International Concrete Abstracts Portal

With the aid of modern digital computers and sophisticated computational techniques such as the finite element method, it is now possible to simulate the structural behavior of an arbitrary reinforced concrete shell structure under general loading through its elastic, cracking, inelastic, and ultimate load ranges, taking into account nonlinear material, nonlinear geometry and time-dependent effects of creep and shrinkage. In this paper, a method of analysis and a computer program based upon a composite layered finite element displacement model are briefly described. The analysis recognizes the nonlinearities due to cracking, nonlinear stress-strain behavior in concrete, yielding of the steel reinforcement and the tension stiffening between cracks. The effects of the countinuously changing structural geometry are taken into account by an updated Lagrangian formulation. The time dependent effects of creep and shrinkage are also included by an initial strain procedure. Numerical results for reinforced concrete shells obtained with the computer program are presented which indicate that in some cases an increase and in other cases a large reduction in the calculated ultimate load occurs as each of the nonlinear factors is included in the computer analysis.

Presents the results from a study of modeling concrete in the postcracking range using a three dimensional finite element analysis. The analytical work was based on an experimental study of concrete foundations which were loaded through bearing plates. The discrete cracking model was used, resulting in cracking which closely followed that in the tests. Comparisons have been made for different meshes, variable concrete material properties, and variable foundation dimensions. Failure occurred when the concrete foundation broke into segments, with a resulting loss in load-carrying capacity. The approach used is conceptually straightforward, lying between three-dimensional elastic analyses used in the past for concrete foundations and highly rigorous theoretical ones which have been used only for very limited applications.

Because of the presence of lateral loads and high-end eccentricities, the ACI 318-83 empirical design method cannot be used for design of tilt-up walls. Analysis must be performed during design to account for the P-{delta} effects. To confirm various design concepts and to evaluate the slenderness limitations, a series of tests on concrete wall panels was conducted. Several simplified design procedures were used to compare analytical results to test observations of slender load-bearing walls. Results of computer program TILT for IBM-PC (or compatible) computers were compared with the results of simplified design procedure calculations and test observations. Investigations show that the actual strength of load-bearing tilt-up walls are considerably higher than predicted by simplified analysis. The paper briefly discusses the theory of geometrical and material nonlinearities and presents methods for solutions that are incorporated in the program TILT. Conclusions and effectiveness of the TILT computer program for analyses of tilt-up load-bearing walls are shown.

The microcomputer and associated digital technology has changed the way things are done both in the structural laboratory and in the field. The impact of microcomputers on the science of field measurement is mainly with regard to cost and time. The many benefits of field monitoring of structures are now available at an acceptable cost. Cost is reduced due to automatic recording rather than manual methods. This paper discusses the benefits of field monitoring during construction and the life of the structure. Two proven measuring systems are described in detail. The paper also describes a system for dynamic analysis of structures. The reduced cost of determining the behavior of buildings and bridges is not the only benefit of these three new measuring systems. Data returned for analysis are in a form that can be quickly reduced and evaluated by computer. A short turn-around time means that the behavior data are available when needed.

Microcomputer applications are continually expanding into new fields, including the area of concrete construction. The dissemination of information concerning these applications promotes their growth and development and benefits the construction industry. When the Bureau of Reclamation began planning Upper Stillwater Dam, the largest roller-compacted concrete (RCC) dam to date in the U.S., due consideration was given to the management of the myriad of concrete test data that would be generated during this rapid method of construction. Using a microcomputer system to facilitate proper treatment of these data would serve several important purposes: 1) provide an overall view of quality control of the RCC, and act as a quality assurance tool; 2) provide a quick method for updating mix design quantities based on variations in materials; and 3) provide access to the data for a comprehensive review of this state-of-the-art method of construction. Both the programming structure and the capabilities of the program will be discussed. The qualifications for developing an RCC quality control system required that the program be user friendly so that it could be readily used by construction inspectors and laboratory technicians. The system provides record keeping for all RCC tests and RCC materials tests, including concrete unit weight, concrete consistency measurements by vibrating table, nuclear density readings, cylinder compressive brake strengths, and aggregate gradations and moisture contents. The program also calculates adjusted mix proportions based on moisture content and clean separation of the aggregate. The RCC quality control system is written in dBASE III, and the host is an IBM-XT microcomputer. The system is connected to a mainframe computer in Denver via modem so that data can be periodically reviewed by designers and for long-term storage.