Arturo E. Schultz

Self-Centering Behavior of Unbonded, Post-Tensioned Precast Concrete Shear Walls

Self-centering ability of unbonded post-tensioned precast concrete shear walls has been attributed to the presence of post-tensioning force. However, the experimental results presented in this paper indicate that the post-tensioning force may completely die out during cyclic loading while the walls are able to retain their superior self-centering characteristic. Moreover, the analytical study presented in this article indicates that with proper configuration of end-anchorages for post-tensioned tendons, self-centering of post-tensioned walls can be achieved even when the post-tensioning force vanishes. This study also investigates the effects of tendon layout, tendon end-anchorage configuration, and external vertical load on the self-centering ability of unbonded precast concrete shear walls subjected to earthquake loading.

Nonlinear Finite-Element Analysis of Critical Gusset Plates in the I-35W Bridge in Minnesota

Reported evidence suggests that failure of gusset plates initiated the collapse of the I-35W Bridge in Minneapolis, Minnesota. The particular gusset plates were at a panel point designated as U10. Therefore, an analytical investigation was conducted on the condition of the U10 gusset plates at the time of bridge collapse. The forces delivered to panel point U10 were reproduced using available information of the bridge. These forces were introduced to detailed nonlinear three-dimensional finite-element models to calculate stress and strain states of the gusset plates. The results indicate that substantial portions of the U10 gusset plates were yielded at the time of collapse, confirming earlier findings from federal and state investigations. Weight increase due to past deck reconstruction and construction material and equipment staged on the day of collapse, along with insufficient thickness of the gusset plate, were identified as the main contributing factors to the substantial yielding. The results also suggest that the interaction of compression and shear played an important role in the gusset plate failure.

Improved Coefficient of Restitution Estimation for Free Rocking Members

AbstractIn 1963, a geometry-dependent approach to estimate the coefficient of restitution (COR) was proposed for free rocking structures. Since then, this estimation has been reported as being consistently lower than results obtained from experimental data. An assumption used by the original model is shown to be the cause of this underestimation. Identifying that the rocking takes place over a contact region, this study introduces a modified formulation for free rocking bodies and proposes an improved COR estimation to accurately quantify the energy dissipation of these structures. Using experimental data, it is shown that the improved CORs consistently provide better correlation to those established from tests than the COR obtained from the original approach.

Bridge life extension using semiactive vibration control

This paper focuses on the use of a control system to extend the life of a highway bridge. The safe life of a bridge can be more than tripled if the peak strain levels it experiences are reduced by just 33%. As of 2012, over 5000 bridges in the country have been deemed to be structurally deficient. Hence, the use of a vibration control system to extend the lives of bridges can be of tremendous societal impact. This paper utilizes a dynamic model of the Cedar Avenue tied arch steel bridge in Minnesota to investigate avenues for peak strain reduction. Simulations show that the use of passive structural modification devices such as stiffeners and dampers is inadequate to reduce the key resonant peaks in the frequency response of the bridge. Both active and semiactive vibration control strategies are then pursued. Active vibration control can effectively reduce all resonant peaks of interest, but is practically difficult to implement on a bridge due to power, size, and cost considerations. Semiactive control with a variable orifice damper in which the damping coefficient is changed in realtime using bridge vibration feedback can be practically implemented. Simulation results show that, when employed with multiple devices, the proposed semiactive control system can reduce the response at all critical resonant frequencies. Further analysis reveals that the location and number of actuators on the bridge is critical for controlling these specific resonant frequencies.

A New Data Set for Full-Scale Reinforced Concrete Columns under Collapse-Consistent Loading Protocols

A series of eight full-scale reinforced concrete column tests was recently carried out at the NEES (Network for Earthquake Engineering Simulation) Multi-Axial Subassemblage Testing (MAST) site at the University of Minnesota as part of a National Science Foundation (NSF) NEES research program. The tests were conducted to address the shortcomings in the available database of reinforced concrete (RC) columns tested with large drift ratios under monotonic and cyclic loading protocols. The specimens were designed based on ACI 318-11 and featured two different cross-sectional dimensions, both larger than nearly all of the columns tested previously. They were subjected to several large displacement loading protocols, including a monotonic and a cyclic biaxial loading protocol. Also, to investigate the effectiveness of novel materials, one specimen was constructed with ultra-high-performance fiber-reinforced concrete (UHP-FRC). This paper presents a description of and potential uses for the data set that is made accessible via a digital object identifier (DOI) (data set DOIs: 10.4231/D33T9D65T, 10.4231/D3028PD2G, 10.4231/D3V97ZR8Z, 10.4231/D3QN5ZB62, 10.4231/D3KW57J3S, 10.4231/D3G44HQ9B, 10.4231/D3BC3SX4Q, and 10.4231/D36M3340C).

Response Modification Approach for Safe Extension of Bridge Life

A large portion of highway bridges in the United States are reaching or have reached their intended design lives. To avoid replacing a large number of bridges simultaneously, methodologies to safely extend their lives are important to help avoid high replacement costs and to schedule bridge replacement over a longer time window. This paper proposes an approach to extend the fatigue life of vulnerable steel bridges through a response modification apparatus, consisting of a mechanical amplifier and a response modification device, which provides supplemental stiffness and damping to the bridge. Because of the relatively small deflections encountered under typical service loads, the use of a mechanical amplifier allows for a smaller apparatus and enables a more efficient device to provide adequate response modification forces to the bridge. Herein, the use of a scissor jack as the mechanical amplifier is proposed for use in bridge applications, and its utility in concert with a passive stiffness device is demonstrated by application to a simple beam structure. Reductions in moment ranges of 37% and safe life extensions of 300% are achieved on a simple beam model with the proposed response modification apparatus.

Characterizing the In-Plane Rocking Response of Masonry Walls with Unbonded Posttensioning

AbstractUnlike the use of bonded reinforcement to anchor a masonry wall to its foundation, the use of unbonded posttensioning may result in a controlled rocking response of the wall. Considering th...

Lifetime Extension of a Realistic Model of an In-Service Bridge through a Response Modification Approach

Many highway bridges in the United States are reaching their intended design lives and are in need of attention. To avoid replacing these bridges simultaneously, methodologies to safely extend their lives are important to help avoid high replacement costs and to allow for bridge replacement to occur over a longer time window. This paper expands an approach to extend the fatigue life of vulnerable steel bridges through a response modification (RM) apparatus, consisting of a mechanical amplifier and a RM device, which provide efficient supplemental stiffness and damping to the bridge. Because of the relatively small deflections encountered under typical service loads, the use of a mechanical amplifier allows for a more efficient and less intrusive apparatus to provide the required RM forces imparted to the bridge for increased bridge life. This paper presents a parameter study exploring the flexibility of the elements in the RM apparatus, the length of the apparatus, and the characteristics of the RM device. The analyses also add superstructure damping and other model improvements to a comprehensive numerical model of a realistic in-service bridge. The paper carries out dynamic analyses in the frequency domain to ensure the robustness of the RM apparatuses for various loading frequencies. The most important characteristic of the RM apparatus is found to be the cross-sectional area of the members. Additionally, the parameter study showed that a smaller apparatus is most cost effective. Finally, the dynamic analyses showed that the use of a semiactive device may be beneficial to the effectiveness of the RM approach.

New Design Detail to Enhance the Seismic Performance of Ordinary Reinforced Partially Grouted Masonry Structures

AbstractRecent studies have shown that in the event of a strong earthquake, partially grouted (PG) masonry walls would most likely not perform according to code expectations. The research reported herein is focused on introducing an economically competitive design detail to enhance the seismic performance and safety index of PG reinforced masonry shear walls. Besides the conventional design details of single grouted vertical cells with single bond beams, two other details called double grouted vertical cells with double bond beams, and double grouted vertical cells with single bond beams plus joint reinforcement, were constructed and tested in this study. Test results demonstrated that the single grouted wall failed in a low ductility shear-dominated mode, while the modified design details resulted in a change to the high ductility shear failure mode. Results of nonlinear static and incremental dynamic analyses showed that using the proposed enhanced detail can significantly improve the seismic performanc...

Analysis of Critical Gusset Plates in the Collapsed I-35W Bridge

Investigation led by the National Transportation Safety Board (NTSB) suggests that inadequate design of gusset plates played a key role in the collapse of the I-35W Bridge in Minneapolis, Minnesota. The particular gusset plate connection was at a panel point designated as U10. Further understanding of the behavior of the U10 gusset plates is essential. In the present study, the U10 gusset plates were analyzed using detailed nonlinear finite element models. The forces delivered to panel point U10 were reproduced using available information of the bridge. These forces were, in turn, used to calculate possible stress and strain states of the U10 gusset plates. The results indicate that substantial portions of the U10 gusset plates were yielded at the time of collapse. Weight increase due to deck reconstruction, staged construction materials, and thermal effects, along with insufficient strength of the gusset plate, seem to be the main contributing factors to the substantial yielding. The results also suggest that the interaction of large compression and large shear should be addressed. This interaction is not well understood.