Degree Of Rotational Restraint Research Articles

Lateral Bearing Behaviors of Slightly Inclined Single Pile with Different Pile Head Restraint Under Combined Loads

For a laterally loaded pile with its head keyed into the cap, pile head actually rotates in spite of the restraint of the cap. Being aware of this fact, some parameters were put forward to represent the degree of rotational restraint at pile top, and many calculation methods of lateral pile responses were then developed. However, the presented solutions are only for piles under pure lateral loads. In fact, they are usually under the vertical loads simultaneously, caused by the weights of themselves and superstructures. Besides, the slight initial inclination of pile shaft is inevitable in engineering. Some researchers raised solutions of lateral responses of the slightly inclined single pile under combined vertical and lateral loads, but the partially fixed-head condition and the elastoplasticity of soil were not considered. In this study, elastoplastic semi-analytical solutions of lateral responses of the slightly inclined single pile under combined vertical and lateral loads were deduced, in which the rotational restraint coefficient was used to represent the degree of rotational restraint at pile top, and the three-parameter model of the coefficient of subgrade reaction was employed. The computer program was developed thereafter. The effectiveness and advantage of the obtained solutions were validated by the comparison among existing solutions, presented solutions and model test results. Sensitivity analysis was carried out for parameters such as the initial inclination angle of pile shaft, the rotational restraint coefficient, and the vertical load. Eventually, effects of each parameter on lateral pile responses were presented and discussed.

Lateral deformation behavior of eccentrically loaded slender RC columns with different levels of rotational end restraint at elevated temperatures

Purpose In literature, previous studies have focused on analyzing rienforced concrete (RC) columns with idealized end conditions when subjected to fire. In nature, full fixity or free rotation at column ends is not attained. Such ends may be considered partially restrained in rotation. This paper aims to shed a new light on the effect of different degrees of rotational restraint on the lateral deformation behavior of slender heated RC columns subjected to non-linear strain distributions produced by a time-dependent temperature history. Design/methodology/approach To find the strain distribution on the cross section, an iterative technique is adopted using Newton–Raphson method. By introducing a reliable calculation procedure, the lateral deformational behavior is expressed using numerical and searching techniques. A methodology is presented to calculate the effective length factor for RC columns at elevated temperature. Findings The results of the proposed model showed good agreement with available experimental test results. It was also found that the variation of rotational end restraint level has a considerable effect on the lateral deformation behavior of heated slender RC columns. In addition, the effectiveness and the validity of an analytical model should be verified by simultaneously validating the axial and lateral deformations. Moreover, the effective length factor for heated column is higher than that for the corresponding column at ambient temperature. Originality/value This paper shows the impact of different boundary conditions on the behavior of heated slender RC columns. It suggests powerful techniques to determine the lateral deflection and the effective length factor at high temperatures.

The introduction and the influence of semi-rigid connections in framed structures subjected to fire

This paper describes a recent development in a finite element software dedicated to the modeling of structures in fire which deals with the way connections are simulated in global structure analyses. This development allows modeling semi-rigid, temperature-dependent connections between beam-type finite elements. It relies on the definition of additional internal degrees of freedom in the elements. The objective is to enable efficient analysis of the influence of semi-rigid connections on the global structural response and on the demands for these connections. The theory and implementation are described in a geometrically non-linear software with large displacements. Then, a 3D frame structure is analyzed as a case study. The analyses show that structural capacity and failure mode depend on the degree of rotational restraint at the beam-column connections and at the base of the columns. The maximum fire resistance is obtained for an intermediate degree of restraint between beams and columns, while higher restraints lead to an unfavorable sway failure mode. The case study illustrates the capabilities introduced by the new development, and demonstrates that the effects of the connections on global response is complex, justifying the need for practical numerical methods for design and parametric analyses of structures in fire.

Shear in reinforced concrete slabs—Experimental investigations in the effective shear width of one‐way slabs under concentrated loads and with different degrees of rotational restraint

The shear design of reinforced concrete (RC) slabs under concentrated loads calls for the definition of an effective width, which can be used to assess the slab's shear capacity. However, currently the shear strength and effective shear width of one‐way RC slabs is only poorly investigated. Therefore, this paper presents the results of 34 shear tests on RC slabs and slab strips without shear reinforcement. To analyze the effective shear width, 0.5 m wide slab strips and slabs with a width of up to 3.5 m were tested under concentrated loads with different shear‐span‐to‐depth ratios (varying between 1.4 and 5.4). While the slab strips were activated over their full width (beam action), the shear capacity of the wide slabs was significantly influenced by their effective shear width. To also clarify the impact of the structural system and the support conditions, the slabs were clamped at one end with different degrees of rotational restraint. Beginning with simply supported, single‐span slabs, the rotational restraint was stepwise increased to 100% representing a fully clamped support. Further investigated parameters were the transverse reinforcement ratio and the arrangement of multiple loads. The resulting shear capacities of all tests are compared with code provisions of Eurocode 2. The results illustrate remarkable differences in the shear behavior of wide slabs and slab strips with predominant beam action. Besides the influence of the effective shear width, this paper analyzes the direct load transfer to supports via strut mechanisms (arching action).

Determination of the axial force on stay cables accounting for their bending stiffness and rotational end restraints by free vibration tests

Determination of the axial force in terms of its natural frequencies may be significantly influenced by the bending stiffness of the cable and the rotational elastic restraints at the ends, depending on the geometrical and mechanical parameters of the cable and its supports and restraints, particularly in cement-grouted parallel-bundle wire cables. The paper presents an explicit analytical expression for the natural frequencies taking into account both the bending stiffness of the cable and the rotational restraint at the ends that may be used to determine the axial force. While the bending stiffness of the cable and the axial force are selected as variables to attain an optimal match between analytical and experimental data, the rotational stiffness at the ends is treated as a known parameter in that process. The degree of rotational restraint at the ends cannot be accurately inferred from the sequence of the experimentally determined natural frequencies, since this parameter does not appreciably affect the progression of their values. Techniques are discussed that allow approximate determination of the rotational stiffness at the ends for the most common arrangements of anchors and cables with, and without, intermediate supports provided by deviators located near the ends. The axial force and the bending stiffness of the cable are both simultaneously adjusted by matching the natural frequencies of the analytical model with the experimental values. The proposed approach leads to a reduction of the error in the estimation of the axial force for short cables with relatively high bending stiffness such as those typical of cement-grouted parallel-bundle wire cables often used as cable stays for bridges until the early 1990s.

Buckling behaviour of plates partially restrained against rotation under stress gradient

In this paper, the behavior of plates partially restrained against rotation under stress gradient is investigated. As a first stage, an energy formulation is presented to model this boundary condition and a general expression is derived for the prediction of the elastic buckling of the plate under this general loading condition. The accuracy of the derived expression is compared numerically using the Galerkin method with other available data for the two limiting conditions of rotationally free and clamped boundaries. Results show that the prediction is within a 5% difference. The influence of rotational restraint and stress gradient upon the buckling load and the associated buckling mode is investigated. Numerical results show sensitivity of the buckling mode to the degree of rotational restraint and the variation of the buckling load with the stress gradient.

A study on local buckling behavior of hybrid beams

In this paper, the local buckling behavior of hybrid beams, with high-strength steel webs and mild steel flanges, is investigated. A wide-flange shaped member is essentially an assemblage of plate elements and then the plate buckling has a significant effect on the plastic deformation capacity of a beam, while the web provides the flange with some degree of rotational restraint against local buckling. The torsional restraint of the web against the flange inelastic buckling depends on the web stiffness, namely, the length of the plastic region in the web. A hybrid beam with high-strength steel webs and mild steel flanges is considered to be effective in carrying loads after the flange local buckling. The results of investigation are presented herein.

異種鋼材を用いたはり部材の連成局部座屈性状に関する研究

Abstract In this paper, the local buckling behavior of hybrid beams, with high-strength steel webs and mild steel flanges, is investigated. A wide-flange shaped member is essentially an assemblage of plate elements and then the plate buckling has a significant effect on the plastic deformation capacity of a beam, while the web provides the flange with some degree of rotational restraint against local buckling. The torsional restraint of the web against the flange inelastic buckling depends on the web stiffness, namely, the length of the plastic region in the web. A hybrid beam with high-strength steel webs and mild steel flanges is considered to be effective in carrying loads after the flange local buckling. The results of investigation are presented herein.

CONICAL HOPPERS WITH VARYING WALL THICKNESS

ABSTRACT An iterative numerical solution is presented for determining the bending stresses and displacements in conical hoppers. Hoppers having tapered wall thickness, and hoppers with sudden discontinuities in geometry are treated. Applications to steel and concrete hoppers are presented. The influence on the bending stresses of the following parameters is evaluated: Degree of rotational restraint at the hopper-ring-cylinder junction, hopper of equivalent uniform thickness, Poisson's ratio, and hopper self weight.

Free vibration of annular sector plates with edges possessing different degrees of rotational restraint

Results for the natural frequencies of annular sector plates possessing different degrees of elastic restraint along the edges are presented. The analysis is based on a numerical method developed by the author. The functions in the circumferential direction satisfying the boundary conditions along the radial edges, which are required in the analysis, are indicated. To the best of the author's knowledge, no previous results exist for such plates.

Free vibration of rectangular plates with edges having different degrees of rotational restraint

A numerical method developed by the author has been used as a basis for determining natural frequencies of rectangular plates possessing different degrees of elastic restraints along the edges. The basic functions satisfying the boundary conditions along two opposite edges for such cases have been derived. Comparison of results with others that are available indicates excellent accuracy. Many new results have been presented.