scholarly journals CONSIDERATIONS ON THE DIFFUSE SEISMICITY ASSUMPTION

2015 ◽  
Vol 12 (2) ◽  
Author(s):  
Jorge Daniel Riera ◽  
Ignacio Iturrioz
Keyword(s):  
Steel Structures ◽  
Direct Analysis ◽  
Second Order ◽  
Effective Length ◽  
Order Effects ◽  
Analysis Method ◽  
Order Analysis ◽  
3D Space ◽  
Effective Length Method ◽  
Diffuse Seismicity

Second-order effects were historically included by the effective length method (K concept). All the studies about that methodology have been developed in frame plane, with regular rectangular frames. The new way to include those effects is the use of second-order analysis, direct analysis method or alternative simplified options. This methodology was included in ANSI AISC360 in the 2005 version and in the 2010 version. As before, the studies already developed for DAM analysis are in plane. In this paper, the K concept is revisited by numerical analysis, and extended to the 3D space. Using models of symmetric and non-symmetric industrial steel structures in plane, 3D stability analyses were developed, and the results were compared with plane behavior. Several conclusions and recommendations were exposed, resulting from the analyzed models. Keywords: Second-order analyses, steel structures, irregular 3D frames.

STABILITY AND SIMULATION-BASED DESIGN OF STEEL SCAFFOLDING WITHOUT USING THE EFFECTIVE LENGTH METHOD

2003 ◽  
Vol 03 (04) ◽  
pp. 443-460 ◽  
Author(s):  
S. L. CHAN ◽  
A. Y. T. CHU ◽  
F. G. ALBERMANI
Keyword(s):  
Bending Moment ◽  
Nonlinear Problems ◽  
Second Order ◽  
Effective Length ◽  
Analysis And Design ◽  
Order Analysis ◽  
Effective Length Factor ◽  
Highly Nonlinear ◽  
Reliable Design ◽  
Effective Length Method

A robust computer procedure for the reliable design of scaffolding systems is proposed. The design of scaffolding is not detailed in design codes and considered by many researchers and engineers as intractable. The proposed method is based on the classical stability function, which performs excellently in highly nonlinear problems. The method is employed to predict the ultimate design load capacities of four tested 3-storey steel scaffolding units, and for the design of a 30 m×20 m×1.3 m 3-dimensional scaffolding system. As the approach is based on the rigorous second-order analysis allowing for the P-δ and P-Δ effects and for notional disturbance forces, no assumption of effective length is required. It is superior to the conventional second-order analysis of plotting only the bending moment diagram with allowance for P-Δ effect since it considers both P-Δ and P-δ effects such that section capacity check is adequate for strength and stability checking. The proposed method can be applied to large deflection and stability analysis and design of practical scaffolding systems in place of the conventional and unreliable effective length method which carries the disadvantages of uncertain assumption of effective length factor (L e /L).

New Canadian provisions for the design of steel beam–columns

1990 ◽  
Vol 17 (6) ◽  
pp. 873-893 ◽  
Author(s):  
D. J. L. Kennedy ◽  
A. Picard ◽  
D. Beaulieu
Keyword(s):  
Traditional Method ◽  
Geometric Analysis ◽  
Steel Structures ◽  
Second Order ◽  
Effective Length ◽  
Order Effects ◽  
Limit States ◽  
Cross Sectional ◽  
Out Of Plane ◽  
Areas Of Concern

The beam–column interaction equations of the Canadian Standards Association Standard CAN3-S16.1-M84 "Steel structures for buildings — limit states design" are reviewed and areas of concern in the formulations are addressed. The interaction equations developed for the 1989 edition of the standard, CAN3-S16.1-M89 "Limit states design of steel structures," and the methods of dealing with the areas of concern in the previous standard are presented. The new standard requires that at least an approximate second-order geometric analysis be carried out. For frames dependent on the frame stiffness for lateral stability, no longer is the traditional method, using effective length factors greater than one, allowed. Unlike the current American Institute of Steel Construction "Load and resistance factor design'' (AISC LRFD) specification, two sets of interaction equations, one for in-plane member strength and the other for out-of-plane stability, are used. This results in considerably less unnecessary conservatism. In both sets of interaction equations, the component of the moment due to translation is increased by the second-order effects. The "double ω" problem has been resolved and the minimum sway effects for the gravity loading case have been increased substantially to guard against sidesway buckling. A design example using the new standard is given. By means of a series of analytical examples, the requirements of S16.1-M89 are compared with the traditional method of S16.1-M84. For frames with direct-acting bracing, S16.1-M89 gives interaction values about 1.15 times those of the previous standard with a coefficient of variation of 0.08, while for unbraced frames the corresponding values are 0.98 and 0.07. The S16.1-M89 values reflecting greater rigor in a number of areas are considered the more valid. The S16.1-M89 standard would give comparable results to the AISC LRFD specification for class 1 sections when out-of-plane behaviour governs. The latter specification does not specifically cover cross-sectional strength and in-plane behaviour as does S16.1-M89. Key words: beam–column, stability, strength, bending, compression, standards.

scholarly journals Alternative Design Procedure for RC-Braced Long Columns Based on New Moment Magnifiers Matrix

2021 ◽  
Vol 2021 ◽  
pp. 1-20
Author(s):  
Mohamed Farouk ◽  
Majed Alzara ◽  
A. Ehab ◽  
A. M. Yosri
Keyword(s):  
Flexural Rigidity ◽  
Design Procedure ◽  
Bending Moment ◽  
Order Effect ◽  
Second Order ◽  
Effective Length ◽  
Column Height ◽  
Order Effects ◽  
Order Analysis ◽  
Proposed Model

Based on modified methods for the results of first-order analysis of RC columns, different codes approximate the second-order effects by using equations focusing on the maximum additional moment through the column height. These equations did not refer to the additional moments between the column and the connected beam, only the effect of the connected beams is taken into consideration by dealing with the effective length of the column, not the total length. Moreover, these equations did not take into account the second-order effect, which is caused by axial force and the inverse moments due to beam restriction for the column ends. This paper presents a new moment magnifiers matrix for the additional moments at the connection between braced columns and the connected beams as a simplified computation that can be used in the design procedure. That is through an equation based on transforming the original long column in second-order analysis to an equivalent isolated column. The equivalent column was represented as an element restricted with rotational spring support at its ends, and it is subjected to lateral distributed loads that have the same influence of the second-order effect on the induced additional moments in the long column. The suggested equivalent column can be used to form the additional bending moment diagram, also to compute the additional deformations as well. Numerous factors were analyzed linearly by using the presented new moment magnifiers matrix and finite element method, and the results proved the efficiency of the proposed model. Although the presented suggested model is based on the isolated analysis of the long column, the effect of the additional moments in the adjacent long column can be considered by presented two suggestions to improve the model. Also, development was proceeded on the model by modifying the flexural rigidity (EI) which is recommended in ACI to appropriate the time of failure. The additional moment values of the developed model were close to the values calculated by the ACI equation.

Refined Beam Element for Second Order Analysis of Latticed Shells

2014 ◽  
Vol 1065-1069 ◽  
pp. 1208-1211
Author(s):  
Lin Qi ◽  
Hai Feng Huo
Keyword(s):  
Geometrical Nonlinearity ◽  
Single Layer ◽  
Second Order ◽  
Order Effects ◽  
Analysis Method ◽  
Maclaurin Series ◽  
Order Analysis ◽  
Stability Functions ◽  
Beam Elements ◽  
Spatial Beam

Based on equilibrium equation of beam, the displacement interpolating functions with shear effect of spatial beam elements which are used to simulate the structure members of latticed shells are deduced. The different displacement interpolating functions in compression and tension spatial beam-column elements are unified by the method of Maclaurin series expansion, and the unified expressions which are used to simulate structure members are equivalent to those expressed by stability functions. Numerical analyses results indicate that the second-order elastic analysis method for beam structures proposed in this paper, which can perfectly incarnate the second-order effects and the geometrical nonlinearity of the single-layer cylindrical reticulated shell, is of better accurateness and higher effectiveness.

scholarly journals Second-order Direct Analysis of Steel Structures made of tapered members

2018 ◽  
Author(s):  
Siu-lai Chan ◽  
SW Liu ◽  
YP Liu
Keyword(s):  
Steel Structures ◽  
Direct Analysis ◽  
Rolling Process ◽  
Second Order ◽  
Steel Plates ◽  
Effective Length ◽  
Robotic Welding ◽  
Weight Saving ◽  
Tapered Members ◽  
Hot Rolled

Mild steel hot-rolled sections are commonly prismatic because of the rolling process with a furnace, but welded sections made from steel plates do not have such a constraint, especially when robotic welding machines are used. The weight saving could be very significant by, say, using wide flanged section at mid-span and a small flanged section at ends of a simply supported beam. However, design codes do not provide formulae for buckling check of tapered members. This paper proposes a code-free second-order direct analysis for stabilty design of steel frames made of tapered members. The design is further applied to a single layered mega space frame of 136m span. In the whole design process based on the concept of Second-order Direct Analysis, no uncertain effective length and independent member buckling checking are required. 

scholarly journals ANALYSIS OF THE GLOBAL AND LOCAL IMPERFECTION OF STRUCTURAL MEMBERS AND FRAMES

2019 ◽  
Vol 25 (8) ◽  
pp. 805-818 ◽  
Author(s):  
Charlotte Mercier ◽  
Abdelouahab Khelil ◽  
Ali Khamisi ◽  
Firas Al Mahmoud ◽  
Rémi Boissiere ◽  
...  
Keyword(s):  
Second Order ◽  
Structural Defects ◽  
Order Effects ◽  
Structural Members ◽  
Buckling Mode ◽  
New Approach ◽  
Order Analysis ◽  
Main Challenge ◽  
Buckling Failure ◽  
Global And Local

Stresses of a structure are determined with a first or a second order analysis. The choice of the method is guided by the potential influence of the structure’s deformation. In general, considering their low rigidity with regard to those of buildings, scaffolding and shoring structures quickly reach buckling failure. Imperfections, such as structural defects or residual stresses, generate significant second order effects which have to be taken into account. The main challenge is to define these imperfections and to include them appropriately in the calculations. The present study suggests a new approach to define all the structure’s imperfections as a unique imperfection, based on the shape of elastic critical buckling mode of the structure. This study proposes a method allowing to determine the equation of the elastic critical buckling mode from the eigenvectors of the second order analysis of the structure. Subsequently, a comparative study of bending moments of different structures calculated according to current Eurocode 3 or 9 methods or according to the new method is performed. The obtained results prove the performance of the proposed method.

Analysis of the Overall Reliability Slender Concrete Columns

2017 ◽  
Vol 259 ◽  
pp. 203-208
Author(s):  
Vladimír Benko ◽  
Tomas Gúcky ◽  
Adrián Valašík
Keyword(s):  
Concrete Columns ◽  
Design Methods ◽  
Second Order ◽  
Order Effects ◽  
Design Strength ◽  
Order Analysis ◽  
Non Linear ◽  
Buckling Failure ◽  
Overall Reliability ◽  
General Method

Standard for designing of concrete structures STN EN 1992-1-1 offers three methods of analysis of second order effects with axial load. Namely, a general method based on non-linear second order analysis and two simplified methods: Method based on nominal stiffness and method based on nominal curvature. According to three series of the experiments of slender concrete columns and after calibration of the non-linear calculations, the authors in following paper compare the global reliability of above mentioned design methods with parametric study. According to executed research is possible to say that the differences in reliability of the design methods are considerable in several cases of the slender concrete columns design.The experiments were executed in the Central laboratory of Faculty of Civil Engineering STU in Bratislava in cooperation with company STRABAG ltd. The series of columns differed only in strength class of concrete (C45/55 for S1, C70/85 for S2, C80/95 for S3) and each series included six tested samples. The geometry and reinforcement of the columns as well as the initial eccentricity of the axial force were design so, that the buckling failure of the columns occurred earlier than the design strength of materials in the most stressed cross-section ran out.

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