International Concrete Abstracts Portal

A finite element procedure is presented for the analysis of reinforced concrete shearwalls. The wall is idealized as a two-dimensional structure, and the global behavior of the wall under static loading conditions is emphasized. A combination of a new family of higher-order quadrilateral elements and beam elements is employed in the finite element discretization of the wall. Constitutive models of material behavior are based on the nonlinear elasticity. The main material nonlinear effects accounted for in the analysis are the tensile cracking, the biaxial compressive response of concrete, and the yielding of steel reinforcement. A smeared approach is used in the representation of concrete cracking and steel bars. Simplified uniaxial and biaxial material models for reinforced concrete are developed and presented in detail. The incremental-iterative nonlinear solution techniques employ both constant and variable stiffness with the option of selective updating of the stiffness matrix in the load increment. Numerical examples are presented and compared with other existing solutions.

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.

A computational procedure is described for determining nonlinear response of a building system subjected to earthquake motion. The method is sufficiently simple for use with a microcomputer because system response is expressed in terms of a single generalized coordinate. Deflected shapes for the systems are assumed to be invariant for all amplitudes of motion. The equation of motion is integrated for each instant of response on the basis of a normalized relation between base shear and top-level deflection. The hysteretic relation is constructed for each new cycle using cubic segments to express a path from initial unloading through force and deflection reversals to the point of maximum deflection. The base motion is selected from a menu of earthquake records stored on diskette. Results displayed on screen consist of histories of acceleration at the top-level and maximum interstory drift, and the computed force-deflection relation.

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.