Ultimate Strength Analysis Research Articles

Analysis of Welded Tubular Connections Using Continuum Damage Mechanics

A new modeling technique for the ultimate strength analysis of welded tubular connections subjected to general loading is presented. Based upon the finite element method, the model includes shell and solid elements, large deformations, and elastoplasticity. Unlike other approaches, the ability to simulate the initiation and propagation of fracture is included through the application of continuum damage mechanics (CDM). With this method, cracking is predicted on the basis of a damage variable, and its effect is applied as a reduction in the element stiffness. The development of the material constants is described and numerical results are obtained for two tubular joints that exhibit fracture failure. A comparison between the computed failure loads and those observed experimentally shows a close correlation. With this approach, welded connections that are subjected to arbitrary loading can be efficiently evaluated for strength.

Ultimate Strength of Seismic Isolation System Using High Damping Rubber Bearing for Buildings. 2nd Report, Ultimate Strength Analysis for a Full-Scale Seismic Isolation System.

The ultimate strength of a full-scale seismic isolation system which used multiple (n×n layers) high damping rubber bearings was analyzed by applying an analytical method. The method consisted of analyzing the response of the rubber bearings and evaluating the result in comparison with breaking conditions. It was determined that the system's ultimate strength was significantly affected by both the number of layers in the bearing and the building's design configuration, i.e., the building's height to width ratio. As either the layer number or the length ratio increases, the tensile/compressive stress applied on the bearings fluctuates, thus redusing the ultimate strength. It was additionally found that the rubber bearings break not only in the tensile and shear states, but also in the compression and shear states. This results because stress fluctuations are biased towards the compression direction when the rubber bearing vertical stiffness has deteriorated in the tensile region. When this condition is present, the building's base plain rotation center moves in the horizontal direction, and in some cases the tensile stress acts on more than half the bearings; thus the compressive stress applied on the compression-side bearing increases by 4.7 times that under normal load conditions.

RC‐Coupled Shear Wall Structures. I: Analysis of Coupling Beams

The structural behavior of reinforced concrete coupled shear wall structures is greatly influenced by the behavior of their coupling beams. Flexure and shear are the two main modes of failure of reinforced concrete coupling beams. The behavior of coupling beams in the shear mode of failure, known as diagonal splitting, is represented by a mathematical model, and a method for the ultimate strength analysis is presented. The proposed method of analysis for RC coupling beams is used to verify the results of nine beams tested by a previous investigator.

Stiffened Hull Structure

In order to make a system safety and reliability assessment of ship structures in the longitudinal strength point of view, it is essential to analyze ultimate longitudinal strength of ship's hull girder under sagging or hogging bending moment. In the previous report, the author formulated an idealized plate element using idealized structural unit method and the developed method was then applied to ultimate longitudinal strength analysis of unstiffened hull structure as an example, concluding that the method is useful for ultimate collapse strength analysis of plate structure.In this study, an attempt is made to analyze ultimate longitudinal strength of stiffened hull structure by using idealized structural unit method. For this purpose, an idealized stiffened plate element subjected to biaxial load is developed taking account of the influence of initial imperfections as well as the interaction effect between local and global failure in the structure. The developed method is then applied to ultimate longitudinal strength analysis of Suezmax-sized double skin hull girder as an example for the intact and the damaged condition in the event of accidents of grounding and collision. A new deterministic measure of safety based on the absorbed energy capacity is proposed. Based on the obtained results, ultimate longitudinal strength-based safety and reliability assessment is made using the proposed measure of safety in addition to the conventional one, concluding that the objective hull structure has relatively sufficient safety and the present procedure is useful when ultimate longitudinal strength-based safety assessment or optimization is made in the structural design stage for a new type of hull structure.

A Method for Reliability Assessment of Spatial Plate Structures Through Automatic Generation of Ultimate Collapse Modes

This paper is concerned with the ultimate strength and reliability analysis of ship's hull girders, which are composed of the spatial membrane elements and subjected to combined static loads and extreme wave loads. The linearised failure condition of an element is first introduced, which takes account of the yielding and buckling collapse under the plane stress condition. The failure criterion facilities the generation of safety margins and the calculation of failure probabilities. Structural failure is defined as the generation of large deformation due to collapse. The so called branch-and-bound method is applied to select the probabilistically dominant failure modes, which saves the computational efforts to perform a reliability analysis on large-scale structures. Finally, the proposed methods are applied to spatial plate structures idealised for modelling main hull girders of an oil tanker and a bulk carrier under two loading conditions. Through numerical examples, the properties of proposed methods are investigated.

Ultimate strength analysis of structural components using the continuum damage mechanics approach

In this study, an analytical model is developed to include the effect of material fracture on the overall behavior of a structure. The continuum damage mechanics approach is used to describe the continuous deterioration of the material stiffness that leads to total failure. The damage evolution is assumed to be anisotropic and the effect of the triaxiality of stress on the fracture criterion is included in the analysis. The above modifications were applied to an existing finite element program which is capable of including both geometric and material nonlinearities in the analysis. The program was used to analyze a welded tubular connection (T-joint). This joint was chosen because fracture was shown experimentally to control its ultimate behavior. Solid finite elements were used to model the chord and the branch in the intersection region, wedge elements were used for the weld profile, and the rest of the geometry was modeled using shell elements. The joint was subjected to an increasing amount of displacement at the far end of the branch. The loading was continued until total failure. During this process, the evolution of the damage and its propagation were monitored. Divergence of the solution was obtained at a failure load of 42.4 kips compared to 44.0 kips obtained experimentally. In addition, the failure mode of the joint predicted by the analysis was identical to that observed experimentally.

Limit analysis of thin shell structures by using a simplified element model. 1st Report, Ultimate strength analysis by the total lagrangian approach.

A new simplified element model for the limit analysis of thin shells combining the rigid bodies-spring model for the bending deformation and the constant-strain finite element for the in-plane behavior is proposed. This discrete model is so simple that the stiffness matrices can be derived explicitly both for elastic and plastic deformations, and each node has only three degrees of freedom which are three-dimensional translational displacements. Therefore it is expected that the computing cost can be considerably reduced, although the computational accuracy is a little distorted. The first report of the present study contains the formulation by the total Lagrangian approach and its applications to the ultimate strength analysis of flat and curved plates. The validity of the present method is confirmed by comparing the calculated solutions with the results of conventional finite element shell analysis.

A STATIC AND DYNAMIC NONLINEAR BEHAVIOUR OF STEEL TOWERS OF LONG-SPAN SUSPENSION BRIDGES SUBJECT TO WIND AND EARTHQUAKE LOADINGS

The static ultimate strength analyses of the tower-cable system of Akashi-Kaikyo Bridge are performed for the investigations of the planar and spatial behaviour of the structures subject to a variety of the combinations of the vertical dead and live loads, and the horizontal wind loads both in the directions of perpendicular-to-bridge axis and bridge axis. The obtained ultimate loads based on three different loading paths are compared with the design loads specified in the current codes of huge towers. The nonlinear dynamic responses of the planar tower and tower-cable models are obtained to examine the safety of the superstructures of Akashi towers against horizontal ground motions of the 1940 El Centro record with variable amplitudes up to four times the design acceleration specified in the codes.

A Method for Reliability Assessment of Spatial Frame Structures Based on Ultimate Strength Analysis

This paper is concerned with reliability assessment of ship main structures, which are modelled as spatial frame structures and subjected to quasi-static extreme loads, based on ultimate strength analysis. Ultimate strength of the structure is evaluated by using a linearized plasticity condition of the section of the structural element under the combined effect of internal forces and moments to generate the safety margins of structural failure modes, using a matrix method and plastic node method. Probabilistically dominant collapse modes are selected by applying the so-called branch-andbound method combined with heuristic operations. The above methods are successfully applied to main structures of a large tanker (240, 000DWT) under various notional loading conditions. Probabilistic properties of ultimate strength of ship main structures are investigated through the numerical examples and comparison with previous results for plane frame models.

Simulation of Collapse of Framed Structures (Part 1)

The present study is concerned with the development of a finite element program for collapse analysis of three-dimensional framed structures under static loading, which has the following features : (1) A linear Timoshenko beam-column element is employed with a variable location of an integration point, which is equivalent to the beam bending element including the effect of shear deformation in the RBSM (Rigid Bodies-Spring Models) family, and can be considered to be suitable to the analysis of highly nonlinear problems including crush analysis.(2) The program is equipped with the updated Lagrangian formulation as well as the total Lagrangian formulation, the former of which is used in the crush analysis accompanied by extremely large rotations and strains, and the latter is used in the ultimate strength analysis with moderately large deformations.(3) A formulation using generalized stresses is adopted for the derivation of incremental stiffness equations, and the yield functions expressed in terms of resultant forces are assumed in the elastoplastic analysis, from a point of view of the generalization of the method of limit analysis.Numerical studies for crush as well as elastica and inelastic stability problems are conducted to show the validity of the developed code. The treatment of strain-hardening and the experimental verifications for the crush analysis will be contained in a further report.

A NONLINEAR BEHAVIOUR AND STRENGTH OF STEEL TOWERS OF LONG-SPAN SUSPENSION BRIDGES SUBJECT TO DEAD AND LIVE LOADS

An ultimate strength analysis of the steel towers of the long-span suspension bridges is presented within the framework of an inelastic finite displacement theory of planar and spatial structures. The combined tower-cable system is employed to study the nonlinear effect of cables on the behaviour of huge towers. The Akashi-Kaikyo Bridge now under the first stage of construction for its seabed is selected in this study for investigations of ultimate strength behaviour of its steel towers subjected to the vertical dead and live loads. The current design practice of the Akashi towers is examined based on the present numerical results.

Connection Flexibility and Beam Design in Non-sway Frames

Attention is drawn to the fact that virtually all commonly used types of steelwork beam-to-column connections function as semirigid. Representation of this behavior is best achieved by means of the connections moment-rotation (M—f) curve. For the types of connection normally used in non-sway frames, where "simple framing" is customarily employed, this means true behavior differs from that assumed in design. Beam-end moments are produced, the magnitude of which depends upon the M—f characteristics of the particular connection types used. The implications of this for the design of beams in non-sway frames is discussed. Connection behavior is reviewed and the results of a series of tests on a variety of types, conducted under identical arrangements, used to illustrate the range of M—f behavior expected. Special tests incorporating fabrication induced imperfections have been included so as to assess the likely variability of M—f data. A series of ultimate strength analyses on laterally supported beams provided with various forms of end connection are reported. The results provide quantitative indications of the ability of end restraint to reduce deflections and to increase load carrying capacity. Some results from a preliminary study of laterally unsupported beams are also presented. These suggest proper allowance for end restraint, which in this case should include both in plane and out-of-plane components, will also lead to worthwhile economies.

ULTIMATE STRENGTH DESIGN PROVISIONS FOR FIXED-END STEEL ARCHES WITH VARIABLE CROSS-SECTIONS

First of all, size and change location of cover plates which compose variable box cross sections adopted in fixed-end steel arch ribs are examined using their core-moments analyzed by a first-order-elastic analysis. Then, strain behavior at ultimate states of the arches with several patterns of the variable cross-sections are discussed using an ultimate strength analysis. Relationships between the ultimate strengths of the arches with variable cross-sections and those of arches with uniform cross-sections are also investigated. Based on the results a practical estimate on their relationships is carried out. Finally presented are design provisions which are able to take into account the effects of the variable cross-section on the ultimate strength.

Ultimate strength analysis of three-dimensional column subassemblages with flexible connections

Abstract The effect of semi-rigid connections on the behaviour and strength of three-dimensional column subassemblages has been investigated using a finite element method. The connection is modelled as an element with its force-deformation characteristics being represented by a piecewise linear curve. The analysis allows for the effect of initial deflection, residual stress and plastic action. It also includes the unloading of connections. The validity of the program has been verified by comparisons against available experimental work. A limited parametric study has been conducted to evaluate the influence of connection flexibility. These results have been assessed against the predictions of the UK Steelwork Code and it has been concluded that it is possible to incorporate an allowance for connection flexibility in the column design procedure of the code.

ULTIMATE STRENGTH OF COMPRESSION MEMBERS IN TRUSS PLANE

In this paper, a strut model is developed to evaluate the ultimate strength of the compression members in truss plane. The struts are restrained by the rotational springs at both ends concerning the restraining effect of the adjecent members, and are compressed by the axial load with eccentricity concerning the end moment. The accuracy of the ultimate strength analysis using the strut model is examined by the comparative calculations of the full truss models. The relations between the ultimate strength of the struts and the restraint, eccentricity and slenderness parameters are clarified by a number of parametrical calculations. And a design formula on the strength of truss compression members is proposed as a function of these mechanical parameters.

Lateral-Torsional buckling of end-restrained beams

Abstract The influence of semi-rigid joint action on the behaviour and strength of laterally unsupported beams has been investigated using a finite element approach. The ultimate strength analysis allows for the effects of initial deflections, residual stresses and the gradual development of yielded zones. Connection behaviour is modelled with a multi-linear representation of in-plane moment-rotation (M-φ) behaviour. The validity of the program has been verified by checking against both analytical and experimental results. A parametric study has been conducted to assess both the importance of end-restraint effects and the sensitivity of the beam's strength to variations in the main problem variables. Studies of the spread of yield have been employed to explain the various phenomena observed. The results have been used as the basis for an assessment of the methods used to allow for end restraint in the new UK steelwork code.

Probability-based design criteria for shear walls in nuclear power plants

The development of probability-based criteria for the design of reinforced concrete shear walls subjected to dead load, live load and in-plane earthquake forces in nuclear plants is described. These criteria are determined for flexure and shear limit states in a load and resistance factor design (LRFD) format. The flexure limit state is defined according to traditional principles of ultimate strength analysis, while the shear limit state is established from experimental results. Resistance factors for shear and flexure, load factors for dead and live load, and a load factor for effect of Safe-Shutdown Earthquake are determined for target limit state probabilities of 1.0 × 10 −6 and 1.0 × 10 −5 over a a period of 40 years. Comparisons among the proposed design criteria, ACI 349 and US NRC Standard Review Plan 3.8.4 are included.

The strength of fillet welds under longitudinal and transverse shear: a paradox

Fillet welds loaded only by transverse forces exhibit considerably greater strength than those loaded only by longitudinal forces. Current design standards in North America generally base the strength on the minimum value obtained in the longitudinal direction and consider that the strength is independent of the direction of loading. These standards require as well, that fillet welds loaded simultaneously by both longitudinal and transverse components be designed such that the vector sum of the components does not exceed the longitudinal strength. Experimental data, although limited, indicate that this vector approach is very conservative. Some standards do allow an ultimate strength analysis, although the method is not given. The transverse strength of fillet welds is about 1.45 times the longitudinal strength, and for angles of loading of up to 45° from the longitudinal axis, welds with transverse components have longitudinal capacities in excess of the longitudinal strength. Based on available test data, two alternative interaction relationships are proposed for the design of fillet welds loaded simultaneously by longitudinal and transverse forces. Key words: connections, design, fillet welds, longitudinal strength, transverse strength, steel.

Computerized ultimate strength analysis of reinforced concrete sections subjected to axial compression and biaxial bending

This article presents a method of evaluating the ultimate strength capacities of reinforced concrete sections of arbitrary shapes and with or without voids subjected to axial compression and biaxial bending. The concept of load fraction is introduced so as to provide a quantitative measure of structural adequacy. An iterative procedure to determine the load fractions is proposed. Necessary integration over arbitrary domains is dealt with by boundary integration method. This procedure can be computerized readily to high automation. A wide range of reinforced concrete sections are analysed, as examples, using a desk-top computer.

Analysis of Two‐Way Acting Composite

An ultimate strength analysis procedure was formulated for five full-scale, two-way slabs tested to failure. The concrete slabs were reinforced with composite corrugated cold-formed steel decking. Three slabs contained supplementary reinforcing in the form of welded wire fabric. Nominal out-to-out plan dimensions of the slabs were 16 ft by 12 ft (4.88 m by 3.66 m). All slabs were subjected to four symmetrically placed, concentrated loads. Ultimate failure occurred by a shear-bond action initiated by slippage between the steel deck and the concrete. The analysis procedure was founded on the principles of yield-line theory and of shear-bond regression analysis. A collapse mechanism established by yield-line procedures was utilized to determine the effective load-carrying-segment width of the slabs. A shear-bond regression analysis was used on the effective width to predict the total shear force distributed to the reactive edge perpendicular to the deck corrugations. The shear existing along the sides of the effective load-carrying segment was subsequently added to the shear-bond component to give the predicted ultimate load for each slab. The calculated load agreed very closely (within 9%) with the experimental ultimate for all five slabs.