International Concrete Abstracts Portal

Professor Dennis Mertz passed away after a prolonged battle with cancer. He spent a large portion of his professional career working on advancing of the state-of-the-art of bridge engineering. He was a great friend and colleague to many at ACI and ASCE. Joint ACI-ASCE Committee 343, joined with ACI Committees 342 and 348, sponsored four sessions to honor his contributions and achievements in concrete bridge design and evaluation. These sessions highlighted the important work and collaborative efforts that Dr. Mertz had with others at ACI and ASCE on various topics. These sessions also combined the efforts among ACI and ASCE researchers and practitioners in addressing various topics related to the design and evaluation of concrete bridges. The scope and outcome of the sessions are relevant to ACI’s mission. They raise awareness on established design methodologies applied for various limit states covering topics related flexure, shear, fatigue, torsion, etc. They address problems related to emerging design and evaluation approaches and recent development in design practices, code standards, and related applications. The Symposium Publication (SP) is expected to be an important reference in relation to design philosophies and evaluation methods of new and existing concrete bridges and structures.

Fire is a possible hazard on highway bridges which causes significant economic damage, and it is also one of the least investigated of all hazards. There is a lack of knowledge on the long term performance and structural integrity of fire damaged and fiber reinforced polymer (FRP) laminate retrofitted bridges. One such rare in-service bridge was selected for this study. The fire damaged cast-in-place non-prestressed girders were previously repaired with mortar and strengthened with FRP wrapping. The girders were instrumented with strain gages and displacement transducers, and a non-destructive live load test was carried out to evaluate the structural response. The results from the load testing were used to compare two identical girder spans with and without CFRP strengthening. A full-scale non-linear finite element model of the overall bridge superstructure was created, and the test results used to calibrate the model. The carbon (CFRP) strengthened girder exhibited similar stiffness compared to the undamaged girder as evidenced by almost equivalent mid-span deflection. The girder moment capacity decreased significantly due to fire damage, and the CFRP strengthening plus mortar repair was successful in restoring the moment capacity. The finite element model provided good correlation with load test results.

The root causes of uncertainties in new concrete structures have been evidenced to be substantially different from those in safety evaluation of existing structures. Therefore, the design methodology in ACI 318 shall be re-calibrated to better reflect the effects of these significant differences, particularly for the spatial variation of concrete strength in existing structures. The degree of uncertainties that whether the testing data can reliably represent the concrete strength at the critical locations of interesting has been identified to play a vital role in developing an effective structural safety evaluation methodology. This paper presents a novel statistical procedure, where the semi-variogram modeling is used to establish the spatial variation of concrete strength so that the degree of uncertainty mentioned above can be quantified as a function of the spacing intervals of the testing points. Kriging is used to estimate the expected concrete strength with the desired confidence levels for the locations between the measurement locations to ensure the critical locations are covered. The actual concrete coring data were analyzed to illustrate how to estimate the spatial variation. The proposed methodology can also be applied to any testing data that can characterize the stochastic properties of concrete strength in existing structures.

Dr. Dennis Mertz was involved with the AASHTO LRFD Bridge Design Specifications [1] for 30 years. Starting with the original development of the specifications and continuing with maintenance and related course development and presentations. His last major contribution to the Specifications was to serve as Principal Investigator for the reorganization of Section 5, Concrete Structures. This presentation summarizes the changes to the structure of the Section including the increased emphasis on design of “B” and “D” regions of flexural members and introduces new and expanded material on beam ledges and inverted T-caps, shear and torsion, anchors, strut and tie modeling and durability. The product of this work was included in the 8th Edition of the Specifications as a complete replacement of Section 5.

This paper presents a numerical study of novel configurations in reinforced concrete wall systems that exhibit large structural ductility and increased post-ultimate strength, leading to potentially better performing structures under large and sustained loads. A Gravity-Based Structure (GBS) under extreme ice loading is used as use-case to investigate various scenarios to increase post-ultimate ductility. It is shown that the largest increase in the out-of-plane toughness of the exterior reinforced concrete walls is gained using post-tensioned tendons and mild “core” steel placed at the center of the exterior wall cross section. These structural features show promise in improving the global post-ultimate behavior, which would make them desirable to use in structures that are deployed in locations where extreme ice feature impacts pose a foreseeable risk and where designing the structure to remain elastic under ice impact may not be economically feasible. Lessons-learned from the GBS evaluation can also be applied to various reinforced concrete structures.