupling beams consisted of nonlinear beam-column elements discretized into fibers with areas and material properties that accurately depicted the measured concrete and steel properties in the structure. The PT steel and unbonded lengths of the ED mild steel bars in the coupling beams were modeled using truss elements. An initial load was applied to the PT steel elements to accurately represent the measured prestress force in the tendons near the test date. This accounted for any prestress losses that occurred between the initial post-tensioning phase and the test date.

The wall pier forces determined from this reversed-cyclic analysis were then applied to the top of the 3-story test specimen using a total of 7 servo-controlled actuators and 4 hydraulic gravity jacks, simulating the behavior of the upper 5 stories of the 8-story building. Fig. 4(a) shows a schematic of the test setup, including the steel reaction frame surrounding the structure. The forces from the actuators and gravity jacks were transferred to the specimen through a load block fixed to the top of each wall pier. Combinations of these forces were used to impose the prescribed shear force, axial force, and overturning moment from the upper 5 stories at the top of each wall pier [see Fig. 4(b)], resulting in equilibrium between the physical and analytical sub-structures at the interface. In the E-W horizontal direction (i.e., direction of the coupling beams), one servo-controlled hydraulic actuator was connected to the west loading block (at the top of the west wall pier, see Fig. 4) to simulate the lateral forces acting on the 3-story sub-structure from all of the stories above (i.e., 4th through the 8th stories). The ELF forces on the 1st, 2nd, and 3rd floors were also lumped at the west loading block level in a manner to result in the appropriate overturning moment at the base of the structure. Two additional horizontal actuators were placed between the east and west loading blocks (one on each of the north and south sides of the loading blocks) to appropriately distribute the applied shear force between the east and west wall piers. In the vertical direction, two servo-controlled hydraulic actuators were connected to the loading block at the top of each wall pier to control the axial force and bending moment boundary conditions at the top of the 3-story sub-structure, representing the forces transferred from the upper 4th through 8th stories. Additional hydraulic jacks placed on top of each wall pier simulated the tributary gravity loads on the structure, including the gravity loads from the upper stories (i.e., 4th through 8th stories). The load blocks were designed to perform as a rigid body with small deformations under the large forces applied during testing. The connections between the load blocks and the wall piers were also designed to have very little deformations, thus allowing the applied forces and displacements to be controlled accurately.

The specimen was tested under a pseudo-static reversed-cyclic lateral displacement history applied in the direction of the coupling beams. The lateral displacement history was similar to the validation testing requirements specified by ACI ITG-5.1 ([12]) for the classification of unbonded post-tensioned precast concrete structural walls as “special” RC shear walls in moderate and high seismic regions of the U.S. While pseudo-dynamic tests may be more representative of the inertial loads from an earthquake, including higher mode effects, pseudo-static reversed-cyclic tests are typically more demanding and allow for better observation of the structure performance under a well-defined loading scheme. Furthermore, the structure behavior during a conventional reversed-cyclic test is not dependent on any particular earthquake record and can be more readily compared with other test data available in the literature.

Experimental Results

The measured total base shear force (Vb) versus average 3rd floor drift (Δ3) behavior of the specimen is shown in Fig. 5. Although minimal, the effects of foundation slip and rotation were removed from the drift calculation. The testing started in the negative drift direction with the specimen displaced towards the east. The structure demonstrated ductile behavior up to -2.70% and +2.53% drift at the 3rd floor level, reaching a maximum base shear of -432 kips and +416 kips in the negative and positive directions of loading, respectively. Note that the corresponding drifts at the roof of the 8-story structure would be greater than -2.70% and +2.53% due to the nonlinear displaced shape of the building under lateral loads. According to the analytical model, at large lateral displacements, the 8th floor drift is about 20% greater than the 3rd floor drift, implying that the 8-story coupled core wall likely obtained a roof drift ratio greater than 3.00% at the end of the test, which was the maximum roof drift used in the design of the 8-story structure.

(a) (b)

Figure 4. Specimen test setup: (a) schematic; (b) interface forces

The strength loss from the overall ultimate strength to

the peak load during the last cycle of the test was 22.2% and 20.7% in the negative and positive directions, respectively. Fig. 6 depicts the damage state of various components of the structure at the completion of the test. Most of the lateral strength loss during the last two drift cycles was largely caused by low-cycle fatigue fracture (preceded by buckling) of the vertical mild steel bars at the extreme edges of all four wall pier toes at the base. Audio evidence of these bar fractures throughout the last two cycles and post-test excavation of the wall pier toe regions led to this conclusion. For example, Fig. 6(a) shows the excavated north toe of the west wall pier base and Fig. 6(b) shows the north toe of the east wall pier base prior to excavation, each depicting two buckled and fractured vertical bars above the foundation. Improved detailing to prevent the buckling and fracture of these bars will be investigated in a second specimen to be tested by the project. Spalling of the cover concrete and subsequent buckling (with no fracture) of the vertical mild steel bars at the wall pier outer corners [i.e., intersection of flange and web of pier; see Figs. 3(a) and (c)] were also noted [e.g., see Fig. 6(c) for the damage at the outer south corner of the west wall pier base]. The damage in the wall piers was significantly reduced away from the corners and toes of the C-shaped piers.

(a) (b) (c)

(d) (e) (f)

Figure 6. Specimen damage at completion of test: (a) north toe of west wall pier base; (b) north toe of east wall pier base; (c) south corner of west wall pier base; (d) 1st floor south coupling beam; (e)

ED bar buckling in 3rd floor north coupling beam; (f) bottom of 1st floor slab

Overall, the post-tensioned coupling beams performed well during the test. The observed damage included localized crushing of the concrete at the beam ends [Fig. 6(d)], which was mostly limited to cover spalling, confirming the design of the confinement reinforcement. The damage pattern in Fig. 6(d) was generally representative of all of the six coupling beams in the structure. The beams underwent significant deformations at the ends where large concentrated

Figure 5. Measured base shear versus 3rd floor drift behavior

cracks formed. Minimal cracking was found in the rest of the span, validating the design philosophy for the post-tensioned system. Additionally, the large compression stresses at the beam ends resulted in concrete spalling in the adjacent wall pier regions. In the 3rd floor north beam, buckling within the unbonded length of one of the bottom ED bars was also observed, which caused additional concrete spalling and splitting in this region [Fig. 6(e)]. This was the only ED bar in the structure that exhibited buckling. The ED bar buckling occurred immediately outside of the closely-spaced hoop region [see Fig. 3(d)], which may indicate the need for extending the closely spaced hoops along the entire unbonded length of the ED bars.

As shown for the bottom of the 1st floor slab in Fig. 6(f), significant concrete cracking and spalling was observed in the post-tensioned slabs. These cracks (and the corresponding spalling regions) propagated outward from the beam ends due to the termination of the mild steel slab reinforcement to allow for the intended behavior with concentrated cracks at the beam ends. The presence of cold construction joints in the slabs (perpendicular to the beam length and near each beam end) may have also contributed to the observed spalling of the concrete in these regions. The cold joints could be moved further away from the beam ends and a small amount of mild steel could be added within the effective slab width to help reduce this spalling.

Ongoing and Future Work

Construction of the second post-tensioned coupled core wall test specimen is currently underway. The design of this structure includes improvements to the first specimen, particularly addressing the buckling and fracture of the vertical bars at the wall pier toes. Other specimen changes include the use of fully post-tensioned coupling beams (i.e., with no ED bars), reduced coupling beam length-to-depth aspect ratio, and modified slab reinforcement details to reduce the amount of concrete damage in the slabs. More information can be found at http://ptcoupledwalls.nd.edu.

Summary

Large-scale testing of a novel post-tensioned coupled core wall structure under lateral loads combined with tributary gravity loads was recently completed. Overall, the specimen performed as predicted, and validated the design approach. The behavior of the structure was ductile up to a 3rd floor drift of -2.70% and +2.53% in the negative and positive directions, respectively. Analytical models indicate that these results translate to drift levels greater than 3.00% at the roof of the 8-story structure, which was the maximum drift used in design. Strength loss near the end of the test was largely caused by the low-cycle fatigue fracture (preceded by buckling) of the vertical reinforcing bars in the wall pier toes at the base. Additional damage was observed in the form of localized concrete crushing and cracking at the coupling beam ends, buckling of one ED bar in the 3rd floor north beam, and cover concrete spalling and subsequent buckling of the vertical mild steel bars at the outer corners of the wall pier bases. The post-tensioned coupling beams performed well during the test, demonstrating the advantages of the new system. These results may ultimately form the basis for the implementation of post-tensioned coupled wall systems as “special” RC shear walls in medium and high seismic regions of the U.S.

Acknowledgments This project is a collaborative effort that includes the University of Notre Dame, the University of Texas at Tyler, and Lehigh University. The research is funded by the National Science

Foundation (NSF) under Grant No. CMMI 1041598 as a part of the “George E. Brown, Jr. Network for Earthquake Engineering Simulation (NEES) Research (NEESR).” This award is a part of the National Earthquake Hazards Reduction Program (NEHRP). Support of the NSF Program Director Dr. J. Pauschke is gratefully acknowledged. At the University of Texas at Tyler, students M. Lisk and M. Holloman worked on the development of the multiple DIC sensor protocol. At the Lehigh University NEES equipment site, laboratory staff (C. Bowman, P. Bryan, D. Fritchman, T. Maurullo, G. Novak, and E. Tomlinson), faculty members (S. Pakzad and J. Ricles), graduate students (M. Tillotson and K. Kazemibidokhti), and undergraduate students (A. Breden, M. Davis, F. Tao, E. Salazar, C. Fallon, and K. Brinkhoff) worked on the construction, instrumentation, and testing of the coupled wall specimen. The design of the test specimen was conducted in collaboration with practicing engineers from Magnusson Klemencic Associates (D. Fields, A. Haaland, and J. Mouras). The contributions of K. Bondy, Consulting Structural Engineer, to the project are also acknowledged. The concrete used to construct the test specimen was donated by Essroc Italcementi Group, the PT anchors were donated by Hayes Industries, Ltd., the PT strand was donated by Sumiden Wire Products Corporation (SWPC), and the formwork was donated by A.H. Harris & Sons, Inc. Additional material donations were made by Dayton Superior and Casilio Concrete. The findings, conclusions, and/or recommendations expressed in this paper are those of the authors and do not necessarily represent the views of the individuals or organizations noted above.

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