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.

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.

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.

A new bridge system was recently developed for short span bridges in low clearance areas. This system uses the same concept as spread box beam bridges in which standard TxDOT precast prestressed slab beams are spaced apart. The deck is composed of stay-in-place precast concrete panels spanning between beams with a cast-in-place reinforced concrete deck. This paper presents a comprehensive approach for the investigation and development of this alternative spread slab beam bridge system including design, construction, field testing, modeling, and derivation of live load distribution factors (LLDFs). A parametric design study was conducted to evaluate the potential bridge spans when considering the four standard TxDOT slab beam types, a range of beam spacings, and potential bridge widths. One of the challenging geometries with widely spaced slab beams was constructed at full-scale to assess constructability and in-service behavior. The full-scale test bridge and a recently constructed on-system bridge with more closely spaced slab beams were tested under static and dynamic truck loads to obtain important insight into their structural performance and live load distribution behavior, while also providing data to guide analytical and computational modeling studies. Finite element models were developed to investigate an array of possible bridge geometries and determine the effect of key parameters on the load sharing behavior. Based on the research findings, it was concluded that spread slab beam bridges with a topped panelized deck provide a viable construction method for short-span bridges. For both tested bridges, the desired performance was achieved for in-service loading. Experimental and computational LLDFs were evaluated, and LLDF equations for spread box beams were reviewed for applicability to spread slab beam bridges. The AASHTO LRFD spread box beam LLDFs range from being unconservative to very conservative. Unique moment and shear LLDFs were developed for use in design of spread slab beam bridges.