Nonlinear Finite Element Analysis to Evaluate Lateral Torsional Buckling Moment of Elliptical Cellular Steel Beams

In evaluation the lateral torsional buckling moment of Elliptical Cellular beams, it cannot be directly accurately calculated because the sectional properties of the Elliptical Cellular beam are not constant along the beam length. Consideration of sectional properties at web-post section will certainly affect to unconservative result, and the consideration the sectional properties at web-opening section is also unreal and unduly conservative design. Therefore, the main objective of this paper is to present the guideline to evaluate the lateral torsional buckling moment of Elliptical Cellular beam for conservative result and more precisely. The study has been performed throughout finite element analysis in both elastic and inelastic buckling behavior subject of equal beam-ends moment. More than 15 sections, 120 of beam models were simulated and analyzed with verified finite element modelling by using shell element. The results of this study show that the most of beam has behavior in elastic buckling range, calculation the lateral torsional buckling moment of Elliptical Cellular beam with the original equation given in AISC standard with using the sectional properties at web-post section is given unsafe result about 5% in elastic range and up to 20% in inelastic and plastic range. Evaluation the lateral torsional buckling moment by use the reduction factor, R_ECB, that proposed from this study has yielded the conservative result and has more precisely, more economically and less distribution of the result than the evaluation that using sectional properties at web-opening section

Shear Behavior of RC Deep Beam Strengthened by V-Shaped External Rods

This research investigated the shear strengthening technique of Reinforced Concrete (RC) deep beams using a V-shaped external rod system. Shear behavior, the stress in an external rod, and the shear capacity at the diagonal shear failure of a strengthened beam were focused mainly. Experimental tests of control and two strengthened beams were carried out to observe the effect of the external rod on shear behavior of RC deep beam. A theoretical approach to compute the stress in the external rod and the nominal strength of the strengthened beam in the diagonal shear failure were examined based on the experimental test results and verified using Finite Element Method (FEM) in ABAQUS. The computed nominal shear strength of the strengthened beam was 10% higher than the experimental test. The strengthening technique shifted the brittle shear failure to ductile shear failure and improved the performance of RC deep beam

An Analytical Method for Determining the Load Distribution of Single-Column Multibolt Connection

The purpose of this research was to investigate the effect of geometric variables on the bolt load distributions of a cold-formed steel bolt connection. The study was conducted using an experimental test, finite element analysis, and an analytical method. The experimental study was performed using single-lap shear testing of a concentrically loaded bolt connection fabricated from G550 cold-formed steel. Finite element analysis with shell elements was used to model the cold-formed steel plate while solid elements were used to model the bolt fastener for the purpose of studying the structural behavior of the bolt connections. Material nonlinearities, contact problems, and a geometric nonlinearity procedure were used to predict the failure behavior of the bolt connections. The analytical method was generated using the spring model. The bolt-plate interaction stiffness was newly proposed which was verified by the experiment and finite element model. It was applied to examine the effect of geometric variables on the single-column multibolt connection. The effects were studied of varying bolt diameter, plate thickness, and the plate thickness ratio (t2/t1) on the bolt load distribution. The results of the parametric study showed that the t2/t1 ratio controlled the efficiency of the bolt load distribution more than the other parameters studied

A finite element for the nonlinear analysis of reinforced concrete slabs

The nonlinear behavior of reinforced concrete (RC) structural systems is complex. Depending on the loading, both concrete and steel can behave nonlinearly. Cracking of concrete is the main source of material nonlinearity, and usually occurs at low levels of applied load due to the low resistance of concrete to tensile loads. Thus, in order to more accurately simulate these systems, there is a need for the development of efficient sophisticated elements that can be incorporated in a nonlinear finite element framework. Two techniques exist for modeling RC slabs: discrete and layered modeling. In the discrete modeling, concrete is modeled by three-dimensional solid elements while the reinforcing steel is modeled by truss elements. The drawback of the discrete modeling is that a large number of degrees of freedom are required. This is of particular concern in nonlinear analyses. In the layered modeling, concrete is divided into a set of layers, while the reinforcing steel is smeared into a layer between concrete layers. Layered modeling of RC slabs is simple, but provides an unrealistic representation of the reinforcing steel. Since real reinforcement is discrete, only highly reinforced slabs can be appropriately modeled by the layered approach. Furthermore, the interaction between concrete and reinforcement bars, i.e. bond-slip effect, can not be modeled directly. This research presents a new finite element for the nonlinear analysis of RC slabs. The element combines a four-node Kirchhoff shell element for concrete with two-node Euler beam elements for the steel reinforcement bars. The connectivity between reinforcement beam elements and concrete shell element is achieved by means of rigid links. By using the transformation method for rigid links, beam nodes are eliminated from the final mesh of the structure. The stiffness and resisting forces from the reinforcement are implicitly included in the new element. In this manner, this finite element is able to take into account the location of the reinforcement bars. This is in contrast to the smeared method, which is often adopted in the layered modeling. The proposed RC shell element is further extended to include the effect of bond-slip between concrete and reinforcement bars

Simplified Load Distribution Factor for Use in LRFD Design

The “S-over” equation for the load distribution factor (LDF) was first introduced in the 1930s in the AASHTO Standard. Finite element studies, however, have shown it to be unsafe in some cases and too conservative in others. AASHTO LRFD 1994 introduced a new LDF equation as a result of the NCHRP 12-26 project. This equation is based on parametric studies and finite element analyses (FEA). It is considered to be a good representation of bridge behavior. However, this equation involves a longitudinal stiffness parameter, which is not initially known in design. Thus, an iterative procedure is required to correctly determine the LDF value. This need for an iterative design procedure is perceived by practicing engineers as the major impediment to widespread acceptance of the AASHTO LRFD equation. In this study, a new simplified equation that is based on the AASHTO LRFD formula and does not require an iterative procedure is developed. A total of 43 steel girder bridges and 17 prestressed concrete girder bridges in the state of Indiana are selected and analyzed using a sophisticated finite element model. The new simplified equation produces LDF values that are always conservative when compared to those obtained from the finite element analyses and are generally greater than the LDF obtained using AASHTO LRFD specification. Therefore, the simplified equation provides a simple yet safe specification for LDF calculation. This study also investigates the effects of secondary elements and bridge deck cracking on the LDF of bridges. The AASHTO LRFD LDF equation was developed based on elastic finite element analysis considering only primary members, i.e., the effects of secondary elements such as lateral bracing and parapets were not considered. Meanwhile, many bridges have been identified as having significant cracking in the concrete deck. Even though deck cracking is a well-known phenomenon, the significance of pre-existing cracks on the live load distribution has not yet been assessed in the literature. First, secondary elements such as diaphragms and parapet were modeled using the finite element method, and the calculated load distribution factors were compared with the code-specified values. Second, the effects of typical deck cracking and crack types that have a major effect on load distribution were identified through a number of nonlinear finite element analyses. It was found that the presence of secondary elements can result in a load distribution factor up to 40 % lower than the AASHTO LRFD value. Longitudinal cracking was found to increase the load distribution factor; the resulting load distribution factor can be up to 17 % higher than the LRFD value. Transverse cracking was found to not significantly influence the transverse distribution of moment. Finally, for one of the selected bridges, both concrete cracking and secondary elements are considered to invesitigate their combined effect on lateral load distribution. The increased LDF due to deck cracking is offset by the contributions from the secondary elements. The result is that the proposed simplified equation is conservative and is recommended for determination of LDF