This paper describes a study of the S650 high strength steel material properties including the effect of cold-formed angle. Coupon specimens with different cold-formed angles (90 degrees, 100 degrees, 120 degrees, 140 degrees, 160 degrees and 180 degrees) and different thicknesses (4 mm and 6 mm) were examined. Relationships between cold-formed angle and yield stress as well as tensile stress of the material were determined, based on the tensile coupon test results. Yield and tensile stresses assessed by consid ering the influence of the cold-formed angles were compared with those without considering this influence. Analyses revealed that both yield and tensile stresses decreased with increasing cold-formed angle. Ductile-damage material models available in the finite element analysis software ABAQUS were used to simulate tensile coupon tests. The experimental and numerical results showed good agreements. Copyright (C) 2019 by The Hong Kong Institute of Steel Construction. All rights reserved.

This paper describes a study of the behaviour of cold-formed high strength steel angles. Thirty-six specimens with different cold-formed angles (90°, 100°, 120°, 140°, 160°, and 170°) and different thicknesses (4 mm and 6 mm) were considered. The initial geometric imperfections of the specimens were determined using the 3D laser scanning method. The magnitudes of these geometric imperfections for torsional and torsional-flexural buckling and flexural buckling analyses were proposed. The commercial finite element analysis (FEA) programme ABAQUS with shell elements S4R was used for finite element analyses. Different material strengths in corner and flat parts along with different proof stresses (0.2%, 0.01%, and 0.006%) were considered in the numerical models. The experimental and FEA results showed good agreement. Influence of cold-formed angle on non-dimensional slenderness and reduction factor curves of the 4 mm thick columns with 90° and 120° cold-formed angles was analysed.

At a full scale loading test to failure a 50 year old concrete railway trough bridge in Örnsköldsvik, in northern Sweden was tested to failure. The test was a part of the European Research Project “Sustainable Bridges” regarding assessment and strengthening of existing bridges. In the project new calculation methods were developed to capture the behaviour of the bridge during increasing load. The bridge was strengthened in bending with rods of Carbon Fiber Reinforced Polymer (CFRP) before the loading test. Failure was reached for an applied load of 11.7 MN by pulling a steel beam placed in the middle of one of the two spans downwards. The achieved failure was a combination of bond, shear, torsion and bending. The developed model, a 3D -non-linear finite element (FE) model with discrete reinforcement, gave accurate accounts of the response of the bridge. The FE calculations show the effect of the strengthening with CFRP and even the effect of the epoxy when using the Near Surface Mounted Reinforcement (NSMR) strengthening method.

Methods for assessment and strengthening of existing bridges need to be tested and calibrated. To do this, a full-scale loading to failure was carried out in 2014 on a 55 year-old post-tensioned five span girder bridge in Kiruna, Sweden, with a total length of 121.5 m. The tests focussed on: (a) failure of the main girders, (b) failure of the slab, (c) condition of post-tensioned tendons, and (d) the performance of two carbon fibre reinforced polymer (CFRP) strengthening systems. The following are the results: 1. The main girders failed after extensive yielding of the reinforcement in a combined bending- shear failure. Preliminary comparisons with existing codes indicate a high safety. Preliminary comparisons with finite element assessment methods give good correspondence. 2. The slab failed suddenly due to punching shear. Preliminary comparisons with codes indicate a very high safety. 3. The post-tension tendons generally were in a good condition. 4. The first strengthening system consisting of prestressed laminates of CFRP was applied to one of the outer main girders. The system failed due to debonding of the CFRP at about ¾ of the ultimate load. The second system consisted of near surface mounted CFRP rods applied to the mid main girder. It showed no signs of slip in the anchorage zones and the CFRP sustained maximum strains of about 1.2 % without fibre rupture.

A finite element (FE) model was calibrated using the data obtained from a full-scale test to failure of a 50 year old reinforced concrete (RC) railway bridge. The model was then used to assess the effectiveness of various strengthening schemes to increase the load-carrying capacity of the bridge. The bridge was a two-span continuous single-track trough bridge with a total length of 30 m, situated in Ornskoldsvik in northern Sweden. It was tested in situ as the bridge had been closed following the construction of a new section of the railway line. The test was planned to evaluate and calibrate models to predict the load-carrying capacity of the bridge and assess the strengthening schemes originally developed by the European research project called Sustainable bridges. The objective of the test was to investigate shear failure, rather than bending failure for which good calibrated models are already available. To that end, the bridge was strengthened in flexure before the test using near-surface mounted square section carbon fiber reinforced polymer (CFRP) bars. The ultimate failure mechanism turned into an interesting combination of bending, shear, torsion, and bond failures at an applied load of 11.7 MN (2,630 kips). A computer model was developed using specialized software to represent the response of the bridge during the test. It was calibrated using data from the test and was then used to calculate the actual capacity of the bridge in terms of train loading using the current Swedish load model which specifies a 330 kN (74 kips) axle weight. These calculations show that the unstrengthened bridge could sustain a load 4.7 times greater than the current load requirements (which is over six times the original design loading), whilst the strengthened bridge could sustain a load 6.5 times greater than currently required. Comparisons are also made with calculations using codes from Canada, Europe, and the United States.

A reinforced concrete railway trough bridge in ornskoldsvik, Sweden, was strengthened in bending with rods of carbon-fibre-reinforced polymer and loaded to failure. The aim was to test and calibrate methods developed in the European Research Project 'Sustainable Bridges' regarding assessment and strengthening of existing bridges. A steel beam was placed in the middle of one of the two spans and was pulled downwards. Failure was reached at an applied load of 11.7MN. It was initiated by a bond failure caused by a combined action of shear, torsion as well as bending after yielding in the longitudinal steel reinforcement and the stirrups. The bond failure led to a redistribution of the internal forces from the tensile reinforcement to the stirrups, causing the final failure. The computer models developed to simulate the loading process were improved step by step from linear shell models to more detailed models. The most developed model, a three-dimensional nonlinear finite element model with discrete reinforcement, gave accurate accounts of the response of the bridge.

To calibrate methods for condition assessment of prestressed concrete (PC) bridges, tests are planned for a 50 year old five-span bridge with a length of 121 m in Kiruna in northern Sweden. Both non-destructive and destructive full-scale tests will be performed. This paper summarises the test programme, which comprises evaluation of the structural behaviour of the bridge, the residual forces in the prestressed steel, methods for strengthening using carbon fibre reinforced polymers (CFRP) and the shear resistance of the bridge slab.

There is a need to extend the life and capacity of many existing railway bridges. One of the objects of the EC-FP7-Project MAINLINE, 2011-2014, is to facilitate this. Guidelines for assessment and strengthening methods are presented as well as case studies in which existing bridges are being studied in order to extend their life length. Case studies on bridges tested to failure in order to calibrate assessment methods are also presented. Fatigue is often a vital question. A Life Cycle Assessment Tool (LCAT) is being prepared to enable Infrastructure Managers to choose optimal maintenance strategies.

A structure is typically designed for a long life and it is probable that the demands on it change over time, e.g. carry larger loads or fulfill new standards. The structure might also have been ex ...

The subject of variable blankholder force has become one of the most popular research topics in the area of sheet metal forming during the past few years Some of the well-established "truths" in this field are critically examined in the present study. This work has involved thorough numerical studies of the forming of a few different parts. Various types of blankholder force trajectories are applied, and their influences on the forming process are evaluated. As a part of the present work a closed-loop control of the blankholder force has been implemented in the simulation code. This blankholder force control is based on the suppression of wrinkles on the flange of the formed part.

Argues that the dynamic‐explicit approach has in recent years been successfully applied to the solution of various quasi‐static, elastic‐plastic problems, especially in the metal forming area. A condition for the success has, however, been that the problems have been displacement‐driven. The solution of similar force‐driven problems, using this approach, has been shown to be much more complicated and computationally time consuming because of the difficulties in controlling the unphysical dynamic forces. Describes a project aiming to develop a methodology by which a force‐driven problem can be analysed with similar computational effort as a corresponding displacement‐driven one. To this end an adaptive loading procedure has been developed, in which the loading rate is controlled by a prescribed velocity norm. Presents several examples in order to exhibit the merits of the proposed procedure.

An algorithm for finite element analysis of problems in elastoplasticity with continuous stress and strain approximation is presented. By a global iteration procedure, equilibrium is preserved at the nodes in a weak sense, and the local constitutive relation between stresses and strains is satisfied. A high order numerical integration is used to achieve a good quality stiffness matrix and to evaluate the boundary between elastic and plastic regions in the case of partly plastic elements.

The industrial aim for shorter lead times in the development process for new products has encouraged a fast development of finite-element procedures for the simulation of sheet-metal forming. These procedures can shorten the design stage for new sheet-forming tools and the try-out period. In order to reach these goals robust calculation procedures and extensive verification of results are required. This paper presents a detailed validation of one promising type of finite-element code, namely the explicit code DYNA3D. Experiments for verification were performed on a zinc-coated sheet steel with a hot-dip galvanized coating. Stretch forming and deep drawing of cylindrical cups were performed. Rectangular boxer, were formed from rectangular blanks and from blanks with cut corners. Dies both with and without draw beads were used. Punch forces, flange draw-in and strain distributions were measured. The pressings with cylindrical shape were used to determine coefficients of friction with a fitting procedure based on comparison of data from pressings and from the DYNA3D calculations. These tribological data and constitutive data of the steels were used in the simulation of pressings of rectangular boxes. The calculations with DYNA3D gave a good description of flange draw-in and the strain distributions in the pressings. In most of the cases studied the punch-force curves were well reproduced. It is concluded that the present code is well suited for the simulation of sheet-forming operations.

An adaptive h-version finite element procedure is presented for a 2D elastodynamic transient analysis using direct integration. The procedure modifies the spatial discretization, i.e. the mesh, in time so that the spatial discretization error can be controlled in each time instant. We analyse an a priori error estimate for the total energy which shows that an a posteriori error estimate developed by Zienkiewicz and Zhu for linear elastostatics can reasonably be extended to dynamic transient analysis. For the time integration, both explicit and implicit time integration schemes can be coupled with the procedure. However, the study is this paper is confined to the use of the Newmark scheme. Numerical examples are used to study the performance of the error estimate and to illustrate the adaptive procedure. Obtained numerical results indicate that: (i) the extension of the Zienkiewicz-Zhu estimate to dynamic transient analysis is useful; (ii) the presented adaptive procedure can, in an efficient way, provide a finite element solution with a user-controlled accuracy.

Sheet metal forming by punching is a quasistatic process with large elastoplastic deformations. Complicating factors are moving contact boundaries with friction, instabilities in compressed regions and springback after the punching process. Following an idea presented in 1989 by Honecker and Mattiasson [7] this paper presents a quasi-dynamic approach to this problem. The calculations with this approach are shown to be fast and more stable than with a quasi-static approach.

AbstractThe efficiency of iterative methods in linear structural mechanics is studied. The efficiency concerns the calculation time, the numerical accuracy and the core storage needed. We state that iterative methods are effective in connection with hierarchical improvement of a primary approximation. Three iterative methods are studied: the conjugate gradient method preconditioned by a modified incomplete factorization matrix, the same method preconditioned by a matrix obtained from natural factors on elemental level, and a Jacobi integration preconditioned by viscous relaxation split in an element‐by‐element way. We make comparisons with direct methods, Gaussian elimination and factorization by use of natural factors.

AbstractNumerical techniques applied to the consistent formulation of plasticity, which is based on convex analysis, are investigated. For each time step the stress is found as the projection in complementary energy of the elastic stress onto the set of plastically admissible stresses, while the velocity field is the extremal of a non‐quadratic functional. Explicit formulas for von Mises' yield criterion with mixed hardening are developed and the nonlinear equations arising from finite element discretization are solved, for comparison, by a number of Newton‐type iteration procedures with line search and are‐length control. A few numerical examples with proportional and non‐proportional loading are analyzed.