Browsing by Author "Haas, T. N."

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    Accounting for moment-rotation behaviour of connections in portal frames
    (South African Institution of Civil Engineering, 2014-04) Albertyn, Heindrich L.; Haas, T. N.; Dunaiski, Peter E.
    Portal frames are steel structures used to construct industrial buildings. Conventional analysis techniques used by practising engineering professionals assume that the eave, ridge and base connections are either infinitely rigid or perfectly pinned. This approach leads to less accurate analysis of the displacement behaviour of portal frames when subjected to external loading. Portal frames must therefore be analysed with rotational springs at all connections to yield accurate displacement behaviour. This investigation focused on determining the accuracy and economic feasibility of modelling portal frame connections with rotational springs. The rotational spring stiffnesses of all connections were required before the portal frame could be analysed in a second-order two-dimensional non-linear analysis. The rotational spring stiffnesses unique to each connection were determined from the moment-rotation behaviour obtained from a series of finite element analysis simulations of each connection. Thereafter these stiffnesses were used to determine the vertical and horizontal displacements of the portal frame. These displacements were compared with experimental test results. The reasons for the discrepancies between the numerical and experimental results were investigated through a sensitivity analysis. The findings suggest that it is not computationally feasible to analyse portal frames with rotational springs, even though the model’s predicted results are more accurate than those of conventional analysis using rigid and pin connections.
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    The effect of parameters on the end buffer impact force history of the crane
    (South African Institution of Civil Engineering, 2012-04) Haas, T. N.; Maincon, P.; Dunaiski, P. E.
    ENGLISH ABSTRACT: An overarching investigation was conducted to provide engineers with guidelines for designing crane supporting structures. The focus of this study was to determine whether the identified parameters had an effect on the end buffer impact force history when the electric overhead travelling crane collides with the end stops of the supporting structure. Seven design codes which were reviewed do not consider the crane and its supporting structure as a coupled system. This simplification ignores some of the parameters which have a significant influence on the impact force, which could lead to the codified estimates being sometimes unconservative. During the experimental tests it was discovered that some of the parameters could not be accurately controlled and/or monitored. This led to the development of a finite element (FE) model of the full-scale experimental configuration which was used to conduct advanced simulations. The FE model considered the crane and the supporting structure as a coupled system, in which the parameters were individually varied to obtain its effect on the impact force history. The results showed that some of the individual parameters do have a significant effect on the impact force history.
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    Estimation of the maximum end buffer impact force for a given level of reliability
    (South African Institution of Civil Engineering, 2012-04) Haas, T. N.; Maincon, P.; Dunaiski, P. E.
    ENGLISH ABSTRACT: The first paper in this set of two, titled The effect of parameters on the end buffer impact force history of the crane (see page 55), examined the effect of a change in the magnitude of the parameter on the end buffer impact force history. This paper investigates to what degree a change in the magnitude of the parameter alters the impact force history. This was accomplished through a sensitivity analysis performed by individually varying the magnitude of the parameter in the FE model. For each case individual maximum impact forces were obtained. The maximum impact force could not simply be selected by choosing the greatest value from the sensitivity study. A constraint optimisation technique for a given level of reliability (β) using the FE simulation data was used to determine the maximum impact force. A comparison between the constraint optimisation and codified results showed that SABS 0160-1989 underestimates the impact force by 18%, while SANS 10160-2010 substantially overestimates the impact force by 64% for a level of reliability of β = 3. If the relevant clauses of SANS 10160-6 that pertain to end stop design are used in their present form, this will result in a conservative design, whereas SABS 0160 has a probability of 2.3% of being exceeded.
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    Seismic evaluation of the northbound N1/R300 bridge interchange
    (South African Institution of Civil Engineering, 2016) Solms, M. N.; Haas, T. N.
    The design of the Stellenberg Interchange was finalised in 1982, with construction completed in 1986. The bridge was designed using a code of practice which did not include any requirements for seismic excitation. This code was superseded by the Code of Practice for the Design of Highway Bridges and Culverts, which provides detailed analysis guidelines for bridges located in seismic-prone areas. According to this code, the bridge is located in a seismic-prone area with an anticipated peak ground acceleration of 0.1 g. Current research suggests that this region could be exposed to a peak ground acceleration of approximately 0.2 g. Upon inspection of the bridge, it was noted that the bridge does not conform to modern-day best practice guidelines for bridges located in seismic-prone regions. These factors necessitated an exploratory investigation to determine whether the bridge can sustain earthquake magnitudes between 0.05 g and 0.2 g. The study was conducted by experimentally determining the natural frequencies with its corresponding mode shapes, which were used to calibrate a finite element model. The finite element model was subjected to different magnitude earthquakes to determine its structural integrity. The results show that, for an earthquake of 0.1 g, the bending moment at one of the column bases is exceeded, while two other column base moments are within 15% of its design capacity. For a 0.2 g magnitude earthquake, the design bending moments at five columns are significantly exceeded, while three other columns' design moments are close to being exceeded. The exceedance of the design moments could lead to significant damage, with the possibility of collapse of the bridge.