Interaction of buckling modes in castellated steel beams

This paper investigates the behaviour of normal and high strength castellated steel beams under combined lateral torsional and distortional buckling modes. An efficient nonlinear 3D finite element model has been developed for the analysis of the beams. The initial geometric imperfection and material nonlinearities were carefully considered in the analysis. The nonlinear finite element model was verified against tests on castellated beams having different lengths and different cross-sections. Failure loads and interaction of buckling modes as well as load-lateral deflection curves of castellated steel beams were investigated in this study. An extensive parametric study was carried out using the finite element model to study the effects of the change in cross-section geometries, beam length and steel strength on the strength and buckling behaviour of castellated steel beams. The parametric study has shown that the presence of web distortional buckling causes a considerable decrease in the failure load of slender castellated steel beams. It is also shown that the use of high strength steel offers a considerable increase in the failure loads of less slender castellated steel beams. The failure loads predicted from the finite element model were compared with that predicted from Australian Standards for steel beams under lateral torsional buckling. It is shown that the Specification predictions are generally conservative for normal strength castellated steel beams failing by lateral torsional buckling, unconservative for castellated steel beams failing by web distortional buckling and quite conservative for high strength castellated steel beams failing by lateral torsional buckling.     

Nonlinear behaviour of unprotected composite slim floor steel beams exposed to different fire conditions

An efficient nonlinear 3D finite element model has been developed to investigate the structural performance of composite slim floor steel beams with deep profiled steel decking under fire conditions. The composite steel beams were unprotected simply supported with different cross-sectional dimensions, structural steel sections, load ratios during fire and were subjected to different fire scenarios. The nonlinear material properties of steel, composite slim concrete floor and reinforcement bars were incorporated in the model at ambient and elevated temperatures. The interface between the structural steel section and composite slim concrete floor was also considered, allowing the bond behaviour to be modelled and the different components to retain its profile during the deformation of the composite beam. Furthermore the thermal properties of the interface were included in the finite element analysis. The finite element model has been validated against published fire tests on unprotected composite slim floor steel beams. The time–temperature relationships, deformed shapes at failure, time–vertical displacement relationships, failure modes and fire resistances of the composite steel beams were evaluated by the finite element model. Comparisons between predicted behaviour and that recorded in fire tests have shown that the finite element model can accurately predict the behaviour of the composite steel beams under fire conditions. Furthermore, the variables that influence the fire resistance and behaviour of the unprotected composite slim floor steel beams, comprising different load ratios during fire, cross-section geometries, beam length and fire scenarios, were investigated in parametric studies. It is shown that the failure of the composite beams under fire conditions occurred for the standard fire curve, but did not occur for the natural fires. The use of high strength structural steel considerably limited the vertical displacements after fire exposure. It is also shown that presence of additional top reinforcement mesh is necessary for composite beams exposed to short hot natural fires. The fire resistances of the composite beams obtained from the finite element analyses were compared with the design values obtained from the Eurocode 4 for composite beams at elevated temperatures. It is shown that the EC4 predictions are generally conservative for the design of composite slim floor steel beams heated using different fire scenarios.     

Investigation of concrete encased steel composite columns at elevated temperatures

This paper presents a nonlinear 3-D finite element model investigating the behaviour of concrete encased steel composite columns at elevated temperatures. The composite columns were pin-ended axially loaded columns having different cross-sectional dimensions, different structural steel sections, different coarse aggregates and different load ratios during fire. The nonlinear material properties of steel, concrete, longitudinal and transverse reinforcement bars as well as the effect of concrete confinement at ambient and elevated temperatures were considered in the finite element models. The interface between the steel section and concrete, the longitudinal and transverse reinforcement bars, and the reinforcement bars and concrete were also considered allowing the bond behaviour to be modelled and the different components to retain its profile during the deformation of the column. The initial overall (out-of-straightness) geometric imperfection was carefully included in the model. The finite element model has been validated against published tests conducted at elevated temperatures. The time–temperature relationships, deformed shapes at failure, time–axial displacement relationships, failure modes and fire resistances of the columns were evaluated by the finite element model. It has been shown that the finite element model can accurately predict the behaviour of the columns at elevated temperatures. Furthermore, the variables that influence the fire resistance and behaviour of the composite columns comprising different load ratios during fire, different coarse aggregates and different slenderness ratios were investigated in parametric studies. It is shown that the fire resistance of the columns generally increases with the decrease in the column slenderness ratio as well as the increase in the structural steel ratio. It is also shown that the time–axial displacement relationship is considerably affected by the coarse aggregate. The fire resistances of the composite columns obtained from the finite element analyses were compared with the design values obtained from the Eurocode 4 for composite columns at elevated temperatures. It is shown that the EC4 is conservative for all the concrete encased steel composite columns, except for the columns having a load ratio of 0.5 as well as the columns having a slenderness ratio of 0.69 and a load ratio of 0.4.     

Fire tests on bonded post-tensioned concrete slabs

The results from eight fire tests conducted on bonded post-tensioned one-way spanning concrete slabs are presented in this paper. The fire tests were augmented with two additional tests at ambient temperature, carried out to failure on slabs with identical geometry and prestressing tendons. The different structural response between using plastic and metallic ducts, Limestone and Thames Gravel aggregates, and different axial restraint conditions to longitudinal thermal expansion, have been highlighted. Slabs with Thames Gravel aggregates were shown to have a much higher deflection compared to slabs with Limestone aggregates, with restrained slabs having a lower vertical deflection compared to equivalent unrestrained slabs. In all the fire tests, cracks directly inline and parallel to the tendons occurred due to thermal stresses at relatively low tendon temperatures, which were not observed in the ambient tests. It is shown that the use of plastic ducts resulted in slightly higher tendon temperatures due to the ease at which water migrated from the grout once the duct had melted. The fire tests have shown that the fire resistance specified in current codes of practice are generally conservative for bonded post-tensioned one-way spanning concrete slabs. The tests have provided detailed experimental data in the form of temperature distributions within the slab, vertical and horizontal displacements and strains in the tendons, which will allow validation of future computer models to predict the behaviour of bonded post-tensioned concrete slabs under fire conditions.     

Would LEED-UHI greenery and high albedo strategies mitigate climate change at neighborhood scale in Cairo,Egypt?

Neighborhood has always been of significant interest to built environment stockholders as a basic planning unit. However, any discussion in these concerns, without drawing attention to sustainable microclimate approaches, would still in a mess at a time of increasing population and climate change. Emergence of the sustainable development concept at the mid-20th century and its emphasis led to increasing crucial role that the urban green infrastructure along with reflective materials can play in mitigating neighborhood microclimate’s symptoms of climate change. Considering the lack of studies for urban heat island (UHI) in hot arid regions, particularly in Egypt and the limited number of studies concerning the numerical simulation of all mitigation strategies incorporated, this research studies the mitigation of UHI phenomenon in a case study in Cairo in present and future (2020, 2050 and 2080) through applying the criteria of tree lines, green roofs, high albedo pavements and shading structures within the neighborhood sustainability assessment tool (Leadership in Energy and Environmental Design for Neighborhood; LEED-ND). The microclimatic numerical CFD simulations of ENVI-met 4.0 was used following the measurement of LAI and Albedo of selected Egyptian trees to assess UHI through air and radiant temperature differences before and after applying mitigation strategies. Results demonstrate a considerable ability to acclimatize the microclimate in terms of better conditions in present and future.     

Construction and performance characteristics of a metformin electrode based on the metformin phosphotungstate ion-associate

A new metformin (Mf) ion selective PVC membrane electrode based on the ion-associate of Mf with phosphotungstic acid was prepared. The electrode exhibited a mean calibration graph slope of 58 mV Mf concentration decade^?1, at 25°C, within the concentration range 2·0 × 10^?5?1·0 × 10^?2 M MfCl. The change of pH within the range 4·0–11·0 did not affect the electrode performance. The standard electrode potentials were determined at different temperatures and used to calculate the isothermal coefficient of the electrode (0.000352 V°C^?1). The electrode showed a very good selectivity for Mf with respect to a large number of inorganic and organic cations. The standard addition method and potentiometric titration were applied to determine Mf in pure solutions and in metformin-containing tablets.     

Krill herd algorithm based on cuckoo search for solving engineering optimization problems

This paper presents a hybrid krill herd (CSKH) approach to solve structural optimization problems. CSKH improved the Krill herd algorithm (KH) by combining KU/KA operator originated from cuckoo search algorithm (CS) with KH. In CSKH, a greedy selection scheme is used and often overtakes the original KH and CS. In addition, in order to further enhance the assessment of CSKH, a fraction of the worst krill is thrown away and substituted with newly randomly generated ones by KA operator at the end of each generation. The CSKH is applied to five real engineering problems to verify its performance. The experimental results have proven that CSKH algorithm is well capable of solving constrained engineering design problems more efficiently and effectively than the basic CS and KH algorithm.

     

Analyzing the Simple Ranking and Selection Process for Constrained Evolutionary Optimization

Many optimization problems that involve practical applications have functional constraints,and some of these constraints are active,meaning that they prevent any solution from improving the objective function value to the one that is better than any solution lying beyond the constraint limits.Therefore,the optimal solution usually lies on the boundary of the feasible region.In order to converge faster when solving such problems,a new ranking and selection scheme is introduced which exploits this feature ...