Quantifying Statistical Uncertainties for Temperature Gradient Analysis of Bridges
Ahmed Elshoura, Louisiana State UniversityShow Abstract
Ayman Okeil (firstname.lastname@example.org), Louisiana State University
The philosophy of current AASHTO Bridge Design Specifications is based on considering uncertainties inherent in the structural design process by proposing load and resistance factors. Factors used in the Load and Resistance Factor Design (LRFD) method are calibrated using theory of reliability. Research efforts to calibrate load factors for gravity loads can be found in the literature. Calibration of load factors for temperature loads has not received similar attention. Temperature loads are inevitable environmental loads that affect bridges on a daily and diurnal basis causing additional stresses and deformations. The first step in conducting such a calibration is to understand the uncertainties inherent therein. This study establishes the probability distribution of maximum daily temperature gradient affecting bridges using field data, and extrapolates the largest extreme values over the expected design life of the bridge using Extreme Value Theory. Bridge temperatures were monitored for a bridge case study; John James Audubon Bridge, for 5 years. Recorded data were used to investigate the best-fit distribution type for maximum daily temperature differences. Peak Over Threshold method is used to specify the largest extreme maximum daily temperature difference values. Results showed that the Beta distribution type is the best fit for maximum daily temperature data. Moreover, extrapolated temperature values were found lower than those specified in AASHTO LRFD.
Effect of Taper on Shear Stiffness of Reinforced Neoprene Bearing Pads
Satyajeet Patil, University of FloridaShow Abstract
Gary Consolazio, University of Florida
H. Hamilton, University of Florida
Steel reinforced elastomeric bearing pads are widely used in bridge construction to vertically support girders on piers while also accommodating translational and rotational girder deformations caused by live loads and temperature changes. To support sloped girders, flat bearing pads of uniform thickness are typically used with either tapered steel shim plates or an inclined concrete bearing seat. The use of tapered pads have the potential to reduce both construction time and cost by eliminating the need for tapered plates or seats to match the girder slope. Little research, however, has been performed to investigate and quantify relevant design properties for tapered bearing pads. In this paper, results are presented from experimental testing that was performed to quantify shear stiffnesses of tapered pads having varied geometric characteristics (plan view dimensions, elastomer thickness, and slope angles). An experimental bearing pad test device was designed and utilized to impose shear loads in accordance with ASTM standards, while simultaneously maintaining constant axial load. Bearing pads chosen for testing were tapered variations of standard flat bridge bearing pads used in the state of Florida. Results obtained from the study revealed that shear stiffness was not significantly influenced by the introduction of taper angle, the direction of shear along the length of pads, or axial load level. The shear stiffness of tapered pads remained within approximately 10% of the shear stiffness of corresponding flat pads.
Material Redundancy for Enhancing the Resistance to Collapse of the Florida International University (FIU) Bridge
Xiao Tan, Stevens Institute of TechnologyShow Abstract
Weina Meng, Stevens Institute of Technology
Yi Bao, Stevens Institute of Technology
Hani Nassif, Rutgers University
Victor Li, University of Michigan
A prestressed concrete bridge near the Florida International University in Miami, USA, collapsed during construction in 2018. The incident spurred bridge engineers to rethink the design and construction of bridges. Recently, particular emphases have been placed on enhancing structural redundancy in bridges. In a bridge system, the use of redundant structural members may prevent bridge collapse if some members fail. This paper presents the concept of material redundancy – a new pathway, to supplement the structural redundancy concept for improving the safety and resiliency of bridges. This study interprets the collapse mechanism of the bridge near FIU using a finite element model, which analyzes the evolution of internal loading and damage during bridge construction. The material redundancy concept is demonstrated by testing the effects of two families of high-performance fiber-reinforced cementitious composites on the damage of the bridge. Specially, this study investigates ultra-high-performance concrete (UHPC) and engineered cementitious composite (ECC), which feature high tensile properties, such as high crack resistance, tensile strength, and ductility. A parametric study is performed to evaluate the effects of the tensile strength and strain capacity of UHPC and ECC on the initiation and development of damage in the bridge. The results show that the use of ECC or UHPC can significantly decrease damage, and, thus, is promising to avoid the collapse of the bridge, because after concrete matrix cracks the dispersed fibers in ECC and UHPC can take over the load and provide redundancy at the material aspect.
AN INVESTIGATION OF REINFORCED CONCRETE BEAMS RETROFITTED WITH ULTRA-HIGH PERFORMANCE CONCRETE
Alireza Valikhani, Florida International UniversityShow Abstract
Azadeh Jaberi, Washington State Department of Transportation
Atorod Azizinamini, Florida International University
A number of in-service bridges need retrofitting or repair which is an economical alternative to new construction. Existing retrofit methodologies exhibit early signs of deterioration or undesired failure modes which may severely affect the retrofitted concrete member’s serviceable life. To this aim, new advanced materials are required which appends the structural strength and improves the durability characteristics of the member. Ultra-high performance concrete (UHPC) has excellent mechanical properties and rheological characteristics similar to concrete allowing easy use for retrofitting deteriorated bridge elements such as beams and girders. Also, lower porosity and compact microstructure provides an external protective layer. In this paper, an experimental program is devised for retrofitting UHPC beams using different damage indices and surface preparation techniques. The beams were retrofitted only in segments where controlled artificial damages were introduced. The results show that the retrofitted beams using sandblasting or mechanical connectors exhibit improved structural behavior. To complement the study, a brief numerical work is presented to comprehend the effect of various configurations of retrofitting. At the conclusion, a design example is presented which offers designers a framework for calculating the enhancement of structural strength using UHPC.
DISCLAIMER: All information shared in the TRB Annual Meeting Online Program is subject to change without notice. Changes, if necessary, will be updated in the Online Program and this page is the final authority on schedule information.