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Legacy software from 1975 for general static and dynamic analysis of nonlinear structures. Source code in FORTRAN and related reports can be downloaded from the earthquake engineering online archive maintained by University of California Berkeley.
ANSR-1: Analysis of Nonlinear Structural Response
Mondkar, Digambar P.; Powell, Graham H.; Riahi, Ali; Row, Dennis G.; Maison, Bruce F.; Popov, Egor P.
Department of Civil Engineering, University of California, Berkeley, 1975,
ANSR is a general purpose computer program for static and dynamic analysis of nonlinear structures. In it, a structure is idealized as an assemblage of discrete finite elements. Each node may possess up to six degrees of freedom. The structure mass is assumed to be lumped at the nodes. Viscous damping effects may be included, or damping proportional to mass, specified. Static loads are applied in a series of load increments, each load increment being specified as a linear combination of static force patterns. This feature permits nonproportional loads to be applied. Dynamic loading may consist of earthquake ground accelerations, time-dependent nodal loads, or prescribed initial values of nodal velocities and accelerations. The elements available are:  A three-dimensional truss element, which may yield in tension and yield or buckle elastically in compression. Large displacement effects may be included.  A two-dimensional 4-to-8 node finite element for plane stress, plane strain, and axisymmetric analysis. Large displacements may be included and the material may be specified to be isotropic linearly elastic, orthotropic linearly elastic, or isotropic elastic-perfectly plastic with the Von Mises yield function. Nonlinearities are introduced at the element level only and may be due to large displacements, large strains, and/or nonlinear materials.  INEL2, beam-column element which has two-dimensional stiffness and yield characteristics, may be located arbitrarily in a three-dimensional structure and is intended primarily for modeling beams.  INEL3, a beam-column element which has three-dimensional stiffness and yield characteristics, can be used for modeling columns in which biaxial bending effects may be important and also for structures such as elevator shafts. In INEL2 and INEL3, allowance has been made for rigid floor diaphragms by means of a "slaving" feature incorporated into the elements at the element level because ANSR-1 cannot account for slaving at the nodal level. Both elements also allow for rigid end zones and for initial element actions.  The inelastic brace element, INEL4, is a simplified model to describe the macrobehavior of a brace (i.e., the axial force-displacement hysteretic rule). The axial force-displacement algorithm simulates the observed behavior with nine piecewise linear zones. The orientations of the zones are defined by: member properties, control displacements, forces, and slopes. All of these properties are user selected input to the algorithm. The code is organized to permit the addition of new finite elements to the library with relative ease. The program permits the user considerable flexibility in selecting a variety of solution schemes, including step-by-step, iterative, and mixed schemes. For static analysis, a different solution scheme may be employed for each load increment. The dynamic response is computed by stepwise time integration using Newmark's beta-gamma-delta operator.