National code recommended resistance factors for drilled shafts are not always reflective of the true level of design uncertainty at the regional levels. Moreover, several of these resistance factors still rely on factors of safety formerly used in the Allowable Stress Design approach, and, consequently, they do not comply with the Load and Resistance Factor Design principles and may be unable to achieve desired target levels of reliability consistently. Regional calibrations, while a solution to these issues, can be challenging to implement due to the limited quantity of quality load test data available at state levels. In this study, it is proposed and shown that a segmental procedure based on strain gauge data can be implemented in the resistance factor calibration framework to overcome the challenge in using a limited set of load test data to statistically characterize side resistance uncertainties. Using estimated statistical parameters, resistance factors are calibrated and observed differences with code recommended values are discussed.

Ultra-high-performance concrete (UHPC) has en¬hanced compressive and postcracking tensile strengths and durability properties. A tapered 10 in. (254 mm) deep, H-shaped prestressed UHPC pile was developed as an alternative to conventional steel HP piles with several benefits. To facilitate field implementation of the UHPC piles, a dry splice detail with steel angles and shear studs was developed with a focus on con¬structibility. Its performance under flexural, shear, and direct tension loading was evaluated through large-scale testing of full-scale spliced UHPC pile units. Flexural tests were conducted on spliced UHPC piles in weak- and strong-axis directions using a four-point loading configuration. A total of three shear tests were conducted using three-point loading, subjecting the spliced region to different shear demands. The flex¬ural and shear tests confirmed the adequacy of the pile-splice capacity under shear and flexural loading. A direct tension test was also conducted on a spliced UHPC pile by subjecting it to 225 kip (1000 kN) of tension. This resulted in a few microcracks in the test pile with no damage observed in the splice region. A simplified analytical method based on first principles accurately captured the observed performance of the test piles.

While conventional wind towers operate at heights of 80 to 90 m across many regions, including the United States, emerging tower technologies enable higher hub heights that are expected to reduce the levelized cost of energy (LCOE) and increase profit margins. This paper investigates whether increased hub heights, as well as different turbine technologies, deliver measurable economic and performance benefits in wind-rich regions using measured and simulated wind data. First, a model for estimating hourly and monthly energy production is validated with data from a site in Minnesota. To evaluate the advantages of tall towers, the model is extended to estimate the annual energy production (AEP) at various hub heights across multiple sites using different wind datasets. The results confirm that simulated data can be effectively used for predicting AEP and capacity factors in wind-rich regions. Next, it is demonstrated that increasing the hub height by 20 m yielded an average 11% increase in AEP and an 18% reduction in LCOE. Finally, the integration of advanced turbine technologies with taller towers shows the potential to reduce the LCOE of wind power by 23% while increasing profit margins by over 40%.

Recently, a precast concrete bridge railing with unique connection details for barrier-to-deck and barrier-to-barrier interfaces was developed at the Institute of Transportation (InTrans)-Iowa State University (ISU). Successful laboratory experiments led to the current study, in which the primary objectives were to determine if the bridge railing system complied with the American Association of State Highway and Transportation Officials (AASHTO) Manual for Assessing Safety Hardware (MASH) Test-Level 4 (TL-4) impact safety standards through a sequence of stages, including pre-crash simulations and one full-scale crash test with a 10000S single-unit truck (SUT). Initial analyses incorporated LS-DYNA computer simulations emulating MASH TL-4 impacts on two prototype barrier configurations: a single-slope shape and a near-vertical shape. These simulations facilitated the discernment of the bridge rail length, reinforcement details, crashworthiness for passenger vehicles, selection of the single-slope shape for crash testing, and determination of a critical impact point for the 10000S SUT crash test. Subsequent modifications to the single-slope barrier system with inclined bar connections were predicated on these computational findings. A full-scale crash test assessed the bridge railing and the loading to the inclined steel anchor bars under MASH test designation no. 4-12, focusing on its impact safety performance and potential damage to the barrier and bridge deck. In test no. ABCBRM-1, the single-unit truck, was successfully contained and redirected, with the barrier and deck sustaining negligible damage, and all safety performance criteria were within acceptable limits as defined in MASH. The study findings demonstrated that the modified single-slope, precast concrete bridge rail system met the MASH TL-4 impact safety criteria.

Ultra-high-performance concrete (UHPC) is a cementitious concrete material known for its sustained post-cracking tensile performance. Various specimen geometries and different test approaches have been used to establish the tensile characteristics of UHPC. Intending to standardize a direct tension test method, this paper independently evaluates a procedure developed by the Federal Highway Administration (FHWA), which has been adopted into AASHTO T 397. To verify the reliability and repeatability of the test method, 216 tensile specimens were cast from three different UHPC types with fiber-volume fractions of 1, 2, and 3% and tested at six laboratories. The measured responses were characterized for different phases of the tensile behavior and analyzed to understand the scatter in the test data. It was found that testing can be executed with a 60 to 70% success rate with carefully prepared samples and some modifications to the proposed test method. The test results show an increase in both the tensile strength and multicracking phase with an increase in fiber-volume fraction, but the crack straining phase depends primarily on the type of UHPC. Using the test data, average and characteristic tensile responses were established, which are intended, respectively, for analysis and design purposes.

Unbonded post-tensioned rocking walls have demonstrated superior seismic performance with greatly reduced damage and exceland representative research on rocking walls are summarized in this paper. Some inconsistencies and voids in the major design parameters for rocking walls are identified. A brief description is provided for two rocking-wall specimens tested under quasi-static cyclic loading. Force flow and failure mechanisms of rocking walls observed from the tests were studied, and it is discovered that they are very different from those of special structural walls. The test data showed that the concentration of compressive strain in concrete at the corners of rocking walls was a local behavior such that the need for confinement reinforcement higher above the toe region was diminished. Fiber grout weaker than concrete in rocking walls used as ductile bearing materials at the wall-foundation interface is a reasonable alternative to ACI 550.7. Design recommendations for height and volumetric ratio of confinement reinforcement are provided. A requirement for the aspect ratio of rocking walls stricter than that in ACI 550.7 is proposed to prevent shear sliding of the walls.

This paper explores the development of 3D-printed self-sensing Ultra-High Performance Concrete (UHPC) by incorporating graphite (G) powder, milled carbon microfiber (MCMF), and chopped carbon microfiber (CCMF) as additives into the UHPC matrix to enhance piezoresistive properties while maintaining workability for 3D printing. Percolation curves were established to identify optimal filler inclusion levels, and a series of compressive tests, including quasi-static cyclic, dynamic cyclic, and monotonic compressive loading, were conducted to evaluate the piezoresistive and mechanical performance of 29 different mix designs. It was found that incorporating G powder improved the conductivity of the UHPC but decreased compressive strength for both mold-cast and 3D-printed specimens. However, incorporating either MCMF or CCMF into the UHPC resulted in the maximum 9.8% and 19.2% increase in compressive strength and Young’s modulus, respectively, compared to the plain UHPC. The hybrid combination of MCMF and CCMF showed particularly effective in enhancing sensing performance, achieving strain linearity over 600 με. The best-preforming specimens (3G250M250CCMF) were fabricated using 3 wt% of G, 0.25 wt% of MCMF, and 0.25 wt% of CCMF, yielding a maximum strain gauge factor of 540, a resolution of 68 με, and an accuracy of 4.5 με under axial compression. The 3D-printed version of the best-performing specimens exhibited slightly diminished piezoresistive and mechanical behaviors compared to their mold-cast counterparts, yielding a maximum strain gauge factor of 410, a resolution of 99 με, and an accuracy of 8.6 με.

Post-tensioned Box Girder (PBG) bridges are frequently used when spans range from 100 to 250 ft, especially in the western US. Due to aging, environmental factors, and increasing traffic load demands, the decks of these bridges experience extensive damage. Replacing the deck in PBG bridges is difficult and costly. This paper will present the results of a research project that uses the UHPC deck overlay concept to cost-effectively rehabilitate PBG bridge decks. To confirm the beneficial outcomes of the proposed solution, a large-scale test unit is designed and is under construction. Test outcomes from the laboratory test confirming the anticipated benefits of the new solution to PBG bridge decks will also be presented.

Various Accelerated Bridge Construction (ABC) techniques, such as structural precast elements or complete modular bridge systems, are being developed and implemented throughout the United States to reduce on-site construction time and improve mobility. One of the major constraints of ABC is that precast elements can be very large and need to be broken into transportable pieces. In addition, larger cranes are required for assembly on-site. In this work, components fabricated using ultra-high-performance concrete (UHPC) are investigated. The ordinary standard bridge seat type abutment, typical in the Caltrans inventory, is used as a prototype. By using UHPC, the sectional sizes have been reduced, making it possible for the abutment to be transported to the site as a single large piece. The abutment stem proposed is a hollow section with a thickness of 6 inches and has corbels to provide the seat width of 36 inches required by Caltrans Seismic Design Criteria (SDC). Also included is a cast-in-place (CIP) or precast back wall on top of the stem wall. The precast abutment cap will be designed with corrugated metal pipe sockets, which shall be filled with UHPC CIP closure pours to ensure fixed connections with steel H piles. The investigation incorporates service, strength, and extreme loads. The performance of the new system and its components will be validated by a half-scale experimental test unit. It is anticipated that Caltrans will implement this detail in constructing two-lane standard ordinary bridges with two or three spans.

Ultra-high-performance concrete (UHPC), with its superior mechanical characteristics and durability, provides a potential way for sustainable highway infrastructure in the United States and worldwide. To attain these properties, the presence of fibers plays an integral part in ultra-high-performance concrete (UHPC) mixes. This paper studies the influence of fiber volume on the compressive strength and tensile behavior of UHPC. To investigate these material dependencies, specimens were cast using UHPC from three different suppliers with three fiber volume fractions of 1%, 2%, and 3%. AASHTO T397 test procedure was used to quantify the direct tensile behavior of UHPC. In addition, longer dog-bone specimens than specified in AASHTO 397 were cast to investigate the effects of change in gauge length on tensile behavior. Cubes of 2 in x 2 in x 2 in. and cylinders with dimensions 3 in. (diameter) x 6 in. (length) were tested for compression strength comparisons at four different ages. At 3% fiber volume, the strength ratio of cylinders to cubes was found to be around 1. However, the strengths of cylinders were higher than cube strengths at lower fiber volumes. The strength ratio did not vary with the age of UHPC. Varying fiber volume fractions significantly influenced the tensile strength and post-cracking tensile response of UHPC. A higher volume of fibers resulted in higher tensile strength and a more extensive multi-cracking phase. The crack straining phase was dependent on the UHPC type and did not depend on fiber volume. An increase in gauge length resulted in reduced residual tensile load-carrying capacities.

Through a Change Proposal, Facca Incorporated was approved by the Ontario Ministry of Transportation (MTO) to replace the as-tendered steel H-piles by the UHPC piles for supporting the west abutment of the Lily River Detour Bridge. The 11.8 in. deep UHPC piles were designed and installed at the west abutment based on the previous successful development and testing of a tapered H-shaped pile at Iowa State University in partnership with the Iowa Department of Transportation. The east abutment, as tendered, was designed to be supported by six steel H-shaped battered piles driven to bedrock. For the west abutment, six UHPC piles were produced and installed using the same batter. Since the site contained occasional boulders and the design intent to drive the piles to bedrock, the UHPC piles were fitted with steel shoes. All piles were successfully installed to reach the targeted load bearing capacities. After the replacement bridge was constructed, the detour bridge was removed and the UHPC piles were extracted to examine the conditions of the piles. This presentation will provide details of the innovative design of the piles, fabrication and driving of the piles, and lessons learned from analyzing the driving data and removal of the piles. As well, a comparison of the environmental impact of the UHPC and steel piles will be provided.

Unbonded post-tensioned (UPT) tendons have been used in structural masonry walls to enhance the self-centering capability of the walls. However, the lateral displacement capacity of masonry walls with UPT tendons can be compromised by early crushing of the compression toes. To prevent toe crushing, this research study employed rubber pads underneath the bottom corners of a full-scale one-story wall. This concept was investigated by subjecting the wall sequentially to free vibration and quasistatic tests, which minimized damage to the masonry and reduced the strength degradation of the wall with increasing lateral drift. Two major damping components were identified: one is due to the instantaneous impact of the wall on the foundation base, and the other is due to the inelastic action occurring within the rubber pads during the continuous phase of rocking motion. Using the test results, a procedure is presented for designing masonry walls with rubber pads and UPT tendons.

Vertical ground accelerations are not always considered in bridge design practice, which is partially due to the lack of consistent recommendations in the design codes and standards. However, undeniably, the vertical ground acceleration component in an earthquake can be large. While the effects of vertical ground acceleration on bridges have been studied in the past, the focus has mostly been on performance of the substructure, especially columns. This study thus investigates the effects of large magnitude of vertical ground accelerations on the response of bridge superstructures as it can experience significant impact, particularly in the connections and bearing forces. To quantify the effects of vertical ground accelerations and compare the outcomes with existing design recommendations, an analytical study is undertaken on the seismic response of straight, skewed, and curved steel bridge superstructures with drop pier caps. The results show that the vertical accelerations can amplify the superstructure moment demands at the midspan and support locations by as much as above 100%. It is further shown that the current design practice to account for vertical ground acceleration effect is not sufficient for earthquakes with high vertical ground accelerations. Although the superstructure used in this study incorporated steel girders, the results are also applicable to bridges with concrete superstructure.

Precast concrete members need to be connected effectively to form an integral structural system. Use of unstressed strands provides a cost-effective and practical solution to reinforce the connection regions of precast concrete members, especially for precast concrete bridge girder applications. With the limited understanding of bonding characteristics for unstressed strands, a combination of experimental and analytical programs, which focused on unstressed strands as a connection between precast concrete girders and cap beams for seismic applications, was designed to investigate the fundamental load-transfer characteristics of unstressed strands anchored in grout and concrete based on pullout tests. The relationship between strand stress and loaded-end displacement was developed, and the bond stress of unstressed strands embedded in concrete and grouted duct was examined. The average bond stress of unstressed strands anchored in concrete and grouted duct is recommended to be five and seven times the square root of concrete compressive strength, respectively. The results of this research provide qualitative embedment length requirements to design connections between precast concrete members using unstressed strands.

Two large-scale structural assemblages, which had equivalent PreWEC (Precast Wall with End Columns) rocking-wall systems but different surrounding structures, were tested under quasi-static cyclic loading to study the impact of wall-floor interaction on the performance of rocking-wall buildings. The first specimen (PFS1) included cast-in-place (CIP) edge columns and a CIP unbonded post-tensioned slab with rigid wall-floor connections, which maximized wall-floor interaction. The second specimen (PFS2) included precast edge columns and a precast slab with special vertical-isolation wall-floor connectors, which minimized wall-floor interaction. Test results showed that both structural assemblages demonstrated great seismic performance with limited damage and self-centering behavior. The strength of PFS1 was more than twice that of PFS2; PFS2 encountered less damage and had better self-centering performance than PFS1, but it possessed less energy-dissipation capacity. The difference in the performance of the two assemblages was mainly attributed to the different gravity load transfer paths and constraint effects of the surrounding structures. Contributions to the strength and the self-centering behavior of the two assemblages from different structural elements were quantified and compared.

A half-scale field test was conducted on a pile group installed at a stiff clay site. The pile group consisted of eight steel H-piles, with a battered pile at each corner, and connected to a precast pile cap using preformed socket connections. The pile foundation system was tested under different combinations of vertical and lateral loads. The magnitude of the loads, as well as the height of the lateral loads, were varied to produce different overturning moment-to-lateral load ratios. These load combinations enabled the researchers to investigate the foundation system for both nonseismic and seismic conditions as well as its behavior under extreme loading. The pile group produced excellent resistance during different phases of testing although there were differences in the behavior of battered and vertical piles. Under simulated seismic loading, the battered piles sustained 17% more axial compression forces, 100% more axial tension forces, and 33% lower bending moments than the vertical piles. A numerical model developed to investigate the pile behavior produced a good agreement between the measured and computed pile responses.