International Concrete Abstracts Portal

Describes an expert system with a knowledge base consisting of freeze-thaw, sulfate, alkali-aggregate, and corrosion aspects of concrete durability. The system was developed on a microcomputer using an expert-system shell facility. This paper discusses knowledge acquisition, knowledge representation, issues relating to the maintenance of expert systems, and recommendations for field implementations.

Design and construction of bridges composed of simple-span, pretensioned girders made continuous for composite dead and live loads have become widespread. The design of these structures in the U.S. has been generally based on the procedure outlined in "Design of Continuous Highway Bridges with Precast, Prestressed Concrete Girders," published by the Portland Cement Association (PCA) in 1969. Although existing bridges designed by this procedure are generally performing well, it is believed that this method may not accurately predict the true behavior of these structures. One of the major uncertainties in the design of these structures is prediction of positive and negative moments in the cast-in-place connections at the piers. This uncertainty is due to the different loading and construction stages, time-dependent effects, and details used to make the connection. To resolve such uncertainties, an analytical study was conducted to develop guidelines for more rational design of the continuity connections. Paper summarizes results of an extensive parametric study to consider the effects of 1) construction sequence, including simple span behavior before and continuous behavior after casting the deck and diaphragms; 2) time-dependent behavior, including concrete creep and shrinkage, and steel relaxation; 3) live load applied at any stage of service life; 4) cracking resulting from both positive and negative moment, including "tension stiffened" stress-strain relationships for reinforcement; and 5) closing of cracks when combined dead load plus time-dependent moments are reversed by application of live loads.

The knowledge contained in Computer Applications in Concrete Technology will prove invaluable. This symposium volume of 10 papers will provide you with the information you need to build high-quality, cost efficient structures. Presenting various practical applications of computer technology, the topics covered include: computer analysis of time-dependent behavior of continuous precast prestressed bridges; substructure modeling of two-way slab systems; an automatic quantitative image analysis system for cement and concrete research; maintenance and implementation of an expert system for durable concrete; and prediction of shear failure in concrete structures using nonlinear finite element analysis. Other subjects covered include: a three-dimensional stability analysis/ design computer program for concrete monolithic structures; and a programming environment for structural engineering applications based on interactive computer graphics." Note: The individual papers are also available as .pdf downloads.. Please click on the following link to view the papers available, or call 248.848.3800 to order. SP106

A substructuring technique to analyze equivalent frames according to ACI 318-83 is presented. A more consistent implementation of the equivalent frame method is formulated. The width of the column strip and the percentage of torsional stiffness required are studied. A program that will analyze a building system subjected to gravity as well as lateral loads is developed.

The complex factors that influence behavior and strength of concrete components failing in shear pose serious obstacles to the use of traditional linearly elastic analysis techniques. However, recent developments in the application of nonlinear finite element methods and in modeling nonlinear material properties have allowed the development of a computer model to effectively analyze complex nonlinear situations. The model includes material laws representing the full inelastic response of concrete cracking and crushing (including effects of triaxial confinement) and the yielding of reinforcing steel bars. This computer model is verified using data from a test program involving nine reinforced concrete shear-sensitive beams of varying dimensions and span-to-depth ratios. Calculated and measured failure modes, deflection and cracking patterns, and ultimate capacities corresponded well in all of the beams compared. A computer program based on the verified model has been used by the authors in several applications to predict ultimate capacity and failure modes for complex systems of walls, beams, and slabs. One such application, the prediction of shear strength in the reinforced concrete ice walls of an offshore concrete gravity-based structure, is discussed in detail.