Adapting the Simple Through Girder to Sit in Nature, The Wupperthal Footbridge

<p>Some places are hard to get to and Wupperthal, a small town nestled deep within in the Cederberg Mountains, in South Africa is one of those places. Founded by German missionaries in 1830 the town is home to 1400 inhabitants and a growing tourist destination. An adjacent river, however, is a barrier during the wet seasons for farm children trying to reach the town’s school. A permanent footbridge was therefore recently commissioned to replace temporary structures that have proved dangerous. This paper tells the story of the single span through girder footbridge. Designed to sit as a comfortable object in its natural surroundings the new footbridge is both functional and attractive. The tapering steel plated cross section presents a profiled elevation that splits to create an arched opening at the midspan of the bridge. To create this elegant form the design had to prevent the buckling of the unbraced top chord of the girder. This was achieved through an iterative study of various cross sections and the transitioning of the plate girder into a box section over the opening. Developing a three-dimensional CAD model of the bridge helped engineers conceive the slender form. The model was then exported to create the finite element plated model and then developed into full workshop drawings. The bridge is considered simple but striking in its appearance and this paper aims to highlight that standard solutions can be transformed where appropriate within limited means.</p>

Assessment of the Bending Moment Capacity of Naturally Corroded Box-Section Beams

The steel constructions of mine shaft steelwork are particularly exposed to aggressive environments, which cause large, nonuniform corrosion loss throughout the steel members. A correct assessment of corrosion loss and load-carrying capacity of shaft steelwork is crucial for its maintenance and safe operation. In this article, we present the results of laboratory, numerical, and analytical investigations conducted on naturally corroded steel guides disassembled from shaft steelwork. The steel guides considered had a closed profile formed by welding two hot-rolled channel sections. Laboratory bending tests were carried out on beams with various levels of corrosion loss, corresponding to compact, non-compact, and slender cross sections. Multiple detailed measurements of the thicknesses of naturally corroded walls were used in order to reproduce their nonuniform geometry in finite element (FE) models. The results of numerical simulations of five bending tests showed good agreement with laboratory measurements and replicated the observed failure modes, therefore confirming the applicability of this modeling approach for assessing the moment capacity of highly corroded steel beams when the deteriorated geometry is known. For the purpose of generalization, a series of derived models reflecting the natural corrosion pattern was then developed, and moment capacity statistics were collected through multiple simulations. They showed that the mean moment capacity is determined by the mean wall thickness. However, the minimum moment capacity is strongly affected by corrosion loss variation, particularly for the highly corroded beams. A simplified, analytical modeling approach was also examined, providing fairly good assessments of the mean; however, the minimum moment capacity could not be estimated. This study contributes to the body of knowledge on the mechanical behavior of highly corroded hot-rolled box-section beams.

Effect of residual stress in longitudinal and transverse weld on global stability of box section steel column

In order to study the influence of welding residual stress on the global stability of box section steel column, the simulation of the side effects from the welding process of Q345 box section steel column by ABAQUS thermal-structure coupling analysis was conducted. A temperature-displacement explicit analysis step was established, and the residual stress caused by the temperature difference of the welding specimen was simulated by applying the body heat flux directly to the solid element within the same thickness range of the weld seam and defining the load amplitude; The calculated welding residual stress was taken as the initial defect of the structure and the global stable bearing capacity of the box section steel column was solved by the arc length method. Considering the influence of thickness and welding residual stress on the global stability of box section steel column, the calculation results of 12 finite element models were compared. The results show that under the same body heat flux, the residual stress of steel columns with different thicknesses during welding is different, and the maximum value can reach 791MPa; Under the condition of the same residual stress, the global stability bearing capacity of the box section steel column will also change irregularity with the change of thickness, and the global stability bearing capacity can be reduced by 3.07% compared with that no residual stress.

Equivalent Geometric Imperfections for Local Buckling of Slender Box-section Columns

Determining the plate or the local buckling resistance is highly important in designing steel buildings and bridges. The EN 1993-1-5Annex C provides a FEM-based design approach to calculate the buckling resistance based on numerical design calculations (geometrical and material nonlinear analysis - GMNIA). Within the GMNIA analysis-based stability design, the application of the imperfections has a special role. Thus, the applicability of the EN 1993-1-5 based buckling curve (Winter curve) has been questioned for pure compression, and previous investigations showed the buckling curve of EN 1993-1-5 Annex B is more appropriate for the design of slender box-section columns subjected to pure compression, the magnitude of the equivalent geometric imperfection to be applied in numerical models for local buckling is also questioned and investigated by the authors within the current paper. The aim of the current research program is to investigate the necessary equivalent geometric imperfections to be applied in FEM-based design calculations using GMNIA calculations. A numerical parametric study is executed to investigate the imperfection sensitivity of box-section columns having different local slenderness. The necessary imperfection magnitudes are determined to each analyzed geometry leading to the buckling resistance predicted by the standardized buckling curves. Based on the numerical parametric study, a proposal for the applicable equivalent geometric imperfection magnitude is developed, which conforms to the plate buckling curves of the EN 1993-1-5 and giving an improvement proposal to the local buckling imperfection magnitudes of the prEN 1993-1-14, which is currently under development.