International Concrete Abstracts Portal

This paper presents the implications of creep-fatigue interactions for the long-term behavior of bulb-tee bridge girders prestressed with either steel strands or carbon fiber-reinforced polymer (CFRP) tendons. A large amount of weigh-in-motion data incorporating 194 million vehicles are classified to realistically represent live loads. Computational simulations are conducted as per the engagement of discrete autonomous entities in line with time-dependent material models. In general, the properties of the CFRP tendons insignificantly vary over 100 years; however, the stress range of CFRP responds to fatigue cycles. Regarding prestress losses, the conventional method with initial material properties renders conservative predictions relative to refined approaches considering time-varying properties. The creep and fatigue effects alter the post-yield and post-cracking responses of the steel- and CFRP-prestressed girders, respectively. From deformational capability standpoints, the steel-prestressed girders are more vulnerable to fatigue in comparison with the CFRP-prestressed ones. It is recommended that the fatigue truck and the compression limit of published specifications be updated to accommodate the ramifications of contemporary traffic loadings. Although the operational reliability of both girder types is satisfactory, the CFRP-prestressed girders outperform their steel counterparts in terms of fatigue safety. Technical findings are integrated to propose design recommendations.

Current design provisions pertaining to the shear transfer strength of concrete-to-concrete interfaces, including those of the AASHTO LRFD design specifications and ACI 318 code, are based on limited physical test data from studies conducted decades ago. Since the development of these design provisions, many studies have been conducted to investigate additional parameters. In addition, modern concrete technology has expanded the range of materials available and often includes the use of high-strength concrete and high-strength reinforcing steel. Recent studies examined the applicability of current shear friction design approaches to interfaces that comprise high-strength concrete and/or high-strength steel and identified a need for revision to the existing provisions. To this end, this study leveraged a comprehensive database of test results collected from the literature to propose a deep learning-based predictive model for normalweight concrete-to-concrete interfacial shear strength. Additionally, a new computation scheme is proposed to estimate the nominal shear strength with a higher prediction accuracy than the existing AASHTO LRFD and ACI 318 design provisions.

The results of an experimental program conducted to evaluate the performance of shear-critical post-tensioned I-girders with grouted and ungrouted ducts are presented. The experimental program involved the design, construction, and testing to failure of six fullscale specimens with different duct layouts (straight, parabolic, or hybrid) and using both grouted or ungrouted ducts. All tests resulted in similar failure modes, such as localized web crushing in the vicinity of the duct, regardless of the duct condition or layout. Furthermore, the normalized shear stresses at ultimate were similar for the grouted and ungrouted specimens. The current shear design provisions in the AASHTO LRFD Bridge Design Specifications (AASHTO LRFD) were reviewed, and updated shear-strength reduction factors to account for the presence of the duct in the web and its condition (that is, grouted or ungrouted) were proposed. The data generated from these tests served as the foundation for updated shear-strength reduction factors proposed for implementation in AASHTO LRFD.

This paper presents mechanics-based modeling methodologies to predict the shear strength of squat walls incorporating boundary elements. Developed with the intention of surmounting the limitations of empirical models that are prevalent in the structural engineering community, these approaches are composed of an iterative analytical method and simplified design equations. Conforming to experimental observations, a failure criterion is established to determine the web crushing and shear compression of each wall component. Upon validating the methodologies against 123 test data compiled from the literature, detailed responses of the wall system are examined to comprehend the behavior of the web and the compression and tension boundary elements subjected to lateral loading. Model outcomes indicate that the overall strength of the squat walls is distributed to the web and the boundary elements by 58% and 42%, respectively, signifying that the contribution of the boundary elements should not be ignored, unlike the case of most customary models. In contrast to the provision of published design specifications, both horizontal and vertical reinforcing bars affect the shear strength of the web concrete. The growth of compressive principal strains, which dominate the failure of the members, is a function of the reinforcement ratio. According to statistical evaluations, the proposed models outperform existing models in terms of capacity prediction. The effects of major parameters are articulated from a practical standpoint.

The rapid growth of the construction industry in Asia and the consequent updating of design specifications put forward higher performance requirements for structural components, which results in a large number of existing shear walls that are not compliant with the current seismic standards. A prospective retrofitting method, which is based on replacing the existing boundary concrete or attaching external boundary columns to nonconforming shear walls, is experimentally studied. Four shear-wall specimens were designed according to the current Chinese design code: one using plain concrete boundary columns and three using ultra-high-toughness boundary columns (UHTBCs), adopting three different strengthening strategies relevant to the boundary size and the connection form. Cyclic performance, damage patterns due to UHTBCs, and connection form are discussed based on the experimental results, from which it was ascertained that shear walls with UHTBCs show improved seismic performance, compatible with the requirements of the current seismic design code, even for the reduced-boundary UHTBCs and non-connection specimens. The predictive equation for the sectional moment capacity of shear walls with UHTBCs was discussed as a practical tool for retrofitting applications. This study highlights the most important features of a rapid retrofitting measure to improve the resilience of existing nonconforming shearwall structures, while also proving to be an effective measure for newly constructed structures.