LARSA: Element Library and Load Types

LARSA's element library comprises basic elements including beams and plates, seismic elements, and inelastic elements.

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Linear and Nonlinear Elements

Beam and Truss
Cable, tension-only with rebirth
Tension-Only, Compression-Only Truss
Grounded Spring (translational/rotational)
2-Node Spring (translational/rotational)
Coupled 6x6 Foundation Stiffness
Compression-Only Foundation Spring
Hook and Gap Element
Plate, Shell, and Membrane Elements
Lumped Mass

Standard sections can be added into the project by opening the Standard Sections tool, which include ARBED, AISC, Canadian, UK, Euro, and many other databases.

LARSA Section Composer is a graphical tool for modeling arbitrary sections for use in LARSA 4D. Section Composer supports nonprismatic and composite sections based on standard, parametric, and custom shapes, and it is able to compute section properties in real time. Also see Parametric and Nonprismatic Sections in LARSA 4D.

Load Types

Joint loads, displacements, and temperature changes
Auto self-weight
Beam loads: local, global, and projected; point, trapezoidal, uniform, partial, and distributed
Uniform and gradient thermal loading for beams and plates
Floor and area loads
Prestressing for cable, truss, and beam
Post-tensioning cable elements with option to lock the cable tension
Shell, plate, and membrane loads in global, local, or projected directions
Post-tensioning from tendons

Element Features

User Coordinate Systems can be rectangular, cylindrical, or spherical
Displacement coordinate systems using user coordinate systems
Supports, springs, and loads specified in global or user coordinate systems
Member rigid end zones, semi-rigid connections, and end-offsets
Slaved degrees of freedom
Nonprismatic tapered sections

Seismic Element Library

The isolator and bearing elements are used to model isolation devices, energy dissipation devices and bearings, and they exhibit nonlinear force-deformation relationship with hysteretic behavior. The following types of isolator and bearing elements are included in LARSA 2000/4D. These elements can be used in any nonlinear analysis.

Elastomeric Bearings, Steel Dambers: This element models the behavior of low damping rubber bearings, high damping rubber dampings in the range of strain prior to stiffening, and lead-rubber bearings.
Viscous Fluid Dampers: Suitable for modeling the behavior of fluid viscous dampers or other devices displaying viscous behavior. Time history analysis only.
Lead-core Elastomeric
Elastomeric with Stiffening
Sliding Friction Bearings
Friction Pendulum

Inelastic Element Library

Uniaxial Hysteretic Spring: This element works in translation and rotation or as axial or torsional springs. The hysteretic spring uses a polygonal hysteretic model (PHM), the same material model used in the computer program IDARC2D and in the FEMA program NONLIN. The material model has strength and stiffness degradation capabilities.
Connection Beam Element: This element consists of an elastic beam with built-in yielding springs at the ends. This is uncoupled plasticity with concentrated yielding model. There can be up to four such end-springs - two springs at each end, one for each direction of bending. The properties of these springs can be assigned so as to model the elastic-plastic behavior of the beam itself and/or to model the flexibility and inelastic behavior of the end connections.
Hysteretic Beam Element: This element models the continuous spread of plasticity along the length of a member and represents the interaction between axial force and strong and weak-axes bending moments using the smooth yield surface equation at a specified number of Gauss points along the length of the member.
Triaxial Hysteretic Spring: This 2D and 3D force interaction spring element is used to couple the local axial force and bending moments by means of a yield surface or an interaction force diagram.
Yield Surface-Based Element: In contrast to the hysteretic beam element the yield surface-based element accounts for interaction at the Gauss integration points using the piecewise planar yield surface.

A Graph Produced by LARSA 2000 Shows the Yield Surface Changing

Our Collaborative Effort with MCEER Earthquake Research Group at the University at Buffalo

The nonlinear analysis of structures has become increasingly important in the study of structural response to hazardous loading such as earthquake and blast.

The latest tools available for this type of analysis are impractical for professional use, generally University research projects that lack convenient user interfaces or overload the user with questions only important to researchers. The general purpose Finite Element programs that require very fine-grained modeling are often impractical to the engineer.

Larsa, Inc. is working with the earthquake research group MCEER at the University at Buffalo to bring the latest nonlinear earthquake analysis technologies into mainstream use by integrating their research into the already user-friendly analysis environment that Larsa provides.

With the inelastic analysis tools developed through this collaboration, LARSA 2000/4D takes away the overhead of entering fine-grained details for these advanced analysis options, providing engineers new realistic capabilities for seismic and collapse applications.

LARSA's inelastic and seismic element library is based on the works of professors M.C. Constantinou, A.M. Reinhorn, P.C. Tsopelas and Dr. M. Sivaselvan at the National Center for Earthquake Engineering Research and the University at Buffalo.