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Plant aggregates and fibers in earth construction materials: A review

The City of Los Angeles, the City and County of San Francisco, and other communities on the West Coast are undergoing a boom in the construction of high-rise buildings that involve a variety of unusual configurations, innovative structural systems, and high performance materials. Various jurisdictions, with the active involvement of peer review committees, are considering performance-based methods to assess the adequacy of these new designs. These parallel efforts create a timely opportunity for collaboration to improve and increase the application of performance-based designs for tall buildings, thereby assuring that new high-rise construction meets intended safety and performance objectives, ensuring safe and usable buildings after future major earthquakes. The Pacific Earthquake Engineering Research Center (PEER) is presently undertaking a multiyear program to develop guidelines to aid the engineering community with the design, analysis and construction of these tall buildings.

ATC-72 of the PEER Tall Buildings Initiative: Interim Guidelines on Modeling and Acceptance Criteria for Seismic Design and Analysis of Tall Buildings

A review of research on steel eccentrically braced frames

A conceptual model for the prediction of the shear-flexural strength of slender reinforced concrete beams with and without transverse reinforcement is presented. The model incorporates the shear transferred by the un-cracked concrete chord, along the crack's length, by the stirrups, if they are, and, in that case by the longitudinal reinforcement. After the development of the first branch of the critical shear crack, failure is considered to occur when the stresses at any point of the concrete compression chord reach the assumed biaxial stress failure envelope. A physical explanation is provided for the evolution of the shear transfer mechanisms, and the contribution of each one at ultimate limit state is formulated accordingly. Simple equations are derived for shear strength verification and for designing transverse reinforcement. The method is validated by comparing its predictions with the results of 1131 shear tests, obtaining very good results in terms of mean value and coefficient of variation. Beca...

Shear-flexural strength mechanical model for the design and assessment of reinforced concrete beams

A 3D numerical model for reinforced and prestressed concrete elements subjected to combined axial, bending, shear and torsion loading

In this work we consider solutions for the Euler- Bernoulli and Timoshenko theories of beams in which material behavior may be elastic or inelastic. The formu- lation relies on the integration of the local constitutive equation over the beam cross section to develop the relations for beam resultants. For this case we include axial, bending and shear effects. This permits consider- ation in a direct manner of elastic and inelastic behavior with or without shear deformation. A finite element solution method is presented from a three-field variational form based on an extension of the Hu-Washizu principle to permit inelastic material be- havior. The approximation for beams uses equilibrium satisfying axial force and bending moments in each ele- ment combined with discontinuous strain approximations. Shear forces are computed as derivative of bending mo- ment and, thus, also satisfy equilibrium. For quasi-static applications no interpolation is needed for the displace- ment fields, these are merely expressed in terms of nodal values. The development results in a straight forward, variationally consistent formulation which shares all the properties of so-called flexibility methods. Moreover, the approach leads to a shear deformable formulation which is free of locking effects - identical to the behavior of flexibility based elements. The advantages of the approach are illustrated with a few numerical examples.

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A mixed finite element method for beam and frame problems

In this paper a beam element that accounts for inelastic axial-flexure–shear coupling is presented. The mathematical model is derived from a three-field variational form. The finite element approximation for the beam uses shape functions for section forces that satisfy equilibrium and discontinuous section deformations along the beam. No approximation for the beam displacement field is necessary in the formulation. The coupling of the section forces is achieved through the numerical integration of an inelastic multi-axial material model over the cross-section. The proposed element is free from shear-locking. Examples confirm the accuracy and numerical robustness of the proposed element and showcase the interaction between axial force, shear, and bending moment.

Inelastic axial-flexure-shear coupling in a mixed formulation beam finite element

Strengthening the structural behavior of adobe walls through the use of plaster reinforcement mesh

Numerical integration of a class of 3d plastic-damage concrete models and condensation of 3d stress–strain relations for use in beam finite elements

This paper presents the variational bases for the non-linear force-based beam elements. The element state determination of these elements is obtained exactly from a two-field functional with independent stress and strain fields. The variational base of the non-linear force-based beam elements implemented in a general purpose displacement-based finite element program requires the inclusion of independent displacement field in the formulation. For this purpose, a three-field functional is considered with independent displacement, stress, and strain fields. Various local and global solution strategies come out from the mixed formulation of the beam element, and these are shown to yield the algorithms presented for non-linear force formulation beam elements in literature; thus removing any doubts on their variational bases. The presented numerical examples demonstrate the accuracy and robustness of the solution algorithms adapted for mixed formulation elements over popularly used displacement-based beam finite elements even for large structural systems.

Afsin Saritas

Papers

A mixed finite element method for beam and frame problems

Inelastic axial-flexure-shear coupling in a mixed formulation beam finite element

Strengthening the structural behavior of adobe walls through the use of plaster reinforcement mesh

Numerical integration of a class of 3d plastic-damage concrete models and condensation of 3d stress–strain relations for use in beam finite elements

Variational base and solution strategies for non-linear force-based beam finite elements