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.

In the new generation of design code, safety of structures is provided in form of load and resistance factors. Safety is measured in terms of the reliability index. The acceptability criterion in the selection of load and resistance factors is closeness to the target reliability index which can be different depending on limit state. The paper presents a procedure to determine these factors using the concept of “design point”. The coordinates of design point are equal to factored load or factored resistance. The required input data includes for each load component and resistance: mean values, bias factor (ratio of mean to nominal), standard deviation or coefficient of variation. The procedure is demonstrated on example of bridge design code (AASHTO[1]) and design code for concrete buildings (ACI 318[2]) for prestressed concrete girders and reinforced concrete beams in flexure and shear.

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.

The research paper presents an analysis of autogenous shrinkage development in self-consolidating concrete (SCC). The first stage of the study involved an evaluation of concrete susceptibility to cracking caused by shrinkage of SCC with natural and lightweight aggregate. The shrinkage was tested on concrete rings according to ASTM C 1581/C 1581M- 09a. The influence of aggregate composition, the water content in lightweight aggregate, and SRA admixture on the reduction of concrete susceptibility to cracking, due to the early-age shrinkage deformation was determined. In the second stage of the research, the innovative method measurement of autogenous shrinkage was developed and implemented. The tests were performed on concrete block samples, dimensions 35x150x1150 mm, that had the same concrete volume as ring specimen in the ASTM method. Linear deformation of the concrete samples was measured in constant periods of 500 s using dial gauges with digital data loggers. The investigation allowed evaluating of the influence of water/cement (w/c) ratio of 0.28, 0.34, 0.42, and of aggregate composition on the development of autogenous shrinkage in different stages of curing SCC. The results were compared to existing material models proposed by other researchers. The conducted study indicated a significant influence of the w/c ratio and composition of aggregate on the concrete susceptibility to crack caused by the autogenous shrinkage deformation.